Construction method for water-rich tunnel to pass through large dissolving cavity

Abstract

The invention relates to the technical field of tunnel construction, in particular to a construction method for a water-rich tunnel to penetrate through a large dissolving cavity, the process method is suitable for the water-rich tunnel with large dissolving cavities and cracks and with water in the dissolving cavity cracks or other underground engineering, and through the supporting and reinforcing effects of foot-lock steel pipes and grouting and the reinforcing and anchoring effects of inverted arch vertical anchor pipes, the large dissolving cavity and cracks can penetrate through the water-rich tunnel. The tunnel main body structure and the surrounding rock are connected into a whole, uneven settlement generated after construction and inverted arch upheaval caused by the hull effect generated by the tunnel in the water-rich solution cavity during grouting reinforcement can be effectively avoided, and the safety of the tunnel main body structure is improved. Meanwhile, by the adoption of the construction method, the use amount of grouting materials can be saved, the project treatment time is saved, the construction cost is reduced, the work efficiency is improved, the construction progress is accelerated, and the great application and popularization value is achieved.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a method for constructing a water-rich tunnel through a large karst cavity. Background Technology

[0002] Groundwater is a common hazard in karst tunnel construction. In highway construction in karst mountainous areas, tunnels frequently pass through large cavities and fissures. During construction, unfavorable geological conditions such as fractured invert bases and mud-filled areas are common, and conventional replacement methods are often ineffective. When tunnels pass through large karst fissure zones, uneven settlement can easily occur, posing safety risks to the main structure. Furthermore, during grouting reinforcement, tunnels in water-rich karst fissure zones are highly susceptible to the "ship effect," leading to invert heave.

[0003] Therefore, this invention provides a method for constructing water-rich tunnels through large karst cavities, aiming to solve the above-mentioned problems and, while ensuring project quality, construction progress and construction safety, achieve the goals of saving grouting material usage, saving treatment time, reducing costs and improving work efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing water-rich tunnels through large karst cavities.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The construction method for water-rich tunnels traversing large karst cavities according to the present invention includes the following steps: Step 1: After investigating the development of karst and fissures, tunnel excavation and initial support construction are carried out according to the design drawings; Step 2: Install locking steel pipes within a 5m range before and after the large karst cavity, drill Φ91 holes at the arch foot and clean the holes, fill in the drilling record, make and install steel pipe locking feet in the holes, connect the locking steel pipes to the initial support steel, inject grout into the locking steel pipes to block water, seal the holes after grouting, and conduct quality inspection. Step 3: Carry out the lower excavation according to the design drawings; Step 4: When constructing the invert arch in this section, replace the foundation with rubble and stone chips according to the foundation conditions, and then construct the invert arch. Step 5: Install vertical steel anchor pipes on the invert arch within a 5m range before and after the large karst cavity. Drill Φ91 holes at the arch foot and clean the holes. Fill in the drilling record, fabricate and install the steel anchor pipes in the holes, inject grout into the steel anchor pipes to block water, seal the holes after grouting, and conduct quality inspection.

[0006] Preferably, in the construction method for a water-rich tunnel traversing a large karst cavity described in this invention, in step two: the spacing of the locking steel pipes is determined according to the spacing of the initial support steel of the main tunnel, with one set of locking steel pipes for each steel section; the drilling angle for drilling Φ91 holes alternates between 30 degrees and 60 degrees downwards, and the drilling depth is: if the length of the karst cavity is less than or equal to 6m, the hole depth is not less than 2m into the rock; if the length of the karst cavity is greater than 6m, the hole depth is 10-15m.

[0007] Preferably, in the construction method for water-rich tunnels crossing large karst cavities described in this invention, the depth of the replacement filling in step four is 3-4m.

[0008] Preferably, in the construction method for a water-rich tunnel traversing a large karst cavity described in this invention, in step five: the spacing of the steel anchor pipes is 1.5×1.5m, arranged in a quincunx pattern; the drilling direction of the Φ91 holes is vertically downward, and the drilling depth is: if the length of the karst cavity is less than or equal to 6m, the hole depth is not less than 2m into the rock; if the length of the karst cavity is greater than 6m, the hole depth is 10-15m.

[0009] In a further preferred embodiment, the technical requirements for drilling Φ91 holes in step two or five of the water-rich tunnel construction method for traversing large karst cavities described in this invention are as follows: drilling equipment equipped with diamond drill bits is used for drilling; the entire locking steel pipe or steel anchor pipe and the borehole pipe are combined into one, and a borehole sealing device is installed at the pipe end; the drilling method is either a forward grouting method or a one-time hole formation and one-time grouting method; the drilling speed is 2-3 m / h.

[0010] Preferably, in the construction method for water-rich tunnels crossing large karst cavities described in this invention, in step two or step five: The technical requirements for cleaning the hole are as follows: flush the hole with pressurized water until it is clean. If silt cannot be flushed out, flush for at least 30 minutes until the return water is not turbid. The drilling records include: borehole number; borehole location and station number; drilling angle; borehole elevation; opening and closing times; backflow of cuttings, water or air during segmented drilling and the determination of rock properties based on cuttings; borehole diameter changes; drilling rig malfunctions; borehole accidents; and final borehole depth, diameter, and inclination.

[0011] Preferably, in the construction method of water-rich tunnel crossing large karst cavity described in this invention, the locking steel pipe in step two and the steel anchor pipe in step five have the same shape, specifications, and material. Both are made of Φ76 seamless steel pipe. The length of the pipe is determined on-site according to the drilling depth. A hole sealer is installed at the outer end of the pipe. The pipe head is sharpened. At a distance of more than 3m from the outer end of the pipe, overflow holes with a diameter of 1cm are drilled in four directions: up, down, left, and right. The overflow holes are symmetrical up and down and symmetrical left and right, with a spacing of 1m along the length of the pipe. Both the locking steel pipe and the steel anchor pipe are fitted with three Φ20 threaded steel bars bundled together.

[0012] Preferably, in the construction method for water-rich tunnels crossing large karst cavities described in this invention, the grouting and water plugging in step two or five follows a step-by-step continuous process, proceeding from key areas to general areas, from the sides to the middle, from thin to thick grout, from low pressure and small pump volume to gradually increase, and drilling one hole and grouting one hole at a time. The grouting technical requirements are as follows: 1) After drilling to the water-bearing hole section, the "hole-mouth sealing pure pressure full-hole section one-time grouting process method" is adopted; 2) The water-cement ratio of the grout used in the formal grouting process is 0.5:1; 3) The design pressure for water plugging grouting is 1.0-2.0 MPa, and the total pressure is the sum of the inrush pressure and the design pressure; 4) If the grouting pressure and injection rate do not change when the grouting of a single hole exceeds 10t, accelerator material should be added and grouting should continue. 5) When the grouting material is added to a single hole of 20t, if the grouting pressure and injection rate do not change, the grouting injection rate should be controlled within 30L / min and grouting should continue until the end.

[0013] Preferably, in the construction method for water-rich tunnels crossing large karst cavities described in this invention, the completion standard for grouting and water plugging in step two or five is: grouting can be completed when no grout is absorbed under the specified maximum design pressure; after grouting and water plugging, the grout should be held for 1-2 hours and allowed to set for 24-48 hours.

[0014] Preferably, in the construction method for water-rich tunnels crossing large karst cavities described in this invention, the qualification standard for the quality inspection in step two or step five is: no water gushing out when the grouting gate valve is opened after the grouting time is over, or no obvious cracks and water storage are detected in the grouting area by ground-penetrating radar.

[0015] The beneficial effects of this invention are: 1. This invention provides a construction method for water-rich tunnels passing through large karst cavities. This method is applicable to water-rich tunnels or other underground projects with large karst cavities and fissures containing water. The construction method provided by this invention can effectively avoid uneven settlement after construction and the occurrence of inverted arch heave in the water-rich karst cavity during grouting reinforcement, thereby increasing the safety of the main tunnel structure. This is of great significance for ensuring project quality and construction safety.

[0016] 2. By adopting the construction method provided by this invention, the water seepage in the tunnel passes through the karst cavity, and the water plugging work is postponed. This can ensure the construction progress, save the amount of grouting materials, save the engineering treatment time, reduce the construction cost, and improve the efficiency. It has significant advantages for the normal construction of the tunnel, and at the same time, it can accelerate the construction progress and ensure that the tunnel and the highway are completed and opened to traffic on schedule, which has significant social benefits.

[0017] 3. By employing the construction method of this invention, grouting reinforcement is performed post-construction, saving construction time. When encountering large cavities, the method of first traversing and then treating them can save at least 15 days of construction time. Based on the fixed cost of approximately 600,000 yuan per month for a single tunnel on a two-lane highway, each crossing of a large cavity can save 300,000 yuan. Simultaneously, because this invention uses post-grouting reinforcement, it can save grouting material within the tunnel outline (calculated at a fissure ratio of 0.2, saving 21.4 cubic meters of grouting material per linear meter, equivalent to 25.68 tons, and costing approximately 39,800 yuan). Furthermore, the construction method of this invention allows for flexible adjustment of setting time and diffusion radius by adjusting the mix ratio and adding different admixtures, effectively solving problems such as grout loss, diffusion radius, and penetration distance, and controlling engineering treatment costs. Therefore, the construction method of this invention can significantly save construction time and costs, resulting in significant economic benefits. Attached Figure Description

[0018] Figure 1 A site photo of advanced drilling at the working face; Figure 2 This is a photo of the excavation site at the tunnel face. Figure 3 This is a site diagram of the initial support construction. Figure 4 This is a site photo of the drilling at the arch foot. Figure 5 Site diagram for installing the locking foot steel pipe; Figure 6 Photos of the grouting process for the locking steel pipes; Figure 7 This is a site photo of the steel anchor pipe drilling operation. Figure 8 This is a site photo of grouting for steel anchor pipes. Figure 9 Design drawings for grouting reinforcement treatment of steel anchor pipes and long steel pipe locking feet; Figure 10 Detail drawing of the locking foot of a Φ76×5 long steel pipe; Figure 11 This is a detailed drawing of a Φ76×5 steel anchor pipe. Figure 12 This is the design drawing for the initial support of the I-beam. Detailed Implementation

[0019] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The following embodiments are for explanation and illustration only, and do not constitute a limitation on the technical solution of the present invention.

[0020] Example 1 The construction method for a water-rich tunnel passing through a large karst cavity includes the following steps: Step 1: After investigating the development of karst and fissures, tunnel excavation and initial support construction are carried out according to the design drawings; Step 2: Install footing steel pipes within a 5 m range before and after the large karst cavity (the spacing is determined according to the spacing of the initial support steel of the main tunnel, with one set of footing steel pipes for each steel section). Drill Φ91 holes at the arch foot (drilling angles alternate between 30 degrees and 60 degrees downward, and the drilling depth is 3 meters into the rock) and clean the holes. Fill in the drilling record, fabricate and install the steel pipe footings in the holes, connect the footing steel pipes to the initial support steel sections, inject grout into the footing steel pipes to block water, seal the holes after grouting, and conduct quality inspection. Step 3: Carry out the lower excavation according to the design drawings; Step 4: When constructing the invert arch in a section, replace the base with rubble and stone chips (replacement depth is 3 m) according to the base conditions, and then construct the invert arch; Step 5: Within a 5 m range before and after the large karst cavity, construct vertical steel anchor pipes on the invert arch (spaced 1.5×1.5 m in a quincunx pattern). Drill Φ91 holes at the arch foot and clean the holes, fill in the drilling record, fabricate and install the steel anchor pipes in the holes, grout and plug the water inside the steel anchor pipes, seal the holes after grouting, and conduct a quality inspection.

[0021] In step two, the locking steel pipe and the steel anchor pipe in step five have the same shape, specifications, and material, both using Φ76 seamless steel pipe. The pipe length is determined according to the drilling depth. A borehole sealer is installed at the outer end of the pipe, and the pipe head is sharpened. Overflow holes with a diameter of 1 cm are drilled at a distance of 3 m from the outer end of the pipe in four directions: top, bottom, left, and right. The overflow holes are symmetrical both vertically and horizontally, spaced 1 m apart along the length of the pipe. Both the locking steel pipe and the steel anchor pipe contain bundles of three Φ20 threaded steel bars. Furthermore, other technical requirements in step two or step five are as follows: The technical requirements for drilling Φ91 holes are as follows: drilling equipment equipped with diamond drill bits shall be used; the entire locking steel pipe or steel anchor pipe and the hole opening pipe shall be integrated into one, and a hole opening seal shall be installed at the pipe end; the drilling method shall be either the forward grouting method or the one-time hole formation and one-time grouting method; the drilling speed shall be 2 m / h.

[0022] The technical requirements for cleaning the hole are as follows: flush the hole with pressurized water until it is clean. If there is silt that cannot be flushed out, flush for at least 30 minutes until the backflow is not turbid.

[0023] Drilling records include: borehole number; borehole location and station number; drilling angle; borehole elevation; opening and closing times; information on backfilling, water return, or air return during segmented drilling, as well as information on rock characteristics based on rock cuttings; borehole diameter changes; drilling rig malfunctions; borehole accidents; and final borehole depth, diameter, and inclination.

[0024] The technical requirements for grouting and water plugging are as follows: 1) After drilling to the water-bearing hole section for grouting and water plugging, the "hole-mouth sealing pure pressure full-hole section one-time grouting process method" is adopted; 2) The water-cement ratio of the grout used in the formal grouting process is 0.5:1; 3) The design pressure for water plugging grouting is 1.0-2.0 MPa, and the total pressure is the sum of the inrush pressure and the design pressure; 4) When the grouting volume of a single hole exceeds 10 tons, if the grouting pressure and injection rate do not change, accelerator material should be added to continue grouting; 5) When the grouting material is added to a single hole to 20 t, if the grouting pressure and injection rate do not change, the grouting injection rate should be controlled within 30 L / min and grouting should continue until the end.

[0025] The criterion for ending grouting and water plugging is: grouting can be ended when no grout is absorbed under the specified maximum design pressure. After the grouting and water plugging is completed, the grout should be held for 1-2 hours and allowed to set for 24-48 hours.

[0026] The quality inspection qualification standard is: no water flows out when the grouting gate valve is opened after the grouting time is over, or no obvious cracks and water storage are detected in the grouting area by ground-penetrating radar.

[0027] Example 2 The construction method for a water-rich tunnel passing through a large karst cavity includes the following steps: Step 1: After investigating the development of karst and fissures, tunnel excavation and initial support construction are carried out according to the design drawings; Step 2: Install locking steel pipes within 5 m before and after the large cavity (the spacing is determined according to the spacing of the initial support steel of the main tunnel, with one set of locking steel pipes for each steel section). Drill Φ91 holes at the arch foot (drilling angles alternate between 30 degrees and 60 degrees downward, with a drilling depth of 10 meters) and clean the holes. Fill in the drilling record, fabricate and install steel pipe locking feet in the holes, connect the locking steel pipes to the initial support steel sections, inject grout into the locking steel pipes to block water, seal the holes after grouting, and conduct quality inspection. Step 3: Carry out the lower excavation according to the design drawings; Step 4: When constructing the invert arch in a section, replace the base with rubble and stone chips (replacement depth is 4 m) according to the base conditions, and then construct the invert arch; Step 5: Within a 5 m range before and after the large karst cavity, construct vertical steel anchor pipes on the invert arch (spaced 1.5×1.5 m in a quincunx pattern). Drill Φ91 holes at the arch foot and clean the holes, fill in the drilling record, fabricate and install the steel anchor pipes in the holes, grout and plug the water inside the steel anchor pipes, seal the holes after grouting, and conduct a quality inspection.

[0028] In step two, the locking steel pipe and the steel anchor pipe in step five have the same shape, specifications, and material, both using Φ76 seamless steel pipe. The pipe length is determined according to the drilling depth. A borehole sealer is installed at the outer end of the pipe, and the pipe head is sharpened. Overflow holes with a diameter of 1 cm are drilled at a distance of 3 m from the outer end of the pipe in four directions: top, bottom, left, and right. The overflow holes are symmetrical both vertically and horizontally, spaced 1 m apart along the length of the pipe. Both the locking steel pipe and the steel anchor pipe contain bundles of three Φ20 threaded steel bars. Furthermore, other technical requirements in step two or step five are as follows: The technical requirements for drilling Φ91 holes are as follows: drilling equipment equipped with diamond drill bits shall be used; the entire locking steel pipe or steel anchor pipe and the hole opening pipe shall be integrated into one, and a hole opening seal shall be installed at the pipe end; the drilling method shall be either the forward grouting method or the one-time hole formation and one-time grouting method; the drilling speed shall be 3 m / h.

[0029] The technical requirements for cleaning the hole are as follows: flush the hole with pressurized water until it is clean. If there is silt that cannot be flushed out, flush for at least 30 minutes until the backflow is not turbid.

[0030] Drilling records include: borehole number; borehole location and station number; drilling angle; borehole elevation; opening and closing times; information on backfilling, water return, or air return during segmented drilling, as well as information on rock characteristics based on rock cuttings; borehole diameter changes; drilling rig malfunctions; borehole accidents; and final borehole depth, diameter, and inclination.

[0031] The technical requirements for grouting and water plugging are as follows: 1) After drilling to the water-bearing hole section for grouting and water plugging, the "hole-mouth sealing pure pressure full-hole section one-time grouting process method" is adopted; 2) The water-cement ratio of the grout used in the formal grouting process is 0.5:1; 3) The design pressure for water plugging grouting is 1.0-2.0 MPa, and the total pressure is the sum of the inrush pressure and the design pressure; 4) When the grouting volume of a single hole exceeds 10 tons, if the grouting pressure and injection rate do not change, accelerator material should be added to continue grouting; 5) When the grouting material is added to a single hole to 20 t, if the grouting pressure and injection rate do not change, the grouting injection rate should be controlled within 30 L / min and grouting should continue until the end.

[0032] The criterion for ending grouting and water plugging is: grouting can be ended when no grout is absorbed under the specified maximum design pressure. After the grouting and water plugging is completed, the grout should be held for 1-2 hours and allowed to set for 24-48 hours.

[0033] The quality inspection qualification standard is: no water flows out when the grouting gate valve is opened after the grouting time is over, or no obvious cracks and water storage are detected in the grouting area by ground-penetrating radar.

[0034] Example 3 The construction method for a water-rich tunnel passing through a large karst cavity includes the following steps: Step 1: After investigating the development of karst and fissures, tunnel excavation and initial support construction are carried out according to the design drawings; Step 2: Install foot-locking steel pipes within a 5 m range before and after the large karst cavity (the spacing is determined according to the spacing of the initial support steel of the main tunnel, with one set of foot-locking steel pipes for each steel section). Drill Φ91 holes at the arch foot (drilling angles alternate between 30 degrees and 60 degrees downward, with a drilling depth of 15 meters) and clean the holes. Fill in the drilling record, fabricate and install steel pipe foot-locking pipes in the holes, connect the foot-locking steel pipes to the initial support steel sections, inject grout into the foot-locking steel pipes to block water, seal the holes after grouting, and conduct quality inspection. Step 3: Carry out the lower excavation according to the design drawings; Step 4: When constructing the invert arch in a section, replace the base with rubble and stone chips (replacement depth is 3.5 m) according to the site conditions, and then construct the invert arch; Step 5: Within a 5 m range before and after the large karst cavity, construct vertical steel anchor pipes on the invert arch (spaced 1.5×1.5 m in a quincunx pattern). Drill Φ91 holes at the arch foot and clean the holes, fill in the drilling record, fabricate and install the steel anchor pipes in the holes, grout and plug the water inside the steel anchor pipes, seal the holes after grouting, and conduct a quality inspection.

[0035] In step two, the locking steel pipe and the steel anchor pipe in step five have the same shape, specifications, and material, both using Φ76 seamless steel pipe. The pipe length is determined according to the drilling depth. A borehole sealer is installed at the outer end of the pipe, and the pipe head is sharpened. Overflow holes with a diameter of 1 cm are drilled at a distance of 3 m from the outer end of the pipe in four directions: top, bottom, left, and right. The overflow holes are symmetrical both vertically and horizontally, spaced 1 m apart along the length of the pipe. Both the locking steel pipe and the steel anchor pipe contain bundles of three Φ20 threaded steel bars. Furthermore, other technical requirements in step two or step five are as follows: The technical requirements for drilling Φ91 holes are as follows: drilling equipment equipped with diamond drill bits shall be used; the entire locking steel pipe or steel anchor pipe and the hole opening pipe shall be integrated into one, and a hole opening seal shall be installed at the pipe end; the drilling method shall be either forward grouting or one-time hole formation and one-time grouting; the drilling speed shall be 2.5 m / h.

[0036] The technical requirements for cleaning the hole are as follows: flush the hole with pressurized water until it is clean. If there is silt that cannot be flushed out, flush for at least 30 minutes until the backflow is not turbid.

[0037] Drilling records include: borehole number; borehole location and station number; drilling angle; borehole elevation; opening and closing times; information on backfilling, water return, or air return during segmented drilling, as well as information on rock characteristics based on rock cuttings; borehole diameter changes; drilling rig malfunctions; borehole accidents; and final borehole depth, diameter, and inclination.

[0038] The technical requirements for grouting and water plugging are as follows: 1) After drilling to the water-bearing hole section for grouting and water plugging, the "hole-mouth sealing pure pressure full-hole section one-time grouting process method" is adopted; 2) The water-cement ratio of the grout used in the formal grouting process is 0.5:1; 3) The design pressure for water plugging grouting is 1.0-2.0 MPa, and the total pressure is the sum of the inrush pressure and the design pressure; 4) When the grouting volume of a single hole exceeds 10 tons, if the grouting pressure and injection rate do not change, accelerator material should be added to continue grouting; 5) When the grouting material is added to a single hole to 20 t, if the grouting pressure and injection rate do not change, the grouting injection rate should be controlled within 30 L / min and grouting should continue until the end.

[0039] The criterion for ending grouting and water plugging is: grouting can be ended when no grout is absorbed under the specified maximum design pressure. After the grouting and water plugging is completed, the grout should be held for 1-2 hours and allowed to set for 24-48 hours.

[0040] The quality inspection qualification standard is: no water flows out when the grouting gate valve is opened after the grouting time is over, or no obvious cracks and water storage are detected in the grouting area by ground-penetrating radar.

[0041] To further verify the reliability of the present invention, the inventors applied the construction method for water-rich tunnels traversing large karst cavities to the Dejiang Tunnel of the Dezhou-Wuchuan Expressway, as follows: 1. Materials and Equipment The main materials are listed in Table 1, and the main equipment is listed in Table 2.

[0042] ; ; 2. Construction Method (1) Step 1: After investigating the development of karst and fissures, tunnel excavation and initial support construction are carried out according to the design drawings. A site diagram of the advanced drilling at the tunnel face is shown below. Figure 1 As shown in the diagram, the excavation site at the tunnel face is as follows. Figure 2 As shown in the diagram, the initial support construction site is as follows: Figure 3 As shown.

[0043] (2) Step Two: Install anchor steel pipes within a 5 m range before and after the large karst cavity. The spacing is determined according to the spacing of the initial support steel of the main tunnel. Each steel section has one set of anchor steel pipes. Drill Φ91 holes at the arch foot, with the drilling angle alternating between 30° and 60° downwards. The drilling depth should be no less than 2 m into the rock. The drilling site diagram at the arch foot is shown below. Figure 4 As shown. Clean the hole and fill in the drilling record. Fabricate and install steel pipe locking feet inside the hole. A site diagram of the steel pipe locking feet installation is shown below. Figure 5As shown, the locking steel pipe is connected to the initial support steel section, and grout is injected into the locking steel pipe to plug the water. The on-site grouting diagram of the locking steel pipe is shown below. Figure 6 As shown. After grouting is completed, the holes are sealed and a quality inspection is performed.

[0044] Drilling equipment: 2 long-distance drilling machines, equipped with Φ91 mm and Φ75 mm diamond drill bits; 2 small rock drills. Operators: 10 people, 5 people per shift, divided into two shifts.

[0045] Drilling technical requirements: Drilling speed should be controlled at 2-3 m / h; Drilling should be done by grouting while advancing, with the grouting section length controlled at 5 m. Depending on the degree of fracture and joint development of the surrounding rock and the amount of water inflow and seepage, drilling can also be done in one go and grouting at the same time; If a large water inflow occurs when drilling reaches a certain depth and it is difficult to continue drilling, or if a solution hole or solution channel is encountered, drilling must be stopped, grouting should be performed, and drilling should be resumed after solidification until the designed hole depth is reached; The borehole opening section should be drilled with a diameter of Φ91 mm, and the entire locking steel pipe and the borehole opening pipe should be combined into one, with a borehole sealing device installed at the pipe end.

[0046] Hole cleaning technique requirements: Flush the hole with pressurized water until it is clean. If mud cannot be flushed out, flush for at least 30 minutes to flush away as much mud and sand as possible around the borehole until the backflow water is not turbid.

[0047] Drilling Records: A complete drilling record must be kept for each borehole. During drilling, detailed records must be made of various conditions observed, such as water inflow, water loss, return water color, changes in drilling speed, external leakage, borehole collapse, rock spalling, stuck drill bit, changes in lithology, and changes in formation. These records should be reflected in the comprehensive borehole results table as basic data for analyzing the quality of consolidation grouting. The drilling record includes: borehole number; borehole location and station number; borehole angle; borehole elevation; start-up and end-of-hole times; information on backflow of cuttings, water, or air during segmented drilling, and information on rock characteristics determined based on cuttings; borehole diameter changes; drilling rig malfunctions; borehole accidents; and final borehole depth, diameter, and inclination.

[0048] Fabrication and installation of the anchor pipe: Φ76 seamless steel pipe is used, with the length determined by the drilling depth. A borehole sealer is installed at the outer end of the pipe. The pipe head is sharpened. Overflow holes with a diameter of 1 cm are drilled at a distance of 3 m from the outer end of the pipe in four directions: top, bottom, left, and right. These overflow holes are symmetrical both vertically and horizontally, spaced 1 m apart along the pipe length. Three bundled Φ20 threaded steel bars are inserted into both the anchor pipe and the steel anchor pipe. A borehole sealer is installed at the end of the anchor pipe, and the anchor pipe is securely welded to the steel section.

[0049] Grouting for water plugging includes grout preparation and grouting steps, as detailed below: ①Preparation of slurry Cement mortar: After accurately weighing according to the specified batching list, pour the cement, admixtures and sand into the mixing drum, dry mix for about 30 seconds, then add the required amount of water and mix well. It is mainly used for the consolidation of orifice pipes.

[0050] Cement grout: First, pour the required amount of water into the mixing drum, start the mixer, and slowly pour in the cement and admixtures while continuously stirring (do not pour cement before water). Mix until the grout is of uniform consistency, uniform color, and free of lumps, then it is ready to be discharged. To avoid sedimentation, the grout storage tank should be continuously stirred by high-pressure air, a circulating pump, a mixer, or manually. Depending on the grout absorption situation, thickeners and other additives can be added appropriately, mainly for high-pressure grouting to form a solid structure.

[0051] Thickening agent addition: To reduce grout loss during water plugging, a thickening agent is added to increase the grout consistency for grouting. Based on the on-site water plugging grouting conditions, a special thickening material is added to the 0.5:1 pure cement grout delivered from the grouting station to the grouting work surface for on-site preparation.

[0052] Adding anti-dispersant agent: To reduce the loss of grout during water plugging and increase the grout diffusion range, an anti-dispersant agent is added to the grout. This is done by adding a special anti-dispersant material to the 0.5:1 pure cement grout delivered from the grouting station to the grouting work surface for on-site preparation.

[0053] ② Grouting The grouting sequence follows the principle of prioritizing key areas before general areas, grouting the sides before the middle, gradually increasing the grout density from thin to thick, starting with low pressure and small pump volume and gradually increasing, and grouting one hole at a time, proceeding step by step and continuously. The grouting technical requirements are as follows: 1) After drilling to the water-bearing hole section for grouting and water plugging, the "hole-mouth sealing pure pressure full-hole section one-time grouting process method" is adopted; 2) The water-cement ratio of the grout used in the formal grouting process is 0.5:1; 3) The design pressure for water plugging grouting is 1.0-2.0 MPa, and the total pressure is the sum of the inrush pressure and the design pressure; 4) When the grouting volume of a single hole exceeds 10 tons, if the grouting pressure and injection rate do not change, accelerator material should be added to continue grouting; 5) When the grouting material is added to a single hole to 20 t, if the grouting pressure and injection rate do not change, the grouting injection rate should be controlled within 30 L / min and grouting should continue until the end.

[0054] Grouting and water plugging completion criteria: Grouting can be terminated when no grout is absorbed under the specified maximum design pressure. After grouting and water plugging is completed, the grout should be held for 1-2 hours and allowed to set for 24-48 hours.

[0055] Sealing: After grouting is completed, a plug plate is installed on the flange of the orifice pipe, and cement grout is injected to seal the orifice.

[0056] The qualified standard for water plugging grouting quality inspection is: no water flows out when the grouting gate valve is opened after the grouting time is over, or no obvious cracks and water storage are detected in the grouting area by ground-penetrating radar.

[0057] (3) Step 3: Carry out the lower guide excavation according to the design drawings.

[0058] (4) Step 4: When constructing the invert arch in the section, replace it with rubble and stone chips according to the base conditions. The replacement depth is 3 m. Then construct the invert arch.

[0059] (5) Step 5: Within a 5 m range before and after the large cavity, vertical steel anchor pipes are installed on the invert arch. The spacing between the steel anchor pipes is 1.5 × 1.5 m, arranged in a quincunx pattern. The drilling site diagram of the steel anchor pipes is shown below. Figure 7 As shown. Drill a Φ91 hole at the arch foot, with a depth of at least 2 m into the rock. Clean the hole and fill in the drilling record. Fabricate and install steel anchor pipes inside the hole, and install hole sealers at the pipe ends. The steel anchor pipes can be directly inserted into the drilled hole. Grouting is then performed inside the steel anchor pipes to plug water. The on-site grouting diagram of the steel anchor pipes is shown below. Figure 8 As shown. After grouting is completed, the hole is sealed and a quality inspection is performed. The technical requirements for this step are the same as for step two.

[0060] 3. Technical Support Measures (1) Drilling shall be carried out strictly in accordance with the design parameters. The drilling position and angle deviation shall comply with the relevant specifications. If the drilling position on site cannot meet the design requirements due to objective conditions, it shall be moved and calculated to determine the parameters. If necessary, additional holes shall be drilled.

[0061] (2) The grouting material shall meet the design requirements. Expired and lumpy cement shall not be used. If necessary, it shall be inspected.

[0062] (3) The slurry ratio should meet the design requirements, and the maximum error during slurry preparation is ±5%.

[0063] (4) The slurry should be stirred evenly. Generally, the stirring time for cement slurry is 3-5 minutes, and the storage time should not exceed 30 minutes. Slurry that is not stirred evenly, has settled, or has initially set is strictly prohibited from use.

[0064] (5) During the grouting process, pay close attention to the changes in pump pressure and flow rate. If the grout intake is large or the pressure suddenly drops, or if the grouting pressure does not rise for a long time, the cause should be investigated. If the working face is leaking grout, sealing measures can be taken. If the grout is leaking, the grout solution can be changed, the grout ratio can be adjusted, the grout gel time can be shortened, and grouting with a large pump volume and low pressure can be carried out. If necessary, intermittent grouting can be used to achieve the purpose of controlled grouting.

[0065] (6) If the pressure suddenly increases during the grouting process, the cause should be found and dealt with in time. If it is indeed due to the grout gel time being too short, the setting time should be adjusted in time by adding retarders.

[0066] (7) If a pump fails, a standby pump should be used immediately to continue grouting.

[0067] (8) During the grouting process, the grouting pipeline should be kept unobstructed to prevent the judgment of the grouting end standard from being affected by pipeline blockage.

[0068] (9) Grouting shall be carried out in segments in strict accordance with the segment length of the forward grouting design. The segment length shall not be extended arbitrarily. If necessary, repeated grouting may be carried out to ensure the grouting quality.

[0069] (10) Strictly inspect and evaluate the grouting effect, and the grouting operation can only be ended when it meets the requirements.

[0070] The schematic diagram of the water-rich tunnel project using long steel pipe anchors and inverted arch steel anchor pipes to traverse large karst cavities provided by this invention is shown below. Figure 9-12 As shown.

[0071] 4. Explanation of the maturity and reliability of the process method The process method provided by this invention has been successfully applied in the construction of the water-rich section of the Dejiang Tunnel, and subsequently promoted and applied in the Zimuyan Tunnel of the Wulong-Daozhen Expressway Section 1 and the Caijiapo Tunnel of the Liuzhi-Anlong Expressway Section 1. This process method avoids uneven settlement after construction, preventing safety risks to the main structure. It also avoids the "hull effect" and inverted arch heave that can occur in the water-rich karst cavity during grouting reinforcement. The method allows water to flow through the karst cavity, postponing the water-blocking work and ensuring construction progress. Furthermore, this process method has the following advantages: saving grouting material, saving treatment time, reducing costs, and improving efficiency. It has significant advantages for normal tunnel construction, accelerates the construction progress, and ensures the timely completion and opening of the tunnel and expressway, resulting in significant social benefits. By postponing grouting reinforcement, this process method saves time and costs. For the increasingly complex hydrogeological conditions, especially for tunnel construction projects with large water-bearing karst cavities, the tunnel construction method for traversing large karst cavities provided by this invention has significant economic and social benefits and is worthy of reference and promotion.

[0072] 5. Benefit Analysis 5.1 Social Benefits During the implementation process, the following approach was adopted: first, the development of karst and fissures was investigated before deciding to excavate through them. Then, boreholes were drilled at the arch foot and anchor steel pipes were installed for grouting reinforcement. When the lower bench was constructed to this point, vertical steel anchor pipes were installed. This method aims to: avoid uneven settlement after construction, which would pose a safety risk to the main structure, and at the same time, avoid the hull effect in the water-rich karst cavity during grouting reinforcement, which could cause the invert arch to heave.

[0073] Water seepage through the karst cavity in the tunnel allows for postponing the water plugging work, which ensures construction progress, saves grouting material, reduces treatment time, lowers costs, and improves efficiency. This has significant advantages for normal tunnel construction and accelerates the construction progress, ensuring that the tunnel and highway are completed and opened to traffic on schedule, resulting in significant social benefits.

[0074] 5.2 Economic Benefits (1) The construction method of the present invention is mainly applicable to water-rich tunnels or other underground projects where there are large cavities and fissures, and where there is water in the cavities and fissures.

[0075] (2) By adopting the construction method of the present invention, the grouting reinforcement is placed after the construction period, which saves the construction period. According to the curtain grouting, it takes 15 days at the fastest. Therefore, when encountering similar large cavities, the method of crossing first and then treating can save at least 15 days of construction period. According to the fixed cost of a single tunnel of a two-lane highway tunnel of about 600,000 yuan / month, each crossing of a large cavity can save 300,000 yuan.

[0076] (3) Because the present invention adopts post-grouting reinforcement treatment, it can save grouting material in the tunnel outline. According to the crack ratio of 0.2, the grouting material saved per linear meter is 107*0.2=21.4 cubic meters, which is equivalent to 21.4*1.2=25.68 tons. The cost is approximately 25.68*1550=39,800 yuan / m (where 107 is the tunnel face area, 1.2 is the cement consumption per ton of grouting material, and 1550 is the unit price of high-pressure grouting labor).

[0077] (4) The construction method of the present invention can flexibly adjust the setting time and diffusion radius by adjusting the proportion and adding different admixtures, such as retarders, quick-setting agents, inert fiber materials, special nano water-blocking materials, and anti-dispersion thickening materials, so as to effectively solve the problems of slurry loss, diffusion radius, and penetration distance, and control the engineering treatment cost.

[0078] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for constructing a water-rich tunnel through a large karst cavity, characterized in that, The construction method includes the following steps: Step 1: After investigating the development of karst and fissures, tunnel excavation and initial support construction are carried out according to the design drawings; Step 2: Install locking steel pipes within a 5 m range before and after the large cavity, drill Φ91 holes at the arch foot and clean the holes, fill in the drilling record, make and install steel pipe locking feet in the holes, connect the locking steel pipes to the initial support steel, inject grout into the locking steel pipes to block water, seal the holes after grouting, and conduct quality inspection. Step 3: Carry out the lower excavation according to the design drawings; Step 4: When constructing the invert arch in this section, replace the foundation with rubble and stone chips according to the foundation conditions, and then construct the invert arch. Step 5: Construct vertical steel anchor pipes on the invert arch within a 5 m range before and after the large karst cavity. Drill Φ91 holes at the arch foot and clean the holes. Fill in the drilling record, fabricate and install the steel anchor pipes in the holes, grout and plug the water inside the steel anchor pipes, seal the holes after grouting, and conduct a quality inspection.

2. The construction method according to claim 1, characterized in that, In step two: The spacing of the locking foot steel pipes is determined according to the spacing of the initial support steel of the main tunnel, and one set of locking foot steel pipes is provided for each steel section. The drilling angle for the Φ91 hole alternates between 30 degrees and 60 degrees downwards. The drilling depth is as follows: if the length of the cavity is less than or equal to 6 m, the hole depth should be no less than 2 m into the rock; if the length of the cavity is greater than 6 m, the hole depth should be 10-15 m.

3. The construction method according to claim 1, characterized in that, The depth of the replacement in step four is 3-4 m.

4. The construction method according to claim 1, characterized in that, In step five: The steel anchor pipes are spaced 1.5 × 1.5 m apart and arranged in a quincunx pattern. The drilling direction of the Φ91 hole is vertically downward, and the hole depth is as follows: if the length of the cavity is less than or equal to 6 m, the hole depth should be no less than 2 m into the rock; if the length of the cavity is greater than 6 m, the hole depth should be 10-15 m.

5. The construction method according to any one of claims 1, 2, or 4, characterized in that, The technical requirements for drilling Φ91 holes in step two or five are as follows: Drilling equipment equipped with diamond drill bits shall be used; the entire locking steel pipe or steel anchor pipe and the hole opening pipe shall be combined into one, and a hole opening seal shall be installed at the pipe end; the drilling method shall be either the forward grouting method or the one-time hole formation and one-time grouting method; the drilling speed shall be 2-3 m / h.

6. The construction method according to claim 1, characterized in that, In step two or step five: The technical requirements for cleaning the hole are as follows: flush the hole with pressurized water until it is clean. If silt cannot be flushed out, flush for at least 30 minutes until the return water is not turbid. The drilling records include: borehole number; borehole location and station number; drilling angle; borehole elevation; opening and closing times; backflow of cuttings, water or air during segmented drilling and the determination of rock properties based on cuttings; borehole diameter changes; drilling rig malfunctions; borehole accidents; and final borehole depth, diameter, and inclination.

7. The construction method according to claim 1, characterized in that, The locking steel pipe mentioned in step two has the same shape, specifications, and material as the steel anchor pipe mentioned in step five. Both are made of Φ76 seamless steel pipe. The length of the pipe is determined according to the drilling depth. A hole sealer is installed at the outer end of the pipe. The pipe head is sharpened. At a distance of 3 m from the outer end of the pipe, overflow holes with a diameter of 1 cm are drilled in four directions: up, down, left, and right. The overflow holes are symmetrical up and down and left and right, and are spaced 1 m apart along the length of the pipe. Both the locking steel pipe and the steel anchor pipe are fitted with three Φ20 threaded steel bars bundled together.

8. The construction method according to claim 1, characterized in that, The technical requirements for grouting and water plugging described in step two or five are as follows: 1) After drilling to the water-bearing hole section for grouting and water plugging, the "hole-mouth sealing pure pressure full-hole section one-time grouting process method" is adopted; 2) The water-cement ratio of the grout used in the formal grouting process is 0.5:1; 3) The design pressure for water plugging grouting is 1.0-2.0 MPa, and the total pressure is the sum of the inrush pressure and the design pressure; 4) When the grouting volume of a single hole exceeds 10 tons, if the grouting pressure and injection rate do not change, accelerator material should be added to continue grouting; 5) When the grouting material is added to a single hole to 20 t, if the grouting pressure and injection rate do not change, the grouting injection rate should be controlled within 30 L / min and grouting should continue until the end.

9. The construction method according to claim 1, characterized in that, The completion criteria for grouting and water plugging in step two or five are as follows: grouting can be completed when no grout is absorbed under the specified maximum design pressure. After grouting and water plugging is completed, the grout should be held for 1-2 hours and allowed to set for 24-48 hours.

10. The construction method according to claim 1, characterized in that, The quality inspection criteria described in step two or five are as follows: no water flows out when the grouting gate valve is opened after the grouting time is over, or no obvious cracks or water storage are detected in the grouting area by ground-penetrating radar.

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