A method for construction disposal of a multi-cave foundation pit in a weathered rock stratum area

Abstract

The application discloses a kind of weathered rock zone in multiple karst cave foundation pit construction disposal method, and multiple frame structures are arranged in foundation pit, middle part of frame structure is provided with center column, pile foundation is arranged below center column, slope protection pile is arranged on the outside of frame structure, slope protection pile passes through weathered rock layer, and pile body full filling karst cave and pile body half karst cave are distributed in the middle part of slope protection pile, pile bottom karst cave is distributed in the bottom of slope protection pile, foundation pit inner karst cave and pit bottom karst cave are respectively distributed in the middle and bottom of foundation pit, and pile foundation karst cave is distributed at pile foundation;The application is respectively disposed for three types of karst caves;And disposal method is respectively disposed by different drilling, grouting or feeding hole;By classification according to the position of karst cave, further refine disposal method and dispose according to building characteristics;Different ways of monitoring and detection are carried out for different karst cave types, which is beneficial to ensure construction quality and cost control.

Description

Technical Field

[0001] This invention belongs to the field of foundation pit construction technology, and specifically relates to a method for constructing and treating foundation pits with multiple karst caves in weathered rock strata. Background Technology

[0002] During foundation pit construction, due to the deep underground location of the building's basement, special geological features such as karst caves are often encountered, and the forms and locations of these caves are diverse. How to construct underground foundation pits in areas with numerous karst caves is a major challenge. Generally, the approach is to avoid karst caves during the design phase and fill and seal them during construction. However, there is a lack of corresponding designs for handling karst caves at different developmental stages and pile types. Simply avoiding or filling them is extremely detrimental to construction progress and cost control. Therefore, a targeted solution design is needed to address the multiple karst caves in weathered rock layers while balancing construction quality and efficiency. Summary of the Invention

[0003] This invention provides a method for constructing and treating foundation pits with multiple karst caves in weathered rock strata, which solves the technical problems of classifying and locating multiple karst caves in weathered rock strata areas and treating them in combination with the characteristics of pile bodies.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for constructing and treating a foundation pit with multiple karst caves in a weathered rock stratum area. The foundation pit is equipped with a multi-layered frame structure. A central column is set in the middle of the frame structure, and pile foundations are set below the central column. Retaining piles are set around the outside of the frame structure. The retaining piles penetrate the weathered rock stratum and have fully filled karst caves and partially filled karst caves in the middle of the retaining piles. Pile bottom karst caves are distributed at the bottom of the retaining piles. In the middle and bottom of the foundation pit, there are karst caves inside the foundation pit and karst caves at the bottom of the pit, respectively. Pile foundation karst caves are also distributed at the pile foundations. The cave is filled with filling material, partially filled with filling material, or completely empty. The cave is demarcated by its boundary line before drilling and grouting are carried out. The specific steps for constructing and treating foundation pits with multiple karst caves in weathered rock strata areas are as follows: Step 1: Before excavating the foundation pit, conduct karst exploration of the soil through geological drilling; treat known karst caves to ensure that the permeability meets the design requirements; Step 2: Before excavating the foundation pit and after excavating to the foundation, geophysical exploration methods are used to investigate the development of karst caves, following the principle of geophysical exploration before drilling. Step 3: All karst caves within 5m below the bottom slab of the frame structure and within 3m of the external wall of the structure shall be treated. According to the type of karst cave, they shall be divided into fully filled karst caves, semi-filled karst caves and empty karst caves. Fully filled karst caves that are not exposed during the excavation shall be grouted with pure cement grout. Step 4: For karst caves with a height greater than 1m that are partially filled or hollow, intermittent static pressure grouting shall be used. Step 5: For karst caves with a diameter greater than 4m, first fill them with crushed stone and then reinforce them with grouting. When filling the crushed stone, drill two additional injection holes near the sand blowing hole. The center of the two injection holes and the center of the sand blowing hole are on the same line. The two sand blowing holes serve as air outlets for each other. Step Six: For karst caves with a height of no more than 1m, and semi-filled karst caves, static pressure grouting is carried out directly using pure cement grout. Step 7: Based on the characteristics of the foundation pit, the frame structure, and the location of the central column and its pile foundation, the identified karst caves are classified according to their location into karst caves that are fully filled in the pile body, karst caves that are partially filled in the pile body, karst caves inside the foundation pit, karst caves at the bottom of the pile, karst caves at the bottom of the pit, and karst caves at the pile foundation. Then, the karst caves are treated and reinforced according to their respective types. Step 8: After reinforcement is completed, the filling material of the grouting in the karst cave is subjected to a compressive strength test using the random drilling core extraction method. For fully filled karst caves, the unconfined compressive strength after grouting treatment is ≥0.2MPa. For karst cave cavities and semi-filled karst caves, the unconfined compressive strength of the filling material is ≥0.8MPa. After the test is qualified, the construction and treatment of the multi-karst cave foundation pit in the weathered rock layer area is completed.

[0005] Furthermore, in step three, when part of the cave body is above the 5-meter line of the floor and part is below the 5-meter line, it also needs to be treated; when the thickness of the rock layers between the cave bodies cannot meet the condition of drilling into the cave floor 1m below, the lower cave should also be treated.

[0006] Furthermore, during the excavation of the foundation pit, any karst caves exposed at the bottom of the pit should have their filling material removed and be filled with C15 plain concrete.

[0007] Furthermore, for karst caves that have already been exposed at the bottom of the pit, if they are fully filled or partially filled, the filling material within 2m of the pit bottom should be removed first, and then C15 plain concrete should be used to fill them directly.

[0008] Furthermore, for the intermittent static pressure grouting in step four, the first grouting uses cement mortar, and the grouting time is controlled at 20 minutes. After a 6-hour interval, the second grouting is performed. The second grouting can use cement mortar or cement grout. If pressure is not achieved within 20 minutes, grouting is stopped, and after a 6-hour interval, the third grouting is performed. This process is repeated until the hole is closed. The grouting pressure is controlled at 0.3 to 0.5 MPa. The grouting pressure should be gradually increased during the grouting process to reach the design grouting pressure and continue grouting for more than 30 minutes. If necessary, an accelerator can be added appropriately to the cement mortar or cement grout.

[0009] Furthermore, in fully filled karst caves, drilling holes are spaced at the locations where the caves have been explored. These drilling holes serve as both exploration and grouting holes. Additionally, additional grouting holes are located at the center of the karst cave. A semi-filled karst cave consists of a partially filled area and the remaining karst cavity. A sand-blowing hole is drilled at the center of the karst cave; this hole serves as both a drilling hole and a gravel-pouring hole. The drilling hole is used to explore the karst cave's development and determine its boundary. Injection and discharge holes are symmetrically spaced around the sand-blowing hole; these holes serve as both grouting and material-pouring holes. Drilling and injection holes are spaced around the injection and discharge holes until they reach near the karst cave boundary. At least on one side of the karst cavity area, there is an injection and discharge hole, which serves as both grouting and venting holes. Specifically, the sand-blowing hole extends through the filled area to the rock strata, the injection and discharge hole extends to the filled area, the drilling and injection hole extends to the rock strata, and the injection and discharge hole extends to the upper part of the karst cavity. The cave is a hollow cave with a sand blowing hole in the center. A symmetrical injection hole is set around the sand blowing hole, and a drilling hole is set around the injection hole and near the edge of the cave. At least one injection and drainage hole is set on one side of the cave cavity area. The sand blowing hole is drilled to the rock stratum, the drilling hole is drilled to the rock stratum area, the injection hole is drilled to the bottom of the cavity, and the injection and drainage hole is drilled to the upper middle part of the cavity.

[0010] Furthermore, when the pile body of the slope protection pile is fully filled with karst caves, it is simultaneously filled when passing through the construction pile body. The pile body semi-karst caves are semi-filled karst caves, which are treated with cement mortar.

[0011] Furthermore, karst caves within the foundation pit are directly excavated; karst caves at the bottom of the pit within 5m are treated with grouting according to their type.

[0012] Furthermore, for the karst cave at the bottom of the slope protection pile, the pile bottom is inserted into the karst cave and embedded below the karst cave, provided that the design pile bottom elevation is met. If the distance between the bottom of the karst cave and the bottom of the slope protection pile is greater than 2m, a cover plate is used for pile driving; if it is greater than 1m, open excavation is used for pile driving. For pile foundations containing karst caves, the pile foundations that directly penetrate the karst caves and are embedded in the moderately weathered rock layer below the karst caves for no less than 2m, and the karst caves within a range of 3 times the diameter of the pile foundation below the central column, shall be treated according to their type.

[0013] Furthermore, the evaluation of grouting should focus on comparing test data before and after grouting. The number of test boreholes should be no less than 5% of the total number of grouting holes, and no less than 3 points. For complex sites with karst foundations, the number of test points should be appropriately increased. For filling and reinforcement, each karst cave should be tested once. The borehole layout should be 200-300mm away from the filling grouting holes. For the permeability evaluation of grouting, the water pressure test should be conducted, with the number of test points no less than 2% of the number of grouting holes and no less than 3 points for a single project, and the test points should meet the design requirements.

[0014] The beneficial effects of this invention are reflected in: 1) This invention classifies karst caves in weathered rock strata into three types: fully filled karst caves, semi-filled karst caves, and hollow karst caves, and treats each type of karst cave separately; and the treatment methods are carried out separately through different boreholes, grouting or material feeding holes; 2) This invention further refines the treatment methods and combines them with architectural characteristics by classifying the caves according to their location; 3) This invention utilizes different monitoring and detection methods for different types of karst caves, which helps ensure construction quality and cost control. Other features and advantages of this invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention; the main objectives and other advantages of this invention can be realized and obtained by means of the methods particularly pointed out in the description. Attached Figure Description

[0015] Figure 1 It is a structure for the construction and treatment of foundation pits with multiple karst caves in weathered rock strata; Figure 2 It is a fully filled karst cave treatment structure; Figure 3 It is a semi-filled karst cave treatment structure; Figure 4 It is a structure for treating cavities in karst caves; Figure 5 This is a map showing the distribution of some of the holes.

[0016] Attached diagram labels: 1-Foundation pit, 2-Slope protection pile, 3-Frame structure, 4-Central column, 5-Pile foundation under column, 6-Pile body fully filled with karst cave, 7-Pile body partially filled with karst cave, 8-Karst cave inside the foundation pit, 9-Karst cave at the bottom of the pile, 10-Karst cave at the bottom of the pit, 11-Karst cave in the pile foundation, 12-Foundation pit bracing, 13-Karst cave edge, 14-Filling material, 15-Drilling hole, 16-Increased grouting hole, 17-Ground surface, 18-Injection hole, 19-Sand blowing hole, 20-Injection and drainage hole, 21-Karst cave cavity, 22-Geological borehole. Detailed Implementation

[0017] Taking the construction of a train station's basement as an example, such as Figures 1 to 5 As shown, a foundation pit 1 is excavated below ground level 17. A multi-layered frame structure 3 is set inside the foundation pit 1. A central column 4 is set in the middle of the frame structure 3. A pile foundation 5 is set below the central column 4. Slope protection piles 2 are set around the outside of the frame structure 3. Foundation pit bracing 12 is set between the slope protection piles 2. The slope protection piles 2 penetrate the weathered rock layer and have fully filled karst caves 6 and partially filled karst caves 7 distributed in the middle of the slope protection piles 2. Pile bottom karst caves 9 are distributed at the bottom of the slope protection piles 2. Foundation pit karst caves 8 and pit bottom karst caves 10 are distributed in the middle and bottom of the foundation pit 1, respectively. Pile foundation karst caves 11 are distributed at the pile foundation 5.

[0018] The cave is filled with filling material 14, partially filled with filling material 14, or completely empty cave 21. The cave is demarcated by the cave boundary line 13 before drilling and grouting are carried out.

[0019] Combination Figures 1 to 5 To further explain the construction and treatment methods for foundation pits with multiple karst caves in weathered rock strata areas, the specific steps are as follows: Step 1: Before excavating the foundation pit 1, conduct karst exploration of the soil through geological borehole 22; treat known karst caves to ensure that the permeability meets the design requirements.

[0020] Step 2: Before excavating foundation pit 1 and after excavation to the foundation, geophysical exploration methods were used to investigate the development of karst caves, following the principle of geophysical exploration before drilling.

[0021] Step 3: All karst caves within 5m below the bottom slab of frame structure 3 and within 3m of the external wall of the structure shall be treated. According to the type of karst cave, they shall be divided into fully filled karst caves, semi-filled karst caves and karst cave cavities 21. Fully filled karst caves that are not exposed during the excavation shall be grouted with pure cement grout.

[0022] In this embodiment, the fully filled karst cave is provided with drilling holes 15 at intervals at the developed locations of the karst cave. The drilling holes 15 are dual-purpose holes for drilling exploration and grouting. At the center of the karst cave, additional grouting holes 16 are provided.

[0023] In this embodiment, the semi-filled karst cave includes a partially filled area and the remaining karst cave cavity 21. A sand blowing hole 19 is drilled at the center of the karst cave, wherein the sand blowing hole 19 is a dual-purpose hole for drilling and crushing stone placement. The drilling is used to explore the development of the karst cave and determine the karst cave boundary 13. A symmetrical injection hole 18 is arranged at intervals around the sand blowing hole 19, wherein the injection hole 18 is a dual-purpose hole for grouting and material placement. Drilling and injection holes 15 are arranged at intervals around the injection and injection holes 18 to the vicinity of the karst cave boundary 13. At least on one side of the karst cave cavity 21 area, an injection and drainage hole 20 is provided, which is a dual-purpose hole for grouting and venting. The sand blowing hole 19 is drilled through the filled area to the rock strata, the injection and drainage hole 18 is drilled to the filled area, the drilling and injection hole 15 is drilled to the rock strata area, and the injection and drainage hole 20 is drilled to the upper part of the karst cave cavity 21. In this embodiment, the cavern 21 is a cavern entirely composed of cavities. A sand blowing hole 19 is drilled at the center of the cavern, and injection holes 18 are symmetrically arranged at intervals around the sand blowing hole 19. Drilling holes 15 are arranged at intervals around the injection holes 18 and near the edge of the cavern 13. At least one side of the cavern 21 area is provided with injection and drainage holes 20. The sand blowing hole 19 is drilled to the rock stratum, the drilling holes 15 are drilled to the rock stratum area, the injection holes 18 are drilled to the bottom of the cavity, and the injection and drainage holes 20 are drilled to the upper middle part of the cavity.

[0024] In step three, when part of the cave is above the 5-meter line of the bottom slab and part is below the 5-meter line, the same treatment is required. When the rock layer thickness between the caves is insufficient to allow drilling to reach 1 meter below the bottom slab of the cave, the lower cave should also be treated. During the excavation of foundation pit 1, the filling material 14 exposed at the bottom of foundation pit 1 should be removed and filled with C15 plain concrete. For through-type caves already exposed at the bottom of the pit, if they are fully filled or partially filled, first remove the filling material 14 within 2 meters of the pit bottom, and then directly fill with C15 plain concrete.

[0025] Step 4: For karst caves with a height greater than 1m and that are partially filled or have voids 21, intermittent static pressure grouting shall be used.

[0026] For the intermittent static pressure grouting in step four, the first grouting uses cement mortar, and the grouting time is controlled at 20 minutes. After a 6-hour interval, the second grouting is performed. The second grouting can use cement mortar or cement grout. If pressure is not achieved within 20 minutes, grouting is stopped, and after a 6-hour interval, the third grouting is performed. This process is repeated until the hole is closed. The grouting pressure is controlled at 0.3 to 0.5 MPa. The grouting pressure should be gradually increased during the grouting process to reach the design grouting pressure and continue grouting for more than 30 minutes. If necessary, an accelerator can be added appropriately to the cement mortar or cement grout.

[0027] Step 5: For the karst cave 21 with a diameter greater than 4m, first throw crushed stone and then reinforce it with grouting; when throwing crushed stone, drill two injection holes 18 near the sand blowing hole 19. The center of the two injection holes 18 and the center of the sand blowing hole 19 are on the same line, and the two sand blowing holes 19 serve as air outlets for each other.

[0028] Step Six: For karst caves with a height of no more than 1m, including hollow caves 21 and semi-filled caves, static pressure grouting is carried out directly using pure cement grout.

[0029] Step 7: Based on the characteristics of the foundation pit 1, the frame structure 3, the central column 4, and the location of its pile foundation 5, the discovered karst caves are classified according to their location into karst caves that are fully filled in the pile body 6, karst caves that are partially filled in the pile body 7, karst caves inside the foundation pit 8, karst caves at the bottom of the pile 9, karst caves at the bottom of the pit 10, and karst caves at the pile foundation 11. Then, the karst caves are treated and reinforced according to their respective types.

[0030] In this embodiment, the pile body of the slope protection pile 2 is fully filled with karst cave 6, and the pile body is simultaneously filled when passing through the construction pile. The pile body semi-filled karst cave 7 is treated with cement mortar. Karst cave 8 in the foundation pit is directly excavated; karst cave 10 at the bottom of the foundation pit within 5m of the bottom of the foundation pit 1 is grouted according to the type of karst cave.

[0031] In this embodiment, for the pile bottom karst cave 9 at the bottom of the slope protection pile 2, the pile bottom is embedded below the karst cave while meeting the design pile bottom elevation. If the distance between the bottom of the karst cave and the bottom of the slope protection pile 2 is greater than 2m, a cover plate is used for pile lowering; if it is greater than 1m, open excavation is used for pile lowering. For the pile foundation 5 where the pile foundation karst cave 11 is located, the pile foundation 5 directly passes through the karst cave and is embedded in the moderately weathered rock layer below the karst cave for no less than 2m. All karst caves within 3 times the diameter of the pile foundation 5 below the central column 4 are treated according to their type.

[0032] Step 8: After reinforcement is completed, the filling material 14 of the karst cave is subjected to a compressive strength test by random drilling core extraction. The unconfined compressive strength of the grout after grouting treatment of fully filled karst caves is ≥0.2MPa. The unconfined compressive strength of the filling material for karst cave cavities 21 and semi-filled karst caves is ≥0.8MPa. After the test is qualified, the construction and treatment of the multi-karst cave foundation pit 1 in the weathered rock layer area is completed.

[0033] For grouting evaluation, the evaluation of grouting effect and strength focuses on the comparison of test data before and after grouting. The number of test boreholes should be no less than 5% of the total number of grouting holes, and no less than 3 points. For complex sites with karst foundations, the number of test points should be appropriately increased. For filling and reinforcement, each karst cave should be tested once. The borehole layout should be 200-300mm away from the filling grouting holes. For the permeability evaluation of grouting effect, the water pressure test should be conducted. The number of test points should be no less than 2% of the number of grouting holes, and no less than 3 points for a single project, and should meet the design requirements.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing and treating foundation pits with multiple karst caves in weathered rock strata, characterized in that, A multi-layered frame structure (3) is set inside the foundation pit (1). A central column (4) is set in the middle of the frame structure (3). A pile foundation (5) is set below the central column (4). Slope protection piles (2) are set around the outside of the frame structure (3). The slope protection piles (2) pass through the weathered rock layer and are distributed in the middle of the slope protection piles (2) with pile body full-filled karst caves (6) and pile body half-karst caves (7). Pile bottom karst caves (9) are distributed at the bottom of the slope protection piles (2). In the middle and bottom of the foundation pit (1), there are foundation pit karst caves (8) and pit bottom karst caves (10) respectively, and pile foundation karst caves (11) are distributed at the pile foundation (5). The cave is filled with filling material (14), partially filled with filling material (14), or completely empty (21). The cave is delineated by the cave boundary line (13) before drilling and grouting are carried out. The specific steps for constructing and treating foundation pits with multiple karst caves in weathered rock strata areas are as follows: Step 1: Before excavating the foundation pit (1), conduct karst exploration of the soil through geological boreholes (22); treat known karst caves to ensure that the permeability meets the design requirements; Step 2, Foundation Pit (1) Before excavation and after excavation to the foundation, geophysical exploration methods are used to investigate the development of karst caves according to the principle of geophysical exploration first and drilling later; Step 3: For the karst caves within 5m below the bottom slab of the frame structure (3) and within 3m of the outer wall of the structure, they are treated. According to the type of the karst caves, they are divided into fully filled karst caves, semi-filled karst caves and karst cave cavities (21). Fully filled karst caves that are not exposed during the excavation process are grouted with pure cement grout. During the excavation of the foundation pit (1), the filling material (14) of the karst cave exposed at the bottom of the foundation pit (1) is removed and filled with C15 plain concrete; For the exposed karst cave at the bottom of the pit, if it is a fully filled or semi-filled karst cave, first remove the filling material (14) within 2m from the bottom of the pit inside the karst cave, and then directly fill it with C15 plain concrete. Step 4: For karst caves with a height greater than 1m and that are partially filled or hollow (21), intermittent static pressure grouting shall be used for grouting. Step 5: For karst caves (21) with a diameter greater than 4m, first throw crushed stone and then reinforce with grouting; when throwing crushed stone, drill two injection holes (18) near the blowing hole (19). The center of the two injection holes (18) and the center of the blowing hole (19) are on the same line. The two blowing holes (19) serve as air outlets for each other. Step 6: For karst caves with a height of no more than 1m (21) and semi-filled karst caves, static pressure grouting is carried out directly using pure cement grout; Step 7: Based on the characteristics of the foundation pit (1), the frame structure (3), the central column (4), and the location of its pile foundation (5), the discovered karst caves are classified according to their location into pile-filled karst caves (6), pile-partial karst caves (7), foundation pit karst caves (8), pile bottom karst caves (9), pit bottom karst caves (10), and pile foundation karst caves (11). Then, the karst caves are treated and reinforced according to their various types. Step 8. After reinforcement is completed, the filling material (14) of the grouting of the karst cave is subjected to a compressive strength test by random drilling core extraction method. The unconfined compressive strength of the grouting material of the fully filled karst cave is ≥0.2MPa. The unconfined compressive strength of the filling material of the karst cave cavity (21) and the semi-filled karst cave is ≥0.8MPa. After the test is qualified, the construction and treatment of the multi-karst cave foundation pit (1) in the weathered rock layer area is completed.

2. The method for constructing and treating foundation pits with multiple karst caves in weathered rock strata as described in claim 1, characterized in that, In step three, when part of the cave body is above the 5-meter line of the floor and part is below the 5-meter line, it also needs to be treated; when the rock layer thickness between the cave bodies cannot meet the condition of drilling into the cave floor 1m below, the lower cave should also be treated.

3. The method for constructing and treating foundation pits with multiple karst caves in weathered rock strata as described in claim 1, characterized in that, For the intermittent static pressure grouting in step four, the first grouting uses cement mortar, and the grouting time is controlled at 20 minutes. After a 6-hour interval, the second grouting is performed. The second grouting can use cement mortar or cement grout. If pressure is not achieved within 20 minutes, grouting is stopped, and after a 6-hour interval, the third grouting is performed. This process is repeated until the hole is closed. The grouting pressure is controlled at 0.3 to 0.5 MPa. The grouting pressure should be gradually increased during the grouting process to reach the design grouting pressure and continue grouting for more than 30 minutes. If necessary, an accelerator can be added appropriately to the cement mortar or cement grout.

4. The method for constructing and treating foundation pits with multiple karst caves in weathered rock strata as described in claim 1, characterized in that, The fully filled karst cave has drill holes (15) set at intervals at the developed locations of the karst cave. The drill holes (15) are dual-purpose holes for drilling exploration and grouting. At the center of the karst cave, there are also additional grouting holes (16). A semi-filled karst cave includes a partially filled area and the remaining karst cave cavity (21). A sand blowing hole (19) is drilled at the center of the karst cave. The sand blowing hole (19) is a dual-purpose hole for drilling and crushing stone placement. The drilling hole is used to explore the development of the karst cave and determine the karst cave boundary (13). A symmetrical injection hole (18) is set at intervals around the sand blowing hole (19). The injection hole (18) is a dual-purpose hole for grouting and material placement. A drilling injection hole (15) is set at intervals around the injection injection hole (18) and near the karst cave boundary (13). An injection and discharge hole (20) is set on at least one side of the karst cave cavity (21). The injection and discharge hole (20) is a dual-purpose hole for grouting and air venting. The sand blowing hole (19) is drilled through the filled area to the rock stratum, the injection hole (18) is drilled to the filled area, the drilling injection hole (15) is drilled to the rock stratum area, and the injection and discharge hole (20) is drilled to the upper part of the karst cave cavity (21). The cave cavity (21) is a cave that is entirely hollow. A sand blowing hole (19) is drilled in the center of the cave. A symmetrical injection hole (18) is set at intervals around the sand blowing hole (19). A drilling hole (15) is set at intervals around the injection hole (18) and near the edge of the cave (13). An injection and drainage hole (20) is set on at least one side of the cave cavity (21). The sand blowing hole (19) is drilled to the rock layer, the drilling hole (15) is drilled to the rock layer area, the injection hole (18) is drilled to the bottom of the cavity, and the injection and drainage hole (20) is drilled to the upper middle part of the cavity.

5. The method for constructing and treating foundation pits with multiple karst caves in weathered rock strata as described in claim 1, characterized in that, When the pile body of the slope protection pile (2) is fully filled with karst cave (6) and passes through the construction pile body, it is simultaneously filled. The pile body semi-karst cave (7) is a semi-filled karst cave and is treated with cement mortar.

6. The method for constructing and treating foundation pits with multiple karst caves in weathered rock strata as described in claim 1, characterized in that, The karst caves (8) inside the foundation pit are directly excavated; the karst caves (10) at the bottom of the foundation pit (1) within 5m of the bottom are grouted according to the type of karst cave.

7. The method for constructing and treating foundation pits with multiple karst caves in weathered rock strata as described in claim 1, characterized in that, For the pile bottom karst cave (9) at the bottom of the slope protection pile (2), the pile bottom is embedded below the karst cave under the premise of meeting the design pile bottom elevation. If the distance between the bottom of the karst cave and the bottom of the slope protection pile (2) is greater than 2m, the pile is lowered by cover plate; if it is greater than 1m, the pile is lowered by open excavation. For the pile foundation (5) where the pile foundation (11) is located, the pile foundation (5) directly penetrates the karst cave and is embedded in the moderately weathered rock layer below the karst cave for no less than 2m. The karst cave within 3 times the diameter of the pile foundation (5) below the central column (4) is treated according to its type.

8. The method for constructing and treating foundation pits with multiple karst caves in weathered rock strata as described in claim 1, characterized in that, For grouting evaluation, the evaluation of grouting effect and strength focuses on the comparison of test data before and after grouting. The number of test holes should be no less than 5% of the total number of grouting holes and no less than 3 points. For complex sites with karst foundations, the number of test points should be appropriately increased. The filling and reinforcement requirements stipulate that each karst cave must be tested once, and the drilling layout should be 200-300mm away from the filling grouting hole; the water pressure test for the grouting effect permeability assessment shall have no less than 2% of the number of grouting holes and no less than 3 points for a single project, and shall meet the design requirements.

Images