CN109611102B - Construction method for cold excavation underpass overpass - Google Patents

Abstract

The invention discloses a construction method of a cold excavation underpass overpass, and relates to the technical field of tunnel construction; the construction steps are as follows: advanced pre-support construction; excavating a hole body; processing and installing a steel frame; constructing a mortar anchor rod; primary branch sprayed concrete; and (5) secondary lining of the tunnel. The disturbance to the surrounding environment when reducing tunnel excavation reduces the construction risk, guarantees existing overpass operation safety.

Description

Construction method for cold excavation underpass overpass

Technical Field

The invention relates to the technical field of tunnel construction, in particular to a cold excavation underpass overpass construction method.

Background

The urban rail transit tunnel penetrates through the existing bridge more and more, the bridge is guaranteed to be normally used during tunnel construction, and engineering is guaranteed to be smoothly developed, stratum deformation and stress release generated by tunnel excavation inevitably disturb the existing bridge, so that the use and safety of the bridge are threatened, and therefore, it is very important to explore reasonable protection measures and correct tunnel construction methods.

Disclosure of Invention

The invention aims to provide a cold excavation underpass overpass construction method which is simple in structure, reasonable in design and convenient to use, reduces disturbance to the surrounding environment during tunnel excavation, reduces construction risks and ensures the operation safety of the existing overpass, aiming at the defects and shortcomings of the prior art.

In order to achieve the purpose, the invention adopts the technical scheme that: the construction steps are as follows:

1. advanced pre-support construction

1.1, advance small conduit support

1.1.1, preparation of advanced small conduit grouting equipment and grouting materials: the grouting equipment adopts an FBY double-liquid grouting machine; the grouting material is silicate cement slurry of P.O42.5, and the water-cement ratio is 0.5: 1-1: 1; the test is carried out before grouting, and the actual operation is carried out after the sample meets the standard requirement; pouring the required water into a stirring barrel, pouring the cement into the stirring barrel according to the proportion, mechanically stirring, uniformly stirring for later use, and using the cement slurry along with stirring;

1.1.2, processing and installing an advanced small guide pipe: the small guide pipe is processed by a phi 42 seamless steel pipe, and the front end of the small guide pipe is processed into a cone shape so as to be convenient for inserting and beating and prevent slurry from rushing forwards; drilling 6-8 mm grouting holes in the middle of the small guide pipe, arranging the grouting holes in a quincunx shape, enabling the distance to be 20cm, not drilling holes in the range of 1m at the tail part, preventing slurry leakage, welding an annular iron hoop at the tail end, and preventing the end part from cracking during driving to influence the connection of grouting pipes, wherein during construction, holes are drilled by an air pick, and the air drill is jacked; connecting the small guide pipe after drilling and sealing the hole opening;

1.1.3, leading small conduit grouting: grouting from no water hole to water hole, from less water to more water hole, and jumping to pressure grouting; recording the length, the pressure injection time, the slurry consumption and various problems and solutions on site of each small conduit in a specified format record table during construction;

1.1.4, leading small conduit grouting end standard definition:

single well end criteria: when grouting, firstly slow and then fast, firstly low pressure and then high pressure are needed, the pressure is not more than 0.2Mpa when grouting is started, the pressure is gradually increased along with the increase of the grouting amount until the designed value (0.5-1 Mpa), the standard of grouting ending is that the single-hole grouting amount reaches the designed value, grouting is continued for 2min when the grouting pressure reaches the designed value, and the grouting amount is less than 1/4 of the initial grouting amount, so that grouting can be ended;

end of full segment criterion: finishing grouting according to the standard in all grouting holes, wherein no obvious water leakage point exists in the tunnel;

1.1.5, quality acceptance of the advanced small catheter;

1.2 Large pipe shed support

1.2.1, preparing grouting equipment and grouting materials for the large pipe shed: the grouting equipment adopts an FBY (fluid bed bio-grouting) machine, the grouting material adopts P.O42.5 silicate cement slurry, the water-cement ratio is 0.5: 1-1: 1, when groundwater development or the slurry diffusion range is large, the grouting slurry is cement-water glass dual-liquid slurry, required water is poured into a stirring barrel firstly, cement is poured into the stirring barrel according to the proportion, mechanical stirring is carried out, the cement slurry is uniformly stirred for later use, and the cement slurry is used along with stirring;

1.2.2, processing and installing a large pipe shed:

specification of the conduit: the hot-rolled seamless steel perforated pipe has the advantages that the outer diameter is 159mm, the wall thickness is 10mm, the length of a left tunnel is 26m, and the length of a right tunnel is 20 m; tube distance: the circumferential distance is 35 cm; inclination angle: the external insertion angle is 0-3 degrees; connecting steel pipes of the large pipe shed are connected by connecting steel pipes of phi 180 x 10mm and 40cm in length, in order to enable joints of the large pipe shed to be arranged in a staggered mode, pipe shed sections with odd-numbered holes are arranged according to 4 x 4.5m +2.0m, pipe shed sections with even-numbered holes are arranged according to 2.0m +4 x 4.5m, pipe shed sections with odd-numbered holes are arranged according to 5 x 4.5m +3.5m, and pipe shed sections with even-numbered holes are arranged according to 3.5m +5 x 4.5 m; the large pipe shed is formed by processing a phi 159 seamless steel pipe, the front end of the large pipe shed is processed into a cone, a reinforcement cage is additionally arranged in the guide pipe and consists of four C18HRB400 main reinforcements and a fixing ring, the fixing ring adopts a short pipe joint, the fixing ring is welded with the main reinforcements and is arranged at an interval of 1m, phi 10-16 mm grouting holes are drilled in the middle of the pipe shed and are arranged in a quincunx shape, the interval is 20cm, and no hole is drilled in the range of 1.5m at the tail part; the large pipe shed is constructed by adopting a pipe-following drilling method so as to reduce the problem of ground settlement caused by construction of the pipe shed;

1.2.3, grouting a large pipe shed: the grouting sequence is from no water hole to water hole, from little water to many water holes, and the pressure grouting is required to be jumped off, and the length of each pipe shed, the pressure grouting time, the slurry consumption and various problems and solutions on site need to be recorded into a specified format recording table in the construction process so as to analyze the front geological condition;

1.2.4, the grouting end standard of the large pipe shed is defined as follows:

single well end criteria: gradually raising the grouting pressure, and stabilizing for 10min when the designed final pressure is reached; the grouting amount is not less than 80% of the designed grouting amount; 1/4, the slurry inlet speed is less than the initial slurry inlet speed;

1.2.5, checking and accepting the quality of the large pipe shed;

2. digging hole body

2.1 non-blasting excavation upper step

Section of application

Supporting at the initial stage; is at the completion of

Temporarily suspended after 5m of primary support

Excavating, and spraying C25 concrete with the thickness of 5cm to seal the tunnel face;

2.2 non-blasting excavation upper step

Section of application

Supporting at the initial stage; is at the end ofBecome into

Temporarily suspended after 5m of primary support

Excavating, and spraying C25 concrete with the thickness of 5cm to seal the tunnel face;

2.3 laying the waterproof layer of the inverted arch in time and pouring

Concrete for the inverted arch and the side wall;

2.4 filling inverted arch

Part to design height;

2.5, constructing the waterproof layer of the arch wall and pouring the waterproof layer at one time

Partial arch wall concrete;

2.6, repeating the working procedures 2.1-2.6 to carry out the next lining circulating construction after the strength of the second lining concrete reaches 80% of the design strength;

3. steel frame processing and mounting

3.1, steel frame processing: technical personnel recheck the technical parameters of steel frame unit division, radius, arc length and the like of each unit according to the drawing size, issue a technical intersection after no error, and process the steel frame through a section steel cold bending machine on site;

the steel frame is machined on the steel bar machining shed according to the design size, the steel frame connecting steel plates need to be drilled by using a bench drill, electric welding or acetylene hole burning is not needed, the unit steel frames need to be organized and assembled after being machined, and batch production and use can be realized after the steel frame size and the outline are inspected to be qualified;

3.2, measurement and positioning: after excavation is finished, after concrete is sprayed for the first time, a steel frame is installed, a center line elevation method is adopted for steel frame positioning, a center line of a tunnel is determined according to a total station, the support distance of the end of the steel frame is measured symmetrically according to the center line to enable the steel frame to meet design values, meanwhile, a leveling instrument is adopted to measure the elevations of control points of an arch crown, an arch foot, an inverted arch bottom and the like of the steel frame, and the steel frame is adjusted to enable the steel frame to meet design requirements;

3.3, steel frame installation: after the steel frame positions are adjusted, bolts between steel frames are screwed, phi 22 longitudinal connecting steel bars are arranged between two steel frames, the circumferential distance is 1000mm, the steel bars are arranged in a single layer, the connecting steel bars are lengthened by adopting double-sided lap welding, and the steel bars on two sides are ensured to be on the same axis during welding;

3.4, laying a reinforcing mesh: the reinforcing mesh adopts phi 8 reinforcing steel bars, the spacing is 200mm multiplied by 200mm, reinforcing mesh sheets are processed outside the hole for standby according to the designed arch center spacing in advance, the reinforcing mesh sheets are processed by a reinforcing binding machine, and the reinforcing mesh sheets are paved after anchor rods are applied; the reinforcing mesh is tightly attached to the primary spraying surface along with the height, shallow holes are drilled by using impact drills to embed expansion bolts, and the reinforcing mesh is fixed on the bolts and is welded with the tail part of the anchor rod; manufacturing the holes in a split mode, wherein the lap joint length is not less than 10cm during installation; manually laying, and if necessary, using a pneumatic drill pneumatic leg for jacking to be close to the rock surface, and firmly binding and connecting with the anchor rod and the steel frame; when the reinforcing mesh and the steel frame are bound, the reinforcing mesh and the steel frame are bound on one side close to the rock surface; when concrete is sprayed, the distance from the spray head to a sprayed surface and the air pressure are adjusted, so that the vibration of the reinforcing mesh is reduced, and the resilience is reduced; the thickness of the concrete protective layer of the reinforcing mesh is not less than 2 cm;

4. mortar anchor rod construction

4.1, drilling: the drilling machine is selected according to the type and the specification of the anchor rod and the surrounding rock condition; the allowable deviation of the hole positions is +/-150 mm, and the drilling quantity meets the design specification; the diameter of the drilled hole must be larger than the diameter of the anchor rod body by 15 mm; the hole depth is not less than the effective length of the anchor rod body, but the depth overlength value is not more than 100 mm;

4.2, grouting: the holes must be blown clean before grouting; the cement mortar must be uniformly mixed and used along with the mixing; grouting is full, the grouting is uniformly carried out from the bottom of the hole without interruption, and the phenomenon that the pipe is pulled out too fast to cause mortar dislocation and insufficient grouting is strictly prevented; the grouting pipe must be inserted to a position 5-10 cm away from the bottom of the hole, and is slowly pulled out at a constant speed along with the injection of cement mortar, and then the rod body is rapidly inserted, the length of the anchor rod body inserted into the hole is not shorter than 95% of the designed length, if no mortar flows out from the hole opening, the rod body must be pulled out and re-grouted, the anchor rod cannot be knocked randomly after being installed, and a heavy object cannot be hung at the end part of the anchor rod within 3 days;

4.3, anchor rod installation: before installation, the reinforcing steel bars need to be derusted and straightened; after grouting, the reinforcing steel bars must be inserted at a constant speed and centered; the hole opening can be temporarily sealed by a wood wedge; the exposed length of the tail end of the steel bar is slightly smaller than the thickness of the spraying layer; knocking and collision cannot occur after the installation is finished, and the insertion depth of the anchor rod is not less than 95% of the design requirement; when the cement mortar anchor rod is adopted in a water section, if water flows in the hole, a hole is additionally drilled nearby to be used as a flow guide pipe, and anchor rod operation is carried out after water is discharged;

5. hollow grouting anchor rod construction

5.1, construction preparation: carrying out anchor rod installation operation in time after the concrete is initially sprayed, and checking whether an anchor rod hole is smooth or not; checking whether the air compressor, the pipeline of the air compressor and the air gun are in good states;

5.2, anchor rod drilling: drilling the anchor rod by using a rock drilling machine such as an air-leg air gun, and determining a hole position according to design requirements and by combining the attitude of surrounding rock before drilling to mark; aligning a drill bit to a calibrated position, enabling the drilling direction to be perpendicular to a rock stratum structure surface as much as possible so as to play a better reinforcing role, and keeping the length of an exposed section of the anchor rod within 10-15 cm when drilling is finished;

5.3, cleaning holes: after drilling to the designed depth, cleaning the hole with water or high-pressure air, and detaching the drill rod connecting sleeve after the smoothness is confirmed;

5.4, driving the anchor rod: driving an anchor rod in a jacking mode of an air gun;

5.5, grouting: adopting an extrusion type grouting pump for grouting, wherein the grouting slurry is M20 cement slurry, driving a grout stop plug into an orifice through the exposed end of the anchor rod by using a hole cap assembly, checking grouting equipment, preparing the cement slurry according to a mixing proportion, starting the grouting pump for grouting until the grout is extruded from the periphery of the orifice or a pressure gauge reaches a designed pressure value, stopping grouting when the pressure of the orifice is 0.7-1.0 MPa for the hollow grouting anchor rod, stopping grouting after the pressure is reached for 15min, and cleaning the grouting machine and a pipeline by using water in time after the grouting is finished;

5.6, mounting a base plate and a nut: after the strength of the grouting liquid reaches the preset strength, a backing plate is installed and is tightly attached to the rock surface, a rod end nut is tightened to generate certain prestress, the effect of better reinforcing surrounding rock is achieved, the anchor rod and the backing plate are kept perpendicular and are in full contact with sprayed concrete, and the nut needs to be tightened;

6. primary support sprayed concrete

6.1, preparing concrete spraying raw materials:

cement: the ordinary Portland cement with the design requirement label is adopted, and the strength rechecking test is carried out before the use, so that the performance of the Portland cement meets the current cement standard;

fine aggregate: sieving medium coarse sand with fineness modulus of more than 2.5 with 5mm sieve;

coarse aggregate: machine-made crushed stone with the particle size of 5 mm-15 mm;

water: tap water is adopted;

accelerator: the liquid setting accelerator is adopted, a compatibility test is carried out on the liquid setting accelerator and cement before use, and a clear slurry test with a water-cement ratio of 0.4 meets the requirements that the initial setting time is less than 5min, the final setting time is less than 10min, the doping amount is less than 5% of the cement amount, and the 28-day strength retention rate is more than 70%;

6.2, stirring the concrete wet material: stirring by a forced stirrer to form a spray material, wherein the stirring time is not less than 3 minutes; the used material metering device that throws of regular inspection stirring, the configuration deviation accords with standard requirement, and the ash-bone ratio: 1: 3.5-1: 4.0, water cement ratio of 0.42-0.50, and concrete slump of 8-12 cm;

6.3, concrete spraying construction: processing the sprayed surface, burying a sprayed layer thickness mark, connecting ventilation water and electricity, testing, transporting sprayed materials by using a mixer truck, carrying out primary concrete spraying operation, after the primary concrete spraying operation is finished, carrying out secondary concrete spraying operation after additional spraying and mixing ratio adjustment, and finally carrying out quality inspection;

7. tunnel secondary lining

7.1, base surface cleaning and measurement paying-off: cleaning up sundries on the waterproof protective layer of the bottom plate, and then paying off and popping up position lines of two side walls of the secondary lining and a control line of the bottom plate, wherein the distance between control points is not more than 5m, and iron nails or short steel bars are not needed to be used so as to avoid damaging the waterproof layer;

7.2, installing waterproof equipment;

7.3, binding inverted arch steel bars: the stressed steel bars are arranged in a double-layer mode, and the inverted arch steel bar protective layer is controlled by a mortar cushion block; a split heads control protective layer and positioning are arranged between the double layers of steel bars; the maximum model diameter of the secondary lining main reinforcement is phi 20, double-sided welding is adopted, and the joint positions are staggered for 35 d; the stressed steel bar joint is arranged at a position with small stress, and the joint positions are staggered for 35 d; the stressed reinforcement joints are connected by straight threads, the joints arranged in the same component are staggered, the area percentage of the reinforcement joints meets the requirements of specification and design, and the tension area is not more than 50%; when the steel bars are bound and lapped, the middle part and the two ends are bound together, and the steel bars are bound with the crossed bars after being bound separately; the main ribs and the distribution ribs can be bound in a cross way except for the binding of 2-3 rows of frameworks at the deformation joints, and binding points are buckled into a splayed shape by iron wires; binding the cross points of the stirrups and the main reinforcements;

7.4, inverted arch concrete pouring and maintenance: before concrete pouring, a pouring packway is erected on the steel bars and the split heads by adopting scaffold boards to prevent the steel bars from deforming; a ground pump is adopted for concrete pouring, and the concrete slump is controlled to be 120-160 mm; the left line and the right line of the thickness of the two concrete-lined bottom plates are 0.8m and 1m respectively, the two concrete-lined bottom plates are poured by adopting an inclined plane layering method, the mortar is poured from one end, the vibrating hands are closely matched, the concrete is kept to be pushed forwards along the bottom of the two concrete-lined bottom plates by a 'mortar driving method', the two concrete-lined bottom plates are scraped by a scraping bar while vibrating, a wooden trowel is compacted and leveled, and the two surfaces are pressed for the second time before initial setting so as to reduce concrete cracks; timely curing within 12 hours after concrete pouring, wherein the curing time is not less than 14 d;

7.5, binding the reinforcing steel bars of the arch wall: the reinforcing steel bar protective layer is controlled by a plastic cushion block; an S-shaped tie bar is arranged between two layers of reinforcing steel bars of the arch wall to control the clear distance of the reinforcing steel bars, the spacing between the tie bars is 1m, the tie bars are arranged in a quincunx shape, and other binding technologies require binding with the reinforcing steel bars of the bottom plate;

7.6, pouring the arch wall concrete: pumping concrete into a warehouse from bottom to top, filling fine stone concrete with the thickness of about 50mm and the same label as that of wall concrete from the joint of the poured section to the non-poured direction before pouring, fully utilizing a template reserved window in the pouring process, symmetrically pouring the concrete in layers, and additionally connecting a 3-5m hose with the same diameter at the front end of a discharge pipe to enable the pipe orifice to face downwards so as to avoid horizontally aligning the concrete surface with a straight pump; when the concrete pouring surface is close to the top, entering a capping stage, and in order to ensure that air can be smoothly discharged, installing an exhaust pipe in a reserved grouting hole, wherein one end of the exhaust pipe is close to the top of the waterproof plate as much as possible, and the other end of the exhaust pipe is fixed in the template trolley and is firmly fixed; when water flows out of the exhaust pipe along with the continuous pouring, namely the bin is indicated to be completely filled with concrete, the concrete pouring is stopped, the exhaust pipe is dredged, and the pumping hose is withdrawn; pouring concrete from the inner side to the end mold direction as much as possible to remove air during capping, and filling a gap generated by concrete shrinkage by grouting the vault through an exhaust pipe at the later stage;

7.7, dismantling the template: the mould can be disassembled after the concrete reaches 80% of the design strength;

7.8, concrete curing: and (3) spraying water for curing in time after the arch wall concrete is finally set, wherein the arch wall concrete is in a wet state during curing, and the curing time is not less than 14 d.

Furthermore, the over-excavated part in the excavation in the step 2.1 and the step 2.2 needs to be backfilled densely, and a grouting hole is reserved for secondary grouting filling.

Furthermore, in the excavation process of the step 2, overbreak is reduced as much as possible, underexcavation is strictly controlled, and only when the rock stratum is complete and the compressive strength is more than 30MPa and the stability and the strength of the lining structure are not influenced, the individual protruding part (more than 0.1m in each square meter) of the rock can invade the lining, and the invasion amount is not more than 50 mm; the section of the arch foot and the wall foot which are 1m above is strictly prohibited from underdigging.

Further, in the step 2, for the excavation of the shallow buried section of the tunnel, surface subsidence needs to be strictly controlled, and the footage of circular excavation and the collapse are reduced, and the concrete measures are as follows: excavating by adopting an excavator and an air pick, the influence of buildings on a large section is reduced, the construction footage speed is reduced, and the footage of each excavation is not more than one; and the observation and feedback of the surface subsidence and the vault subsidence are enhanced to guide the construction.

Further, the steel frame machining tolerance in step 3.1 is as follows: the contour error along the periphery of the tunnel is not more than 3cm, the plane warpage is less than 2cm, and the connector connection requirements can be interchanged among the same types; the standard type and unit number of each unit of the steel frame must be determined, and the units are piled in the semi-finished product storage area for standby.

Further, when the steel frame processed finished product in the step 3.1 is subjected to a structural test, the steel frame is assembled into a ring on a workbench, an oil top seat is welded on the outer side of the ring, an oil top is adopted, and an instrument is pressurized according to a design load. And measuring the internal force and deformation condition of the steel frame by using a stress meter and a convergence instrument.

Further, the steel frame installed in step 3.3 must ensure that the arch center plane is perpendicular to the tunnel center line, the vertical perpendicularity is measured by using a plumb sphere, the longitudinal measurement is performed by using an equidistant method, and a measurer needs to measure the accurate mileage of the steel frame and correct the previous cycle when each machine team steel frame is installed.

Furthermore, in the step 3.3, the type and the use part of each steel frame are marked during the installation of the steel frame, so that the phenomenon that the construction time is delayed due to the fact that workers take mistakes is prevented; the blanking length of each section of steel frame is reasonably designed, so that each section of steel frame is not too heavy and is convenient to operate; the connecting steel plate bolt holes are drilled by a bench drill in a unified mode, so that the bolt holes are guaranteed to be in one-to-one butt joint, and the operation is convenient; when the upper step steel frame is installed, the steel frame arch foot connecting steel plate bolt holes are wrapped by geotextile, and bolt connecting time can be saved when the lower step steel frame is constructed.

Further, the primary shotcrete operation of the step 6 is performed in a segmented and segmented manner, and the shotcrete operation is performed from bottom to top by firstly spraying the gap part between the steel frame and the arch wall and then spraying the part between the two steel frames; spraying the concrete layer by layer, wherein the thickness of one-time spraying is determined according to the spraying position and the design thickness, the arch part is preferably 5-6 cm, the side wall is 7-10 cm, and the later spraying layer is sprayed after the former layer is finally set or after one hour is separated; during spraying, the materials are sprayed from bottom to top, namely, the wall foot is firstly sprayed to the wall top, the arch top is secondly sprayed to avoid dead angles, the material bundle moves in a spiral rotating track, half circle is pressed for one circle, the materials are longitudinally sprayed in a snake shape, and the length of the snake-shaped spray is 50mm each time; spraying water for curing after the sprayed concrete is finally set for 2 hours, wherein the spraying time is determined to ensure that the concrete has a sufficient wet state, and the curing time is not less than 14 days; the sprayed concrete surface should be compact and flat without cracks, falling off, spray leakage, hollowing, water leakage and the like, and the unevenness tolerance is +/-3 cm.

Further, the remarks of step 6 are as follows:

1) the concrete construction mixing proportion is strictly controlled, the mixing proportion is determined by tests, all indexes of the concrete must meet the design and specification requirements, and the weighing precision of the concrete mixing materials must meet the specification requirements;

2) the quality of the raw materials is strictly controlled, and all indexes of the raw materials must meet the requirements;

3) the reasonable air pressure is determined in the concrete spraying construction, and the spraying is ensured to be uniform and continuous. Meanwhile, the maintenance of the equipment is enhanced, and the working performance of the equipment is ensured;

4) the spraying operation is operated by an experienced and skilled spraying hand, so that the close connection of all layers of sprayed concrete is ensured;

5) before spraying concrete, the installation work of the advanced small guide pipe, the reinforcing mesh and the steel frame is completed according to the design requirement;

6) spraying water for curing the sprayed concrete by a specially-assigned person to reduce cracking caused by hydration heat, marking the cracks with red paint, observing and monitoring to determine whether the cracks continue to develop or not, and finding out reasons and processing if the cracks continue to develop;

7) the 'four not' system is firmly implemented: namely, the working procedure of spraying concrete is not finished, the tunnel face does not advance, the thickness of the sprayed concrete is not enough to advance, the problem found after the concrete is sprayed is not solved and does not advance, and the monitoring result shows that the concrete is unsafe and does not advance. The system is executed by the on-site pilot, and the pilot takes charge of the personnel and makes a record in the project construction log for inspection;

8) grouting after primary support of the back: a42 grouting steel perforated pipes are pre-buried in the range of the arch wall during primary support construction, and cement paste is timely injected after the treatment is completed by 3-5m, so that the density of the primary support is ensured. Grouting parameters: the length of the pipe is 0.5m of the thickness of the initial branch, the wall thickness is 4mm, the distance between grouting pipes is 1.5 multiplied by 2.0m (ring multiplied by longitudinal), the grouting water cement ratio is 0.5-1.0MPa, and the grouting pipe is arranged in a quincunx manner.

Further, the construction precautions in step 7 are as follows:

1) rechecking whether the trolley template, the center line and the elevation meet the requirements, whether the clearance size meets the requirements and whether the trolley and the stop head die are firmly installed and positioned;

2) whether the joints of the templates are tightly filled or not and whether the release agent is uniformly coated or not;

3) whether the substrate is cleaned up or not and whether the construction joint is processed or not;

4) whether the water stop strip and the water stop belt meet the design and standard requirements or not.

Further, the tunnel secondary lining of the step 7 adopts segmented construction, namely YDK35+ 440- +445, accounting for 5 m; YDK35+445 to +450, accounting for 5 m; YDK35+ 450- +455, accounting for 5 m; YDK35+ 455- +460, 5 m; a total of 20 m; ZDK35+ 448- +453, accounting for 5 m; ZDK35+ 453- +458, accounting for 5 m; ZDK35+ 458- +463, counting 5 m; ZDK35+ 463- +468, 5 m; ZDK35+ 468- +474, accounting for 6 m; totaling 26 m.

After the steps are adopted, the invention has the beneficial effects that: according to the construction method of the cold excavation underpass overpass, advanced geological forecast must be carried out according to design and specification requirements before construction. And guiding construction and correcting support parameters through the fed-back advanced geological forecast information. Drilling and grouting the advanced small guide pipes for the V-grade and IV-grade surrounding rocks, and adjusting the drilling arrangement of the small guide pipes according to the joint structure and bleeding of the surrounding rocks. After the advance support is completed, a tunnel can be excavated, and the underground water level, the underground stress and the joints can be properly adjusted during construction. According to the design drawing, the steel frame must be assembled in a trial mode before the steel frame is installed, the bolt connection is adopted, and the connection steel plates must be guaranteed to be attached closely. During installation, the steel frame is attached to the surrounding rock as closely as possible, the steel frame is positioned by using the connecting steel bars, and the plane warpage, the longitudinal and transverse line deviation, the thickness of the protective layer and the like of the steel frame are checked. And (4) after the primary support of the inverted arch is finished, flatly paving a waterproof material, and then constructing an inverted arch secondary lining and filling the inverted arch. The second lining construction is carried out only after the primary support change of the tunnel is basically stable, the section center and the arch top height are rechecked, the clearance and linearity of the tunnel are controlled through the last procedure, the second lining adopts C35 molded concrete, the disturbance to the surrounding environment during tunnel excavation is reduced, the construction risk is reduced, and the operation safety of the existing overpass is ensured.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a flow chart of the construction process of the advanced small conduit in the invention.

Fig. 2 is a schematic view of the structure of the small advancing catheter in the present invention.

Figure 3 is a table of the quality standards for acceptance of the advanced small catheter of the present invention.

Fig. 4 is a longitudinal arrangement diagram of the large pipe shed advance support in the invention.

Fig. 5 is a layout view of a reinforcement cage in a conduit according to the present invention.

FIG. 6 is a flow chart of the construction process of the large pipe shed.

Fig. 7 is a structural view of a large pipe shed duct in the invention.

FIG. 8 is a table of quality standards for acceptance of large pipe sheds in the present invention.

Fig. 9 is a table of the quality acceptance criteria of the mesh reinforcing bar of the present invention.

Fig. 10 is a table of bolting quality standards according to the present invention.

FIG. 11 is a schematic cross-sectional view of a step construction process according to the present invention.

Detailed Description

The invention will be further described with reference to the accompanying drawings.

Referring to fig. 1 to fig. 11, the technical solution adopted by the present embodiment is: the construction steps are as follows:

1. advanced pre-support construction

1.1, advance small conduit support and its construction process flow chart as shown in figure 1 advance small conduit construction process flow chart

1.1.1, preparation of advanced small conduit grouting equipment and grouting materials: the grouting equipment adopts an FBY double-liquid grouting machine which can realize single-liquid grouting; the grouting material is silicate cement slurry of P.O42.5, and the water-cement ratio is 0.5: 1-1: 1; the test is carried out before grouting, and the actual operation is carried out after the sample meets the standard requirement; pouring the required water into a stirring barrel, pouring the cement into the stirring barrel according to the proportion, mechanically stirring, uniformly stirring for later use, and using the cement slurry along with stirring;

1.1.2, processing and installing an advanced small guide pipe: the small guide pipe is processed by a phi 42 seamless steel pipe, and the front end of the small guide pipe is processed into a cone shape so as to be convenient for inserting and beating and prevent slurry from rushing forwards; drilling 6-8 mm grouting holes in the middle of the small guide pipe, arranging the grouting holes in a quincunx shape, enabling the distance to be 20cm, not drilling holes in the range of 1m at the tail part, preventing slurry leakage, welding an annular iron hoop at the tail end, and preventing the end part from cracking during driving to influence the connection of grouting pipes, wherein during construction, holes are drilled by an air pick, and the air drill is jacked; connecting the small guide pipe after drilling and sealing the hole opening; big picture of small catheter see figure 2 advanced small catheter

1.1.3, leading small conduit grouting: grouting from no water hole to water hole, from less water to more water hole, and jumping to pressure grouting; recording the length, the pressure injection time, the slurry consumption and various problems and solutions on site of each small conduit in a specified format in the construction process so as to analyze the front geological condition;

1.1.4, leading small conduit grouting end standard definition:

single well end criteria: when grouting, firstly slow and then fast, firstly low pressure and then high pressure are needed, the pressure is not more than 0.2Mpa when grouting is started, the pressure is gradually increased along with the increase of the grouting amount until the designed value (0.5-1 Mpa), the standard of grouting ending is that the single-hole grouting amount reaches the designed value, grouting is continued for 2min when the grouting pressure reaches the designed value, and the grouting amount is less than 1/4 of the initial grouting amount, so that grouting can be ended;

end of full segment criterion: finishing grouting according to the standard in all grouting holes, wherein no obvious water leakage point exists in the tunnel;

1.1.5, quality acceptance of the advanced small catheter; quality standard of acceptance of small catheter see fig. 3 advanced quality standard of acceptance of small catheter

1.2 Large pipe shed support

1.2.1, preparing grouting equipment and grouting materials for the large pipe shed: the grouting equipment adopts an FBY double-liquid grouting machine which can realize single-liquid grouting. The grouting material is silicate cement slurry of P.O42.5, the water cement ratio is 0.5: 1-1: 1, when groundwater development or slurry diffusion range is large, the grouting slurry is cement-water glass double-liquid slurry, required water is poured into a stirring barrel firstly, cement is poured into the stirring barrel according to the proportion, mechanical stirring is carried out, the cement slurry is uniformly stirred for later use, and the cement slurry is used along with stirring;

1.2.2, processing and installing a large pipe shed:

specification of the conduit: the hot-rolled seamless steel perforated pipe has the advantages that the outer diameter is 159mm, the wall thickness is 10mm, the length of a left tunnel is 26m, and the length of a right tunnel is 20 m; tube distance: the circumferential distance is 35 cm; inclination angle: the external insertion angle is 0-3 degrees; connecting steel pipes of the large pipe shed are connected by connecting steel pipes of phi 180 x 10mm and 40cm in length, in order to enable joints of the large pipe shed to be arranged in a staggered mode, pipe shed sections with odd-numbered holes are arranged according to 4 x 4.5m +2.0m, pipe shed sections with even-numbered holes are arranged according to 2.0m +4 x 4.5m, pipe shed sections with odd-numbered holes are arranged according to 5 x 4.5m +3.5m, and pipe shed sections with even-numbered holes are arranged according to 3.5m +5 x 4.5 m; the large pipe shed is made of phi 159 seamless steel pipe, and the front end of the large pipe shed is tapered so as to facilitate insertion and beating and prevent slurry from rushing forward. In order to improve the bending resistance of the conduit, a reinforcement cage is additionally arranged in the conduit, the reinforcement cage consists of four C18HRB400 main reinforcements and a fixing ring, the fixing ring adopts a short pipe joint, the short pipe joint is welded with the main reinforcements and is arranged at an interval of 1m, a phi 10-16 mm grouting hole is drilled in the middle of the pipe shed and is arranged in a quincunx shape, the interval is 20cm, and no hole is drilled in the range of 1.5m at the tail part; the slurry leakage is prevented, and the tail end is welded with an annular stirrup to prevent the end part from cracking when the grouting pipe is arranged and influence the connection of the grouting pipe. The large sample of the large pipe shed is shown in the schematic diagram of the advanced large pipe shed in FIG. 7. The large pipe shed is constructed by adopting a pipe-following drilling method so as to reduce the problem of ground settlement caused by construction of the pipe shed;

1.2.3, grouting a large pipe shed: the grouting sequence is from no water hole to water hole, from little water to many water holes, and the pressure grouting is required to be jumped off, and the length of each pipe shed, the pressure grouting time, the slurry consumption and various problems and solutions on site need to be recorded into a specified format recording table in the construction process so as to analyze the front geological condition;

1.2.4, the grouting end standard of the large pipe shed is defined as follows:

single well end criteria: gradually raising the grouting pressure, and stabilizing for 10min when the designed final pressure is reached; the grouting amount is not less than 80% of the designed grouting amount; 1/4, the slurry inlet speed is less than the initial slurry inlet speed;

1.2.5, checking and accepting the quality of the large pipe shed; the quality standard of the large pipe shed is shown in figure 8

2. Excavating the tunnel body (the section size of the tunnel body excavating meets the requirements of drawings, namely considering over-excavating and reserving settlement, and carrying out according to the marked excavating line)

2.1, non-blasting excavation of an upper step ① part, ① parts of preliminary bracing are performed, after 5m of ① parts of preliminary bracing is completed, ① parts of excavation is suspended, and C25 concrete with the thickness of 5cm is sprayed to form a closed tunnel face (one truss is excavated and supported, and rings are formed one by one);

2.2, non-blasting excavation of an upper step ② part, namely, ② parts of preliminary bracing are performed, after 5m of ② parts of preliminary bracing is completed, ② parts of excavation is suspended, and C25 concrete with the thickness of 5cm is sprayed to form a closed tunnel face (one truss is excavated and braced, and rings are formed one by one);

2.3 laying the waterproof layer of the inverted arch in time and pouring

Concrete for the inverted arch and the side wall;

2.4 filling inverted arch

Part to design height;

2.5, constructing the waterproof layer of the arch wall and pouring the waterproof layer at one time

Partial arch wall concrete;

2.6, repeating the working procedures 2.1-2.6 to carry out the next lining circulating construction after the strength of the second lining concrete reaches 80% of the design strength;

3. steel frame processing and mounting

3.1, steel frame processing: technical personnel recheck the technical parameters of steel frame unit division, radius, arc length and the like of each unit according to the drawing size, issue a technical intersection after no error, and process the steel frame through a section steel cold bending machine on site;

the steel frame is machined on the steel bar machining shed according to the design size, a steel frame connecting steel plate needs to be drilled by using a bench drill, electric welding or acetylene hole burning is not needed, and bolt connection is facilitated during installation; after the processing of each unit steel frame is finished, the unit steel frames are required to be organized and assembled, the steel frame can be produced in batches and put into use after the dimension and the outline of the steel frame are checked to be qualified (the technical parameters of the steel frame meet the IV d lining section: the steel frame interval is 0.5m, the V d section: the steel frame interval is 0.35 and 0.45m, the quality standard of the steel frame meets the deviation of the steel frame assembling outline of +/-30 mm, the plane warpage of +/-20 mm, the welding between a steel plate and an I-shaped steel requires full welding seam, no welding leakage, no burn and clean welding slag, the base surface is required to be cleaned and solid before the steel frame is installed, the steel frame is required to be vertical to the central line of a tunnel, the allowable deviation is +/-30 mm in the transverse direction, +/-50 mm in the longitudinal direction, +/-30 mm and 0.5 mm in the verticality, the inner and outer protective layers for installing the steel frame are 4cm, steel bar connection is strictly forbidden; the bottom of each steel frame must fall to a hard and stable basement rock surface, and a square wood or steel plate support pad is adopted for the suspended steel frame; two adjacent steel frames are longitudinally connected by phi 22 threaded steel bars, the distance is 1 meter, and the allowable error is +/-50 mm; installing and lapping a reinforcing mesh sheet by 1-2 holes (30 cm));

3.2, measurement and positioning: after excavation is finished, after concrete is sprayed for the first time, a steel frame is installed, a center line elevation method is adopted for steel frame positioning, a center line of a tunnel is determined according to a total station, the support distance of the end of the steel frame is measured symmetrically according to the center line to enable the steel frame to meet design values, meanwhile, a leveling instrument is adopted to measure the elevations of control points of an arch crown, an arch foot, an inverted arch bottom and the like of the steel frame, and the steel frame is adjusted to enable the steel frame to meet design requirements;

3.3, steel frame installation: after the steel frame positions are adjusted, bolts between steel frames are screwed, phi 22 longitudinal connecting steel bars are arranged between two steel frames, the circumferential distance is 1000mm, the steel bars are arranged in a single layer, the connecting steel bars are lengthened by adopting double-sided lap welding, and the steel bars on two sides are ensured to be on the same axis during welding;

3.4, laying a reinforcing mesh: the reinforcing mesh adopts phi 8 reinforcing steel bars, the spacing is 200mm multiplied by 200mm, reinforcing mesh sheets are processed outside the hole for standby according to the designed arch center spacing in advance, the reinforcing mesh sheets are processed by a reinforcing binding machine, and the reinforcing mesh sheets are paved after anchor rods are applied; the reinforcing mesh is tightly attached to the primary spraying surface along with the height, shallow holes are drilled by using impact drills to embed expansion bolts, and the reinforcing mesh is fixed on the bolts and is welded with the tail part of the anchor rod; manufacturing the holes in a split mode, wherein the lap joint length is not less than 10cm during installation; manually laying, and if necessary, utilizing a pneumatic drill pneumatic leg to support so as to be close to the rock surface, and firmly binding and connecting (or spot welding) the anchor rod and the steel frame; when the reinforcing mesh and the steel frame are bound, the reinforcing mesh and the steel frame are bound on one side close to the rock surface; when concrete is sprayed, the distance from the spray head to a sprayed surface and the air pressure are adjusted, so that the vibration of the reinforcing mesh is reduced, and the resilience is reduced; the thickness of the concrete protective layer of the reinforcing mesh is not less than 2cm (the quality standard of the reinforcing mesh is shown in figure 9, the laying of the reinforcing mesh must ensure that the reinforcing mesh must be cleaned before use, the reinforcing mesh must be firmly connected with an anchor rod or other fixing devices, and the reinforcing mesh must not shake when the concrete is sprayed);

4. mortar anchor rod construction

4.1, drilling: the drilling machine is selected according to the type and the specification of the anchor rod and the surrounding rock condition; the allowable deviation of the hole positions is +/-150 mm, and the drilling quantity meets the design specification; the diameter of the drilled hole must be larger than the diameter of the anchor rod body by 15 mm; the hole depth is not less than the effective length of the anchor rod body, but the depth overlength value is not more than 100 mm;

4.2, grouting: the holes must be blown clean before grouting; the cement mortar must be uniformly mixed and used along with the mixing; grouting is full, the grouting is uniformly carried out from the bottom of the hole without interruption, and the phenomenon that the pipe is pulled out too fast to cause mortar dislocation and insufficient grouting is strictly prevented; the grouting pipe must be inserted to a position 5-10 cm away from the bottom of the hole, the grouting pipe is slowly pulled out at a constant speed along with the injection of cement mortar, the rod body is immediately and rapidly inserted, the length of the anchor rod body inserted into the hole is not shorter than 95% of the designed length, if no mortar flows out from the hole opening, the rod body must be pulled out and re-grouted, the anchor rod cannot be knocked randomly after being installed, and a heavy object cannot be hung at the end part of the anchor rod within 3 days.

4.3, anchor rod installation: before installation, the reinforcing steel bars need to be derusted and straightened; after grouting, the reinforcing steel bars must be inserted at a constant speed and centered; the hole opening can be temporarily sealed by a wood wedge; the exposed length of the tail end of the steel bar is slightly smaller than the thickness of the spraying layer; the mounting is not required to be knocked and collided. The insertion depth of the anchor rod is not less than 95% of the design requirement; when cement mortar anchor rods are adopted in a water section, if water flows in the holes, holes are additionally drilled nearby to serve as guide pipes, and anchor rod operation is carried out after water is discharged (the anchor rod support quality standard refers to figure 10);

5. hollow grouting anchor rod construction

5.1, construction preparation: carrying out anchor rod installation operation in time after the concrete is initially sprayed, and checking whether an anchor rod hole is smooth or not; checking whether the air compressor, the pipeline of the air compressor and the air gun are in good states;

5.2, anchor rod drilling: drilling the anchor rod by using a rock drilling machine such as an air-leg air gun, and determining a hole position according to design requirements and by combining the attitude of surrounding rock before drilling to mark; aligning a drill bit to a calibrated position, enabling the drilling direction to be perpendicular to a rock stratum structural surface as much as possible so as to play a better reinforcing role, and keeping the length of an exposed section of the anchor rod within 10-15 cm (the drilled hole meets the following requirements that the drilled hole is round and straight, the drilling direction is perpendicular to a main structural surface of the rock stratum as much as possible, and the aperture of the anchor rod is larger than the diameter of the rod body by 15mm) when the drilling is finished;

5.3, cleaning holes: after drilling to the designed depth, cleaning the hole with water or high-pressure air, and detaching the drill rod connecting sleeve after the smoothness is confirmed;

5.4, driving the anchor rod: driving an anchor rod in a jacking mode of an air gun;

5.5, grouting: the grouting adopts an extrusion type grouting pump, the grouting slurry is M20 cement slurry, a hole cap is used for matching, a grout stop plug is driven into an orifice through the exposed end of an anchor rod for about 30cm, a grouting device is checked, the cement slurry is prepared according to the matching ratio, the grouting pump is started for grouting until the grout is extruded from the periphery of the orifice or a pressure gauge reaches a designed pressure value, the grouting is stopped when the pressure of the orifice is 0.7-1.0 MPa, the grouting is continued for 15min when the pressure is reached, after the grouting is finished, a grouting machine and a pipeline are cleaned by water in time (if the pipe is blocked in the grouting process, the anchor rod, a grouting pipe and a grouting pump are respectively checked, the grouting pressure is firstly subtracted before the checking to avoid hurting people by the grouting, the anchor rod is drilled in place, the grout stop plug is installed, after the air pressure in the hole is recovered, a drill hole except the grout stop plug is filled by quick setting cement slurry tightly to ensure that the grout cannot flow out during the grouting, the anchor rod cannot be knocked randomly after, the end part of the steel tube is not hung with a heavy object within 3 days; the tail end of the anchor rod is welded with a steel arch frame or a steel frame as much as possible so as to form a common stress system);

5.6, mounting a base plate and a nut: after the strength of the grouting liquid reaches a preset strength, a backing plate (200 multiplied by 10mm A3 steel plate) is installed to be tightly attached to the rock surface, a rod end nut is tightened to generate a certain prestress to play a better role in reinforcing surrounding rocks, the anchor rod and the backing plate are kept perpendicular to each other and are in full contact with sprayed concrete, and the nut must be screwed;

6. the primary shotcrete (the primary tunnel adopts wet shotcrete, which solves the problem of dust and resilience, improves the quality of shotcrete, and eliminates free cement particles from the finished concrete, so that no dust is generated during the transportation, feeding and feeding processes of the shotcrete machine, and protects the working environment

6.1, preparing concrete spraying raw materials:

cement: the ordinary Portland cement with the design requirement label is adopted, and the strength rechecking test is carried out before the use, so that the performance of the Portland cement meets the current cement standard;

fine aggregate: sieving medium coarse sand with fineness modulus of more than 2.5 with 5mm sieve;

coarse aggregate: machine-made crushed stone with the particle size of 5 mm-15 mm;

water: tap water is adopted;

accelerator: the liquid setting accelerator is adopted, a compatibility test is carried out on the liquid setting accelerator and cement before use, and a clear slurry test with a water-cement ratio of 0.4 meets the requirements that the initial setting time is less than 5min, the final setting time is less than 10min, the doping amount is less than 5% of the cement amount, and the 28-day strength retention rate is more than 70%;

6.2, stirring the concrete wet material: stirring by a forced stirrer to form a spray material, wherein the stirring time is not less than 3 minutes; the used material metering device that throws of regular inspection stirring, the configuration deviation accords with standard requirement, and the ash-bone ratio: 1: 3.5-1: 4.0, water cement ratio of 0.42-0.50, and concrete slump of 8-12 cm;

6.3, concrete spraying construction: processing the sprayed surface, burying a sprayed layer thickness mark, connecting ventilation water and electricity, testing, transporting sprayed materials by using a mixer truck, carrying out primary concrete spraying operation, after the primary concrete spraying operation is finished, carrying out secondary concrete spraying operation after additional spraying and mixing ratio adjustment, and finally carrying out quality inspection;

7. tunnel secondary lining (tunnel excavation, preliminary bracing, secondary lining take the alternative, section by section propulsion construction process)

7.1, base surface cleaning and measurement paying-off: cleaning up sundries on the waterproof protective layer of the bottom plate, and then paying off and popping up position lines of two side walls of the secondary lining and a control line of the bottom plate, wherein the distance between control points is not more than 5m, and iron nails or short steel bars are not needed to be used so as to avoid damaging the waterproof layer;

7.2, installing waterproof equipment;

7.3, binding inverted arch steel bars: the stressed steel bars are arranged in a double-layer mode, and the inverted arch steel bar protective layer is controlled by a mortar cushion block; a split heads control protective layer and positioning are arranged between the double layers of steel bars; the maximum diameter of the two-lining main rib is phi 20, and double-side welding is adopted. Joint positions are staggered by 35 d; the stressed steel bar joint is arranged at a position with small stress, and the joint positions are staggered for 35 d; the stressed reinforcement joints are connected by straight threads, the joints arranged in the same component are staggered, the area percentage of the reinforcement joints meets the requirements of specification and design, and the tension area is not more than 50%; when the steel bars are bound and lapped, the middle part and the two ends are bound together, and the steel bars are bound with the crossed bars after being bound separately; the main ribs and the distribution ribs can be bound in a cross way except for the binding of 2-3 rows of frameworks at the deformation joints, and binding points are buckled into a splayed shape by iron wires; binding the cross points of the stirrups and the main reinforcements;

7.4, inverted arch concrete pouring and maintenance: before concrete pouring, a pouring packway is erected on the steel bars and the split heads by adopting scaffold boards to prevent the steel bars from deforming; a ground pump is adopted for concrete pouring, and the concrete slump is controlled to be 120-160 mm; the left line and the right line of the thickness of the two concrete-lined bottom plates are 0.8m and 1m respectively, the two concrete-lined bottom plates are poured by adopting an inclined plane layering method, the mortar is poured from one end, the vibrating hands are closely matched, the concrete is kept to be pushed forwards along the bottom of the two concrete-lined bottom plates by a 'mortar driving method', the two concrete-lined bottom plates are scraped by a scraping bar while vibrating, a wooden trowel is compacted and leveled, and the two surfaces are pressed for the second time before initial setting so as to reduce concrete cracks; timely curing within 12 hours after concrete pouring, wherein the curing time is not less than 14 d;

7.5, binding the reinforcing steel bars of the arch wall: the reinforcing steel bar protective layer is controlled by a plastic cushion block; an S-shaped tie bar is arranged between two layers of reinforcing steel bars of the arch wall to control the clear distance of the reinforcing steel bars, the spacing between the tie bars is 1m, the tie bars are arranged in a quincunx shape, and other binding technologies require binding with the reinforcing steel bars of the bottom plate;

7.6, pouring the arch wall concrete: pumping concrete into a warehouse from bottom to top, filling fine stone concrete with the thickness of about 50mm and the same label as that of wall concrete from the joint of the poured section to the non-poured direction before pouring, fully utilizing a template reserved window in the pouring process, symmetrically pouring the concrete in layers, and additionally connecting a 3-5m hose with the same diameter at the front end of a discharge pipe to enable the pipe orifice to face downwards so as to avoid horizontally aligning the concrete surface with a straight pump; when the concrete pouring surface is close to the top (the concrete pouring surface is higher than the top of the template as a limit), entering a capping stage, and in order to ensure that air can be smoothly discharged, arranging an exhaust pipe (adopting a phi 20mm galvanized pipe) in a reserved grouting hole, wherein one end of the exhaust pipe is close to the top of the waterproof plate as much as possible, and the other end of the exhaust pipe is fixed in the template trolley and is firmly fixed; when water (actually, segregation water and slurry on the surface layer of the concrete) flows out of the exhaust pipe along with the continuous pouring, namely the bin is indicated to be completely filled with the concrete, the concrete pouring is stopped, the exhaust pipe is dredged, and the pumping hose is withdrawn; pouring concrete from the inner side to the end mold direction as much as possible to remove air during capping, and filling a gap generated by concrete shrinkage by grouting the vault by using an exhaust pipe at the later stage (the concrete strength reaches over 70 percent of the design); when the concrete is vibrated by the plug-in vibrator, the following regulations should be met: the moving distance is not more than 1.5 times of the acting radius of the vibrator; the depth of inserting the concrete into the lower layer is preferably 5-10 cm, so that the upper layer and the lower layer are well combined; the vibrator is inserted into the concrete as vertically as possible, if the conditions are difficult, the vibrator can be slightly inclined, but the included angle between the vibrator and the horizontal plane is not smaller than 45 degrees; the tamping time of each hole site is generally 10-30 s based on that concrete does not significantly sink, moisture and air bubbles do not escape and the concrete begins to spread; the vertical distance from the template to the template is not less than 1/2 of the effective radius of the vibrator when the template, the steel bar and the embedded pipe fitting are not collided during vibration; the concrete must be vibrated compactly, and the phenomena of leakage vibration and over vibration are avoided; the vibration of the two lining side walls takes manual vibration as pouring, at least two grouting holes are reserved in each lining of the vault part during pouring, and the gap between the primary support and the secondary lining is backfilled and grouted after the strength of the secondary lining concrete reaches 100 percent, so that the close adhesion of the primary support and the secondary lining is ensured.

7.7, dismantling the template: the mould can be disassembled after the concrete reaches 80% of the design strength;

7.8, concrete curing: and (3) spraying water for curing in time after the arch wall concrete is finally set, wherein the arch wall concrete is in a wet state during curing, and the curing time is not less than 14 d.

Furthermore, the over-excavated part in the excavation in the step 2.1 and the step 2.2 needs to be backfilled densely, and a grouting hole is reserved for secondary grouting filling.

Furthermore, in the excavation process of the step 2, overbreak is reduced as much as possible, underexcavation is strictly controlled, and only when the rock stratum is complete and the compressive strength is more than 30MPa and the stability and the strength of the lining structure are not influenced, the individual protruding part (more than 0.1m in each square meter) of the rock can invade the lining, and the invasion amount is not more than 50 mm; the section of the arch foot and the wall foot which are 1m above is strictly prohibited from underdigging.

Further, in the step 2, for the excavation of the shallow buried section of the tunnel, surface subsidence needs to be strictly controlled, and the footage of circular excavation and the collapse are reduced, and the concrete measures are as follows: in the construction process, in order to reduce disturbance to surrounding rocks, excavating machines and pneumatic picks are adopted for excavating soft strata and loose and broken sections, buildings affect large sections, the construction footage speed is reduced, and the footage of each excavation is not more than one; and the observation and feedback of the surface subsidence and the vault subsidence are enhanced to guide the construction.

Further, the steel frame machining tolerance in step 3.1 is as follows: the contour error along the periphery of the tunnel is not more than 3cm, the plane warpage is less than 2cm, and the connector connection requirements can be interchanged among the same types; the standard type and unit number of each unit of the steel frame must be determined, and the units are piled in the semi-finished product storage area for standby.

Further, when the steel frame processed finished product in the step 3.1 is subjected to a structural test, the steel frame is assembled into a ring on a workbench, an oil top seat is welded on the outer side of the ring, an oil top is adopted, and an instrument is pressurized according to a design load. And measuring the internal force and deformation condition of the steel frame by using a stress meter and a convergence instrument.

Further, the steel frame installed in step 3.3 must ensure that the arch center plane is perpendicular to the tunnel center line, the vertical perpendicularity is measured by using a plumb sphere, the longitudinal measurement is performed by using an equidistant method, and a measurer needs to measure the accurate mileage of the steel frame and correct the previous cycle when each machine team steel frame is installed.

Furthermore, in the step 3.3, the type and the use part of each steel frame are marked during the installation of the steel frame, so that the phenomenon that the construction time is delayed due to the fact that workers take mistakes is prevented; the blanking length of each section of steel frame is reasonably designed, so that each section of steel frame is not too heavy and is convenient to operate; the connecting steel plate bolt holes are drilled by a bench drill in a unified mode, so that the bolt holes are guaranteed to be in one-to-one butt joint, and the operation is convenient; when the upper step steel frame is installed, the steel frame arch foot connecting steel plate bolt holes are wrapped by geotextile, and bolt connecting time can be saved when the lower step steel frame is constructed.

Further, the primary shotcrete operation of the step 6 is performed in a segmented and segmented manner, and the shotcrete operation is performed from bottom to top by firstly spraying the gap part between the steel frame and the arch wall and then spraying the part between the two steel frames; spraying the concrete layer by layer, wherein the thickness of one-time spraying is determined according to the spraying position and the design thickness, the arch part is preferably 5-6 cm, the side wall is 7-10 cm, and the later spraying layer is sprayed after the former layer is finally set or after one hour is separated; during spraying, the materials are sprayed from bottom to top, namely, the wall foot is firstly sprayed to the wall top, the arch top is secondly sprayed to avoid dead angles, the material bundle moves in a spiral rotating track, half circle is pressed for one circle, the materials are longitudinally sprayed in a snake shape, and the length of the snake-shaped spray is 50mm each time; spraying water for curing after the sprayed concrete is finally set for 2 hours, wherein the spraying time is determined to ensure that the concrete has a sufficient wet state, and the curing time is not less than 14 days; the sprayed concrete surface should be compact and flat without cracks, falling off, spray leakage, hollowing, water leakage and the like, and the unevenness tolerance is +/-3 cm.

Further, the remarks of step 6 are as follows:

1) the concrete construction mixing proportion is strictly controlled, the mixing proportion is determined by tests, all indexes of the concrete must meet the design and specification requirements, and the weighing precision of the concrete mixing materials must meet the specification requirements;

2) the quality of the raw materials is strictly controlled, and all indexes of the raw materials must meet the requirements;

3) the reasonable air pressure is determined in the concrete spraying construction, and the spraying is ensured to be uniform and continuous. Meanwhile, the maintenance of the equipment is enhanced, and the working performance of the equipment is ensured;

4) the spraying operation is operated by an experienced and skilled spraying hand, so that the close connection of all layers of sprayed concrete is ensured;

5) before spraying concrete, the installation work of the advanced small guide pipe, the reinforcing mesh and the steel frame is completed according to the design requirement;

6) spraying water for curing the sprayed concrete by a specially-assigned person to reduce cracking caused by hydration heat, marking the cracks with red paint, observing and monitoring to determine whether the cracks continue to develop or not, and finding out reasons and processing if the cracks continue to develop;

7) the 'four not' system is firmly implemented: namely, the working procedure of spraying concrete is not finished, the tunnel face does not advance, the thickness of the sprayed concrete is not enough to advance, the problem found after the concrete is sprayed is not solved and does not advance, and the monitoring result shows that the concrete is unsafe and does not advance. The system is executed by the on-site pilot, and the pilot takes charge of the personnel and makes a record in the project construction log for inspection;

8) grouting after primary support of the back: a42 grouting steel perforated pipes are pre-buried in the range of the arch wall during primary support construction, and cement paste is timely injected after the treatment is completed by 3-5m, so that the density of the primary support is ensured. Grouting parameters: the length of the pipe is 0.5m of the thickness of the initial branch, the wall thickness is 4mm, the distance between grouting pipes is 1.5 multiplied by 2.0m (ring multiplied by longitudinal), the grouting water cement ratio is 0.5-1.0MPa, and the grouting pipe is arranged in a quincunx manner.

Further, the construction precautions in step 7 are as follows:

1) rechecking whether the trolley template, the center line and the elevation meet the requirements, whether the clearance size meets the requirements and whether the trolley and the stop head die are firmly installed and positioned;

2) whether the joints of the templates are tightly filled or not and whether the release agent is uniformly coated or not;

3) whether the substrate is cleaned up or not and whether the construction joint is processed or not;

4) whether the water stop strip and the water stop belt meet the design and standard requirements or not.

Further, the tunnel secondary lining of the step 7 adopts segmented construction, namely YDK35+ 440- +445, accounting for 5 m; YDK35+445 to +450, accounting for 5 m; YDK35+ 450- +455, accounting for 5 m; YDK35+ 455- +460, 5 m; a total of 20 m; ZDK35+ 448- +453, accounting for 5 m; ZDK35+ 453- +458, accounting for 5 m; ZDK35+ 458- +463, counting 5 m; ZDK35+ 463- +468, 5 m; ZDK35+ 468- +474, accounting for 6 m; totaling 26 m.

After the steps are adopted, the beneficial effects of the specific embodiment are as follows: the cold excavation underpass overpass construction method reduces disturbance to the surrounding environment during tunnel excavation, reduces construction risks, and ensures the operation safety of the existing overpass.

The above description is only for the purpose of illustrating the technical solutions of the present invention and not for the purpose of limiting the same, and other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention should be covered within the scope of the claims of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims (9)

1. A cold excavation underpass overpass construction method is characterized by comprising the following steps: the construction steps are as follows:

(1) advanced pre-support construction

(1.1) advanced small catheter support

(1.1.1), preparation of the advanced small conduit grouting equipment and grouting materials: the grouting equipment adopts an FBY double-liquid grouting machine; the grouting material is silicate cement slurry of P.O42.5, and the water-cement ratio is 0.5: 1-1: 1; the test is carried out before grouting, and the actual operation is carried out after the sample meets the standard requirement; pouring the required water into a stirring barrel, pouring the cement into the stirring barrel according to the proportion, mechanically stirring, uniformly stirring for later use, and using the cement slurry along with stirring;

(1.1.2) processing and installing the advanced small guide pipe: the small guide pipe is processed by a phi 42 seamless steel pipe, and the front end of the small guide pipe is processed into a cone shape so as to be convenient for inserting and beating and prevent slurry from rushing forwards; drilling 6-8 mm grouting holes in the middle of the small guide pipe, arranging the grouting holes in a quincunx shape, enabling the distance to be 20cm, not drilling holes in the range of 1m at the tail part, preventing slurry leakage, welding an annular iron hoop at the tail end, and preventing the end part from cracking during driving to influence the connection of grouting pipes, wherein during construction, holes are drilled by an air pick, and the air drill is jacked; connecting the small guide pipe after drilling and sealing the hole opening;

(1.1.3) leading small conduit grouting: grouting from no water hole to water hole, from less water to more water hole, and jumping to pressure grouting; recording the length, the pressure injection time, the slurry consumption and various problems and solutions on site of each small conduit in a specified format record table during construction;

(1.1.4) leading small pipe grouting finishing standard definition:

single well end criteria: when grouting, firstly slow and then fast, firstly low pressure and then high pressure are needed, the pressure is not more than 0.2Mpa when grouting is started, the pressure is gradually increased along with the increase of the grouting amount until the designed value is reached, the standard of the grouting ending is that the single-hole grouting amount reaches the designed value, the grouting pressure reaches the designed value and continues grouting for 2min, and the grouting amount is less than 1/4 of the initial grouting amount, so that the grouting can be ended;

end of full segment criterion: finishing grouting according to the standard in all grouting holes, wherein no obvious water leakage point exists in the tunnel;

(1.1.5) quality acceptance of the advanced small catheter;

(1.2) Large pipe shed support

(1.2.1), preparing grouting equipment and grouting materials for the large pipe shed: the grouting equipment adopts an FBY (fluid bed bio-grouting) grouting machine, the grouting material adopts P.O 42.5.5 silicate cement slurry, the water-cement ratio is 0.5: 1-1: 1, when groundwater development or the slurry diffusion range is large, the grouting slurry is cement-water glass dual-liquid slurry, required water is poured into a stirring barrel firstly, cement is poured into the stirring barrel according to the proportion, mechanical stirring is carried out, the cement slurry is uniformly stirred for later use, and the cement slurry is used along with stirring;

(1.2.2) processing and installing a large pipe shed:

specification of the conduit: the hot-rolled seamless steel perforated pipe has the advantages that the outer diameter is 159mm, the wall thickness is 10mm, the length of a left tunnel is 26m, and the length of a right tunnel is 20 m; tube distance: the circumferential distance is 35 cm; inclination angle: the external insertion angle is 0-3 degrees; connecting steel pipes of the large pipe shed are connected by connecting steel pipes of phi 180 x 10mm and 40cm in length, in order to enable joints of the large pipe shed to be arranged in a staggered mode, pipe shed sections with odd-numbered holes are arranged according to 4 x 4.5m +2.0m, pipe shed sections with even-numbered holes are arranged according to 2.0m +4 x 4.5m, pipe shed sections with odd-numbered holes are arranged according to 5 x 4.5m +3.5m, and pipe shed sections with even-numbered holes are arranged according to 3.5m +5 x 4.5 m; the large pipe shed is formed by processing a phi 159 seamless steel pipe, the front end of the large pipe shed is processed into a cone, a reinforcement cage is additionally arranged in the guide pipe and consists of four C18HRB400 main reinforcements and a fixing ring, the fixing ring adopts a short pipe joint, the fixing ring is welded with the main reinforcements and is arranged at an interval of 1m, phi 10-16 mm grouting holes are drilled in the middle of the pipe shed and are arranged in a quincunx shape, the interval is 20cm, and no hole is drilled in the range of 1.5m at the tail part; the large pipe shed is constructed by adopting a pipe-following drilling method so as to reduce the problem of ground settlement caused by construction of the pipe shed;

(1.2.3) grouting the large pipe shed: the grouting sequence is from no water hole to water hole, from little water to many water holes, and the pressure grouting is required to be jumped off, and the length of each pipe shed, the pressure grouting time, the slurry consumption and various problems and solutions on site need to be recorded into a specified format recording table in the construction process so as to analyze the front geological condition;

(1.2.4) grouting the large pipe shed, and defining the grouting end standard:

single well end criteria: gradually raising the grouting pressure, and stabilizing for 10min when the designed final pressure is reached; the grouting amount is not less than 80% of the designed grouting amount; 1/4, the slurry inlet speed is less than the initial slurry inlet speed;

(1.2.5) checking and accepting the quality of the large pipe shed;

(2) digging hole body

(2.1) non-blasting excavation upper step

Section of application

Branch of early dawnProtecting; is at the completion of

Temporarily suspended after 5m of primary support

Excavating, and spraying C25 concrete with the thickness of 5cm to seal the tunnel face;

(2.2) non-blasting excavation upper step

Section of application

Supporting at the initial stage; is at the completion of

Temporarily suspended after 5m of primary support

Excavating, and spraying C25 concrete with the thickness of 5cm to seal the tunnel face;

(2.3) paving an inverted arch waterproof layer in time and pouring

Concrete for the inverted arch and the side wall;

(2.4) perfusion invert filling

Part to design height;

(2.5) applying and casting the waterproof layer of the arch wall at one time

Partial arch wall concrete;

(2.6) repeating the steps (2.1) - (2.6) to carry out next lining circulating construction after the strength of the second-lining concrete reaches 80% of the design strength;

(3) steel frame processing and mounting

(3.1) steel frame processing: technical personnel recheck the technical parameters of the steel frame unit division and the radius and the arc length of each unit according to the drawing size, issue a technical intersection after no error, and process the steel frame through a section steel cold bending machine on site;

the steel frame is machined on the steel bar machining shed according to the design size, the steel frame connecting steel plates need to be drilled by using a bench drill, electric welding or acetylene hole burning is not needed, the unit steel frames need to be organized and assembled after being machined, and batch production and use can be realized after the steel frame size and the outline are inspected to be qualified;

(3.2) measuring and positioning: after excavation is finished, after concrete is sprayed for the first time, a steel frame is installed, a center line elevation method is adopted for positioning the steel frame, a center line of a tunnel is determined according to a total station, the support distance of the end of the steel frame is measured symmetrically according to the center line to enable the steel frame to meet design values, meanwhile, a leveling instrument is adopted to measure the elevations of control points of the arch crown, the arch foot and the inverted arch bottom of the steel frame, and the steel frame is adjusted to enable the steel frame to meet design requirements;

(3.3) steel frame installation: after the steel frame positions are adjusted, bolts between steel frames are screwed, phi 22 longitudinal connecting steel bars are arranged between two steel frames, the circumferential distance is 1000mm, the steel bars are arranged in a single layer, the connecting steel bars are lengthened by adopting double-sided lap welding, and the steel bars on two sides are ensured to be on the same axis during welding;

(3.4) paving the reinforcing mesh: the reinforcing mesh adopts phi 8 reinforcing steel bars, the spacing is 200mm multiplied by 200mm, reinforcing mesh sheets are processed outside the hole for standby according to the designed arch center spacing in advance, the reinforcing mesh sheets are processed by a reinforcing binding machine, and the reinforcing mesh sheets are paved after anchor rods are applied; the reinforcing mesh is tightly attached to the primary spraying surface along with the height, shallow holes are drilled by using impact drills to embed expansion bolts, and the reinforcing mesh is fixed on the bolts and is welded with the tail part of the anchor rod; manufacturing the holes in a split mode, wherein the lap joint length is not less than 10cm during installation; manually laying, and if necessary, using a pneumatic drill pneumatic leg for jacking to be close to the rock surface, and firmly binding and connecting with the anchor rod and the steel frame; when the reinforcing mesh and the steel frame are bound, the reinforcing mesh and the steel frame are bound on one side close to the rock surface; when concrete is sprayed, the distance from the spray head to a sprayed surface and the air pressure are adjusted, so that the vibration of the reinforcing mesh is reduced, and the resilience is reduced; the thickness of the concrete protective layer of the reinforcing mesh is not less than 2 cm;

(4) mortar anchor rod construction

(4.1), drilling: the drilling machine is selected according to the type and the specification of the anchor rod and the surrounding rock condition; the allowable deviation of the hole positions is +/-150 mm, and the drilling quantity meets the design specification; the diameter of the drilled hole must be larger than the diameter of the anchor rod body by 15 mm; the hole depth is not less than the effective length of the anchor rod body, but the depth overlength value is not more than 100 mm;

(4.2) grouting: the holes must be blown clean before grouting; the cement mortar must be uniformly mixed and used along with the mixing; grouting is full, the grouting is uniformly carried out from the bottom of the hole without interruption, and the phenomenon that the pipe is pulled out too fast to cause mortar dislocation and insufficient grouting is strictly prevented; the grouting pipe must be inserted to a position 5-10 cm away from the bottom of the hole, and is slowly pulled out at a constant speed along with the injection of cement mortar, and then the rod body is rapidly inserted, the length of the anchor rod body inserted into the hole is not shorter than 95% of the designed length, if no mortar flows out from the hole opening, the rod body must be pulled out and re-grouted, the anchor rod cannot be knocked randomly after being installed, and a heavy object cannot be hung at the end part of the anchor rod within 3 days;

(4.3) anchor rod installation: before installation, the reinforcing steel bars need to be derusted and straightened; after grouting, the reinforcing steel bars must be inserted at a constant speed and centered; the hole opening can be temporarily sealed by a wood wedge; the exposed length of the tail end of the steel bar is slightly smaller than the thickness of the spraying layer; knocking and collision cannot occur after the installation is finished, and the insertion depth of the anchor rod is not less than 95% of the design requirement; when the cement mortar anchor rod is adopted in a water section, if water flows in the hole, a hole is additionally drilled nearby to be used as a flow guide pipe, and anchor rod operation is carried out after water is discharged;

(5) hollow grouting anchor rod construction

(5.1) construction preparation: carrying out anchor rod installation operation in time after the concrete is initially sprayed, and checking whether an anchor rod hole is smooth or not; checking whether the air compressor, the pipeline of the air compressor and the air gun are in good states;

(5.2) drilling the anchor rod: an anchor rod is drilled by adopting an air-leg air gun rock drilling machine, and a hole position is determined according to design requirements and in combination with the occurrence of surrounding rock before drilling to mark; aligning a drill bit to a calibrated position, enabling the drilling direction to be perpendicular to a rock stratum structure surface as much as possible so as to play a better reinforcing role, and keeping the length of an exposed section of the anchor rod within 10-15 cm when drilling is finished;

(5.3) cleaning the holes: after drilling to the designed depth, cleaning the hole with water or high-pressure air, and detaching the drill rod connecting sleeve after the smoothness is confirmed;

(5.4) driving the anchor rod: driving an anchor rod in a jacking mode of an air gun;

(5.5) grouting: adopting an extrusion type grouting pump for grouting, wherein the grouting slurry is M20 cement slurry, driving a grout stop plug into an orifice through the exposed end of the anchor rod by using a hole cap assembly, checking grouting equipment, preparing the cement slurry according to a mixing proportion, starting the grouting pump for grouting until the grout is extruded from the periphery of the orifice or a pressure gauge reaches a designed pressure value, stopping grouting when the pressure of the orifice is 0.7-1.0 MPa for the hollow grouting anchor rod, stopping grouting after the pressure is reached for 15min, and cleaning the grouting machine and a pipeline by using water in time after the grouting is finished;

(5.6), mounting a base plate and a nut: after the strength of the grouting liquid reaches the preset strength, a backing plate is installed and is tightly attached to the rock surface, a rod end nut is tightened to generate certain prestress, the effect of better reinforcing surrounding rock is achieved, the anchor rod and the backing plate are kept perpendicular and are in full contact with sprayed concrete, and the nut needs to be tightened;

(6) primary shotcrete

(6.1) preparing concrete spraying raw materials:

cement: the ordinary Portland cement with the design requirement label is adopted, and the strength rechecking test is carried out before the use, so that the performance of the Portland cement meets the current cement standard;

fine aggregate: sieving medium coarse sand with fineness modulus of more than 2.5 with 5mm sieve;

coarse aggregate: machine-made crushed stone with the particle size of 5 mm-15 mm;

water: tap water is adopted;

accelerator: the liquid setting accelerator is adopted, a compatibility test is carried out on the liquid setting accelerator and cement before use, and a clear slurry test with a water-cement ratio of 0.4 meets the requirements that the initial setting time is less than 5min, the final setting time is less than 10min, the doping amount is less than 5% of the cement amount, and the 28-day strength retention rate is more than 70%;

(6.2) stirring the concrete wet material: stirring by a forced stirrer to form a spray material, wherein the stirring time is not less than 3 minutes; the used material metering device that throws of regular inspection stirring, the configuration deviation accords with standard requirement, and the ash-bone ratio: 1: 3.5-1: 4.0, water cement ratio of 0.42-0.50, and concrete slump of 8-12 cm;

(6.3) concrete spraying construction: processing the sprayed surface, burying a sprayed layer thickness mark, connecting ventilation water and electricity, testing, transporting sprayed materials by using a mixer truck, carrying out primary concrete spraying operation, after the primary concrete spraying operation is finished, carrying out secondary concrete spraying operation after additional spraying and mixing ratio adjustment, and finally carrying out quality inspection;

(7) secondary lining of tunnel

(7.1), base surface cleaning, measurement and paying-off: cleaning up sundries on the waterproof protective layer of the bottom plate, and then paying off and popping up position lines of two side walls of the secondary lining and a control line of the bottom plate, wherein the distance between control points is not more than 5m, and iron nails or short steel bars are not needed to be used so as to avoid damaging the waterproof layer;

(7.2) installing waterproof equipment;

(7.3) binding inverted arch steel bars: the stressed steel bars are arranged in a double-layer mode, and the inverted arch steel bar protective layer is controlled by a mortar cushion block; a split heads control protective layer and positioning are arranged between the double layers of steel bars; the maximum model diameter of the secondary lining main reinforcement is phi 20, double-sided welding is adopted, and the joint positions are staggered for 35 d; the stressed steel bar joint is arranged at a position with small stress, and the joint positions are staggered for 35 d; the stressed reinforcement joints are connected by straight threads, the joints arranged in the same component are staggered, the area percentage of the reinforcement joints meets the requirements of specification and design, and the tension area is not more than 50%; when the steel bars are bound and lapped, the middle part and the two ends are bound together, and the steel bars are bound with the crossed bars after being bound separately; the main ribs and the distribution ribs can be bound in a cross way except for the binding of 2-3 rows of frameworks at the deformation joints, and binding points are buckled into a splayed shape by iron wires; binding the cross points of the stirrups and the main reinforcements;

(7.4) pouring and maintaining inverted arch concrete: before concrete pouring, a pouring packway is erected on the steel bars and the split heads by adopting scaffold boards to prevent the steel bars from deforming; a ground pump is adopted for concrete pouring, and the concrete slump is controlled to be 120-160 mm; the left line and the right line of the thickness of the two concrete-lined bottom plates are 0.8m and 1m respectively, the two concrete-lined bottom plates are poured by adopting an inclined plane layering method, the mortar is poured from one end, the vibrating hands are closely matched, the concrete is kept to be pushed forwards along the bottom of the two concrete-lined bottom plates by a 'mortar driving method', the two concrete-lined bottom plates are scraped by a scraping bar while vibrating, a wooden trowel is compacted and leveled, and the two surfaces are pressed for the second time before initial setting so as to reduce concrete cracks; timely curing within 12 hours after concrete pouring, wherein the curing time is not less than 14 d;

(7.5) binding the arch wall reinforcing steel bars: the reinforcing steel bar protective layer is controlled by a plastic cushion block; an S-shaped tie bar is arranged between two layers of reinforcing steel bars of the arch wall to control the clear distance of the reinforcing steel bars, the spacing between the tie bars is 1m, the tie bars are arranged in a quincunx shape, and other binding technologies require binding with the reinforcing steel bars of the bottom plate;

(7.6) pouring the arch wall concrete: pumping concrete into a warehouse from bottom to top, filling fine stone concrete with the thickness of about 50mm and the same label as that of wall concrete from the joint of the poured section to the non-poured direction before pouring, fully utilizing a template reserved window in the pouring process, symmetrically pouring the concrete in layers, and additionally connecting a 3-5m hose with the same diameter at the front end of a discharge pipe to enable the pipe orifice to face downwards so as to avoid horizontally aligning the concrete surface with a straight pump; when the concrete pouring surface is close to the top, entering a capping stage, and in order to ensure that air can be smoothly discharged, installing an exhaust pipe in a reserved grouting hole, wherein one end of the exhaust pipe is close to the top of the waterproof plate as much as possible, and the other end of the exhaust pipe is fixed in the template trolley and is firmly fixed; when water flows out of the exhaust pipe along with the continuous pouring, namely the bin is indicated to be completely filled with concrete, the concrete pouring is stopped, the exhaust pipe is dredged, and the pumping hose is withdrawn; pouring concrete from the inner side to the end mold direction as much as possible to remove air during capping, and filling a gap generated by concrete shrinkage by grouting the vault through an exhaust pipe at the later stage;

(7.7) removing the template: the mould can be disassembled after the concrete reaches 80% of the design strength;

(7.8) concrete curing: and (3) spraying water for curing in time after the arch wall concrete is finally set, wherein the arch wall concrete is in a wet state during curing, and the curing time is not less than 14 d.

2. The cold excavation underpass overpass construction method of claim 1, characterized in that: and (3) backfilling the over-excavated part in the excavation in the step (2.1) and the step (2.2) to be compact, and reserving a grouting hole for secondary grouting filling.

3. The cold excavation underpass overpass construction method of claim 1, characterized in that: in the step (2), overbreak is reduced as much as possible in the excavation process, underbreak is strictly controlled, and the outburst part of the rock, which is more than 0.1m per square meter, can invade the lining only when the rock stratum is complete and the compressive strength is more than 30MPa and the stability and the strength of the lining structure are not influenced, and the invasion amount is not more than 50 mm; the section of the arch foot and the wall foot which are 1m above is strictly prohibited from underdigging.

4. The cold excavation underpass overpass construction method of claim 1, characterized in that: in the step (2), for the excavation of the shallow buried section of the tunnel, the surface subsidence needs to be strictly controlled, the footage of the circular excavation is reduced, and the collapse is placed, and the concrete measures are as follows: excavating by adopting an excavator and an air pick, the influence of buildings on a large section is reduced, the construction footage speed is reduced, and the footage of each excavation is not more than one; and the observation and feedback of the surface subsidence and the vault subsidence are enhanced to guide the construction.

5. The cold excavation underpass overpass construction method of claim 1, characterized in that: the steel frame machining tolerance in the step (3.1) is as follows: the contour error along the periphery of the tunnel is not more than 3cm, the plane warpage is less than 2cm, and the connector connection requirements can be interchanged among the same types; the standard type and unit number of each unit of the steel frame must be determined, and the units are piled in the semi-finished product storage area for standby.

6. The cold excavation underpass overpass construction method of claim 1, characterized in that: when the steel frame processed finished product in the step (3.1) is subjected to a structural test, assembling the steel frame on a workbench into a ring, welding an oil top seat on the outer side, adopting an oil top, and pressurizing an instrument according to a design load; and measuring the internal force and deformation condition of the steel frame by using a stress meter and a convergence instrument.

7. The cold excavation underpass overpass construction method of claim 1, characterized in that: and (3.3) ensuring that the plane of the arch frame is vertical to the central line of the tunnel by the installed steel frame, measuring the vertical verticality by adopting a vertical ball, measuring the vertical verticality by adopting an equidistant method, and measuring the mileage of the steel frame accurately by measuring staff and correcting the previous cycle when each class steel frame is installed.

8. The cold excavation underpass overpass construction method of claim 1, characterized in that: the primary support concrete spraying operation in the step (6) is carried out in a segmented and separated mode, the spraying operation is carried out from bottom to top, the gap part between the steel frame and the arch wall is sprayed firstly, and the part between the two steel frames is sprayed secondly; spraying the concrete layer by layer, wherein the thickness of one-time spraying is determined according to the spraying position and the design thickness, the arch part is preferably 5-6 cm, the side wall is 7-10 cm, and the later spraying layer is sprayed after the former layer is finally set or after one hour is separated; during spraying, the materials are sprayed from bottom to top, namely, the wall foot is firstly sprayed to the wall top, the arch top is secondly sprayed to avoid dead angles, the material bundle moves in a spiral rotating track, half circle is pressed for one circle, the materials are longitudinally sprayed in a snake shape, and the length of the snake-shaped spray is 50mm each time; spraying water for curing after the sprayed concrete is finally set for 2 hours, wherein the spraying time is determined to ensure that the concrete has a sufficient wet state, and the curing time is not less than 14 days; the sprayed concrete surface should be compact and flat without cracks, falling off, spray leakage, hollowing and water leakage, and the unevenness tolerance deviation is +/-3 cm.

9. The cold excavation underpass overpass construction method of claim 1, characterized in that: the tunnel secondary lining of the step (7) adopts segmented construction, namely YDK35+ 440- +445, which is counted as 5 m; YDK35+445 to +450, accounting for 5 m; YDK35+ 450- +455, accounting for 5 m; YDK35+ 455- +460, 5 m; a total of 20 m; ZDK35+ 448- +453, accounting for 5 m; ZDK35+ 453- +458, accounting for 5 m; ZDK35+ 458- +463, counting 5 m; ZDK35+ 463- +468, 5 m; ZDK35+ 468- +474, accounting for 6 m; totaling 26 m.

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