Construction method of inverted trapezoidal anchor cable anchoring structure

Abstract

The application discloses a construction method of an inverted trapezoidal anchor cable anchoring structure, belongs to the field of geotechnical engineering anchoring, and comprises the following steps: drilling into a hard rock layer in a conventional mode, switching to other drilling tools to continuously drill, synchronously lowering a casing to perform stepped reaming, forming an inverted trapezoidal hole, completing the forming of the inverted trapezoidal anchor cable anchoring structure, and triggering hole wall reinforcement by recovering the drill rod. The application forms a construction closed loop through three continuous time sequence actions of drilling, reaming and recovering, reconfigures the geometric shape of the anchoring body through the inverted trapezoidal multi-stage reaming, eliminates the stress concentration at the hole mouth, utilizes the casing to synchronously protect the wall to guarantee the hole forming accuracy in a complex stratum, and realizes systematic improvement of the anchoring force. The application can complete the stepped reaming of the casing while switching to the continuous drilling of a down-the-hole hammer drill bit, and solves the interruption problem in the existing hard rock drilling. The drill rod lifting movement automatically activates the hole wall trimming, and no manual intervention is needed. The gravity direction change of the drill rod triggers the physical effect, and the slurry penetration depth reaches 15 mm.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering anchoring technology, specifically relating to a construction method for an inverted trapezoidal anchor cable anchoring structure. Background Technology

[0002] With the continuous expansion of modern construction projects, geotechnical engineering technology has gradually achieved phased development. Anchoring technology plays a vital role in geotechnical engineering. By using anchoring technology for fixation in geotechnical engineering and strictly adhering to technical specifications during construction, technicians maximize the effectiveness of anchoring technology in geotechnical engineering, thereby improving the overall level of geotechnical engineering.

[0003] Chinese patent CN114991667A discloses a re-entry directional positioning device for branch wells. This device employs a segmented drill-up and replacement process, mainly comprising: a casing coupling sent downhole along with the well casing, with at least one positioning groove within the casing coupling; a positioning component, including at least one positioning key and an orientation key, the positioning key being configured to move radially to engage with the positioning groove; the orientation key being radially movable, with an orientation groove on the casing coupling for orienting the orientation key. The construction process of this device involves: separation of the drill rig power head, manual replacement of the drill bit, repeated positioning of the borehole location, and isobaric grouting to form a cylindrical anchor body. The device uses a conventional drill bit to drill to a hard rock layer, then removes the drill bit to replace it with a down-the-hole hammer drill bit, performs a second drilling to complete the hard rock section drilling, and after removal of the drill bit, lowers an independent reamer for equal-diameter reaming (without changing the borehole diameter).

[0004] Chinese patent CN117071943A discloses a support device and auxiliary moving component for steel structure construction. This device employs a casing drilling and wall-protection process and mainly includes a load-bearing box with three movable openings, a locking opening, a storage hole, and a sliding groove on its surface. During operation, pressing the pressing plate according to the height of the component to be supported causes the connecting column to slide upwards and engage with the fixing component for fixation. Simultaneously, pulling the handle downwards adjusts the connecting column, and pressing down the horizontal plate causes the first wedge to slide down, causing the second wedge to move outwards, extending the pull ring out of the storage hole. This facilitates movement of the device via the pull ring control, achieving the effect of auxiliary movement. The construction process involves: rigid connection between the drill bit and casing, synchronous rotary drilling, and grouting after the drill rod is pulled out. This device uses synchronous drilling of the casing and drill bit to prevent hole collapse, forming a straight hole of uniform diameter throughout (without stepped hole-enlarging function). Grouting is performed directly after the drill rod is retrieved, without any hole wall reinforcement measures.

[0005] Existing geotechnical engineering anchoring methods have the following main problems in hard rock formations: 1. Inefficient anchor body shape leads to a significant decrease in pull-out resistance: The anchor bodies formed by existing geotechnical engineering anchoring methods are all cylindrical (equal diameter straight holes). This shape is prone to stress concentration when subjected to force, especially in hard rock strata. The contact area between the anchor body and the rock mass is limited, resulting in a loss of ultimate pull-out resistance of more than 30% (according to the Chinese Journal of Geotechnical Engineering 2023,45(2):321).

[0006] For example, in Chinese patent CN114991667A, the "constant diameter reaming" process is used, keeping the hole diameter constant, resulting in a cylindrical anchor body that cannot change the stress distribution. In Chinese patent CN117071943A, a constant diameter straight hole is formed throughout the casing drilling process, without stepped reaming or variable diameter design, also producing a cylindrical anchor body. The uneven distribution of lateral resistance in cylindrical anchor bodies leads to stress concentration at the ends of the anchor body when the anchor cable is under tension, easily causing early failure and reducing the safety reserve of the anchoring system. Furthermore, this shape wastes material and fails to fully utilize the rock mass strength.

[0007] 2. Hard rock drilling interruption and low construction efficiency: When encountering hard rock layers, it is necessary to lift the drill and change the drill bit (such as changing to a down-the-hole hammer drill bit), which leads to the interruption of the construction process. Repeated positioning and drill changing operations reduce efficiency by about 60%.

[0008] For example, Chinese patent CN114991667A explicitly requires "replacing the drill bit with a down-the-hole hammer," including steps such as separating the drill rig's power head, manually replacing the drill bit, and repeatedly positioning the borehole. This not only increases working hours but also introduces the risk of human error. While casing drilling in Chinese patent CN117071943A can protect the borehole wall, it doesn't solve the efficiency problem of drilling in hard rock. If extremely hard rock formations are encountered, drill bit replacement or special treatment may still be necessary, but this patented technology does not provide an efficient drilling solution. Drilling interruptions not only prolong the construction period but also increase equipment wear and labor costs. In complex formations, repeated drill bit removal may cause borehole wall collapse or positioning deviations, further affecting construction quality.

[0009] 3. Lack of technology in the drill pipe recycling stage and insufficient hole wall reinforcement: After the drill pipe is recycled, there is a lack of effective hole wall reinforcement measures. The grouting penetration depth is only 5-8mm, resulting in insufficient bonding strength between the anchor body and the rock mass, which affects long-term durability.

[0010] For example, in Chinese patent CN114991667A, an independent reamer is lowered after the drill rod is retrieved to enlarge the borehole, but the grouting process is "isobaric grouting" without pressure control or permeability enhancement measures, and the grout cannot penetrate deep into the rock fissures. In Chinese patent CN117071943A, cement grout is directly injected after the drill rod is pulled out, without any borehole wall strengthening steps (such as high-pressure grouting or chemical treatment). The grout only covers the surface of the borehole wall, resulting in shallow penetration. Shallow penetration creates a weak interface between the anchor body and the rock mass, making it prone to slippage under load. Simultaneously, the unreinforced borehole wall is susceptible to groundwater or weathering, reducing the service life of the anchor cable.

[0011] Existing geotechnical anchoring methods in hard rock formations suffer from core technical problems such as unreasonable anchor body morphology design, low drilling efficiency, and insufficient borehole wall reinforcement. These shortcomings stem from the limitations of traditional processes and urgently require innovative solutions. Summary of the Invention

[0012] To address the problems existing in current geotechnical engineering anchoring methods, this invention provides a construction method for an inverted trapezoidal anchor cable anchoring structure. By optimizing the hole formation and construction sequence, this invention creates a high-bearing-capacity inverted trapezoidal anchor cable anchoring structure, primarily applicable to engineering scenarios such as slope protection and foundation pit reinforcement.

[0013] The technical solution adopted by this invention to solve the technical problem is as follows: The present invention provides a construction method for an inverted trapezoidal anchor cable anchoring structure, comprising the following steps: Step S1: Drill conventionally to the hard rock layer, then switch to other drilling tools for continuous drilling; Step S2: The casing is simultaneously lowered and the hole is enlarged in a stepped manner to form an inverted trapezoidal hole, thus completing the inverted trapezoidal anchor cable anchoring structure. Step S3: Drill rod recovery triggers hole wall reinforcement.

[0014] In a preferred embodiment, in step S1, the other drilling tool is a down-the-hole hammer.

[0015] In a preferred embodiment, during continuous drilling in step S1, the drilling proceeds directly to the designed depth.

[0016] As a preferred implementation, in step S1, the drill bit type is seamlessly switched using the drill rig power head quick-change interface to ensure drilling continuity.

[0017] In a preferred embodiment, in step S2, the casing and the drill bit are lowered synchronously, with a distance of 1.5-2m between the drill bit and the casing.

[0018] In a preferred embodiment, in step S2, the free section uses the same diameter, and after reaching the anchoring section, the casing end expander expands the hole, and the anchoring section forms an inverted trapezoid with a bottom diameter larger than the opening diameter.

[0019] As a preferred embodiment, in step S2, a two-stage borehole enlargement is used when the designed length of the anchorage section is 8-15m; a three-stage borehole enlargement is used when the designed length of the anchorage section is greater than 15m; and a three-stage borehole enlargement is used when the geological conditions are complex.

[0020] In a preferred embodiment, in step S3, the dressing operation is automatically activated when the drill pipe is lifted, without the need for external power, to remove slag and compact rock cuttings, forming a micro-serrated interface.

[0021] In a preferred embodiment, in step S3, the micro-serrated interface is a permeation groove formed by the pore wall and the slurry.

[0022] In a preferred embodiment, in step S3, when the drill bit is retrieved, the casing end reamer reverses its operation to trim the hole wall.

[0023] The beneficial effects of this invention are: 1. Third-order continuous-time closed loop; This invention employs three consecutive sequential actions: drilling (switching drill bits in hard rock formations), reaming (one-time forming), and recycling (strengthening the borehole wall), forming a closed-loop construction process. This breaks through the traditional fragmented "drilling-pulling-reaming" model and, for the first time, transforms the drill rod recycling stage into a technology value-added step.

[0024] 2. Stepped hole enlargement parameter control; This invention reconstructs the geometry of the anchor body through multi-stage trapezoidal hole enlargement, transforming the single frictional force of the traditional cylindrical hole into a stepped end-bearing-frictional synergistic force, eliminating stress concentration at the hole opening, and simultaneously using the casing for synchronous wall protection to ensure the drilling accuracy in complex strata, thereby achieving a systematic improvement in anchoring force.

[0025] This invention requires no complex mechanical modifications; the optimization of the anchor body's morphology can be achieved solely through process parameter design. The stress concentration factor for traditional cylindrical holes reaches 1.8, while this invention reduces it to 1.0.

[0026] 3. Drill bit switching and stepped reaming are synchronized; This invention can complete casing step enlargement while switching to continuous drilling with a down-the-hole hammer drill bit, solving the problem of interruption in existing hard rock drilling, with a response time of ≤15 minutes and an efficiency improvement of 212%.

[0027] 4. Automatic recycling trigger mechanism; In this invention, the upward movement of the drill rod automatically activates the hole wall trimming without manual intervention. It utilizes the change in the direction of gravity of the drill rod to trigger a physical effect (non-electronic control), and the slurry penetration depth reaches 15mm. Attached Figure Description

[0028] Figure 1The flowchart illustrates a construction method for an inverted trapezoidal anchor cable anchoring structure provided by this invention.

[0029] Figure 2 The figures show a comparison of anchoring structures. In the figures, (a) is the existing cylindrical hole anchoring structure; and (b) is the inverted trapezoidal anchor cable anchoring structure obtained in specific embodiment 1 of the present invention.

[0030] Figure 3 The results are compared using finite element stress analysis.

[0031] Figure 4 The results show the test results of the pore wall-slurry interface. In the figure, (a) is the existing smooth pore wall; (b) is the serrated pore wall of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings.

[0033] This invention provides a construction method for an inverted trapezoidal anchor cable anchoring structure, which mainly achieves efficient forming of the inverted trapezoidal anchor cable anchoring structure through three consecutive sequential actions, such as... Figure 1 As shown, the specific implementation process is as follows: I. Continuous Drilling Stage; The continuous drilling stage mainly adopts the technical means of conventional drilling to hard rock layers, and then switching to other drilling tools (such as down-the-hole hammer) for continuous drilling in hard rock layers, which mainly solves the problem of efficiency defects.

[0034] According to the present invention, when encountering hard rock formations (rock saturated compressive strength ≥ 60 MPa), the drill bit is switched to a down-the-hole hammer drill bit (response time ≤ 15 minutes). After switching, the drill can be continuously drilled to the designed depth directly, avoiding the interruption of the traditional two drill bit pulls.

[0035] Specifically, the drill bit type can be seamlessly switched using the drill rig power head quick-change interface (industry standard JTG / T 3365-2022) to ensure drilling continuity.

[0036] This invention improves construction efficiency through continuous drilling: the drill bit can be switched quickly within 15 minutes, eliminating the defects of construction interruption and increasing construction efficiency by 212%.

[0037] II. Stepped hole enlargement stage; The stepped hole enlargement stage mainly adopts the technical means of synchronously lowering the casing for stepped hole enlargement and forming an inverted trapezoidal anchor cable anchoring structure, which mainly solves the problem of morphological defects.

[0038] According to this invention, the casing and drill bit are lowered synchronously, with a distance of 1.5-2m between them. The free section uses the same diameter (meaning the casing and drill bit have the same diameter). After reaching the anchoring section, the casing end expander is used to enlarge the hole, forming an inverted trapezoid with a bottom diameter larger than the opening diameter. When the designed length of the anchoring section is 8-15m, two-stage reaming is preferred. When the designed length of the anchoring section is greater than 15m, three-stage reaming is preferred. If the geological conditions are complex, with abundant soft soil and fractured rock, three-stage reaming is preferred.

[0039] Anchoring structure comparison diagram as follows Figure 2 As shown, this invention ensures drilling accuracy through synchronous casing wall protection, and forms a stepped bearing structure by multi-stage inverted trapezoidal hole expansion in the anchoring section: secondary hole expansion (8-15m) disperses stress and improves bearing capacity, and tertiary hole expansion (>15m or complex strata) compensates for insufficient strength of soft rock / soil by increasing mechanical interlocking points, thereby achieving efficient transfer of load to deep strata.

[0040] This invention increases anchoring force by using a stepped hole enlargement method: the inverted trapezoidal hole enlargement forms a stepped load-bearing structure, which can fundamentally solve the stress concentration problem of cylindrical anchor holes and significantly improve anchoring force.

[0041] III. Recycling Enhancement Phase; The recovery and strengthening stage mainly adopts the technical means of triggering hole wall strengthening by recovering the drill pipe, which mainly solves the problem of interface defects.

[0042] According to the present invention, the dressing operation is automatically activated when the drill pipe is lifted (1-3 seconds per meter), without the need for external power, to remove slag and compact rock cuttings, forming a micro-serrated interface.

[0043] Specifically, the drill rod is applied to the borehole wall and retrieved at a speed of 0.5 m / min. During the lifting process, the borehole wall is trimmed, and a 15 mm permeation groove is formed between the borehole wall and the slurry.

[0044] This invention achieves hole wall strengthening through the recovery stage: when the drill bit is recovered, the casing end expander works in reverse to trim the hole wall, solving the problem of insufficient interface adhesion and increasing the penetration depth by 87.5%.

[0045] This invention transforms the traditional "ineffective recovery idle time" into an "interface strengthening window," pioneering a three-stage continuous closed loop of drilling-reaming-strengthening, filling a technological gap in the recovery stage. Simultaneously, this invention achieves one-time forming of the inverted trapezoidal anchor cable anchoring structure through gradient reaming parameter control (non-mechanical modification), circumventing patent barriers related to complex equipment. This invention employs a strategy of simultaneous drill bit switching and stepped reaming, reducing working time by 52.3%. Specific Implementation Example 1 This embodiment 1 takes a granite stratum (saturated compressive strength of the granite stratum is 80MPa, XY-180 drilling rig, anchoring depth 25m) as an example. The specific implementation process of the construction method of the inverted trapezoidal anchor cable anchoring structure provided by the present invention is as follows: Step S1: Continuous drilling; Using conventional drill bits, the drill can penetrate 0-5m into the soil. When encountering hard rock layers with a saturated compressive strength ≥60MPa, the torque sensor will alarm, and the drill bit will be pulled up to switch to a down-the-hole hammer drill bit. This process takes 12 minutes, with a response time of ≤15 minutes. After switching, the drill can be continuously drilled to the anchoring depth of 25m, avoiding the interruption caused by two traditional drill pulls.

[0047] Step S2: Stepped hole enlargement; (1) The casing is lowered synchronously to enlarge the borehole in a stepped manner; The casing and drill bit are lowered synchronously, with a distance of 1.5-2m between them. The free section uses the same diameter (meaning the casing and drill bit have the same diameter). After reaching the anchoring section, the casing end expander is used to enlarge the hole, forming an inverted trapezoid with a bottom diameter larger than the opening diameter in the anchoring section.

[0048] The expansion range of the anchoring section is controlled as follows: The anchorage section is designed to be 8-15m long and uses a two-stage enlargement method; For anchorage sections with a design length greater than 15m or with a lot of soft soil or broken rock, a three-stage borehole expansion method is adopted.

[0049] (2) An inverted trapezoidal anchor cable anchoring structure is formed by simultaneously lowering the casing in a stepped manner to expand the hole.

[0050] Step S3: Recycling and strengthening; The drill rod is applied to the borehole wall and retrieved at a speed of 0.5 m / min. During the drill rod lifting process, the borehole wall is trimmed, and a 15 mm penetration groove is formed between the borehole wall and the slurry.

[0051] Enhanced parameters: A 2-second dressing is triggered every 1 meter the drill rod is lifted, and the measured hole wall roughness Ra = 17.5 μm (the hole wall roughness of the traditional process is Ra = 12.5 μm).

[0052] For the specific embodiment 1 above, the following experiment was conducted to demonstrate the effect of the construction method for the inverted trapezoidal anchor cable anchoring structure provided by the present invention.

[0053] 1. In terms of construction efficiency; The above-described specific embodiment 1 is compared with Chinese patent CN114991667A, and the results are as follows: Chinese patent CN114991667A: Hard rock drilling time is 1.2h / m, the total construction period for a single hole is 6.5h, two drill lifting operations are required, and the switching response time is greater than 45 minutes.

[0054] Specific Implementation Example 1: Hard rock drilling time is 0.38h / m, total construction period for a single hole is 3.1h, and switching response time is less than 15 minutes.

[0055] Compared with Chinese patent CN114991667A, this invention improves hard rock drilling efficiency by 216%, reduces the total drilling time per hole by 52.3%, and improves switching response time by 66.7%.

[0056] 2. Anchorage structure performance; The inverted trapezoidal anchor cable anchoring structure obtained in the above specific embodiment 1 is compared with the cylindrical hole anchoring structure. The finite element stress analysis comparison results are as follows: Figure 3 As shown, the stress concentration factors of the anchorage section are compared: "cylindrical hole": 1.8; "inverted trapezoidal hole": 1.0. The stress concentration degree of the cylindrical hole is significantly higher, 80% higher than that of the inverted trapezoidal hole, indicating that local stress is more likely to concentrate under load. The inverted trapezoidal hole design effectively reduces stress concentration (factor = 1.0), resulting in better structural safety. Therefore, inverted trapezoidal holes should be preferred in engineering to reduce the risk of failure caused by stress concentration.

[0057] 3. On-site pull-out test; Traditional cylindrical hole: ultimate pull-out resistance 850KN, construction time 6.5h / hole, average displacement coefficient 5.3mm.

[0058] Inverted trapezoidal borehole enlargement: ultimate pull-out resistance 1292KN, construction time 3.1h / hole, average displacement coefficient 2.1mm.

[0059] Data comparison: Compared with traditional cylindrical holes, the inverted trapezoidal enlarged hole has a 52% higher ultimate pull-out resistance, a 52.3% reduction in construction time, and a 60.4% reduction in the average displacement coefficient.

[0060] 4. The interface and performance have undergone a qualitative leap. The test results of the pore wall-slurry interface are as follows: Figure 4 As shown. Visualization of technical effects: Serration depth: 40μm, corresponding roughness Ra=17.5μm; slurry tooth-like penetration depth: 15mm (industry standard ≤8mm). Specific comparison data are as follows: Traditional process: pore wall roughness 12.5μm, slurry penetration depth 8mm, interfacial bonding strength 1.2MPa.

[0061] After the drill pipe of this invention is recycled and strengthened, the borehole wall roughness is 17.5μm, the slurry penetration depth is 15mm, and the interfacial bonding strength is 1.8MPa.

[0062] Compared with traditional processes, this invention improves the pore wall roughness by 40%, increases the slurry penetration depth by 87.5%, and improves the interfacial bonding strength by 50%.

[0063] Roughness was obtained using a 3D profilometer (ISO 4287 standard), grout penetration depth was obtained by cutting the grout and observing the staining, and interfacial bond strength was measured using a pull-out test (ASTM D4435).

[0064] This invention solves the morphological defects of existing technologies and optimizes the anchor body structure. Traditional uniform-diameter cylindrical holes lead to stress concentration (ultimate pull-out force loss >30%). This invention improves the anchoring force by one-time forming of an inverted trapezoidal anchor cable anchoring structure through stepped hole expansion, increasing the anchoring force by 52% (the anchoring force in specific embodiment 1 is 1292kN, while the anchoring force of the traditional process is 850kN).

[0065] This invention addresses the efficiency deficiencies of existing technologies and ensures continuous construction. Existing technologies require repeated drilling and equipment changes, leading to decreased efficiency. This invention employs continuous drill bit switching technology (response time ≤ 15 minutes), enabling uninterrupted drilling in hard rock formations and improving construction efficiency by 212% (construction speed of this invention is 2.5 m / h, compared to 0.8 m / h for traditional methods).

[0066] This invention solves the interface defect problem existing in the prior art and enhances the bonding performance of the borehole wall. The drill pipe recovery stage is a technological gap, with slurry penetration depth only 5-8 mm (bonding strength 1.2 MPa). This invention innovatively utilizes the drill pipe recovery action to trigger borehole wall strengthening, enabling slurry penetration depth to reach 15 mm and increasing the interface bonding strength to 1.8 MPa.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A construction method for an inverted trapezoidal anchor cable anchoring structure, characterized in that, Includes the following steps: Step S1: Drill conventionally to the hard rock layer, then switch to other drilling tools for continuous drilling; Step S2: The casing is simultaneously lowered and the hole is enlarged in a stepped manner to form an inverted trapezoidal hole, thus completing the inverted trapezoidal anchor cable anchoring structure. Step S3: Drill rod recovery triggers hole wall reinforcement; In step S2, the casing and drill bit are lowered synchronously, with a distance of 1.5-2m between the drill bit and the casing; In step S2, the free section uses the same diameter. After reaching the anchoring section, the casing end expander expands the hole, and the anchoring section forms an inverted trapezoid with the bottom diameter of the hole larger than the opening diameter. In step S3, when the drill bit is retrieved, the casing end reamer reverses its operation to trim the hole wall.

2. The construction method for an inverted trapezoidal anchor cable anchoring structure according to claim 1, characterized in that, In step S1, the other drilling tool is a down-the-hole hammer.

3. The construction method for an inverted trapezoidal anchor cable anchoring structure according to claim 1, characterized in that, In step S1, during continuous drilling, the drill is carried out directly to the designed depth.

4. The construction method for an inverted trapezoidal anchor cable anchoring structure according to claim 1, characterized in that, In step S1, the drill bit type is seamlessly switched using the drill rig power head quick-change interface to ensure drilling continuity.

5. The construction method for an inverted trapezoidal anchor cable anchoring structure according to claim 1, characterized in that, In step S2, a two-stage borehole enlargement is used when the designed length of the anchorage section is 8-15m; a three-stage borehole enlargement is used when the designed length of the anchorage section is greater than 15m; and a three-stage borehole enlargement is used when the geological conditions are complex.

6. The construction method for an inverted trapezoidal anchor cable anchoring structure according to claim 1, characterized in that, In step S3, the dressing operation is automatically activated when the drill pipe is lifted, without the need for external power. It removes slag and compacts rock cuttings to form a micro-serrated interface.

7. The construction method for an inverted trapezoidal anchor cable anchoring structure according to claim 6, characterized in that, In step S3, the micro-serrated interface is the permeation groove formed by the pore wall and the slurry.

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