A deep roadway anchoring body progressive damage simulation mold and test method

Abstract

The present application relates to geotechnical engineering, mining engineering and physical simulation test technical field, specifically relates to a kind of deep roadway anchoring body progressive damage simulation mould and test method, including rigid box, rigid box is equipped with model cavity, hollow anchor rod is equipped in model cavity middle, hollow anchor rod outside is equipped with similar material test piece, annular grouting space is formed between similar material test piece and hollow anchor rod, annular grouting space is filled with filling material slurry, similar material test piece, filling material slurry, hollow anchor rod form anchoring body, anchoring body is applied seepage, rigid box is equipped with the pre-tightening assembly connected with hollow anchor rod, according to the sequence consistent with field construction and loading process, complete simulation anchoring hole forming, hole grouting consolidation, anchoring force quantitative application and mechanical locking, on this basis, apply and long-term keep three independent stress and seepage effect with clear liquid inlet and outlet boundary, to continuously characterize the progressive damage process of anchoring body.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering, mining engineering, and physical similarity simulation testing, specifically to a simulation mold and testing method for progressive damage of anchor bodies in deep roadways. Background Technology

[0002] After the excavation of deep coal and rock roadways, the surrounding rock is usually in a complex environment influenced by high ground stress, groundwater seepage, and mining disturbance. The anchor body, formed by anchor bolts, anchor cables, and grouting materials, is an important load-bearing structure for maintaining the stability of the roadway's surrounding rock. Its stress state and durability directly affect the roadway support effect. As the support time increases, the anchor body may experience phenomena such as interface debonding, grouting material cracking, surrounding rock fissure propagation, and anchor bolt axial force attenuation. Ultimately, this manifests as progressive damage or progressive instability under long-term loads. Long-term loads include continuously applied triaxial stress and anchor bolt preload. After the grouting material reaches the predetermined consolidation state, groundwater seepage is further applied to simulate the long-term stress-seepage coupling environment of the anchor body in deep roadways.

[0003] Indoor testing to simulate the progressive damage or instability of anchor bodies under long-term loads is a common method. However, existing analytical methods are difficult to replicate the progressive damage or instability under long-term loads, specifically: Existing indoor tests on anchored solids mostly employ uniaxial loading, conventional triaxial loading, true triaxial loading, or rigid indenter loading. Conventional triaxial tests typically only allow independent control of axial stress and circumferential confining pressure, with the two lateral principal stresses being equal. While true triaxial devices can control the three principal stresses separately, their loading structures usually do not simultaneously consider the arrangement and long-term sealing of through-hole hollow anchors, pre-tightening locking mechanisms, and internal grouting / seepage channels. Furthermore, they are difficult to simultaneously simulate the triaxial unequal pressure environment of surrounding rock in deep roadways. Rigid contact loading is also prone to local stress concentration at the specimen boundaries, causing deviations between the test results and the actual stress state of the surrounding rock.

[0004] Furthermore, existing anchor bolt positioning methods in molds are typically quite simple, making eccentricity during installation prone to occur, leading to uneven stress on the anchoring section. Preload is often obtained through experience-based tightening of ordinary nuts, lacking reliable loading, testing, and long-term locking mechanisms. Anchor bolt preload can only be effectively applied after a reliable reaction force is generated in the anchoring section or a reliable reaction element is installed at the end; otherwise, the entire anchor bolt may move, preventing effective preload formation. Conventional triaxial tests can only independently control axial stress and circumferential confining pressure, with the two lateral principal stresses being equal. While true triaxial devices can control the three principal stresses separately, their loading structures typically do not simultaneously consider the arrangement and long-term sealing of the through-type hollow anchor bolt, preload locking mechanism, and internal grouting / seepage channels.

[0005] The formation process of anchor bodies is essentially closely related to borehole formation, grout diffusion, grout consolidation, and interface bonding. If the anchor is directly embedded in a similar material and then grouted, it is often difficult to form a clear three-layer interface between the anchor, the grout, and the surrounding rock. The test results are difficult to accurately reflect the grouting and interface deterioration process in the anchor hole on site.

[0006] Groundwater seepage further weakens the durability of the grout and anchorage interface. Existing technologies can perform true triaxial loading, anchor tensioning, grouting, or seepage tests separately, but these functions are usually performed by different devices or different specimens. It is difficult to establish and maintain coupled test conditions with independently controllable and repeatable parameters on the same specimen in the order of hole drilling, grouting consolidation, pre-tightening and locking, triaxial stress loading, and long-term seepage.

[0007] Therefore, it is necessary to propose a mold and testing method that integrates three-dimensional flexible loading, anchor bolt guiding and sealing, simulated anchor hole forming, quantitative application of preload and mechanical locking, grouting / controlled seepage inside the hollow anchor bolt, and long-term monitoring functions within the same mold and specimen made of the same similar material, and to coordinate the operation of each function according to the on-site construction and loading sequence. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a simulation mold and testing method for progressive damage of anchor bodies in deep tunnels. This method is used to simulate anchor hole formation, grouting consolidation, quantitative application of anchor bolt preload, and mechanical locking within the same similar anchor body specimen and mold, following a sequence consistent with the on-site construction and loading process. Furthermore, it applies and maintains triaxial independent stress and seepage with clearly defined inlet and outlet fluid boundaries to continuously characterize the progressive damage process of the anchor body.

[0009] To address the aforementioned technical problems, this invention provides a simulation mold for progressive damage of anchor bodies in deep tunnels, comprising a rigid box with a model cavity. A hollow anchor rod is located in the center of the model cavity, and a similar material specimen is located on the outer side of the hollow anchor rod. An annular grouting space is formed between the similar material specimen and the hollow anchor rod, and the annular grouting space is filled with filling slurry. The similar material specimen, filling slurry, and hollow anchor rod constitute the anchor body. Three sets of relatively arranged flexible hydraulic bladders are provided on the inner wall of the model cavity to provide the vertical principal stress, maximum horizontal principal stress, and minimum horizontal principal stress of the anchor body. The oil inlets of the flexible hydraulic bladders are connected to an independent oil source and control system. Seepage is applied to the anchor body. A pre-tightening assembly connected to the hollow anchor rod is provided on the top of the rigid box.

[0010] Furthermore, the hollow anchor rod has a hollow cavity inside, and a perforated tube section is set in the anchoring section located in the model cavity. The length of the perforated tube section is 50% to 80% of the design anchoring length of similar material specimens. Multiple slurry outlet holes are opened in the perforated tube section. The outside of the perforated tube section is covered with an anti-clogging filter membrane. The slurry outlet holes are distributed in a spiral shape along the outer periphery of the perforated tube section, and the diameter of the slurry outlet holes is 1mm to 2mm.

[0011] Furthermore, the top of the hollow anchor is connected to a grouting seepage assembly, which includes an injection pump, a high-pressure pipeline, a rotary joint, an vent / overflow interface, and a controllable drainage / collection interface. One end of the rotary joint is connected to the top of the hollow anchor, and the other end is connected to the high-pressure pipeline, which is connected to the injection pump. The injection pump is used to deliver grout or water. The grout delivered by the injection pump is used to fill the annular grouting space, and the water delivered by the injection pump is used to apply seepage to the anchor body. The vent / overflow interface is located on one side plate of the rigid box. The inner end of the vent / overflow interface is connected to the highest position of the annular grouting space via a pre-embedded branch pipe, and the outer end is connected in sequence to a stop valve, a transparent return grout pipe, and a grout collection container. The controllable drainage / collection interface is located on the other side plate. Its inner end is connected to the model cavity via a filter plate, permeable stone, and a particle-preventing filter screen, and the outer end is connected in sequence to a back pressure valve and a water collection device.

[0012] Furthermore, the grouting seepage assembly also includes a pressure detection element and a flow detection element, which are respectively installed on the high-pressure pipeline between the injection pump outlet and the rotary joint, and on the liquid outlet pipeline between the back pressure valve and the water collection device.

[0013] Furthermore, a thin-walled, removable, detachable perforated sleeve is provided on the outside of the hollow anchor rod, which is used as a molding boundary template for similar material specimens inside the model cavity.

[0014] Furthermore, the top and bottom of the hollow anchor rod are respectively provided with a top plate guide sleeve and a bottom plate guide sleeve, which are fixedly connected to the top plate and bottom plate of the rigid box.

[0015] Furthermore, the pre-tightening assembly includes a miniature through-hole jack, a ring load sensor, and a locking nut. The ring load sensor, locking nut, and miniature through-hole jack are sequentially mounted on the hollow anchor rod above the top plate of the rigid box. The ring load sensor is used to measure the axial load of the hollow anchor rod.

[0016] Furthermore, acoustic emission probes and strain gauges were embedded inside the similar material specimens, and anchor displacement gauges were installed on the hollow anchor rods.

[0017] Furthermore, a pressure-bearing pad is provided between the flexible hydraulic bladder and the anchor.

[0018] A method for simulating progressive damage to anchor bodies in deep tunnels includes the following steps: Step 1: Start the jack to slowly pull the hollow anchor rod. When the ring load sensor reaches the design preload, tighten the lock nut to press it against the ring load sensor. Step 2: Independent oil source and control system supply oil to the three sets of flexible hydraulic bladders respectively, and independently apply vertical principal stress, maximum horizontal principal stress and minimum horizontal principal stress; Step 3: The injection pump introduces pressurized water, mine water simulation liquid, or a preset chemical solution into the hollow anchor bolt. The constant water pressure, graded water pressure, or circulating water pressure is set. The water, mine water simulation liquid, or preset chemical solution seeps into the anchor body through the grout outlet. At the same time, the controllable drainage / collection interface is opened to allow the pressurized water, mine water simulation liquid, or preset chemical solution to be discharged or collected through the drainage / collection interface. Step 4: According to the test requirements, set the time and flow rate of pressurized water, mine water simulation liquid, or preset chemical solution to conduct seepage. Acoustic emission probe, strain gauge, ring load sensor, and anchor displacement meter monitor the acoustic emission events and energy, strain, axial load of hollow anchor, and end displacement of hollow anchor under the vertical principal stress, maximum horizontal principal stress, minimum horizontal principal stress, and seepage conditions of water, mine water simulation liquid, or preset chemical solution within the preset time window. Flow detection element monitors the seepage flow of the anchor. Calculate the acoustic emission event rate and energy rate, strain change rate, anchor axial force attenuation rate, end displacement rate, and seepage flow change rate based on the above monitoring data. Step 5: Within the preset test time, if any key indicator such as acoustic emission event rate and energy rate, strain change rate, anchor axial force attenuation rate, end displacement rate, and seepage flow change rate exceeds the corresponding threshold for multiple consecutive preset time windows, or if at least two of the acoustic emission event rate and energy rate, strain change rate, anchor axial force attenuation rate, end displacement rate, and seepage flow change rate simultaneously reach the preset criteria, the anchor body is determined to have entered the accelerated damage or instability stage and the test is terminated. Or, the test will be terminated when the preset test time is reached; Step 6: After the test, unload the load in the following order: first, remove the seepage water pressure; then, remove the vertical principal stress, the maximum horizontal principal stress, and the minimum horizontal principal stress in stages; and finally, release the anchor bolt preload.

[0019] The beneficial effects of this invention are as follows: (1) In the same mold and the same similar material specimen, the present invention establishes and maintains multi-field coupling test conditions in the order of hole forming - grouting consolidation - pre-tightening and locking - three-dimensional independent loading - long-term seepage - disturbance loading - continuous monitoring, thereby reducing the boundary differences between different devices or different specimens.

[0020] (2) Three pairs of flexible hydraulic bladders control the three principal stress directions respectively and are loaded synchronously in the relative directions. This can simulate the deep geostress environment where the vertical principal stress, the maximum horizontal principal stress and the minimum horizontal principal stress are not equal, and avoid the problem of the specimen shifting as a whole caused by the six hydraulic bladders being loaded completely independently.

[0021] (3) The top and bottom flexible hydraulic bladders adopt a ring structure with a central opening and are equipped with a bearing pad that can move slightly axially, so that the hollow anchor rod passage and the vertical loading boundary do not interfere with each other, while improving the pressure distribution on the end face of the specimen.

[0022] (4) The detachable hole-forming sleeve can form a simulated anchor hole in a similar material specimen, so that there is a clear annular grouting space between the outer wall of the anchor rod and the hole wall, which is conducive to forming a three-layer anchoring structure of anchor rod-grouting material-surrounding rock similar material, and improving the engineering similarity of the anchoring interface test.

[0023] (5) The pre-tightening force application and locking components work after the reaction force is generated in the anchoring section. The pre-tightening force is loaded, maintained and tested for a long time by quantitative tensioning with a through-hole jack, verification by a ring load sensor and mechanical locking with a locking nut.

[0024] (6) The hollow anchor rod also serves as a grouting and seepage water channel. The vent / overflow grout interface is connected to the highest point of the annular grouting space. The controllable drainage / water collection interface is connected to the flow control component. By detecting the flow at both ends of the inlet and outlet, the seepage flow through the anchor body and the change in the liquid storage volume inside the specimen can be distinguished. This forms a test condition where the grouting fullness can be comprehensively judged and the boundaries between the inlet and outlet are clear and the seepage flow can be measured.

[0025] (7) When the transparent observation window is used, the fit of the flexible hydraulic bladder can be observed without canceling the lateral loading. Combined with acoustic emission, strain, anchor bolt axial force and seepage parameter monitoring, the internal damage evolution of the anchor body can be continuously characterized.

[0026] (8) Similar material specimens can be prepared by layering in the mold or by prefabricating perforated specimens, which can adapt to different test precision, different sensor layout and different similar material curing conditions, thus enhancing the operability and applicability of the device. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall front cross-sectional structure of the deep tunnel anchor body progressive damage simulation mold of the present invention; Figure 2 for Figure 1 Schematic diagram of the cross-sectional structure along the AA direction; Figure 3 This is a partially enlarged schematic diagram of the pre-tightening assembly and the upper connection structure of the hollow anchor bolt in the deep roadway anchor progressive damage simulation mold of the present invention. Figure 4 This is a schematic diagram of the hollow anchor bolt and its perforated tube section structure of the deep roadway anchor body progressive damage simulation mold of the present invention. Figure 5 This is a partial enlarged cross-sectional view of the connection structure between the flexible hydraulic bladder and the box side plate of the deep tunnel anchor body progressive damage simulation mold of the present invention. Explanation of reference numerals in the attached drawings: 1-Base plate; 2-Side plate; 3-Top plate; 4-Flexible hydraulic bladder; 5-Pressure ring; 6-Sealing gasket; 7-Oil inlet; 8-Independent oil source and control system; 9-Base plate guide sleeve; 10-Top plate guide sleeve; 11-Outer fixing sleeve; 12-Inner quick-change sleeve; 13-Sealing retaining ring; 14-Guide ring; 15-Hollow anchor bolt; 16-Hollow cavity; 17-Perforated pipe section; 18-Slurry outlet hole; 19-Anti-clogging filter membrane; 20-Miniature through-hole 21-Jack piston; 22-Annular load sensor; 23-Locking nut; 24-Rotary joint; 25-Injection pump; 26-High pressure pipeline; 27-Acoustic emission probe; 28-Strain gauge; 29-Sealed lead socket; 30-Data acquisition system; 31-Transparent observation window; 32-Similar material specimen; 33-Pressure bearing pad; 34-Controllable drainage / water collection interface; 35-Removable perforated sleeve; 36-Exhaust / overflow interface. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0029] like Figures 1-5 As shown, a simulation mold for progressive damage of anchor bodies in deep tunnels includes a rigid box with a model cavity. A hollow anchor rod 15 is located in the middle of the model cavity, and a similar material specimen 32 is located on the outside of the hollow anchor rod 15. An annular grouting space is formed between the similar material specimen 32 and the hollow anchor rod 15. The annular grouting space is filled with filling slurry. The similar material specimen 32, the filling slurry, and the hollow anchor rod 15 constitute the anchor body. Three sets of relatively arranged flexible hydraulic bladders 4 are provided on the inner wall of the model cavity to provide the vertical principal stress, maximum horizontal principal stress, and minimum horizontal principal stress of the anchor body. The oil inlet 7 of the flexible hydraulic bladders 4 is connected to an independent oil source and control system 8. Seepage is applied to the anchor body. A pre-tightening assembly connected to the hollow anchor rod 15 is provided on the top of the rigid box.

[0030] In this embodiment, the rigid box is made of a bottom plate 1, a top plate 3 and four side plates 2 spliced ​​together by high-strength bolts or made of high-strength alloy plates. Reinforcing ribs can be set on the outside according to the pressure level. A model cavity is formed inside the box. At least one side plate 2 is provided with a transparent observation window 31. The transparent observation window 31 is only used to observe the working status and sealing of the flexible hydraulic bladder 4 or to assist in the inspection after demolding. It is not used as a structure to directly observe the surface cracks of the specimen during the loading process. A metal protective frame or a transparent explosion-proof protective plate can be set on the outside of the transparent observation window 31.

[0031] In this embodiment, the bottom plate 1, top plate 3, and four side plates 2 are machined with grooves on the side facing the model cavity. An annular clamping step is formed around the groove. A sealing gasket 6 is laid on the sealing surface of the clamping step. The non-expansion clamping edge of the flexible hydraulic bladder 4 covers the outside of the sealing gasket 6, and a pressure ring 5 covers the clamping edge. Multiple fastening bolts pass through the pressure ring 5 and are screwed into the threaded holes of the corresponding plates, pressing the clamping edge and sealing gasket 6 tightly against the sealing surface of the plates without penetrating the effective filling cavity of the flexible hydraulic bladder 4. The oil inlet 7 on the back of the flexible hydraulic bladder 4 passes through the housing plate and connects to an independent oil source and control system 8.

[0032] Six flexible hydraulic bladders 4 are arranged in the model cavity in six directions: top, bottom, left, right, front, and back. However, in terms of loading control, they form three pairs of opposing loading units according to the three principal stress directions. Two flexible hydraulic bladders 4 in the same principal stress direction adopt synchronous or coordinated loading to maintain the mechanical balance of the similar material specimen 32 during loading. Each pressure control loop can be equipped with a pressure sensor, overflow protection valve, and pressure relief valve to provide feedback control and overpressure protection for the loading pressure.

[0033] In this embodiment, the similar material specimen 32, the filling grout, and the hollow anchor rod 15 form a three-layer anchoring structure of anchor rod—grouting material—surrounding rock similar material, which better simulates actual working conditions; three sets of relatively arranged flexible hydraulic bladders 4 can achieve the application of triaxial non-uniform forces to simulate the pressure of actual rock on the anchor body. This invention applies a pre-tightening force, a triaxial non-uniform force, and seepage to the three-layer anchoring structure of anchor rod—grouting material—surrounding rock similar material, to simulate the damage to the three-layer anchoring structure of anchor rod—grouting material—surrounding rock similar material by applying a pre-tightening force, a triaxial non-uniform force, and a pre-tightening force.

[0034] In this embodiment, the hollow anchor rod 15 is a tubular component with a hollow cavity 16 inside. The anchoring section of the hollow anchor rod 15 located in the model cavity is provided with a perforated tube section 17. Multiple grout outlet holes 18 are opened on the side wall of the perforated tube section 17. The length of the perforated tube section 17 is 50% to 80% of the designed anchoring length of the similar material specimen 32. The grout outlet holes 18 are spirally distributed along the outer circumference of the perforated tube section 17, and the diameter of the grout outlet holes 18 is 1mm to 2mm. The outside is covered with an anti-clogging filter membrane 19. The upper end of the hollow anchor rod 15 is provided with an external thread locking section and a fluid connector connection section in sequence. The former is screwed into the locking nut 23, and the latter is located above the locking nut 23 and is sealed to the lower end of the rotary joint 24.

[0035] The grout enters the perforated pipe section 17 through the hollow cavity 16, and is discharged radially along the designed anchorage length through multiple grout outlets 18, filling the annular grouting space. After consolidation, it forms a three-layer structure of anchor rod, grout, and surrounding rock similar materials. Subsequent seepage tests use the same hollow channel to input pressurized water into the existing anchorage section to simulate the damage to the anchor body under seepage.

[0036] The top of the hollow anchor bolt 15 is connected to a grouting and seepage assembly, which includes an injection pump 25, a high-pressure pipeline 26, a rotary joint 24, an vent / overflow port 36, and a controllable drainage / collection port 34. One end of the rotary joint 24 is connected to the top of the hollow anchor bolt 15, and the other end is connected to the high-pressure pipeline 26, allowing the hollow anchor bolt 15 to rotate relative to each other while maintaining a fluid seal, even when the external pipeline is relatively fixed. The high-pressure pipeline 26 is connected to the injection pump 25. The injection pump 25 is used to deliver slurry or water, and the slurry delivered by the injection pump 25 is used to fill the annular ring. In the grouting space, the water delivered by the injection pump 25 is used to apply seepage into the anchor body. The vent / overflow port 36 is located on one side plate 2 of the rigid box. The inner end of the vent / overflow port 36 is connected to the highest position of the upper end of the annular grouting space through a pre-embedded branch pipe. The outer end is connected in sequence to a stop valve, a transparent return grout pipe and a grout collection container. The controllable drainage / water collection port 34 is located on the other side plate 2. Its inner end is connected to the model cavity through a filter plate, a permeable stone and a particle loss prevention filter screen. The outer end is connected in sequence to a back pressure valve and a water collection device to control the liquid outlet boundary pressure and measure the seepage flow.

[0037] The grouting seepage assembly also includes pressure detection elements and flow detection elements. The pressure detection elements include two liquid pressure sensors, and the flow detection elements include an inlet flow meter and an outlet flow meter. One liquid pressure sensor and the inlet flow meter are installed on the high-pressure pipeline 26 between the outlet of the injection pump 25 and the rotary joint 24, respectively, to obtain the inlet pressure, instantaneous inlet flow rate, and cumulative inlet volume. The other liquid pressure sensor and the outlet flow meter are installed on the outlet pipeline outside the controllable drain / collection interface 34, between the back pressure valve and the collection device, respectively, to obtain the outlet back pressure, instantaneous outlet flow rate, and cumulative outlet volume. The collection device is used to control the outlet boundary pressure and measure the seepage flow. The collection device can be a measuring cylinder or a graduated storage tank, used to collect the seepage liquid and verify the cumulative outlet volume.

[0038] During grouting, the shut-off valve is opened to release air. The degree of grout fullness is judged by combining the grouting volume, the stable state of grouting pressure, and the continuous return of grout without obvious air bubbles in the transparent return pipe. The stable state of grouting pressure refers to calculating the average value X, standard deviation s, and relative fluctuation coefficient CV=s / X of the liquid pressure over a preset time window of length Δt, and calculating the rate of change R=X of the mean value between adjacent time windows. k -X k-1 / X k-1 Where K is a certain time window. When the liquid pressure simultaneously satisfies the conditions that CV is not greater than a preset fluctuation threshold and R is not greater than a preset change threshold within N consecutive time windows, it is determined to have entered a stable state. Δt, N, and the corresponding thresholds are determined through a benchmark test with the same mix ratio; in one embodiment, Δt can be 1 to 5 minutes, and N can be 3 to 5 minutes.

[0039] During the seepage test, the controllable drainage / collection interface 34 is opened, and pressurized water is delivered through the injection pump 25. The pressurized water enters the hollow anchor 15 through the high-pressure pipeline 26, the liquid pressure sensor, the inlet flow meter, and the rotary joint 24. Then, it seeps outward from the perforated pipe section 17 of the hollow anchor 15 and is discharged through the controllable drainage / collection interface 34. The discharged water passes through the back pressure valve, the liquid pressure sensor, the outlet flow meter, and is finally collected by the water collection device. Throughout the process, the pressurized water has a clear inflow and outflow end, thus forming a controllable seepage field, rather than simply accumulating water in a closed box.

[0040] The instantaneous inflow and outflow rates, as well as the corresponding cumulative flow rates, are collected using inflow and outflow meters, respectively. When the relative difference between the inflow and outflow rates within multiple consecutive preset time windows does not exceed a preset flow balance threshold, a stable seepage state is determined, and the arithmetic mean of the inflow and outflow rates is used as the seepage flow rate of the anchor body. When flow balance is not reached, the inflow and outflow rates are recorded separately, and the difference between the cumulative inflow and cumulative outflow rates is used to characterize the change in the amount of liquid stored in the anchor body and the model cavity.

[0041] The preset flow balance threshold is determined through a benchmark test under the same operating conditions before the formal test. The relative flow difference is defined as the ratio of the absolute value of the difference between the average influent flow rate and the average effluent flow rate within the k-th time window to their average value. The preset flow balance threshold is determined by summing the average of the relative flow differences obtained from multiple benchmark tests and three times the standard deviation. When the relative flow difference within multiple consecutive preset time windows is not greater than the threshold, and there is no continuous unidirectional change trend in the influent and effluent flow rates, a stable seepage state is determined to have been reached.

[0042] Multiple preset time windows within the stable damage stage of the anchor body are selected as benchmark time periods. The average value and standard deviation of each monitoring indicator are calculated, and the sum of (average value + 3 * standard deviation) is determined as the preset threshold for the corresponding monitoring indicator. Specifically, acoustic emission indicators are deemed to have met preset criteria when the acoustic emission event or acoustic emission energy reaches the corresponding preset threshold; deformation indicators are deemed to have met preset criteria when the absolute value of the strain change rate or the end displacement rate reaches the corresponding preset threshold; bearing capacity indicators are deemed to have met preset criteria when the anchor bolt axial force attenuation rate reaches the corresponding preset threshold; and seepage indicators are deemed to have met preset criteria when the absolute value of the seepage flow rate change rate reaches the corresponding preset threshold. When at least two types of monitoring indicators reach their respective preset criteria within the same preset time window, and this state is maintained for three consecutive preset time windows, the anchor body is determined to have entered the accelerated damage stage.

[0043] A thin-walled, removable, detachable perforated sleeve 35 is provided on the outside of the hollow anchor rod 15, which is used as the forming boundary template for the similar material specimen 32 inside the model cavity.

[0044] In this embodiment, to form an anchor body that more closely resembles the on-site grouting process of the anchor hole, a thin-walled, removable, detachable hole-forming sleeve 35 is provided on the outside of the hollow anchor rod 15. After the similar material specimen 32 reaches its initial strength, the detachable hole-forming sleeve 35 is pulled out or removed, so that an annular grouting space is formed between the outer wall of the hollow anchor rod 15 and the simulated anchor hole wall.

[0045] In this embodiment, the top and bottom flexible hydraulic bladders 4 can be annular bladders with a central opening, symmetrical split bladders, or multi-cavity connected bladders to avoid the top plate guide sleeve 10, bottom plate guide sleeve 9, and hollow anchor bolt 15. The flexible hydraulic bladder 4 is made of oil-resistant rubber-reinforced fabric, and the working surface of the flexible hydraulic bladder 4 has a corrugated expansion section with an effective expansion stroke of not less than 20mm.

[0046] A pressure-bearing plate 33 is provided between the flexible hydraulic bladder 4 and the anchor. The pressure-bearing plate 33 is used to allow the preload of the flexible hydraulic bladder 4 and the hollow anchor rod 15 to be transmitted more evenly to the similar material specimen 32. The flexible hydraulic bladders at the top and bottom can be provided with annular pressure-bearing plates 33 around the central clearance hole to avoid uneven pressure on the end face caused by the central clearance area, so that the vertical pressure bypasses the top plate guide sleeve 10 and the bottom plate guide sleeve 9 and is transmitted to the end face of the similar material specimen 32.

[0047] The top and bottom of the hollow anchor rod 15 are respectively provided with a top plate guide sleeve 10 and a bottom plate guide sleeve 9, which are fixedly connected to the top plate 3 and bottom plate 1 of the rigid box.

[0048] In this embodiment, a top plate guide sleeve 10 is provided at the center of the top plate 3, and a bottom plate guide sleeve 9 is provided at the center of the bottom plate 1. Both the top plate guide sleeve 10 and the bottom plate guide sleeve 9 can adopt a combination structure of an outer fixed sleeve 11 and an inner quick-change sleeve 12. The outer fixed sleeve 11 of the top plate guide sleeve 10 is fixedly connected to the top plate 3 through a flange, and the outer fixed sleeve 11 of the bottom plate guide sleeve 9 is fixedly connected to the bottom plate 1 through a flange. The inner quick-change sleeve 12 is detachably installed in the corresponding outer fixed sleeve 11. The inner wall of the inner quick-change sleeve 12 is provided with a sealing ring 13 and a guide ring 14. The sealing ring 13 can be a V-shaped combined sealing ring or other wear-resistant sealing element, and the guide ring 14 can be made of polytetrafluoroethylene or copper-based wear-resistant material. The hollow anchor rod 15 passes through the top plate guide sleeve 10 and the bottom plate guide sleeve 9 and is arranged along the center of the model cavity, thereby ensuring that the axis of the anchor rod is basically coincident with the central axis of the similar material specimen 32.

[0049] The pre-tightening assembly includes a miniature through-hole jack 20, a ring load sensor 22, and a locking nut 23. The ring load sensor 22, the locking nut 23, and the miniature through-hole jack 20 are sequentially mounted on the hollow anchor rod 15 above the top plate 3 of the rigid box.

[0050] like Figure 3As shown, in this embodiment, the pre-tensioning assembly is positioned above the top plate 3 and coaxial with the hollow anchor rod 15. The piston 21 is located inside the miniature through-hole jack 20, which surrounds the hollow anchor rod 15. The annular load sensor 22 is sleeved on the outside of the hollow anchor rod 15 and located between the top plate 3 and the locking nut 23, used to measure the axial load of the hollow anchor rod 15. The locking nut 23 engages with the external threaded locking section of the hollow anchor rod 15. During the tensioning process of the miniature through-hole jack 20, the slurry-consolidated anchoring section provides anchoring reaction force to the hollow anchor rod 15. The jack piston 21 pulls the hollow anchor rod 15 to produce axial elongation, and the reaction force of the jack cylinder passes sequentially through the locking nut 23 to the top plate 3. When the value detected by the annular load sensor 22 reaches the set value, the locking nut 23 is tightened until it presses against the annular load sensor 22. After the miniature through-hole jack 20 is depressurized, the locking nut 23 and the annular load sensor 22 together maintain the axial preload of the hollow anchor rod 15, which acts on the similar material specimen 32. To ensure the effectiveness of the preload, after the grout around the perforated section 17 of the hollow anchor rod 15 solidifies to form an anchoring section, the miniature through-hole jack 20 is started for tensioning. During the tensioning process, the annular load sensor 22 displays the axial preload in real time. When the preload reaches the set value, the locking nut 23 is tightened and the hydraulic pressure of the jack is released, so that the preload is mechanically maintained by the locking nut 23.

[0051] An acoustic emission probe 27 and a strain gauge 28 are embedded inside the similar material specimen 32, and an anchor displacement gauge is installed on the hollow anchor rod.

[0052] like Figure 2 As shown, in this embodiment, acoustic emission probes 27 and strain gauges 28 can be embedded around the anchoring section inside the similar material specimen 32 according to the test purpose. The acoustic emission probes 27 are used to obtain acoustic emission events and energy, and the strain gauges 28 are used to obtain the strain of the anchor body. Monitoring elements such as anchor displacement gauges can also be installed. The anchor displacement gauge is sleeved on the hollow anchor 15 and is used to measure the displacement of the end of the hollow anchor 15. The acoustic emission probes 27 and strain gauges 28 can be installed using waterproof protection and thin-walled protective sleeves to avoid sensor failure during the filling and curing process of wet-mixed similar materials. The leads of each sensor are led out through the sealed lead socket 29 and connected to the data acquisition system 30.

[0053] A method for simulating progressive damage to anchor bodies in deep tunnels includes the following steps: When conducting tests using the aforementioned mold, first assemble the base plate 1, side plates 2, flexible hydraulic bladder 4, base plate guide sleeve 9, controllable drainage / water collection interface 34, and vent / slurry overflow interface 36. Check the sealing status of the flexible hydraulic bladder 4, oil inlet 7, base plate guide sleeve 9, high-pressure pipeline 26, rotary joint 24, vent / slurry overflow interface 36, and controllable drainage / water collection interface 34. Apply a release agent to the flexible hydraulic bladder 4 and the inner wall of the mold cavity. Keep the top plate 3 in an openable state to allow for layered filling of similar materials.

[0054] With the top plate 3 not installed and the upper opening of the model cavity open, the hollow anchor rod 15 and the detachable perforated sleeve 35 are inserted from above the model cavity, with their lower ends passing through the bottom plate guide sleeve 9, and centered and fixed by the detachable centering beam set on the upper end of the side plate 2. Then, similar materials are filled in layers from the upper opening of the model cavity to the perforated sleeve 35 and compacted layer by layer; when the filling reaches the predetermined height, acoustic emission probes 27 and strain gauges 28 are installed and led out through the sealed lead wire socket 29. After the filling is completed, the top plate 3, the top plate guide sleeve 10, and the top flexible hydraulic bladder 4 are installed, so that the upper end of the hollow anchor rod 15 passes through the top plate guide sleeve 10.

[0055] After the similar materials reach the allowable initial strength for casing extraction and grouting, the detachable perforated casing 35 is extracted or removed, forming an annular grouting space between the outer wall of the hollow anchor rod 15 and the borehole wall. The injection pump 25 is started for low-pressure grouting. The grout enters the annular grouting space through the high-pressure pipeline 26, rotary joint 24, hollow cavity 16, and perforated pipe section 17; simultaneously, the shut-off valve of the exhaust / overflow interface 36 is opened to release air. When the actual grouting volume reaches the target range determined according to the annular space volume and grout loss coefficient, and the grouting pressure remains stable within the set time and continuous, bubble-free return grout appears in the transparent return grout pipe, the grouting is deemed to have reached the preset fullness. The shut-off valve is closed and grouting is stopped, and curing continues until the grout reaches the set consolidation strength.

[0056] The grouting pressure should be determined based on the strength of similar material specimens (32), the size of the simulated anchoring hole, the pore structure, and the model similarity ratio, to avoid exceeding the pressure that could cause undesigned hydraulic fracturing of the specimen. If the purpose of the test is to study the effect of fracturing grouting, a separate fracturing grouting condition can be set and distinguished from the conventional in-hole filling grouting condition.

[0057] After the grout solidifies to form the anchoring section, a ring load sensor 22, a locking nut 23, and a miniature through-hole jack 20 are installed sequentially above the top plate 3. The miniature through-hole jack 20 is activated to slowly pull the hollow anchor rod 15. When the ring load sensor 22 reaches the designed preload, the locking nut 23 is tightened within the operating space reserved in the reaction support structure, pressing it against the ring load sensor 22. Then, the hydraulic pressure on the jack is released, and the tensioning connector of the miniature through-hole jack 20 is removed. After depressurization, the reading of the ring load sensor 22 is checked. If the preload after locking is lower than the allowable deviation range, additional tensioning is performed, and the jack is re-locked.

[0058] After the anchor bolts are pre-tightened, oil is supplied to three pairs of flexible hydraulic bladders 4 through three pressure control loops. Vertical principal stress, maximum horizontal principal stress, and minimum horizontal principal stress are applied independently according to the test plan. Two relatively flexible hydraulic bladders 4 in the same principal stress direction are controlled by synchronous feedback to prevent overall displacement of the similar material specimen 32 that is not for the test purpose. Loading is applied in stages, with each stage maintained until the boundary pressure, anchor bolt axial force, and monitoring signals enter a preset stable range before proceeding to the next stage.

[0059] After the confining pressure and anchor bolt preload stabilize, long-term seepage loading can be carried out. The medium in the injection pump 25 is replaced with water, simulated mine water, or a preset chemical solution, and a constant water pressure, graded water pressure, or circulating water pressure is set. At the same time, the controllable drainage / collection interface 34 is opened, allowing pressurized water to seep outward from the hollow anchor bolt 15 perforated pipe section 17 and be discharged or collected through the drainage / collection interface 34. The inlet flow rate, outlet flow rate, and cumulative outlet volume are recorded by the inlet flow meter, outlet flow meter, and collection device, respectively. The outlet boundary is detected and controlled by the liquid pressure sensor and back pressure valve. The anchor solid seepage flow rate refers to the volume of liquid passing through the anchor solid and discharged from the outlet end per unit time. After reaching a stable seepage state, the arithmetic mean of the instantaneous inlet and outlet flow rates is taken as the anchor solid seepage flow rate. When a stable state has not been reached, the inlet and outlet flow rates are recorded separately, and the difference between the cumulative inlet volume and the cumulative outlet volume is used to characterize the change in liquid storage. This simulates the long-term weakening effect of groundwater seepage on the slurry liquid, the anchor bolt-slurry interface, and similar materials of the surrounding rock.

[0060] The long-term loading time can be set to several hours, several days or longer, depending on the strength evolution of similar materials, the slurry consolidation time and the purpose of the test. The aging damage process can be accelerated by adjusting the seepage water pressure, the concentration of chemical solution or by applying graded disturbances. During long-term loading, the data acquisition system 30 synchronously records optional environmental parameters such as boundary pressure in the three principal stress directions, anchor axial load and end displacement, acoustic emission events and energy, strain, inlet pressure, outlet back pressure, instantaneous flow rate, and cumulative outflow. Recording the boundary pressure in the three principal stress directions is used to verify whether the actual load applied by the flexible hydraulic bladder 4 has reached and been maintained at the set value for a long period. It identifies boundary changes caused by hydraulic circuit leakage or specimen deformation, and the independent oil source and control system 8 provides feedback compensation accordingly to ensure that the anchor body damage response is obtained under known and repeatable stress boundaries. Recording the inlet pressure, outlet back pressure, and flow rate is used to characterize and verify the hydraulic boundary conditions. Recording the anchor axial load, end displacement, acoustic emission events and energy, and strain is used to characterize anchor body load degradation, interface slippage, and crack propagation. Recording the changes in outlet back pressure, instantaneous outlet flow rate, and cumulative outflow is used to reflect the evolution of the seepage channel. The above parameters are analyzed synchronously to identify the transition of the anchor body from stable damage to accelerated damage and instability stages.

[0061] When simulating mining disturbances, one or more flexible hydraulic bladders 4 in the principal stress direction can be pressurized in stages or cyclically during the stable damage stage, while the relatively arranged bladders maintain coordinated loading. Before the test, the stable mean value and allowable fluctuation range of each monitoring parameter are determined through a benchmark test with the same mix ratio or the previous stable loading stage. During long-term loading, the acoustic emission event rate and energy rate, strain change rate, anchor bolt axial force attenuation rate, end displacement rate, and seepage flow change rate are calculated according to a preset time window, based on which the stable damage stage and its transition to the accelerated damage stage are determined.

[0062] When any key indicator exceeds the corresponding threshold for multiple consecutive preset time windows, or when at least two types of monitoring indicators simultaneously reach the preset criteria, the anchor body is determined to have entered the accelerated damage or instability stage and the test is terminated. The test termination conditions may be: a sudden increase in acoustic emission event rate, a sudden change in strain, the anchor axial force decaying to a preset threshold, the anchor displacement exceeding the limit, the anchor being pulled out, the similar material specimen 32 forming a through-fracture surface, or reaching the preset test duration. The hollow anchor 15 is pulled out by the continuous increase in end displacement accompanied by a continuous decrease in axial force. The through-fracture surface is confirmed after unloading and demolding.

[0063] After the test, the load was removed in the following order: first, the seepage water pressure was removed; then, the confining pressure was removed in stages; and finally, the anchor bolt preload was released. The rigid box was then dismantled, and the anchor body rupture morphology, grout diffusion range, and interface failure characteristics were analyzed.

[0064] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. All equivalent substitutions, improvements, or modifications made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A simulation mold for progressive damage of anchor bodies in deep tunnels, characterized in that, The device includes a rigid housing with a model cavity. A hollow anchor rod is located in the middle of the model cavity, and a similar material specimen is placed on the outside of the hollow anchor rod. An annular grouting space is formed between the similar material specimen and the hollow anchor rod, and the annular grouting space is filled with filling grout. The similar material specimen, filling grout, and hollow anchor rod constitute the anchor body. Three sets of relatively arranged flexible hydraulic bladders are set on the inner wall of the model cavity to provide the vertical principal stress, maximum horizontal principal stress, and minimum horizontal principal stress of the anchor body. The oil inlet of the flexible hydraulic bladder is connected to an independent oil source and control system. Seepage is applied to the anchor body. A pre-tightening assembly connected to the hollow anchor rod is located on the top of the rigid housing.

2. The deep tunnel anchor body progressive damage simulation mold according to claim 1, characterized in that, The hollow anchor rod has a hollow cavity inside, and the anchoring section located in the model cavity is equipped with a perforated tube section. The length of the perforated tube section is 50% to 80% of the designed anchoring length in similar material specimens. The perforated tube section has multiple slurry outlet holes. The outside of the perforated tube section is covered with an anti-clogging filter membrane. The slurry outlet holes are distributed in a spiral shape along the outer periphery of the perforated tube section, and the diameter of the slurry outlet holes is 1mm to 2mm.

3. The deep tunnel anchor body progressive damage simulation mold according to claim 2, characterized in that, The top of the hollow anchor rod is connected to a grouting seepage assembly, which includes an injection pump, a high-pressure pipeline, a rotary joint, an vent / overflow grout interface, and a controllable drainage / collection interface. One end of the rotary joint is connected to the top of the hollow anchor rod, and the other end is connected to the high-pressure pipeline, which is connected to the injection pump. The injection pump is used to deliver grout or water. The grout delivered by the injection pump is used to fill the annular grouting space, and the water delivered by the injection pump is used to apply seepage to the anchor body. The vent / overflow grout interface is located on one side plate of the rigid box. The inner end of the vent / overflow grout interface is connected to the highest position of the annular grouting space through a pre-embedded branch pipe, and the outer end is connected in sequence to a stop valve, a transparent return grout pipe, and a grout collection container. The controllable drainage / collection interface is located on the other side plate. Its inner end is connected to the model cavity through a filter plate, permeable stone, and a particle-preventing filter screen, and the outer end is connected in sequence to a back pressure valve and a water collection device.

4. The deep tunnel anchor body progressive damage simulation mold according to claim 3, characterized in that, The grouting seepage assembly also includes a pressure detection element and a flow detection element. The pressure detection element and the inlet flow meter are respectively installed on the high-pressure pipeline between the injection pump outlet and the rotary joint, and on the outlet pipeline between the back pressure valve and the water collection device.

5. The deep tunnel anchor body progressive damage simulation mold according to claim 1, characterized in that, The hollow anchor rod is a tubular component. A thin-walled, removable, and detachable perforated sleeve is installed on the outside of the hollow anchor rod, which is used as a molding boundary template for similar material specimens inside the model cavity.

6. The deep tunnel anchor body progressive damage simulation mold according to claim 1, characterized in that, The top and bottom of the hollow anchor rod are respectively provided with a top plate guide sleeve and a bottom plate guide sleeve, which are fixedly connected to the top plate and bottom plate of the rigid box.

7. The deep tunnel anchor body progressive damage simulation mold according to claim 1, characterized in that, The pre-tightening assembly includes a miniature through-hole jack, a ring load sensor, and a locking nut. The ring load sensor, locking nut, and miniature through-hole jack are sequentially mounted on the hollow anchor rod above the top plate of the rigid box. The ring load sensor is used to measure the axial load of the hollow anchor rod.

8. The deep tunnel anchor body progressive damage simulation mold according to claim 1, characterized in that, Acoustic emission probes and strain gauges were embedded inside the similar material specimens, and anchor displacement gauges were installed on the hollow anchor rods.

9. The deep tunnel anchor body progressive damage simulation mold according to claim 1, characterized in that, A pressure-bearing pad is provided between the flexible hydraulic bladder and the anchor.

10. A method for simulating progressive damage of anchor bodies in deep roadways, applied to the simulation mold for progressive damage of anchor bodies in deep roadways as described in any one of claims 1-9, comprising the following steps: Step 1: Start the jack to slowly pull the hollow anchor rod. When the ring load sensor reaches the design preload, tighten the lock nut to press it against the ring load sensor. Step 2: Independent oil source and control system supply oil to the three sets of flexible hydraulic bladders respectively, and independently apply vertical principal stress, maximum horizontal principal stress and minimum horizontal principal stress; Step 3: The injection pump introduces pressurized water, mine water simulation liquid, or a preset chemical solution into the hollow anchor bolt. The constant water pressure, graded water pressure, or circulating water pressure is set. The water, mine water simulation liquid, or preset chemical solution seeps into the anchor body through the grout outlet. At the same time, the controllable drainage / collection interface is opened to allow the pressurized water, mine water simulation liquid, or preset chemical solution to be discharged or collected through the drainage / collection interface. Step 4: According to the test requirements, set the time and flow rate of pressurized water, mine water simulation liquid, or preset chemical solution to conduct seepage. Record the seepage situation through pressure detection element and flow detection element. Acoustic emission probe, strain gauge, ring load sensor, and anchor displacement gauge collect acoustic emission events and energy, strain, hollow anchor axial load, and hollow anchor end displacement of the anchor body under vertical principal stress, maximum horizontal principal stress, minimum horizontal principal stress, and seepage of water, mine water simulation liquid, or preset chemical solution within the preset time window. Calculate the acoustic emission event rate and energy rate, strain change rate, anchor axial force attenuation rate, end displacement rate, and seepage flow rate change rate based on the above monitoring data. Step 5: Within the preset test time, if any key indicator such as acoustic emission event rate and energy rate, strain change rate, anchor axial force attenuation rate, end displacement rate, and seepage flow change rate exceeds the corresponding threshold for multiple consecutive preset time windows, or if at least two of the acoustic emission event rate and energy rate, strain change rate, anchor axial force attenuation rate, end displacement rate, and seepage flow change rate simultaneously reach the preset criteria, the anchor body is determined to have entered the accelerated damage or instability stage and the test is terminated. Or, the test will be terminated when the preset test time is reached; Step 6: After the test, unload the load in the following order: first, remove the seepage water pressure; then, remove the vertical principal stress, the maximum horizontal principal stress, and the minimum horizontal principal stress in stages; and finally, release the anchor bolt preload.

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