A method for sinking well wall type broken rock-soil body multi-stage expansion hole depth coordination anchoring

Abstract

This invention discloses a method and process for multi-stage borehole enlargement and shallow-depth coordinated anchoring of fractured rock and soil using a caisson-wall protection system. The anchoring method includes drilling anchor holes, constructing multi-stage borehole enlargement cavities, installing anchor cables, grouting, and anchoring. The multi-stage borehole enlargement cavities, from top to bottom, include at least one borehole body enlargement cavity and one borehole bottom enlargement cavity. After the anchor hole construction reaches the designed depth, drilling continues along the extension direction of the anchor hole, forming a bottom caisson connected to the bottom enlargement cavity to accommodate the debris and soil discharged during the multi-stage borehole enlargement construction. The bottom caisson has a columnar structure, and its diameter is smaller than the diameter of the bottom enlargement cavity. After the anchor hole construction is completed, multi-stage borehole enlargement is performed from top to bottom at different depths and shallow locations within the fractured rock and soil using a combination of casing and packers, forming boreholes of different levels at the bottom and body. This invention provides a technical solution for the active reinforcement of fractured rock and soil, effectively improving the stability of such structures.

Description

Technical Field

[0001] This invention relates to the field of rock and soil anchoring technology, specifically a multi-stage borehole expansion method for coordinating shallow and deep anchoring in fractured rock and soil using a caisson wall protection system. Background Technology

[0002] Fractured rock and soil are common problems in various engineering projects such as water conservancy and hydropower projects, road and transportation projects, and building construction projects. Reinforcing fractured rock and soil to improve their strength is the foundation for ensuring the safety, reliability, and longevity of the project.

[0003] Currently, the reinforcement of fractured rock and soil often adopts passive protection methods such as retaining walls and anti-slide piles. These technical methods cannot effectively improve the strength of the rock and soil itself. They mainly rely on the passive resistance of the rock and soil acting on the structure to prevent deformation and slippage of the rock and soil. They have disadvantages such as large engineering workload, high cost and poor durability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a multi-stage borehole expansion and shallow-depth coordinated anchoring method for fractured rock and soil bodies using a caisson wall protection system. This method offers a technical solution for the active reinforcement of fractured rock and soil bodies and can effectively improve their stability.

[0005] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0006] A method for coordinating the depth and type of multi-stage borehole enlargement and anchoring in fractured rock and soil with caisson wall protection includes the steps of drilling anchor holes, constructing multi-stage borehole enlargement cavities, installing anchor cables, grouting, and anchoring. The multi-stage borehole enlargement cavities include at least one borehole body enlargement cavity and one borehole bottom enlargement cavity from top to bottom. After the anchor hole construction reaches the designed depth, drilling continues along the extension direction of the anchor hole. A bottom caisson is formed below the bottom borehole enlargement cavity and is connected to it to accommodate the debris rock and soil discharged during the construction of the multi-stage borehole enlargement cavity. The bottom caisson has a columnar structure and its diameter is smaller than the diameter of the bottom borehole enlargement cavity.

[0007] After the anchor hole construction is completed, a casing with several screen hole groups spaced along its length on the sidewall is lowered into the borehole. The spacing between two adjacent screen hole groups is the same as the spacing between two adjacent enlarged boreholes to be constructed. Each screen hole group has a flushing section including several flushing screen holes and a slag discharge section below the flushing section containing several slag discharge screen holes. Two spaced packers are installed in the casing at positions corresponding to the predetermined screen hole groups. The two packers are located above the flushing section and above the slag discharge section, respectively. High-pressure water is injected into the sealed space formed by the two packers and the inner wall of the casing using a punching machine. The high-pressure water flows through the flushing screen holes to form a cavity on the anchor hole wall. The debris and soil generated during the cavity formation process pass through the slag discharge screen holes into the casing and flow into the bottom caisson along the casing. The packers and the nozzles of the punching machine are positioned at different screen hole groups on the casing in a top-down sequence, and the above steps are repeated to form a multi-stage enlarged borehole in the anchor hole.

[0008] Furthermore, the diameter of the slag discharge screen holes is 5cm-8cm, and the diameter of the flushing screen holes is less than 0.5cm.

[0009] Furthermore, after the multi-stage enlarged hole construction is completed, the packer and casing are removed from the anchor hole, and then several anchor cables are inserted into the anchor hole. The anchor cables correspond one-to-one with the enlarged hole, and the anchor cables extend to the bottom of the corresponding enlarged hole.

[0010] Furthermore, the anchor cable includes an anchor cable body and a composite structure passing through the upper part of the anchor cable body. The composite structure is bonded to the anchor cable body by a high-ductility adhesive material. The composite structure includes a connecting pipe, and an opening protective pipe and a tensioning protective pipe installed at both ends of the connecting pipe.

[0011] Furthermore, the components and mass fraction of the grouting fluid used for grouting are as follows: cement slurry 93%-97.9%, fiber filaments 0.5%, water-reducing agent 1.5%-2.5%, and early-strength agent 0.1-4%; wherein the cement slurry is made by mixing cement and water in a mass ratio of 1:0.3.

[0012] Furthermore, grouting is carried out from bottom to top using grouting equipment. After grouting is completed, it is naturally cured for a period of time to allow the grout to solidify, and each anchor cable is anchored by the grout, thus forming segmented anchoring.

[0013] Furthermore, tensioning components are installed at the composite structure of each anchor cable. Each tensioning component includes an opening anchor fixed outside the borehole of the anchoring borehole, and a limiting plate, a through jack, and a tensioning anchor arranged sequentially from bottom to top on the opening anchor. The opening anchor has a tapered hole that is larger at the top and smaller at the bottom. The composite structure passes through the opening anchor, the limiting plate, and the through jack in sequence, and the opening protective tube is held tightly by a tapered clamp set in the tapered hole.

[0014] Furthermore, the lower part of the hole protection pipe is located in the anchor hole, the upper part is located in the tensioning assembly, and the connecting pipe is located in the through-hole jack.

[0015] Furthermore, the tensioning assembly also includes a jack oil pump connected to the through-hole jack. After the maintenance is completed, the jack oil pump is started so that the through-hole jack tensions the corresponding anchor cables respectively. The applied tension force is transmitted to the enlarged hole through the anchor cables. The tension force applied to the enlarged hole at the bottom of the hole is greater than the tension force applied to the enlarged hole in the body of the hole.

[0016] Furthermore, after applying the target load to each anchor cable, the through-hole jack is closed, the tension anchor, through-hole jack and limiting plate are disassembled, each anchor cable is cut off from the connecting pipe, and then cement protective anchor upsets are used to protect the anchor at the opening and the exposed end of the anchor cable.

[0017] The anchoring method provided by this invention is based on active protection and mainly includes the following innovations: (1) By drilling anchor holes in the fractured rock and soil, the length of the anchor holes exceeds the designed hole depth to form a bottom caisson, which is used to collect and contain the debris rock and soil discharged from the enlarged hole. The size of the bottom caisson should be able to contain all the debris rock and soil discharged from the enlarged hole. (2) Using a casing with a group of screen holes, on the one hand, the borehole wall of the fractured rock and soil is protected to avoid damage to the non-enlarged hole section. On the other hand, combined with the setting of packers, the punching machine is opened, and the enlarged hole is formed radially around the corresponding position through the flushing screen holes in the sealed space formed by the two packers. The debris rock and soil in the enlarged hole flows into the bottom caisson automatically under its own weight through the slag discharge screen holes, avoiding secondary treatment of the debris rock and soil. The pressure of the punching pump in the punching machine should be determined according to factors such as the size of the enlarged hole, the strength of the fractured rock and soil, and the size of the flushing screen holes, with the flushing screen holes being able to form a water jet as the standard. (3) From top to bottom, using a combination of casing and packers, multi-stage borehole enlargement is carried out at different depths and shallows in the fractured rock and soil, forming borehole cavities of different levels at the bottom and body of the borehole. (4) According to the location of the borehole cavities, corresponding to each borehole cavity, bottom anchor cables and body anchor cables with easily cut ends are inserted into the borehole. The anchor cable includes the anchor cable body and a composite structure passing through the upper part of the anchor cable body. The composite structure consists of a borehole opening protection pipe, a connecting pipe (such as a PVC pipe), and a tensioning protection pipe. With the help of the borehole opening anchor, the limiting plate, and the through-hole jack, the anchor cable can be tensioned and locked, and it is also beneficial for the protection of the borehole opening. (5) A grouting fluid with both diffusivity and strength is prepared by using fiber filaments, cement grout, water-reducing agent, and early-strength agent. Grouting is carried out from the bottom of the caisson upwards, forming bottom caisson grouting body, bottom hole enlargement cavity grouting body, hole body grouting body, and hole body enlargement cavity grouting body at different depths and shallow locations. The bottom anchor cable and the hole body anchor cable are anchored to form deep and shallow segmented anchoring of the fractured rock and soil. Among them, the bottom caisson grouting body, the bottom hole enlargement cavity grouting body, the hole body grouting body, and the hole body enlargement cavity grouting body form a whole during the grouting process. Since the bottom caisson grouting body is buried at the deepest depth and its diameter is smaller than that of the bottom hole enlargement cavity, it has the strongest resistance to pull-out and damage under the pressure of the fractured rock and soil, which plays a role in improving the pull-out and damage resistance of the entire grouting body. (6) Through-core jacks are used to perform graded tensioning, locking, end treatment and protection of the bottom anchor cable and the hole body anchor cable respectively. In this method, the tension applied to the bottom anchor cable is greater than that applied to the shallow anchor cable, thus forming a deep and shallow coordinated anchoring. Through these steps, the multi-stage borehole enlargement method for coordinating deep and shallow anchoring in caisson wall protection of fractured rock and soil significantly improves the stability of the fractured rock and soil, effectively ensuring the safety of related engineering projects.

[0018] By adopting the above technical solution, the present invention provides a multi-stage borehole expansion depth-coordinated anchoring method for fractured rock and soil in caisson wall protection. This method realizes the formation of multi-stage borehole expansion cavities and segmented anchoring within the fractured rock and soil, which can distribute the prestress (i.e., the tension force of the through-hole jack) to the anchor bodies of each borehole expansion cavity, thereby achieving the application of prestress at different parts of the fractured rock and soil and effectively improving the reinforcement effect of the fractured rock and soil.

[0019] Beneficial effects:

[0020] 1) This technology incorporates a bottom caisson at the bottom of the borehole in the fractured rock and soil body. During the hydraulic drilling process, it can accommodate and collect the debris rock and soil discharged from the borehole. It is time-saving, labor-saving, and simple in process. Compared with traditional slag removal treatment, it avoids the secondary treatment of debris rock and soil.

[0021] 2) By combining casing with screen holes and packers, it is possible to create a cavity by hydraulic perforation at different locations such as the bottom and body of the hole, based on the engineering characteristics of the fractured rock and soil, thus forming a multi-stage enlarged cavity with radial circumference at the bottom and body of the hole.

[0022] 3) Based on the number and location of the boreholes, corresponding bottom anchor cables and body anchor cables are inserted into the boreholes. Combined with grouting anchoring operations and prestressing, segmented anchoring and deep and shallow coordinated anchoring of different parts of the fractured rock and soil can be achieved.

[0023] 4) By setting up a bottom caisson and grouting operations, the bottom caisson grouting body can be integrated with the bottom hole enlargement cavity grouting body, the hole body grouting body, and the hole body enlargement cavity grouting body to form a whole. After the prestress applied to each anchor cable is transferred to the corresponding bottom hole enlargement cavity grouting body and the hole body enlargement cavity grouting body, it can be further transferred to the bottom caisson grouting body. Since the bottom caisson grouting body is buried at the deepest depth and its diameter is smaller than that of the bottom hole enlargement cavity, it has the strongest resistance to pull-out and damage under the pressure of fractured rock and soil, thus improving the pull-out and damage resistance of the entire grouting body.

[0024] 5) The components and mass fraction of the grout used in this technology are as follows: cement grout 93%-97.9%, fiber filament 0.5%, water-reducing agent 1.5%-2.5%, and early strength agent 0.1-4%. The high-diffusion, high-strength grout developed according to the characteristic proportions has a strength far higher than that of fractured rock and soil.

[0025] 6) The anchor cables used in this technology (including bottom anchor cables and body anchor cables) have a special structure. Specifically, the anchor cable at the borehole opening includes a composite structure consisting of a borehole opening protection pipe, a PVC pipe, and a tensioning protection pipe. With the help of anchors, limit plates, and through-hole jacks, the anchor cable can be tensioned, locked, and the opening can be protected. Attached Figure Description

[0026] Figure 1 This is a diagram of the borehole structure in the fractured rock and soil mass of this invention.

[0027] Figure 2 This is a diagram of the enlarged cavity in the fractured rock and soil mass of this invention.

[0028] Figure 3 This is a diagram showing the insertion of anchor cables into fractured rock and soil in this invention.

[0029] Figure 4 This is a schematic diagram of the anchor cable structure in this invention.

[0030] Figure 5 This is a diagram showing the deep and shallow multi-stage enlarged cavity grouting process for fractured rock and soil in this invention.

[0031] Figure 6 This is a schematic diagram of anchor cable tensioning in this invention.

[0032] Figure 7 This is a cross-sectional view of the cone-shaped opening anchor in this invention.

[0033] Figure 8 This is a schematic diagram of the tapered sliding clamp in this invention.

[0034] Figure 9 This is a schematic diagram of the overall grouting and anchoring of fractured rock and soil in this invention.

[0035] Illustration markings: 1. Fractured rock and soil, 2. Anchor hole, 3. Casing, 31. Slag discharge screen hole, 32. Flushing screen hole, 4. Perforating pipe, 5. Perforating pump, 6. Hole body enlargement cavity, 7. Hole bottom enlargement cavity, 8. Bottom caisson, 9. Second packer, 10. First packer, 11. Debris rock and soil, 12. Anchor cable, 12-1. Bottom anchor cable, 12-2. Hole body anchor cable, 121. Portal protection pipe, 122. Connecting pipe, 123. Tensioning 124. Anchor cable body, 13. Jack oil pump, 14. Grouting pipe, 15. Grouting pump, 16. Ductile bonding material, 17. Hole body enlargement cavity grouting body, 18. Hole body grouting body, 19. Hole bottom enlargement cavity grouting body, 20. Bottom caisson grouting body, 21. Hole opening anchor, 211. Conical hole, 22. Limiting plate, 23. Through-hole jack, 24. Tensioning anchor, 25. Conical wedge, 26. Cement protective anchor. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0037] This invention provides a method for multi-stage borehole enlargement and shallow-depth coordinated anchoring of fractured rock and soil using a caisson wall protection system. The method includes the following steps: 1) For the fractured rock and soil body 1, a drilling-percussion combined approach is used to enlarge the borehole in multiple stages, forming boreholes at different levels at the bottom and body of the borehole. The multi-stage boreholes, from top to bottom, include at least one borehole body borehole 6 and one borehole bottom borehole 7. The number of borehole body boreholes 6 can be determined based on factors such as the thickness, slope, degree of fracture, water proximity, slip surface location, and geological conditions of the rock and soil body. The anchor hole 2 can be constructed using a core drill or a down-the-hole hammer. After the anchor hole 2 reaches the designed depth, drilling continues along the extension direction of the anchor hole 2, forming a bottom caisson 8 connected to the bottom borehole 7. The bottom caisson 8 has a columnar structure and its diameter is smaller than the diameter of the bottom borehole 7. This step, by designing the bottom caisson 8 at the bottom of the borehole in the fractured rock and soil body 1, can collect the debris rock and soil 11 discharged from the boreholes during the hydraulic percussion process. In practical applications, each enlarged cavity is approximated as having a radius of R. i Sphere, R i If the value is taken as half of the major axis of each enlarged cavity, then the volume of each enlarged cavity is... The bottom caisson 8 is a column with radius r. The depth L of the bottom caisson 8 needs to be calculated based on the volume of debris rock and soil 11 discharged from each enlarged cavity, i.e. Therefore, when the bottom caisson 8 is greater than L, it can be ensured that the volume of the bottom caisson 8 is greater than the volume of all the enlarged holes, and can accommodate the debris and soil 11 discharged from the enlarged holes.

[0038] 2) After the anchor hole 2 is completed, the casing 3, which has several screen hole groups spaced along its length on the sidewall, is lowered into the borehole. The spacing between two adjacent screen hole groups is the same as the spacing between two adjacent boreholes to be enlarged. Each screen hole group has a flushing section including several flushing screen holes 32 and a slag discharge section below the flushing section including several slag discharge screen holes 31. The size of the slag discharge screen holes 31 is determined based on the particle size of the broken rock and soil 1. The size of the flushing screen holes 32 is determined based on the flow velocity of the water jet required for hydraulic flushing. Two screen holes 32 are installed inside the casing 3 at the positions corresponding to the predetermined screen hole groups. Two packers are positioned at intervals, one above the flushing section and the other above the slag discharge section. High-pressure water is injected into the sealed space A formed by the two packers and the inner wall of the casing 3 using a perforating tool. The high-pressure water flows through the flushing screen holes to form a cavity in the wall of the anchor hole 2. The debris and soil 11 generated during the cavity formation process passes through the slag discharge screen holes 31 and enters the casing 3, flowing along the casing 3 into the bottom caisson 8. Using a top-down sequence, the nozzles of the packers and the perforating tool are positioned at different screen hole groups on the casing 3, and the above steps are repeated to form a multi-stage enlarged cavity in the anchor hole 2. This step uses a combination of casing 3 with screen hole groups and packers, which can achieve fixed-point radial hydraulic perforation to create cavities at different depths and shallows in the hole bottom and body, based on the engineering conditions of the fractured rock and soil, forming a multi-stage enlarged cavity at the hole bottom and body. It should be noted that for the fractured rock and soil mass 1, hydraulic reaming is performed in a top-down sequence. This effectively protects the already formed reamed holes from clogging the upper reamed holes and the corresponding flushing screen holes 32 and slag discharge screen holes 31 as the debris 11 discharged from the lower reamed holes flows along the casing 3 to the bottom caisson 8 during the flushing process. The flushing time for each reamed hole is determined based on its diameter. Previous engineering experience shows that for fractured rock and soil masses, forming a 30cm diameter reamed hole requires 10 minutes of flushing. The size of the reamed hole and the flushing time have an approximately linear relationship; however, specific engineering cases require laboratory simulation experiments to determine the optimal timeframe.

[0039] 3) After the multi-stage enlarged borehole construction is completed, the packer along with the sleeve 3 is removed from the anchor hole 2. Then, several anchor cables 12 are lowered into the anchor hole 2. Each anchor cable 12 corresponds to one of the enlarged boreholes, and the anchor cable 12 extends to the bottom of the corresponding enlarged borehole. Each anchor cable 12 includes an anchor cable body 124 and a composite structure passing through the upper part of the anchor cable body 124. The composite structure and the anchor cable body 124 are bonded together by a high-ductility bonding material 16. The high-ductility bonding material 16 can be a steel bonding adhesive with added basalt fibers, or other materials, or determined according to the specific project requirements. The composite structure includes a connecting pipe 122, and a borehole protection pipe 121 and a tensioning protection pipe 123 installed at both ends of the connecting pipe 122.

[0040] 4) Grout preparation: Based on the degree of fragmentation of the fractured rock and soil mass 1, in this engineering embodiment, a grout with high final setting strength and significant fluidity is prepared by using 93%-97.9% cement slurry, 0.5% fiber, 1.5%-2.5% water-reducing agent, and 0.1-4% early-strength agent. The cement slurry is composed of cement and water mixed at a mass ratio of 1:0.3. The proportions of each component need to be adjusted according to the engineering geological conditions of the fractured rock and soil mass 1 for each engineering application. This step, through specific material proportioning design, produces a highly diffusive and high-strength grout with strength far exceeding that of the fractured rock and soil mass 1.

[0041] 5) Grouting is carried out from bottom to top using grouting equipment. After grouting is completed, it is naturally cured for a period of time to allow the grout to solidify. Each anchor cable 12 is anchored by the grout, and segmented anchoring is achieved through each anchor cable 12 (including the bottom anchor cable 12-1 and the body anchor cable 12-2).

[0042] 6) Tensioning components are installed at the composite structure of each anchor cable 12. Each tensioning component includes an opening anchor 21 fixed outside the opening of the anchor hole 2, a limiting plate 22, a through jack 23, and a tensioning anchor 24 arranged sequentially from bottom to top on the opening anchor 21, and a jack oil pump 13. The opening anchor 21 is provided with a conical hole 211 that is larger at the top and smaller at the bottom. The composite structure passes through the opening anchor 21, the limiting plate 22, and the through jack 23 in sequence, and the opening protective tube 121 is held tightly by the conical clamp 25 provided in the conical hole 211.

[0043] 7) After the maintenance is completed, start the hydraulic pump 13 of the jack, so that the through jack 23 can tension the corresponding anchor cable 12 respectively. The tension applied is transmitted to the hole enlargement cavity through the anchor cable 12; among them, the tension applied to the hole enlargement cavity 7 at the bottom of the hole is greater than the tension applied to the hole enlargement cavity 6 in the body of the hole.

[0044] 8) After applying the target load to each anchor cable 12, close the through jack 23, disassemble the tension anchor 24, the through jack 23 and the limiting plate 22, cut each anchor cable 12 from the connecting pipe 122, and then use cement protective anchor upset 26 to protect the exposed ends of the anchor 21 at the opening and the anchor cable 12. The cement protective anchor upset 26 is formed by applying cement slurry at the target position.

[0045] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0046] Example 1

[0047] This embodiment provides a multi-stage borehole expansion and shallow-depth coordinated anchoring method for caisson wall protection in fractured rock and soil, which specifically includes the following steps:

[0048] (1) Due to the low strength of the fractured rock and soil mass 1 and its fragmented structure, geological analysis determined that a borehole enlargement cavity 6 would be formed at a borehole depth of 4m, and a borehole bottom enlargement cavity 7 would be formed at a borehole depth of 8m, as shown in the figure. Figure 1 or Figure 2 The borehole 6 and bottom 7 are marked in the diagram. The anchor hole 2 is drilled using a down-the-hole hammer technique. During the drilling process, wind energy is used to automatically discharge the debris and soil generated during drilling. The anchor hole 2 is 12m deep, which exceeds the depth of the bottom 7 of the lowest point of the fractured rock and soil body 1. The 4m depth of the drilled hole forms a bottom caisson 8 to accommodate the debris and soil 11 discharged from the borehole 6 and bottom 7.

[0049] (2) such as Figure 1 As shown, after the fractured rock and soil body 1 is drilled, a casing 3 is lowered into the anchor hole 2 to protect the borehole wall of the fractured rock and soil body 1 and prevent the borehole wall from collapsing. Before lowering the casing 3 into the borehole, the positions of the enlarged cavity to be formed in the fractured rock and soil body 1 are marked on the casing 3 one by one, and then a group of screen holes is opened at each marked position. In this embodiment, combined with the position of the enlarged cavity, a group of screen holes is opened from the opening of the anchor hole 2 downwards at lengths of 4m and 8m on the steel casing 3, respectively. The group of screen holes includes a slag discharge screen hole 31 and a flushing screen hole 32. The size of the slag discharge screen hole 31 is 7cm, which is large enough to allow the formation of clastic rock and soil 11 by hydraulic flushing. The diameter of the flushing screen hole 32 is 0.4cm. With this hole size, the water pressure of the flushing pump 51 is set to 4MPa. The water jet formed by the flushing screen hole 32 hydraulically breaks the cohesion between the particles of the fractured rock and soil body 1, forming clastic rock and soil 11.

[0050] (3) such as Figure 1 and Figure 2As shown, from top to bottom, for all the required enlarged holes, the first packer 10 and the second packer 9 are sequentially lowered into the screen hole group at the corresponding position of the required enlarged hole inside the casing 3. The first packer 10 is located above the flushing screen hole 32, and the second packer 9 is located below the flushing screen hole 32. The first packer 10 and the second packer 9 are used to isolate the flushing screen hole 32 on the casing 3. The perforating pipe 4 is connected to the sealing space A formed between the first packer 10 and the second packer 9 through the inlet switch on the first packer 10. According to the strength characteristics of the broken rock and soil body 1, the perforating pump 5 is started with a set water pressure of 4MPa to perform hydraulic perforation on the broken rock and soil body 1. The perforation time is 10 minutes. The water pressure is used to break the cohesion between the broken rock and soil bodies. The broken rock and soil fragments 11 are discharged through the slag discharge screen hole 31. The discharged rock and soil fragments 11 flow down along the casing 3 to the bottom caisson 8. The perforation operation forms the enlarged hole 6. Based on the required number and location of borehole enlargement caves 6, hydraulic enlargement is carried out sequentially from top to bottom until the final borehole bottom enlargement cave 7 is formed, thereby realizing the formation of a multi-stage enlargement cave system in the fractured rock and soil mass 1, consisting of at least one borehole body enlargement cave 6 and one borehole bottom enlargement cave 7.

[0051] (4) such as Figure 3 As shown, after the fractured rock and soil body 1 forms a multi-stage enlarged hole cavity, the first packer 10 and the second packer 9, along with the sleeve 3, are removed from the fractured rock and soil body 1. Then, the bottom anchor cable 12-1 and the body anchor cable 12-2 are lowered into the anchor hole 2. The number of body anchor cables 12-2 lowered depends on the number of enlarged hole cavities 6 in the body. In this embodiment, the number of enlarged hole cavities 6 in the body is 1. The bottom anchor cable 12-1 and the body anchor cable 12-2 are respectively inserted into the bottom of the corresponding enlarged hole cavity.

[0052] (5) such as Figure 4 As shown, the bottom anchor cable 12-1 and the body anchor cable 12-2 used in this case are identical in material and structure. Both are made of lightweight, corrosion-resistant composite reinforcement, such as basalt fiber reinforcement or glass fiber reinforcement. The bottom anchor cable 12-1 is longer than the body anchor cable 12-2. One end of the anchor cable body 124 in both the bottom anchor cable 12-1 and the body anchor cable 12-2 is equipped with a composite structure consisting of a borehole protector 121, a connecting pipe 122, and a tensioning protector 123. The borehole protector 121 and the tensioning protector 123 are respectively inserted into the connecting pipe 122. Then, the composite structure consisting of the borehole protector 121, connecting pipe 122, and tensioning protector 123 is fitted onto the anchor cable body 124 and bonded using a high-ductility bonding material 16, ensuring that the protector and the anchor cable can resist large deformations. The high-ductility bonding material 16 can be a steel-bonding adhesive with added basalt fiber filaments.

[0053] (6) Preparation of grouting fluid: Based on the degree of fragmentation of the fractured rock and soil body 1, in this embodiment of the project, a grouting fluid with a final setting strength of 40 MPa and obvious fluidity is prepared by using 93% cement slurry, 0.5% basalt fiber, 2.5% water-reducing agent, and 4% early-strength agent. The cement slurry is made by mixing cement and water at a mass ratio of 1:0.3. This step, through the specific material ratio design, produces a high-diffusivity, high-strength grouting fluid with a strength far exceeding that of the fractured rock and soil body, which can be used as the anchoring material for the bottom hole enlargement cavity and the hole body enlargement cavity as described in the following steps.

[0054] (7) such as Figure 5 As shown, after each anchor cable 12 is inserted into the corresponding enlarged cavity position in the anchor hole 2, the grouting pipe 14 is lowered into the bottom caisson 8, and the grouting pump 15 is started to inject the grouting liquid prepared in step (6) into the anchor hole 2. The grouting operation proceeds upward from the bottom caisson 8, forming the bottom caisson grouting body 20, the bottom hole enlarged cavity grouting body 19, the hole body grouting body 18, and the hole body enlarged cavity grouting body 17 at different depths and shallow locations in sequence, anchoring the bottom anchor cable 12-1 and the hole body anchor cable 12-2, forming deep and shallow segmented anchoring of the fractured rock and soil. During the grouting process, the bottom caisson grouting body, the bottom borehole enlargement cavity grouting body, the borehole body grouting body, and the borehole body enlargement cavity grouting body form a unified whole. Because the bottom caisson grouting body is buried at the deepest depth and its diameter is smaller than the bottom borehole enlargement cavity, it has the strongest resistance to pull-out and damage under the pressure of the fractured rock and soil, thus improving the overall pull-out and damage resistance of the grouting body. After grouting is completed, the bottom anchor cable 12-1 and the borehole body anchor cable 12-2 are anchored by the bottom borehole enlargement cavity grouting body 19 and the borehole body enlargement cavity grouting body 17, respectively. The grouting liquid is then allowed to cure naturally for one day to solidify, ultimately forming the bottom borehole enlargement cavity anchoring body and the borehole body enlargement cavity anchoring body. At this point, the deep bottom anchor cable 12-1 and the shallow borehole body anchor cable 12-2 achieve segmented anchoring of the fractured rock and soil body 1.

[0055] (8) such as Figure 6 , Figure 7 and Figure 8 As shown, the composite structure on the anchor cable body 124 passes through the conical hole 211 and the limiting plate 22 of the hole anchor 21, then through the through-hole jack 23, and finally through the tension anchor 24. One end of the hole liner 121 is located in the anchor hole 2, avoiding direct contact between the composite reinforcement and the fractured rock and soil 1 at the hole opening, effectively preventing the composite reinforcement from being ground down by the fractured rock and soil 1 under external force. The connecting pipe 122 is located in the through-hole jack 23. The hole liner 121 is held by a conical clamp 25 located in the conical hole 211. The conical clamp 25 can move slightly along the side wall of the conical hole 211 as the anchor cable body 124 is tensioned by the through-hole jack 23.

[0056] (9) After installing the hole anchor 21, limiting plate 22, through jack 23 and tensioning anchor 24 according to the above steps (8), start the jack oil pump 13 to allow the through jack 23 to tension the bottom anchor cable 12-1 and the body anchor cable 12-2 respectively. At this time, the load acting on the bottom anchor cable 12-1 and the body anchor cable 12-2 is transferred to the bottom hole enlargement cavity grouting body 19 and the body hole enlargement cavity grouting body 17. After the target load is applied, turn off the jack oil pump 13 and remove the tensioning anchor 24. When the anchor 24 is pulled, the bottom anchor 12-1 or the body anchor 12-2 retracts slightly. When the bottom anchor 12-1 and the body anchor 12-2 retract, they drive the conical wedge 25 in the hole anchor 21 to move along the side wall of the conical hole 211 toward the small end of the conical opening. When the conical wedge 25 reaches the small end of the conical hole 211, it stops sliding, thereby locking the hole guard 121 on the bottom anchor 12-1 or the body anchor 12-2 onto the hole anchor 21. In this step, the bottom anchor cable 12-1 and the body anchor cable 12-2 are applied according to the design values. Here, the bottom anchor cable 12-1 is prestressed with 100KN, and the body anchor cable 12-2 is prestressed with 60KN. The applied prestress is borne by the bottom hole enlargement cavity grouting body 19 and the body hole enlargement cavity grouting body 17. At the same time, the retraction force of the anchor cable 12 evenly presses the fractured rock and soil body 1 distributed from the borehole opening to the bottom hole enlargement cavity 7, realizing the coordinated anchoring of the deep and shallow parts of the fractured rock and soil body 1, and effectively improving the reinforcement effect of the fractured rock and soil body. Most importantly, the bottom caisson grouting body 20 formed in step 7) above, together with the bottom hole enlargement cavity grouting body 19, the hole body grouting body 18, and the hole body enlargement cavity grouting body 17, forms a whole. When the tension applied to each anchor cable 12 is transmitted to the corresponding bottom hole enlargement cavity grouting body 19 and hole body enlargement cavity grouting body 17, it can be further transmitted to the bottom caisson grouting body 20. Since the bottom caisson grouting body 20 is buried at the deepest depth and its diameter is smaller than the bottom hole enlargement cavity 7, it has the strongest resistance to pull-out and damage under the pressure of the fractured rock and soil body 1, which plays a role in improving the pull-out and damage resistance of the entire grouting body.

[0057] (10) such as Figure 9 As shown, after completing the above step (9), the tensioning anchor 24, the through jack 23, and the limiting plate 22 are removed in sequence. Then, a cutting machine is used to cut the connecting pipe 122. Then, a cement protective anchor 26 is used to protect the exposed ends of the anchor 21 and the connecting pipe 122 at the opening. The connecting pipe 122 is an easily cut plastic pipe, which can be easily cut with a cutting machine, thereby shortening the exposed length of the anchor cable 12 outside the anchor hole 2 opening. This makes it easier for the cement protective anchor 26 to protect the anchor hole 2 opening. Otherwise, if the cement protective anchor 26 is too long, it will easily fall off under long-term aging and will not play a role in protecting the anchor 21 at the opening.

[0058] By comprehensively employing the technical solutions described in steps 1 to 10 above, multi-stage borehole expansion and shallow-depth coordinated anchoring of fractured rock and soil in caisson wall reinforcement can be achieved. The order of each step can be adjusted according to the actual engineering situation. The anchoring method of this invention achieves the formation of expanded boreholes and coordinated shallow-depth anchoring within the fractured rock and soil, distributing the tension force of the through-hole jack to the anchor bodies in each borehole, thus applying prestress to different parts of the fractured rock and soil and effectively improving the reinforcement effect.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention in any way. All equivalent transformations or modifications made in accordance with the essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for multi-stage borehole enlargement and depth-coordinated anchoring of fractured rock and soil in caisson wall protection, comprising the steps of drilling anchor holes, constructing multi-stage borehole enlargement tunnels, lowering anchor cables, grouting, and anchoring; characterized in that: The multi-stage borehole expansion cave includes at least one borehole body expansion cave and one borehole bottom expansion cave from top to bottom. After the anchor hole construction reaches the design depth, drilling continues along the extension direction of the anchor hole. A bottom caisson is formed below the bottom expansion cave to accommodate the debris and soil discharged during the construction of the multi-stage borehole expansion cave. The bottom caisson has a columnar structure and its diameter is smaller than the diameter of the bottom expansion cave. After the anchor hole construction is completed, a casing with several screen hole groups spaced along its length on the sidewall is lowered into the borehole. The spacing between two adjacent screen hole groups is the same as the spacing between two adjacent enlarged boreholes to be constructed. Each screen hole group has a flushing section including several flushing screen holes and a slag discharge section below the flushing section containing several slag discharge screen holes. Two spaced packers are installed in the casing at positions corresponding to the predetermined screen hole groups. The two packers are located above the flushing section and above the slag discharge section, respectively. High-pressure water is injected into the sealed space formed by the two packers and the inner wall of the casing using a punching machine. The high-pressure water flows through the flushing screen holes to form a cavity on the anchor hole wall. The debris and soil generated during the cavity formation process pass through the slag discharge screen holes into the casing and flow into the bottom caisson along the casing. The packers and the nozzles of the punching machine are positioned at different screen hole groups on the casing in a top-down sequence, and the above steps are repeated to form a multi-stage enlarged borehole in the anchor hole.

2. The method for multi-stage borehole expansion and depth coordination anchoring of fractured rock and soil for caisson wall protection as described in claim 1, characterized in that, The diameter of the slag discharge screen holes is 5cm-8cm, and the diameter of the flushing screen holes is less than 0.5cm.

3. The method for multi-stage borehole expansion and depth coordination anchoring of fractured rock and soil for caisson wall protection as described in claim 1, characterized in that, After the multi-stage enlarged hole construction is completed, the packer and casing are removed from the anchor hole, and then several anchor cables are placed into the anchor hole. Each anchor cable corresponds to one of the enlarged holes, and the anchor cable extends to the bottom of the corresponding enlarged hole.

4. The method for multi-stage borehole expansion and depth coordination anchoring of fractured rock and soil for caisson wall protection as described in claim 3, characterized in that, The anchor cable includes an anchor cable body and a composite structure passing through the upper part of the anchor cable body. The composite structure is bonded to the anchor cable body by a high-ductility adhesive material. The composite structure includes a connecting pipe and opening protective pipes and tensioning protective pipes installed at both ends of the connecting pipe.

5. The method for multi-stage borehole expansion and depth coordination anchoring of fractured rock and soil for caisson wall protection according to claim 4, characterized in that, The components and mass fraction of the grouting fluid used for grouting are as follows: cement slurry 93%-97.9%, fiber filaments 0.5%, water-reducing agent 1.5%-2.5%, and early strength agent 0.1-4%; among which, cement slurry is made by mixing cement and water in a mass ratio of 1:0.

3.

6. The method for multi-stage borehole expansion and depth coordination anchoring of fractured rock and soil for caisson wall protection according to claim 5, characterized in that, Grouting is carried out from bottom to top using grouting equipment. After grouting is completed, it is naturally cured for a period of time to allow the grout to solidify. Each anchor cable is anchored by the grout, thus forming segmented anchoring.

7. The method for multi-stage borehole expansion and depth coordination anchoring of fractured rock and soil for caisson wall protection according to claim 6, characterized in that, Tensioning components are installed at the composite structure of each anchor cable. Each tensioning component includes an opening anchor fixed outside the borehole of the anchoring borehole, and a limiting plate, a through jack, and a tensioning anchor arranged sequentially from bottom to top on the opening anchor. The opening anchor has a tapered hole that is larger at the top and smaller at the bottom. The composite structure passes through the opening anchor, the limiting plate, and the through jack in sequence, and the opening protective pipe is held tightly by a tapered clamp set in the tapered hole.

8. The method for multi-stage borehole expansion and depth coordination anchoring of fractured rock and soil for caisson wall protection according to claim 7, characterized in that, The lower part of the protective pipe is located in the anchor hole, and the upper part is located in the tensioning assembly. The connecting pipe is located in the through-hole jack.

9. A method for coordinating shallow and large-scale hole enlargement and anchoring in fractured rock and soil for caisson wall protection, as described in claim 7, is characterized in that... The tensioning assembly also includes a jack oil pump connected to the through-hole jack. After the curing is completed, the jack oil pump is started so that the through-hole jack can tension the corresponding anchor cables respectively. The applied tension force is transmitted to the hole enlargement cavity through the anchor cables. The tension force applied to the hole enlargement cavity at the bottom of the hole is greater than the tension force applied to the hole enlargement cavity in the hole body.

10. A method for coordinating shallow and large-scale hole enlargement and anchoring in fractured rock and soil for caisson wall protection, as described in claim 9, is characterized in that... After applying the target load to each anchor cable, close the through-hole jack, disassemble the tension anchor, through-hole jack and limiting plate, cut each anchor cable from the connecting pipe, and then use cement protective anchor upset to protect the anchor at the opening and the exposed end of the anchor cable.

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