CN111997624A - A construction method for shallowly buried large-section undercut rectangular tunnel - Google Patents

Abstract

The present invention provides a construction method for a shallow-buried and large-section undercut rectangular tunnel, which includes the following steps: S1: the undercut section of the tunnel is constructed by the CRD method. 0.5m below the excavation surface; S2: Grout reinforcement of the broken rock strata on the surface to prevent deformation and damage of the surrounding ground during the excavation construction; S3: Use advanced large pipe shed and advanced grouting small conduit for advanced support; S4: Concave excavation section After excavation or sub-excavation is completed, initial spraying is carried out immediately, the exposed surface of surrounding rock is closed in time, and the support of profiled steel arches, bolts and steel mesh is coordinated with the excavation cycle footage; S5: re-shot concrete; S6: initial stage After supporting, grouting shall be carried out in time for the gap of the back of the arch. Through the above technical measures, the invention realizes the functions of strengthening the surrounding rock of the tunnel and controlling the subsidence of the ground surface, solves the problem of difficult deformation control of the surrounding rock of the shallow-buried large-section rectangular tunnel, and provides the construction of the shallow-buried large-section rectangular tunnel. Effective security.

Description

A construction method for shallowly buried large-section undercut rectangular tunnel

technical field

The invention belongs to the technical field of tunnel engineering, and in particular relates to a construction method for a shallow-buried large-section undercut rectangular tunnel.

Background technique

With the accelerating process of urbanization in my country, the construction of urban rail transit (subway) has entered a period of rapid development. However, since the subway station is mainly located in the main urban area, the main urban area has busy road traffic, and the underground pipelines are crisscrossed. The requirements are high, and the applicability of the project with shallow burial depth is poor; the mining method is suitable for tunnel engineering with large burial depth and the construction site is located in the rock layer. The underground excavation method can overcome the shortcomings of the above methods, and has the characteristics of flexible construction and wide application range.

However, the conventional underground excavation method cannot be applied to the construction of underground tunnels in areas with heavy rainfall, because the underground tunnels traverse communication pipelines, water supply pipelines, sewage pipelines, power pipelines, rainwater pipelines and pipeline maintenance wells at a short distance, and there are also rainwater tank culverts. Crossing the top of the tunnel, the distance from the undercut section is short, affected by tides, the daily variation of groundwater is large, the control requirements for the undercut construction process are high, and the tunnel structure is complex, which brings great challenges to the construction.

Based on the above reasons, there is an urgent need for a shallow-buried large-section rectangular tunnel construction method to ensure the stability of the excavated surrounding rock and the safety of pipelines in the shallow overburden above during the construction process.

SUMMARY OF THE INVENTION

The invention provides a construction method for a shallow buried large-section undercut rectangular tunnel, so as to solve the problems existing in the above-mentioned existing methods and solve the construction problem of the shallow buried large-section undercut rectangular tunnel in the main urban area.

The technical scheme of the present invention is: a shallow-buried large-section undercut rectangular tunnel construction method, the main construction steps of which are as follows:

S1: The CRD method is used for the construction of the tunnel in the undercut section. Before construction, the undercut area is fully dewatered, and the groundwater level is lowered to 0.5m below the excavation surface of the foundation pit;

S2: Grout reinforcement of the broken rock layer on the surface to prevent the surrounding ground from being deformed and damaged during the excavation construction. The specific process includes (1) Drilling positioning: After the site is cleaned, according to the reviewed control points, measure the positioning axis to carry out the pile The size of the sample pile should meet the design and construction requirements, and the allowable deviation should be controlled within 10mm; (2) The drilling rig is in place: After the drilling rig is commissioned, it is installed in place, carefully leveled, and supported firmly to ensure that it does not occur during construction. Inclination, displacement; (3) Drilling of the drilling rig: the drilling rig is in place, the equipment is leveled, and the drilling is carried out. After the drilling is in place, the steel pipe is installed. After the steel pipe is processed in the processing plant, it is transported to the site for installation; (4) ) Hole cleaning: flush the debris in the seamless steel pipe before grouting, and then insert the grouting pipe into the bottom of the hole; (5) grouting: grouting sequentially from bottom to top until the slurry flows out of the top of the seamless steel pipe. until;

S3: The advanced large pipe shed and the advanced grouting small pipe are used for advanced support;

S4: The initial spraying is carried out immediately after the excavation or sub-excavation is completed in the underground excavation section, and the exposed surface of the surrounding rock is closed in time, and the support of profiled steel arches, bolts and steel mesh is carried out in coordination with the excavation cycle footage;

S5: Re-spray concrete in time after the steel arch, anchor rod and steel mesh support are completed;

S6: After the initial support, grouting should be carried out to the back of the arch in time to prevent the arch from leaving a gap, so that the support and surrounding rock can be analyzed.

The scheme further, in the above step S1, large-diameter pipe wells are used for dewatering at the entrance and exit, and the well points in the foundation pit are arranged at an interval of 8-12m, the diameter of the well pipe is 0.8m, and the depth of the pipe in the dewatering well is not less than 5m below the bottom of the foundation pit.

The scheme further, in the above step S2, the grouting range is 2m outside the excavation contour line, the grouting process adopts the sleeve valve pipe grouting reinforcement, the rotary jet pile is inserted into the Φ108 steel pipe, the steel pipe goes deep into the base 2m, and the grouting reinforcement adopts Cement-water glass double slurry, water-cement ratio 1:1, grouting pressure 1.0 MPa-2.0 MPa.

Scheme Further, in the above step S3, the construction process of the advanced large pipe shed includes (1) measuring and laying out lines; (2) resting and adjusting the pipe shed operating platform; (3) drilling rigs in place to drill holes. A down-the-hole drilling rig is used for the operation, and the construction sequence is carried out according to the excavation sequence of the foundation pit; (4) Jacking into the pipe shed, in order to stagger the steel pipe joints, the steel pipe shall be numbered when the steel pipe is processed. When the wall is not easy to collapse, use the direct impact method to hit the pipe to the design position. When the hole wall is easy to collapse, use the method of drilling the pipe and the drill at the same time; (5) After the comprehensive inspection is qualified, grouting is carried out, and the inspection is carried out after the grouting is completed. , using a full-hole grouting, the pipe shed grouting reaches a slurry diffusion radius of not less than 0.5m, and the grouting method is selected according to the rock conditions. The initial pressure is 0.5~1MPa, and the final pressure is 2MPa. Before grouting, the grouting field test should be carried out, and the grouting parameters should be adjusted according to the actual situation through the field test.

Scheme Further, in the above-mentioned step S3, the construction process of the advance grouting small conduit includes (1) measuring the hole position of the conduit, and designing the advance grouting small conduit within the arch of the undercut section, the circumferential spacing is 30cm, and the camber angle of the small conduit is 10 cm. ～15°, the vertical and horizontal lap length is 1m, one end of the grouting pipe is made into a cone head, and the other end is welded with an iron hoop; (2) Drilling, start drilling at a distance of 1.0m from the iron hoop, and the drill holes are spaced along the pipe wall 150mm, arranged in a plum-shaped pattern, the holes are 90° to each other, the diameter of the hole is 8mm, and the pneumatic drill can be used for jacking directly; (3) Install the guide pipe, use the pneumatic drill to push the small guide pipe, and the tail end of the guide pipe is exposed for a sufficient length, and the tail is connected to the steel frame. Weld together; (4) Close the grouting surface with shotcrete; (5) grouting the conduit, the grouting slurry adopts cement-water glass double-liquid slurry, and the grouting pressure is proposed to be 0.4 ~ 0.6MPa.

Scheme Further, in the above-mentioned step S4, the construction process of the profiled steel arch is (1) section inspection and measurement and positioning, and the profiled steel arch varies according to the design section; (2) the steel support is assembled, erected in place, and the anchor rod is locked. , the initial support steel frame adopts I20a I-shaped steel, the temporary vertical support and temporary inverted arch use I18 I-shaped steel, the spacing is 0.5m, and the two adjacent steel frames are connected by Φ20 steel bars, and the circumferential spacing of the connecting bars is 0.5m. The channel steel grooves of the steel frame are reserved at the arch foot and the wall feet on both sides to ensure that the arch foot is implemented. When the concrete is initially sprayed, a wooden wedge shall be driven into the groove to leave a connecting plate or channel steel position for the erection of the steel frame. For the overall stability of the steel frame, the steel frame and the anchor rod are welded together; (3) Longitudinal connecting steel bars and steel meshes are installed. Alternately arranged, the connecting bars should be firmly welded with the steel frame; (4) Shotcrete is fixed, and the anchor is shot as soon as possible after the steel frame is erected. The spraying sequence should be symmetrical from the bottom to the top. The gap between the steel frame and the surrounding rock should be sprayed first, and then spray The concrete between the steel frame and the steel frame shall be completely covered with the steel frame, and the thickness of the protective layer shall not be less than 40mm, so that the steel frame and the shotcrete shall be stressed together. The arch foot or wall foot is sprayed upward to prevent the upper spray material from covering the arch foot or the wall foot is not compact, resulting in insufficient strength and instability of the arch foot or wall foot.

Scheme Further, in the above-mentioned initial support, the shotcrete adopts the strength grade C25 concrete, the thickness is 300mm, and the wet spraying method is used for construction. The spraying sequence is from bottom to top, first the side wall, then the arch foot, and finally the vault. The nozzle moves slowly and evenly in a spiral shape. Each circle presses the front half circle. The diameter of the circle is about 30cm. Flat, the nozzle is perpendicular to the rock surface, 1.5-2.0m away from the sprayed surface. After the excavation, the initial spraying should be carried out in time, and the re-spraying should be carried out in time after the ballast is discharged; The concrete is sprayed flat and has enough protective layer. The sprayed concrete is segmented and segmented sequentially from bottom to top. When re-spraying concrete, the concrete between the steel frame support and the arch wall is sprayed first, and then the concrete between the two arch frames is sprayed.

The scheme further, in the above step S6, the back of the arch is grouted, that is, during the initial support construction, the side wall of the arch is pre-buried Ф32mm steel welded as a grouting pipe, and the length of the grouting pipe is generally 0.8 according to the lining design requirements. , The circumferential spacing of each row is 1m. After the initial support is closed into a ring, 1:1 cement mortar is injected with a grouting pump in time to fill the pores behind the initial lining.

The advantages of the present invention are as follows: the present invention proposes a construction method of shallowly buried large-section underground excavation rectangular tunnels, which adopts the method of sub-excavation, additional temporary inverted arches, advanced large pipe sheds and small pipes for grouting reinforcement, and controls the construction of the tunnel. The deformation of the surrounding rock and the surface of the tunnel solves the problem of difficulty in controlling the deformation of the surrounding rock of the shallow-buried large-section rectangular tunnel, and provides an effective safety guarantee for the construction of the shallow-buried large-section rectangular tunnel.

Description of drawings

Fig. 1 is the surface grouting reinforcement construction process flow diagram of a shallow buried large-section undercut rectangular tunnel construction method of the present invention;

Fig. 2 is the construction process flow chart of the advanced large pipe shed construction method of a shallow-buried large-section undercut rectangular tunnel construction method of the present invention;

Fig. 3 is the construction process flow chart of the advance grouting small conduit construction method of a shallow buried large-section undercut rectangular tunnel construction method of the present invention;

Fig. 4 is a process flow chart of the construction of a profiled steel arch of a method for constructing a shallow-buried large-section rectangular tunnel according to the present invention.

Detailed ways

The present invention will be clearly and completely described below with reference to the accompanying drawings, so that those skilled in the art can fully implement the present invention without creative work.

The specific embodiment of the present invention is: as shown in Figure 1-4, a kind of shallow buried large section undercut rectangular tunnel construction method, its main construction steps are as follows:

S1: The CRD method is adopted for the construction of the undercut section of the tunnel. Before construction, the undercut area is fully dewatered, and the groundwater level is lowered to 0.5m below the excavation surface of the foundation pit;

S2: Grout reinforcement of the broken rock layer on the surface to prevent the surrounding ground from being deformed and damaged during the excavation construction. The specific process includes (1) Drilling positioning: After the site is cleaned, according to the reviewed control points, measure the positioning axis to carry out the pile The size of the sample pile should meet the design and construction requirements, and the allowable deviation should be controlled within 10mm; (2) The drilling rig is in place: After the drilling rig is commissioned, it is installed in place, carefully leveled, and supported firmly to ensure that it does not occur during construction. Inclination, displacement; (3) Drilling of the drilling rig: the drilling rig is in place, the equipment is leveled, and the drilling is carried out. After the drilling is in place, the steel pipe is installed. After the steel pipe is processed in the processing plant, it is transported to the site for installation. Both ends of the steel pipe should be processed with 15cm long threads, and A10mm slush holes should be machined on the steel pipe every 10cm to form a plum-shaped arrangement. According to the length of the piles, in order to make the joints of two adjacent piles on the same vertical plane not exceed the main pipe 50% of the number of holes; (4) hole cleaning: flush the debris in the seamless steel pipe before grouting, and then insert the grouting pipe into the bottom of the hole; (5) grouting: sequentially grouting from bottom to top until the grout is completely free of until the thick slurry flows out from the top of the seamed steel pipe;

S3: The advanced large pipe shed and the advanced grouting small pipe are used for advanced support;

S4: The initial spraying is carried out immediately after the excavation or sub-excavation is completed in the underground excavation section, and the exposed surface of the surrounding rock is closed in time, and the support of profiled steel arches, bolts and steel mesh is carried out in coordination with the excavation cycle footage;

S5: Re-spray concrete in time after the steel arch, anchor rod and steel mesh support are completed;

S6: After the initial support, grouting should be carried out to the back of the arch in time to prevent the arch from leaving a gap, so that the support and surrounding rock can be analyzed.

Further, in the above step S1, large-diameter pipe wells are used for dewatering at the entrance and exit, and the well points in the foundation pit are arranged at an interval of 8 to 12m, the diameter of the well pipe is 0.8m, and the depth of the pipe in the dewatering well is not less than 5m below the bottom of the foundation pit. .

The present invention further, in the above step S2, the grouting range is 2m outside the excavation contour line, the grouting process adopts the sleeve valve pipe grouting reinforcement, the rotary jet pile is inserted into the Φ108 steel pipe, the steel pipe is deep into the base 2m, grouting reinforcement Cement-water glass double slurry is adopted, the water-cement ratio is 1:1, and the grouting pressure is 1.0 MPa-2.0 MPa.

The present invention further, in the above step S3, the construction process of the advanced large pipe shed includes (1) measuring and laying out the line; (2) resting and adjusting the operating platform of the pipe shed. Length 4m or 6m, the inclination angle is upwards <2°, grouting holes of Ф10-16mm are drilled around the pipe wall of the steel pipe, and the drill holes are arranged at intervals of 150mm along the pipe wall in a plum-shaped arrangement. Slurry-stopping section of the hole; a steel cage is added in the pipe to improve the bending resistance of the conduit. The steel cage is composed of four main bars and a fixed ring, and the circumferential spacing of the large pipe shed is 40cm; (3) The drilling rig is in place to drill, according to the geological Conditions and construction conditions, a down-the-hole drilling rig is used for the operation. The construction sequence is carried out according to the excavation sequence of the foundation pit. The distance between the drilling rig and the working face is generally not less than 2m when drilling, and the drilling is impacted by pneumatic down-the-hole drilling. Drilling method is the main method, supplemented by alloy tube drill, the diameter of the drill hole is 150mm, the circumferential spacing is 40cm, and the core tube is used to sweep the hole. The length of the core tube is not less than 3m. The inside is cleaned and the pipe wall of φ108mm steel pipe is perforated, the hole diameter is 10-16mm, and the hole spacing is 150mm. Shed, in order to stagger the steel pipe joints, the steel pipe is numbered when processing the steel pipe. When the pipe is down, when the hole wall is not easy to collapse, the direct impact method is used to hit the pipe to the design position. When the hole wall is easy to collapse, use the pipe to In the method of drilling at the same time, in order to stagger the steel pipe joints, for the convenience of construction, the first pipe with an odd number uses a 4m pipe, the first pipe with an even number uses a 6m steel pipe, and each subsequent pipe uses a 6m long steel pipe. If there is a failure in the jacking of the steel pipe, if the jacking fails, find out the reason, and if necessary, re-scan the hole and then jack the steel pipe; (5) After the comprehensive inspection is qualified, grouting is carried out, and the inspection is carried out after the grouting is completed, and a full drilling is adopted. Hole grouting, pipe shed grouting to reach a slurry diffusion radius of not less than 0.5m, grouting method is selected according to rock conditions, grouting adopts cement slurry, cement slurry water-cement ratio 1:1, grouting pressure: initial pressure 0.5 ~ 1MPa , the final pressure is 2MPa, and the grouting field test should be carried out before grouting. The grouting parameters should be adjusted according to the actual situation through the field test. If the groundwater is large, cement-water glass slurry can be used. Before grouting, use 10mm steel plate to make a steel pipe plug at the pipe shed, weld it with the pipe shed, burn the hole to weld the grouting pipe, and install a grouting valve on the grouting pipe thread. Install a φ15mm plastic hard pipe along the pipe wall in the steel flower pipe to the bottom of the hole, and weld the steel pipe at the nozzle (outer end) and the grouting pipe as an exhaust hole (install a grouting valve). The grouting adopts one injection from the orifice. In order to make the slurry in the pipe full and dense, the final pressure grouting shall be carried out until the design grouting pressure or design grouting volume is reached. Close its valve.

The present invention further, in the above step S3, the construction process of the advance grouting small conduit includes (1) measuring the hole position of the conduit, designing the advance grouting small conduit within the arch of the undercut section, the circumferential spacing is 30cm, and the camber angle of the small conduit is 30 cm. 10 ~ 15°, the longitudinal and horizontal lap length is 1m, one end of the grouting pipe is made into a cone head, and the other end is welded with an iron hoop; (2) Drilling, start drilling at a distance of 1.0m from the iron hoop, and drill along the pipe wall The spacing is 150mm, and it is arranged in a plum blossom shape. The holes are 90° to each other, and the hole diameter is 8mm. It can be directly jacked with a pneumatic drill; (3) Install a guide pipe, use a pneumatic drill to push the small guide pipe, and the tail end of the guide pipe is exposed for a sufficient length. (4) Shotcrete closed grouting surface; (5) Pipe grouting, the grouting slurry adopts cement-water glass double-liquid slurry, and the grouting pressure is proposed to be 0.4-0.6MPa.

The present invention further, in the above-mentioned step S4, the construction process of the profiled steel arch is (1) section inspection and measurement and positioning, and the profiled steel arch varies according to the design section; (2) the steel support assembly, erection, anchor rod Locked, I20a I-beam steel is used for the initial support steel frame, I18 I-beam steel is used for the temporary vertical support and temporary inverted arch, and the spacing is 0.5m. The two adjacent steel frames are connected by Φ20 steel bars, and the circumferential spacing of the connecting bars is 0.5m. The channel steel grooves of the steel frame are reserved at the two arch feet and the wall feet on both sides to ensure that the arch feet are implemented. When the concrete is initially sprayed, a wooden wedge shall be driven into the groove, and the connecting plate or channel steel position shall be reserved for the erection of the steel frame. Strengthen the overall stability of the steel frame, and weld the steel frame and the anchor rod together; (3) Set up longitudinal connecting steel bars and install steel mesh, and connect each longitudinal steel arch with a φ8@200 double-layer steel mesh. The layers are arranged alternately, and the connecting bars should be firmly welded to the steel frame; (4) Shotcrete is fixed, and the anchors are shot as soon as possible after the steel frame is erected. The spraying sequence should be symmetrical from the bottom to the top. Spray the concrete between the steel frame and the steel frame, and cover the steel frame completely. Spray upward from the arch foot or wall foot to prevent the upper spray material from concealing the arch foot or the wall foot is not dense, resulting in insufficient strength and instability of the arch foot or wall foot.

Further, in the above-mentioned initial support, the shotcrete adopts the strength grade C25 concrete, the thickness is 300mm, and the wet spraying method is used for construction. , the spraying sequence is from bottom to top, first the side wall, then the arch foot, and finally the vault. The nozzle moves slowly and evenly in a spiral shape. Each circle presses the front half circle. The diameter of the circle is about 30cm. If there are large depressions, spray first. Fill and level, the nozzle is perpendicular to the rock surface, and the distance from the spray surface is 1.5 to 2.0m. After the excavation, the initial spraying should be carried out in time, and the re-spraying should be carried out in time after the ballast is discharged; The concrete is sprayed flat and has enough protective layer. The sprayed concrete is segmented and segmented sequentially from bottom to top. When re-spraying concrete, the concrete between the steel frame support and the arch wall is sprayed first, and then the concrete between the two arch frames is sprayed.

The present invention further, in the above step S6, the back of the arch is grouted, that is, during the initial support construction, the side wall of the arch is pre-buried Ф32mm steel welded as a grouting pipe, and the length of the grouting pipe is generally 0.8 according to the lining design requirements. The circumferential spacing of each row is 1m. After the initial support is closed into a ring, 1:1 cement mortar is injected with a grouting pump in time to fill the pores behind the initial lining.

The preferred embodiments of the present invention have been described above. It should be pointed out that the present invention is not limited to the above-mentioned specific embodiments, and the devices and structures not described in detail should be understood as being implemented in ordinary ways in the art; Any person skilled in the art, without departing from the scope of the technical solution of the present invention, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still belong to the protection of the technical solution of the present invention. within the range.

Claims (8)

1. A construction method of a shallow-buried large-section underground rectangular tunnel is characterized by comprising the following main construction steps:

s1: constructing the tunnel at the underground excavation section by adopting a CRD method, carrying out comprehensive precipitation treatment on an underground excavation area before construction, and reducing the underground water level to 0.5m below the excavation surface of the foundation pit;

s2: broken rock stratum slip casting of earth's surface is consolidated, prevents to arouse among the excavation work progress that peripheral ground warp to destroy, and concrete process includes (1) drilling location: after the on-site cleaning is finished, according to the rechecked control points, measuring and setting a positioning axis to perform pile position lofting, wherein the size of a pile of the loft is required to meet the design and construction requirements, and the allowable deviation is controlled within 10 mm; (2) positioning a drilling machine: after the drilling machine enters a field and is debugged, the drilling machine is installed in place, carefully leveled and firmly supported, so that the drilling machine is ensured not to incline or shift in construction; (3) drilling by a drilling machine: the drilling machine is in place, equipment is leveled, drilling is carried out, steel pipes are installed after the drilling is in place, and the steel pipes are transported to the site for installation after being processed in a processing factory; (4) hole cleaning: before grouting, washing impurities in the seamless steel pipe, and inserting the grouting pipe into the bottom of the hole; (5) grouting: sequentially grouting from bottom to top until thick slurry flows out of the top opening of the seamless steel pipe;

s3: an advanced large pipe shed and an advanced grouting small pipe are adopted for advanced support;

s4: the underground excavation section immediately carries out primary spraying after the excavation or the subsection excavation is finished, the exposed surface of the surrounding rock is closed in time, and the support of the profile steel arch frame, the anchor rod and the reinforcing mesh is carried out in cooperation with the excavation circulation footage;

s5: after the steel arch frame, the anchor rod and the reinforcing mesh are supported, concrete is sprayed again in time;

s6: grouting the arch back gap in time after primary support to prevent gaps from being left in the arch part, so that support and surrounding rock analysis are realized.

2. The method for constructing a shallow-buried large-section underground rectangular tunnel according to claim 1, wherein in step S1, the precipitation at the entrance and exit is large-diameter well precipitation, the well points in the foundation pit are arranged at intervals of 8-12 m, the diameter of the well pipe is 0.8m, and the insertion depth of the precipitation well steel pipe is not less than 5m lower than the bottom of the foundation pit.

3. The method for constructing a shallow-buried large-section underground rectangular tunnel according to claim 1, wherein in the step S2, the grouting range is 2m outside the excavation contour line, the grouting process adopts sleeve valve pipe grouting reinforcement, a phi 108 steel pipe is inserted into a jet grouting pile, the steel pipe extends to 2m below the basement, the grouting reinforcement adopts cement-water glass double-liquid cement, the water cement ratio is 1: 1, grouting pressure is 1.0 MPa-2.0 MPa.

4. The method for constructing a shallow-buried large-section underground rectangular tunnel according to claim 1, wherein in the step S3, the construction process of the advanced large pipe shed includes (1) measuring and setting-out; (2) laying down a pipe shed operating platform; (3) the drilling machine is in place to drill holes, a down-the-hole drilling machine is adopted to operate according to geological conditions and construction conditions, and construction is carried out according to the foundation pit excavation sequence in the construction sequence; (4) jacking a pipe shed, numbering steel joints of the steel pipes when the steel pipes are processed in order to stagger the joints of the steel pipes, adopting a direct impact method to impact a conduit to a designed position when the wall of the hole is not easy to collapse during pipe descending, and simultaneously drilling the conduit and a drill bit when the wall of the hole is easy to collapse; (5) carry out the slip casting after the comprehensive inspection is qualified, detect after the slip casting is accomplished, adopt a full drilling slip casting, the pipe roof slip casting reaches the grout diffusion radius and is not less than 0.5m, select the slip casting mode according to the rock condition, the slip casting adopts the grout, grout water cement ratio 1: 1, grouting pressure: the initial pressure is 0.5-1 MPa, the final pressure is 2MPa, a grouting field test is performed before grouting, and grouting parameters are adjusted according to actual conditions through the field test.

5. The method for constructing a shallow-buried large-section underground excavation rectangular tunnel according to claim 1, wherein in the step S3, the construction process of the small advanced grouting pipes comprises (1) measuring pipe hole positions, designing the small advanced grouting pipes within the arch part of the underground excavation section, wherein the circumferential distance is 30cm, the camber angle of the small pipes is 10-15 degrees, the longitudinal horizontal lap joint length is 1m, one end of each grouting pipe is made into a conical head, and an iron hoop is welded at the other end; (2) drilling, namely, drilling at a position 1.0m away from the iron hoop, wherein the drill holes are distributed at intervals of 150mm along the pipe wall in a quincunx manner, the hole positions mutually form 90 degrees, the hole diameter is 8mm, and the drill holes can be directly jacked by a wind drill; (3) installing a guide pipe, jacking the small guide pipe by using an air drill, exposing the tail end of the guide pipe for a sufficient length, and welding the tail end of the guide pipe and the steel frame together; (4) spraying concrete to close the grouting surface; (5) and (3) grouting by using a guide pipe, wherein the grouting slurry is cement-water glass double-liquid slurry, and the grouting pressure is set to be 0.4-0.6 MPa.

6. The method for constructing a shallow-buried large-section underground rectangular tunnel according to claim 1, wherein in the step S4, the construction process of the steel arch is (1) section inspection and measurement positioning, and the steel arch is different according to the design section; (2) the steel supports are assembled, erected in place and locked by anchor rods, the primary support steel frames adopt I20a I-shaped steel, the temporary vertical supports and the temporary inverted arches adopt I18I-shaped steel, the distance is 0.5m, two adjacent steel frames are connected by phi 20 steel bars, the circumferential distance of connecting ribs is 0.5m, grooves for mounting steel frame channel steel are reserved at two arch feet and two side wall feet to ensure the arch feet to be solid, wood wedges are driven into the grooves when concrete is sprayed for the first time, connecting plates or channel steel positions are reserved for erecting the steel frames, and the steel frames and the anchor rods are welded together for enhancing the overall stability of the steel frames; (3) arranging longitudinal connecting steel bars and installing steel bar nets, wherein each longitudinal steel arch truss is connected by a phi 8@200 double-layer steel bar net, the inner layer and the outer layer are arranged alternately, and the connecting steel bars are firmly welded with the steel frame; (4) the concrete spraying is fixed, the anchor spraying operation is carried out as soon as possible after the steel frame is erected, the spraying sequence is carried out symmetrically from bottom to top, a gap between the steel frame and surrounding rocks is sprayed firstly, the concrete between the steel frame and the steel frame is sprayed later, the steel frame is covered completely, the thickness of a protective layer of the protective layer is not smaller than 40mm, the steel frame and the spray anchor are stressed together, the spray anchors are carried out in a layered mode, the thickness of each layer is about 50-60 mm, the spray anchors are sprayed upwards from the arch springing or the wall springing position firstly to prevent the upper spray material from covering the arch springing or the wall springing loosely, the strength is insufficient, and the arch spring.

7. The method for constructing a shallow-buried large-section underground excavation rectangular tunnel according to claim 1, wherein the sprayed concrete in the primary support is strength grade C25 concrete with the thickness of 300mm, the construction is performed by a wet spraying method, the sprayed concrete is mixed at the site by a mixing station, transported to a working surface, and subjected to spray anchor construction by a wet spraying machine, the spraying heads slowly and uniformly move in a spiral shape from bottom to top in the sequence of first side wall, rear arch foot and last arch top, each circle presses the front half circle, the diameter of each circle is about 30cm, a large concave part is formed, the sprayed concrete is firstly sprayed and filled, the spraying nozzles are perpendicular to the rock surface and 1.5-2.0 m away from the sprayed surface, the concrete is sprayed in time after excavation, and the concrete is sprayed again in time after slag is discharged; the re-spraying concrete is carried out after the anchor rods, the hanging net and the steel frames are installed, the whole stress of the anchor spraying support is formed as soon as possible to inhibit the change of surrounding rocks, the steel frames are sprayed with the concrete and are leveled by the concrete, enough protective layers are arranged, the concrete spraying is carried out in a segmentation and fragmentation mode from bottom to top, when the re-spraying concrete is carried out, the concrete between the steel frame support and the arch wall is sprayed firstly, and then the concrete between the two arch frames is sprayed.

8. The method for constructing a shallow-buried large-section underground rectangular tunnel according to claim 1, wherein in the step S6, arch back grouting, that is, during primary support construction, the pre-buried Φ 32mm steel of the arch side wall is welded as a grouting pipe, the length of the grouting pipe is generally embedded in one row according to the lining design requirement, 0.8, and the circumferential distance of each row is 1m, and after the primary support is closed into a ring, the grouting pump is used for grouting in time 1: 1 cement mortar, filling the pores after primary backing.

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