A new hollow grouting drainage anchoring test method

Abstract

This invention relates to the field of geotechnical anchoring testing technology, specifically a novel hollow grouting drainage anchoring test method. The method includes: preparing a hollow anchor body with axial through holes; prefabricating multiple radial grouting microchannels connecting the axial through holes on the inner wall of the anchor body; placing the anchor body into a borehole in the formation; filling the annular space with a pre-set thickness of simulated weak interlayer material; and installing a sealing and loading assembly containing grouting, drainage pipes, and a loading mechanism at the borehole opening. A pre-set pressure grout is injected into the axial through holes, and the grout enters the annular space through the microchannels, acting on the simulated weak interlayer. During grouting, the flow rate and turbidity of the drainage liquid are monitored. Grouting is stopped and the pressure is stabilized after the liquid becomes clear and the flow rate stabilizes. Graded axial pull-out forces are applied to the anchor body, and at each load level, the anchor body displacement, interlayer normal stress, and secondary seepage data are simultaneously collected. This method can simulate weak interlayer conditions, achieving precise grouting and multi-dimensional test data acquisition, and fully reflecting the grouting and pull-out characteristics of the anchoring system.

Description

Technical Field

[0001] This invention relates to the field of rock and soil anchorage testing technology, and in particular to a novel hollow grouting drainage anchorage testing method. Background Technology

[0002] Conventional hollow anchor grouting tests often employ methods such as grouting through openings in the outer wall of the anchor body or direct grouting into the annular space. Anchoring test systems typically place the anchor body directly into a pre-drilled borehole in the stratum. Grouting completion is often determined by grouting pressure and volume. Pull-out tests only collect stress and displacement data of the anchor body, and drainage monitoring only records simple seepage. No suitable test procedures have been developed for weak interlayer conditions. Conventional testing methods cannot accurately reflect the real-world engineering conditions of weak interlayers between the anchor body and the stratum. The layout of the grouting channels can lead to uneven effects of the grout on the surrounding medium. The method for determining grout termination does not directly reflect the degree of grout filling in the weak medium. During pull-out testing, information on stress and seepage changes within the weak interlayer cannot be simultaneously obtained. Therefore, the test data cannot fully reflect the grouting and load-bearing characteristics of the anchoring system under special conditions.

[0003] The lack of a radially connected microchannel structure for grouting during the experiment made it impossible to achieve precise penetration and compression of the grout into the simulated weak interlayer. The absence of a simulated weak interlayer material of fixed thickness within the annular space made it difficult to construct standardized test conditions for the weak interlayer. The grouting state could not be determined by the changes in turbidity and flow rate of the drainage liquid during the grouting process. During pull-out loading, it was impossible to simultaneously collect multiple parameters such as anchor displacement, interlayer normal stress, and secondary seepage, making it difficult to meet the experimental requirements for accurate simulation and multi-dimensional data monitoring. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a novel hollow grouting drainage anchoring test method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a novel hollow grouting drainage anchoring test method, comprising: A hollow anchor body with axial through holes is prepared, and multiple radial grouting microchannels communicating with the axial through holes are prefabricated on the inner wall of the hollow anchor body. The hollow anchor body is placed into a pre-drilled formation borehole, and a simulated weak interlayer material of a predetermined thickness is filled in the annular space between the hollow anchor body and the borehole wall. A sealing and loading assembly is installed at the borehole opening of the formation. The sealing and loading assembly includes a grouting pipe connected to the upper end of the axial through hole, a drainage pipe connected to the lower end of the axial through hole, and a loading mechanism that can apply an axial pull-out force to the upper end of the hollow anchor body. Grout at a preset pressure is injected into the axial through hole through the grouting pipeline. The grout enters the annular space through the radial grouting microchannel to penetrate and compress the simulated weak interlayer material. During the grouting process, the flow rate and turbidity changes of the liquid discharged through the drainage pipeline are monitored and recorded in real time. When the liquid discharged from the drainage pipe changes from turbid to clear and the flow rate tends to stabilize, stop grouting and maintain the grout pressure for the preset stabilization time; The loading mechanism applies progressively increasing axial pull-out forces to the hollow anchor solid. Under each pull-out force, the displacement of the hollow anchor solid, the change in normal stress inside the simulated weak interlayer material, and the secondary seepage data in the drainage pipeline are collected simultaneously.

[0006] As a further aspect of the present invention, the preparation of the radial grouting microchannel includes: Inside the tube wall of the hollow anchor solid, a plurality of annular grooves are pre-set at equal intervals along its axial direction; At the bottom of each annular groove, multiple micro-holes are uniformly drilled circumferentially to the axial through hole to form a primary channel; Using laser etching technology, a capillary network communicating with the annular groove is etched on the outer wall surface of the hollow anchor solid corresponding to the micro-hole, forming a secondary channel. The primary channel and the secondary channel together constitute the radial grouting microchannel. A soluble filter membrane with a predetermined porosity is covered on the outer surface of the radial grouting microchannel, and a hydrophobic isolation coating is sprayed onto the entire outer wall of the hollow anchor solid, wherein the hydrophobic isolation coating does not cover the area of ​​the soluble filter membrane.

[0007] As a further aspect of the present invention, the filling of the simulated weak interlayer material includes: Clay particles, standard sand, and superabsorbent polymer are mixed in a preset mass ratio, and an aqueous solution containing a fluorescent tracer is added and stirred to prepare the simulated weak interlayer material with an initial water content. Before filling, a miniature fiber optic stress sensing array is uniformly distributed on the borehole wall of the stratum and the outer wall surface of the hollow anchor solid. The prepared simulated weak interlayer material is filled into the annular space in layers, and each layer of material is vibrated and compacted using a micro vibration compaction device until it is filled to the predetermined thickness, ensuring that the micro fiber stress sensing array is uniformly wrapped in the material. After filling, the simulated weak interlayer material is pre-compressed and consolidated to achieve the preset initial density and strength indicators.

[0008] As a further aspect of the present invention, injecting grout at a preset pressure into the axial through hole through the grouting pipeline includes: A two-component slurry containing insoluble color particles and conductive ions is prepared, wherein the particle size of the insoluble color particles is smaller than the size of the narrowest part of the radial grouting microchannel; The two-component grout is placed in a constant pressure grouting device, and the two-component grout is pumped into the axial through hole of the hollow anchor body through the grouting pipeline at a constant initial pressure. Under pressure, the two-component slurry flows sequentially through the axial through hole and the radial grouting microchannel, and penetrates into the simulated weak interlayer material in the annular space. Throughout the grouting process, the spatial distribution of conductive ion concentration in the simulated weak interlayer material is measured by using conductivity probes embedded at different depths in the annular space. The position of the diffusion front of the insoluble colored particles is recorded through a transparent observation window set on the sidewall of the borehole in the formation.

[0009] As a further aspect of the present invention, the slurry enters the annular space through the radial grouting microchannel to permeate and compress the simulated weak interlayer material, including: The two-component slurry entering the annular space first dissolves the soluble filter membrane, and then penetrates into the simulated weak interlayer material under the grouting pressure. The water in the two-component slurry is partially absorbed by the superabsorbent polymer, causing the slurry viscosity to increase dynamically during the penetration process. At the same time, the insoluble color particles are retained in the penetration path. The infiltration process of the two-component slurry compresses the surrounding simulated weak interlayer material, causing a change in the porosity of the simulated weak interlayer material, and the normal stress growth signal is detected by the micro-fiber stress sensing array. Some of the unabsorbed and retained slurry components continue to migrate towards the distal end of the simulated weak interlayer material under pressure, and reach the inlet of the drainage pipe.

[0010] As a further aspect of the present invention, the real-time monitoring and recording of changes in the flow rate and turbidity of the liquid discharged through the drainage pipe includes: A flow meter and a laser turbidity sensor are installed at the outlet end of the drainage pipe to continuously sample and record the instantaneous flow rate and turbidity of the discharged liquid. Establish a drainage time series, which includes the liquid flow rate, turbidity value and cumulative drainage volume at each sampling time. When the turbidity value detected by the laser turbidity sensor begins to decrease from an initial high value, it is marked as the moment when the slurry front begins to reach the drainage end; By analyzing the turbidity value change curve over time, the rapid decrease in turbidity and the stable low-value plateau phase were identified. The stable low-value plateau phase corresponds to the state in which the liquid discharged from the drainage pipe changes from turbid to clear.

[0011] As a further aspect of the present invention, when the liquid discharged from the drainage pipe changes from turbid to clear and the flow rate tends to stabilize, grouting is stopped and the grout pressure is maintained, including: When the turbidity value is detected to enter and remain at a low plateau stage, and the fluctuation range of the instantaneous flow rate within a time window is detected to be less than a preset threshold, it is determined that the grouting stop condition has been met. Close the grout inlet valve of the grouting pipeline and stop pumping in new two-component grout, but keep the pressure system in the constant pressure grouting equipment in working condition; Maintain the slurry pressure in the axial through hole and the annular space at the preset pressure value, and start timing the pressure stabilization time; During the stabilization period, the instantaneous flow rate of the drainage pipeline is continuously recorded, and it is observed whether the normal stress data measured by the micro fiber optic stress sensing array continues to increase or tends to stabilize.

[0012] As a further aspect of the present invention, applying a graded, progressively increasing axial pull-out force to the hollow anchor solid includes: Set a series of progressively increasing target pull-out forces, and the holding time for each pull-out force level; The servo control system of the loading mechanism controls the loading head to apply tension to the upper end of the hollow anchor solid, so that the tension gradually increases to the first-level pull-out force target value and maintains the corresponding holding time at the first-level pull-out force target value; During the loading and holding of each level of pull-out force, the axial displacement of the hollow anchor solid relative to the borehole opening of the formation is collected by a displacement sensor to form a force-displacement curve segment. The micro-fiber stress sensing array continuously collects normal stress data at different locations inside the simulated weak interlayer material to form a stress distribution evolution dataset. Check whether there is liquid leakage in the drainage pipeline during the load-bearing phase. If so, record it as the secondary seepage data, including the force level of the seepage, the seepage flow rate, and the duration.

[0013] As a further aspect of the present invention, synchronously collecting normal stress variation data within the simulated weak interlayer material includes: During the loading and holding of each stage of pull-out force, real-time wavelength or light intensity signals are read from the sensing units of all the micro-fiber stress sensing arrays. The wavelength or light intensity signal is converted into the corresponding normal stress value to obtain the multi-point stress values ​​along the depth and radial directions inside the simulated weak interlayer material. Compare the stress distribution under the current pulling force with the stress distribution under the previous pulling force, and calculate the spatial location and variation range of the stress growth zone, stress transfer zone and stress relaxation zone. The coordinates of areas with significant stress changes are associated with the locations of surface deformations or cracks in the simulated weak interlayer material as observed through the transparent viewing window.

[0014] As a further aspect of the present invention, the method also includes a post-test data integration and anchorage interface analysis step: After all pull-out force loading tests are completed, the sealing and loading components and the hollow anchor solid are unloaded and removed; The simulated weak interlayer material was dissected layer by layer to observe and record the spatial morphology of the actual solidified solid formed by the slurry in the simulated weak interlayer material, the interface with the surrounding material, and the development of cracks. Extract the grouting pressure curve, drainage flow and turbidity curve, force-displacement full-process curve, normal stress spatiotemporal evolution dataset and secondary seepage data recorded during the experiment; The spatial morphology of the actual solidified solid is superimposed and compared with the spatial distribution variation data of the conductive ion concentration and the diffusion front position record of the insoluble color particles to reconstruct the penetration and solidification process of the slurry. Based on the force-displacement full-process curve, the normal stress spatiotemporal evolution dataset, and the reconstructed slurry penetration and solidification process, the shear stress transfer characteristics and failure modes of the anchorage interface at different locations are calculated.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are as follows: Multiple radial grouting microchannels, connected to axial through-holes, are prefabricated on the inner wall of the hollow anchor body. Grout flows from the axial through-holes through these channels into the annular space, allowing the grout to act uniformly on the simulated weak interlayer material. This achieves continuous penetration and compression of the simulated weak interlayer material, weakening local aggregation during grout flow and ensuring that the filling effect of the grout matches the medium characteristics of the simulated weak interlayer. The grouting path relies on the microchannels on the inner wall to form a directional transport pattern, reducing grout loss during transport and ensuring that the grout's effective range covers the entire pre-set annular space. This allows the simulated weak interlayer material to exhibit a uniform stress and penetration state under the action of the grout.

[0016] The annular space between the hollow anchor body and the borehole wall is filled with a simulated weak interlayer material of a predetermined thickness, which can closely match the weak interlayer environment of the anchoring system in actual engineering. Real-time monitoring of the flow rate and turbidity changes of the liquid discharged from the drainage pipe during grouting directly reflects the progress of the grout's penetration and filling of the simulated weak interlayer material. Changes in the liquid state visually indicate the density of the grout filling within the interlayer. When applying progressively increasing axial pull-out forces to the hollow anchor body, simultaneous data collection of anchor body displacement, normal stress changes within the simulated weak interlayer, and secondary seepage data from the drainage pipe allows for a complete record of the mechanical and seepage changes in the anchoring system during pull-out, refining the dimensions of experimental parameter acquisition and obtaining complete experimental data corresponding to the working conditions. Attached Figure Description

[0017] Figure 1 This is a flowchart of the novel hollow grouting drainage anchoring test method described in this invention.

[0018] Figure 2 A flowchart simulating the filling of weak interlayer materials.

[0019] Figure 3 This is a diagram showing the relationship between pull-out force level, holding time, and maximum normal stress.

[0020] Figure 4 The graph shows the relationship between seepage flow and time in the hollow grouting drainage anchoring test. Detailed Implementation

[0021] See Figure 1 A hollow anchor body with an axial through hole is prepared. Multiple radial grouting microchannels communicating with the axial through hole are prefabricated on the inner wall of the hollow anchor body. The hollow anchor body is placed into a pre-drilled formation borehole. A simulated weak interlayer material of a predetermined thickness is filled in the annular space between the hollow anchor body and the borehole wall. A sealing and loading assembly is installed at the borehole opening. This assembly includes a grouting pipe communicating with the upper end of the axial through hole, a drainage pipe communicating with the lower end of the axial through hole, and a loading mechanism that can apply an axial pull-out force to the upper end of the hollow anchor body. A predetermined grouting material is injected into the axial through hole through the grouting pipe. Pressurized grout enters the annular space through radial grouting microchannels, permeating and compressing the simulated weak interlayer material. During the grouting process, the flow rate and turbidity changes of the liquid discharged through the drainage pipe are monitored and recorded in real time. When the liquid discharged from the drainage pipe changes from turbid to clear and the flow rate tends to stabilize, the grouting is stopped and the grout pressure is maintained until the preset stabilization time. The hollow anchor body is subjected to graded and progressively increasing axial pull-out force through the loading mechanism. Under the action of each pull-out force, the displacement of the hollow anchor body, the normal stress change data inside the simulated weak interlayer material, and the secondary seepage data appearing in the drainage pipe are collected simultaneously.

[0022] In one embodiment of the present invention, multiple annular grooves are pre-set at equal intervals along the axial direction inside the tube wall of the hollow anchor solid. Multiple micro-holes penetrating to the axial through-hole are uniformly drilled circumferentially at the bottom of each annular groove to form a primary channel. A capillary network communicating with the annular grooves is etched on the outer wall surface of the hollow anchor solid corresponding to the micro-holes using laser etching technology to form a secondary channel. The primary and secondary channels together constitute a radial grouting microchannel. A soluble filter membrane with a predetermined porosity is covered on the outer surface of the radial grouting microchannel, and a hydrophobic isolation coating is sprayed onto the entire outer wall of the hollow anchor solid, excluding the area of ​​the soluble filter membrane. (See also...) Figure 2 Clay particles, standard sand, and superabsorbent polymer are mixed in a preset mass ratio, and an aqueous solution containing a fluorescent tracer is added and stirred to prepare a simulated weak interlayer material with an initial moisture content. Before filling, a micro-fiber stress sensing array is uniformly distributed on the borehole wall of the stratum and the outer surface of the hollow anchor solid. The prepared simulated weak interlayer material is filled into the annular space in layers, and each layer of material is vibrated and compacted using a micro-vibration compaction device until it is filled to the predetermined thickness and the micro-fiber stress sensing array is uniformly wrapped in the material. After filling, the simulated weak interlayer material is pre-compressed and consolidated to achieve the preset initial density and strength index.

[0023] In specific implementations, the hollow anchor body with axial through holes is prepared and radial grouting microchannels are pre-fabricated on its inner wall. This involves pre-setting multiple annular grooves at equal intervals along the axial direction inside the tube wall of the hollow anchor body. In some embodiments, the depth of the annular grooves is precisely controlled by a CNC machine tool, and the ratio of the depth of the annular grooves to the thickness of the hollow anchor body tube wall satisfies the following relationship: ; in: Indicates the depth of the annular groove. The thickness of the hollow anchor body is represented by k, a preset coefficient between 0.15 and 0.3. Multiple micro-holes, penetrating to the axial through-hole, are uniformly drilled circumferentially at the bottom of each annular groove, forming a primary channel. Using laser etching, a capillary network communicating with the annular groove is etched onto the outer surface of the hollow anchor body corresponding to the micro-holes, forming a secondary channel. The parameters of the laser etching process include laser power, scanning speed, and repetition frequency to ensure that the channel cross-sectional shape and size of the capillary network meet preset requirements. The primary and secondary channels together constitute the radial grouting microchannel. A soluble filter membrane with a predetermined porosity is covered on the outer surface of the radial grouting microchannel, and a hydrophobic isolation coating is sprayed onto the entire outer wall of the hollow anchor body, covering areas where the hydrophobic isolation coating does not cover the soluble filter membrane. Optionally, the soluble filter membrane material is polyvinyl alcohol, and its predetermined porosity is adjusted by dissolution time and concentration. It can be understood that the hydrophobic isolation coating is used to prevent the adhesion of external materials in non-designated areas, thereby ensuring the preset function of the radial grouting microchannel.

[0024] In specific implementation, the filling of the simulated weak interlayer material involves mixing clay particles, standard sand, and superabsorbent polymer (SAP) at a predetermined mass ratio, adding an aqueous solution containing a fluorescent tracer, and stirring to prepare a simulated weak interlayer material with an initial moisture content. The predetermined mass ratio is determined based on the calibrated values ​​of the physical and mechanical properties of the target soil. Before filling, a micro-fiber stress sensor array is uniformly distributed on the borehole wall and the outer surface of the hollow anchor body. The sensing units of the micro-fiber stress sensor array are distributed in a matrix and fixed by a flexible substrate. The prepared simulated weak interlayer material is filled layer by layer into the annular space between the hollow anchor body and the borehole wall, and each layer is vibrated using a micro-vibration compaction device until the predetermined thickness is reached. The vibration process ensures that the micro-fiber stress sensor array is uniformly encapsulated within the simulated weak interlayer material. In some embodiments, the operating frequency and amplitude of the micro-vibration compaction device are constant. After filling, the simulated weak interlayer material is pre-compressed and consolidated to achieve the preset initial density and strength indicators.

[0025] In one embodiment of the present invention, a two-component slurry containing insoluble color particles and conductive ions is prepared. The particle size of the insoluble color particles is smaller than the size of the narrowest part of the radial grouting microchannel. The two-component slurry is placed in a constant pressure grouting device and pumped into the axial through hole of the hollow anchor body through the grouting pipeline at a constant initial pressure. Under pressure, the two-component slurry flows sequentially through the axial through hole, the radial grouting microchannel and penetrates into the simulated weak interlayer material in the annular space. During the entire grouting process, the spatial distribution change of the conductive ion concentration in the simulated weak interlayer material is measured by conductivity probes buried at different depths in the annular space, and the position of the diffusion front of the insoluble color particles is recorded through a transparent observation window set on the side wall of the formation borehole. The two-component slurry entering the annular space first dissolves the soluble filter membrane, and then, under the grouting pressure, penetrates into the simulated weak interlayer material. The water in the two-component slurry is partially absorbed by the superabsorbent polymer, causing the slurry viscosity to increase dynamically during the penetration process. At the same time, insoluble color particles are retained along the penetration path. The penetration process of the two-component slurry compresses the surrounding simulated weak interlayer material, causing changes in the porosity of the simulated weak interlayer material. The normal stress growth signal is detected by a micro-fiber stress sensing array. Some of the slurry components that are not absorbed or retained continue to migrate to the far end of the simulated weak interlayer material under pressure and reach the inlet of the drainage pipe.

[0026] In practice, a grout with a preset pressure is injected into the axial through-hole through the grouting pipeline. This grout consists of a two-component grout containing insoluble color particles and conductive ions. The particle size of the insoluble color particles is smaller than the size of the narrowest part of the radial grouting microchannel. The two-component grout is placed in a constant pressure grouting device and pumped into the axial through-hole of the hollow anchor body through the grouting pipeline at a constant initial pressure. Under pressure, the two-component grout flows sequentially through the axial through-hole, the radial grouting microchannel, and penetrates into the simulated weak interlayer material in the annular space. During the entire grouting process, the spatial distribution of conductive ion concentration in the simulated weak interlayer material is measured by conductivity probes buried at different depths in the annular space. The position of the diffusion front of the insoluble color particles is recorded through a transparent observation window set on the side wall of the formation borehole. In some embodiments, the mass fraction of insoluble colored particles and the concentration of conductive ions in the two-component grout are preset based on the porosity characteristics of the simulated weak interlayer material and the detection sensitivity requirements, and the constant initial pressure value maintained by the constant pressure grouting equipment is set based on the permeability coefficient of the simulated weak interlayer material and the preset grouting rate.

[0027] In practice, the slurry enters the annular space through radial grouting microchannels and permeates and compresses the simulated weak interlayer material. The two-component slurry entering the annular space first dissolves the soluble filter membrane, and then, under grouting pressure, permeates into the simulated weak interlayer material. Part of the water in the two-component slurry is absorbed by the superabsorbent polymer, causing the slurry viscosity to dynamically increase during permeation. Simultaneously, insoluble color particles are retained along the permeation path. The permeation process of the two-component slurry compresses the surrounding simulated weak interlayer material, causing changes in its porosity. A micro-fiber stress sensor array detects the increase in normal stress. Some unabsorbed and retained slurry components continue to migrate towards the distal end of the simulated weak interlayer material under pressure and reach the drainage pipe inlet. The dynamic increase in slurry viscosity follows the following relationship: ; in: This indicates the instantaneous viscosity of the slurry during the infiltration process. Indicates the initial viscosity of the slurry. This represents a correction factor related to the absorption characteristics of superabsorbent polymers. This indicates the volume fraction of water absorbed per unit volume of slurry.

[0028] Optionally, the insoluble colored particles are surface-dyed silica microspheres, whose particle size distribution is sieved to ensure that all particles are smaller than the narrowest part of the radial grouting microchannel. It is understood that the conductive ions are sodium or potassium ions, and their concentration is calibrated and mapped using readings from the conductivity probe. Optionally, the transparent observation window is made of high-strength tempered glass and embedded at a specific depth in the sidewall of the formation borehole. It is understood that the arrangement density and depth interval of the conductivity probes are determined based on the uniformity of the simulated weak interlayer material and the grouting influence range.

[0029] In one embodiment of the present invention, a flow meter and a laser turbidity sensor are installed at the outlet end of the drainage pipe to continuously sample and record the instantaneous flow rate and turbidity of the discharged liquid, and establish a drainage time series. The drainage time series includes the liquid flow rate value, turbidity value and cumulative drainage volume corresponding to each sampling moment. When the turbidity value detected by the laser turbidity sensor shows a downward trend from the initial high value, it is marked as the moment when the slurry front begins to arrive at the drainage end. The curve of turbidity value change over time is analyzed to identify the rapid turbidity decrease stage and the stable low value plateau stage. The stable low value plateau stage corresponds to the state in which the liquid discharged from the drainage pipe changes from turbid to clear. When the turbidity value is detected to enter and remain at a low plateau stage, and the fluctuation of the instantaneous flow rate within a time window is less than the preset threshold, it is determined that the grouting stop condition has been met. The grout inlet valve of the grouting pipeline is closed to stop pumping in new two-component grout, but the pressure system in the constant pressure grouting equipment is kept in working condition. The grout pressure in the axial through hole and annular space is maintained at the preset pressure value. The pressure stabilization time is started. During the pressure stabilization time, the instantaneous flow rate of the drainage pipeline is recorded, and it is observed whether the normal stress data measured by the micro fiber optic stress sensing array continues to increase or tends to stabilize.

[0030] In practical implementation, real-time monitoring and recording of the flow rate and turbidity changes of the liquid discharged through the drainage pipeline includes installing a flow meter and a laser turbidity sensor at the outlet end of the drainage pipeline. The instantaneous flow rate and turbidity of the discharged liquid are continuously sampled and recorded to establish a drainage time series. The drainage time series includes the liquid flow rate value, turbidity value, and cumulative drainage volume corresponding to each sampling moment. When the turbidity value detected by the laser turbidity sensor shows a decreasing trend from an initial high value, it is marked as the moment when the slurry front begins to reach the drainage end. Analyzing the turbidity value change curve over time identifies the rapid turbidity decrease phase and the stabilization at a low value plateau phase. The stabilization at the low value plateau phase corresponds to the state where the liquid discharged from the drainage pipeline changes from turbid to clear. In some embodiments, the sampling frequency of the laser turbidity sensor and the sampling frequency of the flow meter are synchronously set to once per second, and the drainage time series is stored in the data acquisition system indexed by timestamps. Optionally, the cumulative drainage volume is calculated by numerical integration of the instantaneous flow rate. It can be understood that the initial high value of the turbidity value corresponds to the turbid state of the discharged liquid initially containing water in the simulated weak interlayer material.

[0031] In specific implementation, grouting is stopped when the liquid discharged from the drainage pipe changes from turbid to clear and the flow rate tends to stabilize. Grouting pressure is maintained, including when the turbidity value is detected to enter and remain at a low plateau, and the fluctuation amplitude of the instantaneous flow rate within a time window is less than a preset threshold. When this condition is met, the grouting stop condition is met, the grout inlet valve of the grouting pipe is closed to stop pumping in new two-component grout, but the pressure system within the constant pressure grouting equipment remains operational. The grout pressure in the axial through-hole and annular space is maintained at a preset pressure value. A pressure stabilization time is started, and during this time, the instantaneous flow rate of the drainage pipe is continuously recorded, and the normal stress data measured by the micro-fiber stress sensing array is observed to see if it continues to increase or tends to stabilize. In some embodiments, the length of the time window is set to sixty seconds. The preset threshold is set based on the grouting rate and the permeability characteristics of the simulated weak interlayer material. The fluctuation amplitude of the instantaneous flow rate is evaluated by calculating the ratio of the standard deviation to the average value of the flow rate within the time window. The ratio satisfies... When the flow rate is determined to be stable, among which Indicates the fluctuation range. This represents the standard deviation of instantaneous flow rate within a time window. This represents the average instantaneous flow rate over a time window. Indicates a preset threshold. Optional, preset threshold. The value is set to 0.05. This is understandable, as the stabilization time is determined based on the slurry's solidification characteristics and the consolidation requirements of the simulated weak interlayer material.

[0032] In one embodiment of the present invention, a series of progressively increasing target values ​​for pull-out force and the holding time for each level of pull-out force are set. The servo control system of the loading mechanism controls the loading head to apply a pull force to the upper end of the hollow anchor solid, so that the pull force gradually increases to the first level of target pull-out force and is held for the corresponding time at the first level of target pull-out force. During the loading and holding process of each level of pull-out force, the axial displacement of the hollow anchor solid relative to the borehole opening of the formation is collected by a displacement sensor to form a force-displacement curve segment. The normal stress data at different locations inside the simulated weak interlayer material is continuously collected by a micro fiber optic stress sensing array to form a stress distribution evolution dataset. The drainage pipe is checked for liquid seepage during the holding stage. If there is seepage, it is recorded as secondary seepage data, including the force level of seepage, seepage volume and duration. During the loading and holding of each stage of pull-out force, real-time wavelength or light intensity signals are read from the sensing units of all micro-fiber stress sensing arrays. The wavelength or light intensity signals are converted into corresponding normal stress values ​​to obtain multi-point stress values ​​along the depth and radial directions inside the simulated weak interlayer material. The stress distribution under the current stage of pull-out force is compared with the stress distribution under the previous stage of pull-out force to calculate the spatial location and variation range of the stress growth zone, stress transfer zone, and stress relaxation zone. The coordinates of areas with significant stress changes are associated with the locations of surface deformation or cracks of the simulated weak interlayer material observed through the transparent observation window.

[0033] In specific implementation, applying progressively increasing axial pull-out forces to the hollow anchor solid involves setting a series of progressively increasing target pull-out force values ​​and a holding time for each level of pull-out force. The servo control system of the loading mechanism controls the loading head to apply a pull force to the upper end of the hollow anchor solid, gradually increasing the pull-out force to the first target value and maintaining the corresponding holding time at that target value. During the loading and holding process of each pull-out force level, displacement sensors collect the axial displacement of the hollow anchor solid relative to the borehole opening in the formation, forming a force-displacement curve segment. A micro-fiber stress sensor array continuously collects normal stress data at different locations within the simulated weak interlayer material, forming a stress distribution evolution dataset. The system checks for liquid seepage in the drainage pipe during the holding stage; if so, it records secondary seepage data, including the force level, seepage volume, and duration of the seepage. In some embodiments, the target pull-out force value is preset based on the design pull-out bearing capacity of the hollow anchor solid and the strength characteristics of the simulated weak interlayer material, and the holding time is set according to the stable reading requirements of the data acquisition system. Optionally, a graded pull-out force loading scheme is shown in Table 1, which lists the target pull-out force values ​​and corresponding holding times from the first to the sixth stage. It can be understood that force-displacement curve segments are recorded and stored in real time during each stage of pull-out force loading and holding.

[0034] Table 1: Example Table of Graded Pull-out Force Loading Schemes Load Level Target pull-out force (kN) Duration of load (s) 1 10 60 2 20 60 3 30 60 4 40 120 5 50 120 6 60 180 ; In specific implementation, synchronously acquiring data on the normal stress variation within the simulated weak sandwich material includes reading real-time wavelength or light intensity signals from the sensing units of all micro-fiber stress sensing arrays during the loading and holding of each pull-out force stage. The wavelength or light intensity signals are then converted into corresponding normal stress values ​​to obtain multi-point stress values ​​along the depth and radial directions within the simulated weak sandwich material. The stress distribution under the current pull-out force stage is compared with that under the previous stage to calculate the spatial location and variation amplitude of the stress growth zone, stress transfer zone, and stress relaxation zone. The coordinates of areas with significant stress changes are correlated with the locations of surface deformations or cracks observed through a transparent viewing window of the simulated weak sandwich material. In some embodiments, the stress variation amplitude is calculated using the following formula: ; in: Indicates the magnitude of stress variation. This represents the normal stress value measured by a certain sensing unit under the nth level of pull-out force. This represents the normal stress value measured by the same sensing unit under the (n-1)th level of pull-out force. Optionally, when the stress variation range... When the stress exceeds a preset threshold, the area where the sensing unit is located is marked as a region of significant stress change. This association is achieved by spatially registering the coordinate data of the miniature fiber optic stress sensing array with the image data acquired through the transparent observation window.

[0035] See Figure 3 This is a graph showing the relationship between pull-out force level, holding time, and maximum normal stress, used to analyze the matching between the material's mechanical response and the loading strategy during graded pull-out processes. The holding time for levels 1-3 is constant at 60 seconds, corresponding to the low-load stage, meeting the stability requirements for basic data acquisition. For levels 4-5, the holding time increases to 120 seconds; as the load increases, a longer period is needed to allow stress and displacement to stabilize sufficiently. For level 6, the holding time extends to 180 seconds, representing the highest load level, focusing on monitoring the mechanical behavior near the limit state. The maximum normal stress generally shows an approximately linear increase, continuously rising with the increase in pull-out force level, simulating a continuous increase in the maximum normal stress within the weak interlayer. The average growth rate is approximately 0.17 MPa / level, indicating uniform stress transmission at the anchorage interface without significant stress abrupt changes or relaxation. At level 6 pull-out force, the peak value of 1.08 MPa is reached, approaching the preset strength limit of the simulated weak interlayer material.

[0036] In one embodiment of the present invention, after completing all pull-out force loading tests, the sealing and loading components and the hollow anchor body are unloaded and removed. The simulated weak interlayer material is dissected layer by layer to observe and record the spatial morphology of the actual solidified solid formed by the grout in the simulated weak interlayer material, the interface with the surrounding material, and the development of cracks. The grouting pressure curve, drainage flow rate and turbidity curve, force-displacement full-process curve, normal stress spatiotemporal evolution dataset, and secondary seepage data recorded during the test are extracted. The spatial morphology of the actual solidified solid is superimposed and compared with the spatial distribution change data of conductive ion concentration and the diffusion front position record of insoluble colored particles to reconstruct the grout penetration and solidification process. Based on the force-displacement full-process curve, normal stress spatiotemporal evolution dataset, and the reconstructed grout penetration and solidification process, the shear stress transfer characteristics and failure modes of the anchor interface at different locations are calculated.

[0037] In specific implementation, the post-test data integration and anchorage interface analysis steps include unloading and removing the sealing and loading components and the hollow anchor body after completing all pull-out force loading tests. The simulated weak interlayer material is then dissected layer by layer to observe and record the spatial morphology of the actual solidified material formed by the grout within the simulated weak interlayer material, the interface with the surrounding material, and crack development. In some embodiments, the simulated weak interlayer material is dissected along directions parallel and perpendicular to the axis of the hollow anchor body. Information including the contour, branches, and thickness distribution of the actual solidified material is observed and recorded. The interface includes the roughness and bonding of the contact surface between the grout solidified material and the simulated weak interlayer material. Crack development includes the length, width, direction, and relative position of the cracks to the actual solidified material. Optionally, high-resolution photography and 3D scanning techniques are used for recording. The grouting pressure curve, drainage flow and turbidity curve, force-displacement curve, normal stress spatiotemporal evolution dataset, and secondary seepage data recorded during the test are extracted and aligned and integrated based on time or loading level.

[0038] In specific implementation, the spatial morphology of the actual solidified body is superimposed and compared with the spatial distribution variation data of conductive ion concentration and the diffusion front position record of insoluble color particles to reconstruct the grout penetration and solidification process. Based on the force-displacement full-process curve, the normal stress spatiotemporal evolution dataset, and the reconstructed grout penetration and solidification process, the shear stress transfer characteristics and failure modes of the anchorage interface at different locations are calculated. In some embodiments, the superposition comparison involves registering and fusing the three-dimensional scanning model of the actual solidified body, the isosurface cloud map of conductive ion concentration at different grouting times, and the time series position of the diffusion front of insoluble color particles in a unified coordinate system to reconstruct the dynamic penetration path, filling range, and final solidification morphology of the grout in the simulated weak interlayer material. It can be understood that the reconstructed grout penetration and solidification process provides a spatial correlation basis for analyzing the interaction between grouting effect and anchorage body. Based on the force-displacement full-process curve and the normal stress spatiotemporal evolution dataset, the interface shear stress distribution at different locations along the anchorage depth is calculated. One calculation method is described as follows: ; in: This represents the average interfacial shear stress at depth z. This represents the integral of the total normal force exerted by the weak interlayer material on the hollow anchor body within the range from the orifice to depth z. This represents the perimeter of the interface between the hollow anchor solid and the simulated weak interlayer material. Optional, the integral of the total normal force. The failure mode is obtained by numerically integrating the normal stress data measured by the miniature fiber optic stress sensing array within the corresponding depth range. It can be understood that the failure mode is comprehensively determined by analyzing the abrupt change points of the force-displacement curve, the peak shift location of the interfacial shear stress distribution, and the crack development morphology and location of the actual solidified solid.

[0039] See Figure 4 This is a graph showing the relationship between seepage flow and time in a hollow grouting drainage anchoring test, visually reflecting the coupling relationship between secondary seepage behavior and load level during the staged pull-out process. From 0 to 60 minutes, the seepage flow fluctuates little, generally remaining in the range of 0.3 to 0.7 mL, indicating that the simulated weak interlayer material is structurally stable under low load, with only a small amount of residual pore water being discharged. Around 50 minutes, the seepage flow drops to its lowest point, indicating that the initial drainage is basically complete and the material has entered a relatively dry state. From 60 to 120 minutes, after the pull-out force is increased, the seepage flow begins to increase continuously, gradually rising from 0.8 mL to 1.45 mL. The seepage in this stage is mainly driven by stress compression; the pull-out force causes the weak interlayer to undergo compressive deformation, the pores are further compacted, and residual water and grout components are squeezed out. From 120 to 170 minutes, after the pull-out force is increased again, the seepage flow rises sharply to a peak of 2.6 mL, and then slowly declines.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A novel hollow grouting drainage anchoring test method, characterized in that, The method includes: A hollow anchor body with axial through holes is prepared, and multiple radial grouting microchannels communicating with the axial through holes are prefabricated on the inner wall of the hollow anchor body. The hollow anchor body is placed into a pre-drilled formation borehole, and a simulated weak interlayer material of a predetermined thickness is filled in the annular space between the hollow anchor body and the borehole wall. A sealing and loading assembly is installed at the borehole opening of the formation. The sealing and loading assembly includes a grouting pipe connected to the upper end of the axial through hole, a drainage pipe connected to the lower end of the axial through hole, and a loading mechanism that can apply an axial pull-out force to the upper end of the hollow anchor body. Grout at a preset pressure is injected into the axial through hole through the grouting pipeline. The grout enters the annular space through the radial grouting microchannel to penetrate and compress the simulated weak interlayer material. During the grouting process, the flow rate and turbidity changes of the liquid discharged through the drainage pipeline are monitored and recorded in real time. When the liquid discharged from the drainage pipe changes from turbid to clear and the flow rate tends to stabilize, stop grouting and maintain the grout pressure for the preset stabilization time; The loading mechanism applies progressively increasing axial pull-out forces to the hollow anchor solid. Under each pull-out force, the displacement of the hollow anchor solid, the change in normal stress inside the simulated weak interlayer material, and the secondary seepage data in the drainage pipeline are collected simultaneously.

2. The novel hollow grouting drainage anchorage test method according to claim 1, characterized in that, The preparation of the radial grouting microchannels includes: Inside the tube wall of the hollow anchor solid, a plurality of annular grooves are pre-set at equal intervals along its axial direction; At the bottom of each annular groove, multiple micro-holes are uniformly drilled circumferentially to the axial through hole to form a primary channel; Using laser etching technology, a capillary network communicating with the annular groove is etched on the outer wall surface of the hollow anchor solid corresponding to the micro-hole, forming a secondary channel. The primary channel and the secondary channel together constitute the radial grouting microchannel. A soluble filter membrane with a predetermined porosity is covered on the outer surface of the radial grouting microchannel, and a hydrophobic isolation coating is sprayed onto the entire outer wall of the hollow anchor solid, wherein the hydrophobic isolation coating does not cover the area of ​​the soluble filter membrane.

3. The novel hollow grouting drainage anchorage test method according to claim 2, characterized in that, The filling of the simulated weak interlayer material includes: Clay particles, standard sand, and superabsorbent polymer are mixed in a preset mass ratio, and an aqueous solution containing a fluorescent tracer is added and stirred to prepare the simulated weak interlayer material with an initial water content. Before filling, a miniature fiber optic stress sensing array is uniformly distributed on the borehole wall of the stratum and the outer wall surface of the hollow anchor solid. The prepared simulated weak interlayer material is filled into the annular space in layers, and each layer of material is vibrated and compacted using a micro vibration compaction device until it is filled to the predetermined thickness, ensuring that the micro fiber stress sensing array is uniformly wrapped in the material. After filling, the simulated weak interlayer material is pre-compressed and consolidated to achieve the preset initial density and strength indicators.

4. The novel hollow grouting drainage anchorage test method according to claim 3, characterized in that, Injecting grout at a preset pressure into the axial through-hole through the grouting pipeline includes: A two-component slurry containing insoluble color particles and conductive ions is prepared, wherein the particle size of the insoluble color particles is smaller than the size of the narrowest part of the radial grouting microchannel; The two-component grout is placed in a constant pressure grouting device, and the two-component grout is pumped into the axial through hole of the hollow anchor body through the grouting pipeline at a constant initial pressure. Under pressure, the two-component slurry flows sequentially through the axial through hole and the radial grouting microchannel, and penetrates into the simulated weak interlayer material in the annular space. Throughout the grouting process, the spatial distribution of conductive ion concentration in the simulated weak interlayer material is measured by using conductivity probes embedded at different depths in the annular space. The position of the diffusion front of the insoluble colored particles is recorded through a transparent observation window set on the sidewall of the borehole in the formation.

5. A novel hollow grouting drainage anchorage test method according to claim 4, characterized in that, The grout enters the annular space through the radial grouting microchannels, permeating and compressing the simulated weak interlayer material, including: The two-component slurry entering the annular space first dissolves the soluble filter membrane, and then penetrates into the simulated weak interlayer material under the grouting pressure. The water in the two-component slurry is partially absorbed by the superabsorbent polymer, causing the slurry viscosity to increase dynamically during the penetration process. At the same time, the insoluble color particles are retained in the penetration path. The infiltration process of the two-component slurry compresses the surrounding simulated weak interlayer material, causing a change in the porosity of the simulated weak interlayer material, and the normal stress growth signal is detected by the micro-fiber stress sensing array. Some of the unabsorbed and retained slurry components continue to migrate towards the distal end of the simulated weak interlayer material under pressure, and reach the inlet of the drainage pipe.

6. The novel hollow grouting drainage anchorage test method according to claim 5, characterized in that, The real-time monitoring and recording of changes in the flow rate and turbidity of the liquid discharged through the drainage pipe includes: A flow meter and a laser turbidity sensor are installed at the outlet end of the drainage pipe to continuously sample and record the instantaneous flow rate and turbidity of the discharged liquid. Establish a drainage time series, which includes the liquid flow rate, turbidity value and cumulative drainage volume at each sampling time. When the turbidity value detected by the laser turbidity sensor begins to decrease from an initial high value, it is marked as the moment when the slurry front begins to reach the drainage end; By analyzing the turbidity value change curve over time, the rapid decrease in turbidity and the stable low-value plateau phase were identified. The stable low-value plateau phase corresponds to the state in which the liquid discharged from the drainage pipe changes from turbid to clear.

7. A novel hollow grouting drainage anchorage test method according to claim 6, characterized in that, When the liquid discharged from the drainage pipe changes from turbid to clear and the flow rate tends to stabilize, grouting is stopped and grout pressure is maintained, including: When the turbidity value is detected to enter and remain at a low plateau stage, and the fluctuation range of the instantaneous flow rate within a time window is detected to be less than a preset threshold, it is determined that the grouting stop condition has been met. Close the grout inlet valve of the grouting pipeline and stop pumping in new two-component grout, but keep the pressure system in the constant pressure grouting equipment in working condition; Maintain the slurry pressure in the axial through hole and the annular space at the preset pressure value, and start timing the pressure stabilization time; During the stabilization period, the instantaneous flow rate of the drainage pipeline is continuously recorded, and it is observed whether the normal stress data measured by the micro fiber optic stress sensing array continues to increase or tends to stabilize.

8. A novel hollow grouting drainage anchorage test method according to claim 7, characterized in that, Applying a graded, progressively increasing axial pull-out force to the hollow anchor body includes: Set a series of progressively increasing target pull-out forces, and the holding time for each pull-out force level; The servo control system of the loading mechanism controls the loading head to apply tension to the upper end of the hollow anchor solid, so that the tension gradually increases to the first-level pull-out force target value and maintains the corresponding holding time at the first-level pull-out force target value; During the loading and holding of each level of pull-out force, the axial displacement of the hollow anchor solid relative to the borehole opening of the formation is collected by a displacement sensor to form a force-displacement curve segment. The micro-fiber stress sensing array continuously collects normal stress data at different locations inside the simulated weak interlayer material to form a stress distribution evolution dataset. Check whether there is liquid leakage in the drainage pipeline during the load-bearing phase. If so, record it as the secondary seepage data, including the force level of the seepage, the seepage flow rate, and the duration.

9. A novel hollow grouting drainage anchorage test method according to claim 8, characterized in that, Synchronously collect data on the normal stress variation within the simulated weak interlayer material, including: During the loading and holding of each stage of pull-out force, real-time wavelength or light intensity signals are read from the sensing units of all the micro-fiber stress sensing arrays. The wavelength or light intensity signal is converted into the corresponding normal stress value to obtain the multi-point stress values ​​along the depth and radial directions inside the simulated weak interlayer material. Compare the stress distribution under the current pulling force with the stress distribution under the previous pulling force, and calculate the spatial location and variation range of the stress growth zone, stress transfer zone and stress relaxation zone. The coordinates of areas with significant stress changes are associated with the locations of surface deformations or cracks in the simulated weak interlayer material as observed through the transparent viewing window.

10. A novel hollow grouting drainage anchoring test method according to claim 9, characterized in that, The method also includes post-experiment data integration and anchorage interface analysis steps: After all pull-out force loading tests are completed, the sealing and loading components and the hollow anchor solid are unloaded and removed; The simulated weak interlayer material was dissected layer by layer to observe and record the spatial morphology of the actual solidified solid formed by the slurry in the simulated weak interlayer material, the interface with the surrounding material, and the development of cracks. Extract the grouting pressure curve, drainage flow and turbidity curve, force-displacement full-process curve, normal stress spatiotemporal evolution dataset and secondary seepage data recorded during the experiment; The spatial morphology of the actual solidified solid is superimposed and compared with the spatial distribution variation data of the conductive ion concentration and the diffusion front position record of the insoluble color particles to reconstruct the penetration and solidification process of the slurry. Based on the force-displacement full-process curve, the normal stress spatiotemporal evolution dataset, and the reconstructed slurry penetration and solidification process, the shear stress transfer characteristics and failure modes of the anchorage interface at different locations are calculated.

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