Karst cave hole excavation stability maintaining device and using method thereof

Abstract

The invention discloses a karst cave hole excavation stability maintaining device and a using method thereof.The karst cave hole excavation stability maintaining device comprises a steel casing inserted into a hole, the steel casing comprises a main casing on the outer layer and an elastic expansion set on the inner layer, and a first pressure sensor is installed at the top of the steel casing and used for monitoring the pressure of a slurry liquid column; due to the fact that a traditional steel pile casing is high in cost due to the fact that the traditional steel pile casing cannot be recycled, a permanent pile casing is blocked by stratum deformation after sinking, and the recycling rate is zero, an elastic expansion set is arranged, the inner layer of the elastic expansion set is made of high-water-absorption polyurethane coating fiber cloth, the volume of the elastic expansion set expands by 0.5-1.0 time after the elastic expansion set encounters water, and a temporary supporting layer with the compressive strength larger than or equal to 0.2 MPa is formed; the permanent supporting structure is formed by the concrete; the outer layer is hydrophobic polytetrafluoroethylene coating fiber cloth and forms a waterproof isolating membrane with the permeability coefficient of less than or equal to 1 * 10cm / s after meeting water, so that the stability of the hole wall is doubly guaranteed. After the main casing is pulled out, the elastic expansion group remains in the hole to replace the function, and the problem that a traditional steel casing is low in recovery rate is solved.

Description

Technical Field

[0001] The invention relates to a stabilization device for karst cave excavation and a use method thereof, belonging to the technical field of karst cave excavation. Background Art

[0002] The Cave Hole Excavation and Stabilization Device is a dynamic closed-loop control system designed specifically for pile foundation construction in complex strata in karst regions. It is suitable for pile foundation projects involving multi-layered interconnected caves, such as "gourd-shaped" caves, and in soft, easily collapsible strata, such as fluidized clay and plain fill, where precise control of the concrete filling coefficient is required.

[0003] During pile foundation construction in karst areas, the prevalence of multi-layer interconnected caves and plastically weak strata in the "gourd string" pattern leads to a sudden drop in slurry pressure during drilling. Traditional manual monitoring is slow to respond and cannot provide timely slurry replenishment, resulting in uncontrolled slurry leakage and hole wall collapse. At the same time, the unsealed cave channel allows the slurry to seep into the cracks during concrete pouring, and the impact pressure of the steel cage disturbs the hole wall, causing over-pouring of concrete and waste of materials. Furthermore, because traditional permanent steel casings lack a detachable support structure, they become stuck due to ground deformation after sinking, resulting in zero recovery rate and significantly increasing costs. In addition, the flow rate of the fixed conduit does not match the dynamic filling requirements of the cave. High-speed pouring expands the cracks, while low-speed pouring retains floating slurry, resulting in mud defects in the pile body, and eventually forming a vicious cycle of leakage → hole collapse → over-pouring → casing abandonment → pile body defects, which reduces construction efficiency.

[0004] Therefore, the purpose of this study is to design a technology that transforms from passive emergency response to active intervention, and to realize the solution of cave hole excavation and stabilization device and its use method for solving the problems of cave collapse, slurry leakage, and uncontrolled filling coefficient in complex cave areas. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a cave hole excavation and stabilization maintenance device and a method of using the same to solve the problems of the existing technology.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions: A stabilization device for cave excavation, comprising: a steel casing inserted into the hole, the steel casing comprising an outer main casing and an inner elastic expansion group, a first pressure sensor mounted on the top of the steel casing for monitoring the pressure of a mud column; The elastic expansion group includes an outer layer that fits the main casing and an inner layer near the middle. The inner layer expands when exposed to water to form a temporary support layer. When the main casing is pulled out, the elastic expansion group remains in the hole and forms a permanent support layer together with the concrete. The outer layer forms a waterproof isolation membrane when exposed to water. A plurality of spiral grouting pipes are distributed and embedded along the outer wall of the main casing, and the ends of the plurality of spiral grouting pipes are connected to an annular distribution component, through which the dual-liquid slurry is injected toward the outer wall of the main casing; A steel cage group is placed inside the main casing to reduce the impact pressure of concrete; The invention also includes a conduit inserted into the interior of the main casing, the conduit is externally connected to a concrete delivery pump, a flow regulating assembly is provided at the bottom of the conduit, the flow regulating assembly includes a second pressure sensor embedded in the exterior of the conduit, and a slurry isolation assembly is provided inside the conduit, the concrete pressure inside the main casing is monitored by the second pressure sensor, and the slurry is isolated by the slurry isolation assembly; The invention also includes a control module, the control module is electrically connected to the first pressure sensor, the grouting pump, the concrete delivery pump, and the second pressure sensor. When the first pressure sensor detects a sudden drop in the pressure of the mud liquid column, the control module cooperates with the grouting pump to inject dual-liquid slurry toward the outer wall of the main casing through the spiral grouting pipe and the annular distribution component; When the second pressure sensor detects that the fluctuation of concrete flow resistance is greater than a preset value, it switches to low-speed pouring mode; When the second pressure sensor detects that the concrete flow resistance is stable within the range of ±5% of the preset value, it switches to high-speed pouring mode.

[0007] As a further improvement, the inner layer is made of highly absorbent polyurethane coated fiber cloth, which expands 0.5 to 1.0 times in volume when exposed to water, forming a temporary support layer with a compressive strength of ≥0.2 MPa; The outer layer is made of hydrophobic polytetrafluoroethylene coated fiber cloth, which forms a permeability coefficient of ≤1×10⁻ after contacting water. 8 cm / s waterproof isolation membrane.

[0008] As a further improvement, the annular distribution assembly includes an annular flow channel arranged inside the steel casing, and a plurality of output ports embedded in the outer side of the steel casing, and the output ports are connected to the annular flow channel.

[0009] As a further improvement, the first pressure sensor is triggered when it detects a sudden drop in the mud liquid column pressure of >0.02MPa, the concrete flow resistance fluctuation is >10% of the preset value, the casting speed in the low-speed casting mode is 0.5~2.0m³ / min, and the casting speed in the high-speed casting mode is 4~6m³ / min.

[0010] As a further improvement, the slurry isolation assembly includes a plurality of one-way check valves integrally fixed inside the conduit, an elastic band connecting the plurality of one-way check valves, the ends of the one-way check valves being inclined toward the conduit outlet, and the plurality of one-way check valves being closed by the elastic band.

[0011] As a further improvement, a magnetic strip is embedded in the side edge of the end of the one-way check flap, and the positive and negative poles of the magnetic strips on the sides of adjacent one-way check flaps are opposite.

[0012] A method for using a stabilization device for cave excavation, comprising the following steps: S1: Use the total station to set out the pile position, and use the rotary drilling rig to drill through the bearing layer, with the rock embedment depth ≥ 0.5m; S2: Steel casing is sunk and installed. Vibratory hammer is used to sink the casing to the rock surface elevation in sections. The steel casing is sunk to a depth of 10m~17m, with the top 0.5m~1m above the ground. The elastic expansion layer is activated. S3: The first pressure sensor installed on the top of the main casing monitors the slurry column pressure in real time, and grouting is quickly performed on the periphery of the main casing in case of leakage. S4: The steel cage is placed inside the main casing and reinforced; S5: pouring concrete into the main casing through an external concrete pump connected to the conduit, and dynamically controlling the concrete flow rate through the second pressure sensor; S6: Start the vibratory hammer to pull out the main casing in sections before the concrete begins to set. Pull it out at a speed of ≤0.5m / min, and the elastic expansion layer will remain to replace the main casing.

[0013] As a further improvement, in step S2, the elastic expansion layer is activated specifically by: the volume of the inner layer expands by 0.5 to 1.0 times to form a temporary support layer with a compressive strength ≥ 0.2 MPa.

[0014] As a further improvement, in step S3, when a sudden pressure drop of >0.02MPa and a liquid level drop of ≥1m is detected, the grouting linkage is triggered to fill the cave cracks, and the dual-liquid slurry is automatically grouted. The control module links the grouting pump and injects cement-water glass dual-liquid slurry through the spiral grouting pipe, with an initial setting time of ≤30 seconds.

[0015] As a further improvement, in step S5, the flow resistance of the concrete is monitored by the second pressure sensor on the conduit, and the control module is linked to the concrete delivery pump. When the pressure fluctuation is greater than 10% of the preset value, it switches to a low-speed mode with a flow rate of 0.5-2.0 m³ / min. When the pressure stabilizes at the preset value ±5%, it switches to a high-speed mode with a flow rate of 4-6 m³ / min. The filling coefficient of the concrete is precisely controlled at 1.1-1.3. The slurry isolation component on the conduit utilizes the density difference to block the slurry with a density of 1.0-1.2 t / m³, and only allows concrete with a density of 2.4 t / m³ to pass through. The end of the one-way check valve is tilted, and the elastic belt and the magnetic strip are closed in coordination to prevent the slurry from entering the cave area.

[0016] The beneficial effects of the present invention are: Since traditional steel casings cannot be recycled, resulting in high costs, and permanent casings are stuck due to stratum deformation after sinking, with a recovery rate of zero, the present invention sets an elastic expansion group. The inner layer uses highly absorbent polyurethane coated fiber cloth, which expands 0.5 to 1.0 times in volume after contacting water, forming a temporary support layer with a compressive strength of ≥0.2MPa, which together with the concrete constitutes a permanent support structure; the outer layer is a hydrophobic polytetrafluoroethylene coated fiber cloth, which forms a permeability coefficient of ≤1×10⁻ after contacting water. 8 The waterproof isolation membrane with a speed of 100 cm / s provides double protection for the stability of the borehole wall. After the main casing is pulled out, the elastic expansion group remains in the hole to replace it, solving the problem of low recovery rate of traditional steel casing.

[0017] While the elastic expansion layer provides basic support, if the cave connectivity is poor or leakage occurs suddenly, the stability of the borehole wall still needs dynamic reinforcement. This is achieved by installing a spiral grouting assembly, with three spiral grouting pipes embedded in the outer wall of the main casing. The ends are connected to an annular distribution assembly, which evenly injects cement-water glass dual slurry through an annular flow channel and multiple outlets. When the first pressure sensor detects a sudden drop in the slurry column pressure greater than 0.02MPa, the control module activates the grouting pump to start grouting. The initial setting time is ≤30 seconds, and the cave is completely filled within 30 minutes, restoring the pressure to above 0.04MPa, quickly blocking the leakage channel.

[0018] During the concrete pouring phase, laitance can seep into cracks through incompletely sealed karst caves. Combined with the impact pressure disturbances from the reinforcement cage, this can lead to mud inclusion defects in the pile shaft. A laitance isolation assembly integrates a one-way check valve and a magnetic strip within the conduit. Elastic bands hold the check valves together, with the ends angled. This utilizes the density difference between concrete and laitance to allow only high-density concrete to pass through, preventing laitance from seeping into the karst caves and thus preventing mud inclusion defects in the pile shaft.

[0019] After the slurry is isolated, the concrete filling speed still needs to adapt to the changes in the connectivity of the cave to avoid secondary leakage or over-pouring caused by improper flow rate. A fixed flow rate cannot cope with the fluctuations in the cave filling resistance. High-speed pouring may destroy the closed cracks, and low-speed pouring reduces efficiency. By setting the pouring control component, the second pressure sensor monitors the concrete flow resistance in real time. When the fluctuation is greater than 10% of the preset value, it switches to low-speed mode to prevent high-speed pouring from expanding the cracks; when the pressure is stable within the range of ±5% of the preset value, it switches to high-speed mode to accurately control the filling coefficient at 1.1~1.3, reducing over-pouring and material waste.

[0020] The elastic expansion layer's water-expanding properties, combined with the waterproof membrane, create a dual physical and chemical barrier, replacing traditional permanent casing. After the main casing is vibrated and removed, the elastic expansion layer remains within the hole, providing permanent support. This increases the casing recovery rate to over 80% and reduces the cost per pile by approximately 35%.

[0021] A graded pouring strategy based on concrete flow resistance overcomes the bottleneck of a fixed flow rate that cannot adapt to the dynamic filling of karst caves. The low-speed mode prevents crack expansion, while the high-speed mode improves efficiency, raising the pile integrity pass rate to over 98%.

[0022] The outer side of the steel cage is covered with two layers of fine wire mesh and one layer of coarse wire mesh, and fixed with stirrups to effectively disperse the impact pressure, reduce the disturbance to the hole wall, and avoid the risk of hole collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 It is a schematic diagram of the three-dimensional structure of a karst cave hole excavation and stabilization device of the present invention.

[0025] Figure 2 yes Figure 1 A magnified schematic diagram of the structure in the middle.

[0026] Figure 3 yes Figure 1 Schematic diagram of the one-way check valve closed state structure at section B in the middle.

[0027] Figure 4 yes Figure 1 Schematic diagram of the structure of the one-way check valve in the fully open state in the cross section at point B.

[0028] Figure 5It is a schematic diagram of the top view of the structure of a karst cave hole excavation and stabilization device of the present invention.

[0029] Figure 6 This is a schematic diagram of the module connection of a karst cave hole excavation and stabilization device of the present invention.

[0030] Figure 7 This is a step diagram of a method for using a karst cave hole excavation and stabilization maintenance device according to the present invention.

[0031] 1. Hole; 2. Main casing; 3. Elastic expansion group; 31. Inner layer; 32. Outer layer; 4. First pressure sensor; 5. Spiral grouting pipe; 6. Annular flow channel; 61. Output port; 7. Rebar cage group; 71. Rebar cage body; 72. Fine wire mesh; 73. Coarse wire mesh; 8. Concrete pump; 9. Conduit; 91. Second pressure sensor; 92. One-way check valve; 93. Elastic band; 94. Magnetic strip; 10. Control module; 11. Grouting pump. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0034] Reference Figure 1-6 As shown, a stabilization device for excavating a karst cave 1 includes: A steel casing is inserted into the hole 1, and the steel casing includes an outer main casing 2 and an inner elastic expansion group 31. A first pressure sensor 4 is installed on the top of the steel casing to monitor the mud column pressure; the main casing 2 has a wall thickness of 10~12mm, a segment length of 9~17m, and a normal value of the mud column pressure is 0.02~0.05MPa.

[0035] The elastic expansion group 3 includes an outer layer 32 that fits the main casing 2 and an inner layer 31 near the middle. The inner layer 31 expands in water to form a temporary support layer. When the main casing 2 is pulled out, the elastic expansion group 3 remains in the hole and forms a permanent support layer together with the concrete. The outer layer 32 forms a waterproof isolation membrane when it comes into contact with water. Multiple spiral grouting pipes are embedded along the outer wall of the main casing 2, and the ends of the multiple spiral grouting pipes 5 are connected to the annular distribution assembly, and the double liquid slurry is injected toward the outer wall of the main casing 2 through the spiral grouting pipes 5; There are three spiral grouting pipes 5, and the spacing between the spiral grouting pipes 5 is 120 degrees. The double liquid slurry is a mixed liquid composed of cement and water glass, and its initial setting time is ≤30 seconds.

[0036] Double-liquid slurry ratio, cement slurry A liquid ratio, ordinary Portland cement P.O42.5 or P.O52.5, or sulphoaluminate cement is suitable for low temperature or ultra-early strength requirements.

[0037] Water-cement ratio W / C0.6~1.0 Low water-cement ratio improves early strength, while high water-cement ratio enhances permeability.

[0038] Additives include accelerators, triethanolamine 0.05%-0.1% or sodium aluminate 1%-3%, which shorten the initial setting time to 10-30 seconds. Thickeners, bentonite 2%-5% or carboxymethyl cellulose (CMC), 0.1%-0.5%, improve slurry stability.

[0039] The proportion of water glass solution B is as follows: modulus M: 2.4~3.0. The higher the modulus, the faster the coagulation speed and the higher the strength. Concentration Be′: 30°~45° Baume. High concentration enhances gelation, and low concentration prolongs the injectability time. pH adjustment: a small amount of phosphoric acid H3PO4 or sulfuric acid H2SO4 is used to adjust the pH to 8~10 to avoid premature reaction.

[0040] The volume ratio of A / B liquid is: 1:0.5~1:1. Liquid A is the main agent and liquid B is the coagulant.

[0041] Rapid plugging type cave has strong connectivity and serious slurry leakage ratio: Liquid A: P.O52.5 cement + W / C=0.6 + triethanolamine 0.1%, Liquid B: Water glass modulus 3.0 + concentration 40°Be′ + pH=9, A / B=1:0.8, performance initial setting time ≤15 seconds, final setting time ≤60 seconds, 28-day compressive strength ≥15MPa, permeability coefficient ≈5×10⁻ 6 cm / s.

[0042] The cracks of the penetration reinforcement type are small and need to be filled densely. The ratio is: Liquid A: sulphoaluminate cement + W / C=0.8 + bentonite 3%, Liquid B: water glass modulus 2.6 + concentration 35°Be′ + CMC0.2%, A / B=1:1, the performance is initial setting time ≈30 seconds, final setting time ≈90 seconds, 28-day compressive strength ≈10MPa, permeability coefficient ≈1×10⁻ 7 cm / s is close to the clay layer.

[0043] Low-temperature adaptable formation temperature <10℃ mix ratio: Liquid A: P.O42.5 cement + W / C=0.7 + sodium aluminate 2%, Liquid B: water glass modulus 2.4 + concentration 30°Be′ + phosphoric acid to adjust pH=8, A / B=1:0.6, initial setting time ≤45 seconds at -5℃ environment, 28-day compressive strength ≈8MPa, no significant attenuation at low temperature.

[0044] According to the characteristics of cave development: Large cave diameter > 1m: Use low-viscosity slurry W / C = 1.0 + water glass concentration 30°Be′ to improve permeability.

[0045] Micro crack width <1mm: high modulus water glass M=3.0 + low water-cement ratio W / C=0.6, enhance the cementitious filling capacity.

[0046] According to groundwater activity, in a strong seepage environment, the ratio of accelerator can be increased, for example, sodium aluminate can be increased to 5%, which can shorten the setting time to within 10 seconds.

[0047] In a static water environment, the water glass concentration is reduced to 30°Be′ and the injectability time is extended to more than 60 seconds.

[0048] According to the construction response, when the pressure drops sharply by more than 0.02MPa, switch to the rapid plugging type with a ratio of A / B = 1:0.8, and restore the liquid column pressure to above 0.04MPa within 30 minutes.

[0049] During the concrete pouring stage, a penetration reinforcement mix is used to prevent slurry from invading the pile body and causing mud inclusion defects.

[0050] A steel cage group 7 is placed inside the main casing 2 to reduce the concrete impact pressure. The steel cage group 7 includes a steel cage body 71 and two layers of fine wire mesh 72 and one layer of coarse wire mesh 73 wrapped around the outside of the steel cage body 71, which are fixedly connected by stirrups; The system also includes a conduit 9 inserted within the main casing 2, connected to a concrete pump 8. A flow control assembly is located at the bottom of the conduit 9. The flow control assembly includes a second pressure sensor 91 embedded in the outside of the conduit 9 and a slurry isolation assembly located within the conduit 9. The second pressure sensor 91 is used to monitor the concrete pressure within the main casing 2, and the slurry isolation assembly is used to isolate the slurry. The conduit 9 has an inner diameter of 200mm-250mm, and the bottom of the conduit 9 is 0.5m-1m from the bottom of the hole. The slurry isolation assembly includes several one-way check valves 92 integrally fixed to the interior of the conduit 9, and an elastic band 93 connecting the multiple one-way check valves 92. The ends of the one-way check valves 92 are tilted toward the outlet of the conduit 9, and the multiple one-way check valves 92 are closed by the elastic band 93. The slurry isolation assembly prevents slurry with a density of 1.0 to 1.2 t / m³ from entering the cave area.

[0051] It also includes a control module 10, which is electrically connected to the first pressure sensor 4, the grouting pump 11, the concrete pump 8, and the second pressure sensor 91. When the first pressure sensor 4 detects a sudden drop in the pressure of the mud liquid column, the control module 10 cooperates with the grouting pump 11 to inject double liquid slurry toward the outer wall of the main casing 2 through the spiral grouting pipe 5; wherein, the first pressure sensor 4 is triggered when it detects a sudden drop in the pressure of the mud liquid column >0.02MPa.

[0052] When the second pressure sensor 91 detects that the fluctuation of the concrete flow resistance is greater than a preset value, it switches to the low-speed pouring mode; When the second pressure sensor 91 detects that the concrete flow resistance is stable within the range of ±5% of the preset value, the high-speed pouring mode is switched.

[0053] By setting the elastic expansion group 3, its inner layer 31 is made of highly absorbent polyurethane coated fiber cloth, which expands 0.5 to 1.0 times in volume after contacting water, forming a temporary support layer with a compressive strength of ≥ 0.2 MPa, which together with the concrete constitutes a permanent support structure; the outer layer 32 is a hydrophobic polytetrafluoroethylene coated fiber cloth, which forms a permeability coefficient of ≤ 1×10⁻ after contacting water. 8 The waterproof isolation membrane with a speed of 1000 cm / s provides double protection for the stability of the borehole wall. After the main casing 2 is pulled out, the elastic expansion group 3 remains in the hole to replace it, solving the problem of low recovery rate of traditional steel casing.

[0054] By installing a spiral grouting assembly, three spiral grouting pipes 5 are embedded in the outer wall of the main casing 2, with the ends connected to an annular distribution assembly. Cement-water glass dual slurry is evenly injected through an annular flow channel 6 and multiple output ports 61. When the first pressure sensor 4 detects a sudden drop in the slurry column pressure greater than 0.02 MPa, the control module 10 activates the grouting pump 11 to start grouting. The initial setting time is ≤ 30 seconds, and the cave is completely filled within 30 minutes, restoring the pressure to above 0.04 MPa, quickly blocking the leakage channel.

[0055] The slurry isolation assembly integrates a one-way check valve 92 and a magnetic strip 94 within the conduit 9. Elastic bands 93 close the check valves, with the ends angled. This utilizes the density difference between concrete and slurry to allow only high-density concrete to pass through, preventing slurry from seeping into the karst cave and preventing mud inclusion defects in the pile body.

[0056] By setting the pouring control component to monitor the concrete flow resistance in real time at the second pressure sensor 91, when the fluctuation is greater than 10% of the preset value, it switches to the low-speed mode of 0.5~2.0m³ / min to prevent high-speed pouring from expanding cracks; when the pressure is stable within the range of ±5% of the preset value, it switches to the high-speed mode of 4~6m³ / min, and accurately controls the filling coefficient at 1.1~1.3 to reduce over-pouring and material waste.

[0057] The water-expanding properties of the elastic expansion group 3, combined with the waterproof membrane, create a dual physical and chemical barrier, replacing traditional permanent casing. After the main casing 2 is vibrated and pulled out, the elastic expansion layer remains in the hole, forming a permanent support. This increases the casing recovery rate to over 80%, reducing the cost per pile by approximately 35%.

[0058] A graded pouring strategy based on concrete flow resistance overcomes the bottleneck of a fixed flow rate that cannot adapt to the dynamic filling of karst caves. The low-speed mode prevents crack expansion, while the high-speed mode improves efficiency, raising the pile integrity pass rate to over 98%.

[0059] The outer side of the steel cage is covered with two layers of fine wire mesh 72 and one layer of coarse wire mesh 73 and fixed with stirrups to effectively disperse the impact pressure, reduce the disturbance to the hole wall, and avoid the risk of hole collapse.

[0060] Among them, the fluctuation of the concrete flow resistance is >10% of the preset value, the pouring speed in the low-speed pouring mode is 0.5~2.0m³ / min, and the pouring speed in the high-speed pouring mode is 4~6m³ / min.

[0061] The diameter of the main casing 2 is 20mm-30mm larger than the designed pile diameter, the wall thickness of the main casing 2 is 10mm-15mm, and the segment length of the main casing 2 is 9m-15m.

[0062] The low-speed pouring mode is triggered when the second pressure sensor 91 detects a fluctuation in concrete flow resistance greater than 10% of a preset value, indicating possible crack expansion, sudden changes in the filling path, or localized resistance instability in the cavernous area. Using a low-speed pouring method reduces the kinetic energy of the concrete impacting the hole wall, preventing high-speed flow from exacerbating crack expansion and allowing the spiral grouting system more time to fill the cavernous channel.

[0063] Low-speed pouring reduces the shearing effect of concrete on the cave wall and reduces the risk of secondary leakage. The slowly injected concrete can fully penetrate the small cracks in the cave, reduce residual voids, ensure filling density, and provide a time window for rapid filling within 30 seconds for the dual-liquid grouting system. The initial setting time is ≤30 seconds, forming a double wall barrier.

[0064] The trigger condition for the high-speed pouring mode is 4~6m³ / min. When the second pressure sensor 91 detects that the concrete flow resistance is stable within the range of ±5% of the preset value, it indicates that the cave filling path has stabilized. At this time, switching to the high-speed mode can accelerate concrete filling and shorten the construction period.

[0065] High-speed pouring reduces the risk of concrete segregation, ensuring the density of the pile body while shortening construction time. The single pile cycle is shortened by 33%. By dynamically adjusting the flow rate, the filling coefficient is controlled within the range of 1.1-1.3. The traditional process often reaches 1.5-2.0, reducing concrete waste by about 20%. The high-speed flow reduces the residence time of the slurry in the conduit 9. Combined with the slurry isolation component, the pile body integrity qualification rate is improved to more than 98%.

[0066] In this embodiment, the diameter of the main casing 2 is 20-30 mm larger than the designed pile diameter. By reserving an annular gap of 20-30 mm, the error caused by drilling deviation or local hole expansion can be compensated to ensure that the casing sinks smoothly to the designed depth. The gap provides a uniform annular flow channel for concrete to avoid leakage caused by pressure concentration due to local narrowing. The outer layer 32 waterproof membrane and the inner layer 31 support layer expand by 0.5-1.0 times in volume after being exposed to water, which can fill the gap and form a tightly fitting permanent support structure.

[0067] The risk of casing sinking and getting stuck is reduced. When the diameter of traditional casing is the same as the pile diameter, it is easy to get stuck due to uneven strata. The thickness of the concrete protective layer is guaranteed and the durability of the pile body is improved.

[0068] The wall thickness must meet the requirements for compressive and bending resistance during vibratory hammering. A thickness of 10-15mm can withstand the lateral extrusion forces of complex karst formations, such as the creep deformation of fluid-plastic clay. Casings that are too thin (less than 10mm) are prone to instability and buckling during the sinking process, while those that are too thick (greater than 15mm) increase extraction resistance and drive up costs.

[0069] It is necessary to ensure that the casing is not easily deformed when it is pulled out by vibration, and the recovery rate is increased to more than 80% compared to 0% with the traditional process. The weight of the casing per unit length is reduced by 10~15mm wall thickness, corresponding to about 78~117kg per meter, which is convenient for on-site transportation and installation.

[0070] The length of the main casing 2 segments is 9~15m. The segment length needs to match the drilling depth of the rotary drilling rig, which is generally ≤30m, and the exciting force range of the vibratory hammer. A single segment of casing that is too long may easily lead to excessive bottom settlement resistance. The segment length must match the groundwater infiltration path to ensure that the water-expandable material fully absorbs water and expands within 30 minutes. An overly long segment may result in incomplete activation of the bottom material.

[0071] The construction difficulty is reduced by segmented welding to adapt to the different depths of cave development. For example, 9m short sections are used in shallow cave-dense areas, and 15m long sections are used in deep stable areas. The casing can be pulled out in sections before the concrete begins to set.

[0072] A dynamic wall protection system is formed through the synergistic effect of the diameter of the main casing 2 and the elastic expansion layer. Combined with the grouting response, it is activated when the pressure drops suddenly by more than 0.02MPa. The leakage out-of-control rate is reduced from 35%-45% of the traditional process to ≤5%.

[0073] This method increases the casing recovery rate to 80%, reduces the cost of a single pile steel casing by approximately 35%, improves filling coefficient control accuracy by 33%, and reduces concrete waste by approximately 20%. The dynamic pouring mode shortens the construction period for a single pile from 8-10 days to 5-6 days, while also increasing the pile integrity qualification rate to over 98%.

[0074] The flexible combination of diameter, wall thickness and segment length can adapt to different karst development levels, such as the connectivity differences of "gourd-string" caves, ensuring construction stability under complex geological conditions.

[0075] To replace the recyclable support layer of the traditional steel casing, the inner layer 31 is made of highly absorbent polyurethane coated fiber cloth, which expands 0.5 to 1.0 times in volume when exposed to water, forming a temporary support layer with a compressive strength of ≥0.2 MPa; The outer layer 32 is made of hydrophobic polytetrafluoroethylene coated fiber cloth, which forms a permeability coefficient of ≤1×10⁻ when exposed to water. 8 cm / s waterproof isolation membrane.

[0076] Because traditional steel casings become stuck due to ground deformation after sinking and cannot be recovered, resulting in high costs, a highly absorbent polyurethane-coated fiber cloth is used as the inner layer 31. When exposed to water, its volume expands by 0.5 to 1.0 times, forming a temporary support layer with a compressive strength of ≥0.2 MPa, replacing the function of the steel casing.

[0077] After the main casing 2 is removed, the expansion layer remains in the hole and forms a permanent support together with the concrete, increasing the casing recovery rate to over 80% and reducing the cost of each pile by approximately 35%. The expansion process fills the irregular spaces in the cave, adapting to the complex "gourd-shaped" multi-layer cave structure and preventing local stress concentration that can cause cave collapse.

[0078] If the water absorption expansion ratio is too low (less than 0.5 times), it will not be able to fully fill the gaps in the cavities and the support effect will be insufficient. If it is too high (greater than 1.0 times), it may hinder the flow of concrete.

[0079] The hole wall stability requirements during the drilling stage must be met. The lateral water and soil pressure in the karst area is usually less than 0.15 MPa. At the same time, excessive hardening must be avoided to affect the interface bonding during subsequent concrete pouring.

[0080] The outer layer of 32 hydrophobic polytetrafluoroethylene (PTFE) coated fiber cloth can quickly stop water. The hydrophobic contact angle of the PTFE coating is greater than 150°, which can instantly repel water and has long-term stability. The permeability coefficient is ≤1×10⁻ 8 cm / s is close to the anti-seepage performance of natural clay layers. After the concrete is poured, it can continuously block the intrusion of groundwater. In conjunction with the expansion process of the inner layer 31 polyurethane, the waterproof membrane fits tightly to the hole wall during the expansion process, forming a physical-chemical double barrier.

[0081] The CF bond of the PTFE molecular chain has a weak polarity and a low surface energy of ≈18.5mN / m, making it difficult for water molecules to penetrate, forming a stable waterproof layer. The permeability coefficient is ≤1×10⁻ 8 cm / s is much lower than 1×10⁻ of traditional clay retaining wall 5 cm / s, improving anti-seepage performance by three orders of magnitude. The PTFE coating is acid and alkali resistant with a pH range of 3 to 11, and is heat resistant with a long-term operating temperature of ≤260°C, making it suitable for the corrosive environment of groundwater in karst areas.

[0082] The polyurethane in the inner layer 31 of the support layer expands to form a compression-resistant skeleton to resist the lateral pressure of the formation in the cave area and prevent cave collapse.

[0083] The outer layer of the waterproof layer is coated with 32PTFE to isolate mud and groundwater.

[0084] The expansion process drives the waterproof layer to fit tightly against the hole wall, forming a "rigid and flexible" composite wall protection structure, which improves stability by more than 50% compared with a single material solution.

[0085] The inner 31 expansion layer provides temporary bearing capacity before the concrete initially sets, and subsequently forms a permanent support structure with the concrete, eliminating the vacuum period after traditional casing removal. The outer 32 PTFE coating maintains its impermeability even after the concrete hardens, preventing groundwater from eroding the pile shaft and extending the life of the structure.

[0086] The annular distribution assembly includes an annular flow channel 6 arranged inside the steel casing, and a plurality of output ports 61 embedded on the outer side of the steel casing, and the output ports 61 are connected to the annular flow channel 6.

[0087] Due to the strong connectivity of the "gourd-string" multi-layer caves in the karst area, traditional single-point grouting can easily lead to local concentration of slurry, such as only filling the caves near the casing side, and the distal cracks cannot be effectively sealed, and the risk of leakage continues to exist.

[0088] The annular distribution assembly is designed with an annular flow channel 6 and multiple output ports 61 to evenly deliver the dual-liquid slurry to the entire circumferential area of the outer wall of the casing, ensuring that the slurry covers the entire cave communication network.

[0089] When the first pressure sensor 4 detects a sudden drop in the slurry column pressure greater than 0.02 MPa, the grouting pump 11 must be started within 30 seconds and the filling and pressure restoration must be completed within 30 minutes. The annular distribution assembly must be capable of rapid and high-flow slurry distribution.

[0090] The annular flow channel 6 serves as the main slurry delivery channel, with a cross-sectional area ≥500mm², equivalent to a 25mm diameter steel pipe, and is equipped with 6 to 12 output ports 61 with a spacing of 15° to 30°, ensuring a slurry delivery volume of ≥0.5m³ / min per unit time, meeting the rapid filling requirements.

[0091] The main casing 2 has a wall thickness of 10-15mm, requiring the integration of grouting channels within a limited space. The annular flow channel 6 is embedded with a depth of 3-5mm. The outlet 61 is spirally distributed along the outer wall of the casing to match the spiral grouting pipe 5, avoiding additional space occupied by the pile diameter.

[0092] The uniform slurry pressure distribution within the annular flow channel 6, with a pressure differential of ≤0.01 MPa, combined with 616 to 12 equally spaced outlets, ensures that the grouting volume deviation in all directions is less than 5%. Field tests have shown that after grouting with the annular distribution component, the cave filling density reaches over 95%, while traditional single-point grouting only achieves 70% to 80%, and the recurrence rate of grout leakage is reduced by 80%.

[0093] The spacing between the output ports 61 is designed to be 2 to 3 times the average crack width of the cave. For example, if the crack width is 0.5 m, the spacing between the output ports 61 is 1 to 1.5 m to ensure that the slurry can penetrate to the end of the expanded crack.

[0094] The inner diameter of the output port 61 is 8~10mm, matching the dual-liquid slurry particle size ≤0.5mm. The inlet diameter of the annular flow channel 6 gradually decreases from 25mm to 15mm, increasing the slurry flow rate to 1.5~2.0m / s and reducing the risk of sedimentation and blockage.

[0095] The ring-shaped distribution assembly shortens grouting time from 1-2 hours in traditional processes to less than 30 minutes, restoring slurry pressure to above 0.04 MPa. Uniform grouting reduces slurry waste by approximately 30%, while traditional processes require additional filling of ineffective areas.

[0096] In addition, the anti-corrosion coating at the outlet 61, such as epoxy ceramic, has a service life of ≥5 years as the casing, thereby avoiding casing loss caused by frequent maintenance.

[0097] When the annular distribution component is grouting, the double-liquid slurry penetrates into the pores of the inner layer 31 highly absorbent polyurethane expansion layer with a porosity of 5% to 8%, forming a composite wall protection structure of grouting reinforcement combined with expansion support, and the compressive strength is increased to more than 0.3 MPa.

[0098] The control module 10 triggers the grouting pump 11 according to the sudden drop of the signal of the first pressure sensor 4 >0.02MPa. The annular distribution component realizes full circumferential grouting within 10 seconds, and the response speed is more than 10 times higher than that of traditional manual operation.

[0099] After grouting is completed, when the main casing 2 is vibrated and pulled out, the compressive strength of the solidified body formed by the residual slurry in the annular flow channel 6 and the output port 61 is ≥0.5 MPa and can be used as part of the permanent support structure without the need for secondary treatment.

[0100] The design of the annular flow channel 6 and multiple outlets 61 enables the transition from point-based grouting to "full-circumferential dynamic sealing," reducing the uncontrolled leakage rate from 35%-45% to ≤5%. Grouting efficiency increased by 100%, material costs decreased by 30%, and the single pile construction period was shortened by 33%. This system, in conjunction with the elastic expansion layer, intelligent control module 10, and recyclable casing technology, creates an active protection system for pile foundation construction in karst areas, resolving the pain point of uneven grouting in traditional methods.

[0101] The first pressure sensor 4 is triggered when it detects a sudden drop in the mud liquid column pressure of >0.02MPa, the concrete flow resistance fluctuation is >10% of the preset value, the pouring speed in the low-speed pouring mode is 0.5~2.0m³ / min, and the pouring speed in the high-speed pouring mode is 4~6m³ / min.

[0102] Due to the strong connectivity of multi-layered, "gourd-shaped" caves in karst areas, sudden drops in mud column pressure are often triggered by the sudden opening of cave channels or localized cave collapse. A 0.02 MPa pressure drop corresponds to a drop in the liquid level of approximately 1 meter. The head pressure formula is: ΔP = ρgh, where ρ = 1.2 tons / m³ of mud. Rapid intervention is required to prevent uncontrolled leakage.

[0103] If the threshold is set too low (<0.02MPa), grouting may be falsely triggered due to mud pump shutdown or liquid level fluctuations, resulting in slurry waste. If it is too high (>0.02MPa), it may cause excessive slurry leakage. Grouting may not be initiated until the liquid level drops by more than 1m, which may cause the hole wall to become unstable or even collapse.

[0104] Field tests have shown that the 0.02MPa threshold can ensure that grouting can be started when the liquid level drops by 0.5~1m at the initial stage of leakage, and the pressure can be restored to above 0.04MPa within 30 minutes, reducing the leakage rate by 90%.

[0105] It takes 5 to 8 seconds from the detection of the pressure drop by the control module 10 to the start of the grouting pump 11, and the initial setting time of the double-liquid slurry is ≤30 seconds, ensuring that the slurry is filled before the leakage channel completely fails.

[0106] The spacing between the output ports 61 of the annular distribution component is 15°~30°, and the rapid grouting triggered by 0.02MPa is used to make the slurry cover the entire circumferential cave area, with a filling density of more than 95%.

[0107] The 10% fluctuation in concrete flow resistance triggers the switching of pouring modes, which is a dynamic adaptability requirement for cave filling.

[0108] When the stable state is ±5%, the cave connectivity is good, the concrete flow resistance is uniform, and it is suitable for high-speed pouring to improve efficiency.

[0109] Severe fluctuations > 10% may be caused by expansion of cave fissures, local blockage or slurry accumulation, leading to sudden changes in resistance. It is necessary to switch to low-speed mode to prevent the expansion of fissures.

[0110] If the threshold is set too low (less than 10%), frequent switching of pouring modes (e.g., switching every 10 minutes) will reduce efficiency. If it is too high (greater than 10%), the early intervention window for crack expansion may be missed, leading to the risk of grout leakage.

[0111] The pouring speed range is 0.5-2.0 m³ / min at low speed. This reduces the impact force on concrete and prevents high-speed flow from exacerbating crack expansion. The relationship between flow velocity and shear stress is: τ = μ·dv / dr. Low speeds reduce τ. During the initial stages of cave filling or when resistance fluctuations exceed 10%, ensure that the slurry penetrates even small cracks.

[0112] High-speed mode: 4~6m³ / min, shortening the filling time before the initial setting of concrete and reducing the risk of slurry retention. The slurry residence time under high-speed flow is less than 10 seconds. When the resistance is stable, the filling coefficient is precisely controlled at 1.1~1.3, while the traditional process is 1.5~2.0, reducing concrete waste by about 20%.

[0113] By controlling the flow rate through resistance feedback, the mud inclusion defect rate in the pile body is reduced from 15% in the traditional process to below 2%. The single pile casting time in high-speed mode is shortened by 40% from 2 hours to 1.2 hours.

[0114] A closed-loop system for preventing and controlling grouting: pressure-triggered grouting at 0.02 MPa, followed by low-speed pouring at 0.5-2.0 m³ / min, effectively seals the initial leak and simultaneously prevents secondary disturbances. A high-speed, 4-6 m³ / min, control system with stable resistance is used to accelerate filling after grouting is completed, shortening the high-risk window.

[0115] Through the precise triggering mechanism, 0.02MPa pressure drop threshold and 10% resistance fluctuation threshold, the timeliness and effectiveness of leakage prevention and control and pouring regulation are ensured.

[0116] Dynamic speed matching, switching between low-speed 0.5~2.0m³ / min and high-speed 4~6m³ / min casting modes, taking into account both crack sealing safety and construction efficiency.

[0117] Through systematic coordination of grouting triggering, pouring control, and deep coupling of casing structure and material properties, an active protection system for pile foundation construction in karst areas was constructed, achieving a technological breakthrough of less than 5% leakage rate, 80% casing recovery rate, and 35% cost reduction.

[0118] The slurry isolation assembly includes a plurality of one-way check flaps 92 integrally fixed inside the conduit 9, an elastic band 93 connecting the plurality of one-way check flaps 92, and the ends of the one-way check flaps 92 are inclined toward the outlet direction of the conduit 9, and the plurality of one-way check flaps 92 are closed by the elastic band 93.

[0119] The end side of the one-way check flap 92 is embedded with a magnetic strip 94 , and the positive and negative poles of the magnetic strips 94 on the adjacent sides of the one-way check flap 92 are opposite.

[0120] The one-way check valve 92 and the elastic band 93 of the slurry isolation assembly selectively isolate the slurry through density.

[0121] The material of the one-way check valve 92 is required to have sufficient elasticity to enable the valve to open and close (elastic modulus ≈ 10~50MPa), while maintaining structural rigidity to resist the impact of concrete flow (flexural strength ≥ 50MPa).

[0122] Permeability coefficient in closed state ≤1×10⁻ 6 cm / s, preventing micro-leakage of slurry. Withstands long-term erosion by concrete coarse aggregate (particle size ≤ 31.5mm), with a wear rate of <0.1mm / 10,000 cycles.

[0123] Adaptable to karst groundwater (pH 4-9) and alkaline concrete environments (pH 12-13), with a material weight loss rate of less than 2% per year. It can withstand long-term exposure to mud, vibration, and temperature fluctuations (-10°C to 60°C), with a service life of ≥5 years.

[0124] Preferred composite structure of hydrogenated nitrile rubber (HNBR) and polyurethane coating The base material is made of HNBR, which provides high elasticity (tensile strength ≥30MPa, elongation at break ≥250%), ensuring rapid opening and closing of the valve (response time <1 second).

[0125] The coating uses polyurethane (polyether type) alkali-resistant coating with a thickness of 0.2~0.5mm to improve wear resistance (Taber abrasion <50mg / 1000 times) and block chemical corrosion.

[0126] The side magnetic strip 94 adopts an embedded packaging process, and the interface peel strength between HNBR and the magnetic strip 94 is ≥8kN / m.

[0127] Due to the significant density difference between concrete (2.4 t / m³) and laitance (1.0-1.2 t / m³), the one-way check valve 92 is tilted at its end, leveraging the kinetic energy of the concrete flow to push the valve open. However, the laitance, due to its low density and insufficient kinetic energy, is unable to drive the valve open. The elastic band 93 holds the valve closed, preventing the laitance from passing through.

[0128] Requiring no external energy source, the system relies on physical properties to achieve automatic isolation, reducing system complexity. Only high-density concrete is allowed to pass through, with a slurry retention rate of >95%, preventing slurry from seeping into cavities and causing mud defects in the pile body.

[0129] The elastic band 93 provides a basic closing force pre-tightening force of ≈5~10N, ensuring that the valve fits tightly in a no-flow state and preventing micro-leakage of slurry.

[0130] When concrete flows, the valve is opened by pressure, and the elastic band 93 is stretched to store energy; after the flow stops, the valve quickly resets and closes, with a response time of less than 1 second.

[0131] The magnetic strip 94 is used to enhance the sealing performance of the closure, thereby overcoming the risk of failure of the traditional valve seal. Since the traditional check valve relies on mechanical contact sealing, it is easy to cause leakage in the gap due to wear and deviation during vibration, pressure fluctuation or long-term use.

[0132] By embedding magnetic strips 94 with opposite polarities, such as N poles and S poles arranged alternately on the sides of adjacent check flaps, the closure and sealing performance are enhanced by magnetic attraction.

[0133] The magnetic strip 94 provides an additional closing force of ≈20~30N, which increases the valve contact surface pressure by more than 3 times, and the permeability coefficient is ≤1×10⁻ 6 cm / s.

[0134] In particular, magnetic force automatically corrects valve position, compensating for deformation caused by construction vibration or catheter 9 deflection, ensuring a stable seal. The magnetic strip 94 is made of corrosion-resistant NdFeB material with a magnetic energy product of ≥40 MGOe, a service life of >5 years, and is maintenance-free.

[0135] By having magnetic strips 94 on adjacent valves with opposite polarity (e.g., NSN on valve A and SNS on valve B), a multi-point magnetic circuit is created, maximizing the magnetic attraction. The strips are embedded within the valves to prevent concrete particles from attaching and affecting the magnetic force. They are also coated with an epoxy resin anti-corrosion layer.

[0136] With a slurry isolation rate exceeding 95%, the pile integrity qualification rate has increased from 85% with traditional processes to over 98%. By preventing slurry leakage, the filling coefficient is precisely controlled at 1.1-1.3, compared to 1.5-2.0 with traditional processes, reducing concrete waste by approximately 20%.

[0137] In conjunction with dynamic pouring control, the slurry isolation assembly in low-speed mode is coordinated with a flow rate of 0.5-2.0 m³ / min to ensure that the slurry retention time is less than 10 seconds, thereby reducing the risk of deposition in conduit 9.

[0138] In high-speed mode, at a flow rate of 4 to 6 m³ / min, the magnetic strip 94 provides additional sealing force to avoid valve resonance failure caused by high-speed flow.

[0139] A method for using a stabilization device for excavating a karst cave hole 1, comprising the following steps: S1: Use a total station to stake out the pile position according to the designed pile diameter; in this embodiment, the pile diameter can be 800mm, 900mm, 1000mm, etc.

[0140] Use a rotary drilling rig to drill to a depth of 12m, penetrating the plain fill and fluid plastic silty clay layers; The drill bit is switched to an alloy eccentric drill bit, and the drill is continued to penetrate the rock stratum to the bearing layer, with the rock embedded depth ≥ 0.5m; The high torque characteristics of the rotary drilling rig are used to quickly drill holes and reduce the risk of hole collapse.

[0141] S2: Steel casing is sunk and installed by using a vibrating hammer to sink the casing to the rock surface elevation in sections. The steel casing is sunk to a depth of 10m~17m, and the top is 0.5m~1m above the ground. Preventing collapse by isolating unstable formations such as fluid plastic silty clay.

[0142] The wall thickness of the main casing 2 is 12mm, and the length of each section is 9~17m, which is welded layer by layer. The outer diameter is equal to the pile diameter + 100~150mm. For example, if the pile has a diameter of 800mm, a casing with an outer diameter of 924mm is used. S21, the elastic expansion layer is activated, and the volume of the inner layer 31 expands by 0.5 to 1.0 times, forming a temporary support layer with a compressive strength ≥ 0.2 MPa; S3: The first pressure sensor 4 installed on the top of the main casing 2 monitors the slurry column pressure in real time, and grouting is quickly performed on the periphery of the main casing 2 in case of slurry leakage; S31, when a sudden pressure drop of >0.02MPa and a liquid level drop of ≥1m are detected, grouting linkage is triggered to fill the cave cracks; S32, automatic grouting of dual-liquid slurry, the control module 10 links the grouting pump 11, and injects cement-water glass dual-liquid slurry through the spiral grouting pipe 5, with an initial setting time of ≤30 seconds; The cave area is evenly filled through the multiple output ports 61 of the annular distribution component, the cave filling is completed within 30 minutes, and the mud pressure rises back to above 0.04 MPa.

[0143] S4: The steel cage is placed inside the main casing 2 and reinforced; S41, reinforcement cage fabrication, main reinforcement is welded or mechanically connected; The outside is covered with two layers of fine wire mesh 720.5mm×6.3mm×6.3mm combined with one layer of coarse wire mesh 731.3mm×30mm×30mm, and additional φ8 150mm stirrups are added for encryption and fixation. The steel cage is used to reduce the impact pressure of concrete and improve the integrity of the pile body.

[0144] S42, steel cage installation, lifting by crane in sections, simultaneous installation of acoustic testing pipe, verticality deviation ≤1%; The bottom of the steel cage is 0.5m away from the bottom of the hole, and the thickness of the main reinforcement protection layer is 50mm. The acoustic detection tube is used to ensure the accurate position of the steel cage to avoid floating cage.

[0145] S5: pouring concrete into the main casing 2 through the external concrete pump 8 connected to the conduit 9; The bottom of the conduit 9 is 0.5m away from the bottom of the hole, the burial depth is controlled within the range of 2-6m, and the inner diameter of the conduit 9 is 250mm; S51, dynamic flow rate control, monitoring the concrete flow resistance through the second pressure sensor 91 on the conduit 9, the control module 10 links the concrete pump 8, and when the pressure fluctuation is greater than 10% of the preset value, switches to a low-speed mode with a flow rate of 0.5-2.0 m³ / min; When the pressure stabilizes at ±5% of the preset value: switch to high-speed mode with a flow rate of 4~6m³ / min.

[0146] Accurately control the filling coefficient of concrete between 1.1 and 1.3 to reduce concrete waste.

[0147] S52, using the density difference of the laitance isolation assembly on the conduit 9 to block the laitance with a density of 1.0-1.2 t / m³, and only allowing the concrete with a density of 2.4 t / m³ to pass through; By tilting the end of the one-way check valve 92, the elastic band 93 and the magnetic strip 94 are closed in coordination to prevent the floating slurry from entering the cave area, thereby ensuring the quality of the pile top.

[0148] S6: Start the vibratory hammer to pull out the main casing 2 in sections before the concrete begins to set. Pull it out at a speed of ≤0.5m / min to prevent the concrete on the pile top from sinking.

[0149] Specifically, it is within 0.5 to 1 hour after concrete pouring.

[0150] The casing recovery rate can reach ≥80%. At the same time, the outer layer 32 of the residual elastic expansion group 3 forms a composite support layer with the inner layer 31 and concrete. After the steel casing is pulled out, the outer layer 32 forms a permeability coefficient of ≤1×10⁻ 8 cm / s waterproof isolation membrane.

[0151] The elastic expansion group 3 is composed of an inner layer 31 of highly absorbent polyurethane coated fiber cloth and an outer layer 32 of hydrophobic polytetrafluoroethylene coated fiber cloth. The inner layer 31 swells when exposed to water, and the outer layer 32 forms a waterproof isolation membrane. The elastic expansion group 3 replaces the traditional permanent steel casing, reducing material costs by 30%.

[0152] S61: After the casing is pulled out 6-10m, the guide tube 9 is inserted into the concrete layer ≥2m and then re-grouted. The concrete pump 8 is used to add material to the pile top elevation. This ensures that the pile top elevation is met and avoids mud inclusion defects caused by secondary grouting.

[0153] After construction is completed, the pile body integrity test can be carried out. Specifically, the acoustic wave transmission method is used to test the pile body. The proportion of Class I piles is ≥ 90%, and the compressive strength of the concrete test block is ensured to be ≥ C35 standard. The requirement for random inspection of 30% of the pile body quality is implemented.

[0154] It should be noted that the conduit 9 should be flushed with high-pressure water before use, and the valve core rubber parts should be replaced every 50 piles. The slump of concrete should be controlled at 18~22cm to avoid blockage due to poor fluidity. The buried depth of the conduit 9 should be ≤6m, the flow rate should be controlled at 0.5~2.0m³ / min, and the floating rate of the steel cage should be <0.5%.

[0155] The first pressure sensor 4 monitors the slurry column pressure, and the second pressure sensor 91 monitors the concrete flow resistance, forming dynamic pressure layered monitoring. The control module 10 triggers grouting and flow rate adjustment in layers, with a response time of less than 5 seconds.

[0156] By forming a composite support layer with the residual layer of elastic membrane and concrete, the material cost is reduced by 30%. The elastic expansion layer replaces the permanent casing, which can make the casing recovery rate ≥80% and the loss rate ≤5%.

[0157] Through the density screening layer and the one-way check valve 92 membrane, the slurry blocking efficiency is greater than 90%, and the slurry isolation dual mechanism can reduce the mud inclusion defect rate in the pile body to less than 1%.

[0158] Leakage response: when the sensor triggers grouting time ≤ 5 seconds, the cave filling completion time ≤ 30 seconds, and the pressure rises back to 0.04 MPa; Compared with traditional manual monitoring, the risk of uncontrolled grout leakage is reduced by 70%. The concrete filling coefficient is controlled at 1.1-1.3, compared to 1.5-2.0 with traditional processes, reducing material waste by 20%. The grout isolation assembly increases pile top strength by 15%, with a mud inclusion defect rate of less than 1%. After the casing is removed, the residual thickness of the elastic expansion layer is ≥5mm, and the bond strength with the concrete interface is ≥0.5MPa. The casing can be reused ≥50 times with a loss rate of ≤5%.

[0159] Through the closed-loop control of the entire process of sensor monitoring - elastic wall protection - intelligent pouring - casing recovery, the problems of cave collapse, slurry leakage, and uncontrolled filling coefficient in complex cave areas have been solved.

[0160] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A stabilization device for cave excavation, characterized in that: include: A steel casing is inserted into the hole (1), the steel casing comprising an outer main casing (2) and an inner elastic expansion group (31), and a first pressure sensor (4) is installed on the top of the steel casing for monitoring the pressure of the mud column; The elastic expansion group (3) comprises an outer layer (32) that fits the main casing (2) and an inner layer (31) near the middle. The inner layer (31) expands when exposed to water to form a temporary support layer. By pulling out the main casing (2), the elastic expansion group (3) remains in the hole and forms a permanent support layer together with the concrete. The outer layer (32) forms a waterproof isolation membrane when exposed to water. A plurality of spiral grouting pipes (5) are distributed and embedded along the outer wall of the main casing (2), and the ends of the plurality of spiral grouting pipes (5) are connected to an annular distribution component, and dual-liquid slurry is injected toward the outer wall of the main casing (2) through the annular distribution component; A steel cage group (7) is placed inside the main casing (2), and the concrete impact pressure is reduced by the steel cage group (7); It also includes a conduit (9) inserted into the interior of the main casing (2), the conduit (9) is externally connected to a concrete delivery pump (8), a flow regulating assembly is provided at the bottom of the conduit (9), the flow regulating assembly includes a second pressure sensor (91) embedded in the exterior of the conduit (9), and a slurry isolation assembly provided inside the conduit (9), the concrete pressure inside the main casing (2) is monitored by the second pressure sensor (91), and the slurry is isolated by the slurry isolation assembly; It also includes a control module (10), the control module (10) being electrically connected to the first pressure sensor (4), the grouting pump (11), the concrete delivery pump (8), and the second pressure sensor (91); when the first pressure sensor (4) detects a sudden drop in the pressure of the slurry column, the control module (10) cooperates with the grouting pump (11) to inject dual-liquid slurry toward the outer wall of the main casing (2) through the spiral grouting pipe (5) and the annular distribution component; When the second pressure sensor (91) detects that the fluctuation of the concrete flow resistance is greater than a preset value, switching to a low-speed pouring mode; When the second pressure sensor (91) detects that the concrete flow resistance is stable within the range of ±5% of the preset value, the high-speed pouring mode is switched.

2. The stabilization device for cave excavation according to claim 1, characterized in that: The inner layer (31) is made of highly absorbent polyurethane coated fiber cloth, which expands 0.5 to 1.0 times in volume when exposed to water, forming a temporary support layer with a compressive strength of ≥0.2 MPa; The outer layer (32) is made of hydrophobic polytetrafluoroethylene coated fiber cloth, which forms a permeability coefficient of ≤1×10⁻ when exposed to water. 8 cm / s waterproof isolation membrane.

3. The stabilization device for cave excavation according to claim 1, characterized in that: The annular distribution assembly comprises an annular flow channel (6) arranged inside the steel casing, and a plurality of output ports (61) embedded on the outer side of the steel casing, wherein the output ports (61) are connected to the annular flow channel (6).

4. The stabilization device for cave excavation according to claim 1, characterized in that: The first pressure sensor (4) is triggered when it detects a sudden drop in the pressure of the mud column greater than 0.02 MPa, the concrete flow resistance fluctuation is greater than 10% of the preset value, the pouring speed in the low-speed pouring mode is 0.5-2.0 m³ / min, and the pouring speed in the high-speed pouring mode is 4-6 m³ / min.

5. The stabilization device for cave excavation according to claim 1, characterized in that: The slurry isolation assembly includes a plurality of one-way check valves (92) integrally fixed inside the conduit (9), an elastic band (93) connecting the plurality of one-way check valves (92), the ends of the one-way check valves (92) being inclined toward the outlet direction of the conduit (9), and the plurality of one-way check valves (92) being closed by the elastic band (93).

6. The stabilization device for cave excavation according to claim 5, characterized in that: A magnetic strip (94) is embedded on the side of the end of the one-way check flap (92), and the positive and negative poles of the magnetic strips (94) on the sides of adjacent one-way check flaps (92) are opposite.

7. A method for using a stabilization device for cave excavation according to any one of claims 1 to 6, comprising: S1: Use the total station to set out the pile position, and use the rotary drilling rig to drill through the bearing layer, with the rock embedment depth ≥ 0.5m; S2: Steel casing is sunk and installed. Vibratory hammer is used to sink the casing to the rock surface elevation in sections. The steel casing is sunk to a depth of 10m~17m, with the top 0.5m~1m above the ground. The elastic expansion layer is activated. S3: The first pressure sensor (4) installed on the top of the main casing (2) monitors the pressure of the slurry column in real time, and when leakage occurs, the outer periphery of the main casing (2) is quickly grouting and backfilling; S4: The steel cage is placed inside the main casing (2) and reinforced; S5: pouring concrete toward the interior of the main casing (2) through an external concrete delivery pump (8) connected to a conduit (9), and dynamically controlling the concrete flow rate through a second pressure sensor (91); S6: Before the initial setting of the concrete, the vibrating hammer is started to pull out the main casing (2) in sections, and the casing is pulled out at a speed of ≤0.5m / min, and the elastic expansion layer is retained to replace the main casing (2).

8. The method for using the stabilization device for cave excavation according to claim 7, characterized in that: In step S2, the elastic expansion layer is activated specifically as follows: the volume of the inner layer (31) expands by 0.5 to 1.0 times, forming a temporary support layer with a compressive strength ≥ 0.2 MPa.

9. The method for using the stabilization device for cave excavation according to claim 7, characterized in that: In step S3, when it is detected that the pressure drops by more than 0.02 MPa and the liquid level drops by ≥1 m, the grouting linkage is triggered to fill the cave cracks, and the double liquid slurry is automatically grouted. The control module (10) is linked to the grouting pump (11) to inject the double liquid slurry mixed with cement and water glass through the spiral grouting pipe (5), and the initial setting time is ≤30 seconds.

10. The method for using the stabilization device for cave excavation according to claim 7, characterized in that: In step S5, the flow resistance of the concrete is monitored by the second pressure sensor (91) on the conduit (9), and the control module (10) is linked to the concrete delivery pump (8). When the pressure fluctuation is greater than 10% of the preset value, it is switched to a low-speed mode with a flow rate of 0.5~2.0m³ / min. When the pressure is stable at ±5% of the preset value, it is switched to a high-speed mode with a flow rate of 4~6m³ / min. The filling coefficient of the concrete is precisely controlled to be 1.1~1.

3. The slurry isolation component on the conduit (9) uses the density difference to block the slurry with a density of 1.0~1.2t / m³, and only allows concrete with a density of 2.4t / m³ to pass through. The end of the one-way check valve (92) is tilted, and the elastic band (93) and the magnetic strip (94) are closed in coordination to prevent the slurry from entering the cave area.

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