CN117189128A - Karst tunnel crossing karst cave construction method - Google Patents

Abstract

The invention provides a karst tunnel crossing karst cave construction method, which comprises the following steps: (1) karst cave expansion digging and supporting; (2) dredging and backfilling the karst cave substrate; (3) inverted arch and filling construction; (4) construction of the water stop wall and backfilling of concrete on two sides; (5) primary support construction; (6) backfilling the top of the primary support and constructing a waterproof layer; (7) second lining waterproof construction; (8) installing and debugging a water pressure monitoring system; and (9) implementing a monitoring and early warning scheme. The construction method is suitable for poor geological engineering such as the water-rich karst tunnel passing through a large underground karst cave, a fluid bowl, an underground river and the like. In the construction method, the operation difficulty of the steps is relatively small, the construction quality is controllable, the construction blind area is less, and the construction safety is high; the initial runoff balance of the karst cave groundwater can be maintained, and the surrounding ecological environment is protected to the greatest extent.

Description

A construction method for karst tunnel passing through karst cave

Technical Field

The invention relates to the technical field of road, bridge and tunnel engineering construction, and in particular to a construction method for a karst tunnel passing through a karst cave.

Background Art

A karst tunnel is an underground cave or tunnel formed by an underground river, usually formed by long-term erosion and dissolution of rock. Its landform is formed by surface water and groundwater eroding the rock surface vertically, and as the erosion deepens, a huge cavity system is formed inside the cracks and holes in the rock layer. These cavities will expand over time and form caves and karst caves of various sizes and shapes.

The coverage of the transportation network is expanding in depth to the southwestern regions of Yunnan, Guizhou, Hunan, etc., which are full of karst landforms. In this process, it is bound to encounter a large number of water-rich karst tunnels passing through large underground caves, karst troughs, and underground rivers and other unfavorable geological projects. For the above situations, the construction technology of grouting and plugging is usually adopted. However, the traditional technology of grouting and plugging used at this stage has disadvantages in the operation process of on-site construction: the construction period is long and difficult, and the grouting and plugging need to wait for the grouting to fully solidify before the next operation task can be carried out, which prolongs the construction process; at the same time, grouting requires professional technology and experience, and the operation is difficult, and there are certain construction difficulties and risks; in addition, on the one hand, it is difficult to control the construction quality due to the hidden construction, and on the other hand, it will also destroy the balance of groundwater runoff in the cave and the surrounding ecological environment to a certain extent.

Summary of the invention

The main technical problem to be solved by the present invention is to provide a construction method for a karst tunnel passing through a karst cave. The construction method has low operating difficulty, controllable construction quality, reduces construction blind spots, and improves the safety of the construction process.

In order to solve the above technical problems, the present invention provides a construction method for a karst tunnel passing through a karst cave, comprising the following steps:

(1) Cave expansion and support: expansion of the cave and support of the cave top;

(2) Desilting and backfilling of cave base: excavation at the cave base and backfilling with concrete;

(3) Invert and filling construction: carry out invert secondary lining construction and invert filling construction;

(4) Construction of water stop wall and concrete backfill on both sides: A water stop wall is built in the tunnel and concrete backfill is carried out on both sides of the water stop wall;

(5) Initial support construction: Carry out initial support construction of the tunnel according to the design drawings;

(6) Backfill and waterproofing construction at the top of the primary support: backfill construction of the primary support top arch, drainage blind pipe construction, civil engineering cloth construction, PVC waterproofing board construction and water stop strip construction;

(7) Secondary lining waterproofing and drainage construction: carry out water pressure resistant secondary lining construction and inspection channel construction;

(8) Installation and commissioning of water pressure monitoring system: Before installing the water pressure monitoring system, ensure that the equipment on site meets the design pressure requirements and arrange for professional personnel to carry out the construction;

(9) Implementation of monitoring and early warning scheme: When the water pressure outside the tunnel lining monitored by the water pressure gauge exceeds the limit, the electronically controlled pressure control valve is opened through the pressure control system to reduce the pressure to below the limit.

In a preferred embodiment: before executing step (1) of cave expansion and support, construction preparation work is carried out; the construction preparation work includes: establishing and improving the engineering quality and safety responsibility system, quality management organization and engineering quality responsibility system, and setting up a quality leadership group; conducting quality inspections on the entire construction process, and implementing inspections in accordance with the "three inspections"; reviewing construction drawings and maintaining contact with supervision and design units; listing key monitoring areas and key points, and conducting engineering technology, quality and safety briefings for on-site workers; implementing a double inspection and review system for construction measurement and layout, and checking the procedures for raw materials; and doing a good job of data preservation and archiving.

In a preferred embodiment: in step (1) cave excavation and support, the cave excavation includes: cleaning the dangerous rocks within the operation influence range of the cave top and the sediments in the cave cavity before cave excavation; excavating the cave top by drilling and blasting, and using machinery to perform local artificial rock drilling; measuring the cave after excavation;

The support for the top of the cave includes: after the expansion and excavation of the cave is completed, timely support is carried out according to the integrity of the surrounding rock. When the surrounding rock is intact and there is no falling block, mortar anchor rods, steel mesh and shotcrete are used to cooperate with each other for support; when the surrounding rock has falling blocks, anchor rods, steel mesh, steel support and shotcrete support are used to cooperate with each other for support; when the steel support is constructed, crossbeams and locking anchor rods are used to temporarily fix it on the solid surrounding rock, and when the water stop walls on both sides are constructed to the designed elevation, the whole is poured inside.

In a preferred embodiment: the step (2) dredging and backfilling the cave base includes: using an excavator to excavate and dredge the base in layers, conducting a foundation bearing capacity test after the silt is cleared, and flushing the rock wall with high-pressure water after meeting the requirements. After the flushing is completed, the water accumulated in the base is pumped out with a water pump; after the cave base is excavated, backfilling with concrete in layers to the designed elevation, the backfilling is carried out in two steps, and each layer is vibrated and compacted; before the second concrete pouring, the contact surface is roughened and cleaned, and the concrete surface after the roughening treatment is rinsed with clean water.

In a preferred embodiment: the step (3) of inverted arch and filling construction comprises: laying geotextile and fully enclosed waterproof board before pouring the secondary lining of the inverted arch, and reserving the overlapping part with the waterproof layer of the arch wall; before the construction of the inverted arch reinforcement, reserved annular overlapping reinforcement is welded with the secondary lining reinforcement of the arch wall, and the overlapping joints of adjacent reinforcements are staggered; before pouring the concrete of the inverted arch, a double-layer embedded water stop is installed and fixedly positioned between the two layers of reinforcement with reinforcement clamps; the inverted arch and the bottom are constructed with a fully hydraulic self-propelled inverted arch trestle in coordination with the concrete; when pouring the secondary lining of the inverted arch, the entire section is poured together, and the filling concrete is poured separately from the inverted arch concrete; after the pouring of the secondary lining of the inverted arch is completed, the inverted arch filling construction is carried out, and the surface water and debris of the secondary lining of the inverted arch are cleaned before construction, and the transverse construction joint of the inverted arch filling concrete is staggered with the construction joint of the secondary lining of the inverted arch.

In a preferred embodiment: in step (4) of water stop wall construction and backfilling of concrete on both sides, the water stop wall construction includes: the wall body and foundation of the water stop wall are both made of reinforced concrete, and pre-buried I-beams or channel steels are used between the foundation and the base; a base bearing capacity test is carried out before construction, and drainage pipes are pre-buried during construction; measurement and layout are carried out before foundation pouring to determine the template position, and steel bars are tied after the template is erected, and the foundation steel bars are reserved for overlapping parts with the wall steel bars. The foundation is poured once, and adjacent joints are staggered during wall construction; the template uses a customized steel template, which is fixed with tension bolts, and diagonal braces are added on the outside. Before erecting the template, the template is polished and coated with a release agent; the wall is poured in sections, layers, and layers; after each section is poured, the back of the wall is backfilled with concrete in a timely manner, and the concrete backfill surface is used as the construction platform for the next retaining wall, and the pouring construction is carried out section by section until the design elevation;

The concrete backfill construction on both sides of the waterstop wall includes: backfilling with concrete on both sides of the waterstop wall, and the backfill construction is carried out synchronously with the pouring of the waterstop wall in layers until the designed elevation; the last layer of concrete backfill construction is controlled according to the designed slope of 1:2, the high side is flush with the top of the waterstop wall, and the low side follows the terrain in the cave.

In a preferred embodiment: in step (6) of backfilling the top of the primary support and constructing a waterproof layer, the backfilling construction of the primary support top arch includes: after the initial support is completed, using pumped concrete to construct the arch; the top surface is covered with a double-layer steel mesh, and after the pumping is completed, it is fully covered with a waterproof board and a layer of emulsified asphalt waterproof coating is constructed as a waterproof layer;

The construction of the drainage blind pipe includes: before the installation of the annular drainage pipe, first measure and mark the specific position of the annular drainage pipe on the initial support structure surface, drill holes for positioning, drive expansion anchor bolts into the positioning holes or use anchoring agents to pre-embed the steel bar heads in the positioning holes, use steel bar clips to drive into the positioning holes to fix the annular blind pipe, wrap the blind pipe with non-woven fabric, and tie it with wire; clamp the blind pipe with a clip and then fix it on the expansion bolt; the longitudinal drainage pipe is constructed according to the design drawings with reference to the annular drainage blind pipe;

The geotextile construction includes: using a laser profiler or a laser three-dimensional scanner to detect the inner contour of the initial support of the tunnel, and laying the geotextile when the surface flatness of the initial support meets the D/L ratio of not more than 1/6, wherein D is the depth of the concave between two adjacent convex surfaces of the initial support surface, and L is the distance between two adjacent convex surfaces of the initial support surface; during the laying process, nails are used to heat the hot-melt pad for fixing, and fixing points are appropriately added in the concave part;

The construction of the PVC waterproof board includes: before the construction of the waterproof board, check the smoothness of the concrete surface and then construct it after it meets the requirements; use an automatic hot melt climbing welding machine for construction, and use a handheld welding gun for detail processing or repair; the waterproof layer is laid in a circular manner, and there is no longitudinal overlap between the arch and the side wall;

The waterstop construction includes: construction joints are constructed using embedded waterstops, expansion joints are constructed using embedded steel-edged rubber waterstops in combination with back-sticked rubber waterstops, and the back-sticked waterstops are fully wrapped.

In a preferred embodiment: in the step (7) of the secondary lining waterproofing and drainage construction, the water pressure resistant secondary lining construction includes: secondary lining steel mesh construction, secondary lining concrete construction and water blocking wall construction;

The secondary lining steel mesh construction: the secondary lining stress-bearing steel bars are mechanically connected; the steel bar ends are wrapped with customized plastic shells or geotextiles, protective layer pads are set for steel bar installation, and the steel bar extension length is reserved for the invert at the connection between the invert and the side wall;

The secondary lining concrete construction: The secondary lining concrete construction adopts a fully hydraulic automatic walking integral lining trolley, adopts a chute for symmetrical pouring, and the concrete is poured symmetrically in layers from the side walls on both sides to the vault, from bottom to top; the concrete is poured continuously, and manually assisted in vibration, the vault concrete is poured densely at one time, and grouting holes are reserved for the vault, and the vault grouting is carried out after the secondary lining concrete pouring is completed;

The water blocking wall construction includes: constructing a longitudinal secondary lining water blocking wall at the contact position between the pressure-bearing side and the non-pressure-bearing side of the tunnel, and using a waterproof layer, waterproof concrete, waterproof layer and waterproof concrete in combination to block water at the end; the water blocking wall is excavated in advance, and the waterproof layer and secondary lining concrete are integrally cast with the secondary lining of the main tunnel;

The inspection channel construction: after the second lining construction of the inspection channel is completed, the road surface construction in the well will be carried out, and the road surface construction is in a stepped shape; a concrete retaining wall is set at the intersection of the inspection channel and the cave, and a pressure-resistant manhole cover and a valve are embedded in the wall. During the dry season, the manhole cover can be opened through the valve to enter the cave.

In a preferred embodiment: in the construction of the water pressure monitoring system in step (8), the water pressure monitoring system includes: a water pressure gauge, a concrete strain gauge, a concrete surface strain gauge, a strain transmitter, an electric pressure regulating valve, a valve control system, and a seamless steel pipe;

The strain gauge is embedded and installed synchronously during the concrete pouring process, and the remaining control systems will be installed after the tunnel lining construction is completed and the cavity treatment construction is completed. Before installation, ensure that the on-site equipment meets the design pressure requirements, and arrange professional personnel to carry out the construction. The seamless steel pipe is tightly connected to the ditch, and the steel pipe is set into an arc shape in the bending section. At the same time, the ditch side of the steel pipe at the water outlet is wrapped with steel plates, and waterproof mortar is set on the top of the ditch cover.

In a preferred embodiment: during the implementation of the monitoring and early warning scheme in step (9), when the water pressure outside the tunnel lining monitored by the water pressure gauge exceeds the limit value, the electric pressure control valve is opened through the pressure control system to reduce the pressure to below the limit value; when the water pressure outside the tunnel lining monitored by the water pressure gauge exceeds the limit value, but the rising rate does not exceed the limit value, the small diameter seamless steel pipe is automatically opened, and the groundwater outside the pressure section lining is drained to the non-pressure section through the small diameter seamless steel pipe for discharge; when the water pressure outside the tunnel lining monitored by the water pressure gauge exceeds the limit value, and the rising rate also exceeds the limit value, the large diameter seamless steel pipe is automatically opened, and the groundwater outside the pressure section lining is drained to the drainage ditch in the tunnel through the large diameter seamless steel pipe for discharge.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

1. The present invention provides a construction method for a karst tunnel passing through a cave. Compared with traditional grouting and plugging, related processes such as cave top excavation and support, bottom sediment cleaning and concrete backfilling, water stop wall construction and concrete backfilling behind the wall, and pumped concrete arch construction are all non-concealed projects, with relatively low operating difficulty, controllable construction quality, fewer construction blind spots, and higher construction safety.

2. The present invention provides a construction method for a karst tunnel passing through a karst cave, which constructs water-stop walls on both sides of the tunnel and backfills concrete behind the walls, and cooperates with tunnel vault expansion, support, and arch protection to restore the original runoff channel, maintain the initial runoff balance of the karst cave groundwater, do not block the water passage of the groundwater near the karst cave, and protect the surrounding ecological environment to the greatest extent.

3. The present invention provides a construction method for a karst tunnel passing through a karst cave. An inspection passage leading to the karst cave from a pedestrian cross tunnel is constructed in the non-pressure section of the tunnel. The end of the passage is closed with a water pressure-resistant manhole cover and a valve. During the dry season, the water stored on the top of the cave is discharged into the ditch through a pressure-limiting discharge pipe. The inspectors can open the pressure-resistant manhole cover and enter the cave to check the stability of the cave, whether it is silted up, etc. If necessary, it can be cleaned manually to ensure the safety of tunnel operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow chart of a construction method in a preferred embodiment 1 of the present invention.

DETAILED DESCRIPTION

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top/bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise clearly stipulated and limited, the terms "installed", "provided with", "installed/connected", "connected", etc. should be understood in a broad sense. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection. It can be a mechanical connection or an electrical connection. It can be a direct connection or an indirect connection through an intermediate medium. It can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

Example 1

Referring to FIG1 , this embodiment provides a construction method for a karst tunnel passing through a karst cave, comprising the following steps: (1) cave expansion and support: performing cave expansion operations and cave top support operations; (2) cave base dredging and backfilling: excavating the cave base and backfilling with concrete; (3) invert and backfill construction: performing invert secondary lining construction and invert backfill construction; (4) water stop wall construction and backfilling with concrete on both sides: setting up a water stop wall in the tunnel and backfilling with concrete on both sides of the water stop wall; (5) initial support construction: performing initial tunnel support construction according to the design drawings; (6) Initial support top backfill and waterproofing layer construction: perform initial support top arch backfill construction, drainage blind pipe construction, civil engineering cloth construction, PVC waterproofing board construction and water stop belt construction; (7) Secondary lining drainage construction: perform water pressure resistant secondary lining construction and inspection channel construction; (8) Water pressure monitoring system installation and commissioning: before installing the water pressure monitoring system, ensure that the on-site equipment meets the design pressure requirements, and arrange professional personnel to carry out the construction; (9) Implementation of monitoring and early warning plan: when the external water pressure of the tunnel lining monitored by the water pressure gauge exceeds the limit, the pressure control system opens the electronically controlled pressure control valve to reduce the pressure to below the limit. Specifically, the operating points of the construction method of a karst tunnel crossing a cave described in this embodiment are as follows:

1. Construction Preparation

Establish and improve the project quality and safety responsibility system, set up a quality leadership group with the project manager as the team leader, the project deputy manager and chief engineer as deputy team leaders, and the heads of relevant departments and construction teams as team members, and be fully responsible for the quality and safety management of this project. Establish and improve the quality management organization and project quality responsibility system, strengthen the quality management of all employees, and conscientiously formulate and implement the work responsibilities of various functional departments and key management personnel related to project quality. Carry out quality inspections throughout the construction process, and implement inspections from bottom to top in accordance with the "three inspections system" based on the self-inspection procedures.

According to the actual situation on site, carefully review the construction drawings to ensure the correctness and effectiveness of the construction design drawings. If any problems are found, contact the supervision and design units in time. Only after the design units have clarified them can the construction be organized. Strictly implement the technical disclosure system, list the key monitoring parts and key points, and conduct engineering technology, quality, and safety disclosures to on-site workers. Strictly implement the on-site material entry inspection system, check the factory certificates and instructions of all raw materials, and only allow them to enter the site after they are qualified. Implement the construction measurement and line setting double inspection and review system, with the method of "accurate placement, frequent re-measurement, and comprehensive control of points, lines, and surfaces" to ensure the accuracy of the measurement work, and do a good job in preserving and archiving the original measurement data.

2. Cave Excavation and Support

Cave expansion: First, before cave expansion, it is necessary to clean up the dangerous rocks within the scope of the cave top operation and the sediments in the cave cavity. Then, the cave top is expanded by drilling and blasting, and local artificial rock drilling is carried out by machinery. Finally, the cave after expansion is measured to ensure that the distance between the cave top and the top surface of the tunnel arch backfill after expansion can meet the minimum water-passing section of the cave groundwater runoff.

Cave top support: After the cave is expanded, support is carried out in time according to the integrity of the surrounding rock. When the surrounding rock is intact and there is no falling block, mortar anchor rod + steel mesh + shotcrete is used for support. When the surrounding rock has fallen blocks, anchor rod + steel mesh + steel support + shotcrete support is used. When the steel support is constructed, crossbeams and locking anchor rods are used to temporarily fix it on the solid surrounding rock, and the water stop walls on both sides are constructed to the designed elevation before pouring it as a whole.

3. Desilting and backfilling of cave base

Excavation of the cave base: Use an excavator to excavate and dredge the base in layers. After the silt is cleared, conduct a foundation bearing capacity test. If it meets the requirements, use high-pressure water to flush the rock wall to ensure that there is no debris and residual loose soil. After the flushing is completed, use a water pump to drain the accumulated water in the base.

Concrete backfill: After the cave base is excavated, concrete is used to backfill in layers to the designed elevation. The backfill is carried out twice, and the backfill height each time does not exceed 3.0m. The pouring thickness of each layer is controlled at 30cm~50cm, and it is vibrated and compacted layer by layer. Before the second concrete pouring, the contact surface needs to be cleaned by chiseling. The loose and weak layers on the concrete surface can be removed by water washing, manual chiseling, and pneumatic chiseling until the coarse aggregate leaks out. The concrete surface after chiseling should be rinsed with clean water. When water washing and chiseling are used, the strength of the treated layer concrete should reach 0.5MPa; when manual chiseling is used, it should reach 2.5MPa; when pneumatic chiseling is used, it should reach 10MPa.

4. Invert and filling construction

Construction of the secondary lining of the inverted arch: Before pouring the secondary lining of the inverted arch, geotextile and all-inclusive waterproofing board should be laid and the overlap part with the waterproof layer of the arch wall should be reserved. Before the construction of the inverted arch reinforcement, the annular overlap reinforcement should be reserved for welding with the secondary lining reinforcement of the arch wall, and the overlap joints of adjacent reinforcements should be staggered. Before pouring the inverted arch concrete, install a double-layer buried waterstop and use a reinforcement clamp to firmly position it between the two layers of reinforcement. The inverted arch and the bottom of the paving should be constructed with a fully hydraulic self-propelled inverted arch trestle in conjunction with concrete. When pouring the secondary lining of the inverted arch, the entire section should be poured together. It is strictly forbidden to pour separately on the left and right sides, and the pouring length at one time should not be greater than 5m. The filling concrete needs to be poured separately from the inverted arch concrete.

Inverted arch filling construction: Inverted arch filling construction shall be carried out after the pouring of the second lining of the inverted arch is completed, and the surface water and debris of the second lining of the inverted arch shall be cleaned before construction. The transverse construction joint of the inverted arch filling concrete shall be staggered with the construction joint of the second lining of the inverted arch, and the staggered distance shall not be less than 0.5m.

5. Waterstop wall construction

The wall and foundation of the water stop wall are both reinforced concrete. Pre-buried I-beams or channel steels are used between the foundation and the base to ensure a tight connection. The base bearing capacity test is carried out before construction. During the construction process, the drainage pipe is pre-buried according to the design requirements. Before pouring the foundation, measurement and lofting should be carried out to determine the position of the template. After the template is erected, the steel bars should be tied. The foundation steel bars should reserve the overlap part with the wall steel bars, and the foundation should be poured in one go. During the wall construction, attention should be paid to the welding of the reserved steel bars in the foundation, and the adjacent joints should be staggered; the template uses a customized steel template, which is fixed with tension bolts, and the outer side is appropriately increased with diagonal braces. Before erecting the template, the template should be polished and coated with a release agent; the wall casting should be segmented, layered, and vibrated layer by layer. The casting height of each segment should not exceed 2m, and the casting thickness of each layer should be controlled between 30cm and 50cm; after each segment is cast, the back wall concrete should be backfilled in time, and the concrete backfill surface should be used as the construction platform for the next retaining wall, and the casting construction should be carried out segment by segment until the design elevation.

6. Concrete backfill construction on both sides of the water stop wall

Concrete is used to backfill the two sides of the water stop wall. The backfill construction should be carried out in layers simultaneously with the pouring of the water stop wall until the designed elevation. The last layer of concrete backfill construction should be controlled according to the designed slope of 1:2, with the high side flush with the top of the water stop wall and the low side following the terrain inside the cave.

7. Initial support construction

Carry out the initial support construction of the tunnel according to the design drawings. It should be noted that after the installation of the initial support steel arch frame, the pumping pipe should be pre-buried, the pumping pipe should be welded to the steel arch frame, and the pipe opening should be temporarily blocked with hemp wool to avoid the pipe opening being blocked by the sprayed concrete construction.

8. Backfill of the primary support top arch

After the initial support is completed, when its strength reaches 75% of the design value, the arch protection is constructed by pumping concrete. The thickness of the arch protection is not less than 0.5m, the top surface is covered with a double-layer steel mesh, and the thickness of the top surface anti-cracking layer is not less than 5cm. After the pumping is completed, the waterproof board is fully covered and a layer of emulsified asphalt waterproof coating is constructed as a waterproof layer.

9. Drainage and waterproofing construction

Drainage blind pipe construction: Before installing the annular drainage pipe, the specific position of the annular drainage pipe should be measured and marked on the initial support structure surface, drill holes for positioning, drive expansion anchors into the positioning holes or use anchors to embed the steel bar heads in the positioning holes, use steel bar clips to drive into the positioning holes to fix the annular blind pipe, wrap the blind pipe with non-woven fabric, and tie it with wire; clamp the blind pipe with clips and then fix it on the expansion bolts. The longitudinal drainage pipe is constructed according to the design drawings and with reference to the annular drainage blind pipe.

Geotextile construction: Use laser profiler or laser 3D scanner to detect the inner contour of the initial support of the tunnel, and lay the geotextile when the surface flatness of the initial support meets the requirement of D/L not more than 1/6 (D is the depth of the concave between two adjacent convex surfaces of the initial support surface, and L is the distance between two adjacent convex surfaces of the initial support surface). During the laying process, the geotextile is fixed by nailing and heating the hot-melt pad, and appropriate fixing points are added in the concave part.

PVC all-inclusive waterproof board construction: Before the waterproof board is constructed, check the smoothness of the concrete surface first, and then construct it after it meets the requirements. Use an automatic hot-melt climbing welding machine for construction, and a handheld welding gun can be used for detail processing or repair. The waterproof layer should be laid in a circular manner, and there should be no longitudinal overlap between the arch and the side wall. The overlap width of two waterproof boards should not be less than 120mm, and the effective width of a single weld should not be less than 10mm. The weld should be continuous and uninterrupted, without leaking, false welding, welding scorch, or welding penetration, and an inflation test should be performed; the staggered distance between the overlap seam of the waterproof board and the construction seam should not be less than 50cm.

Waterstop construction: Construction joints are constructed with embedded waterstops. Expansion joints are constructed with embedded steel-edged rubber waterstops + back-attached rubber waterstops, and the back-attached waterstops are fully enclosed.

10. Construction of water pressure resistant secondary lining

Construction of secondary lining steel mesh: The secondary lining stress-bearing steel bars are mechanically connected; when welding is used for construction, the single-sided welding lap length is not less than 10d, and the double-sided welding lap length is not less than 5d; when binding is used for connection, the lap length is not less than 35d. The joint rate of steel bars of the same section shall not exceed 50%. The ends of the steel bars should be wrapped with customized plastic shells or geotextiles to prevent the ends of the steel bars from piercing the waterproof board. Protective layer pads should be set for steel bar installation, and through-type pads should be used. The extended length of the reserved steel bars of the invert at the connection between the invert and the side wall should meet the connection requirements.

Secondary lining concrete construction: The secondary lining concrete construction shall adopt a fully hydraulic automatic walking integral lining trolley. The trolley shall have the function of pouring the side walls in the cable trench at the same time, and the chute shall be used for symmetrical pouring. The concrete shall be poured symmetrically from the side walls on both sides to the vault, from bottom to top, in layers. The height difference of the concrete pouring surface on both sides shall not be greater than 1.0m, and the height difference of the concrete pouring surface on the same side shall not be greater than 0.5m. The concrete shall be poured continuously and vibrated manually. The vault concrete shall be poured densely at one time. Grouting holes shall be reserved for the vault, and the vault grouting shall be carried out after the secondary lining concrete pouring is completed.

Water blocking wall construction: A longitudinal secondary lining water blocking wall is constructed at the contact position between the pressure-bearing side and the non-pressure-bearing side of the tunnel. The longitudinal length of the water blocking wall shall not be less than 1.0m, and the waterproof layer + waterproof concrete + waterproof layer + waterproof concrete structure shall be used for end water blocking. The water blocking wall needs to be expanded in advance, and the waterproof layer and secondary lining concrete shall be integrally cast with the secondary lining of the main tunnel.

11. Inspection channel construction

After the second lining construction of the inspection channel is completed, the road surface construction in the well will be carried out. The road surface construction is in a stepped shape. A 1m thick concrete retaining wall is set at the interface between the inspection channel and the cave. A pressure-resistant manhole cover and valve are embedded in the wall. The pressure resistance is 2MPa. During the dry season, the manhole cover can be opened through the valve to enter the cave.

12. Construction of water pressure monitoring system

The water pressure monitoring system is mainly composed of water pressure gauge, concrete strain gauge, concrete surface strain gauge, strain transmitter, electric pressure regulating valve, valve control system, seamless steel pipe, etc. The strain gauge is pre-buried and installed synchronously during the concrete pouring process, and other control systems are installed after the tunnel lining is fully constructed and the cavity treatment is completed. Before installation, it should be ensured that the equipment entering the site meets the design pressure requirements, and professional personnel should be arranged for construction. The connection between the seamless steel pipe and the ditch must be tight and water-free, and the steel pipe should be made into an arc in the bending section. At the same time, in order to prevent the water flow from instantly scouring the ditch, the steel plate is used to wrap the ditch side of the outlet of the steel pipe, and a waterproof mortar of not less than 2cm thick is set on the top of the ditch cover.

13. Implementation of the Monitoring and Early Warning Program

When the external water pressure of the tunnel lining monitored by the water pressure gauge exceeds the limit, the electric pressure control valve is opened through the pressure control system to reduce the pressure to below the limit (manually open if necessary), and normal operation is then carried out.

When the water pressure outside the tunnel lining monitored by the water pressure gauge exceeds the limit, but the rising rate does not exceed the limit, the small diameter seamless steel pipe will be automatically opened, and the groundwater outside the pressure section lining will be drained to the non-pressure section for discharge through the small diameter seamless steel pipe.

When the water pressure outside the tunnel lining monitored by the water pressure gauge exceeds the limit and the rising rate also exceeds the limit, the large-diameter seamless steel pipe will be automatically opened, and the groundwater outside the pressure-bearing section lining will be drained to the drainage ditch in the tunnel for discharge.

In this embodiment, the construction method is strictly implemented in accordance with existing standards and specifications. The main standards, specifications and inspection methods are listed below: "Technical Specifications for Highway Tunnel Construction" (JTG/T 3660-2020), "Technical Specifications for Highway Engineering Construction Safety" (JTG F90-2015), "Highway Engineering Quality Inspection and Evaluation Standards" (Civil Engineering) (JTGF80/1-2017), "Work Safety Law of the People's Republic of China" (2021), etc.

In addition, in the construction methods mentioned above, quality assurance measures, safety measures and environmental protection measures need to be repeatedly emphasized and supervised with practical actions:

1. Quality assurance measures:

The contour of the expanded excavation control section meets the requirements of the water-passing section, and the initial support surface should be smooth. The surface of the shotcrete should be free of leakage, bulging, cracks, and leakage of steel mesh. The base backfill should control the bearing capacity of the foundation after the base is desilted to meet the design requirements, and there should be no weak interlayer on the base. The quality of vibration should be controlled during concrete pouring. Layered pouring and layer-by-layer vibration should be adopted for compaction. The base surface of each newly poured concrete should be roughened and the quality of roughening should be controlled. Before pouring, the loose soil, mud and debris on the base should be cleaned; the concrete strength and verticality of the waterstop wall should meet the requirements; the roughening work of the waterstop wall's multi-casting interface should meet the requirements; and the waterproofing treatment of each construction joint should meet the quality requirements.

The surface of shotcrete should be free of leakage, bulging, cracks, and leakage of steel mesh; the material, type, quality, specification, quantity and performance of the anchor rod must meet the design and specification requirements; the effective length of the anchor rod inserted into the hole shall not exceed 95% of the design length; the anchor rod shall be arranged perpendicular to the excavation contour, and the anchor rod pad shall be close to the rock surface; the steel mesh shall be firmly connected to the anchor rod or other fixing devices, and shall not shake during shotcrete spraying; longitudinal steel bars must be used to connect the steel supports, and the arch foot must be placed on a solid foundation; when the arch foot elevation is insufficient, stone or gravel shall not be used as a pad, but steel plates shall be set for adjustment, or concrete or channel steel shall be used for support; the steel support shall be close to the surrounding rock, and the gap between it and the surrounding rock shall not be backfilled with stone slabs, but shall be backfilled densely with shotcrete.

The quality, specifications, and performance of waterproof materials must meet the design and specification requirements; before laying waterproof membranes, the sprayed concrete base surface should be carefully inspected. There should be no steel bars or protruding sharp objects. If there are any, the sharp objects should be cut off and smoothed with mortar; the surface of the waterproof layer should be smooth, without wrinkles, bubbles, or damage, and should be close to the cave wall, with appropriate tightness and no tension. Mechanical connection should be adopted for the stress-bearing steel bars of the second lining. When welding is adopted, the lap length of single-sided welding shall not be less than 10d, and the lap length of double-sided welding shall not be less than 5d; when binding connection is adopted, the lap length shall not be less than 35d. The joint rate of steel bars of the same section shall not exceed 50%. Positioning fixtures should be used to position the steel bars of the second lining. Limiting bars should be set between the inner and outer stress-bearing bars to ensure that the thickness of the steel bar protective layer meets the design requirements. Protective layer pads should be set for steel bar installation, and through-type pads should be adopted.

The steel bar protective layer pads should be firmly tied to the outer steel bars. The protective layer pads are arranged in a plum blossom shape, and the spacing should be controlled at about 100cm. The pads used should be clean and the color should be basically consistent with the concrete surface. Before pouring concrete, the side form support frame, formwork, steel bars (mainly check whether the wire head is close to the formwork) and embedded parts should be inspected. At the same time, the construction joints should also be inspected to check whether the joint surface is clean and fully moistened. When the inspection meets the requirements, pouring can be carried out.

2. Safety measures

Blasting safety assurance measures: The charging work must be completed by blasters with blasting certificates. Fireworks are strictly prohibited in the charging area. Non-charging personnel must remove the charging points before charging. After the blasting, any blind guns, residual guns, detonators, etc. found during the cleaning process must be reported immediately and handled by the blasters. After each blasting, the blasters should carefully fill in the blasting records. After the blasting, the blasters and custodians must carefully count the blasting equipment and return them directly to the blasting equipment warehouse in a timely manner. After the charging is completed, inspection and acceptance shall be carried out. No operation shall be carried out without inspection and acceptance; and the original records of charging shall be kept. Blasters must be very clear about the role of the warning signal. When blasting in the main hole, all personnel must be evacuated from the hole.

Safety assurance measures for shotcrete: The spraying machine must adopt wet spraying operation, and the materials must be mixed according to the construction mix ratio requirements. The wind source must be a voltage-stabilizing source that meets the requirements, and the power supply, water source, and feeding equipment must be matched. The pipeline must be installed correctly, and the joints must be tightened and sealed. When the pipeline passes through the road, it must be set in the ground trough and covered for protection. Check the wear of the conveying pipe and joints frequently, and deal with them in time when there is wear, breakdown or loosening. The inside of the spraying machine must be kept clean, and the spraying concrete mix ratio must meet the concrete performance and spraying concrete working requirements at the same time. Agglomerated cement and unscreened sand and gravel must not be used. Before starting, ventilation, water, and electricity must be connected first, the air intake valve must be opened to gradually reach the rated pressure, and then the motor must be started to run at no load. After confirming that everything is normal, the material can be fed. The mechanical operator and the spraying operator must have a contact signal. When air is supplied, materials are added, materials are stopped, air is stopped, and blockage occurs, they must be contacted in time and closely cooperated. After the operation, all the spray materials in the bin and the feed hose must be sprayed out, the nozzle must be removed and cleaned, and the concrete and debris adhering to the inside and outside of the machine body must be removed. At the same time, the feed pipe must be cleaned and the seal must be in a relaxed state. The sprayer should wear a protective mask, waterproof cape, protective glasses, dust mask, latex gloves; other staff must also wear dust masks and other protective equipment.

Safety guarantee measures for the use of machinery: During construction, construction machinery produced by qualified enterprises must be used, with certificates of conformity and complete installation, use and maintenance instructions. Before construction machinery enters the site, it should be inspected and confirmed to be qualified. Construction machinery operators must undergo professional training, pass the assessment, and obtain an operator's license issued by the construction administrative department or a motorized driving license issued by the public security and traffic authorities before they can take up their posts. Operators of small construction machinery and tools should undergo safety and technical training and pass the assessment before they can take up their posts. Various safety protection devices and automatic devices such as monitoring, indication, instrumentation, alarm, and signal on the machinery must be intact and complete, and should be repaired in time if they are damaged. Machinery with incomplete or invalid safety protection devices is strictly prohibited from use. The electrical wiring of electric machinery must be operated by electricians. When used in open air and humid areas, moisture-proof protection measures should be taken. Before using construction machinery, the operator should conduct a comprehensive inspection to confirm that all parts of the machinery are intact, the protective devices are complete and effective, and after trial operation, confirm that they are normal before operation. The machinery must be operated correctly and used reasonably in accordance with the technical performance, load-bearing capacity and use conditions specified in the manufacturer's instruction manual. It is strictly forbidden to overload or expand the scope of use at will. The original machine parts shall not be replaced at will. When replacement is necessary, it shall be designed, tested and identified by professional technicians and can only be implemented after confirming that it meets the requirements.

Safety measures for electricity use on site: All mobile electrical appliances should be protected by leakage switches, the wires should not be damaged, the plugs and sockets should be intact, and it is strictly forbidden to directly plug the wires into the sockets without plugs. When inspecting and repairing the distribution box and switch box, the corresponding power switch of the previous level must be disconnected and the power must be cut off, and the power outage sign must be hung. It is strictly forbidden to work with power on. Before and after each shift, the electrical equipment in the cave should be checked to confirm that the equipment is operating normally and the power is cut off in time after the shutdown. Inspections and patrols should be carried out on time during the operation of the equipment. The installation, removal and maintenance of construction electrical equipment must be the responsibility of electricians, and non-electricians are strictly prohibited from performing any electrical work. Electricians must be familiar with various management regulations of the construction site, especially the management regulations on safe use of electricity, safe electrical operation and maintenance, and must be familiar with the electrical performance of various mechanical equipment on site.

3. Environmental protection measures

The layout of production sites such as steel bar processing sites and raw material storage sites is required to be away from residential areas and employee living camps to avoid or reduce visual, noise and dust pollution to people. At the same time, the construction site should be reasonably planned so that the storage and treatment of construction waste and sewage will not pollute the water quality.

When selecting equipment, conduct a detailed building sound assessment of the mechanical equipment used in this division, select low-pollution or low-noise equipment, and take measures such as silencing, sound insulation, and protective plates to reduce noise. Mechanical vehicles should slow down and not honk when passing through residential areas. Build temporary partition barriers near relatively fixed mechanical equipment to reduce noise transmission. When selecting sites for steel bar processing and concrete mixing, try to stay away from residential areas. When arranging construction personnel to work in high-noise areas, they should be equipped with labor protection supplies. During the construction period, first make a good construction organization design and protection engineering design, and then set up a drainage system for the construction site during the construction process, concentrate the sediment-containing sewage and discharge it, and avoid direct discharge of construction wastewater into the water. It is prohibited to discharge or dump waste residues, garbage and other wastes into water bodies. The mixing station is equipped with a three-level sedimentation tank. After the production wastewater is purified by professional mud treatment equipment after three-level sedimentation, it can be discharged.

The ground where oil is stored on site shall be treated for seepage prevention, such as using anti-seepage concrete floor, laying anti-oil felt and other measures. During use, measures shall be taken to prevent oil from running, bubbling, dripping and leaking to prevent soil or river pollution. For operations that are prone to generate dust and dust, optimize the construction process, formulate operating procedures and watering and dust reduction measures. Protect the environment around the site, and do not pile up materials and garbage outside the construction site. Use the land in strict accordance with the approved scope of occupation.

In order to ensure the overall quality of the construction project and efficient production, the building materials and site facilities and equipment in the construction process described in this embodiment need to be explained as follows:

The material list is as follows:

The device table looks like this:

To ensure the orderliness and efficiency of the overall construction, the work of each team is coordinated with each other. The following is the labor organization involved in this construction method:

In summary, the construction method mainly maintains the initial runoff balance of cave groundwater through the water-stop walls on both sides of the tunnel in conjunction with the arch protection arch, so as not to destroy the ecological balance near the cave; the water pressure on the outer side of the tunnel support structure is dynamically maintained by adopting a hierarchical management and monitoring system with limited pressure discharge, so as to ensure that the water pressure is always maintained within the limit, thereby ensuring the safety of the tunnel construction and operation and maintenance period to the greatest extent. This method is mainly suitable for water-rich karst tunnels passing through large underground caves, karst troughs, underground rivers and other unfavorable geological projects. When the tunnel passes through a large cave, the top of the cave is first expanded and supported, and the silt at the bottom of the cave is cleaned and backfilled with concrete; after the construction of the tunnel invert and its filling, the water stop walls on both sides of the tunnel are constructed and the concrete backfill behind the wall is backfilled, and seamless steel pipes for emergency drainage are pre-buried; after the initial support construction of the tunnel, the arch protection is constructed by pumping concrete, and two layers of steel mesh are laid on the top of the arch protection. After the pumping is completed, the whole arch is covered with waterproof board and a layer of emulsified asphalt waterproof coating is constructed on the top of the water surface as a water sealing layer; then, the secondary lining of the tunnel is promptly constructed and an inspection channel is constructed at a suitable location; finally, the monitoring equipment for pressure-limited emission classification management is installed and debugged.

The above is only a preferred specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any technician familiar with the technical field who uses this concept to make non-substantial changes to the present invention within the technical scope disclosed by the present invention shall be deemed to infringe the protection scope of the present invention.

Claims (10)

1. The construction method for the karst tunnel to pass through the karst cave is characterized by comprising the following steps of:

(1) And (5) karst cave expanding, digging and supporting: performing expansion digging operation and karst cave top supporting operation on the karst cave;

(2) Dredging and backfilling karst cave substrate: excavating a karst cave substrate and backfilling concrete;

(3) Inverted arch and filling construction: performing inverted arch secondary lining construction and inverted arch filling construction;

(4) And (3) construction of the water stop wall and backfilling concrete on two sides: setting a water stop wall in the tunnel, and backfilling concrete on two sides of the water stop wall;

(5) And (3) primary support construction: carrying out primary support construction of the tunnel according to the design drawing;

(6) And (3) primary support top backfill and waterproof layer construction: performing primary support top arch protection backfill construction, drainage blind pipe construction, civil engineering cloth construction, PVC waterproof board construction and water stop construction;

(7) And (3) secondary lining waterproof and drainage construction: performing construction of a water pressure resistant secondary lining and construction of an inspection channel;

(8) Installing and debugging a water pressure monitoring system: before the water pressure monitoring system is installed, ensuring that the approach equipment meets the design pressure requirement, and arranging professional personnel for construction;

(9) The implementation of a monitoring and early warning scheme comprises the following steps: when the pressure of the outside water of the tunnel lining obtained through monitoring by the water pressure gauge exceeds the limit value, the electric control pressure control valve is opened through the pressure control system, and the pressure is reduced to be below the limit value.

2. The construction method for a karst tunnel to pass through karst cave according to claim 1, wherein the construction preparation work is carried out before the karst cave expansion and support in step (1) is carried out;

the construction preparation work includes: establishing a sound engineering quality safety responsibility system, a quality management organization and an engineering quality responsibility system, and establishing a quality leader group; performing quality inspection on the whole construction process, and performing detection work according to three inspection; rechecking the construction drawing, and keeping connection with the supervision and design units; listing key monitoring positions and key points, and carrying out engineering technology, quality and safety delivery on site operators; carrying out construction measurement and paying-off double-checking system, and checking the procedure of raw materials; and (5) data storage and archiving work is performed.

3. The method for constructing karst tunnels through karst caves according to claim 1, wherein in the step (1) of karst cave expansion and excavation and support, the karst cave expansion and excavation comprises: before the karst cave is dug, clearing up dangerous stones within the influence range of the karst cave top operation and sediments within the karst cave; adopting drilling blasting to perform karst cave top expansion and digging, and using machinery to perform local artificial rock drilling; measuring the karst cave after the expansion and excavation;

the karst cave top support includes: after the karst cave expansion and excavation operation is finished, supporting according to the complete condition of surrounding rock, and when the surrounding rock is complete and no block is dropped, supporting by adopting the mutual cooperation of a mortar anchor rod, a reinforcing mesh and sprayed concrete; when the surrounding rock has a falling block, supporting is carried out by adopting the mutual coordination of an anchor rod, a reinforcing mesh, a steel support and an shotcrete support; during construction of the steel support, the steel support is temporarily fixed on firm surrounding rock by adopting a cross beam and a foot locking anchor rod, and the steel support is integrally poured when the water stop walls on two sides are constructed to a designed elevation.

4. The method for constructing karst tunnels through karst cave according to claim 1, wherein the step (2) of dredging and backfilling karst cave base comprises: adopting an excavator to excavate and dredge the foundation layer by layer, carrying out a foundation bearing capacity test after the sludge is cleaned, flushing the rock wall by adopting high-pressure water after meeting the requirements, and pumping and draining accumulated water of the foundation by adopting a water pump after flushing; after the karst cave substrate is excavated, backfilling to the designed elevation by adopting concrete layering, wherein the backfilling is carried out twice, and the layers are vibrated and compacted; before the second concrete pouring, the contact surface is subjected to roughening cleaning, and the roughened concrete surface is washed clean by clean water.

5. The method for constructing karst tunnel through karst cave according to claim 1, wherein the step (3) of inverted arch and filling construction comprises: laying geotextile and fully-covered waterproof plates before pouring of the inverted arch secondary lining, reserving a lap joint part with an arch wall waterproof layer, reserving annular lap joint steel bars before constructing inverted arch steel bars, welding the annular lap joint steel bars with the inverted arch wall secondary lining steel bars, and staggering lap joints of adjacent steel bars;

installing a double-layer embedded water stop before inverted arch concrete pouring, firmly positioning the water stop by adopting a steel bar clamp and arranging the water stop between the two layers of steel bars, and constructing an inverted arch and a bottom by adopting a full-hydraulic self-walking inverted arch trestle to be matched with concrete; pouring the whole inverted arch secondary lining together, and pouring filling concrete and inverted arch concrete separately; and after the pouring of the inverted arch secondary lining is completed, performing inverted arch filling construction, cleaning accumulated water and sundries on the surface of the inverted arch secondary lining before construction, and staggering the transverse construction joint of the inverted arch filling concrete and the inverted arch secondary lining construction joint.

6. The construction method for a karst tunnel to pass through karst cave according to claim 1, wherein in the construction of the water-stop wall and the backfilling of concrete at both sides in the step (4),

the water stop wall construction includes: the wall body and the foundation of the water stop wall are made of reinforced concrete, and embedded I-steel or channel steel is adopted between the foundation and the substrate; before construction, carrying out a substrate bearing capacity test, and in the construction process, pre-burying a drain pipe; measuring and lofting before pouring a foundation, determining the position of a template, binding steel bars after the template is erected, reserving a part of the foundation steel bars, overlapping with the steel bars of the wall body, finishing the primary pouring of the foundation, and staggering adjacent joints during the construction of the wall body; the template adopts a customized steel template, is fixed by adopting a split bolt, is additionally provided with an inclined strut on the outer side, and is polished and coated with a release agent before being erected; pouring the wall body for sectioning, layering and vibrating layer by layer; timely backfilling wall back concrete after each section of pouring is completed, and simultaneously utilizing a concrete backfilling surface as a construction operation platform of a next mould retaining wall, and pouring and constructing section by section until the elevation is designed;

The construction of backfilling of the concrete on two sides of the water stop wall comprises the following steps: backfilling two sides of the water stop wall by adopting concrete, wherein backfilling construction is synchronously carried out along with pouring layering of the water stop wall until the elevation is designed; and during the backfilling construction of the last layer of concrete, the slope rate is controlled according to the design ratio of 1:2, the high side is flush with the water stop wall top, and the low side is connected with the topography in the karst cave.

7. The construction method for a karst tunnel to pass through karst cave according to claim 1, wherein in the construction of the primary support top backfill and the waterproof layer in the step (6), the primary support top protection arch backfill construction comprises: after the primary support is completed, adopting pumping concrete to perform arch protection construction; the top surface is covered by a double-layer reinforcing steel bar net, a waterproof board is fully wrapped after pumping is completed, and a layer of emulsified asphalt waterproof paint is constructed to serve as a waterproof layer;

the drainage blind pipe construction includes: before the annular drain pipe is installed, measuring and marking out a specific position of the annular drain pipe on the primary support structural surface, drilling and positioning, driving an expansion anchor bolt into a positioning hole or embedding a reinforcing steel bar head into the positioning hole by using an anchoring agent, fixing an annular blind pipe by adopting a reinforcing steel bar clamping driving positioning hole, wrapping the blind pipe by using non-woven fabrics, and binding by using binding wires; the blind pipe is clamped by a clamp and then fixed on an expansion bolt; the longitudinal drain pipe is constructed according to the design drawing by referring to the annular drain blind pipe;

The civil engineering cloth construction includes: detecting the inner outline of the primary support of the tunnel by adopting a laser section instrument or a laser three-dimensional scanner, and paving geotechnical cloth when the flatness of the surface of the primary support meets the requirement that D/L is not more than 1/6, wherein D is the concave depth between two adjacent convex surfaces of the surface of the primary support, and L is the distance between the two adjacent convex surfaces of the surface of the primary support; in the laying process, the hot melting pad is heated by adopting a nail shooting mode for fixation, and fixing points are properly added in the concave part;

the PVC waterproof board construction includes: before the waterproof board is constructed, checking the smoothness of the concrete surface, and constructing after meeting the requirements; the construction is carried out by adopting an automatic hot-melting climbing welder, and a hand-held welding gun can be adopted for detail treatment or repair; the waterproof layer is laid in the whole circumferential direction, and the arch part and the side wall are not overlapped longitudinally;

the construction of the water stop comprises the following steps: the construction joint adopts a middle-buried type water stop for construction, the deformation joint adopts a middle-buried type steel edge rubber water stop to be matched with a back-attached type rubber water stop for construction, and the back-attached type water stop adopts a full-package arrangement.

8. The construction method for a karst tunnel to pass through a karst cave according to claim 1, wherein in the step (7) of two-lining water-proof and drainage construction, the water-pressure-proof two-lining construction comprises: constructing a second lining reinforcing steel bar net, a second lining concrete and a water shutoff wall;

And (3) construction of the secondary lining reinforcing steel bar net: the second lining stress steel bars are mechanically connected; the end of the steel bar is wrapped by adopting a customized plastic shell or winding geotextile, a protective layer cushion block is arranged on the steel bar installation, and the extension length of the steel bar is reserved on the inverted arch at the connection part of the inverted arch and the side wall;

and (3) the construction of the secondary lining concrete: the second lining concrete construction adopts a full-hydraulic automatic walking integral lining trolley, chute symmetrical pouring is adopted, and concrete is poured from side walls to a vault from bottom to top in a layered symmetrical manner in sequence; continuously pouring concrete, manually assisting in vibrating, pouring the concrete of the arch crown for one time, reserving grouting holes for the arch crown, and grouting the arch crown after the secondary lining concrete pouring is completed;

and (3) construction of the water shutoff wall: constructing a longitudinal secondary lining water shutoff wall at the bearing side and the non-bearing side contact position of the tunnel, and performing end water shutoff by adopting a structure mode that a waterproof layer, waterproof concrete, a waterproof layer and waterproof concrete are combined with each other; the water blocking wall is excavated in advance, and the waterproof layer, the secondary lining concrete and the secondary lining of the main hole are integrally cast;

and (3) constructing the inspection channel: after the construction of the second lining of the inspection channel is finished, carrying out in-well pavement construction, wherein the pavement construction is in a ladder shape; the inspection channel and karst cave intersection sets up a concrete retaining wall, pre-buried resistance to compression well lid and valve in the wall, and the accessible valve is opened the well lid and is got into the karst cave inside in the dead water period.

9. The method for constructing karst tunnels through karst cave according to claim 1, wherein in the construction of the water pressure monitoring system of step (8),

the water pressure monitoring system includes: the hydraulic pressure gauge, the concrete strain gauge, the concrete surface strain gauge, the strain transmitter, the electric pressure regulating valve, the valve control system and the seamless steel pipe; the strain gauges are synchronously embedded and installed in the concrete pouring process, and the rest control system is installed after the tunnel lining is completely constructed and the solution cavity treatment is completed; before installation, the approach equipment is ensured to meet the design pressure requirement, professional personnel are arranged for construction, the seamless steel pipe is tightly connected with the side ditch, the steel pipe is arranged into an arc shape at the bending section, meanwhile, the side ditch side of the water outlet of the steel pipe is covered by a steel plate, and meanwhile, the top of the side ditch cover plate is provided with waterproof mortar.

10. The construction method for the karst tunnel to pass through the karst cave according to claim 1, wherein in the implementation of the monitoring and early warning scheme in the step (9), when the water pressure gauge monitors that the external water pressure of the lining of the tunnel exceeds a limit value, an electric control pressure valve is opened through a pressure control system, so that the pressure is reduced to be below the limit value;

When the pressure of the outside water of the tunnel lining obtained through monitoring by the water pressure gauge exceeds a limit value but the rising speed does not exceed the limit value, automatically opening a small-diameter seamless steel pipe, and draining groundwater outside the lining of the pressure-bearing section to a non-pressure-bearing section through the small-diameter seamless steel pipe;

when the external water pressure of the tunnel lining obtained through monitoring by the water pressure gauge exceeds a limit value and the rising speed exceeds the limit value, the seamless steel pipe with the large diameter is automatically opened, and the underground water outside the bearing section lining is drained to a drainage ditch in the tunnel through the seamless steel pipe with the large diameter.