Large open cavern partial rock building equipment and method

Abstract

This invention discloses a large-scale open-type karst cave local rock-making device and method, belonging to the field of pile foundation construction technology in karst areas. It mainly solves the problems of high risk of borehole collapse, insufficient bearing capacity, and grouting displacement of the reinforcing steel cage in traditional bag pile construction. The device employs a variable-diameter hollow steel cylinder with pre-set staggered overflow holes and an overflow groove at the bottom of the cylinder. A rough structure is embedded on the outside of a bag-shaped fiber bag, with its upper diameter larger than its lower diameter. A steel sleeve is anchored to the top of the steel cylinder and has a larger diameter. A cylindrical plastic sleeve is bonded to the inner wall of the steel cylinder. The grouting pipe passes through the cylindrical plastic sleeve. A ring-shaped clamp, formed by short plastic tubes surrounding the outside of the fiber bag, creates a bamboo-like constraint structure. The upper end of the fiber bag is anchored to the steel sleeve, and the lower end is anchored to the anchor hole at the bottom of the steel cylinder, with the bag body bonded to the cylinder body. This device is used for large-scale open-type karst cave pile foundation construction, improving borehole collapse resistance, increasing bearing capacity, and preventing grouting displacement through the composite structure of the steel cylinder and fiber bag.

Description

Technical Field

[0001] This invention belongs to the field of pile foundation construction technology in karst areas, specifically a large-scale open-type karst cave local rock-making device and method. Background Technology

[0002] Karst landforms are widespread and highly concealed, especially in areas with abundant rainfall, where groundwater continuously erodes soluble rock layers, forming large, open caves. These caves are large in scale, have poor wall stability, and pose a significant risk of collapse, resulting in serious safety hazards for pile foundation construction above them. Existing technologies often employ a construction method combining geotextile bag piles with a reinforced steel frame: the reinforced steel frame enhances the soil's bearing capacity, while the geotextile bags provide waterproofing. However, this process faces three key technical challenges: First, drilling and casing placement are carried out in separate steps, resulting in prolonged exposure of the borehole wall after drilling. This makes the top of the karst cave prone to collapse without support, especially in large open karst caves where the high connectivity increases the risk of collapse. Second, the installation and positioning of the reinforcing steel frame is difficult, and uneven grout pressure distribution during grouting can easily cause the frame to shift, resulting in a weak pile structure. At the same time, the grout cannot fully penetrate the rock fissures, leading to insufficient pile-rock bonding strength. Third, traditional bag piles require drilling first, followed by the placement of the bag and frame. This fragmented process leads to low construction efficiency, and the limited accuracy of geological exploration in karst areas makes it difficult to completely avoid karst cave construction, further exacerbating the pressure on the construction schedule.

[0003] Analysis of the causes of the problem: First, the phased construction mode inevitably prolongs the exposure time of the borehole wall, while groundwater activity in karst areas continuously weakens the cave wall rock mass, leading to an exponential increase in the probability of borehole collapse with prolonged exposure. Second, the installation of the reinforcing steel frame and grouting pipes requires manual operation, making it difficult to guarantee positioning accuracy in deep borehole environments; the higher the grouting pressure, the higher the frame deviation rate. Finally, depth errors exist in the exploration of complex karst caves, but traditional techniques cannot dynamically adjust structural parameters. These shortcomings present a dilemma for existing technologies: shortening the exposure time requires simplifying the construction process, but this sacrifices quality control; strengthening the structure increases the time required for procedures, which in turn exacerbates the risk of borehole collapse. Therefore, a technical solution is urgently needed that can simultaneously address the issues of borehole collapse prevention, bearing capacity improvement, and construction efficiency. Summary of the Invention

[0004] In view of this, in order to overcome the shortcomings of the prior art, the present invention provides a steel cylinder-fiber bag composite structure drilling and piling equipment and construction method for local rock making in large open karst caves. It is particularly suitable for local rock making in large open karst caves. The method is simple, safe, and widely applicable, and provides important technical support for solving the bottleneck problem of pile foundation construction in karst areas and the problem of insufficient bearing capacity of pile foundations in karst areas.

[0005] At the same time, the following issues will be addressed: This method addresses the problems of high risk of steel reinforcement cage displacement, borehole collapse, and insufficient bearing capacity during pile foundation construction in karst areas. Traditional methods suffer from difficulties in installing and positioning the steel reinforcement cage, uneven grouting pressure leading to structural displacement, staged construction extending the borehole wall exposure time and increasing the risk of karst cave roof collapse, and difficulty in grout penetrating rock fissures, resulting in weak pile-rock bonding.

[0006] This addresses the problems of uneven grout filling leading to cementation defects and insufficient coverage of karst caves. Uniformly distributed overflow holes create filling blind spots in complex karst caves; geological exploration errors result in insufficient casing length, significantly increasing the risk of top collapse.

[0007] This addresses the issues of uncontrolled expansion of fiber bag grouting leading to flattening deformation and damage to the grouted sleeve. Free expansion causes ellipticization of the pile cross-section; direct contact between the metal grouted sleeve and the bag causes cutting damage; and the restraint system shifts and fails.

[0008] To address the issues of borehole collapse and grout runaway caused by process interruptions, the following measures were implemented: phased construction to extend borehole exposure time; integral grouting to penetrate the sidewalls of the karst cave; and addressing structural slippage caused by the loose slag layer at the bottom.

[0009] This addresses the issues of pile breakage and pile flattening caused by the tilting of the sinker. Excessive tilting leads to drill rods colliding with the borehole wall; the uniform-diameter fiber bags sink and deform under the weight of the grout; and weak bonding surfaces form at the sleeve joints.

[0010] This addresses the issues of aggregate clogging the grout overflow channel and collision damage to the grouting pipe. Specifically, it addresses problems such as large aggregates jamming the grout overflow trough, conflicts between the fixed grouting pipe and the drill rod recovery path, and significant grout loss from the bag-wall gap.

[0011] This addresses the issue of voids at the pile-rock interface caused by concrete shrinkage. Concrete shrinkage creates microcracks, weakening the interfacial bonding strength; traditional post-grouting processes compromise the integrity of the fiber bags.

[0012] This addresses the problem of grout preload reduction and failure in grouting sleeves. Grout pressure causes creep and loosening of the sleeves, leading to a decline in their restraint function; static preload cannot adapt to dynamic grouting environments.

[0013] This addresses the issue of strength reduction caused by grout dilution in water-rich karst caves. Groundwater dilution of concrete reduces the water-cement ratio; chemical waterproofing methods pollute the environment and require construction to be interrupted.

[0014] To achieve these objectives of the present invention, the present invention provides a large-scale open-type karst cave local rock-making device, comprising: The variable-diameter hollow steel cylinder has a lower cross-section that is larger than the upper cross-section. The cylinder body has symmetrically staggered overflow holes, and the bottom variable-diameter section has symmetrically staggered overflow channels. The bag-shaped fiber bag has a rough structure with fine sand or pebbles embedded on the outside. When not grouted, the diameter of the upper section is larger than that of the lower section. A steel sleeve, anchored to the top of a steel cylinder, has a diameter larger than the cylinder body and is pre-drilled with anchor holes; A cylindrical plastic sleeve is bonded to the inner wall of a steel cylinder using a water-soluble adhesive. The diameter of the auger drill rod is smaller than the inner diameter of the steel cylinder. Hydraulic reamer bit, when opened, has a diameter larger than the outer diameter of the steel cylinder; The grouting pipe is inserted into a cylindrical plastic sleeve; The annular sleeve, through a short plastic tube, surrounds the outside of the fiber bag to form a segmented constraint structure; The fiber bag is anchored at the upper end to a steel sleeve and at the lower end to an anchor hole at the bottom of the steel cylinder. The bag body is bonded to the steel cylinder body with water-soluble adhesive.

[0015] Preferably, the overflow holes and overflow channels are symmetrically distributed at different heights, and the size of the overflow channels is smaller than that of the overflow holes; The length of the steel sleeve from the bottom of the steel cylinder is greater than the depth of the karst cave, so that the length of the fiber bag covers the karst cave and extends by a certain amount.

[0016] Preferably, the plastic short tube is bonded to the outside of the fiber bag with epoxy resin adhesive; The ring-shaped hoop serves as a stirrup, passing through a short plastic tube to divide the fiber bag into multiple bamboo-like segments.

[0017] The present invention provides a construction method based on the aforementioned equipment, comprising the following steps: S10. Determine the location, height, and size of the karst cave based on geological exploration, and calculate the length of the steel cylinder and the size of the fiber bag; S20. Insert the grouting pipe into the cylindrical plastic sleeve, fix the steel cylinder with clamps and ensure that its centerline coincides with the borehole centerline; simultaneously fix the fiber bags in sections and lower the steel cylinder as the drill rod drills, including: S21. Anchor the bottom end of the fiber bag to the bottom of the steel cylinder; S22. The fiber bags are bonded to the cylinder in sections, with a ring-shaped sleeve installed at the top of each section; S23. Repeat S22 until the fiber bag covers the cave, and the top is anchored to the steel sleeve; S30. After drilling to the bottom of the rock layer, retract the reaming drill bit and lower the steel cylinder to the bottom of the hole, then pour fine stone concrete until it is initially set; S40. Grout the fiber bag in sections from bottom to top until grout emerges from the top of the hole and stops, including: S41. Fine aggregate concrete is poured in sections, and the grout fills the gaps in the hole wall through the overflow trough and overflow hole; S42. Each grouting interval must allow the lower concrete to set initially, and finally, after the concrete at the steel sleeve has solidified, the grouting should be used to fill the opening.

[0018] Preferably, in the method described above, in step S20, the deviation between the centerline of the steel cylinder and the centerline of the borehole is ≤30mm; in step S41, the larger diameter of the upper part of the fiber bag exerts a lifting effect on the lower grouting section, and the annular sleeve restricts expansion deformation; in step S42, the height of each grout section must exceed the current position of the annular sleeve.

[0019] Preferably, in the method described above, in step S30, the coarse aggregate of the fine stone concrete has a particle size ≤15mm, and after grouting, it overflows through the overflow trough and binds to the steel cylinder, fiber bag and hole wall; in step S40, the grouting pipe is slowly lifted up as the grouting process proceeds to avoid touching the auger drill rod.

[0020] Preferably, in the method described, after each section of grouting is completed in step S42, a compensation grouting pipe is immediately inserted into the fiber bag of that section, and a compensation grout with an expansion rate of 2-3% is injected. The injection pressure is maintained at 0.15-0.25 MPa for 3 minutes to form a pressure compensation chamber. The water-cement ratio of the compensation grout is 0.12 lower than that of the main fine stone concrete, and 8-10% magnesium oxide expansion agent is added. After the injection is completed, the grouting pipe is kept sealed for 12 hours, and then pulled out after the expansion agent has fully reacted.

[0021] Preferably, in the method described in step S40, during the segmented grouting process, when the grout level reaches the current annular sleeve height, a hydraulic tensioner is used to perform secondary tensioning on the sleeve; the tension force F is calculated according to the formula: F=K·(P·A +F0), where the safety factor K=1.2-1.5, P=grouting pressure, A=cross-sectional area of ​​the fiber bag, and F0=initial preload; after tensioning, the sleeve elongation is controlled to be 105-110% of the initial installation value, and the pressure is maintained until the grout in that segment initially sets.

[0022] Preferably, in the method described, when the borehole reveals a water inflow > 10m³ 3 When filling a water-rich karst cave with a flow rate of / h, before grouting in step S40, add quick-setting water-absorbing resin granules into the fiber bag. The feed rate is Q = 0.15V·t, where V is the water inflow rate in m³ / h. 3 / h, where t is the estimated number of grouting hours; The resin particles have a particle size of 2-4 mm and an expansion rate of ≥300% when exposed to water. After absorbing water, they form a gel with a compressive strength of >0.5 MPa. After feeding the material and letting it stand for 20 minutes, grouting begins, and the grouting flow rate is reduced to 60% of the conventional value.

[0023] The present invention has at least the following beneficial effects: 1. The composite structure of steel cylinder and fiber bag enhances overall stability and avoids the problem of steel reinforcement cage displacement. The steel cylinder sinks synchronously with drilling to provide immediate support to the borehole wall, significantly reducing the risk of borehole collapse; the rough outer structure of the fiber bag enhances the pile-rock interlocking effect and improves the vertical bearing capacity; the cylindrical plastic sleeve protects the grouting pipe from damage caused by drill rod impact.

[0024] 2. The staggered overflow system achieves three-dimensional uniform filling, eliminating the short-circuiting phenomenon of grout in traditional uniformly distributed holes. The extended fiber bag design offsets geological exploration errors, ensuring full coverage of the karst cave; the size-graded overflow structure optimizes the concrete flow path and improves the bonding density.

[0025] 3. The plastic short tube buffer layer prevents the ferrule from cutting and damaging the fiber bag, ensuring the integrity of the bag. The bamboo-shaped restraint system controls expansion deformation, and the lifting force generated by the tapered design of the fiber bag inhibits flattening at the bottom; the pre-tightened ferrule provides continuous circumferential restraint, enhancing the overall cross-sectional integrity.

[0026] 4. The simultaneous drilling process integrates drilling, casing, and bagging, significantly shortening the hole-forming time. The segmented grouting strategy prevents grout from penetrating the karst caves through pressure conditioning; the initial set concrete at the bottom of the hole forms an anti-slip base, improving the structure's shear resistance. 5. Precise positioning of the steel cylinder ensures safe operation of the drill rod and avoids accidents caused by deviation. The tapered design of the fiber bag converts the self-weight of the grout into a beneficial lifting force, improving the roundness of the pile; over-filling of grout eliminates the weak interface of the sleeve, achieving full-section dense bonding.

[0027] 6. Fine aggregate concrete ensures unobstructed grout overflow channels, avoiding the clogging problems of traditional aggregates. The dynamic lifting of the grouting pipe and the recovery of the drill rod are decoupled in time and space, eliminating equipment collision damage; the grout overflow pressure actively fills the gap between the bag and the wall, turning lost grout into a resource to strengthen the structure.

[0028] 7. During the initial setting period, compensating grouting precisely offsets shrinkage deformation and maintains interface compaction. The magnesium oxide expanding agent continues to expand in the confined space, repairing micro-cracks; the low-pressure grouting process protects the integrity of the fiber bag and enhances the synergistic performance of the pile-rock interaction.

[0029] 8. Grouting pressure can be converted into dynamic tension force to compensate for creep relaxation of the hoop in real time. Formulated control of related grouting parameters ensures that the constraint force matches the working conditions; stabilizing the pressure until initial setting solidifies the prestress in the pile body and effectively inhibits the bulging deformation of the fiber bag.

[0030] 9. Water-absorbing resin converts groundwater into reinforcing gel in situ, eliminating the dilution effect. Rapid-setting particles self-adaptively seal seepage channels, improving pile quality in water-rich sections; environmentally friendly materials avoid chemical pollution, and continuous construction shortens the construction period.

[0031] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the steel cylinder drilling follow-up structure; Figure 2 A schematic diagram of the steel cylinder-fiber bag composite structure for drilling follow-up; Figure 3 This is a schematic diagram of the steel cylinder-fiber bag composite structure before grouting; Figure 4 This is a schematic diagram of the steel cylinder-fiber bag composite structure during the segmented grouting process; Figure 5 Schematic diagram of the steel cylinder-fiber bag composite structure for grouting to complete concrete bonding; Figure 6 This is a schematic diagram of the steel sleeve structure; Figure 7 This is a schematic diagram of the cross-section of a circular tube with a sleeve.

[0033] In the diagram: 1. Clamp; 2. Overflow hole; 3. Spiral drill rod; 4. Overflow trough; 5. Grouting pipe; 6. Steel cylinder; 7. Reamer bit; 8. First anchor hole; 9. Steel sleeve; 10. Fiber bag; 11. Plastic short pipe; 12. Annular sleeve; 14. Fine aggregate concrete; 15. Hole wall; 16. Hole bottom; 17. Second anchor hole; 18. Cylindrical plastic sleeve. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to examples, so that those skilled in the art can implement it based on the description.

[0035] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0036] As shown in Figures 1-7, an example of a large-scale open-type karst cave local rock-making device includes: The variable-diameter hollow steel cylinder 6 has a lower cross section that is larger than the upper cross section. The cylinder body has symmetrically staggered overflow holes 2, and the bottom variable-diameter part has symmetrically staggered overflow channels 4. The bag-shaped fiber bag 10 has a rough structure of fine sand or fine stones embedded on its outside, and the diameter of the upper section is larger than that of the lower section when not grouting. A steel sleeve 9 is anchored to the top of a steel cylinder 6, with a diameter larger than that of the steel cylinder 6, and a pre-set first anchor hole 8; A cylindrical plastic sleeve 18 is bonded to the inner wall of the steel cylinder 6 with water-soluble adhesive; The diameter of the auger rod 3 is smaller than the inner diameter of the steel cylinder 6; The hydraulic reamer 7 has a diameter larger than the outer wall diameter of the steel cylinder 6 after it is opened. Grouting pipe 5 is inserted into cylindrical plastic sleeve 18; The annular sleeve 12, through the short plastic tube 11, surrounds the outside of the fiber bag 10 to form a segmented constraint structure; The fiber bag 10 is anchored at the upper end to the steel sleeve 9 and at the lower end to the second anchor hole 17 at the bottom of the steel cylinder 6. The bag body is bonded to the cylinder body of the steel cylinder 6 with water-soluble adhesive.

[0037] Specifically, the steel cylinder 6, as the core support structure, adopts a variable-diameter hollow design, with its lower end diameter larger than its upper end diameter. Preferably, the bottom variable-diameter section forms a conical transition section with a slope not exceeding 15°. Four rows of overflow holes 2 are symmetrically opened on the steel cylinder 6. Preferably, the hole spacing in each row is uniformly distributed at 300 mm, and adjacent rows of overflow holes 2 are staggered by 150 mm in the vertical direction, forming a staggered sawtooth arrangement. Eight overflow grooves 4 can be opened circumferentially on the bottom variable-diameter section of the steel cylinder 6. The groove width can be precisely controlled at 10 mm and the depth at 5 mm, and adjacent overflow grooves 4 are staggered by 20 mm in height. The inner wall of the steel cylinder 6 is fully coated with concrete water-soluble adhesive and bonded to a cylindrical plastic sleeve 18. The plastic sleeve can be 0.5 mm thick and completely covers the entire length of the cylinder, forming an inner protective lining layer for the drill pipe channel.

[0038] The fiber bag 10 can be made of polypropylene geotextile. Preferably, the diameter of its upper, unexpanded portion is designed to be 8% larger than that of the lower portion (e.g., an upper diameter of 800 mm corresponds to a lower diameter of 740 mm). The outer surface of the bag can be uniformly attached with a basalt fine sand layer of 3-5 mm particle size through a welding process, with a fine sand coverage of not less than 90%, forming a rough surface that enhances frictional resistance (or the sand layer can be set through other commonly used processes). The lower end of the fiber bag 10 is mechanically locked by a steel cable passing through the second anchor hole 17 pre-set at the bottom of the steel cylinder 6, with a tensile strength of not less than 80 kN; the upper end is anchored to the first anchor hole 8 of the steel sleeve 9, the diameter of which is 6% larger than the diameter of the steel cylinder 6, and is coaxially connected to the top of the steel cylinder 6 by flange bolts. The fiber bag 10 has a strip of water-soluble adhesive applied longitudinally to its body. Optionally, the adhesive strips are 50 mm wide and 200 mm apart to achieve bonding with the outer wall of the steel cylinder 6. The peel strength of the bonded surface reaches more than 5 kN / m.

[0039] The segmented restraint system is assembled according to the following rules: First, mark circular positioning lines at 1.5-meter intervals on the outside of the fiber bag 10. Apply epoxy resin adhesive circumferentially along the marked lines and then attach 20-mm diameter plastic short pipes 11, ensuring the bonding length equals the pipe circumference. Then, insert a ring-shaped clamp 12 made of 12-mm diameter HPB300 steel reinforcement through the cavity of the plastic short pipe 11, welding the two ends of the clamp to form a closed-loop structure. The installed clamp must be pre-tensioned to no less than 1 kN and maintain a gap of no more than 2 mm from the surface of the fiber bag 10. This restraint system divides the fiber bag 10 into continuous bamboo-like units, effectively controlling grouting expansion deformation.

[0040] The matching design of the drilling and grouting system involves a key dimensional chain: the diameter of the spiral drill rod 3 is 40 mm smaller than the inner diameter of the steel cylinder 6 (for example, when the inner diameter of the cylinder is 600 mm, the drill rod is 560 mm), ensuring that the drill rod can rotate freely within the cylindrical plastic sleeve 18. The diameter of the hydraulic hole-expanding bit 7 after expansion is 50 mm larger than the outer diameter of the steel cylinder 6 (for example, when the outer diameter of the cylinder is 620 mm, the expanded diameter of the bit is 670 mm), forming an effective hole-forming diameter. The grouting pipe 5 penetrates into the interior of the cylindrical plastic sleeve 18 from the top of the steel cylinder 6, and the assembly clearance between the pipe wall and the plastic sleeve is strictly controlled within 5 mm to avoid interference with the spiral drill rod 3.

[0041] The pre-assembly process is carried out in the following steps: On the ground, flatten the fiber bag 10, bond the plastic short pipe 11 according to the marked line and install the annular hoop 12, and then hoist the whole set and put it on the steel cylinder 6. After the fiber bag 10 and the cylinder body are adhesively bonded with hydrocolloid in segments, anchor the lower end of the fiber bag 10 to the second anchor hole 17 at the bottom of the steel cylinder 6 and the upper end to the first anchor hole 8 of the steel sleeve 9 respectively. In the quality inspection stage, high-pressure water is injected from inside the steel cylinder 6 to verify the uniform outflow of the slurry overflow holes 2 and the slurry overflow grooves 4, and it is required that the flow deviation of each hole does not exceed 15%. After the installation of the grouting pipe 5, an empty-load insertion and extraction test needs to be carried out, and the operating resistance should be controlled below 200 N to be qualified.

[0042] This implementation method ensures the engineering effect through three core features: the variable-diameter steel cylinder 6 and the staggered slurry overflow system achieve three-dimensional uniform diffusion of the slurry; the taper design of the fiber bag 10 and the bamboo joint restraint structure cooperate to inhibit flat deformation; the plastic sleeve inside the cylinder and the precise dimensional chain ensure the reliability of the construction during drilling.

[0043] There are the following technical contradictions in the construction process: To prevent hole collapse, it is necessary to strengthen the hole wall protection (such as steel casing), but the traditional steel casing hoisting requires the drilling to stop, resulting in the drilling and hole wall protection being carried out step by step, reducing the efficiency. If continuous drilling is pursued for efficiency, the fiber bag 10 and the hole wall 15 are not fully fitted, and the bearing capacity decreases. The steel reinforcement cage needs high-pressure grouting to ensure dense filling, but uneven pressure is likely to cause the cage to shift, forming a structural weak layer. If the pressure is reduced, the slurry cannot penetrate into the rock fissures, and the bonding strength between the pile and the rock is insufficient. Direct pouring of concrete is likely to cause loss, resulting in significant material waste; while layered grouting reduces the loss, but the construction period is extended.

[0044] The existing steel casing follow-up method uses a single steel casing and is constructed in stages, drilling first and then lowering the casing. It lacks a dedicated grout overflow structure, relies on the drill bit gap, and has no segmented constraints. During grouting, it is prone to lateral expansion, and the grouting pipe 5 is exposed and easily damaged by drill rod impacts. While the steel casing follow-up method can partially solve the hole collapse problem, its structural limitations and fragmented processes prevent it from overcoming the coordination problem. The reasons are: 1. A gap exists between the steel casing and the hole wall 15, preventing grout from penetrating the rock fissures during grouting, resulting in weak bonding between the pile and the rock. This implementation method uses fine sand / gravel on the outside of the fiber bag 10, which embeds into the rock mass under grouting pressure, forming a mechanical interlock and improving the shear strength of the bonding surface. 2. The steel casing needs to be lowered after drilling stops, resulting in a long borehole exposure time and an increased risk of cavern roof collapse; furthermore, excessive casing placement deviation can easily cause drill bit jamming. This implementation method lowers the steel casing 6 simultaneously with drilling, resulting in small centerline deviation and near-zero borehole exposure time, reducing hole collapse. 3. High-pressure grouting is required in a single operation, which can easily penetrate the top slab of the karst cave, or insufficient pressure can lead to incomplete filling. This implementation method uses bamboo-joint-shaped clamps to restrict the grout in sections, allowing it to expand gradually from bottom to top, with controllable pressure and uniform distribution.

[0045] Therefore, this implementation method solves the challenges of balancing quality, efficiency, and cost in karst cave pile foundation construction through a three-pronged design: composite structure, simultaneous drilling, and segmented constraint. Existing technologies such as the steel casing follow-up method suffer from limitations due to their simple structure, fragmented processes, and lack of pressure control mechanisms. This breakthrough provides a new, reliable, and economical approach for high-rise building and bridge pile foundations in karst areas, particularly suitable for complex conditions involving large, open karst caves (e.g., cave height > 5m, unfilled).

[0046] Furthermore, in another embodiment, the overflow hole 2 and the overflow trough 4 are symmetrically distributed at different heights, and the size of the overflow trough 4 is smaller than that of the overflow hole 2; the length of the steel sleeve 9 from the bottom of the steel cylinder 6 is greater than the depth of the karst cave, so that the length of the fiber bag 10 covers the karst cave and extends 2m.

[0047] Specifically, four rows of overflow holes 2 are cut into the steel cylinder 6 using a cutting process. The spacing between each row of holes is strictly controlled at 300 mm, and adjacent rows of holes are staggered by 150 mm in the vertical direction, forming a high-low serrated distribution pattern. Eight overflow grooves 4 are machined in the variable diameter section at the bottom of the cylinder. For example, the groove width is set to 10 mm and the depth to 5 mm. Adjacent groove openings are staggered by 20 mm in the circumferential direction, and the depth gradually changes, with a maximum depth of 7 mm and a minimum depth of 3 mm. After completion, the distribution of holes and grooves is inspected to ensure that the symmetry deviation is ≤0.5 mm.

[0048] Based on the cave depth H in the geological exploration report, the length of fiber bag 10 is determined to be H+2 meters (for example, when the cave depth is 12 meters, the length of fiber bag 10 is 14 meters). The upper diameter of fiber bag 10 is enlarged by 8% proportionally (e.g., the diameter of the cave section is D, and the diameter of the non-cave section is 1.08D). The surface of the bag is uniformly welded with granite crushed sand with a particle size of 3-5 mm (or other structural layers to increase roughness), and the crushed sand coverage is ≥95%. After anchoring the bottom end of fiber bag 10 to the second anchor hole 17 at the bottom of steel cylinder 6, the bag is pulled upward so that the top exceeds the theoretical position of the cave roof by 2 meters, and finally locked in the first anchor hole 8 of steel sleeve 9.

[0049] In areas with ambiguous cave boundaries, such as within an exploration error range of ±15%, the following method is used to verify the effectiveness of the cover: Inject tracer into the fiber bag 10 and confirm, via borehole camera, that the bag extends ≥1.8 meters above the cave ceiling. If this is not met, lengthen the fiber bag 10 on-site and re-anchor it until the H+2 meter cover requirement is met.

[0050] Conventional steel casing construction employs a uniformly distributed overflow hole design, with a single layer of circular holes mechanically punched onto the casing surface. These holes are evenly distributed at 200 mm intervals and have a uniform diameter of 15 mm. The casing length is based on the geological exploration value L. After installation, concrete is directly poured into the entire casing without any in-hole coverage verification during construction; construction is based solely on exploration data. This method has the following drawbacks: First, the uniformly distributed holes create short-circuit dead zones for grout in the irregular cavities of the karst cave, causing grout to leak along a single path, resulting in a decreased filling rate. In contrast, the staggered hole-groove design of this implementation forms a three-tiered overflow network. Higher-level holes fill the top rock fissures, middle-level holes compact the sidewalls, and gradually deepening grooves compensate for bottom sediment, improving the filling rate. Second, exploration errors can easily lead to coverage failure. This implementation uses a certain amount of extension, such as 2 meters, to cover depth errors in the karst cave. Tracers confirm coverage in real time, avoiding the risk of sudden geological changes. It is evident that this implementation method fundamentally solves the problems of filling dead zones that inevitably arise in complex karst caves in the traditional uniformly distributed hole process during karst pile foundation construction; and the structural failure risk that the length of the rigid casing cannot adapt to geological exploration errors. It has irreplaceable advantages, especially for concealed beaded karst caves.

[0051] Furthermore, in another embodiment, the plastic short tube 11 is bonded to the outside of the fiber bag 10 with epoxy resin adhesive; the annular sleeve 12 is a stirrup that passes through the plastic short tube 11 and divides the fiber bag 10 into multiple bamboo-like structures.

[0052] Specifically, fiber bags 10 can be made using polypropylene woven geotextile, and cut in a tapered shape with the upper diameter 8% larger than the lower diameter (for example, when the designed pile diameter is 800 mm, the upper diameter of the bag is 864 mm and the lower diameter is 800 mm). Epoxy resin is evenly coated onto the outer surface of the bag, and immediately followed by the application of 3-5 mm particle size manufactured sand. After vibration and compaction, a permanent roughened layer with a coverage of ≥95% is formed. The surface-treated fiber bags 10 are then cured in a temperature-controlled workshop to ensure complete resin curing.

[0053] A circular baseline can be set every 1.5 meters along the length of the fiber bag 10. Using specialized adhesive application equipment, a 30 mm wide and 2 mm thick epoxy resin layer is applied circumferentially along the baseline. A 20 mm diameter polyethylene plastic short tube 11 is then pressed onto the adhesive layer, and a pressure of 0.3 MPa is applied and held for 60 seconds to achieve full circumferential bonding. After bonding, a shear strength test is performed, requiring a shear strength ≥ 3 MPa between the plastic short tube 11 and the bag body.

[0054] HPB300 plain round steel bars with a diameter of 12 mm can be used, passing through the plastic short pipe 11 to form a ring constraint. The two ends of the sleeve are butt-welded by argon arc welding, and the weld strength is not lower than the standard of the base material. During installation, a hydraulic tensioner is used to apply a preload of 1.2 kN to the sleeve, at which time the surface of the fiber bag 10 will produce a preload deformation of about 3 mm. After installation in sections, a continuous bamboo-like structure is formed, and the tolerance of the spacing between adjacent sleeves is controlled within ±10 mm.

[0055] Traditional metal hoop restraint methods involve directly binding 10 mm diameter steel bars to the outside of the fiber bag 10, with a hoop manually tied every 2 meters, without applying pre-tension. During grouting, expansion is passively restricted by the hoop, while the fiber bag 10 deforms freely. The completed pile often exhibits an irregular elliptical cross-section. This method has the following drawbacks: First, the metal hoop is in direct contact with the fiber bag 10, forming a rigid compression point. In contrast, this implementation uses a short plastic tube 11 to form a buffer interface, resulting in a larger contact area. Second, single-point restraint leads to stress concentration; in this implementation, the annular hoop 12 distributes the load evenly through the short plastic tube 11. Third, the lack of pre-tension results in restraint lag and large expansion deformation. This implementation achieves active restraint through pre-tension, controlling the amount of deformation.

[0056] Example 1 A construction method based on the above-mentioned equipment includes the following steps: S10. Determine the location, height, and size of the karst cave based on geological exploration, and calculate the length of the steel cylinder 6 and the dimensions of the fiber bag 10; S20. Insert the grouting pipe 5 into the cylindrical plastic sleeve 18, fix the steel cylinder 6 with the clamp 1 and ensure that its centerline coincides with the borehole centerline; simultaneously fix the fiber bag 10 in sections and hoist the steel cylinder 6 as the drill rod drills, including: S21. Anchor the bottom of the fiber bag 10 to the bottom of the steel cylinder 6; S22. The fiber bags 10 are bonded to the cylinder in sections, and an annular sleeve 12 is provided at the upper end of each section; S23. Repeat S22 until the fiber bag 10 covers the cave and the top is anchored to the steel sleeve 9; S30. After drilling to the bottom of the rock layer, retract the reaming drill bit 7 and lower the steel cylinder 6 to the bottom of the hole 16, and pour fine stone concrete 14 until it is initially set; S40. Grout the fiber bag 10 in sections from bottom to top until grout emerges from the top of the hole and stops, including: S41. Fine aggregate concrete 14 is poured in sections, and the grout fills the gaps in the hole wall 15 through the overflow groove 4 and the overflow hole 2; S42. Each grouting interval must allow the lower concrete to set initially. Finally, after the concrete at the 9 locations on the steel sleeve has set, the grouting should be poured to fill the opening.

[0057] Specifically, based on the 3D model of the karst cave in the geological exploration report, the total length of the steel cylinder 6 (depth of the karst cave floor + 3 meters embedded in the bedrock + 1.5 meters protruding from the ground) and the number of fiber bag 10 segments (each segment is 1.5 meters) are calculated. The first section of the steel cylinder 6 and fiber bag 10 are pre-assembled on the ground at the construction site: the bottom end of the fiber bag 10 is anchored to the second anchor hole 17 at the bottom of the steel cylinder 6; water-soluble adhesive is applied longitudinally to the bag body to bond it to the cylinder wall; the first plastic short pipe 11 and annular sleeve 12 are installed 1.5 meters from the bottom of the cylinder. The grouting pipe 5 is inserted into the cylindrical plastic sleeve 18, and the bottom of the pipe is fixed 0.3 meters from the lower end of the steel cylinder 6.

[0058] Start the drilling rig so that the auger rod 3 passes through the center of the steel cylinder 6, and the hydraulic reaming drill bit 7 opens to the designed diameter. Drilling and cylinder lowering are synchronized: for every 0.5 meters the drill bit advances, the steel cylinder 6 is lowered 0.5 meters simultaneously and then paused. During the pause, the fiber bag 10 is extended, and a new fiber bag 10 is glued and bonded 30 cm above the previous clamp. After installing the new plastic short pipe 11 and clamp, drilling continues. Repeat this process until the drill bit touches the bottom rock layer of the karst cave. At this point, the total length of the fiber bag 10 = the height of the karst cave + 2 meters.

[0059] Withdraw the under-reamed bit 7 and lower the steel cylinder 6 to the bedrock surface at the bottom of the hole 16. Pour fine aggregate concrete 14 (coarse aggregate ≤ 15 mm) into the bottom of the hole 16 through the grouting pipe 5. Control the pouring volume to overflow the slurry overflow tank 4 and rise to 0.2 m below the first hoop. Let it stand for 90 minutes until the concrete initial sets (compressive strength ≥ 1 MPa) to form the bottom anchoring tray.

[0060] Perform segmented pressure-acclimated grouting and pour fine aggregate concrete 14 in segments from bottom to top: For the first segment, grout until the slurry submerges 10 cm above the first hoop, stop the pump and let it stand for 60 minutes; lift the grouting pipe 5 by 1.6 m and pour the second segment until it submerges the second hoop; repeat until reaching the position of the steel sleeve 9. After the concrete strength reaches 5 MPa, finally pour and fill the hole opening. Control the pressure ≤ 0.8 MPa throughout the grouting process. Observe that the slurry evenly seeps out through the slurry overflow hole 2 as the qualified standard.

[0061] The traditional steel casing process is constructed in three independent steps. First, the drill rig drills the hole to the designed depth. After pulling out the drill pipe, the steel casing is lowered. After the casing is in place, the whole hole is filled with concrete at one time. There are problems such as a high risk of hole collapse and easy loss of control of the slurry. In this embodiment, the steel cylinder 6 always supports the hole wall 15 0.5 m ahead of the drill bit. The overlapping time and space of drilling and support avoid the exposure of the drilled hole. The bamboo-shaped hoops divide the slurry into independent units. The initial-set concrete base absorbs the grouting kinetic energy. The fiber bag 10 forms a continuous restraint body between the upper and lower karst layers. The segmented grouting realizes the gradual release of pressure. Therefore, it can reduce the hole collapse and slurry loss during karst construction.

[0062] Furthermore, in another embodiment, in step S20, the deviation between the center line of the steel cylinder 6 and the center line of the borehole is ≤ 30 mm; in step S41, the larger diameter of the upper part of the fiber bag 10 forms a pulling effect on the lower grouting section, and the annular hoop 12 restricts the expansion deformation; in step S42, the height of each segment of slurry needs to exceed the position of the current annular hoop 12.

[0063] Specifically, a 0.5-second high-precision total station can be installed on the drill rig mast to monitor the center coordinates of the steel cylinder 6 in real time. During the process of drilling and sinking the cylinder, dynamically adjust the hydraulic deviation correction system to ensure that the deviation between the center line of the steel cylinder 6 and the designed pile position is ≤ 30 mm. Conduct laser alignment detection every 1 m of drilling. If the deviation exceeds the limit, immediately start the deviation correction program: Apply a 50 kN deviation correction force through the hydraulic pusher on the side of the cylinder until the deviation value returns to the 25 mm safety range. Record and archive the cumulative deviation curve throughout the process of sinking the cylinder, and control the peak-to-peak value ≤ 15 mm. <00002​Before installing fiber bag 10, verify the taper parameters: upper diameter / lower diameter = 1.08 ± 0.01 (e.g., when the design pile diameter is 800 mm, the upper bag diameter is 864 mm and the lower bag diameter is 800 mm). During installation, calibrate the bag's orientation to ensure the larger diameter end always faces upwards. When extending each bag section, use a tension meter to check the longitudinal preload, requiring the lower bag to be subjected to a pulling force ≥ 12 kN / m from the upper section.

[0065] During segmented grouting, when the grout reaches the current hoop position, the flow rate automatically switches to a velocity ≤0.3m. 3 Continue grouting at a rate of / min until the grout level exceeds the sleeve position by 50-100 mm (over-grouting amount Δh=0.05D, where D is the pile diameter). Monitor the grout pressure above the sleeve in real time using a pressure sensor. When it reaches 0.15 MPa, it is determined to be over-grouting and compacted. After each grouting section is completed, insert a probe to detect the grout height. The measured over-grouting amount is required to be ≥90% of the design value.

[0066] Existing manual measurement methods involve sinking a steel cylinder (6) and checking for deviation with a plumb bob every 5 meters. Fiber bags (10) are made of uniform diameter (without tapering). Grouting is stopped at the clamping position. This method heavily relies on worker experience and is prone to cylinder deviation leading to pile breakage, pile flattening, and a weak interface at the clamping point. This embodiment prevents deviation through deviation control, uses lifting and a ring clamp (12) to prevent pile flattening, controls grout penetration under excessive pressure, pre-compacts the ungrouted upper bag, and forms a 3-5cm reinforcing ring above the clamping point, eliminating the weak interface at the clamping point.

[0067] Furthermore, in another embodiment, in step S30, the coarse aggregate of the fine stone concrete 14 has a particle size ≤15mm, and after grouting, it overflows through the overflow trough 4 and binds to the steel cylinder 6, fiber bag 10 and hole wall 15; in step S40, the grouting pipe 5 is slowly raised as the grouting process proceeds to avoid touching the spiral drill rod 3.

[0068] Specifically, a double-layer vibrating screen is installed at the concrete mixing plant. The upper screen has a 20 mm mesh size to intercept excessive aggregate, while the lower screen has a 15 mm mesh size to ensure that the aggregate particle size is ≤15 mm. During the production of each batch of fine aggregate concrete, the aggregate particle size distribution is randomly checked, requiring that particles >12 mm account for ≤15% and particles <8 mm account for ≥40%. The slump of the mixed concrete is controlled within the range of 180±20 mm, and it is poured within 30 minutes after being transported to the site. The slump is retested before pouring, and batches with a loss rate >15% are scrapped.

[0069] A pressure sensor and positioning chip are installed at the bottom of grouting pipe 5, initially positioned 0.3 meters from the bottom of steel cylinder 6. When grouting fine aggregate concrete 14, the grouting pipe 5 is simultaneously raised 11.5 meters for every 1.2 cubic meters of grout poured, maintaining a 1:1.2 ratio between the lifting rate and the grouting flow rate (e.g., grouting flow rate 1m). 3 / min corresponds to a pipe lifting speed of 1.25m / min. During the pipe lifting process, the bottom of the pipe should be buried at a depth of ≥2 meters below the grout surface. When the pipe is lifted to the position of the steel sleeve 9, the grouting pipe opening should be kept 0.5 meters above the grout surface for grout discharge. Spatial and temporal avoidance should be implemented during drill rod retrieval and grouting pipe 5 movement: the grouting pipe 5 section should be lifted and locked 10 minutes before the drill rod is lifted.

[0070] When slurry seeps out from the top of the hole, maintain the injection pressure at 0.3 MPa for 3 minutes. During this stage, the slurry flows upward along the outside of the fiber bag 10, filling the 5-20 mm gap between the bag and the hole wall 15 to form a closed loop. The gap filling status is monitored by a pre-embedded resistivity sensor, requiring the circumferential resistance value fluctuation to be ≤5%, indicating uniform filling. The final slurry seepage is controlled within 105-110% of the theoretically calculated value; if it exceeds this range, the alarm system is automatically triggered.

[0071] Conventional methods involve direct grouting with commercial concrete (20-40 mm aggregate). The grouting pipe 5 is fixed inside the casing until grouting is complete. During construction, the grout easily overflows from the top of the casing, and the gap between the fiber bag 10 and the borehole wall 15 is not specially treated. This embodiment uses graded concrete to prevent grout overflow and blockage. The grouting volume and pipe lifting distance are precisely linked to prevent the grouting pipe 5 from colliding with the drill rod. The gap is filled to form a reinforcing ring, reducing grout loss.

[0072] Furthermore, in another embodiment, after each grouting section in step S42 is completed, a compensation grouting pipe is immediately inserted into the fiber bag 10 of that section, and a compensation grout with an expansion rate of 2-3% is injected. The injection pressure is maintained at 0.15-0.25 MPa for 3 minutes to form a pressure compensation chamber. The water-cement ratio of the compensation grout is 0.12 lower than that of the main fine stone concrete, and 8-10% magnesium oxide expansion agent is added. After the injection is completed, the grouting pipe is kept sealed for 12 hours, and then pulled out after the expansion agent has fully reacted.

[0073] Specifically, 40±5 minutes after the completion of grouting in each section of fine aggregate concrete, the grout strength is tested using a penetration resistance meter. When the probe penetration depth is ≤25mm (corresponding to a compressive strength of 1.0-1.2MPa), it is determined that the initial setting state has been reached. Immediately switch the original grouting pipe 5 to the compensation grouting mode: close the main pipeline valve and connect the dedicated compensation grout delivery pipeline.

[0074] The expansion-type compensating grout is injected with a mix ratio of P·O 42.5 cement: fly ash: magnesium oxide expansion agent: water-reducing agent = 1:0.25:0.09:0.01 (water-cement ratio 0.32). The injection flow rate is controlled at 0.15m³. 3 The pressure is maintained at 0.20±0.05MPa for 180 seconds at a constant rate of 0.20±0.05MPa. The injection volume is calculated using the formula Vc=0.03Vm (where Vm is the volume of the main concrete in this section). For example, each 3m³ section of main concrete corresponds to a compensation volume of 90L.

[0075] After grouting is completed, close the valve on grouting pipe 5 and keep the pipeline sealed for 12 hours. During this period, the magnesium oxide expanding agent continues to hydrate and expand, and the expansion force is transmitted to the entire cross-section of fiber bag 10 through the sealing grout. After 12 hours, open the vent valve to release pressure; the pressure gauge reading should be >0.8MPa (indicating effective compensation). Finally, pull out grouting pipe 5 and seal the pipe opening with quick-setting mortar.

[0076] Traditional post-grouting technology is implemented 7 days after pile formation. First, a hole is drilled along the pile side to the defective area. Cement grout is then injected under high pressure into the pile-soil interface through the drill rod. The grout penetrates the fiber bag 10 and enters the soil, forming an irregular reinforced zone, which easily leads to damage to the fiber bag 10 and inconsistent reinforcement effect. This embodiment achieves concrete shrinkage control, maintains interface strength, and prevents fiber bag 10 damage through three innovations: precise intervention during the initial setting period, targeted compensation with magnesium oxide expanding agent, and closed pressure curing.

[0077] Meanwhile, the solidification shrinkage of the fine aggregate concrete 14 causes a void layer to form between the fiber bag 10 and the hole wall 15, weakening the pile-soil synergy. In this embodiment, secondary compensation grouting is carried out using the original grouting pipe 5. The magnesium oxide expanding agent continuously expands in the closed space to compensate for the shrinkage, keeping the interface in a compacted state at all times.

[0078] Furthermore, in another embodiment, during the segmented grouting process in step S40, when the grout level reaches the current height of the annular sleeve 12, a hydraulic tensioner is used to perform secondary tensioning on the sleeve; the tension force F is calculated according to the formula: F=K・(P・A + F0), where the safety factor K=1.2-1.5, P=grouting pressure, A=cross-sectional area of ​​the fiber bag, and F0=initial preload; after tensioning, the sleeve elongation is controlled to be 105-110% of the initial installation value, and the pressure is kept stable until the grout in that segment initially sets.

[0079] Specifically, during each grouting process, when the grout level rises to 200mm from the bottom of the current annular sleeve 12, the hydraulic tensioning system is activated. The grouting pressure P and the cross-sectional area A of the fiber bag 10 (A=πD) are collected in real time using strain sensors embedded in the sleeve. 2 / 4, D is the current bag diameter). The data is refreshed every second and input into the control system, and the target tension is dynamically calculated according to the formula F=1.35×(P・A + F0) (F0 is the initial preload, with a value of 1.2kN).

[0080] When the grout surface touches the lower edge of the sleeve, the operator locks the sleeve end with the clamp of the hydraulic tensioner. A tensioning force of 5 kN / s is applied to the target value F and maintained at a stable pressure for 60 seconds. Simultaneously, a laser rangefinder is used to monitor the radial displacement of the sleeve, controlling the elongation to 107 ± 2% of the initial installation value (e.g., if the initial elongation is 3 mm, a second tensioning to 3.21-3.27 mm). Grouting pressure fluctuations are controlled within ±0.05 MPa throughout the tensioning process.

[0081] After tensioning, maintain the grouting pressure at 0.6 MPa until the grout penetration resistance reaches 3.5 MPa (approximately 120 minutes). During this period, check the strain value of the hoop every 15 minutes, and automatically fine-tune the tension if the fluctuation exceeds ±5%. After the structure is finalized, release the tensioning equipment and move it to the next hoop station.

[0082] Traditional clamp installation uses a one-time static pre-tightening: the clamp is tightened to the set value using a torque wrench during ground installation; there is no dynamic adjustment during grouting; the clamp pre-tightening force decays after completion due to creep caused by grouting pressure. This embodiment implements dynamic tensioning during the peak grout pressure period. The tensioning formula is used to correlate grouting parameters, and the P-A term is used to compensate for pressure loss. Elongation control ensures that the fiber bag 10 is in an elastically constrained state, effectively restraining the clamp and preventing the fiber bag 10 from bulging and deforming.

[0083] Furthermore, in another embodiment, when the borehole reveals a water inflow > 10m³ 3 When filling a water-rich karst cave with a flow rate of / h, before grouting in step S40, add quick-setting water-absorbing resin granules into the fiber bag 10. The feed amount is Q=0.15V・t, where V is the inflow rate in m³ / h. 3 / h, where t is the estimated number of grouting hours; The resin particles have a particle size of 2-4 mm and an expansion rate of ≥300% when exposed to water. After absorbing water, they form a gel with a compressive strength of >0.5 MPa. After feeding the material and letting it stand for 20 minutes, grouting begins, and the grouting flow rate is reduced to 60% of the conventional value.

[0084] Specifically, water inflow monitoring should be initiated immediately after the borehole exposes the karst cave: the water inflow should be continuously measured for 10 minutes using an electromagnetic flowmeter, and the peak value Qmax (m³) should be recorded. 3 / h), select resin type according to Qmax: Qmax≤20m 3 / h Select ordinary water-absorbing resin (expansion rate 300%); Qmax > 20m 3 / h Select quick-setting reinforced resin (expansion rate 450%); the amount of material to be added is calculated according to the formula: W=0.18・Qmax・T (T = estimated grouting hours, coefficient 0.18 includes 30% safety margin).

[0085] Resin granules are fed in stages through the feeding port at the top of fiber bag 10. The first 50% is fed to the bottom plate of the cave; the remaining 50% is evenly spread inside fiber bag 10 in the cave section. During the 20-minute standing period, the resin expansion status is monitored by camera inside the hole every 5 minutes. When the gel filling rate is >85% and the compressive strength is >0.3MPa, it is considered to meet the standard.

[0086] During grouting, the grouting parameters are adjusted so that the flow rate is 60% of the conventional value (e.g., conventional 1m). 3 / min decreased to 0.6m 3 The pressure limit is 0.7 times the conventional value (e.g., conventional 1.0 MPa, upper limit 0.7 MPa); the segment height is shortened to 1.0 meter (conventional 1.5 meters); the change in gel resistivity is monitored throughout the grouting process, and grouting is suspended and resin is replenished when the fluctuation is >10%.

[0087] Traditional treatment of water-rich karst caves uses two-liquid grouting, first injecting water glass and cement grout to form a water-stop curtain, and then pouring the pile body concrete 24 hours later. The water-stop curtain is easily damaged, which leads to unavoidable grout dilution and affects the strength of the pile body.

[0088] In this embodiment, the resin particles utilize groundwater expansion to seal seepage channels, absorb water vertically and transform into a gel to resist pressure, becoming an organic component of the pile body and improving the strength of the concrete pile body in the water-rich section; moreover, the resin forms a non-uniformly distributed gel plug group, effectively blocking water; at the same time, the material feeding ensures that the water absorption rate is greater than 120% of the inflow rate, ensuring safety redundancy.

[0089] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Further modifications can be readily implemented by those skilled in the art.

Claims

1. A construction method for a large-scale open-type karst cave local rock-making device, characterized in that the device... include: The variable-diameter hollow steel cylinder has a lower cross-section that is larger than the upper cross-section. The cylinder body has symmetrically staggered overflow holes, and the bottom variable-diameter section has symmetrically staggered overflow channels. The bag-shaped fiber bag has a rough structure with fine sand or pebbles embedded on the outside. When not grouted, the diameter of the upper section is larger than that of the lower section. A steel sleeve, anchored to the top of a steel cylinder, has a diameter larger than the cylinder body and is pre-drilled with anchor holes; A cylindrical plastic sleeve is bonded to the inner wall of a steel cylinder using a water-soluble adhesive. The diameter of the auger drill rod is smaller than the inner diameter of the steel cylinder. Hydraulic reamer bit, when opened, has a diameter larger than the outer diameter of the steel cylinder; The grouting pipe is inserted into a cylindrical plastic sleeve; The annular sleeve, through a short plastic tube, surrounds the outside of the fiber bag to form a segmented constraint structure; The upper end of the fiber bag is anchored to the steel sleeve, the lower end is anchored to the anchor hole at the bottom of the steel cylinder, and the bag body is bonded to the steel cylinder body with water-soluble adhesive. The construction method includes the following steps: S10. Determine the location, height, and size of the karst cave based on geological exploration, and calculate the length of the steel cylinder and the size of the fiber bag; S20. Insert the grouting pipe into the cylindrical plastic sleeve, fix the steel cylinder with clamps and ensure that its centerline coincides with the borehole centerline; simultaneously fix the fiber bags in sections and lower the steel cylinder as the drill rod drills, including: S21. Anchor the bottom end of the fiber bag to the bottom of the steel cylinder; S22. The fiber bags are bonded to the cylinder in sections, with a ring-shaped sleeve installed at the top of each section; S23. Repeat S22 until the fiber bag covers the cave, and the top is anchored to the steel sleeve; S30. After drilling to the bottom of the rock layer, retract the reaming drill bit and lower the steel cylinder to the bottom of the hole, then pour fine stone concrete until it is initially set; S40. Grout the fiber bag in sections from bottom to top until grout emerges from the top of the hole and stops, including: S41. Fine aggregate concrete is poured in sections, and the grout fills the gaps in the hole wall through the overflow trough and overflow hole; S42. Each grouting interval must allow the lower concrete to set initially, and finally, after the concrete at the steel sleeve has solidified, the grouting should be used to fill the opening.

2. The method according to claim 1, characterized in that, The overflow holes and overflow channels are symmetrically distributed at different heights, and the size of the overflow channels is smaller than that of the overflow holes; the length of the steel sleeve from the bottom of the steel cylinder is greater than the depth of the karst cave, so that the length of the fiber bag covers the karst cave and extends by a certain amount.

3. The method according to claim 1, characterized in that, The short plastic tubes are bonded to the outside of the fiber bag with epoxy resin adhesive; the ring-shaped hoop is a stirrup that passes through the short plastic tubes and divides the fiber bag into multiple bamboo-like structures.

4. The method according to claim 1, characterized in that, In step S20, the deviation between the center line of the steel cylinder and the center line of the borehole is ≤30mm; in step S41, the larger diameter of the upper part of the fiber bag has a lifting effect on the lower grouting section, and the annular sleeve restricts expansion deformation; in step S42, the height of each section of grout must exceed the current position of the annular sleeve.

5. The method according to claim 1, characterized in that, In step S30, the coarse aggregate of the fine stone concrete has a particle size ≤15mm. After grouting, it overflows through the overflow trough and binds to the steel cylinder, fiber bag and hole wall. In step S40, the grouting pipe is slowly raised as the grouting process progresses to avoid touching the auger drill rod.

6. The method as described in claim 1, characterized in that, After each section of grouting in step S42 is completed, a compensation grouting pipe is immediately inserted into the fiber bag of that section, and a compensation grout with an expansion rate of 2-3% is injected. The injection pressure is maintained at 0.15-0.25MPa for 3 minutes to form a pressure compensation chamber. The water-cement ratio of the compensation grout is 0.12 lower than that of the main fine stone concrete, and 8-10% magnesium oxide expansion agent is added. After the injection is completed, the grouting pipe is kept sealed for 12 hours, and then pulled out after the expansion agent has fully reacted.

7. The method as described in claim 1, characterized in that, During the segmented grouting process in step S40, when the grout level reaches the current annular sleeve height, a hydraulic tensioner is used to perform secondary tensioning on the sleeve. The tension force F is calculated according to the formula: F=K·(P·A + F0), where the safety factor K=1.2-1.5, P=grouting pressure, A=cross-sectional area of ​​the fiber bag, and F0=initial preload. After tensioning, the sleeve elongation is controlled to be 105-110% of the initial installation value, and the pressure is kept stable until the grout in that segment initially sets.

8. The method as described in claim 1, characterized in that, When the borehole reveals a water inflow >10m 3 When filling a water-rich karst cave with a flow rate of / h, before grouting in step S40, add quick-setting water-absorbing resin granules into the fiber bag. The feed rate is Q = 0.15V·t, where V is the water inflow rate in m³ / h. 3 / h, where t is the estimated grouting hours; the resin particles have a particle size of 2-4mm, an expansion rate of ≥300% when exposed to water, and form a gel with a compressive strength >0.5MPa after absorbing water; grouting begins 20 minutes after the material is added and the grouting flow rate is reduced to 60% of the conventional value.

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