Construction method for tunnel soft stratum

Abstract

The invention relates to the technical field of tunnels and underground engineering, in particular to a construction method of a tunnel soft stratum, which comprises the following steps: preliminarily stabilizing a collapsed cavity through back pressure backfill, building a flexible template system by using woven bag stacking, pumping concrete to form a core supporting body, and constructing an advanced reinforcing arch by using a self-propelled double-layer small guide pipe. And finally, safe and efficient circulating tunneling and supporting are carried out under the guidance of monitoring measurement. By means of the process of first filling and then supporting, the most dangerous pipe shed operation conducted below a collapse cavity is converted into self-propelled small guide pipe construction conducted on a stable concrete filling body, and the major safety risk that operators are exposed under the collapse cavity is fundamentally eliminated. The problems of hole collapse and difficult intubation are solved by using the self-propelled small catheter, and the cavity collapse treatment period is remarkably shortened. The woven bag filled with the tunnel waste slag is adopted as the permanent end formwork, input and waste of measure materials are greatly reduced, and the construction cost is effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel and underground engineering, and particularly relates to a construction method for tunnel soft stratum. BACKGROUND

[0002] In the construction of tunnel engineering, when passing through complex geological conditions such as soft and broken zones and faults, the surrounding rock behind the working face is prone to form a growing fracture surface due to stress disturbance, thereby causing a collapse cavity phenomenon. This problem frequently occurs and has become a key bottleneck that restricts the safe advancement of the tunnel, affects the construction progress and controls the engineering cost.

[0003] At present, the traditional disposal method for such a collapse cavity usually follows the process of "first constructing an advanced pipe shed, and then backfilling a concrete buffer layer". However, this method has obvious drawbacks: on the one hand, due to the inclination of the collapse cavity slope surface, the drill bit is prone to slip when drilling the pipe shed, and it is difficult to be stably positioned. In order to ensure the hole forming accuracy, the construction personnel often need to risk entering the inside of the collapse cavity for manual assistance. On the other hand, during the pipe shed installation stage after the drilling is completed, the mechanical equipment is difficult to realize the precise butt joint of the pipe shed and the hole position, and still relies on personnel to assist in positioning under the collapse cavity, which causes the operating personnel to be exposed to the dangerous environment for a long time, and the safety risk is extremely high.

[0004] In summary, the traditional construction method has significant safety hazards in the disposal process of the collapse cavity, and seriously affects the construction efficiency and economy. Therefore, it is urgent to develop a construction method with high safety, high economy and high speed to effectively deal with the disposal problem of the collapse cavity in the soft stratum. SUMMARY

[0005] The present application aims to provide a construction method for tunnel soft stratum, which solves the problems of poor safety, low efficiency and poor economy caused by the advanced pipe shed construction under the collapse cavity in the prior art.

[0006] To achieve the above-mentioned purpose, the present application provides a construction method for tunnel soft stratum, comprising the following steps: Preparation of personnel, equipment and materials, and backfilling of the collapse cavity behind the working face by counterpressure to form an initial counterpressure body; Based on the working platform provided by the initial counterpressure body, the loose body in the collapse cavity is cleaned, and backfilling is continued to a first predetermined distance from the vault; On the top of the secondary counterpressure body, the woven bags filled with soil are staggered and stacked until a second predetermined distance from the vault, so as to construct a woven bag formwork system adapted to the profile of the collapse cavity, and the concrete delivery pipeline is simultaneously embedded and fixed during the stacking process; Pumping concrete into the collapsed cavity through the pre-embedded concrete delivery pipeline until filling to a third predetermined distance from the tunnel design profile line to form a concrete filling body with a predetermined strength; After the concrete filling body reaches the predetermined strength, it is used as a stable construction surface to construct a double-layer self-advancing grouting small pipe at the tunnel face and conduct grouting to form a reinforced arch around the tunnel face; Under the advanced support of the reinforced arch, the excavation is carried out in cycles. After each cycle of excavation, a support unit interval is immediately constructed with a steel arch, a steel mesh, and a sprayed concrete primary support. Monitoring and measurement are carried out throughout the construction process, and the subsequent construction parameters are dynamically adjusted based on the feedback data.

[0007] Among them, the preparers, equipment and materials are prepared, and the collapsed cavity behind the tunnel face is backfilled with counterpressure to form an initial counterpressure body, and: The counterpressure backfill material is transported to the collapsed cavity site using a loader or a self-unloading truck. The counterpressure backfilling uses a mixture of stone and gravel soil, with stone particle size of 20-50 cm, accounting for 40%-50%; Starting from the bottom of the collapsed cavity, the backfilling is carried out step by step from low to high, and the deformation of the surrounding rock around the collapsed cavity is observed. If there is an abnormality, stop backfilling immediately and take appropriate reinforcement measures; When backfilling to 2-3m from the top of the collapsed cavity, slow down the backfilling speed and use manual work with small mechanical equipment for fine backfilling.

[0008] Among them, based on the working platform provided by the initial counterpressure body, the loose body in the collapsed cavity is cleaned, and the backfilling is continued to a first predetermined distance from the arch top, and: Using the stable working surface provided by the initial counterpressure body, the excavator is controlled to enter the collapsed cavity; Using the excavator, the loose rock-soil body on the wall and the bottom of the collapsed cavity is gradually cleaned from the outside to the inside, and the cleaned loose body is transported out; After cleaning is completed, continue to backfill with counterpressure backfilling material until the top surface of the filling body is at a first predetermined distance from the arch top, wherein the first predetermined distance is 2 meters.

[0009] Among them, at the top of the secondary counterpressure body, the woven bags filled with soil are stacked alternately until a second predetermined distance from the arch top to form a woven bag formwork system that adapts to the profile of the collapsed cavity, and the concrete delivery pipeline is pre-embedded and fixed simultaneously during the stacking process. The specific method is: Use tunnel spoil soil as soil material, fill each woven bag to 3 / 4 of its height, and control the weight of the filled bag to 40-50 kg, then firmly seal the bag opening; The profile line starts from the bottom of the collapsed cavity, and the staggered stacking method is used to stack from bottom to top, so that the upper and lower woven bags are engaged with each other, and the verticality and shape of the stacked body are monitored and adjusted in real time during the stacking process, so that it closely fits the collapsed cavity profile, until it is stacked to a second predetermined distance from the vault, wherein the second predetermined distance is 1 meter; When stacked to the predetermined height, pause the stacking, lay the concrete delivery pipeline on the stacked body according to the preset path, and use wire or rope to bind and fix the pipeline and the woven bag, then continue to stack upward, and wrap the pipeline inside the woven bag stacked body; During the stacking process or after the stacking is completed, nylon ropes or wires are used to connect adjacent woven bags, and connecting pieces are used to additionally fix the contact parts of the stacked body and the surrounding rock wall or supporting structure.

[0010] The concrete is pumped into the collapsed cavity through the pre-buried concrete delivery pipeline until it is filled to a third predetermined distance from the tunnel design profile line, forming a concrete filling body with a predetermined strength, and the specific method is: Before pumping, check the concrete delivery equipment and pre-buried pipeline, and pump cement mortar to lubricate the pipeline; Pump concrete into the collapsed cavity through the pipeline, and use a layered distribution method during pumping, with each layer having a filling thickness of no more than 500mm; Continue pumping until the top surface of the concrete filling body stops at a third predetermined distance from the tunnel design profile line, wherein the third predetermined distance is 1-2 meters; After stopping filling, clean the equipment and pipeline, and maintain the concrete filling body until its strength reaches 70%-80% of the design strength before proceeding to the next step.

[0011] Wherein, after the concrete filling body reaches the predetermined strength, it is used as a stable construction base to construct a double-layer self-advancing grouting small pipe at the tunnel face, and grouting is performed to form a reinforced arch around the face, and the specific method is: Accurately measure and mark the setting position of the double-layer small pipe on the tunnel face, the double-layer small pipe includes an upper layer and a lower layer, the outer insertion angles are 5°-12° for a gentle inclination and 10°-30° for a steep inclination, and the upper and lower layers are arranged in a staggered manner; Use a drilling machine to directly top the self-advancing grouting small pipe into the concrete filling body and the surrounding stratum along the marked position to the designed depth, the outer pipe diameter of the small pipe is 42mm, and the wall thickness is 4mm; Connect the grouting pipeline, inject early-strength single-liquid cement slurry into the small pipe through the ground pump, control the grouting pressure at 0.5-1.0MPa, stop grouting when the pressure reaches 1.0MPa and is stably maintained for more than 10 minutes, so that the slurry fully penetrates into the filling body and the surrounding rock-soil mass, thereby forming a continuous reinforced arch around the face.

[0012] In this process, under the advanced support of the reinforced arch, excavation is carried out in cycles. After excavating one support unit interval in each cycle, the steel arch frame, steel mesh, and shotcrete initial support for that section are immediately constructed. Monitoring and measurement are carried out throughout the construction process, and subsequent construction parameters are dynamically adjusted based on feedback data. The specific method is as follows: Before each excavation cycle, the excavation and support parameters for this cycle are confirmed based on the monitoring and measurement results of the previous cycle. Under the support of the reinforced arch, excavation work is carried out, and the excavation progress in each cycle is strictly controlled. The spacing between each support unit is 0.5 to 0.8 meters to reduce disturbance to the surrounding rock. After each excavation cycle is completed, steel arch frames are immediately installed and steel mesh is hung in the section, and shotcrete is sprayed to form a closed initial support structure. During the excavation and support process, monitoring points were set up, and total stations and levels were used to continuously monitor the displacement of the surrounding rock and the settlement of the arch. Based on the analysis of monitoring data, the construction parameters for subsequent cycles are dynamically adjusted; when the displacement or settlement rate exceeds the warning value, measures to strengthen support or adjust the excavation plan are immediately taken; the dynamically adjusted construction parameters include the length of the self-diving small guide pipe, the circumferential spacing, and the grouting pressure.

[0013] This invention discloses a construction method for tunnels in soft soil strata, employing a method of first filling the collapsed cavity and then providing support, aiming to create a stable foundation for subsequent support work. The concrete used to fill the collapsed cavity must be highly fluid and have high early strength. Under its own weight, the concrete can quickly and evenly fill all corners of the collapsed cavity, effectively avoiding the risk of secondary collapse caused by voids within the cavity. Before filling, the tunnel face is backfilled with counter-pressure. Once a certain height is reached, an excavator is used to clean the cavity, removing loose soil, rocks, and other debris to ensure close contact between the filling material and the cavity walls. Two meters from the arch crown, woven bags filled with soil are used to seal the cavity. Then, using specialized pumping equipment, the filling material is gradually pumped upwards from the bottom of the cavity. During filling, the filling height and material flow are monitored in real time to ensure compaction. When the filling reaches a certain distance from the design outline (determined based on actual conditions, generally 1-2 meters), filling operations are stopped, and the filling material is allowed to reach a certain strength (generally 70%-80% of the design strength) to provide a stable working surface for subsequent self-drilling double-layer small guide pipe construction. After the filling material in the collapsed cavity reaches the predetermined strength, self-advancing double-layer small catheter support operation is carried out. In the advancing process of the small catheter, a drilling device carried by the small catheter is used to directly drill in the filling body and the surrounding stratum. Then, the small catheter is grouted, the grout penetrates into the surrounding stratum and the filling body through the grouting hole, and a continuous reinforced arch with a certain thickness and strength is formed around the working face, which effectively prevents the further deformation and collapse of the surrounding soil and provides reliable support for the subsequent construction of the tunnel. At the same time, this self-advancing construction method avoids the problems of difficult drilling and complex pipe shed installation in the traditional large pipe shed construction, greatly improving the construction efficiency and safety. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows.

[0015] Figure 1 is a flow chart of the construction method of the tunnel soft stratum of the present application.

[0016] Figure 2 is a disposal design drawing of the collapsed cavity of the tunnel soft surrounding rock of the present application.

[0017] Figure 3 is an example drawing of the finally determined concrete mix proportion of the present application.

[0018] Figure 4 is a step flow chart of the construction method of the tunnel soft stratum of the present application. DETAILED DESCRIPTION

[0019] The embodiments of the present application will be described in detail below, examples of which are shown in the drawings. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0020] The first embodiment of the present application is: Please refer to Figures 1 to 4 , wherein, Figure 1 is a flow chart of the construction method of the tunnel soft stratum of the present application. Figure 2 is a disposal design drawing of the collapsed cavity of the tunnel soft surrounding rock of the present application. Figure 3 is an example drawing of the finally determined concrete mix proportion of the present application. Figure 4 is a step flow chart of the construction method of the tunnel soft stratum of the present application.

[0021] The construction method of the tunnel soft stratum of the present application comprises the following steps: S101: personnel, equipment and materials are prepared, and the collapsed cavity behind the working face is backfilled by counterpressure to form an initial counterpressure body; S102: Based on the initial counter-pressure body provided work platform, clean up the loose body in the collapsed cavity, and continue to refill to the first predetermined distance from the vault; Specifically, personnel preparation: 1. Form a professional team: assemble experienced tunnel construction personnel, including project managers, technical directors, construction team leaders, excavator drivers, concrete pouring workers, grouting personnel, etc. Ensure that personnel at each post have the appropriate qualifications and operating skills, are familiar with the construction characteristics of soft ground and safety standards. Organize full-time training before construction, explain the technical points of the collapsed cavity disposal plan, construction process and safety precautions, and clearly define the work responsibilities of each post. 2. Safety management personnel: Assign full-time safety management personnel to be responsible for safety supervision and management of the construction site. Safety management personnel need to have rich experience in tunnel construction safety management, be familiar with various safety regulations and standards, and be able to identify and eliminate safety hazards in a timely manner.

[0022] Equipment deployment: 1. Excavation equipment: deploy excavators with good performance to ensure that their bucket capacity, digging force and other parameters meet the operation requirements of cleaning up the loose body in the collapsed cavity. Before construction, conduct a comprehensive inspection and maintenance of the excavator, including the engine, hydraulic system, running gear and other key parts, to ensure stable operation of the equipment during construction. 2. Concrete conveying equipment: prepare a power-matched concrete pump for concrete backfilling operations in the collapsed cavity. The conveying capacity of the concrete pump should be selected according to the size of the collapsed cavity and the concrete pouring requirements to ensure continuous and stable delivery of concrete to the designated location. At the same time, a sufficient number of concrete delivery pipes should be prepared, which should have good wear resistance and sealing performance, and the connection parts should be firm and reliable. 3. Grouting equipment: purchase grouting pumps, mixers and other equipment required for self-feeding double-layer grouting small guide pipe construction. The pressure and flow rate of the grouting pump should meet the design requirements to meet the needs of grouting operations. The mixer should have good mixing performance to ensure uniform mixing of the slurry. Before construction, the grouting equipment is debugged to check the operation status and grouting effect of the equipment. 4. Monitoring equipment: equip high-precision surrounding rock monitoring equipment such as total station, level, multi-point displacement meter, etc. for monitoring surrounding rock deformation, displacement and other parameters throughout the construction process. The monitoring equipment needs to be calibrated and tested to ensure the accuracy and reliability of the monitoring data.

[0023] Material procurement: 1. Backfill material: sufficient anti-pressure backfill material such as stone, gravel soil, etc. is purchased, and the material texture is required to be hard and well-graded. Prepare the woven bag for soil filling, which should have enough strength and anti-aging performance to meet the requirements of stacking and plugging after filling. 2. Concrete materials: according to the design mix proportion of concrete, purchase cement, sand, gravel, and other raw materials. The quality of raw materials should meet the requirements of relevant standards and specifications, and be inspected and retested after entering the site to ensure that the performance of concrete meets the construction requirements. Contact the concrete mixing station in advance to ensure timely and sufficient supply of concrete during pouring. 3. Grouting material: purchase cement, water glass and other grouting materials for self-propelled double-layer grouting small pipe. The quality of grouting material should be strictly controlled to ensure that the setting time and strength of the slurry meet the design requirements. 4. Buffer sand material: prepare buffer sand that meets the design requirements for filling during excavation to buffer and stabilize the surrounding rock. The buffer sand should be uniform in texture and reasonable in particle size grading. Site layout: 1. Material storage site: a special material storage site is set up near the tunnel portal for the classification and storage of anti-pressure backfill materials, soil-filled woven bags, concrete raw materials, and grouting materials. The site should be hardened and equipped with drainage facilities to prevent materials from being drenched or washed by rain. The materials should be neatly and orderly stacked, and signs should be set up to indicate the material name, specification, origin, etc. 2. Equipment parking site: plan the equipment parking site for parking excavators, pumps, grouting equipment, and other construction machinery. The site should be flat and solid to facilitate the entry and parking of equipment. Set up equipment maintenance area and provide necessary maintenance tools and equipment for daily maintenance and fault repair of construction equipment. 3. Concrete pouring site: set up a concrete pouring site near the collapse cavity area, which should meet the requirements of pump parking and concrete delivery pipe arrangement. Clean and level the site to ensure that construction personnel can safely and conveniently perform concrete pouring operations. 4. Monitor point layout: according to the surrounding rock monitoring scheme, reasonably arrange the monitoring points around the tunnel and near the collapse cavity. The arrangement of monitoring points should be representative and accurately reflect the deformation and displacement of surrounding rock. Mark and protect the monitoring points to ensure they are not damaged during construction.

[0024] Counter-pressure backfill method: 1. Material selection: Counter-pressure backfill material should be selected from a mixture of stone and gravel soil. The stone should be hard and not weathered, with a particle size of 20-50 cm, accounting for about 40%-50%, to provide sufficient support. The gravel soil requires good gradation, with a particle size of less than 2 mm accounting for not less than 30%, to ensure the density and stability of the backfill material. By reasonably matching the stone and gravel soil, a solid and flowable backfill structure is formed, which can effectively resist the pressure of the surrounding soil of the collapse cavity. 2. Backfill operation process: Use a loader or a self-unloading truck to transport the counter-pressure backfill material to the collapse cavity site. Start from the bottom of the collapse cavity and gradually backfill from low to high. As the backfill height increases, closely monitor the deformation of the surrounding rock of the collapse cavity. If there are abnormalities, stop backfilling immediately and take appropriate reinforcement measures. When backfilling to about 2-3 m from the top of the collapse cavity, slow down the backfilling speed and use manual work with small mechanical equipment for fine backfilling to ensure that the backfill material closely adheres to the collapse cavity wall. 3. Backfill height control: The backfilling height needs to be cleaned after a certain height, which is determined according to the size of the collapse cavity and the actual situation on site. Through phased backfilling and cleaning, the collapse cavity bottom and surrounding soil can be effectively stabilized, and the subsequent cleaning work of the loose body in the collapse cavity is facilitated. Finally, backfill to about 1 m from the vault to create conditions for subsequent soil bag stacking and concrete backfilling.

[0025] Cleaning the collapse cavity method: 1. Equipment selection: Choose a excavator with a bucket capacity of 1-1.5 m³, whose digging force should not be less than 150 kN to ensure that it can effectively break and clean the loose rock-soil body in the collapse cavity. The excavator is equipped with high-strength bucket teeth to enhance the digging capacity. At the same time, to facilitate operation in a narrow collapse cavity, the size of the excavator body should be compatible with the space of the collapse cavity, with good mobility. 2. Cleaning operation process: After the counter-pressure backfill reaches the predetermined height and stabilizes, start the excavator to enter the collapse cavity for cleaning. The excavator starts from the bottom of the collapse cavity and gradually cleans the loose body from the outside to the inside. When operating, the excavator should be kept stable to avoid disturbing the collapse cavity wall. For larger rock-soil bodies, the breaking hammer of the excavator can be used for breaking before cleaning. The loose body cleaned out is transported to the designated location in time by a loader or a self-unloading truck to avoid accumulation near the collapse cavity. During the cleaning process, a person is assigned to observe the collapse cavity wall, and if any abnormalities such as falling blocks or crack expansion are found, the excavator driver is immediately notified to stop work and leave the site. 3. Cleaning quality control: After cleaning, the bottom of the collapse cavity should be basically flat, with no obvious large loose body residues. The loose rock-soil body attached to the collapse cavity wall should also be cleaned as much as possible to ensure the smooth progress of subsequent counter-pressure backfilling and other operations. Measure the cleaned collapse cavity to record the size change of the collapse cavity, providing data basis for subsequent construction.

[0026] S103: At the top of the secondary pressure body, the woven bags filled with earth are stacked alternately until the second predetermined distance from the vault top, to build a woven bag formwork system that matches the profile of the collapsed cavity, and to pre-bury and fix the concrete delivery pipeline simultaneously during the stacking process; Specifically, the woven bag stacking: 1. Earth filling: adopt the way of loader cooperating with manual bagging. The loader shovels the earth to the bagging area, and the manual fills the earth into the woven bag with a shovel. When bagging, control the amount of earth filling, so that the weight of each woven bag after filling the earth is 40-50 kg, and the filling height reaches about 3 / 4 of the height of the woven bag, which is convenient for carrying and can ensure the stability after stacking. During the bagging process, the earth in the bag is lightly tamped with a shovel or a small tamping tool to reduce the scattering of the earth during transportation and stacking, and to ensure the compaction of the earth in the woven bag. 2. Sealing treatment: after the woven bag is filled with earth, nylon rope or plastic rope can be used to seal the bag. After winding the rope around the bag opening for 2-3 turns, it is tightened and tied into a dead knot to ensure the tightness of the seal. A sealing machine can also be used for heat sealing. The heat sealing width is generally 2-3 cm. The sealed bag after heat sealing should be flat, without cracks and openings, to prevent the earth from leaking.

[0027] Stacking method: Use the staggered stacking method, starting with the profile line at the bottom of the collapsed cavity. The first layer of woven bags is placed tightly and neatly along the profile line, with no gaps between the bags. The second layer of woven bags is placed perpendicular to the first layer and staggered, so that the upper and lower layers of woven bags interlock, enhancing the stability of the stacked structure. Follow this method to stack layer by layer upwards until the designed height is reached. As the stacking height increases, for higher stacked layers, set up a simple scaffold or operating platform to facilitate the operation of construction personnel, while using measuring instruments to monitor the verticality and positional deviation of the stack in real time. Measure every 3-5 layers of stack, and adjust in time if deviation is found. When stacking to about 1 meter from the vault, slow down the stacking speed, carefully adjust the position and height of the woven bags, and ensure that the top of the stack has a suitable space reserved for the subsequent concrete backfilling and other construction operations. In the last few layers at the top of the stack, smaller size woven bags or appropriately cut woven bags can be used to better fit the shape of the vault, ensuring the sealing effect. The shape of the stack should be as consistent as possible with the profile of the collapsed cavity. For irregular collapsed cavities, arrange and adjust the woven bags reasonably to ensure the sealing and stability of the stacked structure. To enhance the overall stability of the woven bag stacking structure, fix and connect adjacent woven bags during the stacking process. Use nylon ropes or iron wires to connect the corners or edges of adjacent woven bags, with evenly distributed binding points. Each woven bag should be connected to at least two adjacent woven bags to ensure firm connection and prevent displacement of the woven bags during transportation and stacking. At the contact points between the stacked body and the surrounding rock wall or support structure, use expansion bolts, anchor rods, and other connectors to fix the woven bag stack to the surrounding structure. First drill holes in the rock wall or support structure, install expansion bolts or anchor rods, and then connect the woven bag stack to the connectors using steel wire ropes or iron chains to ensure that the woven bag stack is tightly connected to the surrounding structure, jointly bearing external loads and improving the anti-collapse ability of the stacked structure.

[0028] Reserved pipeline: The concrete delivery pipeline uses high-strength and wear-resistant steel pipes. The pipe diameter is determined according to the concrete delivery capacity and the size of the collapsed cavity, generally 100-150 mm, with a pipe wall thickness not less than 5 mm to ensure that the pipeline does not break or deform during concrete delivery. The pipeline should have good sealing performance, and sealing rubber rings should be used between pipe joints to prevent concrete leakage. Prepare the necessary pipe fittings such as elbows and tees, which should match the specifications and models of the pipeline, and the quantity should be determined according to the shape of the collapsed cavity and the concrete delivery path to ensure that the pipeline can be smoothly laid to each part of the collapsed cavity. Before installation, thoroughly inspect each pipeline and fitting for cracks, holes, depressions, and other defects, and check the connection parts of the fittings for completeness. Repair or replace defective pipelines and fittings to ensure pipeline quality.

[0029] The inside of the pipeline is cleaned by high-pressure water gun or compressed air to remove rust, sundries and the like in the pipeline to ensure the inside of the pipeline clean and unobstructed and avoid affecting the concrete conveying. The installation of the reserved pipeline is simultaneously performed in the process of the woven bag stacking. When the woven bags are stacked to a certain height and the height position is suitable for the pipeline installation, the stacking operation is stopped and the pipeline installation is performed. Generally, when the stacking height reaches 2-3 layers of woven bags from the final stacking height, the pipeline installation is started so that the remaining woven bags can be continuously stacked after the pipeline installation is completed to fix and protect the pipeline. According to the shape of the collapsed cavity and the requirement of the concrete backfilling, the installation position of the pipeline is determined. The pipeline should be as close as possible to the central part of the collapsed cavity and be uniformly distributed to ensure that the concrete can uniformly fill each corner of the collapsed cavity. Before the pipeline installation, the installation position of the pipeline is marked on the woven bag stacking body by using a measuring instrument to ensure that the pipeline installation position is accurate. The prepared pipeline is laid on the woven bag stacking body according to the marked position, and the pipeline laying should be kept straight to avoid bending or twisting. The sealing rubber ring is used to connect the pipe sections, the rubber ring is correctly installed at the pipe section interface during the connection, and then a special tool is used to tightly connect the pipe sections to ensure that the interface is well sealed. During the pipeline laying, the pipeline is fixed. A fixing point is set every certain distance (generally 2-3 meters) on the woven bag stacking body, and the pipeline is fixed with the woven bag by using iron wire or rope to prevent the pipeline from moving or shaking during the concrete conveying. For the elbow and tee parts of the pipeline, the fixing points should be increased to ensure that the pipe connection is firm. After the pipeline installation is completed, the remaining woven bags are continuously stacked to wrap the pipeline inside the woven bag stacking body to protect the pipeline. During the wrapping process, attention should be paid to not damaging the pipeline and pipe fittings to ensure that the woven bags around the pipeline are densely stacked to further fix the position of the pipeline. At the same time, a clear signboard is arranged at the inlet and outlet positions of the pipeline to mark the purpose of the pipeline and the matters needing attention to prevent misoperation. After the pipeline installation is completed and wrapped by the woven bags, the pipeline is checked again. Whether the pipeline is fixed firmly, the interface is well sealed, the pipeline is deformed or damaged and the like are checked. The pipeline is checked for the smoothness by injecting water or air into the pipeline. If there is a blockage or leakage problem, it is treated in time. During the concrete conveying, a special person is arranged to patrol the pipeline. Whether the pipeline has the abnormal conditions such as slurry leakage and deformation is observed, and whether there is a blockage phenomenon is judged by listening to the sound of the concrete flowing in the pipeline. If a problem is found, the concrete conveying is immediately stopped, and appropriate measures are taken for repair, such as plugging the slurry leakage position and dredging the blocked pipeline to ensure that the concrete conveying is smoothly performed. The slurry uses M20 grade mortar, and the corresponding mixing ratio is designed and mixed by the laboratory.

[0030] S104: Pumping concrete into the collapsed cavity through the pre-buried concrete conveying pipeline until filling to a third predetermined distance from the tunnel design contour line to form a concrete filling body with a predetermined strength; S105: After the concrete filling body reaches the predetermined strength, it is used as a stable construction surface to construct a double-layer self-advancing grouting small pipe at the tunnel face and to conduct grouting to form a reinforced arch around the tunnel face; Specifically, the concrete pumping filling collapsed cavity: 1. Design principles: according to the characteristics of the tunnel collapsed cavity and the construction requirements, the concrete mix design should meet the following principles: good workability, easy to pump and pour; sufficient strength to meet design requirements; certain impermeability and durability to adapt to the tunnel environment. 2. Mix ratio calculation: according to the performance of cement, aggregate, admixture and admixture, according to the provisions of "Ordinary concrete mix design regulations" (JGJ55), calculate the preliminary mix ratio. When determining the amount of cement, consider the strength grade and durability requirements of the concrete, and adjust it in combination with the amount of admixture. Calculate the amount of coarse and fine aggregate, use volume method or mass method to calculate, so that the aggregate gradation is good, and the workability requirements of the concrete are met. Determine the dosage of admixture, determine the best dosage of water reducing agent, expansive agent and other admixtures through test to improve the performance of concrete. Trial and adjustment: according to the preliminary mix ratio, test and adjust, make concrete test piece, test its slump, spread, setting time, compressive strength and other performance indicators. According to the test results, adjust the mix ratio until the performance indicators of the concrete meet the construction requirements. The final concrete mix ratio is as follows Figure 3 (Example).

[0031] Pumping construction: check whether the parts of the concrete pump are intact, whether the lubricating oil is sufficient, and whether the water tank is full of water. Start the delivery pump and run it empty to check whether the pumping system, hydraulic system, electrical system, etc. are working properly. Lubricate the delivery pipeline with cement mortar, the mix proportion of which is the same as that of the mortar in the concrete, generally cement: sand = 12, water-cement ratio 0.4-0.5. After pumping an appropriate amount of cement mortar, start pumping concrete. After the concrete mixing truck arrives at the construction site, it should be rotated at high speed for 2-3 minutes to make the concrete uniform before unloading. When unloading, the slump and workability of the concrete should be observed. If the concrete is found to have segregation, bleeding, etc., it should be re-mixed or returned to the mixing plant for processing. When pumping starts, the pumping speed should be slow at first and then fast, gradually accelerating. At the same time, the pressure of the concrete pump and the working condition of each part should be observed. If abnormalities are found, pumping should be stopped immediately, and the cause should be found and the fault should be eliminated before continuing pumping. During the pumping process, the continuity of pumping should be maintained, and interruptions should be avoided as much as possible. If pumping needs to be interrupted due to special reasons, the interruption time should not exceed 30 minutes. When it exceeds 30 minutes, pumping should be carried out every 5-10 minutes, and the pumping amount should not exceed 500mm stroke to prevent the concrete from setting in the pipeline. During the pumping process, the connection parts of the delivery pipeline should be checked for good sealing and leakage. If leakage is found, it should be treated in time. At the same time, attention should be paid to the observation of the pumping pressure of the concrete. When the pumping pressure exceeds the rated pressure of the pump, pumping should be stopped, and appropriate measures should be taken to reduce the pumping pressure, such as checking whether the pipeline is blocked, whether the concrete slump is appropriate, etc. The concrete is evenly distributed to the collapsed cavity using the distribution equipment, and the distribution should be carried out in layers, with each layer not exceeding 500mm in thickness. During the pouring process, the concrete should not directly impact the woven bag stacking body and the reserved pipeline. When the concrete pouring is completed, pumping should be stopped in time. The concrete in the delivery pipeline should be emptied first, and then the delivery pump and delivery pipeline should be washed with clean water until the water flowing out of the pipeline is clear. During the cleaning process, attention should be paid to prevent water from flowing into other parts of the tunnel to avoid causing water accumulation. The concrete pump and other equipment should be checked and maintained comprehensively, the concrete residue on the surface of the equipment should be cleaned up, and the worn-out parts should be replaced to prepare for the next pumping construction.

[0032] The construction of the advancing double-layer small pipe: 1. Measurement and positioning: according to the design requirements, the position of the small pipe is accurately measured and marked on the tunnel face. The measurement and positioning should be accurate to ensure that the installation angle and spacing of the small pipe meet the design standards. The outer insertion angle of the double-layer small pipe is 5°~12° for the gentle slope and 10°~30° for the steep slope. The upper and lower layers are staggered and the spacing is usually 20-40 cm. 2. Drilling and small pipe installation: use special drilling equipment to drill according to the marked position. The drilling diameter is slightly larger than the outer diameter of the small pipe to ensure that the small pipe can be inserted smoothly. After drilling, the self-advancing grouting small pipe is directly inserted into the hole through the drilling machine. During the insertion process, the insertion speed and direction should be controlled to ensure that the small pipe reaches the design requirements. The length of the small pipe is usually 3-5 meters. 3. Grouting operation: after the installation of the small pipe, connect the grouting pipeline and use the ground pump for grouting. The early strength single liquid cement slurry is used for small pipe grouting. The initial parameters are: water-cement ratio w / c = 0.6~0.8, grouting cement is ordinary portland cement, and the strength grade is 42.5. During construction, the reasonable grouting parameters should be determined according to the site test. The grouting should be carried out according to the principle of first down and then up, and first dilute and then concentrate. The grouting pressure is mainly controlled by pressure, and the grouting amount is controlled by auxiliary. The grouting pressure is 0.5~1.0MPa. When the grouting pressure of each hole reaches 1.0MPa, continue to maintain for more than 10 minutes before stopping grouting to ensure that the surrounding rock of the small pipe is fully reinforced.

[0033] S106: Under the advance support of the reinforced arch, the split-cycle excavation is carried out. After each cycle of excavation and support unit spacing, the steel arch, steel mesh and sprayed concrete primary support of this section are immediately constructed, and monitoring and measurement are carried out during the whole construction process. According to the feedback data, the subsequent construction parameters are dynamically adjusted.

[0034] Specifically, the cycle construction process is as follows: 1. Summary and preparation of the previous cycle construction: Before starting a new cycle, the construction of the previous cycle is summarized comprehensively. The effect of advanced small pipe grouting is checked, and the stratum reinforcement is checked through geological radar, drilling core taking and other means to see if there are unfilled gaps or weak areas. The stability of the surrounding rock during excavation is evaluated, and abnormal phenomena such as collapse and deformation are recorded. Based on the summary results, the construction parameters of the next cycle are adjusted, such as the length, spacing and grouting pressure of the small pipe. At the same time, the materials needed for construction are prepared to ensure that the self-propelled double-layer advanced small pipe, cement, additive and other materials are sufficient in quantity and qualified in quality, and the construction equipment is checked to ensure that the drilling machine, grouting pump and other equipment are in good working condition. 2. Excavation and initial support: When the small pipe grouting strength reaches about 70% of the design requirement, the tunnel excavation operation begins. A small excavator is used in combination with manual pneumatic picks, and local loose blasting is used to avoid causing excessive disturbance to the surrounding rock. After every interval of one steel arch (usually 0.5-0.8 meters), initial support is immediately provided. The steel arch is installed to fit the tunnel contour and is fixed with lock foot anchor rods, then steel mesh is hung and concrete is sprayed, with a thickness of 15-25 cm to enhance the stability of the surrounding rock. 3. Monitoring and feedback: During the entire cycle construction process, monitoring and measurement work is continuously carried out. By arranging measuring points around the tunnel, using total station, level and other instruments to monitor surrounding rock displacement, vault subsidence and other data, and using pressure boxes to monitor surrounding rock pressure. According to the measurement data, the stability of the surrounding rock is analyzed in a timely manner, and once abnormal data such as excessive displacement rate and excessive vault subsidence are found, construction is immediately suspended, appropriate reinforcement measures such as increasing temporary support and supplementary grouting are taken, and the construction parameters of the next cycle are adjusted according to the feedback results.

[0035] Key points of cycle construction: 1. Close connection between construction links: The construction links should be closely connected to reduce the time interval and prevent the surrounding rock from being exposed for a long time, which may lead to instability. For example, after the small pipe grouting is completed, excavation work should be arranged as soon as possible to avoid the influence of long solidification time of the grout on subsequent construction. 2. Dynamic adjustment of parameters: Based on the construction situation and monitoring and measurement data of each cycle, the construction parameters are dynamically adjusted. For example, in areas with poor surrounding rock conditions, the small pipe spacing can be appropriately reduced, the small pipe length can be increased, and the grouting pressure can be increased; in relatively stable surrounding rock areas, the relevant parameter requirements can be appropriately relaxed. 3. Quality control throughout the process: The construction quality of each cycle is strictly controlled, from material quality inspection to construction quality inspection of each process, which must meet the design and specification requirements. For example, the installation angle of the small pipe, the grouting fullness, the strength of the sprayed concrete of the initial support, etc. are carefully checked and accepted.

[0036] Under the condition of tunnel soft surrounding rock 10m long collapse cavity treatment, the construction method of the application reduces the construction period by 19.17% compared with the commonly used advanced pipe shed support construction method, and the cost investment is reduced by 194897.94 yuan, and the specific comparison is as follows.

[0037] Table 1 Comparison of construction period of different schemes

[0038] Table 2 Comparison of cost

[0039] In summary, the construction method of the application saves 194897.94 yuan compared with the construction method of the support hole first expansion method. At the same time, the work efficiency is improved, the amount of additional advanced support materials is reduced, and the direct cost is reduced. At the same time, the method has no additional waste materials, and has significant economic benefits.

[0040] The construction method of the application improves the idea of whole support of large pipe shed to the collapse cavity to the idea of sectional support of double-layer small pilot pipe with tunnel excavation. The double-layer small pilot pipe is constructed with tunnel excavation, which eliminates the time for leveling pipe shed operation guide wall and expanding hole for pipe shed operation, and greatly improves the construction efficiency. The first filled concrete drill hole can be used as a hard hole for advanced support, which eliminates the difficulty of rod filling due to loose rock layer collapse in the traditional construction method, and speeds up the processing speed.

[0041] The construction method of the application changes the traditional advanced pipe shed support method to self-advancing double-layer self-advancing small pilot pipe. The self-advancing small pilot pipe construction does not need to pull the drill rod, avoids the construction problem of difficult pipe filling due to hole collapse in the later stage, and at the same time, the single drilling length of the support is short, the operability is stronger, the drilling angle is easier to control, and the construction efficiency and support quality are improved.

[0042] The construction method of the application reduces the exposure of personnel to the collapse cavity during the construction of the conventional collapse cavity treatment first advanced pipe shed, reduces the risk of secondary collapse injury to the workers, and adjusts the construction steps of "first advanced support and then filling concrete" to "first filling concrete and then advanced support". The workers only need to stack sand bags on the counter-pressure body and connect the pump pipe, which greatly improves the safety in the construction process and effectively reduces the construction safety risk.

[0043] The construction method of the application improves the concrete filling formwork system after counter-pressure to the end formwork of the earth-filled sand bag as the concrete buffer layer. The sand bag filling uses local materials, directly uses tunnel spoil, and the sand bag end formwork does not need to purchase additional formwork and supporting fixed components, solves the problem of waste of shaped end formwork materials after the collapse cavity treatment is completed, reduces the scheduling and investment of measure materials, and reduces the construction cost.

[0044] The above disclosure only shows one or more preferred embodiments of the present application, and cannot limit the scope of the present application. Those skilled in the art can understand that the implementation of all or part of the above processes, and the equivalent changes made according to the claims of the present application, still belong to the scope covered by the present application.

Claims

1. A method of construction of a tunnel in a soft ground, characterized in that, The method comprises the following steps: Preparation of personnel, equipment and materials, and backfilling of the collapsed cavity behind the tunnel face by counter-pressure to form an initial counter-pressure body; Based on the working platform provided by the initial counter-pressure body, loose bodies in the collapsed cavity are cleaned, and backfilling is continued to a first predetermined distance from the vault; At the top of the secondary counter-pressure body, woven bags filled with earth are used for staggered stacking until a second predetermined distance from the vault, to build a woven bag formwork system that matches the profile of the collapsed cavity, and to pre-bury and fix the concrete delivery pipeline during the stacking process; Through the pre-buried concrete delivery pipeline, concrete is pumped into the collapsed cavity until it is filled to a third predetermined distance from the tunnel design contour line, forming a concrete filling body with a predetermined strength; After the concrete filling body reaches the predetermined strength, it is used as a stable construction base to construct a double-layer self-advancing grouting small pipe at the tunnel face, and grouting is carried out to form a reinforced arch around the tunnel face; Under the advanced support of the reinforced arch, the tunnel is excavated in cycles, and after each cycle of excavation, the steel arch, steel mesh and sprayed concrete primary support for that section are immediately constructed, and monitoring and measurement are carried out throughout the construction process, and the subsequent construction parameters are dynamically adjusted according to the feedback data.

2. The method of constructing a tunnel in a soft ground formation as claimed in claim 1, wherein, Preparation of personnel, equipment and materials, and backfilling of the collapsed cavity behind the tunnel face by counter-pressure to form an initial counter-pressure body, and: The counter-pressure backfilling material is transported to the collapsed cavity site by a loader or a self-unloading truck, wherein the counter-pressure backfilling uses a mixture of stone chips and gravel soil, wherein the stone chip particle size is 20-50 cm, and the proportion is 40%-50%; Starting from the bottom of the collapsed cavity, backfilling is gradually carried out from low to high, and the deformation of the surrounding rock around the collapsed cavity is observed, and if there is an abnormality, backfilling is immediately stopped and appropriate reinforcement measures are taken; When backfilling to 2-3 m from the top of the collapsed cavity, the backfilling speed is slowed down, and manual work with small mechanical equipment is used for fine backfilling.

3. The method of constructing a tunnel in a soft ground formation as claimed in claim 2, wherein, Based on the working platform provided by the initial counter-pressure body, loose bodies in the collapsed cavity are cleaned, and backfilling is continued to a first predetermined distance from the vault, and: Using the stable working surface provided by the initial counter-pressure body, the excavator is controlled to enter the collapsed cavity; The excavator is used to gradually clean the loose rock-soil bodies on the wall and bottom of the collapsed cavity from the outside to the inside, and the cleaned loose bodies are transported out; After cleaning is completed, backfilling is continued using counter-pressure backfilling material until the top surface of the filling body is at a first predetermined distance from the vault, wherein the first predetermined distance is 2 meters.

4. The method of constructing a tunnel in a soft ground formation as defined in claim 3, wherein At the top of the secondary counter-pressure body, woven bags filled with earth are used for staggered stacking until a second predetermined distance from the vault, to build a woven bag formwork system that matches the profile of the collapsed cavity, and to pre-bury and fix the concrete delivery pipeline during the stacking process, and the specific method is: Tunnel spoil is used as earth material, each woven bag is filled to 3 / 4 of its height, and the weight of the filled bag is controlled at 40-50 kg, and then the bag opening is firmly sealed; The profile line starts from the bottom of the collapsed cavity, and the staggered stacking method is used to stack from bottom to top, so that the upper and lower layers of woven bags are engaged with each other, and the verticality and shape of the stacked body are monitored and adjusted in real time during the stacking process, so that it closely fits the collapsed cavity profile, until it is stacked to a second predetermined distance from the vault, wherein the second predetermined distance is 1 meter; When stacked to the predetermined height, pause the stacking, lay the concrete delivery pipeline on the stacked body according to the preset path, and use wire or rope to bind and fix the pipeline and the woven bag, then continue to stack upwards to wrap the pipeline inside the woven bag stacked body; During the stacking process or after the stacking is completed, the adjacent woven bags are connected by nylon ropes or iron wires, and the contact parts between the stacked body and the surrounding rock wall or supporting structure are additionally fixed by connecting pieces.

5. The method of constructing a tunnel in a soft ground formation as defined in claim 4, wherein, Through the pre-embedded concrete delivery pipeline, pump concrete into the collapsed cavity until it is filled to a third predetermined distance from the tunnel design profile line, forming a concrete filling body with a predetermined strength, the specific method being: Before pumping, check the concrete delivery equipment and pre-embedded pipeline, and pump cement mortar to lubricate the pipeline; Pump concrete into the collapsed cavity through the pipeline, and use a layered distribution method during pumping, with each layer having a filling thickness of no more than 500mm; Continue pumping until the top surface of the concrete filling body stops at a third predetermined distance from the tunnel design profile line, wherein the third predetermined distance is 1-2 meters; After stopping filling, clean the equipment and pipeline, and maintain the concrete filling body until its strength reaches 70-80% of the design strength before proceeding to the next step.

6. The method of constructing a tunnel in a soft ground formation as defined in claim 5, wherein, After the concrete filling body reaches the predetermined strength, use it as a stable construction base to construct a double-layer self-advancing grouting small pipe at the tunnel face, and perform grouting to form a reinforced arch around the face, the specific method being: Accurately measure and mark the setting position of the double-layer small pipe on the tunnel face, the double-layer small pipe includes an upper layer and a lower layer, with outer insertion angles of 5°-12° for the gentle slope and 10°-30° for the steep slope, and the upper and lower layers are arranged in a staggered manner; Use a drilling machine to directly drive the self-advancing grouting small pipe into the concrete filling body and the surrounding strata along the marked position to the designed depth, with an outer pipe diameter of 42mm and a wall thickness of 4mm; Connect the grouting pipeline and inject early-strength single-liquid cement slurry into the small pipe through the ground pump, with a grouting pressure controlled at 0.5-1.0MPa, stop grouting when the pressure reaches 1.0MPa and stabilizes for more than 10 minutes, allowing the slurry to fully penetrate into the filling body and the surrounding rock-soil mass, thereby forming a continuous reinforced arch around the face.

7. The method of constructing a tunnel in a soft ground formation as defined in claim 6, wherein, Under the advanced support of the reinforced arch, perform split-cycle excavation, immediately after each cycle of excavation with a support unit interval, construct the steel arch, steel mesh, and sprayed concrete primary support for that section, and perform monitoring and measurement throughout the construction process to dynamically adjust subsequent construction parameters based on feedback data, the specific method being: Before each cycle of excavation, confirm the excavation and support parameters for this cycle based on the monitoring and measurement results of the previous cycle; Under the support of the reinforced arch, the excavation operation is carried out, and the single excavation footage is strictly controlled. The support unit interval is 0.5-0.8 meters per cycle of excavation, so as to reduce the disturbance to the surrounding rock; After each cycle of excavation is completed, the steel arch is installed, the steel mesh is hung, and the concrete is sprayed in the segment, so as to form a closed primary support structure; In the process of excavation and support, the displacement of the surrounding rock and the subsidence data of the arch top are continuously monitored by using a total station and a level through the monitoring points; According to the analysis result of the monitoring data, the construction parameters of the subsequent cycle are dynamically adjusted. When the displacement or the subsidence rate exceeds the early warning value, the measures of strengthening the support or adjusting the excavation scheme are immediately taken. The dynamically adjusted construction parameters include the length of the self-advancing small guide pipe, the ring interval, and the grouting pressure.

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