CN112177635A - Construction method of step multiple advanced small guide pipe and construction method of overlapped tunnel - Google Patents

Abstract

The invention relates to a construction method of a step multiple advanced small conduit and a construction method of an overlapped tunnel, belonging to the technical field of tunnel construction.A row of small conduits are arranged in the range of 120-180 degrees of an arch part of a tunnel for grouting reinforcement; small guide pipes are arranged at certain intervals along the longitudinal direction, and the small guide pipes are longitudinally lapped by 2-4 m; the circumferential spacing of the small guide pipes in the same row is 0.2 m. The invention adopts the step multiple advanced small guide pipe grouting in the arch part, can control the deformation of the surrounding rock, is beneficial to ensuring the stability of the tunnel surrounding rock, and thus achieves the purpose of ensuring the safety of tunnel construction; when the method is used for constructing the overlapped tunnel, the shield tunnel which is already constructed is used as the upper behavior, and the middle soil interlayer is grouted and reinforced before the lower part tunnel is excavated; meanwhile, multi-step advanced small conduit grouting reinforcement is implemented at the arch part of the lower tunnel line, so that the safety of tunnel construction is ensured.

Description

Construction method of step multiple advanced small guide pipe and construction method of overlapped tunnel

Technical Field

The invention relates to the technical field of tunnel construction, in particular to a construction method of a step multiple advanced small guide pipe and an overlapped tunnel construction method.

Background

When the tunnel passes through the weak and broken surrounding rocks, the excavation disturbance can cause larger surrounding rock deformation. If the primary support is unscientific, the deformation of the surrounding rock may exceed the allowable range, and in severe cases, the tunnel face is unstable, the tunnel collapses, and great economic loss is caused.

In addition, with the increasing urban population and urban size, subways have become a major vehicle and regional hub tool in a large city. In recent years, with the continuous development of subway lines, the overlapping of multi-line subways in different space areas becomes the technical difficulty and the key point of municipal engineering construction, and particularly, the technical difficulty of ultra-small clear distance construction between tunnels is more prominent in municipal engineering.

Disclosure of Invention

The invention provides a construction method of a step multiple advancing small conduit and a construction method of an overlapping tunnel, aiming at solving the technical problems.

The invention is realized by the following technical scheme:

the construction method of the step multiple advanced small guide pipe comprises the steps of drilling a row of small guide pipes in the range of 120-180 degrees at the arch part of a tunnel for grouting reinforcement; the small guide pipes are arranged at certain intervals along the longitudinal direction, and are longitudinally lapped by 2-4 m.

Preferably, a row of small ducts is drilled within 150 ° of the tunnel arch.

Preferably, the circumferential spacing of the small ducts of the same row is 0.2 m.

Preferably, the small ducts overlap longitudinally by 3 m.

Further preferably, the small duct has an insertion angle of 15 ° to 20 °.

Furthermore, a row of small guide pipes are arranged for each two steel frames.

Preferably, the small conduit is a seamless steel pipe with a diameter of 42 mm.

Preferably, the small conduit has a length of 3.5m to 4 m.

Furthermore, one end of the small conduit is a conical tip, the other end of the small conduit is connected with an iron hoop, and a plurality of grouting holes are formed in the pipe body of the small conduit.

An overlapping tunnel construction method includes the following steps;

s1, constructing an upper shield tunnel of the overlapping area;

s2, grouting and reinforcing the middle soil interlayer between the overlapped tunnels;

s3, constructing a lower tunnel of the overlapping area; in the step, the construction method of the stepped multiple advanced small conduit is adopted to construct the advanced support.

Compared with the prior art, the invention has the following beneficial effects:

the method adopts the step multiple advanced small guide pipes for grouting in the arch part, can control the deformation of surrounding rocks, is beneficial to ensuring the stability of the surrounding rocks of the tunnel, and thus achieves the purpose of ensuring the safety of tunnel construction;

2, when the method is used for constructing the overlapped tunnel, the shield tunnel which is already constructed is used as the upper action, and the middle soil interlayer is grouted and reinforced before the lower tunnel is excavated; meanwhile, multiple advanced small guide pipe grouting reinforcement of the ladder is implemented at the arch part of the lower tunnel line, and the safety of tunnel construction is favorably ensured.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention.

FIG. 1 is a flow chart of an advanced grouting process;

FIG. 2 is a view of a stepped multiple microcatheter arrangement;

FIG. 3 is a schematic view of a small catheter configuration;

FIG. 4 is a plan view of the overlapping section of the No. 6 line mining tunnel and the No. 9 line shield tunnel;

FIG. 5 is a flow chart of the present invention;

FIG. 6 is a schematic view of a tie-beam reinforced shield tunnel;

FIG. 7 is a flow chart of a forward grouting process;

FIG. 8 is a schematic view of a full face advancing grout hole arrangement;

FIG. 9 is a schematic view of full-face grouting reinforcement and water stop;

FIG. 10 is a greatly enlarged view of an orifice tube;

FIG. 11 is a schematic view of a blasthole charging configuration;

FIG. 12 is a schematic cross-sectional view of a mine tunnel lining;

FIG. 13 is a plan view of the monitoring measuring points of shield segments of No. 9 lines.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

As shown in figure 1, the construction method of the step multiple advanced small guide pipe disclosed by the invention is characterized in that a row of small guide pipes with the diameter of 42mm is arranged in the range of 120-180 degrees of the arch part of the tunnel for grouting reinforcement before excavation.

As shown in fig. 2, in the present embodiment, a row of small ducts 21 is arranged in the arch part of the 6 th tunnel within 150 °. The small catheters 21 are arranged in an encrypted manner, and the circumferential distance is 0.2 m. The small guide pipe 21 adopts a seamless steel pipe with the diameter of 42mm, the wall thickness is 3.5mm, and the length is 3.5m-4.0 m. The external insertion angle of the small conduit 21 is 15-20 degrees.

The steel frame pitch was adjusted to 0.5 m/pin from 0.667 m/pin originally designed. A row of small ducts are arranged on each two steel frames 22 to be supported, grouting is carried out, and the small ducts 21 are longitudinally overlapped by 2-4 m, so that a step multiple advanced small duct structure is formed, and the supporting effect is enhanced. Preferably, the small ducts 21 overlap longitudinally by 3 m.

As shown in fig. 3, one end of the small conduit 21 is made into a tapered shape, and the other end is welded with an iron hoop 23. The length of the cone tip is 0.1 m. A plurality of pulp outlet holes 24 are arranged on the pipe body of the small guide pipe 21, and the pulp outlet holes 24 are arranged in a quincunx shape at intervals of 0.2m along the pipe wall; the holes are mutually 90 degrees, and the aperture is 6-8 mm.

The grout outlet 24 is arranged from a position 0.5-1.0 m away from the iron hoop to the conical tip.

The advance small conduit grouting pressure is determined according to the stratum compactness, and is generally 0.5-1 MPa. The grouting material and the slurry are proportioned as follows;

the grouting material adopts cement water glass double-liquid slurry: water cement ratio 1:1

Water glass slurry water of 35 baume degree: 3:1 water glass

Proportioning cement slurry and water glass: 1:1 of water glass

Concentration regulation principle: the slurry is diluted and then concentrated, and the concentration of the slurry is adjusted in time according to the changes of the slurry feeding amount and the grouting pressure.

Wherein, the grouting amount of the small guide pipe can be calculated according to the formula (1):

Q＝π·R2·L·n·K (1)

in formula (1): r is the diffusion radius of the slurry, which can be considered as 0.2 m; L-Small catheter length; n-porosity of rock mass; k-filling factor of 0.3 to 0.5. K takes a value according to different geological conditions, and the value of the sand layer K is 0.4.

The invention also discloses an overlapped tunnel construction method, which adopts the step multiple advanced small conduit construction method to carry out advanced support.

The embodiment relies on the subway line shown in fig. 4 to describe in detail the overlapping tunnel construction method disclosed by the invention. As shown in figure 4, the line is in an east-west trend, the number 9 line is on, the number 6 line is under, and the length of the area line of the overlapping section of the number 6 line of the underground excavated tunnel and the number 9 line of the shield is 51 meters.

Firstly constructing a shield such as a No. 9 line and the like on site, and then constructing a No. 6 line, wherein the thickness of interlayer soil between the overlapped tunnels of the No. 6 and the No. 9 lines is about 2.3m, and the clear distance of an overlapped area is ultra-small; the geology of the soil-sandwiched layer is mainly strong weathering mixed rock, excavation and supporting construction is carried out by adopting working conditions of firstly going up and then going down, and spray anchoring, profile steel supporting and secondary lining are carried out immediately after excavation. Go up the action and executed 9 lines shield tunnel, be 6 lines mine method undercut tunnels down, before 6 lines excavate, add the tie beam on 9 lines shield section of jurisdiction to ensure 9 lines shield tunnel's wholeness, and carry out the slip casting through the hoisting hole on 9 lines shield section of jurisdiction to 6, 9 lines intermediate interlayer soil layer and consolidate, simultaneously, implement full section advancing type slip casting at 6 lines, ensure the advanced reinforcing effect in stratum. The No. 6 line underground excavation tunnel adopts an annular step method to reserve core soil for excavation, and the primary support is combined by a spraying, anchoring, net and steel frame, and is followed with excavation and protection and followed with a working face.

In the invention, the non-excavated section is subjected to advanced grouting, the supported section is subjected to back grouting, the primary support, the middle soil layer and the surrounding rock form a load bearing system together, and the load bearing system is deformed in a synergistic manner to fully exert the self-bearing capacity of the surrounding rock. Meanwhile, the invention also establishes a monitoring and measuring system to implement informatization management, so as to ensure that the construction process of the No. 6 line underground excavation tunnel is in a controlled state and ensure the integrity of the No. 9 line shield tunnel.

As shown in fig. 5, the overlapping tunnel construction method mainly includes the following steps;

and S1, construction preparation.

S1.1, connecting wind, water and electric pipelines in a tunnel, arranging a construction site, and well preparing machines, personnel and materials;

s1.2, analyzing and knowing engineering geology and hydrogeology conditions in detail according to geological exploration data and construction design, carefully compiling construction organization design and making a construction monitoring plan.

And S2, constructing the upper shield tunnel of the overlapping area, and reinforcing the upper shield tunnel.

As shown in fig. 6, before the tunnel excavation by the line 6 mining method, two connecting beams are respectively and longitudinally arranged in the five-point half direction and the six-point half direction of the shield segment of the line 9. The connecting beam is made of I22b section steel 31, each section steel 31 is 6m long, the section steel 31 and the section steel 31 are firmly connected through steel plates 32, and the section steel 31 and the connecting bolt of the shield segment 4 are firmly connected through a strip steel plate 33, so that the shield segment 4 is reinforced; meanwhile, secondary grouting is carried out on the 6 th line and the 9 th line by clamping a soil layer through a shield segment 4 hoisting hole. The slurry is single cement slurry, the water cement ratio is controlled to be 0.75-1, and the grouting pressure is controlled to be 0.2-0.7 MPa, so that the effect of reinforcing the interlayer soil at the overlapping section of the No. 6 line and the No. 9 line is achieved.

And S3, constructing the lower tunnel by full-face advancing segmented grouting.

And before the lower tunnel is excavated, advanced pre-grouting is adopted to carry out water stopping and soil body reinforcement of the tunnel body within the range of 2 meters outside the excavation outline of the tunnel. Therefore, the water loss of the excavation surface can be reduced, the stability of the tunnel face is increased, the ground subsidence is controlled, and the safety of tunnel construction is ensured.

As shown in fig. 7, the forward sectional grouting process includes the following steps;

s3.1, constructing a grout stopping wall on the tunnel face.

In order to ensure the drilling and grouting of the full section, a steel pipe scaffold is adopted at the opening to set up an operation platform, a guardrail is set up, a safety net is hung, and a large plate with the thickness of more than 25mm is fully paved on the operation platform.

And S3.2, opening a hole on the grout stopping wall.

As shown in fig. 8 and 9, the palm surface is closed, the holes are distributed, and the grouting holes 51 are arranged in a quincunx way at intervals of 1m by 1 m; in fig. 5, L1 is 1m, and L2 is 2 m. And (4) forming holes by adopting a horizontal geological drilling machine according to a hole position layout, wherein the hole diameter is phi 89 mm.

And S3.3, installing an orifice pipe.

As shown in FIG. 10, the orifice pipe 61 is a welded steel pipe with an outer diameter of 89mm and a wall thickness of 3.5mm, the length of the orifice pipe 61 is 1.5m, a phi 89 flange 62 is welded at the outer end, and the flange 62 is provided with a phi 18 bolt hole 66. The orifice pipe 61 is externally wrapped with hemp fiber ointment and is rammed into the hole on the grout stop wall by adopting an impact hammer.

The phi 89 flange plate 62 is 15cm away from the outer surface of the grout stopping wall, so that the connecting screw is convenient to disassemble. The outer gap of the pipe is filled with quick-hardening mortar, and the outer wall of the orifice pipe is required to be closely attached to the concrete surface of the closed tunnel face, so that water leakage and mortar bleeding cannot occur.

S3.4, drilling and grouting

And (3) drilling holes in the orifice pipe 61 by using a down-the-hole drilling machine, wherein the diameter of the drilled hole is 76mm, the depth of the drilled hole is 15 meters, the drilling is carried out twice, the length of one drilling is 6-8 meters, and the drill rod is properly lifted to offset the drooping degree of the drill rod for long-distance drilling during hole drilling. Firstly drilling single holes and then drilling double holes, wherein the two holes are symmetrical from the upper part to the lower part, and meanwhile, the construction of adjacent areas needs to be staggered in the longitudinal direction.

Designing a hole with the depth of 15 meters, drilling for 6-8 meters for the first time, grouting, drilling for the second time, finishing the hole, and then grouting; and the process is circulated.

The depth of the final hole of the grouting hole is 15 meters, the grouting hole is lapped for 3 meters, the outer inserting angle of the grouting hole at the outer edge is 5 degrees, and soil body reinforcement within the range of 2 meters outside the excavation contour line is guaranteed.

The preparation work before grouting is as follows:

a) as shown in fig. 10, a grouting flange head 63 is installed; the grouting flange head 63 is connected with a phi 89 flange plate 62 through bolts, and a sealing rubber gasket is arranged between the grouting flange head 63 and the flange plate 62 to ensure the sealing performance. The grouting flange head 63 is connected with a D32 steel pipe 64, and the D32 steel pipe 64 is used for externally connecting a ball valve, a slip knot and a grouting pipe;

b) overhauling and debugging grouting equipment;

c) preparation of slurry preparation and grouting material: the slurry material is formed by combining single-fluid cement slurry and cement and water glass double-fluid slurry;

d) hole washing: and (4) injecting clear water into the hole for not less than 10 minutes by using a grouting pump to improve the grouting effect and ensure the initial concentration of the grout.

The grouting parameters were as follows:

a) the slurry mixing ratio is as follows:

cement paste: water cement ratio 1:1

35 baume degree water glass slurry: water: 3:1 water glass

Proportioning cement paste and water glass: cement paste: 1:1 of water glass

Concentration regulation principle: the slurry is diluted and then concentrated, and the concentration of the slurry is adjusted in time according to the changes of the slurry feeding amount and the grouting pressure.

b) Diffusion distance: the slurry diffusion radius is 1 meter;

c) grouting final pressure: p is 1-2 MPa;

d) grouting standard: and the grouting amount is less and less, the final grouting pressure is reached and the grouting is continued for half an hour, and the grouting is finished.

The method comprises the steps of constructing a grout stopping wall on the tunnel face, drilling an opening pipe on the grout stopping wall, and drilling and grouting forward in sections in the opening pipe with the diameter of 89mm, wherein drilling and grouting length of each cycle can be properly increased according to geological conditions and grouting effect by each cycle footage. And (3) retreating the drill rod after hole forming, mounting the flange plate and the grouting pipe for grouting, removing the flange plate after slurry is solidified, and then drilling … … for circulation until the drilling and grouting depth meets the design requirements. The repeated follow-up type forward drilling grouting circulating from outside to inside can ensure that a drilling machine drills holes in a reinforced soil body during drilling, effectively prevents hole collapse and difficult hole forming, can control water gushing in the holes, can start grouting when water flows out of the drilled holes, and can block water in time. The last grouting also has the re-grouting effect on the previous drilling grouting part, so the grouting effect is better.

And S4, grouting the small guide pipes in multiple steps.

In order to better play a role of advance support, multiple small pipes with phi 42mm steps are arranged in the range of 150 degrees of the arch part of the No. 6 tunnel before excavation for grouting reinforcement.

And S5, reserving core soil by adopting an annular step method to excavate the lower tunnel. And (3) adding a temporary inverted arch during tunnel excavation, immediately spraying anchor and supporting after excavation, and performing secondary lining by using the method of firstly constructing the inverted arch and then constructing the arch wall by using concrete. And (5) loading slag by adopting an excavator and transporting by using a loader.

Blasting construction can be adopted in the excavation process of part of the sections. The 51m overlapped section is constructed in blasting, and the following principles are strictly followed:

(1) in order to not affect the safety of the shield tunnel with the No. 9 line, the 6 line underground excavation tunnel adopts an annular step method to reserve core soil for excavation, an upper step adopts mechanical cooperation manual excavation, and a lower step adopts loosening blasting excavation properly.

a, charging structure

As shown in fig. 11, a blast hole 1 is provided in the tunnel lower step, and a first explosive layer 11, a second explosive layer 12 and a plugging layer 13 are provided in the blast hole 1 from bottom to top. Isolation layers 16 are arranged between the first explosive layer 11 and the second explosive layer 12 and between the second explosive layer 12 and the plugging layer 13; the spacer 16 may comprise a water bag or an air space.

The initiating explosive package 14 is buried in the first explosive layer 11, the initiating explosive package 14 comprises strip-packed emulsion explosive and a detonator, the detonator is installed in the strip-packed emulsion explosive, the detonator is connected with a detonating tube 15, and the other end of the detonating tube 15 extends to the outside of the blast hole 1.

The strip-packed emulsion explosive with the diameter of 32mm is used as a main explosive and a primary explosive.

b, method of plugging

The shallow hole is blocked by yellow mud or fine sand, tamping is needed, and the blast hole with accumulated water is blocked by coarse sand or wood dust.

c, detonation method

As the blasting environment is complex, a non-electric (detonating tube detonator) detonating network is adopted, and an electric detonator or an exciting needle is used for detonating.

d, detonating network

Adopting an electric and non-electric mixed detonating network: 1-15 sections of differential detonating tube detonators with the length of 5-15 m are adopted, a detonator is arranged in each blast hole, the holes are externally excited by the same-section millisecond electric detonators and are connected in series greatly, and then the parallel-series detonating network is formed.

The YJGN-500 type detonator is adopted for initiation, and the number of detonators per initiation is no more than 300, so that the detonation can be completely and safely initiated.

(2) The influence on the shield tunnel of No. 9 line is small due to the shock absorption effect of the empty face of the upper step in the loosening blasting of the lower step. According to the principle of 'short footage and weak blasting', the footage of each blasting of the lower step is not more than 2 m.

(3) Strictly controlling the blasting vibration speed, adopting differential blasting according to the design requirement, and controlling the blasting vibration speed within 2 cm/s.

(4) And arranging vibration monitoring points on the No. 9 line, and once the vibration speed exceeds the standard, adjusting the blasting design in time to control the blasting vibration speed within an allowable value.

(5) The differential blasting technology is adopted, and the time difference can be 100ms in consideration of the influence of the superposition effect of blasting vibration waveforms.

The primary support method is as follows;

the primary support adopts a spray anchor construction method, and is a main stressed structure consisting of a steel frame, a grouting system anchor pipe, a reinforcing mesh and sprayed concrete.

1) The primary support construction procedure is as follows: measuring and positioning → drilling → anchor pipe supporting → spraying concrete → installing arch frame → hanging reinforcing mesh → spraying concrete.

2) The stability and reliability of the support are judged by monitoring and measuring the geology and the support state, the displacement of the periphery of the tunnel, the sinking of the vault, the sinking of the earth surface, the stress of the arch frame, the drawing force of the anchor pipe and the like, and the support parameters are adjusted if necessary.

3) After the excavated section reaches the required size and slag is discharged in time, spraying concrete 4-5 cm immediately, setting an anchor rod, installing an arch frame according to the design requirement, hanging a reinforcing mesh, and spraying concrete in layers until the designed thickness is reached. When in spraying, the gap between the arch centering and the rock surface is firstly sprayed, then the periphery of the arch centering is sprayed, and finally the gap between the arch centering and the excavation outline is sprayed, so that all the gaps between the arch centering and the excavation outline are filled compactly.

4) The anchor pipe of the system is jacked by a drilling machine, the jacking length is greater than 90% of the pipe length, and the tail part of the steel pipe is firmly welded with the steel frame.

In order to enhance the reinforcing effect of the soil layer sandwiched between the overlapping sections of the No. 6 and No. 9 lines and ensure the safety of the No. 9 line shield tunnel, as shown in figure 12, the invention arranges a radial small conduit 71 at the arch part of the No. 6 line, wherein the radial small conduit 71 adopts a seamless steel pipe with the diameter of 32mm, the length of the seamless steel pipe is 1.2 meters, and the circumferential distance of the seamless steel pipe is 1 meter. The anchor pipe is jacked in by a drilling machine, the tail part of the steel pipe is firmly welded with the steel frame, the orifice is sealed by sprayed concrete, and grouting is performed in the pipe by a grouting machine so as to reinforce the soil interlayer and reduce the settlement of the shield tunnel with the 9 # line.

And monitoring and measuring the No. 6 line and the No. 9 line in the construction process to ensure that the construction is in a controlled state. Therein, line 6 monitors the measurement items, as shown in table 1.

TABLE 1 monitoring measurement items

Note: l.H is the distance between the excavated surface and the measuring device; b is the tunnel excavation width; geological descriptions include engineering geology and hydrogeology.

Wherein, the monitoring measurement of the No. 9 line is as follows:

before the overlapped section of the line-6 underground excavation section is excavated, as shown in fig. 13, monitoring measuring points are arranged on the segment of the shield section of the line-9 shield section at intervals of 5m, and a precise level gauge is adopted to measure the relative height difference between each measuring point and a reference point. Comparing the measured height difference with the last measured height difference, wherein the difference value is the sedimentation value of the time, and comparing the measured height difference with the initial height difference, the difference value is the accumulated sedimentation value. And carefully analyzing the settlement data measured each time and feeding back the data in time to guide construction. If the measured data change is large, measures should be taken immediately to seal the tunnel face and reinforce the soil-sandwiched layer.

Through the observation inside and outside the tunnel, the geological condition of the surrounding rock is checked, and the conditions of the self-standing property of the soil body of the excavation surface, the deformation, the cracking, the groundwater seepage and the like of the supporting structure and the deformation, the sinking and the cracking of the structure building on the ground surface or above are known. If special unstable condition is met, people should be sent to carry out uninterrupted observation, and whether the anchor rod is broken or not, whether the sprayed concrete cracks or peels or is sheared and damaged or not, whether the steel frame is buckled or deformed or not and other adverse conditions are observed for the supported section.

The construction of the overlapped tunnel from top to bottom also comprises the construction of a waterproof layer and mould concrete.

The waterproof layer is arranged between the sprayed concrete layer and the mould lining concrete and is made of geotechnical non-woven fabric and PVC waterproof board. When the waterproof layer is applied, firstly mortar is smeared on the surface of the primary support for leveling, and then a layer of geotextile and a PVC waterproof board are laid. The waterproof board is arranged between the surrounding rock and the lining to prevent the leakage of the underground water from the primary support surface; a layer of geotextile is added between the waterproof layer and the surrounding rock to play a role in buffering and protecting, the waterproof effect is prevented from being influenced by uneven surrounding rock, sharp-angled sharp instruments such as anchor pipes and reinforcing steel bars penetrate through the waterproof plate, and meanwhile, the geotextile has good water permeability and can play a role in dredging underground water.

And after the waterproof layer is laid, binding reinforcing steel bars, and pouring secondary lining concrete by using a vertical mold. The secondary lining concrete pouring should be continuous to improve work efficiency and quality.

The construction method adopts working conditions of excavation and support construction from top to bottom, adopts a new Austrian method and a controlled blasting technology, implements advanced grouting of a multi-step small conduit and advanced sectional grouting of a full section, and excavates in a reasonable sequence and by a method; and after excavation, spray anchoring, profile steel supporting and secondary lining are immediately carried out, the secondary lining adopts comprehensive construction technologies such as firstly inverted arch and secondly arch wall secondary molding concrete, the stability of tunnel surrounding rock and construction structure is ensured, and better economic benefit and social benefit are obtained while the construction progress and safety quality requirements are met.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. The construction method of the stepped multiple advanced small conduit is characterized by comprising the following steps of: a row of small guide pipes are arranged in the range of 120-180 degrees of the arch part of the tunnel for grouting reinforcement; the small guide pipes are arranged at certain intervals along the longitudinal direction, and are longitudinally lapped by 2-4 m.

2. The construction method of the stepped multiple advanced small pipe as claimed in claim 1, wherein: a row of small ducts are arranged in the range of 150 degrees of the arch part of the tunnel.

3. The construction method of the stepped multiple advanced small pipe as claimed in claim 1, wherein: the circumferential spacing of the small guide pipes in the same row is 0.2 m.

4. The method for constructing a stepped multiple advanced small pipe according to claim 1 or 3, wherein: the small ducts longitudinally overlap by 3 m.

5. The construction method of the stepped multiple advanced small pipe as claimed in claim 1, wherein: the outer insertion angle of the small guide pipe is 15-20 degrees.

6. The method for constructing a stepped multiple advanced small pipe according to claim 1 or 2, wherein: a row of small guide pipes are arranged for supporting two steel frames.

7. The method for constructing a stepped multiple advanced small pipe as claimed in claim 6, wherein: the small guide pipe is a seamless steel pipe with the diameter of 42 mm.

8. The method for constructing a stepped multiple advanced small pipe according to claim 1 or 7, wherein: the small conduit has a length of 3.5m-4 m.

9. The method for constructing a stepped multiple advanced small pipe as claimed in claim 8, wherein: one end of the small conduit is a conical tip, the other end of the small conduit is connected with an iron hoop, and a plurality of grouting holes are formed in the pipe body of the small conduit.

10. An overlapping tunnel construction method is characterized in that: comprises the following steps;

s1, constructing an upper shield tunnel of the overlapping area;

s2, grouting and reinforcing the middle soil interlayer between the overlapped tunnels;

s3, constructing a lower tunnel of the overlapping area; in the step, the forepoling is constructed by adopting the construction method of the step multiple forepoling small conduit according to any one of claims 1-9.

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