A method for detecting and treating karst caves in anchor cable zones of limestone retaining structures

Abstract

This invention belongs to the field of karst cave treatment technology and discloses a method for detecting and treating karst caves in the anchor cable area of ​​a limestone stratum retaining structure. The method includes the following steps: S1, delineating the karst cave treatment area in the anchor cable area; S2, advanced drilling in the anchor cable area; S3, exploring the karst cave boundary in the anchor cable area; S4, grouting treatment of the karst cave in the anchor cable area; S5, detecting the grouting effect in the karst cave in the anchor cable area; S6, anchor cable construction and anchor cable bearing capacity testing. Through these six steps, the detection and treatment of karst caves in limestone areas can be effectively achieved, ensuring the stability of the anchor cables in the limestone stratum. This effectively reduces the risk of collapse of the anchor cables during the construction of the retaining structure, reduces the rapid development of karst caves under the disturbance of anchor cable construction, and reduces the risk of water inrush and gushing water. It also effectively improves the bearing capacity and deformation resistance of the anchor cable foundation pit support in limestone stratum retaining structures, and enhances the safety of underground structure construction.

Description

Technical Field

[0001] This invention belongs to the field of karst cave treatment technology, specifically relating to a method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure. Background Technology

[0002] When carrying out engineering construction in limestone strata, it is common to encounter karst caves. Karst caves are an unfavorable geological condition for engineering construction and need to be dealt with. If karst caves are not handled properly, accidents such as ground collapse and failure of engineering retaining structures can easily occur. Once an engineering accident occurs, it will have an adverse impact on people's lives and property and the economy.

[0003] Currently, in foundation pit construction in limestone areas, the support method of "retaining piles or diaphragm walls + internal bracing" is commonly used. The treatment of karst caves is mostly limited to the retaining piles and diaphragm walls. If a pile-anchor support system is used in limestone areas, the "anchor cable anchorage section" anchored in the limestone strata directly affects the safety of the retaining structure. Therefore, when using a pile-anchor support system in limestone areas, attention must be paid not only to the treatment of karst caves within the retaining piles and diaphragm walls, but also to the treatment of karst caves in the "anchor cable area" to avoid anchorage failure caused by encountering karst caves in the limestone strata. Because the use of pile-anchor support systems in limestone strata is relatively rare, there is currently a lack of corresponding methods for treating karst caves in the anchor cable area of ​​limestone retaining structures. Before treating karst caves in limestone strata, it is necessary to conduct detection. Currently, there is a lack of specific methods for detecting and treating karst caves in the anchor cable area of ​​limestone strata retaining structures, in order to effectively reduce the risks of collapse, water inrush, and water surge during anchor cable construction.

[0004] Therefore, a new technology is needed to address the lack of a method for detecting and treating karst caves in anchor cable zones of limestone strata retaining structures, which is currently lacking in existing technologies. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a method for detecting and treating karst caves in anchor cable zones of limestone strata retaining structures. This method is mainly applied to the detection and treatment of karst caves in anchor cable zones of limestone strata, and can effectively reduce the risks of collapse, water inrush, and water surge during anchor cable construction of retaining structures.

[0006] The present invention adopts the following technical solution:

[0007] A method for detecting and treating karst caves in anchor cable zones of limestone strata retaining structures includes the following steps:

[0008] S1. Delineation of the treatment area for karst caves in the anchor cable zone;

[0009] S11. Determine the treatment range of the karst cave in the anchor cable area based on the planar and vertical layout of the anchor cables;

[0010] S2, advance drilling in the anchor cable zone;

[0011] S21. In conjunction with detailed exploration drilling, several advance drilling holes shall be set in the anchoring section layout area of ​​the anchor cable;

[0012] S3. Explore the boundary of the karst cave in the anchor cable area;

[0013] S31. Within the treatment area of ​​the karst cave in the anchor cable area, for the karst caves initially revealed by the detailed exploration boreholes and advance boreholes in the anchor cable anchorage section layout area, exploration holes are drilled to detect the karst cave boundaries.

[0014] S4. Grouting treatment of karst caves in the anchor cable area;

[0015] S41. Some of the "advanced drilling holes or edge probing holes" also serve as grouting holes. According to the karst cave area and boundary, the grouting holes are divided into central holes and peripheral holes; among them, some of the central holes also serve as ventilation holes.

[0016] S42. Grouting is performed on the karst cave through the grouting holes according to the type of karst cave;

[0017] S5. Inspection of grouting effect in the anchor cable zone of the karst cave;

[0018] S51. After the grouting is completed, the filling and reinforcement effects of the karst cave are inspected.

[0019] S6. Anchor cable construction and anchor cable bearing capacity testing;

[0020] S61. After completing the grouting treatment and grouting effect test of the karst cave, locate the anchor cable drilling position at the retaining structure and drill to the designed anchor cable depth.

[0021] S62. Carry out the procedures of laying anchor cables, grouting and constructing anchor cable waist beams;

[0022] S63. After the concrete of the anchor cable waist beam reaches the design strength, the anchor cable is tensioned and the pull-out force and locking force of the anchor cable are tested.

[0023] Furthermore, in step S11, the anchor cable includes an anchored section and a free section; the treatment range of the karst cave in the anchor cable area includes a planar treatment range and a vertical treatment range.

[0024] The planar processing range includes a first planar boundary, a second planar boundary, a third planar boundary, and a fourth planar boundary; the first planar boundary maintains a first predetermined distance from the first side anchor cable, the second planar boundary maintains a second predetermined distance from the second side anchor cable, the third planar boundary maintains a third predetermined distance from the first end of the anchoring section of the anchor cable, and the fourth planar boundary maintains a fourth predetermined distance from the second end of the anchoring section of the anchor cable; the planar area enclosed by the first planar boundary, the second planar boundary, the third planar boundary, and the fourth planar boundary is the planar processing range;

[0025] The vertical processing range includes a ground boundary, an underground boundary, a first vertical boundary, and a second vertical boundary; the ground boundary is a leveled ground surface; the underground boundary maintains a fifth predetermined distance from the lowest point of the anchor cable anchoring section; the first vertical boundary maintains a sixth predetermined distance from the first end of the leftmost anchor cable anchoring section; the second vertical boundary maintains a seventh predetermined distance from the second end of the rightmost anchor cable anchoring section; the vertical area enclosed by the ground boundary, the underground boundary, the first vertical boundary, and the second vertical boundary is the vertical processing range.

[0026] The three-dimensional area formed by the planar treatment range and the vertical treatment range is the area to be determined for the treatment of the anchor cable zone cave.

[0027] Furthermore, in step S21, the detailed exploration borehole also serves as a pre-drilling borehole, and combined with the pre-drilling boreholes obtained from subsequent drilling, there are a total of several pre-drilling boreholes arranged in a row, and the several pre-drilling boreholes are respectively adjacent to the anchoring section of the anchor cable; the several pre-drilling boreholes are perpendicular to the horizontal plane formed by the plane processing range; the several pre-drilling boreholes maintain a set hole spacing between adjacent holes.

[0028] Furthermore, in step S31, (the detailed exploration borehole also serves as the advance borehole, so it can be described simply as the advance borehole) when the karst cave revealed by the advance borehole is within the karst cave treatment range of the anchor cable area, the advance borehole is used as the base point of the "cross" axis, and then a sequential exploration hole is drilled along the four axial length directions of the "cross" axis at a set interval.

[0029] If a karst cave is discovered during the probing of the first-order probing hole, the first-order probing hole is used as the base point of the "+" axis. Then, one or more axial length directions of the "+" axis are selected, and second-order probing holes are drilled at a set interval until the boundary of the karst cave or the boundary of the karst cave treatment range of the anchor cable area is found.

[0030] Furthermore, in step S41, the grouting pipe is embedded in the selected grouting hole, and grouting can only be performed after the gap between the "cavity top plate, grouting pipe" and the "grouting hole wall" is sealed.

[0031] Furthermore, in step S42, the cave is classified into unfilled caves, semi-filled caves, and fully filled caves based on the natural filling material inside.

[0032] The unfilled or partially filled karst caves around the perimeter holes are filled with a cement-water glass double slurry.

[0033] For the central hole, the "unfilled karst cave or the semi-filled karst cave" with a height ≥3m is first filled with cement mortar, and then compacted with cement grout. The "unfilled karst cave or the semi-filled karst cave" with a height less than 3m is filled with mortar or cement grout. For the fully filled karst cave, if the standard penetration test value of the natural infill material is less than 10 blows, compaction grouting with cement grout is used. If the standard penetration test value of the natural infill material in the fully filled karst cave is ≥10 blows, no treatment is required.

[0034] After grouting is completed, cement grout must be used to seal the holes.

[0035] Furthermore, in step S4, an on-site grouting test should be conducted before construction to determine the grouting parameters;

[0036] For the peripheral holes, the grouting pressure is 0.6 MPa to 0.8 MPa, and the number of grouting operations is 3 to 4.

[0037] For the central hole, cement grout should be injected three times at a grouting pressure of 0 MPa to 1.0 MPa and a grouting speed of 30 L / min to 70 L / min. The grouting pressure should be gradually increased. After reaching the final grouting pressure, grouting should continue for more than 10 minutes. The grout should be made of 42.5 grade ordinary Portland cement with a water-cement ratio of 1.0 to 1.5.

[0038] Furthermore, the inspection of the grouting effect for filling the karst cave mentioned in step S51 involves checking the filling rate using a "secondary grouting" method, gradually increasing the pressure from 0 MPa to 0.2 MPa and maintaining it for 10 to 15 minutes; and checking the compaction using the Standard Penetration Test (SPT). A SPT value of "hard" soil is considered excellent, while a SPT value of "hard plastic" soil is considered qualified.

[0039] Furthermore, the inspection of the grouting reinforcement effect of the karst cave mentioned in step S51 shall be carried out by core drilling and by performing compressive strength test, water pressure test and in-situ standard penetration test, with the number of inspections not less than 1% of the number of grouting holes; each karst cave shall be inspected at least once; among them, the test blocks obtained by random core drilling shall be subjected to compressive strength test, and their unconfined compressive strength shall not be less than 0.2 MPa; among them, the water pressure test of the quality inspection holes shall be carried out at least seven days after the completion of the grouting of the unit project; among them, the water permeability of the quality inspection holes after karst cave reinforcement treatment shall not be greater than 10 Lu, the pass rate shall be more than 85%, the maximum permeability of the unqualified hole section shall not exceed 15 Lu, and shall not be concentrated; among them, the standard penetration test shall not be less than 10 blows.

[0040] Furthermore, in step S61, if a karst cave is discovered during the anchor cable drilling process, grout should be injected into the anchor cable hole in a timely manner, and drilling should continue after the treatment is completed.

[0041] In step S62, the effective anchorage length of the anchor cable should not be less than the designed anchorage length and should penetrate the karst cave into the stable rock layer for no less than 3m.

[0042] In step S63, to ensure the effective bearing capacity of the anchor cables in the limestone area, the anchor cables traversing the karst caves, when applying prestress, include the following steps:

[0043] B1. First determine which value is larger, "1.4 times Fm or 0.8 times Fn", where Fm is the "standard value of calculated tensile force" and Fn is the "standard value of ultimate tensile strength of anchor cable".

[0044] B2. If 1.4Fm is a larger value than 0.8Fn, then when applying the preload, the tension should be increased to 1.4Fm first, and then released and retracted to the locking force value to lock.

[0045] If 0.8Fn is a larger value than 1.4Fm, then when applying the preload, the tension should be increased to 0.8Fn first, and then released and retracted to the locking force value to lock.

[0046] In step S63, the number of anchor cables tested for bearing capacity shall not be less than 10% and shall not be less than ten.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0048] The present invention proposes a method for detecting and treating karst caves in anchor cable zones of limestone strata retaining structures, comprising six steps: S1, delineation of the karst cave treatment area in the anchor cable zone; S2, advance drilling in the anchor cable zone; S3, exploration of the karst cave boundaries in the anchor cable zone.

[0049] S4. Grouting treatment of karst caves in the anchor cable area; S5. Inspection of grouting effect in the anchor cable area; S6. Anchor cable construction and anchor cable bearing capacity testing. These six steps effectively enable the detection and treatment of karst caves in limestone areas, ensuring the stability of anchor cables in limestone strata. This effectively reduces the risk of collapse of anchor cables in retaining structures during construction, reduces the rapid development of karst caves and the risk of water inrush and gushing due to disturbance during anchor cable construction, and effectively improves the bearing capacity and deformation resistance of anchor cable foundation pits in limestone strata, thereby enhancing the safety of underground structure construction.

[0050] The method for detecting and treating karst caves in anchor cable zones of limestone strata retaining structures proposed in this invention is mainly applied to the "detection and treatment of karst caves in anchor cable zones" in limestone strata. It solves the problem that anchor cable anchorage sections are prone to anchorage instability when encountering karst caves in limestone strata. To a certain extent, the method proposed in this invention fills the current research gap in this field ("safe construction of pile-anchor support systems in limestone strata with karst caves"), making the construction of pile-anchor support systems in limestone areas more scientific and safe. Attached Figure Description

[0051] The technology of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0052] Figure 1 This is a top view of the area where the karst caves in the anchor cable zone have been treated. Figure 1 (This is also a schematic diagram of the planar treatment range.) (The anchor cables are projected from above and can be understood as the planar arrangement of the anchor cables. Based on the planar arrangement of the anchor cables, engineers can determine the planar treatment range of the karst caves in the anchor cable area. Based on the planar arrangement of the anchor cables, engineers can preliminarily reveal the karst caves in the anchor cable area of ​​the limestone layer through detailed exploration drilling and advance drilling.)

[0053] Figure 2 yes Figure 1 Sectional view at SS ( Figure 2 This is an elevation view of the treatment area for karst caves in the anchor cable zone (i.e., a schematic diagram of the vertical treatment area). (It shows the vertical arrangement of the anchor cables. Based on the vertical arrangement of the anchor cables, engineers can determine the vertical treatment area of ​​the karst caves in the anchor cable zone, so that engineers can initially reveal the karst caves in the limestone anchor cable zone through detailed exploration boreholes and advance boreholes.) Figure 1 and Figure 2 The anchor cable arrangement is derived from the construction drawings, which need to be completed before "determining the scope of karst cave treatment in the anchor cable area";

[0054] Figure 3The diagram shows how engineers drill "first-order probing holes" along the four axes of the "cross" at predetermined intervals, using the pre-drilled hole as the base point of the "cross" axis. (The "cross" axis is a coordinate axis designed for ease of description, so that engineers can understand and correctly locate the drilling position of the "first-order probing hole".)

[0055] Figure 4 The diagram illustrates how the "first-order edge probing hole" serves as the base point of the "cross" axis. Engineers select one or more axial directions of the "cross" axis and drill "second-order edge probing holes" at predetermined intervals. Figure 4 This is the first embodiment using the "first-order edge probing hole" as the base point of the "cross" axis (where the "cross" axis is a coordinate axis designed for ease of description, so that engineers can understand and correctly locate the drilling position of the "second-order edge probing hole");

[0056] Figure 5 The diagram illustrates how the "first-order edge probing hole" serves as the base point of the "cross" axis. Engineers select one or more axial directions of the "cross" axis and drill "second-order edge probing holes" at predetermined intervals. Figure 5 This is the second embodiment using the "first-order edge probing hole" as the base point of the "cross" axis (where the "cross" axis is a coordinate axis designed for ease of description, so that engineers can understand and correctly locate the drilling position of the "second-order edge probing hole");

[0057] Figure 6 This is a schematic diagram of some "advanced drilling or probing holes" serving as grouting holes for treating karst caves (engineers first reveal the karst caves through detailed exploration drilling and advanced drilling, then determine the boundaries of the karst caves through probing holes, and finally allow some "advanced drilling or probing holes" to serve as grouting holes for treating karst caves).

[0058] Figure label:

[0059] 11-Detailed exploration borehole; 12-Advanced drilling borehole; P-Hole spacing; 13-Edge probing hole; 131-First-order edge probing hole; 132-Second-order edge probing hole; L1-Spacing; L2-Spacing; K-Axis length direction;

[0060] 2-Anchor cable; 21-Anchor cable anchorage section; E-First end; F-Second end; 22-Anchor cable free section; C-First side anchor cable; D-Second side anchor cable; X1-Left; X2-Right; T-Vertical mark; Y-Auxiliary line;

[0061] 31-Anchor cable girders; 32-Retaining structure; 33-Underground structure;

[0062] 4-Grouting hole; 41-Peripheral hole; 42-Central hole; 421-Ventilation hole;

[0063] 5 - Planar processing range; 51 - First plane boundary; 52 - Second plane boundary; 53 - Third plane boundary; 54 - Fourth plane boundary; SS - Section symbol;

[0064] 6-Vertical processing range; 61-Ground boundary; 62-Underground boundary; 63-First vertical boundary; 64-Second vertical boundary;

[0065] G1 - First set distance; G2 - Second set distance; G3 - Third set distance; G4 - Fourth set distance; G5 - Fifth set distance; G6 - Sixth set distance; G7 - Seventh set distance;

[0066] M - Boundary of the karst cave; N - Boundary of the karst cave treatment area in the anchor cable zone;

[0067] 7 - Cave; 71 - Unfilled cave; 72 - Partially filled cave; 73 - Fully filled cave;

[0068] R1 - Caves within the treatment area of ​​the anchor cable zone; R2 - Caves outside the treatment area of ​​the anchor cable zone. Detailed Implementation

[0069] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The same reference numerals used throughout the accompanying drawings indicate the same or similar parts.

[0070] It should be noted that, unless otherwise specified, when a feature is referred to as "fixed" or "connected" to another feature, it can be directly fixed or connected to the other feature, or indirectly fixed or connected to the other feature. Furthermore, the descriptions of "up," "down," "left," and "right" used in this invention are only relative to the relative positional relationships of the various components of the invention in the accompanying drawings.

[0071] Reference Figures 1 to 6 A method for detecting and treating karst caves in anchor cable zones of limestone strata retaining structures, comprising the following steps:

[0072] S1. Delineation of the treatment area for karst caves in the anchor cable zone;

[0073] S11. Based on the anchor cable plan and vertical layout (in the anchor cable construction drawings), determine the scope of karst cave treatment in the anchor cable area (by demarcation).

[0074] S2, advance drilling in the anchor cable zone;

[0075] S21. In conjunction with the detailed exploration boreholes 11, several advance boreholes 12 are set in the area of ​​the anchor cable anchorage section 21 (e.g., a row of advance boreholes 12); wherein, the detailed exploration boreholes 11 are obtained from the previous "large-spacing" drilling, and "in conjunction with the detailed exploration boreholes 11, a row of advance boreholes 12 is set in the area of ​​the anchor cable anchorage section 21", which is equivalent to setting advance boreholes 12 for intensified exploration in conjunction with the "large-spacing" detailed exploration boreholes 11 (refer to...). Figure 1 );

[0076] S3, Explore the boundary of cave 7 in the anchor cable area;

[0077] S31. Within the treatment area of ​​the karst cave in the anchor cable zone, for the karst cave 7 initially revealed by the detailed exploration borehole 11 and the advance borehole 12 in the area of ​​the anchor cable anchoring section 21, the edge exploration hole 13 is drilled to detect the boundary M of the karst cave.

[0078] S4. Grouting treatment of karst caves in the anchor cable area;

[0079] S41. Some of the "advanced drilling holes 12 or the edge probing holes 13" also serve as grouting holes 4. According to the area and boundary of the karst cave 7, the grouting holes 4 are divided into central holes 42 and peripheral holes 41. Among them, some of the central holes 42 also serve as ventilation holes 421. The ventilation holes 421 can maintain the atmospheric pressure balance in the karst cave 7 during grouting, so that the karst cave 7 can be grouted normally.

[0080] S42. Grouting is performed on the karst cave 7 through the grouting hole 4 according to the type of karst cave 7.

[0081] S5. Inspection of grouting effect in the anchor cable zone of the karst cave;

[0082] S51. After the grouting is completed, the filling and reinforcement effects of the karst cave are inspected.

[0083] S6, Construction of Anchor Cable 2 and Bearing Capacity Testing of Anchor Cable 2;

[0084] S61. After completing the grouting treatment of the karst cave and testing the grouting effect, locate the anchor cable 2 hole position at position 33 of the retaining structure and drill to the designed depth of anchor cable 2.

[0085] S62, Carry out the process of laying anchor cables 2, grouting and constructing anchor cable waist beams 31;

[0086] S63. After the concrete of the anchor cable waist beam 31 reaches the design strength, the anchor cable 2 is tensioned, and the pull-out force and locking force of the anchor cable 2 are tested.

[0087] Among them, steps S1 to S6 specifically address the problems of the difficulty in constructing anchor cables in underground karst caves in pile-anchor support systems in limestone areas and the lack of stability guarantee after anchoring.

[0088] Reference Figures 1 to 6 In one embodiment, in step S11, the anchor cable 2 includes an anchor cable anchoring section 21 and an anchor cable free section 22; the karst cave treatment range of the anchor cable area includes a planar treatment range 5 and a vertical treatment range 6;

[0089] The planar processing range 5 includes a first planar boundary 51, a second planar boundary 52, a third planar boundary 53, and a fourth planar boundary 54; the first planar boundary 51 maintains a first predetermined distance G1 with the first side anchor cable C, the second planar boundary 52 maintains a second predetermined distance G2 with the second side anchor cable D, the third planar boundary 53 maintains a third predetermined distance G3 with the first end E of the anchor cable anchoring section 21, and the fourth planar boundary 54 maintains a fourth predetermined distance G4 with the second end F of the anchor cable anchoring section 21; the planar area enclosed by the first planar boundary 51, the second planar boundary 52, the third planar boundary 53, and the fourth planar boundary 54 is the planar processing range 5;

[0090] The vertical processing range 6 includes a ground boundary 61, an underground boundary 62, a first vertical boundary 63, and a second vertical boundary 64; the ground boundary 61 is a leveled ground surface; the underground boundary 62 maintains a fifth predetermined distance G5 with the lowest point of the anchor cable anchoring section 21; the first vertical boundary 63 maintains a sixth predetermined distance G6 with the leftmost (X1) first end E of the anchor cable anchoring section 21; the second vertical boundary 64 maintains a seventh predetermined distance G7 with the rightmost (X2) second end F of the anchor cable anchoring section 21; the vertical area enclosed by the ground boundary 61, the underground boundary 62, the first vertical boundary 63, and the second vertical boundary 64 is the vertical processing range 6;

[0091] The three-dimensional area formed by the planar processing range 5 and the vertical processing range 6 (Note: To help people understand the "three-dimensional area", it can be understood as a "three-dimensional plot") is the range of karst cave treatment to be determined in the anchor cable area. The range of karst cave treatment in the anchor cable area is the range of karst cave treatment in the anchor cable anchorage section (the range of karst cave treatment in the anchor cable anchorage section is the range that this method is to clearly define and treat).

[0092] Reference Figures 1 to 6 In one embodiment, the first set distance G1 and the second set distance G2 are both 3m; the third set distance G3 and the fourth set distance G4 are 5m; the fifth set distance G5, the sixth set distance G6, and the seventh set distance G7 are all 5m (Note: also refer to...). Figure 1 and 2 (Understand the auxiliary line Y and the vertical marker T).

[0093] Reference Figures 1 to 6In one embodiment, in step S21, the detailed exploration borehole 11 also serves as the advance borehole 12, and combined with the advance boreholes 12 obtained from subsequent drilling, there are a total of several advance boreholes 12 arranged in a row, and the several advance boreholes 12 are respectively adjacent to the arrangement position of the anchor cable anchoring section 21; the several advance boreholes 12 (the borehole axis) are perpendicular to the horizontal plane formed by the plane processing range 5; the several advance boreholes 12 maintain a set hole spacing P between adjacent ones.

[0094] Reference Figures 1 to 6 In one embodiment, several of the advance boreholes 12 are spaced 3m apart. Preferably, for areas with complex underground conditions or other areas requiring focused study, the layout of the advance boreholes 12 should be appropriately expanded and the spacing P of the advance boreholes 12 should be reduced to achieve intensified exploration. For example, the number of rows of advance boreholes 12 can be increased, or the spacing P of the advance boreholes 12 can be reduced to 2m or 1.5m.

[0095] Reference Figures 1 to 6 In one embodiment, in step S31 (the detailed exploration borehole has also served as a pre-drilling borehole, so it can be described simply as a pre-drilling borehole), when the karst cave 7 revealed by the pre-drilling borehole 12 is within the karst cave treatment range of the anchor cable area, the pre-drilling borehole 12 (such as its center) is used as the base point of the "cross" axis, and then a sequential exploration hole 131 is drilled along the four axial length directions K of the "cross" axis at a set interval L1 (such as 2m).

[0096] If a karst cave 7 is discovered during the probing of the first-order probing hole 131, then using the first-order probing hole 131 as the base point of the "cross" axis, one or more axial length directions K of the "cross" axis are selected, and second-order probing holes 132 are drilled at a set interval L2 (e.g., 2m) until the karst cave boundary M or the boundary N of the karst cave treatment area of ​​the anchor cable zone is found. Preferably, the set interval L1 and the set interval L2 are kept at the same constant value, such as both being kept at 2m.

[0097] For larger karst caves 7, if their extent exceeds the karst cave treatment area of ​​the anchor cable zone (refer to...) Figure 2 The following steps can be used to process it:

[0098] A1. First, drill a hole at point N, the boundary of the karst cave treatment area in the anchor cable zone;

[0099] A2. Then, use quick-setting grout to seal the edges, separating the karst cave R1 within the treatment range of the anchor cable area from the karst cave R2 outside the treatment range of the anchor cable area.

[0100] A3. Then, grouting treatment is carried out on the karst cave R1 within the karst cave treatment range of the anchor cable area.

[0101] Reference Figures 1 to 6 In one embodiment, in step S41, the grouting pipe is embedded in the selected grouting hole 4, and grouting can only be performed after the gap between the "cavity top plate, grouting pipe" and the "grouting hole wall" is sealed.

[0102] Reference Figures 1 to 6 In one embodiment, during step S41, grouting is performed while simultaneously assessing the size and post-treatment state of the karst cave 7. The assessment method involves: based on the grouting volume and the diameter of the karst cave 7 detected by the grouting holes 4, a preliminary estimate of the size of the karst cave 7 is made, followed by the deployment of inspection holes around it. These inspection holes not only check the extension of the karst cave 7 but also the grouting filling status. If a karst cave 7 is found to be under-grouted, grouting should continue using the inspection holes. Preferably, some inspection holes can subsequently serve as "quality inspection holes" (see below for details on quality inspection holes).

[0103] Reference Figures 1 to 6 In one embodiment, in step S42, the cave 7 is divided into unfilled cave 71, semi-filled cave 72 and fully filled cave 73 according to the natural filling material inside it; wherein, natural filling material refers to the filling material that was naturally present inside the cave beforehand.

[0104] At the peripheral holes 41, the unfilled karst cave 71 or the semi-filled karst cave 72 are filled with cement-water glass double slurry.

[0105] For the unfilled karst cave 71 or the semi-filled karst cave 72 at the central hole 42 with a height ≥ 3m, cement mortar is used for filling first, followed by cement grouting for compaction. For the unfilled karst cave 71 or the semi-filled karst cave 72 at the central hole 42 with a height less than 3m, mortar or cement grout is used for filling. For the fully filled karst cave 73 at the central hole 42, if the standard penetration test value of the natural infill material is less than 10 blows, cement grouting for compaction is used. For the fully filled karst cave 73 at the central hole 42, if the standard penetration test value of the natural infill material is ≥ 10 blows, no treatment is required.

[0106] After grouting is completed, cement grout must be used to seal the holes.

[0107] Reference Figures 1 to 6 In one embodiment, in step S4, an on-site grouting test should be conducted before construction, and the grouting parameters should be adjusted according to the test results;

[0108] For the peripheral holes 41, grouting should be controlled with relatively low pressure (e.g., the recommended grouting pressure is 0.6 MPa to 0.8 MPa), multiple times (e.g., the recommended number of grouting times is 3 to 4 times), and a relatively large amount of grout.

[0109] For the central hole 42, cement grout should be injected three times at a grouting pressure of 0 MPa to 1.0 MPa and a grouting speed of 30 L / min to 70 L / min. The grouting pressure should be gradually increased. After reaching the final grouting pressure, grouting should continue for more than 10 minutes. The grout should be made of 42.5 grade ordinary Portland cement with a water-cement ratio of 1.0 to 1.5. The actual grouting parameters should be determined based on field tests.

[0110] If the amount of grout injected during the first grouting of the peripheral hole 41 is already too large and the pressure does not meet the design requirements, the peripheral hole 41 and the central hole 42 can be grouted alternately.

[0111] Reference Figures 1 to 6 In one embodiment, the inspection of the grouting effect of the karst cave filling mentioned in step S51 is carried out by checking the filling rate (after grouting of karst cave 7) using the "secondary grouting" method, with the pressure gradually increased from 0 MPa to 0.2 MPa and maintained for 10 to 15 minutes; the compaction degree (after grouting of karst cave 7) is checked by the Standard Penetration Test (SPT). A SPT value of "hard" soil is considered excellent, and a SPT value of "hard plastic" soil is considered qualified.

[0112] Reference Figures 1 to 6 In one embodiment, the inspection of the grouting reinforcement effect of the karst cave mentioned in step S51 is carried out by core drilling and performing compressive strength tests, water pressure tests, and in-situ standard penetration tests. (Note: The grouting reinforcement of the karst cave 7 is obtained by grouting through several grouting holes 4. If inspection is required, cores can be taken through the grouting holes 4 or additional holes can be drilled for cores. Therefore, the number of inspection locations (i.e., the number of inspections)) The number of inspections shall not be less than 1% of the number of grouting holes 4; each karst cave 7 shall be inspected at least once; among them, the test blocks obtained by random core drilling shall be subjected to compressive strength tests, and their unconfined compressive strength shall not be less than 0.2 MPa; where (quality inspection holes can be obtained by drilling, or part of "grouting hole 4 or inspection hole" can be used as quality inspection holes) the water pressure test of the quality inspection holes should be carried out at least seven days after the completion of the unit project grouting; where, after the karst cave reinforcement treatment, the water permeability of the quality inspection holes should not be greater than 10 Lu, the pass rate should be more than 85%, and the maximum permeability of the remaining unqualified hole sections should not exceed 15 Lu, and should not be concentrated; where, during the in-situ standard penetration test (which can be carried out through grouting hole 4), the standard penetration test blow count is required to be not less than 10 blows.

[0113] Reference Figures 1 to 6 In one embodiment, in step S61, if a karst cave 7 is found during the drilling of the anchor cable 2, grouting should be injected into the anchor cable hole in a timely manner, and drilling should continue after the treatment is completed.

[0114] In step S62, the adverse effects of the anchor group effect and the karst cave 7 should be fully considered during construction. The effective anchorage length of the anchor cable 2 should not be less than the designed anchorage length and should penetrate the karst cave into the stable rock layer for no less than 3m (Note: the effective anchorage length of the anchor cable = the actual length of the anchorage section of the anchor cable - the length of the anchorage section of the anchor cable through the karst cave).

[0115] In step S63, to ensure the effective bearing capacity of the anchor cable 2 in the limestone area, the anchor cable passing through the karst cave, when applying prestress, includes the following steps:

[0116] B1. First determine which value is larger, "1.4 times Fm or 0.8 times Fn", where Fm is the "standard value of calculated tensile force" and Fn is the "standard value of ultimate tensile strength of anchor cable".

[0117] B2. If 1.4Fm is a larger value than 0.8Fn, then when applying the preload, the tension should be increased to 1.4Fm first, and then released and retracted to the locking force value to lock.

[0118] If 0.8Fn is a larger value than 1.4Fm, then when applying the preload, the tension should be increased to 0.8Fn first, and then released and retracted to the locking force value to lock.

[0119] In step S63, the number of anchor cable bearing capacity tests shall be no less than 10% and no less than ten (Note: anchor cable bearing capacity includes the pull-out force and the locking force).

[0120] Reference Figures 1 to 6 In one embodiment, the enclosure structure 32 is a diaphragm wall.

[0121] The present invention provides a method for detecting and treating karst caves in the anchor cable area of ​​a limestone stratum retaining structure. This method reduces the risk of collapse of the pile-anchor support system in the limestone stratum karst cave development area during the construction of anchor cables 2, and reduces the risk of water inrush and gushing during the construction of anchor cables 2 and the excavation of the foundation pit. It can effectively ensure the bearing capacity of anchor cables 2 in the pile-anchor support system in the limestone stratum karst development area and improve the safety of underground structure 33 construction.

[0122] Other aspects of the method for detecting and treating karst caves in anchor cable zones of limestone strata retaining structures described in this invention are available in the prior art and will not be repeated here.

[0123] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure, characterized in that, Includes the following steps: S1. Delineation of the treatment area for karst caves in the anchor cable zone; S11. Determine the treatment range of the karst cave in the anchor cable area based on the planar and vertical layout of the anchor cables; S2, advance drilling in the anchor cable zone; S21. In conjunction with detailed exploration drilling, several advance drilling holes shall be set in the anchoring section layout area of ​​the anchor cable; S3. Explore the boundary of the karst cave in the anchor cable area; S31. Within the treatment area of ​​the karst cave in the anchor cable area, for the karst caves initially revealed by the detailed exploration boreholes and advance boreholes in the anchor cable anchorage section layout area, exploration holes are drilled to detect the karst cave boundaries. S4. Grouting treatment of karst caves in the anchor cable area; S41. Some of the "advanced drilling holes or edge probing holes" also serve as grouting holes. According to the karst cave area and boundary, the grouting holes are divided into central holes and peripheral holes; among them, some of the central holes also serve as ventilation holes. S42. Grouting is performed on the karst cave through the grouting holes according to the type of karst cave; S5. Inspection of grouting effect in the anchor cable zone of the karst cave; S51. After the grouting is completed, the filling and reinforcement effects of the karst cave are inspected. S6. Anchor cable construction and anchor cable bearing capacity testing; S61. After completing the grouting treatment and grouting effect test of the karst cave, locate the anchor cable drilling position at the retaining structure and drill to the designed anchor cable depth. S62. Carry out the procedures of laying anchor cables, grouting and constructing anchor cable waist beams; S63. After the concrete of the anchor cable waist beam reaches the design strength, the anchor cable is tensioned and the pull-out force and locking force of the anchor cable are tested.

2. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 1, characterized in that, In step S11, the anchor cable includes an anchored section and a free section; the treatment range of the karst cave in the anchor cable area includes a planar treatment range and a vertical treatment range. The planar processing range includes a first planar boundary, a second planar boundary, a third planar boundary, and a fourth planar boundary; the first planar boundary maintains a first predetermined distance from the first side anchor cable, the second planar boundary maintains a second predetermined distance from the second side anchor cable, the third planar boundary maintains a third predetermined distance from the first end of the anchoring section of the anchor cable, and the fourth planar boundary maintains a fourth predetermined distance from the second end of the anchoring section of the anchor cable; the planar area enclosed by the first planar boundary, the second planar boundary, the third planar boundary, and the fourth planar boundary is the planar processing range; The vertical processing range includes a ground boundary, an underground boundary, a first vertical boundary, and a second vertical boundary; the ground boundary is a leveled ground surface; the underground boundary maintains a fifth predetermined distance from the lowest point of the anchor cable anchoring section; the first vertical boundary maintains a sixth predetermined distance from the first end of the leftmost anchor cable anchoring section; the second vertical boundary maintains a seventh predetermined distance from the second end of the rightmost anchor cable anchoring section; the vertical area enclosed by the ground boundary, the underground boundary, the first vertical boundary, and the second vertical boundary is the vertical processing range. The three-dimensional area formed by the planar treatment range and the vertical treatment range is the area to be determined for the treatment of the anchor cable zone cave.

3. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 2, characterized in that, In step S21, the detailed exploration borehole also serves as a pre-drilling borehole, and combined with the pre-drilling boreholes obtained from subsequent drilling, there are a total of several pre-drilling boreholes arranged in a row, and the several pre-drilling boreholes are respectively adjacent to the anchoring section of the anchor cable; the several pre-drilling boreholes are perpendicular to the horizontal plane formed by the plane processing range; the several pre-drilling boreholes maintain a set hole spacing between adjacent holes.

4. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 3, characterized in that, In step S31, when the karst cave revealed by the advanced drilling is within the karst cave treatment range of the anchor cable area, the advanced drilling is used as the base point of the "+" axis, and then a sequential exploration hole is drilled along the four axial length directions of the "+" axis at a set interval. If a karst cave is discovered during the first-order probing hole exploration, the first-order probing hole is used as the base point of the "+" axis. Then, one or more axial length directions of the "+" axis are selected, and second-order probing holes are drilled at set intervals until the boundary of the karst cave or the boundary of the karst cave treatment range of the anchor cable area is found.

5. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 1, characterized in that, In step S41, the grouting pipe is embedded in the selected grouting hole. Grouting can only be performed after the gap between the "cavity top plate, grouting pipe" and the "grouting hole wall" is sealed.

6. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 1, characterized in that, In step S42, the caves are classified into unfilled caves, semi-filled caves, and fully filled caves based on the natural filling material inside them. The unfilled or partially filled karst caves around the perimeter holes are filled with a cement-water glass double slurry. For the central hole, the "unfilled karst cave or the semi-filled karst cave" with a height ≥ 3m is first filled with cement mortar, and then compacted with cement grout. The "unfilled karst cave or the semi-filled karst cave" with a height less than 3m is filled with mortar or cement grout. For the fully filled karst cave, if the standard penetration test value of the natural infill material is less than 10 blows, compaction grouting with cement grout is used. If the standard penetration test value of the natural infill material in the fully filled karst cave is ≥ 10 blows, no treatment is required.

7. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 1, characterized in that, In step S4, an on-site grouting test should be conducted before construction to determine the grouting parameters; For the peripheral holes, the grouting pressure is 0.6 MPa to 0.8 MPa, and the number of grouting operations is 3 to 4. For the central hole, cement grout should be injected three times at a grouting pressure of 0 MPa to 1.0 MPa and a grouting speed of 30 L / min to 70 L / min. The grouting pressure should be gradually increased. After reaching the final grouting pressure, grouting should continue for more than 10 minutes. The grout should be made of 42.5 grade ordinary Portland cement with a water-cement ratio of 1.0 to 1.

5.

8. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 1, characterized in that, The inspection of the grouting effect for filling the karst cave mentioned in step S51 involves checking the filling rate using a "secondary grouting" method, gradually increasing the pressure from 0 MPa to 0.2 MPa and maintaining it for 10 to 15 minutes; and checking the compaction using the Standard Penetration Test (SPT). A SPT value of "hard" soil is considered excellent, while a SPT value of "hard plastic" soil is considered qualified.

9. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 1, characterized in that, The inspection of the grouting reinforcement effect of the karst cave mentioned in step S51 shall be carried out by core drilling and performing compressive strength test, water pressure test and in-situ standard penetration test. The number of inspections shall not be less than 1% of the number of grouting holes. Each karst cave shall be inspected at least once. Among them, the test blocks obtained by random core drilling shall be subjected to compressive strength test, and the unconfined compressive strength shall not be less than 0.2 MPa. The water pressure test of the quality inspection holes shall be carried out at least seven days after the completion of the grouting of the unit project. The water permeability of the quality inspection holes after karst cave reinforcement treatment shall not be greater than 10 Lu, the pass rate shall be more than 85%, the maximum permeability of the unqualified hole section shall not exceed 15 Lu, and shall not be concentrated. The standard penetration test in in-situ shall not be less than 10 blows.

10. The method for detecting and treating karst caves in the anchor cable zone of a limestone stratum retaining structure according to claim 1, characterized in that, In step S62, the effective anchorage length of the anchor cable should not be less than the designed anchorage length and should penetrate the karst cave into the stable rock layer for no less than 3m. In step S63, to ensure the effective bearing capacity of the anchor cables in the limestone area, the anchor cables traversing the karst caves, when applying prestress, include the following steps: B1. First determine which value is larger, "1.4 times Fm or 0.8 times Fn", where Fm is the "standard value of calculated tensile force" and Fn is the "standard value of ultimate tensile strength of anchor cable". B2. If 1.4Fm is a larger value than 0.8Fn, then when applying the preload, the tension should be increased to 1.4Fm first, and then released and retracted to the locking force value to lock. If 0.8Fn is a larger value than 1.4Fm, then when applying the preload, the tension should be increased to 0.8Fn first, and then released and retracted to the locking force value to lock. In step S63, the number of anchor cables tested for bearing capacity shall not be less than 10% and shall not be less than ten.

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