Surrounding rock grouting effect evaluation system and method based on radon gas monitoring

Abstract

The invention discloses a surrounding rock grouting effect evaluation system and method based on radon gas monitoring, and relates to the field of surrounding rock grouting effect evaluation. The system comprises a radon gas monitoring system and a laboratory device, the radon gas monitoring system comprises a monitoring grouting anchor rod and a radon measuring assembly. A plurality of monitoring grouting anchor rods are arranged, each monitoring grouting anchor rod comprises a hollow rod body and three air exhaust rods embedded in the hollow rod body in parallel, grouting holes are formed in the pipe wall of the hollow rod body, the tail end of the hollow rod body can be opened and closed, the air outlet ends of the three air exhaust rods are fixedly installed at the tail end of the hollow rod body, and the air inlet ends of the three air exhaust rods are correspondingly located in the ranges of an elastic area, a plastic area and a broken area of surrounding rock. The radon measuring assembly comprises a radon measuring instrument; the laboratory device is a triaxial pressure experiment device. On-site actual measurement and experimental analysis are combined, multi-point radon gas precipitation concentration is synchronously monitored on site and compared with a critical characteristic threshold value, grouting effects at different depths in a rock stratum are inverted according to radon gas concentration distribution characteristics, operation is convenient and fast, system monitoring efficiency is high, and data reliability is high.

Description

Technical Field

[0001] This invention relates to the field of surrounding rock grouting effect evaluation technology, specifically to a surrounding rock grouting effect evaluation system and method based on radon gas monitoring. Background Technology

[0002] In roadway and tunnel engineering, grouting of surrounding rock is a key technology for reinforcing fractured rock masses, sealing fissures, and improving the bearing capacity of the surrounding rock. The accurate evaluation of grouting effectiveness directly affects the long-term stability of the support structure. Radon, as a decay product of the uranium-radium series, is an inert gas whose migration is mainly controlled by the permeability of surrounding rock fissures and pores. When the surrounding rock is damaged and fissures develop due to mining, its permeability increases, and the radon release flux rises significantly. Conversely, effective grouting can fill fissures, reduce the porosity of the surrounding rock, and thus inhibit radon release. Therefore, radon concentration can serve as a natural and sensitive tracer indicator characterizing the opening, closing, and connectivity of fissures within the surrounding rock, laying the physical foundation for accurate evaluation of grouting effectiveness.

[0003] Rock mechanics tells us that surrounding rock damage exhibits distinct zoning characteristics, forming fractured, plastic, and elastic zones from the surface inwards. The degree of fracture development and grouting effectiveness vary significantly across these zones, resulting in different penetration and consolidation effects of the grout. However, existing grouting effectiveness evaluation methods (such as core drilling and sonic testing) often treat boreholes or monitoring points as a homogeneous whole, failing to achieve isolated and graded evaluation of different damaged areas within the same borehole. This leads to coarse evaluation results and difficulty in accurately identifying weak points in the grouting process. Furthermore, existing monitoring methods are mostly single-point, discrete measurements, unable to achieve efficient, continuous, and automated monitoring of multiple monitoring points throughout the entire roadway or tunnel cross-section. This not only results in low efficiency but also makes it difficult to grasp the spatial distribution of grouting effects.

[0004] Therefore, there is an urgent need for a method and system that can couple the damage mechanism of surrounding rock with the radon gas migration law to achieve a zoned, synchronous, and efficient evaluation of grouting effect, thereby realizing a scientific and quantitative evaluation of the grouting effect of surrounding rock from "point" to "surface". Summary of the Invention

[0005] To address the aforementioned issues, this invention discloses a system and method for evaluating the grouting effect of surrounding rock based on radon gas monitoring. It combines on-site measurement with experimental analysis, simultaneously monitors the radon gas emission concentration at multiple points on-site and compares it with critical characteristic thresholds, and uses the radon gas concentration distribution characteristics to invert the grouting effect at different depths in the rock strata. The system is easy to operate, has high monitoring efficiency, and strong data reliability.

[0006] A radon-based evaluation system for grouting effect in surrounding rock, proposed according to the present invention, includes a radon monitoring system and a laboratory apparatus. The radon monitoring system includes monitoring grouting anchors and radon measuring components. Multiple monitoring grouting anchors are arranged, each including a hollow rod body and three parallel suction rods embedded within the hollow rod body. Grouting holes are opened in the wall of the hollow rod body, and the tail end is openable and closable. The exhaust ends of the three suction rods are fixedly installed at the tail end of the hollow rod body, and the intake ends are located within the elastic, plastic, and fractured zones of the surrounding rock. A first sealing sleeve and a second sealing sleeve are fitted outside the hollow rod body to isolate different monitoring sections. The hollow rod body is horizontally... An inflatable sealing rod is provided along the suction rod, and a third sealing sleeve and a fourth sealing sleeve are fixed on the inflatable sealing rod. The axial positions of the third and fourth sealing sleeves correspond to the first and second sealing sleeves. Ventilation holes are opened on the rod wall corresponding to the positions of the third and fourth sealing sleeves. A closable inflation interface is integrated at the tail of the inflatable sealing rod. The radon measuring component includes a radon detector, which is connected to the suction rod through a pipeline. The laboratory device is a triaxial pressure experimental device.

[0007] Preferably, the radon monitoring system further includes a centralized control box, which includes a gas path control unit and a central controller. Multiple gas path control units are configured for each monitored grouting anchor bolt. These control units are located on the pipeline connecting the suction rod and the radon detector. Each monitoring grouting anchor bolt shares a common gas path control unit with the pipelines connected to the ends of the three suction rods. Each gas path control unit includes a solenoid valve, a vacuum pump, and a filter. The central controller centrally controls each gas path control unit and communicates with the radon detection component via a signal line, used to coordinate the measurement process and automatically record concentration data.

[0008] Preferably, the air extraction rod and the air-filled sealing rod are fixed and kept parallel by a narrow-side slot embedded in the hollow rod body; the tail end of the monitoring grouting anchor rod is fitted with a grout stop plug; the tail end of the monitoring grouting anchor rod is fixedly installed with an openable and closable protective end cap, the openable and closable protective end cap is hollow inside, and the top end is flush with the tail end of the air extraction rod.

[0009] Preferably, the grouting holes on the hollow rod are arranged in three sets corresponding to three different surrounding rock zones, and each set of grouting holes has multiple holes evenly distributed along the circumference of the hollow rod.

[0010] Preferably, three radon detectors are provided, and the three radon detectors are connected to three air extraction rods in each grouting anchor rod through pipelines.

[0011] Preferably, the laboratory apparatus includes a triaxial testing machine, a specimen, a fourth radon detector, and a computer; the triaxial testing machine includes a triaxial pressure chamber, an axial pressure rod, a specimen cap, and a base; the specimen is placed in the triaxial pressure chamber, which is also equipped with hydraulic oil to provide confining pressure for the specimen; the specimen is positioned between the specimen cap and the base, and the specimen cap is positioned between the axial pressure rod and the specimen; a high-pressure transect connector is provided at the center of the base, penetrating the base; the fourth radon detector is connected to the outlet of the high-pressure transect connector via a rubber tube; a porous plate is fixedly installed at the upper end of the high-pressure transect connector, and a microporous filter membrane is provided on the porous plate, the microporous filter membrane being in contact with the bottom of the specimen.

[0012] Another method disclosed in this invention for evaluating the grouting effect using the aforementioned radon-based surrounding rock grouting effect evaluation system includes the following steps: S1. Obtain complete and dense rock cores from the area to be tested on site, prepare specimens, and send them to the laboratory; S2. The specimen is installed in a triaxial testing machine, and a set confining pressure is applied to simulate the lateral constraint stress it bears in situ. The specimen is then subjected to continuous axial loading until it fails. Throughout the process, axial stress-strain and radon concentration data of the specimen are collected synchronously and continuously. S3. Based on stress-strain data, calculate the damage variable D(t) at each time point, pair D(t) with the radon concentration C(t) at the same time point to obtain a series of data points (D, C), and perform curve fitting to obtain the complete CD characteristic relationship curve. S4. Analyze the characteristic relationship curve to determine the characteristic radon concentration inflection point that represents the critical transition of the surrounding rock damage state, corresponding to laboratory thresholds C1 and C2. Then measure the background concentration of radon in the field and combine it with the background radon concentration of the indoor rock sample to calibrate the characteristic radon concentration thresholds and obtain the field engineering thresholds A and B applicable to the current engineering site. S5. Install monitoring grouting anchors in the surrounding rock. After grouting and solidification, control the gas circuit control unit and radon measurement component through the central controller to continuously pump air from monitoring points at different depths inside multiple monitoring grouting anchors and record the radon concentration. S6. Compare the radon concentration values ​​R measured at each measuring point in step S5 with the on-site engineering threshold obtained in step S4: If the measured concentration value R < A, the grouting effect of the area where the measuring point is located is judged to be "excellent"; if A ≤ R < B, the grouting effect of the area where the measuring point is located is judged to be "good"; if R ≥ B, the grouting effect of the area where the point is located is judged to be "unqualified".

[0013] Preferably, in S3, the damage variable D(t) corresponding to different loading times is calculated using a model based on elastic modulus degradation: D(t) = 1 - E(t) / E0, where E0 is the initial elastic modulus and E(t) is the secant modulus at time t; the initial elastic modulus E0 is determined by the slope of the initial straight line segment of the stress-strain curve of the specimen, and the secant modulus E(t) is determined by the slope of the line connecting the stress-strain data points at time t to the origin.

[0014] Preferably, in S4, the characteristic radon concentration inflection points include the first inflection point (D1, C1) corresponding to the turning point where the curve slope changes from a slow increase to a sharp increase, and the second inflection point (D2, C2) corresponding to the turning point where the curve slope increases sharply and then decreases. The radon concentration values ​​C1 and C2 corresponding to these two inflection points are the laboratory thresholds. Simultaneously, the average radon concentration C at each monitoring point inside the grouting anchor before grouting is used in the field. field1 C field2 C field3 As the in-situ radon background concentration, the radon concentration C corresponding to the sample D=D1 / 2, D=(D1+D2) / 2, and D=(D2+1) / 2 was extracted from the experimental data. lab1 C lab2 C lab3 As the background concentration of radon in the laboratory, the field calibration factor k=(C) is then calculated. field1 +C field2 +C field3 ) / (C lab1 +C lab2 +C lab3 ), thus obtaining the on-site engineering thresholds: A=k×C1, B=k×C2.

[0015] Preferably, in S5, the anchor bolt installation method includes the following steps: S51. Drill a hole at the designed location in the surrounding rock, insert the hollow rod with the assembled anchor head into the hole, then put in the grout stop plug and the pad in sequence, and tighten the nut to press the pad against the rock surface. S52. Open the openable and closable protective end cap at the tail end of the hollow rod and inject grout into the hollow rod. The grout seeps out from the grouting hole and fills the borehole space and surrounding rock fissures. S53. After grouting is completed, high-pressure gas is immediately injected into the hollow rod to clean the rod and remove any grout that may block the extraction rod and grouting hole. Then, the openable protective end cap is closed. While waiting for the grout to solidify, the openable protective end cap is opened several times to perform inspection cleaning operations into the hollow rod. S54. After the grout has fully solidified, open the openable and closable protective end cap and the closable air inlet, and inflate the air-sealing rod to make the third and fourth sealing sleeves expand radially and uniformly. The expanded sealing sleeves tightly wrap around the air extraction rod in the same cross section and fit tightly against the inner wall of the hollow rod of the monitoring grouting anchor rod, thereby forming an effective physical isolation sealing strip inside the hollow rod. After inflation is completed, close the closable air inlet, connect one end of the pipeline to the tail of the air extraction rod, and the other end to the corresponding radon detector. S55. The solenoid valve inside the gas circuit control unit on the central controller is opened, and the corresponding vacuum pump is started. At the same time, radon gas is extracted from each measuring point in the same grouting anchor rod. The gas is sent to the radon measuring component through the filter for synchronous radon concentration measurement at multiple measuring points. The measurement data is transmitted back in real time through the signal line. The central controller automatically binds and stores the data group with the corresponding anchor rod number and measuring point number information. Then the system automatically performs the measurement of the next grouting anchor rod, thereby realizing synchronous roving monitoring of radon gas inside multiple grouting anchor rods.

[0016] Compared with existing technologies, the advantages of the radon-based rock grouting effect evaluation system and method disclosed in this invention are: 1. This invention integrates grouting and monitoring functions by monitoring the grouting anchor bolt, and uses an internal air extraction rod to perform in-situ, independent radon gas measurement at different depths inside the grouting hole, accurately locating weak areas in the grouting.

[0017] 2. This invention directly correlates the grouting effect with the radon concentration and establishes a multi-level evaluation system by combining indoor experiments with on-site monitoring, thus transforming the judgment of the grouting effect from empirical qualitative to scientific quantitative.

[0018] 3. This invention, through a multi-anchor synchronous patrol monitoring system, can automatically complete continuous measurement and data management of multiple anchors and multiple channels within the same anchor, achieving a breakthrough from "point" to "area", greatly improving monitoring efficiency and coverage. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a structural diagram of a radon gas monitoring system.

[0021] Figure 2 Diagram of grouting anchor bolt structure for monitoring.

[0022] Figure 3 This is a structural diagram of the bottom end of the hollow rod.

[0023] Figure 4 This is a structural diagram of the central control box and radon measurement components.

[0024] Figure 5 This is a structural diagram of the laboratory apparatus.

[0025] Figure 6 This is a schematic diagram of the radon gas measurement channel structure for the specimen.

[0026] Figure 7 This is a schematic diagram showing the relationship between the concentration of radon gas released from the specimen and the damage variable.

[0027] In the diagram: 1-Surrounding rock; 2-Monitoring grouting anchor; 21-Hollow rod body; 211-Openable and closable protective end cap; 212-First sealing sleeve; 213-Second sealing sleeve; 214-Grouting hole; 215-Plate; 216-Nut; 217-Grouting stop plug; 218-Slot; 22-Anchor head; 23-First air extraction rod; 24-Second air extraction rod; 25-Third air extraction rod; 26-Inflatable sealing rod; 261-Third sealing sleeve; 262-Fourth sealing sleeve; 263-Closeable inflation port; 3-Central control box; 31-Air circuit control unit; 311-First pipeline; 31 2-Second pipeline; 313-Third pipeline; 314-Solenoid valve; 315-Vacuum pump; 316-Filter; 32-Central controller; 33-Signal line; 4-Radon measuring assembly; 41-First radon meter; 42-Second radon meter; 43-Third radon meter; 5-Triaxial testing machine; 51-Axial pressure rod; 52-Sample cap; 53-Base; 531-High-pressure chamber connector; 532-Microporous filter membrane; 533-Porous plate; 54-Triaxial pressure chamber; 541-Hydraulic oil; 6-Specimen; 61-Rubber diaphragm; 7-Rubber hose; 8-Fourth radon meter; 9-Computer. Detailed Implementation

[0028] The specific embodiments of the present invention will be briefly described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Figures 1-7 A preferred embodiment of the present invention is shown and analyzed in detail.

[0030] like Figure 1 The diagram illustrates a radon-based system for evaluating the effectiveness of surrounding rock grouting, comprising a radon monitoring system and a laboratory setup. The radon monitoring system includes a monitoring anchor bolt 2, a radon measuring component 4, and a centralized control box 3.

[0031] like Figure 2 As shown, multiple monitoring grouting anchor rods 2 are arranged corresponding to multiple drill holes. Each monitoring grouting anchor rod 2 includes a hollow rod body 21 and three air extraction rods and one air-filled sealing rod 26 embedded parallel within the hollow rod body 21. An anchor head 22 is fixedly installed at the top of the hollow rod body 21, and an openable and closable protective end cap 211 is fixedly installed at the tail end to realize the opening and closing of the tail end of the hollow rod body 21. The openable and closable protective end cap 211 is cylindrical, hollow inside, with its top end flush with the tail ends of the three air extraction rods and the air-filled sealing rod 26, and welded to the hollow rod body 21. A protective cap is hinged to the bottom end to realize opening and closing. Grouting holes 214 are opened in the tube wall of the hollow rod body 21. Three sets of grouting holes 214 are arranged corresponding to the elastic zone, plastic zone, and fracture zone. Multiple grouting holes 214 are evenly distributed along the circumference of the hollow rod body 21 in each set. The elastic zone refers to the area in the surrounding rock 1 that remains basically intact after excavation and disturbance, containing only primary or stress-induced micro-cracks; the plastic zone refers to the area where cracks develop, expand, and interconnect; the fractured zone refers to the area where the surrounding rock 1 is severely fractured and fragmented. The extent of these zones can be determined by borehole inspection or ultrasonic detection. The hollow rod 21 is externally fitted with a first sealing sleeve 212 and a second sealing sleeve 213 to isolate different monitoring sections. Both the first sealing sleeve 212 and the second sealing sleeve 213 are water-swellable sealing sleeves. They are respectively positioned on the outer wall of the hollow rod 21 at the boundaries between the elastic and plastic zones of the surrounding rock 1, and at the boundaries between the plastic and fractured zones. After grouting, both expand upon contact with water, tightly filling the gap between the hollow rod 21 and the borehole wall, forming external physical isolation. A grout stop plug 217 is fitted over the tail end of the hollow rod 21.

[0032] like Figure 3 As shown, the three suction rods are the first suction rod 23, the second suction rod 24, and the third suction rod 25. The air outlets of the three suction rods are fixed and kept parallel to each other at the tail end of the hollow rod body 21 by narrow-sided slots 218 embedded within the hollow rod body 21. This design ensures the suction rods are stable and do not obstruct the grouting channel. The air inlet ends are located within the elastic zone, plastic zone, and fractured zone of the surrounding rock 1. Figure 2 , 3As shown, the inflatable sealing rod 26, like the suction rod, is fixed by a narrow-side slot 218 embedded in the hollow rod body 21. A third sealing sleeve 261 and a fourth sealing sleeve 262 are fixed to the inflatable sealing rod 26. The axial positions of the third sealing sleeve 261 and the fourth sealing sleeve 262 correspond to the first sealing sleeve 212 and the second sealing sleeve 213. Both the third sealing sleeve 261 and the fourth sealing sleeve 262 are inflatable elastic sealing sleeves. Ventilation holes are provided on the rod wall of the inflatable sealing rod 26 at the positions corresponding to the placement of the third sealing sleeve 261 and the fourth sealing sleeve 262. The top of the inflatable sealing rod 26 is closed, and the tail end integrates a closable inflation port 263. The third sealing sleeve 261, the fourth sealing sleeve 262, the closable inflation port 263, and the rod body of the inflatable sealing rod 26 are integrally formed to ensure airtightness. The third sealing sleeve 261 and the fourth sealing sleeve 262 are specially designed and made of highly elastic material. Their inner sides are pre-molded with longitudinal grooves that match the arrangement shape of one or more suction rods. When not inflated, the suction rods are located in the grooves. There are process gaps between the suction rods and the inner grooves of the sealing sleeves, and between the outer side of the sealing sleeves and the inner wall of the hollow rod body 21, which ensures the smooth flow of grouting and rod cleaning channels. When inflated, the sealing sleeves expand, the groove walls deform and are tightly pressed against the entire circumference of each suction rod, thereby eliminating all gaps between the suction rods.

[0033] like Figure 4 As shown, the radon measuring component 4 includes three radon meters: a first radon meter 41, a second radon meter 42, and a third radon meter 43. The tail ends of the first suction rod 23, the second suction rod 24, and the third suction rod 25 within the same monitoring grouting anchor rod 2 are connected to the first pipeline 311, the second pipeline 312, and the third pipeline 313, respectively, when the closable protective end cap is opened. All of these pipelines are controlled by the same gas path control unit 31 and are connected to the first radon meter 41, the second radon meter 42, and the third radon meter 43, respectively, forming a closed measuring gas path.

[0034] like Figure 4As shown, the centralized control box 3 includes a gas path control unit 31 and a central controller 32. The gas path control unit 31 is located on the pipeline connecting the suction rod and the radon detector. Each monitoring grouting anchor 2 shares a set of gas path control units 31 with the pipelines connected to the ends of the three suction rods at the same end, thus controlling the simultaneous suction of the three suction rods within the same monitoring grouting anchor 2. The number of monitoring grouting anchors 2 and gas path control units 31 is the same. Each gas path control unit 31 includes a solenoid valve 314, a vacuum pump 315, and a filter 316. The three pipelines leading out from the same monitoring grouting anchor 2 pass through a filter 316, which is an integrated component with three independent filter channels, ensuring physical isolation between the three pipelines during purification and measurement. The central controller 32 centrally controls each gas path control unit 31 and communicates with the radon detector via a signal line 33, used to coordinate the measurement process and automatically record concentration data.

[0035] like Figure 5 As shown, the laboratory setup includes a triaxial testing machine 5, a specimen 6, a fourth radon meter 8, and a computer 9. The triaxial testing machine 5 includes a triaxial pressure chamber 54, an axial pressure rod 51, a specimen cap 52, and a base 53. The specimen 6 is placed inside the triaxial pressure chamber 54, which is also equipped with hydraulic oil 541 to provide confining pressure for the specimen 6. The specimen 6 is positioned between the specimen cap 52 and the base 53, and the specimen cap 52 is positioned between the axial pressure rod 51 and the specimen 6. Figure 6 As shown, a high-pressure transect connector 531 is provided at the center of the base 53, penetrating the base 53. A sintered stainless steel porous plate 533 is fixedly installed on the upper end of the high-pressure transect connector 531. A microporous filter membrane 532 is provided on the porous plate 533, which is in contact with the bottom of the specimen 6 to block debris, while allowing gas to pass through. The sintered stainless steel porous plate 533 is pressurized and allows radon gas to pass through. The bottom of the sintered stainless steel porous plate 533 is connected to the high-pressure transect connector 531, serving as a radon gas transport channel. The outlet of the high-pressure transect connector 531 is connected to the fourth radon meter 8 through a rubber tube 7. The computer 9 synchronously collects the stress-strain data of the testing machine. The microporous filter membrane 532 can be replaced for multiple tests.

[0036] The specimen 6 is a cylindrical standard rock specimen 6, with a rubber membrane 61 wrapped around its top and sides to isolate the hydraulic oil 541. The contact edges between the rubber membrane 61 and the base 53 are sealed with grease to ensure that the hydraulic oil 541 does not seep into the surface of the specimen 6.

[0037] Another method disclosed in this invention for evaluating the grouting effect using the aforementioned radon-based surrounding rock grouting effect evaluation system includes the following steps: S1. Obtain complete and dense rock cores from the area to be tested on site, make specimen 6, and send them to the laboratory; S2. Specimen 6 is installed in the triaxial testing machine 5. A set confining pressure is applied to simulate the lateral constraint stress it experiences in situ. Specimen 6 is then continuously axially loaded until it fails. Throughout the process, axial stress-strain and radon concentration data from specimen 6 are collected synchronously and continuously. Specifically, a specimen cap 52 is placed on top of specimen 6, with its bottom in contact with the microporous filter membrane 532 on the base 53. The top and sides of specimen 6 are wrapped with a rubber membrane 61, and the contact edges between the rubber membrane 61 and the base 53 are sealed with grease. Hydraulic oil 541 is injected into the triaxial pressure chamber 54, and a set confining pressure (the confining pressure value is determined based on engineering geological data or on-site stress test results, and its range reflects typical lateral pressure conditions at the depth of the surrounding rock 1) is applied to simulate the on-site lateral constraint force. Subsequently, specimen 6 is continuously axially loaded through the axial pressure rod 51 of the triaxial testing machine 5 until specimen 6 is completely destroyed. Throughout the loading process, computer 9 synchronously and continuously collects stress and strain data, which is then connected to the outlet of high-pressure chamber penetration joint 531 via rubber tube 7 by the fourth radon meter 8 to measure the radon concentration data released from specimen 6 in real time. S3. Based on the stress-strain data collected in step S2, calculate the damage variable D(t) of specimen 6 at different loading times. Pair D(t) with the radon concentration C(t) at the same time to obtain a series of data points (D, C). Use data analysis software to fit these data points to obtain a complete CD characteristic relationship curve reflecting the evolution of radon concentration with rock sample damage, such as... Figure 7 As shown. The damage variable D(t) corresponding to different loading times is calculated using a model based on elastic modulus degradation: D(t) = 1 - E(t) / E0, where E0 is the initial elastic modulus and E(t) is the secant modulus at time t; the initial elastic modulus E0 is determined by the slope of the initial straight line segment of the stress-strain curve of specimen 6, and the secant modulus E(t) is determined by the slope of the line connecting the stress-strain data points at time t to the origin.

[0038] S4. Analyze the characteristic relationship curve to determine the inflection point of the characteristic radon concentration that represents the critical transition of the damage state of surrounding rock 1, corresponding to laboratory thresholds C1 and C2. Then, measure the background radon concentration in situ at the site, and combine it with the background radon concentration of the indoor rock samples to calibrate the characteristic radon concentration thresholds, obtaining the field engineering thresholds A and B applicable to the current engineering site. Specifically, from... Figure 7It can be seen that the characteristic radon concentration inflection points include the first inflection point (D1, C1), corresponding to the turning point where the curve slope changes from a slow increase to a sharp increase (the starting point of plastic yielding). This is located by calculating the first derivative of the curve and finding its first significantly increasing inflection point, marking the rock sample's transition from an elastic state to a stable fracture development stage. The second inflection point (D2, C2) corresponds to the turning point where the curve slope increases sharply and then decreases (the formation of the macroscopic main fracture surface), marking the rock sample's transition from the fracture development stage to the macroscopic fragmentation stage. The radon concentration values ​​C1 and C2 corresponding to these two inflection points are the laboratory thresholds. Simultaneously, in the field, the average radon concentration C at three monitoring points within the grouting anchor bolt 2 within all monitored surrounding rock 1 before grouting was used. field1 C field2 C field3 As the in-situ radon background concentration, the radon concentration C corresponding to D=D1 / 2, D=(D1+D2) / 2, and D=(D2+1) / 2 for specimen 6 was extracted from the experimental data. lab1 C lab2 C lab3 As the background concentration of radon in the laboratory, the field calibration factor k=(C) is then calculated. field1 +C field2 +C field3 ) / (C lab1 +C lab2 +C lab3 Using this factor to calibrate the laboratory threshold, we obtain the field engineering threshold: A=k×C1, B=k×C2.

[0039] S5. Install monitoring grouting anchors 2 in the surrounding rock 1. After grouting and solidification, control the gas circuit control unit 31 and radon measurement component 4 through the central controller 32 to continuously pump air from monitoring points at different depths inside multiple monitoring grouting anchors 2 and record the radon concentration. The specific steps include: S51. Drill a hole at the designed location in the surrounding rock 1, insert the hollow rod 21 with the assembled anchor head 22 into the hole, and then put in the grout stop plug 217 and the pad 215 in sequence, and tighten the nut 216 to press the pad 215 against the rock surface. S52. Open the openable and closable protective end cap 211 at the tail end of the hollow rod 21 and inject grout into the hollow rod 21. The grout seeps out from the grouting hole 214 and fills the borehole space and the fissures of the surrounding rock 1. S53. After grouting is completed, immediately inject high-pressure gas into the hollow rod body 21 through the closable protective end cap to perform a rod cleaning operation, expelling any grout that may block the air extraction rod and grouting hole 214. Then close the openable protective end cap 211. While waiting for the grout to solidify, open the openable protective end cap 211 multiple times to perform a check cleaning operation inside the hollow rod body 21 to prevent and remove any possible trace amounts of grout backflow, ensuring that the hollow rod body 21 and the air extraction rod remain unobstructed. During grouting and rod cleaning operations, the closable inflation port 263 on the inflation sealing rod 26 remains closed. At this time, there is no pressure inside the third sealing sleeve 261 and the fourth sealing sleeve 262, which remain in a flat and contracted state, providing full channel space for grout flow and high-pressure rod cleaning gas, without affecting the grouting and rod cleaning operations.

[0040] S54. After the grout has fully solidified, open the openable and closable protective end cap 211 and the closable air inlet 263, and inflate the air-sealing rod 26 to make the third sealing sleeve 261 and the fourth sealing sleeve 262 expand radially and uniformly. The expanded sealing sleeve tightly wraps the air extraction rod in the same cross section and fits tightly against the inner wall of the hollow rod body 21 of the monitoring grouting anchor rod 2, thereby forming an effective physical isolation sealing strip inside the hollow rod body 21. After inflation is completed, close the closable air inlet 263, connect one end of the pipeline to the tail of the air extraction rod, and connect the other end to the corresponding radon detector. S55. The solenoid valve 314 inside the gas control unit 31 on the central controller 32 is opened, and the corresponding vacuum pump 315 is started. At the same time, radon gas is extracted from each measuring point inside the same monitored grouting anchor 2. The gas is sent to the radon measuring component 4 through the filter 316 for synchronous radon concentration measurement at multiple measuring points. The measurement data is transmitted back in real time through the signal line 33. The central controller 32 automatically binds and stores the data group with the corresponding anchor number and measuring point number information. Then the system automatically performs the measurement of the next monitored grouting anchor 2, thereby realizing synchronous cyclic monitoring of radon gas inside multiple monitored grouting anchors 2. The central controller 32 inside the centralized control box 3 uniformly controls all gas control units 31. Each gas control unit 31 controls a monitoring grouting anchor 2 with a corresponding number. For example, when monitoring grouting anchor 2 S1, only gas control unit 31 V1 is running, while V2~V n When the unit is shut down and the measurement is complete, the program automatically adjusts to monitor grouting anchor 2 S2. At this time, only the air circuit control unit 31 V2 is running, while V1, V3 and V... n The unit is shut down to enable synchronous roving monitoring of radon gas inside multiple anchor bolts.

[0041] S6. Compare the radon concentration values ​​R measured at each measuring point in step S5 with the field engineering threshold obtained in step S4: If the measured concentration value R < A, the grouting effect of the area where the measuring point is located is judged to be "excellent", indicating that the surrounding rock 1 fissures in the area are fully filled by grout, the integrity is well restored, and the radon gas release level has dropped to close to the original rock state; if A ≤ R < B, the grouting effect of the area where the measuring point is located is judged to be "good", indicating that the grout has effectively entered the main fissure network and played a reinforcing role, but there may still be some micro-fissures or insufficient filling, and the radon gas release is at a controlled intermediate level; if R ≥ B, the grouting effect of the area where the point is located is judged to be "unqualified", indicating that there is an obvious blank area in the grouting of the area and the radon gas release rate is high. For anchor bolts without any "unqualified" ratings, secondary grouting is unnecessary. For anchor bolts with "unqualified" ratings, the need for secondary reinforcement grouting should be discussed based on the number of "unqualified" monitoring points within the anchor bolt. If two or three monitoring points within an anchor bolt are unqualified, it is determined that there is a large area of ​​grouting defect within the anchor bolt support area, and secondary grouting should be performed first. For grouting anchor bolts with only one unqualified monitoring point, after completing secondary grouting for other anchor bolts, this anchor bolt should be retested. Secondary grouting should only be performed if the retest result is still unqualified, considering that the migration of reinforcement grout may affect the fractured rock mass in the adjacent area. During secondary grouting, ensure that the closable air inlet 263 is opened to release the gas in the third sealing sleeve 261 and the fourth sealing sleeve 262, and then close the closable air inlet 263 to prevent the internal sealing sleeves from clogging the grout. Then, perform reinforcement grouting according to the above grouting method.

[0042] The above description of the disclosed embodiments enables those skilled in the art to make and use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit and scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for evaluating the effect of surrounding rock grouting based on radon gas monitoring, characterized in that, Including radon gas monitoring systems and laboratory equipment; The radon monitoring system includes a monitoring grouting anchor (2) and a radon measuring component (4); multiple monitoring grouting anchors (2) are arranged, each monitoring grouting anchor (2) includes a hollow rod body (21) and three air extraction rods embedded in the hollow rod body (21) in parallel. The hollow rod body (21) has a grouting hole (214) on its pipe wall, and its tail end can be opened and closed. The air outlet end of the three air extraction rods is fixedly installed at the tail end of the hollow rod body (21), and the air inlet end is located in the elastic zone, plastic zone, and fracture zone of the surrounding rock (1); the hollow rod body (21) is fitted with a first sealing sleeve (212) and a second sealing sleeve (213) for isolating different monitoring sections; the hollow rod body (21) is parallel to the air extraction rods. An inflatable sealing rod (26) is provided, on which a third sealing sleeve (261) and a fourth sealing sleeve (262) are fixed. The axial positions of the third sealing sleeve (261) and the fourth sealing sleeve (262) correspond to the first sealing sleeve (212) and the second sealing sleeve (213). A vent hole is provided on the rod wall of the inflatable sealing rod (26) at the position corresponding to the setting position of the third sealing sleeve (261) and the fourth sealing sleeve (262). A closable inflation interface (263) is integrated at the tail of the inflatable sealing rod (26). The radon measuring component (4) includes a radon meter, which is connected to the suction rod through a pipeline. The laboratory device is a triaxial pressure experimental device.

2. The radon-based grouting effect evaluation system for surrounding rock according to claim 1, characterized in that, The radon monitoring system also includes a centralized control box (3), which includes a gas path control unit (31) and a central controller (32). The gas path control unit (31) is provided in multiple sets corresponding to the monitoring grouting anchor rod (2). The gas path control unit (31) is set on the pipeline connecting the suction rod and the radon meter. The pipelines connected to the tail ends of the three suction rods in each monitoring grouting anchor rod (2) share a set of gas path control units (31). Each gas path control unit (31) includes a solenoid valve (314), a vacuum pump (315), and a filter (316). The central controller (32) uniformly controls each gas path control unit (31) and communicates with the radon measuring component (4) through a signal line (33) to coordinate the measurement process and automatically record concentration data.

3. The radon-based grouting effect evaluation system for surrounding rock according to claim 1, characterized in that, The air extraction rod and the air-filled sealing rod (26) are fixed and kept parallel by a narrow-side slot (218) embedded in the hollow rod body (21); the tail end of the monitoring grouting anchor rod (2) is fitted with a grout stop plug (217); the tail end of the monitoring grouting anchor rod (2) is fixedly installed with an openable and closable protective end cap (211), the openable and closable protective end cap (211) is hollow inside, and the top end is flush with the tail end of the air extraction rod.

4. The radon-based grouting effect evaluation system for surrounding rock according to claim 1, characterized in that, The grouting holes (214) on the hollow rod (21) are set in three groups corresponding to three different surrounding rock (1) zones. Each group of grouting holes (214) is evenly distributed along the circumference of the hollow rod (21).

5. The radon-based grouting effect evaluation system for surrounding rock according to claim 1, characterized in that, There are three radon detectors, which are connected to the three air extraction rods in each grouting anchor (2) through pipelines.

6. The radon-based grouting effect evaluation system for surrounding rock according to claim 1, characterized in that, The laboratory apparatus includes a triaxial testing machine (5), a specimen (6), a fourth radon meter (8), and a computer (9); the triaxial testing machine (5) includes a triaxial pressure chamber (54), an axial pressure rod (51), a specimen cap (52), and a base (53). The specimen (6) is placed in the triaxial pressure chamber (54), which is also equipped with hydraulic oil (541) to provide confining pressure for the specimen (6); the specimen (6) is positioned between the specimen cap (52) and the base (53). The sample cap (52) is positioned between the axial pressure rod (51) and the specimen (6); a high-pressure chamber penetration connector (531) is provided at the center of the base (53) and passes through the base (53); the fourth radon meter (8) is connected to the outlet of the high-pressure chamber penetration connector (531) through a rubber tube (7); a porous plate (533) is fixedly installed at the upper end of the high-pressure chamber penetration connector (531), and a microporous filter membrane (532) is provided on the porous plate (533), and the microporous filter membrane (532) is in contact with the bottom of the specimen (6).

7. A method for evaluating grouting effect using a radon-based surrounding rock grouting effect evaluation system according to any one of claims 1-6, characterized in that, Includes the following steps: S1. In the area to be tested on site, obtain complete and dense rock cores to make specimens (6) and send them to the laboratory; S2. Install the specimen (6) in the triaxial testing machine (5), apply the set confining pressure to simulate the lateral constraint stress it bears in situ, and continuously load the specimen (6) axially until the specimen (6) fails. Throughout the process, collect axial stress-strain and radon gas concentration data of the specimen (6) synchronously and continuously. S3. Based on stress-strain data, calculate the damage variable D(t) at each time point, pair D(t) with the radon concentration C(t) at the same time point to obtain a series of data points (D, C), and perform curve fitting to obtain the complete CD characteristic relationship curve. S4. Analyze the characteristic relationship curve to determine the characteristic radon concentration inflection point that represents the critical change of the damage state of the surrounding rock (1), corresponding to laboratory thresholds C1 and C2. Then measure the background concentration of radon in the field and combine it with the background radon concentration of the indoor rock sample to calibrate the characteristic radon concentration threshold and obtain the field engineering thresholds A and B applicable to the current engineering site. S5. Install monitoring grouting anchors (2) in the surrounding rock (1), grout and wait for the grout to solidify, control the gas circuit control unit (31) and radon measurement component (4) through the central controller (32) to continuously pump air from monitoring points at different depths inside multiple monitoring grouting anchors (2) and record the radon concentration. S6. Compare the radon concentration values ​​R measured at each measuring point in step S5 with the on-site engineering threshold obtained in step S4: If the measured concentration value R < A, the grouting effect of the area where the measuring point is located is judged to be "excellent"; if A ≤ R < B, the grouting effect of the area where the measuring point is located is judged to be "good"; if R ≥ B, the grouting effect of the area where the point is located is judged to be "unqualified".

8. The method according to claim 7, characterized in that, In S3, the damage variable D(t) corresponding to different loading times is calculated using a model based on elastic modulus degradation: D(t) = 1 - E(t) / E0, where E0 is the initial elastic modulus and E(t) is the secant modulus at time t; the initial elastic modulus E0 is determined by the slope of the initial straight line segment of the stress-strain curve of the specimen (6), and the secant modulus E(t) is determined by the slope of the line connecting the stress-strain data points at time t to the origin.

9. The method according to claim 7, characterized in that, In S4, the characteristic radon concentration inflection points include the first inflection point (D1, C1), which corresponds to the turning point where the curve slope changes from a slow increase to a sharp increase, and the second inflection point (D2, C2), which corresponds to the turning point where the curve slope increases sharply and then decreases. The radon concentration values ​​C1 and C2 corresponding to these two inflection points are the laboratory thresholds. At the same time, the average radon concentration C at each monitoring point inside the grouting anchor rod (2) before grouting is used in the field. field1 C field2 C field3 As the in-situ radon background concentration, the radon concentration C corresponding to D=D1 / 2, D=(D1+D2) / 2, and D=(D2+1) / 2 of specimen (6) was extracted from the experimental data. lab1 C lab2 C lab3 As the background concentration of radon in the laboratory, the field calibration factor k=(C) is then calculated. field1 +C field2 +C field3 ) / (C lab1 +C lab2 +C lab3 ), thus obtaining the on-site engineering thresholds: A=k×C1, B=k×C2.

10. The method according to claim 7, characterized in that, In S5, the anchor bolt installation method includes the following steps: S51. Drill a hole at the designed location in the surrounding rock (1), insert the hollow rod (21) with the assembled anchor head (22) into the hole, and then put in the grout stop plug (217) and pad (215) in sequence, and tighten the nut (216) to press the pad (215) against the rock surface; S52. Open the openable protective end cap (211) at the tail end of the hollow rod (21) and inject grout into the hollow rod (21). The grout seeps out from the grouting hole (214) and fills the borehole space and the fissures of the surrounding rock (1). S53. After grouting is completed, high-pressure gas is immediately injected into the hollow rod (21) to clean the rod and remove the grout that may block the air extraction rod and the grouting hole (214). Then, the openable protective end cap (211) is closed. While waiting for the grout to solidify, the openable protective end cap (211) is opened multiple times and an inspection cleaning operation is performed into the hollow rod (21). S54. After the grout has fully solidified, open the openable protective end cap (211) and the closable air inlet (263), and inflate the air-sealing rod (26) to make the third sealing sleeve (261) and the fourth sealing sleeve (262) expand radially and uniformly. The expanded sealing sleeve tightly wraps the air extraction rod in the same section and fits tightly against the inner wall of the hollow rod body (21) of the monitoring grouting anchor rod (2), thereby forming an effective physical isolation sealing strip inside the hollow rod body (21). After the inflation is completed, close the closable air inlet (263), connect one end of the pipeline to the tail of the air extraction rod, and connect the other end to the corresponding radon meter. S55. The central controller (32) controls the opening of the solenoid valve (314) inside the gas control unit (31) on the pipeline and starts the corresponding vacuum pump (315). At the same time, the radon gas in each measuring point in the same monitoring grouting anchor (2) is extracted. The gas is sent to the radon measuring component (4) through the filter (316) for multi-point synchronous radon concentration measurement. The measurement data is transmitted back in real time through the signal line (33). The central controller (32) automatically binds and stores the data group with the corresponding anchor number and measuring point number information. Then the system automatically performs the measurement of the next monitoring grouting anchor (2), thereby realizing the synchronous roving monitoring of radon gas inside multiple monitoring grouting anchors (2).

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