Method for reinforcing karst stratum in limited space

Abstract

The invention discloses a karst stratum reinforcing method in a limited space. The karst stratum reinforcing method mainly solves the technical problems that an existing karst stratum reinforcing method is poor in reliability and high in cost. The waste slurry generated in the shield tunneling process is used as one of raw materials for karst reinforcement, the cognition that the slurry cannot be used for reliable karst reinforcement by technicians in the field is broken through, and meanwhile the material cost of karst reinforcement is effectively reduced while the waste slurry treatment problem is solved; through the specific mixing proportion of the raw materials and the requirement for the mesh number of the stone powder, the slurry filling effect can be improved while the slurry reinforcing effect is improved, and the adverse effect on the geological environment is reduced. In addition, by the adoption of the assembly type detachable drilling machine, the operation efficiency in the limited space can be greatly improved, personnel investment is reduced, and use and maintenance are convenient and fast.

Description

Technical Field

[0001] This invention relates to the field of tunnel boring machine (TBM) construction technology, specifically to a method for reinforcing karst formations in confined spaces. Background Technology

[0002] Karst formations are unique geological structures formed by the dissolution of soluble rocks by water. They are highly heterogeneous and complex, posing significant challenges to engineering construction. Compared to other unfavorable geological conditions, subway construction in karst areas is more difficult, carries higher construction risks, and has a greater impact on the surrounding environment. For example, open-cut excavation is prone to ground subsidence and sudden water inrush, while tunnel boring machine (TBM) construction is prone to frequent cutter damage and ground subsidence.

[0003] To reinforce karst formations, the inventors have developed a grouting reinforcement method. This method involves injecting grout into cavities, fissures, or soil to fill voids, consolidate loose material, and block groundwater channels, thereby improving the integrity and bearing capacity of the rock mass. Conventional grouting materials include ordinary silicate cement grout and water glass-cement dual grout. However, in implementing the technical solution in this application, the inventors discovered that ordinary silicate cement grout has poor permeability and shrinks due to water separation, easily forming voids and resulting in unsatisfactory backfilling effects. Furthermore, using water glass-cement dual grout as the grouting material requires strict proportion control; otherwise, an imbalance in the proportion can lead to excessively fast or slow setting times, affecting the filling effect. Additionally, this grouting material is costly, limiting its economic viability.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the background technology of this disclosure and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] In view of at least one of the above technical problems, this disclosure provides a method for reinforcing karst formations in confined spaces, which mainly solves the technical problems of poor reliability and high cost of existing karst formation reinforcement methods.

[0006] According to one aspect of this disclosure, a method for reinforcing karst formations in confined spaces is provided, comprising the following steps: (1) Collect the waste mud generated during the tunnel boring machine excavation process and transport it to the mud collection pool for storage; (2) Transport the drilling rig to the karst site to be reinforced, assemble it, and start the drilling rig to drill holes in the area to be reinforced; (3) Measure the specific gravity of the mud in the mud collection tank and adjust the specific gravity of the mud to 1.1~1.25g / cm³. 3 Then, the mud is transported to a mixer to be mixed with cement to obtain a mixture; (4) Sieve to obtain stone powder with a mesh size of no more than 10 mm, mix the stone powder with the mixture until uniform, and add early strength agent and thickener to form a grouting slurry with a consistency of 10-15 cm; (5) The grouting slurry is pumped into the borehole of the drilling rig through the grouting pipe for backward grouting. After the grouting pressure reaches the design pressure, the grouting pipe is pulled out 0.5m at a time.

[0007] In some embodiments of this disclosure, in step (2), the drilling rig includes a telescopic bracket, detachable traveling wheels on both sides of the telescopic bracket, an assembly power unit fixed to the top of the telescopic bracket, a winch mechanism relatively fixed to one side of the telescopic bracket, and a support frame movably connected to the top of the winch mechanism and the corresponding end of the telescopic bracket; the single section length of the drill rod of the drilling rig is 1 to 2 m.

[0008] In some embodiments of this disclosure, the telescopic bracket includes a support with a sleeve at the bottom and a bracket that is movably fitted into the sleeve on both sides of the support by means of pins.

[0009] In some embodiments of this disclosure, in step (2), the specific gravity of the slurry is adjusted by increasing the amount of bentonite and controlling the water content; the cement is ordinary silicate cement; the mixture is temporarily stored in the slurry tank and continuously or intermittently stirred.

[0010] In some embodiments of this disclosure, the weight ratio of cement, mud, stone powder, early strength agent and thickener in the grout is 200:400:900:3:3 per cubic meter.

[0011] In some embodiments of this disclosure, in step (4), after the grout is prepared, the mixing ratio of the grout is tested and verified, and the compressive strength at 28 days is not less than 0.2 MPa.

[0012] In some embodiments of this disclosure, in step (4), the early strength agent is Na2SiO3 and the thickener is a soil stabilizer.

[0013] In some embodiments of this disclosure, in step (5), the design grouting pressure for the backward grouting is 0.8 to 1.0 MPa.

[0014] In some embodiments of this disclosure, in step (5), before performing the backward grouting, the grout is sent into a secondary mixing tank and a modifier is added until the mixture is uniform.

[0015] One or more technical solutions provided in the embodiments of this application have at least one of the following technical effects or advantages: By utilizing the waste mud generated during shield tunneling as one of the raw materials for karst reinforcement, the perception among those skilled in the art that mud cannot be used for reliable karst reinforcement is broken. Simultaneously, while solving the problem of waste mud disposal, the material cost of karst reinforcement is effectively reduced. Furthermore, by using specific mixing ratios of various raw materials and requirements for the mesh size of stone powder, the slurry reinforcement effect is improved, as is the slurry filling effect, and the adverse impact on the geological environment is reduced. In addition, the use of a prefabricated, detachable drilling rig can greatly improve the operating efficiency in confined spaces, reduce personnel input, and is more convenient to use and maintain. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the drilling rig in one embodiment of this application.

[0017] Figure 2 This is a schematic diagram of a method for reinforcing karst formations in one embodiment of this application.

[0018] Figure 3 This is a diagram illustrating the preparation of the paste specimen and the compressive strength test in one embodiment of this application.

[0019] Figure 4 This is a core sample taken after filling the karst strata in one embodiment of this application.

[0020] Figure 5 This is the test result of the compressive strength of some core samples in one embodiment of this application.

[0021] In the above figures, 1 is the telescopic bracket, 2 is the traveling wheel, 3 is the power unit of the assembly, 4 is the winch mechanism, 5 is the support frame, and 6 is the drill rod. Detailed Implementation

[0022] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inner", "outer", "vertical", "horizontal", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0023] To better understand the technical solution of this application, the above technical solution will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] When using existing technologies to reinforce karst formations, ordinary silicate cement grout is prone to forming voids due to its poor permeability and shrinkage caused by water separation, resulting in unsatisfactory backfilling effects. On the other hand, when using water glass-cement dual grout as the grouting material, the mixing ratio of the grouting material requires high precision. An imbalance in the ratio will lead to unstable setting time of the grouting material, which will affect the filling effect. In addition, the grouting cost of water glass-cement dual grout is high, resulting in poor construction economy.

[0025] Furthermore, during the tunnel boring machine (TBM) excavation process, mud circulation is required to achieve multiple functions such as stabilizing the soil at the tunnel face, lubricating the cutterheads, transporting excavated soil, and protecting the strata. This process generates a large amount of waste mud, and directly disposing of this waste mud would increase the cost of TBM construction. In developing this invention, the inventors proposed applying the waste mud to karst reinforcement, which solves the waste mud disposal problem while also reducing the cost of karst reinforcement. However, during the implementation of this embodiment, the inventors, through further research, discovered that those skilled in the art generally recognize the following: Waste mud has a complex composition, containing soil particles including organic matter and humus, as well as lubricating additives (such as polymers and greases), metal shavings, etc. These complex and variable components are difficult to control. When applied to karst reinforcement, the impurities can cause slow strength development and low final strength of the reinforced body, making it unable to provide reliable support for karst caves or effectively fill fissures. In addition, the organic matter and soluble salts in the mud may cause the reinforced body to soften, disintegrate, dissolve, or be carried away by water flow under long-term groundwater action, resulting in a loss of reinforcement effect. Furthermore, the above-mentioned defects of mud are difficult to overcome by simply mixing in other materials. Specifically, the organic matter, soluble salts, residual additives, and metal ions contained in waste mud can seriously interfere with the hydration reaction of cement or the solidification process of chemical slurry, resulting in problems such as slow strength development of the gel, significantly reduced final strength, abnormal setting time, and poor volume stability. Furthermore, due to the extremely high water content of waste mud and the fact that its solid particles are mainly fine-grained soil, simply adding cement or other cementing materials will dilute the concentration of the cementing materials with a large amount of water, leading to problems such as uncontrolled water-cement ratio, poor permeability, and easy segregation and sedimentation. Therefore, the inventors believe that, as is generally accepted by those skilled in the art, mud cannot be effectively and reliably applied directly or indirectly in karst reinforcement construction, as this would result in poor reinforcement effect and reliability.

[0026] However, to reduce the cost of karst treatment while ensuring the reliability of karst reinforcement, the inventors, through further research, proposed a method for reinforcing karst formations in confined spaces. This method, through special treatment of waste mud, can be applied to the effective reinforcement of karst formations. (See [link to relevant documentation]). Figure 2 Specifically, it includes the following steps: (1) Collect the waste mud generated during the tunneling process of the shield machine and transport it to the mud collection pool for storage.

[0027] In order to reduce or eliminate the cost of waste mud treatment, and to reduce the reinforcement cost during karst reinforcement, in this embodiment, the waste mud generated during the tunnel boring machine excavation process is collected and stored in a mud collection pool on the ground so that the waste mud can be reused for karst reinforcement within the exposed area, so as to ensure that the tunnel boring machine can safely and smoothly pass through the karst area.

[0028] (2) Transport the drilling rig to the karst site to be reinforced, assemble it, and start the drilling rig to drill holes in the area to be reinforced.

[0029] In this embodiment, grouting is performed on the karst area. First, boreholes are drilled in the exposed karst area to allow grout to be injected into the area through these holes. However, since the karst areas to be treated are generally confined, ordinary drilling rigs cannot easily penetrate these areas for drilling. Therefore, this embodiment discloses a drilling rig suitable for confined environments, see [link to documentation]. Figure 1 The drilling rig includes a telescopic bracket 1, traveling wheels 2, a power unit 3, a winch mechanism 4, a support frame 5, and drill rods 6. These components are detachably connected, allowing for convenient modular transportation and rapid assembly in the drilling area. Specifically, considering the varying environmental constraints under different working conditions, this embodiment includes a telescopic bracket 1 to adapt to different environments. The telescopic bracket 1 comprises a support frame with a sleeve fixed to its bottom. Each side of the sleeve has a bracket that engages with the sleeve. Adjusting the position of the bracket along the sleeve direction allows for width adjustment of the telescopic bracket. To ensure stability after width adjustment, positioning holes are provided at the corresponding points where the sleeve and bracket engage within the sleeve. Pins are inserted into these holes to fix the relative positions of the support frame and brackets, preventing instability caused by vibrations during drilling. Specifically, in this example, the drilling rig is 1.6m long and its width can be adjusted within the range of 0.7 to 1.8m, thus adapting to various restricted working conditions.

[0030] Furthermore, considering the ease of movement of the drilling rig after assembly, this example includes wheels on both sides of the telescopic bracket. To facilitate the disassembly and transportation of the wheels, the axles are fixed to the bottom of the telescopic bracket via bearings. Therefore, when wheels are needed, they can simply be installed on either side of the axle, making assembly and disassembly convenient. Additionally, for ease of wheel disassembly and assembly, and also for the overall stability of the drilling rig during operation, see [reference needed]. Figure 1In this example, outriggers are also installed at the four corners of the telescopic bracket. The outer surface of the outriggers is provided with external threads, which are threaded to the bolts at the four corners of the telescopic bracket. Thus, the vertical height of the outriggers can be adjusted by turning them. This allows the telescopic bracket to be raised when the traveling wheels are disassembled and assembled. When the drilling rig is working, the height of each outrigger can be adjusted accordingly to adapt to the uneven ground inside the tunnel, ensuring the stability of the drilling rig. This configuration is also convenient for disassembly, assembly and transportation, minimizing the cost and transportation difficulty of the drilling rig.

[0031] The power unit serves as the power source for the drilling rig. In this example, an M4.5 housing power unit is selected, which is fixed to the telescopic bracket via a slot to provide power for the drilling of the drill rod. The winch mechanism is used to control the drilling of the drill rod. To ensure the stability of the winch mechanism during use, an obliquely arranged support frame is also provided in this example. The support frame and the telescopic bracket are movably connected by a pin. In addition, considering the limited space in the area to be drilled, the length of a single section of the drill rod is set to 1-2m in this embodiment to avoid spatial interference with the surrounding environment due to excessively long drill rods.

[0032] (3) Measure the specific gravity of the mud in the mud collection tank and adjust the specific gravity of the mud to 1.1~1.25g / cm³. 3 Then, the mud is transported to a mixer to be mixed with cement to obtain a mixture.

[0033] To avoid the adverse effects of mud moisture content and fine-grained soil content on karst reinforcement, in this embodiment, the specific gravity of the waste mud needs to be strictly controlled before it is used for karst reinforcement. Specifically, the specific gravity of the mud needs to be controlled to be 1.1–1.25 g / cm³. 3 Upon testing, when the specific gravity of the waste mud exceeded the specified range, the specific gravity was adjusted by increasing bentonite or controlling the water content until it met the requirements. Once the mud's specific gravity was within acceptable limits, it was transported to a fully automatic mixer, where cement was added for mixing. In this example, the cement was silicate cement P042.5, with 200 kg of cement and 400 kg of mud added per cubic meter of mixed slurry. The tricalcium silicate in the cement reacts with water in the mud at a specific moisture content to generate hydrated calcium silicate gel, achieving maximum bonding strength at the specified mud specific gravity and mixing ratio. Furthermore, the ettringite produced by cement hydration compensates for some shrinkage, helping to address poor permeability. Simultaneously, the cement hydration products encapsulate heavy metal ions (such as Pb) in the waste mud. 2+ Cr 6+ (etc.), forming insoluble hydroxides or silicates, reducing the adverse effects of heavy metals in waste mud on the underground environment.

[0034] Furthermore, the inventors discovered in practice that the above-mentioned mixing of cement and slurry only achieves physical mixing, and directly using the mixture does not achieve an effective karst reinforcement effect. Therefore, in this embodiment, the slurry with adjusted specific gravity is mixed with cement in a fully automatic mixer and then transported to a mortar tank for temporary storage and continuous or intermittent slow stirring. The mortar tank provides time for the hydration reaction of the cement and water in the slurry. Analysis of the intermediates revealed that in the mortar tank, cement particles begin to hydrate, forming early-stage hydrated calcium silicate gel and ettringite. This gel can encapsulate fine particles in the slurry (such as harmful organic matter, humus, metal shavings, etc.), acting as an encapsulation or passivation agent, thereby reducing the adverse interference of these impurities on later strength development. If the mortar tank is omitted and subsequent steps are performed directly, it has been found in practice that the huge specific surface area of ​​the stone powder immediately adsorbs a large amount of water and cement particles, severely interfering with the preferential contact and passivation reaction between the cement and harmful components in the slurry, leading to uneven strength and poor durability of the final solidified body. Furthermore, the mortar tank allows the mixture to undergo a brief "maturation" process, stabilizing its viscosity and density. This provides a stable base liquid for the subsequent addition of stone powder and additives. The pre-hydrated base liquid with a certain consistency has better viscosity and encapsulation properties than directly mixed cement and slurry. Subsequent stone powder blending based on this base liquid can more effectively encapsulate each stone powder particle, reducing interfacial defects between the stone powder and the slurry, resulting in a denser "skeleton-filler" structure and enhancing the strength of karst reinforcement.

[0035] (4) Screening to obtain stone powder with a mesh size of no more than 10 mm, and mixing the stone powder with the mixed liquid until uniform, and adding early strength agent and thickener to form a grouting slurry with a consistency of 10-15 cm.

[0036] While mixing cement into waste mud can improve its strength and permeability, experimental verification revealed that it cannot effectively meet the needs of karst reinforcement, still exhibiting insufficient strength and incomplete grouting in gaps. Therefore, through long-term practical research, the inventors proposed adding stone powder and additives to the mixture of waste mud and cement to effectively solve these problems. Specifically, after the stone powder arrives on site, it is transported by a loader to a filter screen with a mesh size no larger than 10mm for sieving. The sieved stone powder is then transported to a forced-mixing grout mixer for further uniform mixing with the mud and cement mixture. 900 kg of stone powder is added per cubic meter of grout. This addition of specially sized stone powder particles fills the pores between mud particles, forming a "skeleton-filler" structure, thereby reducing shrinkage and increasing reinforcement strength. It also helps the grout fill smaller gaps, improving the grouting reinforcement effect. Furthermore, the calcium carbonate in the stone powder can adsorb anions (such as fluoride) in the waste mud. - SO42- To avoid pollutants from contaminating the geological environment.

[0037] After the mud, cement, and stone powder are thoroughly mixed, an accelerator and a thickener are added to the mixer as additives. In this example, the accelerator is specifically Na2SiO3, and the thickener is specifically a soil stabilizer. 3 kg of accelerator and 3 kg of thickener are added per cubic meter of grout. This allows the accelerator to promote early hydration of the cement in the grout mixture, shortening the initial setting time and reducing the risk of the grout being diluted by groundwater. Simultaneously, the thickener forms a network structure, preventing the sedimentation of stone powder and particles, reducing the risk of pipe blockage during grouting, and also reducing the grout loss rate in dynamic water environments.

[0038] After the grout is prepared, its consistency and properties are measured and verified. The consistency should be 10-15 cm, and the 28-day compressive strength should be no less than 0.2 MPa. In this embodiment, see... Figure 3 (a) Based on the above steps and paste ratio, specimens were prepared. In this example, three specimens were prepared, and the 28-day compressive strength of each paste specimen was tested; the test results are shown in [reference]. Figure 3 (b) Under the test parameter setting of 0.3 MPa / s acceleration speed, the compressive strength of each specimen is shown in Table 1, and its compressive strength performance meets the above requirements.

[0039] .

[0040] (5) The grouting slurry is pumped into the borehole of the drilling rig through the grouting pipe for backward grouting.

[0041] In this embodiment, the grouting slurry that meets the corresponding requirements after mixing is pumped into a cement truck by a concrete pump, and then transported to the grouting area by the cement truck.

[0042] In this embodiment, considering the high density and high concentration of solid particles (especially heavy stone powder) of the prepared grout, there is a transportation and waiting time between the completion of grout preparation and pumping. Under static or ordinary transportation and stirring conditions, stone powder and cement particles are prone to sedimentation and segregation, resulting in uneven composition between the upper and lower layers of the grout. Therefore, in this example, before grouting, the grout is first sent to a secondary mixing tank for forced stirring under high shear force to thoroughly disperse the settled or agglomerated particles, ensuring that the grout reaches a highly uniform state. This ensures that the grout mix ratio remains consistent with the design value at each stage of the subsequent grouting process, thereby avoiding problems such as grout pipe blockage and ensuring the final reinforcement quality. In addition, during stirring in the secondary mixing tank, modifiers (such as high-efficiency water-reducing agents and water-retaining agents) can be added to precisely adjust the consistency based on the actual measured grout state on site (such as fluidity tests) to ensure that its consistency is always maintained within the ideal design range.

[0043] During grouting operations, the grouting pipe is connected to the grouting pump using a retreating grouting method. The grouting pipe is first inserted into the grouting hole drilled by the drilling rig, ensuring it is fully inserted. Then, the grouting pump is started to begin grouting. Once the grouting pressure reaches the design pressure, the grouting pipe is pulled outwards by 0.5m. This process is repeated until grouting is complete. In foundation reinforcement and water plugging reinforcement projects, the grouting pressure for retreating grouting is typically 1.0MPa to 3.0MPa. However, practice has shown that while this pressure range can achieve karst reinforcement, cross-sectional surveys have revealed that the actual grouting range exceeds the design range, causing geological changes and unnecessary waste of grout. Therefore, in this example, the design grouting pressure for retreating grouting is set at 0.8 to 1.0MPa. In karst formations where groundwater, filling materials, or complex fracture systems exist, this pressure range provides sufficient kinetic energy for the grout to effectively penetrate to the distal ends of small fissures and cavities in the target area, achieving compaction and filling. Furthermore, it avoids insufficient grout diffusion due to excessively low pressure, which can lead to localized bulges that fail to fill the entire karst cave, leaving reinforcement blind spots. Simultaneously, it prevents excessively high pressure from causing uncontrolled grout loss along a single dominant channel, potentially altering the surrounding geological conditions. Especially in fragile geological environments, geological changes induced by high-pressure grout can lead to collapses in areas unrelated to reinforcement, blockage of waterways, and other new geological problems. For example, in karst strata, particularly in overlying soil and fractured rock masses, there is fracturing pressure. By limiting the grouting pressure, it ensures that the pressure is below the fracturing pressure of most soil or weak rock layers, preventing high-pressure grout from opening up weak strata and creating new fissures, damaging the original geological structure, and even causing safety issues such as uplift and grout leakage. Furthermore, the grouting pressure set in this example for the retreating grouting is also compatible with the prepared grout with a consistency of 10–15 cm. This grout consistency is a relatively thick paste-like grout. A grouting pressure within the range of 0.8–1.0 MPa can effectively propel this type of grout to flow through the fractures without causing segregation or rupture of the flow channels due to excessive pressure. Under this pressure range, the grout is forced into the voids (rather than flowing in), which helps to expel water and air from the voids, resulting in a tighter bond between the grout and the rock mass. This reduces shrinkage and voids after solidification, improving the overall integrity and strength of the reinforcement.

[0044] Taking the tunnel section constructed using the shield tunneling method in the Baiyun Airport T3 to Jiangcun West section of the Guanghe High-speed Railway as an example, 116 boreholes revealed soluble rock strata, and 58 boreholes revealed karst caves, with a karst cave encounter rate of 50.00%. The total length of karst caves and fissures encountered by the boreholes was 338.3m, and the total length of carbonate rock traversed was 2657.8m, with a karst line karst rate of 12.72%. The vertical cave heights of the revealed karst caves ranged from 0.5 to 13.0m, and they were fully filled, partially filled, or unfilled. The filling materials were mainly cohesive soil, sand, breccia, and fragments. Drilling speed varied, water leakage was observed, and dissolution phenomena were seen in the limestone core, with large variations in the dissolution interface and significant undulations in the rock surface within the site. The karst development level within this mileage range is strongly developed, and the stability of the karst site is unstable. Using the method disclosed in this example for karst reinforcement yields significant economic benefits, and the tunnel boring machine successfully passed through the karst area without any collapses or other safety accidents.

[0045] To verify the effectiveness of the karst formation reinforcement method disclosed in this example, the filling effect of each karst cave was tested. See [link to relevant documentation]. Figure 4 Core samples of backfill were taken from the top, middle, and bottom of the karst cave, respectively, and their compressive strength was tested. (See attached diagram.) Figure 5 The test results showed that the compressive strengths of the backfill core samples from the top, middle and bottom of the tunnel were 2.8 MPa, 2.4 MPa and 2.5 MPa, respectively, all of which met the design test requirement of not less than 0.2 MPa, thus meeting the reinforcement requirements of the karst strata. Moreover, the reinforcement effect was excellent, and the compressive strength of the reinforced body far exceeded the design requirements.

[0046] Although some preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0047] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this application and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for reinforcing karst strata in a confined space, characterized by, It comprises the following steps: (1) Collect the waste mud produced in the tunneling process of the shield machine and transport it to the mud collection pool for storage; (2) Transport the drill to the karst area to be reinforced and assemble it, and start the drill to drill the area to be reinforced; (3) Measure the slurry specific gravity in the slurry collecting pool and adjust the slurry specific gravity to 1.1-1.25 g / cm 3 Afterwards, the slurry is delivered to the mixer to mix with cement to obtain the mixed liquid, and the mixed liquid is delivered to the mortar pool. (4) Screen the stone powder with a corresponding mesh size not greater than 10 mm, and mix the stone powder with the mixed liquid until uniform, and add early strength agent and viscosity increasing agent to form grouting slurry with a consistency of 10-15 cm; (5) Pump the grouting slurry into the drill hole through the grouting pipe for backward grouting, and when the grouting pressure reaches the design pressure, pull out the grouting pipe 0.5 m at a time until the grouting is completed.

2. The karst stratum reinforcing method according to claim 1, characterized by, In the step (2), the drill comprises a telescopic bracket, detachable walking wheels on both sides of the telescopic bracket, an assembly power machine fixed to the top of the telescopic bracket, a hoisting mechanism fixed to one side of the telescopic bracket, and a support frame movably connected to the top of the hoisting mechanism and the corresponding end side of the telescopic bracket; the single length of the drill pipe of the drill is 1-2 m.

3. The karst stratum reinforcing method according to claim 2, characterized by, The telescopic bracket comprises a bracket with a sleeve at the bottom, and a bracket movably embedded in the sleeve through a latch on both sides of the bracket.

4. The karst stratum reinforcing method according to claim 1, characterized by, In the step (3), the specific gravity of the mud is adjusted by increasing bentonite and controlling water content; the cement is ordinary Portland cement; the mixed liquid is temporarily stored in the mortar pool and continuously or intermittently stirred.

5. The karst stratum reinforcing method according to claim 1, characterized by, The ratio of cement, mud, stone powder, early strength agent and viscosity increasing agent in the grouting slurry per cubic meter is 200:400:900:3:3 by weight.

6. The karst stratum reinforcing method according to claim 5, characterized by, In the step (4), after the grouting slurry is configured, the mix proportion of the grouting slurry is tested and verified, and the 28d compressive strength is not less than 0.2 MPa.

7. The karst stratum reinforcing method according to claim 5, characterized by, In the step (4), the early strength agent is Na2SiO3, and the viscosity increasing agent is soil stabilizer.

8. The karst stratum reinforcing method according to claim 1, characterized by, In the step (5), the design grouting pressure of the backward grouting is 0.8-1.0 MPa.

9. The karst stratum reinforcing method according to claim 1, characterized by, In the step (5), before the backward grouting, the grouting slurry is sent into the secondary stirring barrel and the modifier is added until it is stirred uniformly.

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