A method for segmented axial force measurement and structural surface early warning of external ultrasonic decoupled anchor bolts

Abstract

This invention relates to a method for segmented axial force measurement and structural surface early warning of externally mounted ultrasonic decoupled anchor bolts. It utilizes the progressively decoupled anchor bolts, already employed in large deformation control in deep hard rock tunnels, as support components, while simultaneously transforming them into passive sensing carriers that can be read by external ultrasonic sensors. Based on the inherent segmented structure of the progressively decoupled anchor bolt—comprising a shallow anchoring section, a decoupling pressure-relief section, and a deep anchoring section—passive impedance mismatch loops are set at the segment boundaries. This allows the external ultrasonic sensor to obtain multiple stable echoes without drilling, slotting, or pre-embedding sensors. The travel time of each segment is obtained through the time difference between adjacent echoes, and the average axial force of each segment is then inverted using the acoustoelastic relationship, thus forming the anchor bolt axial force distribution. Finally, the location and activity state of hidden hard structural surfaces are determined using the changing characteristics of the segmented axial force distribution.

Description

Technical Field

[0001] This invention relates to the field of rock support and monitoring technology for deep underground engineering, and in particular to a method for segmented axial force measurement and structural surface early warning of external ultrasonic decoupled anchor bolts. Background Technology

[0002] In deep hard rock mine roadways, under the combined effects of high ground stress, strong mining disturbance, and dominant structural planes, the hidden hard structural planes within the surrounding rock are prone to closure disturbance, micro-opening, expansion, and local penetration, thereby inducing asymmetric large deformation, spalling, roof fall, and local collapse. The key to such disasters is not simply the result of surface displacement, but the activation and expansion process of the internal structural planes of the surrounding rock.

[0003] Gradual decoupling anchors are a type of anchor technology used for controlling large deformations in deep mine roadways. For example, invention patent application number CN201810283159.7 discloses a structurally simplified large deformation energy-absorbing anchor, which, through its anchored section, non-anchored section, or decoupling section, enables the anchor to withstand pressure, absorb energy, and continuously bear load in stages under conditions of large deformation in the surrounding rock. This type of anchor is suitable for controlling large deformations in deep hard rock, but its original purpose was mainly for support and deformation adaptation, not for directly identifying the expansion state of concealed hard structural surfaces.

[0004] Using anchor bolts as a sensing medium for the internal state of the surrounding rock offers engineering advantages: anchor bolts are widely deployed within the roadway's surrounding rock, directly engaging in mechanical coupling with the rock and structural surfaces. When concealed rigid structural surfaces open, shear slip, or expand, the axial force distribution along the anchor bolts exhibits inter-segment differences, peaking, plateauing, load transfer, or local abrupt changes. If the axial force distribution of anchor bolts on-site can be obtained over a large area, the structural surface identification problem can be transformed into the identification problem of changes in anchor bolt axial force distribution.

[0005] Existing sensing anchor bolts typically require pre-embedded strain gauges, fiber optic gratings, distributed optical fibers, or other electrical sensors. This approach presents three significant problems: First, pre-embedded sensors usually require slotting, patching, encapsulation, and wiring, which may weaken the anchor bolt's strength or affect the continuity of its stress. Second, the durability of sensors, cables, and encapsulation structures is limited in the high-humidity, high-stress, and highly disturbed environments of deep tunnels. Third, it is difficult to install costly pre-embedded sensors on every single anchor bolt in the field; actual monitoring can only cover a small number of representative anchor bolts, making it difficult to achieve identification of structural surface activity space at the tunnel scale.

[0006] Ultrasonic force measurement provides another approach for non-destructive testing of anchor bolts. Current ultrasonic anchor bolt force measurement methods typically involve emitting ultrasonic waves from the anchor bolt end and receiving the echoes, then using the ultrasonic travel time variation along the entire anchor bolt to invert the average axial force. This method does not require pre-embedded sensors in the anchor bolt, but it only obtains the average force across the entire bolt and cannot distinguish the force differences between shallow anchorage sections, decoupled relief sections, and deep anchorage sections. Therefore, it is difficult to determine which section of the anchor bolt contains a hidden rigid structural surface, and it is also difficult to identify the load transfer path caused by structural surface movement.

[0007] To obtain segmented axial force information, existing solutions may involve drilling through holes or cutting grooves along the anchor bolts to create an ultrasonic reflection interface. While drilling and cutting grooves can enhance the echo, they also weaken the cross-section and cause stress concentration. In deep hard rock tunnels with large deformation conditions, this may lead to premature yielding, shearing, or tensile failure of the anchor bolts, violating the engineering requirement that support components should maintain integrity.

[0008] In summary, existing technologies have the following drawbacks: pre-embedded sensor solutions cannot be widely used for all field anchor bolts and may weaken the bolts; conventional ultrasonic force measurement can only obtain the average axial force of the entire bolt; and destructive segmented echo methods weaken the bolt. Therefore, there is an urgent need for a technical solution that does not require pre-embedded sensors, does not damage the anchor bolt, can perform segmented axial force measurement on progressively decoupled anchor bolts, and can use the changes in segmented axial force distribution to identify the location and activity state of hidden rigid structural surfaces. Summary of the Invention

[0009] To address the aforementioned problems, the present invention aims to provide an external ultrasonic method for segmented axial force measurement and structural surface early warning of decoupled anchor bolts. Based on the gradual decoupling of the naturally occurring segmented structure of the anchor bolt, which includes a shallow anchoring section, a decoupling pressure-relief section, and a deep anchoring section, a passive impedance mismatch loop is set at the segment boundaries. This allows the external ultrasonic device to obtain multiple stable echoes without drilling, grooving, or pre-embedded sensors. The travel time of each segment is obtained through the time difference between adjacent echoes, and the average axial force of each segment is then inverted using the acoustoelastic relationship, thus forming the anchor bolt axial force distribution. Finally, the location and activity state of hidden rigid structural surfaces are determined using the changing characteristics of the segmented axial force distribution.

[0010] The technical solution adopted in this invention is as follows:

[0011] The present invention proposes a method for segmented axial force measurement and structural surface early warning of external ultrasonic decoupled anchor bolts, which specifically includes the following steps: S1. Prepare for gradual decoupling of the anchor bolt; the gradually decoupling anchor bolt includes, along the axial direction, a shallow anchoring section, a decoupling pressure relief section, and a deep anchoring section in sequence; S2. A first passive impedance mismatch ring is set at the junction of the shallow anchoring section and the decoupling pressure relief section of the gradually decoupled anchor bolt, and a second passive impedance mismatch ring is set at the junction of the decoupling pressure relief section and the deep anchoring section of the gradually decoupled anchor bolt. S3. Install the progressively decoupled anchor bolt in the surrounding rock borehole, anchoring its shallow and deep anchor sections to the surrounding rock; after the progressively decoupled anchor bolt is installed stably, use a detachable external ultrasonic measuring device to contact the exposed end of the progressively decoupled anchor bolt to collect the reference multi-interface echo signals of longitudinal and transverse waves; and during roadway excavation, mining disturbance, or operation, excite ultrasonic pulses from the exposed end of the progressively decoupled anchor bolt and receive echo signals from the first passive impedance mismatch ring, the second passive impedance mismatch ring, and the end of the bolt. S4. Based on the arrival time difference of adjacent reflected echoes, extract the segmented ultrasonic travel times of the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section; S5. Based on the acoustic elastic calibration relationship, the ultrasonic travel time variation of each segment is inverted into the average axial force of each segment, forming the segmented axial force distribution vector of the gradually decoupled anchor and its temporal evolution; S6. Based on the segmented axial force distribution vector in the initial stable state, calculate at least one of the following characteristic quantities: segmented axial force increment, inter-segment axial force difference, inter-segment axial force difference ratio, deep and shallow anchorage segment axial force ratio, decoupling segment load sharing rate, and decoupling segment plastic elongation. Based on this, identify the section where the hidden rigid structural surface and the gradually decoupling anchor meet. S7. Based on the evolution of the segmented axial force distribution vector and its characteristic quantities over time, the active state of the hidden hard structural surface is identified as a stable state, a micro-activated state, an extended state, or a slip or penetration risk state. S8. Based on the location, activity status and temporal changes of the hidden hard structural surface, output the early warning level, and integrate the identification results of each anchor when multiple gradually decoupled anchors participate in the measurement to form the extended range or extended front edge of the hidden hard structural surface.

[0012] Furthermore, the passive impedance mismatch ring is a non-load-bearing ring-shaped acoustic marker pre-installed on the outer periphery of the segment boundary of the progressively decoupled anchor bolt, and its material acoustic impedance is different from that of the anchor bolt body material, so as to form identifiable segmented reflected echoes when ultrasonic waves propagate along the anchor bolt axis; the passive impedance mismatch ring is fixed at the anchor bolt segment boundary by one or a combination of interference fit, controlled temperature fit, durable acoustic coupling adhesive layer bonding, or external ferrule clamping; when the rod body of the progressively decoupled anchor bolt is made of steel, the passive impedance mismatch ring... The matching ring is made of metal, alloy, or metal-based composite material with an acoustic impedance difference of not less than a preset ratio from that of the steel rod; the preset ratio is 30% to 50%; for brittle acoustic impedance materials, a ductile protective layer or a metal-based composite structure is provided on the outer periphery of the passive impedance mismatch ring; the axial width of the passive impedance mismatch ring is preferably 0.3 to 1.5 times the diameter of the anchor rod, the radial thickness is preferably 0.03 to 0.20 times the diameter of the anchor rod, and the two ends of the ring are provided with rounded or chamfered transition structures.

[0013] Furthermore, the detachable external ultrasonic measuring device includes a sealed outer shell, a positioning sleeve, an end-face fixed acoustic coupling assembly, an ultrasonic excitation receiving assembly, a pulse excitation and echo receiving unit, a coupling clamping positioning assembly, and a signal acquisition and processing unit; the end-face fixed acoustic coupling assembly and the ultrasonic excitation receiving assembly are sequentially and axially arranged inside the sealed outer shell; the positioning sleeve is located on the outer side of the bottom of the sealed outer shell and is provided with an axial limiting step and a circumferential anti-rotation key, and an O-ring is provided between it and the bottom of the sealed outer shell; the end-face fixed acoustic coupling assembly includes a front-end fixed coupling head and an end-face coupling base. The system comprises: a front-end fixed coupling head, which is fixed to the exposed end face of the gradually decoupled anchor rod via a permanently cured acoustic coupling layer; an end-face coupling base, which is coaxially fixed to the top of the front-end fixed coupling head; an ultrasonic excitation receiving component, which is disposed on the top of the end-face coupling base and acoustically coupled to the exposed end face of the gradually decoupled anchor rod via the end-face fixed acoustic coupling component; a coupling clamping and positioning component, which is disposed on the outer side of the bottom of the positioning sleeve and is used to apply a predetermined clamping force; a pulse excitation and echo receiving unit, which is connected to the top of the ultrasonic excitation receiving component; and a signal acquisition and processing unit, which is connected to the pulse excitation and echo receiving unit.

[0014] Furthermore, the ultrasonic excitation receiving assembly includes a multi-channel shielded cable connector, a small shielded PCB, a support plate, a constant force preload spring assembly, a floating conductive plate or elastic electrode, a split backing, a longitudinal wave piezoelectric transducer, a transverse wave piezoelectric transducer, and a temperature sensing unit; the longitudinal wave piezoelectric transducer is a thickness vibration mode piezoelectric transducer, and the transverse wave piezoelectric transducer is a shear vibration mode piezoelectric transducer with a shear direction mechanical positioning mark, and the two are arranged side-by-side coplanarly above the end-face coupling base; the split backing includes components respectively positioned above the longitudinal wave piezoelectric transducer and the transverse wave piezoelectric transducer. The independent backing or damping block is provided, and an insulating isolation groove or damping isolation wall is provided between the two; the constant force preload spring group applies a uniform axial preload to the longitudinal wave piezoelectric transducer and the transverse wave piezoelectric transducer through a floating voltage plate or elastic electrode; the small shielded PCB is set above the constant force preload spring group through a support plate, and is connected to the longitudinal wave channel, the transverse wave channel and the temperature sensing channel respectively, and its top is led out from the middle of the upper end of the sealed shell through a multi-channel shielded cable connector; the temperature sensing unit is set near the end face of the fixed acoustic coupling component or the exposed end face of the anchor rod, and forms thermal contact with it; Furthermore, in step S4, let the arrival time of the first passive impedance mismatch loop echo after deducting equipment delay be T1, the arrival time of the second passive impedance mismatch loop echo be T2, and the arrival time of the pole end echo be T. e Then the one-way travel time of the shallow anchorage section, the decoupling relief section, and the deep anchorage section are respectively: τ s =T1 / 2,τ d =(T2 T1) / 2,τ f=(Te T2) / 2; Calculate the segmented travel time τ of the P-wave separately for the P-wave and S-wave according to the above relationship. p,s τ p,d τ p,f and the segmented travel time τ of the transverse wave S,s τ S,d τ S,f .

[0015] Furthermore, in step S5, the inversion of the average axial force of each segment includes: performing temperature calibration and elastic loading calibration on the same type of progressively decoupled anchor bolts to obtain the longitudinal wave temperature coefficient, transverse wave temperature coefficient, longitudinal wave stress coefficient, and transverse wave stress coefficient of each segment; for the k-th segment, k∈{s, d, f}, using the relative changes in longitudinal wave travel time and transverse wave travel time to simultaneously solve the acoustic elastic equation, weakening or eliminating temperature disturbances, and obtaining the average stress change Δσ of the k-th segment. k And by N k =A k (σ k0 +Δσ k The average axial force N of the k-th segment is obtained. k A k Let σ be the cross-sectional area of ​​the k-th segment of the rod. k0 The axial stress of the k-th segment under the reference state is used. When the observed slope between the relative changes in longitudinal wave travel time and the relative changes in transverse wave travel time of any segment deviates from the elastic calibration slope of that segment by more than a preset threshold, the corresponding segment is identified as entering the yield or decoupling pressure relief state. After entering the yield or decoupling pressure relief state, the stress change and plastic elongation of that segment are separated by combining material constitutive constraints, loading history constraints, or temperature gradual change constraints at adjacent times.

[0016] Furthermore, in step S6, a segmented axial force distribution vector N(t) = [N] is constructed based on the average axial force of the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section. s (t), N d (t), N f [(t)], where Ns(t), Nd(t), and Nf(t) are the average axial forces in the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section, respectively; taking the segmented axial force at the initial stable time t0 as the benchmark, the following characteristic quantity is defined: segmented axial force increment ΔN j (t)=N j (t) N j (t0), j∈{s, d, f}; inter-segment axial force difference D sd (t)=|N s (t) N d (t)|,D df(t)=|N d (t) N f (t)|;Ratio of axial force difference between segments R sd (t)=D sd (t) / (D df (t)+ε); R ratio of axial force in deep and shallow anchorage sections sf (t)=N s (t) / (N f (t)+ε); Load sharing rate of the decoupling section η d (t)=N d (t) / (N s (t)+N d (t)+N f (t)+ε); and the plastic elongation Δl of the decoupling compression section. p,d (t); where ε is a constant to prevent the denominator from being zero.

[0017] Furthermore, step S6 also includes constructing the shallow anchorage segment activity score Q. s Decoupling and pressure segment activity score Q d and deep anchorage section activity score Q f : Q s = a1·|ΔN s (t)| + a2·D sd (t) + a3·|dN s (t) / dt|; Q d = b1·|ΔN d (t)| + b2·D sd (t) + b3·D df (t) + b4·η d (t) + b5·Δl p,d (t); Q f = c1·|ΔN f (t)| + c2·D df (t) + c3·|dN f (t) / dt|; Wherein dN s (t) / dt and d Nf (t) / dt represent the axial force growth rates for the shallow and deep anchorage sections, respectively; a1~a3, b1~b5, and c1~c3 are non-negative weighting coefficients determined by indoor calibration tests, numerical simulations, or field initial stabilization period data; Qs and Q d Q fThe section that achieves the maximum value is determined to be the section where the hidden hard structural surface intersects with the gradually decoupled anchor or the section with the strongest activity influence; when two adjacent activity scores increase simultaneously and exceed the preset threshold, it is determined that the hidden hard structural surface is located near the boundary of adjacent segments or its extended leading edge is migrating across segments.

[0018] Furthermore, in step S7, the active state of the hidden hard structural surface is divided into a stable state, a slightly activated state, an extended state, and a slip or penetration risk state, and is identified according to the following rule: when |ΔN s (t)|、|ΔN d (t)|、|ΔN f (t)|、D sd (t), D df When both (t) are below the stability threshold, it is determined to be a stable state; when D sd (t), D df (t) or its growth rate exceeds the micro-activation threshold, and the decoupling allows for plastic elongation Δl in the compression section. p,d (t) When there is no sustained increase, it is judged to be in a micro-activation state; when the difference in axial force between sections continues to increase and the ratio of axial force between deep and shallow anchorage sections R sf (t) When a sustained shift occurs, or when the segment corresponding to the maximum activity score migrates over time, it is determined to be in an extended state; when the load sharing rate η of the decoupling segment... d (t) exceeds the preset threshold, and the plastic elongation Δl of the decoupling section is reduced. p,d When (t) or its growth rate continues to increase, it is determined to be a slip or breakthrough risk state.

[0019] Furthermore, in step S8, a patrol-style ultrasonic measurement is performed on multiple progressively decoupled anchor bolts with passive impedance mismatch rings on the roadway cross-section or roadway direction. The structural surface section, activity score, and activity status output by each anchor bolt are mapped to spatial coordinates. Interpolation, clustering, or surface fitting methods are used to reconstruct the expansion leading edge, expansion direction, and activity intensity distribution of the hidden hard structural surface.

[0020] Compared with the prior art, the present invention has the following advantages: 1. This invention does not require pre-embedded strain gauges, optical fibers or electrical sensors inside the anchor bolt, nor does it require laying cables and power supply units for each anchor bolt. The portable external ultrasonic device can inspect a large number of anchor bolts on site one by one.

[0021] 2. This invention utilizes a passive impedance mismatch ring as a non-load-bearing acoustic marker. It is positioned on the outer periphery of the anchor rod body through non-cutting, non-hole-opening, and non-welding methods such as interference fit, controlled temperature fit, acoustic coupling adhesive layer bonding, or external ferrule clamping. It does not form through holes, radial holes, axial slots, cutting threads, or welding heat-affected zones on the rod body, thus fundamentally avoiding the problems of weakening anchor rod strength and residual welding stress or local embrittlement caused by traditional segmented echo schemes.

[0022] 3. Compared with conventional ultrasonic force measurement, which can only obtain the average axial force of the entire shaft, this invention can obtain the segmented average axial force of the shallow anchorage section, the decoupling pressure relief section and the deep anchorage section, forming an approximate axial force distribution along the shaft.

[0023] 4. Based on the characteristics of segmented axial force difference, load transfer between deep and shallow anchorage sections, load sharing rate of decoupled sections, and plastic elongation, this invention uses rule-based criteria to quickly identify the engineering section where the hidden rigid structural surface is located and its active state.

[0024] 5. The inspection results of multiple anchor bolts can be merged at the roadway scale to form the leading edge of structural surface expansion and early warning level. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall process of an external ultrasonic decoupled anchor bolt segmental axial force measurement and structural surface early warning method proposed in this invention; Figure 2 This is a schematic diagram of the segmented reflection structure of the gradually decoupled anchor and passive impedance mismatch ring in this invention; Figure 3 This is a partial structural schematic diagram of the external ultrasonic measuring device in this invention; Figure 4 This is a schematic diagram of segmented ultrasonic travel time extraction and segmented axial force distribution in this invention; Figure 5 This is a schematic diagram illustrating the identification of the location and activity state of a hidden rigid structural surface based on changes in segmented axial force distribution in this invention. Figure 6 This is a schematic diagram of the process of longitudinal and transverse wave differential-elastic-plastic full-process inversion-structural surface state prediction in this invention; Figure 7 This is a schematic diagram of the reconstruction of the external ultrasonic inspection measurement and the structural surface expansion state of the anchor bolt group in this invention.

[0026] The attached figures are labeled as follows: 1-Disassembled external ultrasonic measuring device; 2-Exposed threaded section; 3-Nut; 4-Pattern; 5-Shallow anchoring section; 6-Decoupling pressure relief section; 7-Deep anchoring section; 8-First passive impedance mismatch ring; 9-Decoupling sleeve; 10-Gradually decoupling anchor; 11-Second passive impedance mismatch ring; 13-Multi-channel shielded cable connector; 14-Sealed outer shell; 15-Small shielded PCB; 16-Support plate; 17-Constant force pre-tightening spring assembly; 18-Floating conductive plate or elastic electrode; 19-Separate backing; 20-Longitudinal wave piezoelectric transducer; 21-Transverse wave piezoelectric transducer; 22-End face coupling base; 23-Temperature sensing unit; 24-Front-end fixed coupling head; 25-Curing acoustic coupling layer; 26-O-ring seal; 27-Positioning sleeve; 28-Anti-loosening nut; 29-Exposed end face of screw. Detailed Implementation

[0027] To more clearly illustrate the technical solutions in 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] like Figure 1 As shown, the present invention proposes a method for segmented axial force measurement and structural surface early warning of externally mounted ultrasonic decoupled anchor bolts. First, a passive impedance mismatch ring is set at the segment boundary and a progressively decoupled anchor bolt is installed. A permanent end-face acoustic coupling component is fixed at the exposed end of the anchor bolt. After installation and stabilization, longitudinal and transverse wave reference multi-interface echo signals are acquired, and the arrival times of the echoes from the first passive impedance mismatch ring, the second passive impedance mismatch ring, and the bolt end are extracted as references. After entering service, ultrasonic waves are used at a preset cycle or after mining disturbance events. The excitation receiving component repeatedly measures and compares with the benchmark; the ultrasonic travel time of each segment is obtained through the time difference between adjacent echoes, and the average axial force of each segment is inverted according to the acoustic elastic equation to form a segment axial force distribution vector and track its temporal evolution; then, based on characteristic quantities such as the axial force difference between segments, the axial force ratio of deep and shallow anchoring segments, the load sharing rate of decoupled segments, and plastic elongation, as well as the activity score, the segment where the hidden rigid structural surface is located and its activity state are identified; finally, the identification results of multiple anchor bolts are fused to reconstruct the leading edge of the hidden rigid structural surface and output the warning level. The specific implementation steps are as follows: S1. A progressively decoupling anchor bolt 10 is prepared for large deformation control in deep hard rock tunnels; the progressively decoupling anchor bolt 10 includes, in sequence along the axial direction, a shallow anchoring section 5, a decoupling pressure relief section 6, and a deep anchoring section 7. S2, such as Figure 2As shown, a first passive impedance mismatch ring 8 is set at the junction of the shallow anchoring section 5 and the decoupling pressure relief section 6 of the gradually decoupled anchor rod 10, and a second passive impedance mismatch ring 11 is set at the junction of the decoupling pressure relief section 6 and the deep anchoring section 7 of the gradually decoupled anchor rod 10, so that when the external ultrasonic wave propagates along the anchor rod axis, an identifiable segmented reflection echo interface is formed. The passive impedance mismatch ring is a non-load-bearing ring-shaped acoustic marker pre-installed on the outer periphery of the segment boundary of the progressively decoupled anchor bolt. Its material acoustic impedance is different from that of the anchor bolt body material, so as to form an identifiable segmented reflection echo interface when the ultrasonic wave propagates along the anchor bolt axis.

[0029] The passive impedance mismatch ring is positioned against the anchor bolt body using at least one or a combination of methods, including interference fit, temperature-controlled fit, durable acoustic coupling adhesive bonding, and external clamping. This positioning method eliminates the need for through holes, radial holes, axial slots, threaded cuts, weld heat-affected zones, or weakening structures for sensor embedding on the anchor bolt body, thus avoiding factors that may affect support performance, such as residual welding stress, localized embrittlement, and cross-sectional weakening. Unlike traditional embedded sensors, the passive impedance mismatch ring does not contain strain gauges, optical fibers, piezoelectric elements, resistive elements, amplification circuits, or wireless transmission circuits; it exists solely as an acoustic reflection interface. Furthermore, unlike the reflection interface formed by drilling through holes, the passive impedance mismatch ring does not penetrate the bolt cross-section or create a weakened section, thus providing segmented ultrasonic echoes while maintaining the support's load-bearing capacity.

[0030] When the rod body of the gradually decoupled anchor is made of steel, the passive impedance mismatch ring is made of metal, alloy, or metal-based composite material with an acoustic impedance difference of not less than a preset ratio from that of the steel rod body; the preset ratio is 30% to 50%; the passive impedance mismatch ring is preferably made of tungsten-nickel-iron high-density alloy, tungsten-nickel-copper high-density alloy, or other tough alloy materials that meet the acoustic impedance difference condition; the material of the passive impedance mismatch ring should meet the requirements of corrosion resistance, damp heat resistance, and impact resistance in the service environment of underground or underground engineering; for brittle acoustic impedance materials, a ductile protective layer or a metal-based composite structure is provided on the outer periphery of the passive impedance mismatch ring to prevent the ring body from breaking during the anchor rod under stress; the axial width of the passive impedance mismatch ring is preferably 0.3 to 1.5 times the diameter of the anchor rod body, the radial thickness is preferably 0.03 to 0.20 times the diameter of the anchor rod body, and the two ends of the ring body are provided with rounded or chamfered transition structures to reduce disturbance to the anchoring agent coating and the stress state of the anchor rod. The passive impedance mismatch ring is a passive structural component that does not measure, supply power, store data, or require signal lines.

[0031] S3. The progressively decoupled anchor bolt 10 is installed in the surrounding rock borehole, so that its shallow anchoring section 5 and deep anchoring section 7 are anchored to the surrounding rock. The decoupling pressure relief section 6 forms a controllable pressure relief relationship with the anchoring agent through the decoupling sleeve 9, isolation material or anti-friction interface, so that controllable pressure relief or slippage can be generated when the deformation of the surrounding rock reaches the preset conditions. After the progressively decoupled anchor bolt 10 is installed stably, the detachable external ultrasonic measuring device 1 is used to contact the exposed thread section 2 of the progressively decoupled anchor bolt 10 to collect the reference multi-interface echo signals of longitudinal wave and transverse wave. During roadway excavation, mining disturbance or operation, ultrasonic pulses are excited from the exposed end of the progressively decoupled anchor bolt and echo signals from the first passive impedance mismatch ring 8, the second passive impedance mismatch ring 11 and the rod end are received. Among them, such as Figure 3 As shown, the detachable external ultrasonic measuring device 1 includes a sealed housing 14, a positioning sleeve 27, an end-face fixed acoustic coupling assembly, an ultrasonic excitation receiving assembly, a pulse excitation and echo receiving unit, a coupling clamping positioning assembly, and a signal acquisition and processing unit. The end-face fixed acoustic coupling assembly and the ultrasonic excitation receiving assembly are sequentially and axially arranged inside the sealed housing 14, which is used for protection, positioning, and pre-tightening. The positioning sleeve 27 is located on the bottom outer side of the sealed housing 14 and is provided with an axial limiting step and a circumferential anti-rotation key. An O-ring seal 26 is provided between the positioning sleeve 27 and the bottom of the sealed housing. The O-ring seal 26 is only used for external sealing and avoids the main acoustic coupling path. The end-face fixed acoustic coupling assembly includes a front-end fixed coupling head 24 and an end-face coupling base 22. The front-end fixed coupling head 24 is coaxially fixed to the gradually decoupling anchor 10 through a permanently cured acoustic coupling layer 25. On the exposed threaded section 2; the end face coupling base 22 is coaxially fixed to the top of the front fixed coupling head 24; the end face fixed acoustic coupling assembly remains fixed within the monitoring cycle of the same anchor rod and is incorporated into the reference echo or acoustic elastic calibration as part of the fixed acoustic path; the ultrasonic excitation receiving assembly is set on the top of the end face coupling base 22 and repeatedly pressed and engaged with the end face fixed acoustic coupling assembly; the ultrasonic excitation receiving assembly is acoustically coupled to the exposed end face of the gradually decoupled anchor rod 10 through the end face fixed acoustic coupling assembly and is detached from it after the measurement is completed; the coupling clamping positioning assembly is set on the outside of the bottom of the positioning sleeve 27 and threadedly connected to the sealing shell 14, and is used to apply a predetermined clamping force so that the ultrasonic excitation receiving assembly is axially clamped, circumferentially oriented and repeatedly positioned relative to the end face fixed acoustic coupling assembly; in this invention, the coupling clamping positioning assembly is an anti-loosening nut 28 with an anti-loosening structure. The pulse excitation and echo receiving unit is connected to the ultrasonic excitation receiving component through the multi-channel shielded cable connector 13, and respectively completes the transmission and echo reception of longitudinal wave and transverse wave ultrasonic pulses; the signal acquisition and processing unit is connected to the pulse excitation and echo receiving unit, and is used to acquire echo waveforms, extract the arrival time of each reflection interface, and call the acoustoelastic calibration parameters to complete the segmented axial force inversion and structural surface state identification.

[0032] Specifically, the ultrasonic excitation receiving assembly includes a multi-channel shielded cable connector 13, a small shielded PCB 15, a support plate 16, a constant force preload spring assembly 17, a floating conductive plate or elastic electrode 18, a split backing 19, a longitudinal wave piezoelectric transducer 20, a transverse wave piezoelectric transducer 21, and a temperature sensing unit 23; the longitudinal wave piezoelectric transducer 20 is a thickness vibration mode piezoelectric transducer, and the transverse wave piezoelectric transducer 21 is a shear vibration mode piezoelectric transducer with a mechanical positioning mark in the shear direction, and the two are arranged side by side on the same plane above the end face coupling base; the split backing 19 includes independent backings or damping blocks respectively disposed above the longitudinal wave piezoelectric transducer 20 and the transverse wave piezoelectric transducer 21, and an insulating layer is provided between the two. An insulating groove or damping wall is used to reduce mechanical crosstalk between the longitudinal wave channel and the transverse wave channel; the constant force preload spring assembly 17 applies a uniform axial preload to the longitudinal wave piezoelectric transducer 20 and the transverse wave piezoelectric transducer 21 through a floating conductive plate or elastic electrode 18, so that the two maintain reliable acoustic contact with the end face fixed acoustic coupling assembly; the small shielded PCB 15 is set above the constant force preload spring assembly 17 through a support plate 16, and is connected to the longitudinal wave channel, the transverse wave channel and the temperature sensing channel respectively, and its top is led out from the middle of the upper end of the sealed shell 14 through a multi-channel shielded cable connector 13; the temperature sensing unit 23 is set near the end face fixed acoustic coupling assembly or the exposed end face of the anchor rod, and forms thermal contact with it.

[0033] During measurement, the ultrasonic excitation receiving component is mounted on the end-face fixed acoustic coupling component of the corresponding exposed end of the anchor rod. The positioning sleeve 27 ensures it is coaxial or nearly coaxial with the anchor rod axis, and the anti-loosening nut 28 applies a predetermined clamping force. The longitudinal wave piezoelectric transducer 20 and the transverse wave piezoelectric transducer 21 respectively input longitudinal and transverse wave ultrasonic pulses to the exposed end of the anchor rod via the end-face fixed acoustic coupling component, and receive echo signals from the first passive impedance mismatch ring 8, the second passive impedance mismatch ring 11, and the rod end. The small shielded PCB 15 is connected to the longitudinal wave channel, the transverse wave channel, and the temperature sensing channel, and is connected to the pulse excitation and echo receiving unit via a multi-channel shielded cable connector 13. The temperature sensing unit 23 is positioned near the end-face coupling base 22 or the exposed end face of the anchor rod, forming thermal contact with it. It is used to obtain the end temperature during measurement and provide temperature correction parameters for the longitudinal and transverse wave travel time differential inversion. After measurement, the locking nut 28 is released, and the ultrasonic excitation receiving component is detached from the end-face fixed acoustic coupling component, while the end-face fixed acoustic coupling component remains on the exposed end of the anchor bolt. The ultrasonic excitation receiving component can be moved to another gradually decoupled anchor bolt 10 with a pre-set end-face fixed acoustic coupling component for inspection. For each anchor bolt, a reference echo signal is acquired in the initial stable state; during subsequent tunneling, blasting, mining disturbance, or operation, the echo signal is repeatedly acquired at a preset cycle and compared with the reference signal.

[0034] As non-limiting preferred parameters of the present invention, the center frequencies of the longitudinal wave piezoelectric transducer 20 and the transverse wave piezoelectric transducer 21 are preferably 0.5~5MHz, the ultrasonic pulse sampling rate is preferably 50~200MHz, and the single measurement signal is averaged multiple times (e.g., 64 or 128 times) to improve the signal-to-noise ratio; the end-face coupling base 22 is preferably a metal base that matches the acoustic impedance of the anchor rod body, and is cured and bonded to the exposed end face of the anchor rod through an epoxy-based or metal-based permanent acoustic coupling layer; the temperature sensing unit 23 is preferably a Pt100, a thermistor, or an integrated temperature sensor, and the temperature measurement resolution is preferably not less than 0.1℃. These parameters are only exemplary preferred values, and those skilled in the art can adjust them according to the anchor rod length, rod material, and site environment.

[0035] This measurement method does not require pre-embedded sensors during anchor bolt construction, nor does it require long-term cabling, data acquisition, or power supply systems for each anchor bolt. For batches of progressively decoupled anchor bolts with passive impedance mismatch rings installed in roadways, manual inspection, semi-automatic inspection, or fixed-period sampling inspection can be used to measure each bolt individually, thereby significantly expanding the axial force sensing range of the anchor bolts.

[0036] After the measurement is completed, the ultrasonic excitation receiving component, the pulse excitation and echo receiving unit, and the signal acquisition and processing unit can be detached from the anchor rod and moved to another gradually decoupled anchor rod equipped with the end face fixed acoustic coupling component for measurement.

[0037] S4. Based on the arrival time difference of adjacent reflected echoes, extract the segmented ultrasonic travel times of the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section; like Figure 4 As shown, after the detachable external ultrasonic measuring device emits an ultrasonic pulse from the exposed end of the anchor bolt, the ultrasonic wave propagates along the bolt and generates echoes at the first passive impedance mismatch ring 8, the second passive impedance mismatch ring 11, and the bolt end, respectively. Let T1 be the arrival time of the echo from the first passive impedance mismatch ring 8 after deducting equipment delay, T2 be the arrival time of the echo from the second passive impedance mismatch ring 11, and T be the arrival time of the echo from the bolt end. e Then the one-way travel times of the shallow anchorage section 5, the decoupling pressure relief section 6, and the deep anchorage section 7 are respectively: τ s =T1 / 2,τ d =(T2 T1) / 2,τ f =(Te T2) / 2; Calculate the segmented travel time τ of the P-wave separately for the P-wave and S-wave according to the above relationship. p,s τ p,d τ p,f and the segmented travel time τ of the transverse wave S,s τ S,d τ S,f ; The segmented travel time τ of the P-wave is obtained by calculating the P-wave and S-wave separately according to the above relationship. p,s τ p,d τ p,f and the segmented travel time τ of the transverse wave S,s τ S,d τ S,f Unlike conventional ultrasonic force measurement that only uses the echo from the rod end to obtain the average travel time of the entire rod, this invention uses two passive impedance mismatch rings to divide the entire anchor rod into three measurable segments, thereby obtaining segmental axial force information.

[0038] S5. Based on the acoustic elastic calibration relationship, the ultrasonic travel time variation of each segment is inverted into the average axial force of each segment, forming the segmented axial force distribution vector of the gradually decoupled anchor and its temporal evolution; The inversion of the average axial force for each segment includes: temperature calibration and elastic loading calibration of the same type of progressively decoupled anchor bolts to obtain the longitudinal wave temperature coefficient, transverse wave temperature coefficient, longitudinal wave stress coefficient, and transverse wave stress coefficient for each segment; for the k-th segment, k∈{s, d, f}, the acoustic elastic equation is solved simultaneously using the relative changes in longitudinal wave travel time and transverse wave travel time to weaken or eliminate temperature disturbances, thus obtaining the average stress change Δσ for the k-th segment. k And by N k =A k (σ k0 +Δσ k The average axial force N of the k-th segment is obtained. k A k Let σ be the cross-sectional area of ​​the k-th segment of the rod. k0 Let be the axial stress of the kth segment under the reference state.

[0039] When the observed slope between the relative changes in the longitudinal wave travel time and the relative changes in the transverse wave travel time of any segment deviates from the elastic calibration slope of that segment by more than a preset threshold, the corresponding segment is identified as entering a yielding or decoupling pressure relief state. After entering the yielding or decoupling pressure relief state, the stress change and plastic elongation of that segment are separated by combining material constitutive constraints, loading history constraints, or temperature gradual change constraints at adjacent moments.

[0040] During the elastic phase, temperature calibration and elastic loading calibration are performed on anchor bolts of the same model to obtain the longitudinal wave temperature coefficient K for each segment. TL,k Shear wave temperature coefficient K TS,k Longitudinal wave stress coefficient K σL,k and shear wave stress coefficient K σS,k , where k∈{s, d,f}. The relative changes in the travel times of the longitudinal and transverse waves in the k-th segment satisfy the following acoustic elastic relationship: Δτ L,k / τ L,k0 = K σL,k ·Δσ k + K TL,k ·ΔT k ; Δτ S,k / τ S,k0 = K σS,k ·Δσ k + K TS,k ·ΔT k .

[0041] Combining the above two equations can weaken or eliminate the influence of the temperature term, yielding the average stress change Δσ for the k-th segment. k And further obtain the piecewise average axial force N k = A k ·(σ k0 + Δσk ); where A k Let σ be the cross-sectional area of ​​the k-th segment of the rod. k0 Let ΔT be the stress of the k-th segment under the reference state. k This represents the temperature change relative to the baseline state.

[0042] When a segment of the anchor bolt enters the yielding, decoupling, or slipping stage, the ultrasonic travel time variation also includes the influence of plastic elongation. This invention identifies the elasto-plastic transition point by the deviation of the elastic characteristic slope of the relative changes in the travel time of longitudinal and transverse waves: when the observed slope deviates from the elastic calibration slope by more than a preset threshold, the corresponding segment is determined to have entered a yielding or decoupling yielding state; after entering the yielding or decoupling yielding state, stress changes and plastic elongation are separated by combining material constitutive constraints, loading history constraints, or gradual temperature change constraints at adjacent moments. The plastic elongation Δl of the decoupling yielding segment... p,d Its growth rate is an important characteristic for identifying the activity level of hidden hard structural surfaces.

[0043] S6. Based on the segmented axial force distribution vector in the initial stable state, calculate at least one of the following characteristic quantities: segmented axial force increment, inter-segment axial force difference, inter-segment axial force difference ratio, deep and shallow anchorage segment axial force ratio, decoupling segment load sharing rate, and decoupling segment plastic elongation. Based on this, identify the section where the hidden rigid structural surface and the gradually decoupling anchor meet. The segmented axial force distribution vector N(t) is constructed based on the average axial force of the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section. s (t), N d (t), N f [(t)], where N s (t), N d (t), N f (t) represents the average axial force in the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section, respectively; based on the segmented axial force at the initial stable time t0, the following characteristic quantity is defined: segmented axial force increment ΔN j (t)=N j (t) N j (t0), j∈{s, d, f}; inter-segment axial force difference D sd (t)=|N s (t) N d (t)|,D d f(t) = |N d (t) N f (t)|;Ratio of axial force difference between segments R sd (t)=D sd (t) / (D df (t)+ε); R ratio of axial force in deep and shallow anchorage sectionssf (t)=N s (t) / (N f (t)+ε); Load sharing rate of the decoupling section η d (t)=N d (t) / (N s (t)+N d (t)+N f (t)+ε); and the plastic elongation Δl of the decoupling compression section. p,d (t); where ε is a constant to prevent the denominator from being zero; This step also includes constructing the shallow anchorage segment activity score Q separately. S Decoupling and pressure segment activity score Q d and deep anchorage section activity score Q f : Q s = a1·|ΔN s (t)| + a2·D sd (t) + a3·|dN s (t) / dt|; Q d = b1·|ΔN d (t)| + b2·D sd (t) + b3·D df (t) + b4·η d (t) + b5·Δl p,d (t); Q f = c1·|ΔN f (t)| + c2·D df (t) + c3·|dN f (t) / dt|; Wherein dN s (t) / dt and dN f (t) / dt represent the axial force growth rates for the shallow and deep anchorage sections, respectively; a1~a3, b1~b5, and c1~c3 are non-negative weighting coefficients determined by indoor calibration tests, numerical simulations, or field initial stabilization period data; Q s Q d Q f The section that achieves the maximum value is determined to be the section where the hidden hard structural surface intersects with the gradually decoupled anchor or the section with the strongest activity influence; when two adjacent activity scores increase simultaneously and exceed the preset threshold, it is determined that the hidden hard structural surface is located near the boundary of adjacent segments or its extended leading edge is migrating across segments.

[0044] like Figure 5As shown, the identification of concealed hard structural surfaces in this invention does not directly rely on the displacement of the surrounding rock surface, nor is it a simple comparison of ultrasonic waveforms. Instead, it utilizes the change in segmented axial force distribution over time. For a progressively decoupled anchor bolt with three segments—a shallow anchoring segment, a decoupling pressure relief segment, and a deep anchoring segment—the segmented axial force distribution vector is defined as: N(t) = [N s (t), N d (t), N f (t)], Where, N s (t) represents the average axial force in the shallow anchorage section, N. d (t) represents the average axial force in the decoupled pressure relief section, N f (t) represents the average axial force in the deep anchorage section. Using the initial stable state N(t0) as a reference, the axial force increment ΔN in each segment is calculated. j (t) =N j (t)-N j (t0), j∈{s, d, f}.

[0045] When a concealed rigid structural surface intersects with or is within the influence range of the anchor bolt and undergoes opening, shear slip, or expansion, it alters the load transfer path between adjacent surrounding rock blocks and the anchor bolt, causing non-uniform variations in the axial force of the anchor bolt segments. For example, when the structural surface is near the shallow anchoring segment 5, the axial force increment in the shallow anchoring segment 5 and the axial force difference between the shallow and decoupling segments are more sensitive; when the structural surface is near the decoupling relief segment 6, the load sharing rate and plastic elongation of the decoupling segment are more sensitive; and when the structural surface is near the deep anchoring segment 7, the axial force increment in the deep anchoring segment 7 and the axial force difference between the decoupling and deep segments are more sensitive.

[0046] This invention extracts the following feature quantity: inter-segment axial force difference D sd =|N s N d |,D df =|N d N f |;Ratio of axial force difference between segments R sd =D sd / (D df +ε); Axial force ratio of deep and shallow anchorage sections R sf =N s / (N f +ε); Decoupling section load sharing rate η d =N d / (N s +N d +N f +ε); Plastic elongation Δl in the decoupling section p,d ; and the axial force growth rate dN of each segmentj / dt, j∈{s, d, f}. Where ε is a small positive constant to prevent the denominator from being zero (e.g., taking 10 of the full-scale value under the same dimensions). -3 ~10 -2 ).

[0047] To determine the section where the structural plane is located, the activity score Qs for shallow anchorage section 5, the activity score Qd for decoupling and pressure relief section 6, and the activity score Qf for deep anchorage section 7 can be calculated separately: Q s = a1·|ΔN s (t)| + a2·D sd (t) + a3·|dN s (t) / dt|; Q d = b1·|ΔN d (t)| + b2·D sd (t) + b3·D df (t) + b4·η d (t) + b5·Δl p,d (t); Q f = c1·|ΔN f (t)| + c2·D df (t) + c3·|dN f (t) / dt|; In the formula, a1~a3, b1~b5, and c1~c3 are non-negative weighting coefficients determined through indoor experiments, numerical calculations, or field calibration. If Q s If Q is the largest, then the structural surface activity mainly affects the shallow anchorage section 5; if Q d If the maximum value is found, then the structural surface activity mainly affects the decoupling pressure relief segment 6; if Q... f If the maximum value is reached, it is determined that the structural surface activity mainly affects the deep anchorage segment 7. If two adjacent scores increase simultaneously and both exceed the preset threshold, it is determined that the structural surface is located near the boundary of adjacent segments or that the leading edge of the structural surface expansion is migrating across segments.

[0048] S7. Based on the evolution of the segmented axial force distribution vector and its characteristic quantities over time, the active state of the hidden hard structural surface is identified as one of the following: stable state, micro-activated state, extended state, or slip or penetration risk state. This invention classifies the active states of hidden rigid structural surfaces into stable states, micro-activated states, extended states, and slip or penetration risk states, and identifies them according to the following rules: when |ΔN s (t)|、|ΔN d (t)|、|ΔN f (t)|、D sd (t), Ddf When both (t) are below the stability threshold, it is determined to be a stable state; when D sd (t), D df (t) or its growth rate exceeds the micro-activation threshold, and the decoupling allows for plastic elongation Δl in the compression section. p,d (t) When there is no sustained increase, it is judged to be in a micro-activation state; when the difference in axial force between sections continues to increase and the ratio of axial force between deep and shallow anchorage sections R sf (t) When a sustained shift occurs, or when the segment corresponding to the maximum activity score migrates over time, it is determined to be in an extended state; when the load sharing rate η of the decoupling segment... d (t) exceeds the preset threshold, and the plastic elongation Δl of the decoupling section is reduced. p,d When (t) or its growth rate continues to increase, it is judged as a slip or penetration risk state; the stability threshold, micro-activation threshold, expansion threshold, and slip or penetration risk threshold can be determined by indoor structural surface shear slip test, progressive decoupling anchor pull-out test, field initial stabilization period statistics, or historical instability sample training. For field applications, the mean of each characteristic quantity in the initial stabilization period plus several times the standard deviation can be used as the first-level stability threshold, and the second-level (micro-activation, expansion) and third-level (slip or penetration risk) thresholds can be set according to the calibration results of the anchor yield, decoupling initiation, and slip stages. The warning level corresponds one-to-one with the activity status, and can be combined with the retest cycle for suggested output, such as Figure 6 As shown.

[0049] S8. Based on the location, activity status and temporal changes of the hidden hard structural surface, output the early warning level, and integrate the identification results of each anchor when multiple gradually decoupled anchors participate in the measurement to form the extended range or extended front edge of the hidden hard structural surface. like Figure 7 As shown, multiple progressively decoupled anchor bolts with passive impedance mismatch rings are arranged along the cross-section or direction of the roadway. Each anchor bolt serves both a support function and, when needed, its segmental axial force distribution can be read by a detachable external ultrasonic measuring device. Since there is no need to install sensors, lay cables, and establish power supply systems for each anchor bolt for extended periods, this scheme is suitable for expanding the measurement coverage area.

[0050] For each anchor bolt, the system records the anchor bolt number, installation location, installation angle, segment length, passive impedance mismatch ring location, reference travel time, and all previous measurement results. The structural surface identification module maps the structural surface activity segment and activity score output by each anchor bolt to spatial coordinates, and reconstructs the hidden rigid structural surface extension leading edge, extension direction, and activity intensity distribution through interpolation, clustering, or surface fitting methods.

[0051] When multiple anchor bolts in similar spatial locations exhibit an increase in the inter-segment axial force difference in the same direction, an increase in the load sharing rate of the decoupled segment, or an increase in plastic elongation, the system determines that there is a risk of hidden rigid structural surface expansion in the area and raises the warning level; at the same time, it outputs a corresponding retesting cycle suggestion based on the warning level.

[0052] This invention also proposes a monitoring and early warning system for implementing the above method, comprising: Progressive decoupling anchor measurement carrier: progressive decoupling anchor for large deformation control in deep hard rock tunnels and passive impedance mismatch rings set at segment boundaries; External ultrasonic measurement module: used to excite and receive multi-interface ultrasonic echoes from the exposed end of the anchor bolt without removing the anchor bolt or embedding sensors inside the anchor bolt; Segmented travel time extraction module: used to extract the ultrasonic travel time of each segment based on the echo arrival time of the passive impedance mismatch ring and the rod end; Segmented axial force inversion module: used to invert the ultrasonic travel time variation of each segment into the average axial force of each segment, and form the segmented axial force distribution vector; Structural surface identification module: used to identify the segment and activity state of the hidden rigid structural surface based on the segmented axial force distribution vector and its temporal changes; Early warning output module: used to output early warning level, anchor bolt number, active section of structural surface, and recommended retest cycle.

[0053] The external ultrasonic measurement module is a portable inspection and measurement device that can be repeatedly engaged with the pre-set end face fixed acoustic coupling components of different exposed ends of anchor bolts through mechanical clamping seats, magnetic clamping seats, nut end face clamps or hand-held clamping seats; the system establishes a database through anchor bolt numbers, installation positions and measurement times to form a segmented axial force distribution and hidden hard structural surface activity state diagram of anchor bolt groups at the roadway scale.

[0054] The present invention will be further illustrated below through specific embodiments: This embodiment targets deep hard rock mine roadways, where a progressively decoupling anchor bolt 10 is arranged at predetermined intervals on a typical large deformation cross-section. A passive impedance mismatch ring is installed at the junction of the shallow anchoring section 5 and the decoupling relief section 6, and at the junction of the decoupling relief section 6 and the deep anchoring section 7 of each anchor bolt. The ring is made of a tungsten-nickel-iron high-density alloy, with an acoustic impedance difference of approximately 40% compared to the steel anchor bolt body. The axial width of the ring is approximately 0.5 times the diameter of the anchor bolt body, and the radial thickness is approximately 0.08 times the diameter of the anchor bolt body, with rounded corners at both ends. The passive impedance mismatch ring is positioned on the outer periphery of the anchor bolt body using a combination of interference fit and durable acoustic coupling adhesive bonding.

[0055] After the anchor bolts are installed and reach initial stability, a set of end-face fixed acoustic coupling components, including a front-end fixed coupling head 24 and an end-face coupling base 22, is fixed to the exposed end face of each anchor bolt through a permanently cured acoustic coupling layer 25. A portable ultrasonic excitation receiving component is sequentially connected to the end-face fixed acoustic coupling component of each anchor bolt, and longitudinal and transverse wave pulses with a center frequency of 0.5~5MHz are synchronously transmitted and received. A single measurement is averaged 64 or 128 times as a reference echo signal for archiving.

[0056] During tunnel excavation and operation, inspection personnel used the same portable ultrasonic transducer to sequentially measure multiple anchor bolts within a cross-section. For any given anchor bolt, the system identified the echo arrival time of the first passive impedance mismatch ring 8, the second passive impedance mismatch ring 11, and the bolt end, according to τ. s =T1 / 2,τ d =(T2 T1) / 2,τ f =(Te Calculate the P-wave and S-wave travel times for the three segments respectively using T2) / 2; retrieve the P-wave temperature coefficient, S-wave temperature coefficient, P-wave stress coefficient, and S-wave stress coefficient corresponding to the anchor bolt model, and invert the average axial force N for each segment. s N d N f And form a segmented axial force distribution vector N(t) = [N s (t), N d (t), N f (t)].

[0057] When a certain anchor bolt experiences N d Continuously rising, η d Increase, Δl p,d Growth begins, and simultaneously, adjacent anchor bolts also exhibit decoupling and pressure relief sections. (Activity score S) d When the pressure increases, the system determines that the hidden rigid structural surface is crossing or affecting the decoupling pressure relief section 6, and the activity state changes from micro-activation to extended state; if subsequent Δl p,d The growth rate exceeds the risk threshold for slippage or penetration, and the load transfer in the shallow and deep anchorage sections 7 is significant (i.e., R). sf If a continuous offset occurs (t), the system will output the highest level warning and prompt the corresponding section to be re-measured or to take reinforcement and support measures.

[0058] The above embodiments demonstrate that the present invention does not simply measure the average axial force at the end of the anchor bolt, nor does it rely on a few pre-embedded sensor anchor bolts. Instead, it obtains the segmented axial force distribution of a batch of gradually decoupled anchor bolts through a passive segmented reflective interface and external ultrasonic inspection measurement. By utilizing the changes in the segmented axial force distribution, it inverts the location and activity state of the hidden hard structural surface, thereby achieving engineering-level identification and early warning of hidden hard structural surfaces in deep hard rock tunnels without weakening the bolt body or pre-embedding sensors.

[0059] All matters not covered in this invention are common knowledge.

[0060] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for segmented axial force measurement and structural surface early warning of externally mounted ultrasonic decoupled anchor bolts, characterized in that, The method includes the following steps: S1. Prepare for gradual decoupling of the anchor bolt; the gradually decoupling anchor bolt includes, along the axial direction, a shallow anchoring section, a decoupling pressure relief section, and a deep anchoring section in sequence; S2. A first passive impedance mismatch ring is set at the junction of the shallow anchoring section and the decoupling pressure relief section of the gradually decoupled anchor bolt, and a second passive impedance mismatch ring is set at the junction of the decoupling pressure relief section and the deep anchoring section of the gradually decoupled anchor bolt. S3. Install the progressively decoupled anchor bolt in the surrounding rock borehole, anchoring its shallow and deep anchor sections to the surrounding rock; after the progressively decoupled anchor bolt is installed stably, use a detachable external ultrasonic measuring device to contact the exposed end of the progressively decoupled anchor bolt to collect the reference multi-interface echo signals of longitudinal and transverse waves; and during roadway excavation, mining disturbance, or operation, excite ultrasonic pulses from the exposed end of the progressively decoupled anchor bolt and receive echo signals from the first passive impedance mismatch ring, the second passive impedance mismatch ring, and the end of the bolt. S4. Based on the arrival time difference of adjacent reflected echoes, extract the segmented ultrasonic travel times of the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section; S5. Based on the acoustic elastic calibration relationship, the ultrasonic travel time variation of each segment is inverted into the average axial force of each segment, forming the segmented axial force distribution vector of the gradually decoupled anchor and its temporal evolution; S6. Based on the segmented axial force distribution vector in the initial stable state, calculate at least one of the following characteristic quantities: segmented axial force increment, inter-segment axial force difference, inter-segment axial force difference ratio, deep and shallow anchorage segment axial force ratio, decoupling segment load sharing rate, and decoupling segment plastic elongation. Based on this, identify the section where the hidden rigid structural surface and the gradually decoupling anchor meet. S7. Based on the evolution of the segmented axial force distribution vector and its characteristic quantities over time, the active state of the hidden hard structural surface is identified as a stable state, a micro-activated state, an extended state, or a slip or penetration risk state. S8. Based on the location, activity status and temporal changes of the hidden hard structural surface, output the early warning level, and integrate the identification results of each anchor when multiple gradually decoupled anchors participate in the measurement to form the extended range or extended front edge of the hidden hard structural surface.

2. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 1, characterized in that: The passive impedance mismatch ring is a non-load-bearing ring-shaped acoustic marker pre-installed on the outer periphery of the segment boundary of the progressively decoupled anchor bolt. Its material acoustic impedance differs from that of the anchor bolt body material, so as to form identifiable segmented reflected echoes when ultrasonic waves propagate along the anchor bolt axis. The passive impedance mismatch ring is fixed to the anchor bolt segment boundary using one or a combination of interference fit, controlled temperature fit, durable acoustic coupling adhesive bonding, or external clamping. When the progressively decoupled anchor bolt body is made of steel, the passive impedance mismatch ring... The acoustic impedance of the metal, alloy, or metal-based composite material is selected with a difference of not less than a preset ratio between the acoustic impedance of the metal rod and that of the steel rod; the preset ratio is 30% to 50%; for brittle acoustic impedance materials, a ductile protective layer is provided on the outer periphery of the passive impedance mismatch ring or a metal-based composite structure is adopted; the axial width of the passive impedance mismatch ring is preferably 0.3 to 1.5 times the diameter of the anchor rod, the radial thickness is preferably 0.03 to 0.20 times the diameter of the anchor rod, and the two ends of the ring are provided with rounded or chamfered transition structures.

3. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 1, characterized in that: The detachable external ultrasonic measuring device includes a sealed outer shell, a positioning sleeve, an end-face fixed acoustic coupling assembly, an ultrasonic excitation receiving assembly, a pulse excitation and echo receiving unit, a coupling clamping positioning assembly, and a signal acquisition and processing unit; the end-face fixed acoustic coupling assembly and the ultrasonic excitation receiving assembly are axially arranged sequentially inside the sealed outer shell; the positioning sleeve is located on the outer side of the bottom of the sealed outer shell and is provided with an axial limiting step and a circumferential anti-rotation key, and an O-ring is provided between it and the bottom of the sealed outer shell; the end-face fixed acoustic coupling assembly includes a front-end fixed coupling head and an end-face coupling base; The front-end fixed coupling head is fixed to the exposed end face of the progressively decoupled anchor rod through a permanently cured acoustic coupling layer; the end face coupling base is coaxially fixed to the top of the front-end fixed coupling head; the ultrasonic excitation receiving component is disposed on the top of the end face coupling base and is acoustically coupled to the exposed end face of the progressively decoupled anchor rod through the end face fixed acoustic coupling component; the coupling clamping and positioning component is disposed on the outer side of the bottom of the positioning sleeve and is used to apply a predetermined clamping force; the pulse excitation and echo receiving unit is connected to the top of the ultrasonic excitation receiving component; the signal acquisition and processing unit is connected to the pulse excitation and echo receiving unit.

4. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 3, characterized in that: The ultrasonic excitation receiving assembly includes a multi-channel shielded cable connector, a small shielded PCB, a support plate, a constant force preload spring assembly, a floating voltage conductive plate or elastic electrode, a split backing, a longitudinal wave piezoelectric transducer, a transverse wave piezoelectric transducer, and a temperature sensing unit. The longitudinal wave piezoelectric transducer is a thickness vibration mode piezoelectric transducer, and the transverse wave piezoelectric transducer is a shear vibration mode piezoelectric transducer with a shear direction mechanical positioning mark. The two are arranged side-by-side on the same plane above the end-face coupling base. The split backing includes independent backings respectively positioned above the longitudinal wave piezoelectric transducer and the transverse wave piezoelectric transducer. A backing or damping block is provided, with an insulating isolation groove or damping isolation wall between them; the constant force preload spring group applies a uniform axial preload to the longitudinal wave piezoelectric transducer and the transverse wave piezoelectric transducer through a floating voltage plate or elastic electrode; the small shielded PCB is set above the constant force preload spring group through a support plate, and is connected to the longitudinal wave channel, the transverse wave channel and the temperature sensing channel respectively, and its top is led out from the middle of the upper end of the sealed shell through a multi-channel shielded cable connector; the temperature sensing unit is set near the end face of the fixed acoustic coupling component or the exposed end face of the anchor rod, and forms thermal contact with it.

5. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 1, characterized in that: In step S4, let the arrival time of the first passive impedance mismatch loop echo after deducting equipment delay be T1, the arrival time of the second passive impedance mismatch loop echo be T2, and the arrival time of the pole end echo be T. e Then the one-way travel time of the shallow anchorage section, the decoupling relief section, and the deep anchorage section are respectively: τ s =T1 / 2,τ d =(T2 T1) / 2,τ f =(Te T2) / 2; Calculate the segmented travel time τ of the P-wave separately for the P-wave and S-wave according to the above relationship. p,s τ p,d τ p,f and the segmented travel time τ of the transverse wave S,s τ S,d τ S,f ...

6. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 1, characterized in that: In step S5, the inversion of the average axial force of each segment includes: performing temperature calibration and elastic loading calibration on the same type of progressively decoupled anchor bolts to obtain the longitudinal wave temperature coefficient, transverse wave temperature coefficient, longitudinal wave stress coefficient, and transverse wave stress coefficient of each segment; for the k-th segment, k∈{s, d, f}, using the relative changes in longitudinal wave travel time and transverse wave travel time to simultaneously solve the acoustic elastic equation, weakening or eliminating temperature disturbances, and obtaining the average stress change Δσ of the k-th segment. k And by N k =A k (σ k0 +Δσ k The average axial force N of the k-th segment is obtained. k A k Let σ be the cross-sectional area of ​​the k-th segment of the rod. k0 The axial stress of the k-th segment under the reference state is used. When the observed slope between the relative changes in longitudinal wave travel time and the relative changes in transverse wave travel time of any segment deviates from the elastic calibration slope of that segment by more than a preset threshold, the corresponding segment is identified as entering the yield or decoupling pressure relief state. After entering the yield or decoupling pressure relief state, the stress change and plastic elongation of that segment are separated by combining material constitutive constraints, loading history constraints, or temperature gradual change constraints at adjacent times.

7. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 6, characterized in that: In step S6, a segmented axial force distribution vector N(t) = [N] is constructed based on the average axial forces of the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section. s (t), N d (t), N f [(t)], where Ns(t), Nd(t), and Nf(t) are the average axial forces in the shallow anchorage section, the decoupling pressure relief section, and the deep anchorage section, respectively; taking the segmented axial force at the initial stable time t0 as the benchmark, the following characteristic quantity is defined: segmented axial force increment ΔN j (t)=N j (t) N j (t0), j∈{s, d, f}; inter-segment axial force difference D sd (t)=|N s (t) N d (t)|,D df (t)=|N d (t) N f (t)|;Ratio of axial force difference between segments R sd (t)=D sd (t) / (D df (t)+ε); R ratio of axial force in deep and shallow anchorage sections sf (t)=N s (t) / (N f (t)+ε); Load sharing rate of the decoupling section η d (t)=N d (t) / (N s (t)+N d (t)+N f (t)+ε); and the plastic elongation Δl of the decoupling compression section. p,d (t); where ε is a constant to prevent the denominator from being zero.

8. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 7, characterized in that: Step S6 also includes constructing the shallow anchorage segment activity score Q. s Decoupling and pressure segment activity score Q d and deep anchorage section activity score Q f : Q s = a1·|ΔN s (t)| + a2·D sd (t) + a3·|dN s (t) / dt|; Q d = b1·|ΔN d (t)| + b2·D sd (t) + b3·D df (t) + b4·η d (t) + b5·Δl p,d (t); Q f = c1·|ΔN f (t)| + c2·D df (t) + c3·|dN f (t) / dt|; Where, dN s (t) / dt and d Nf (t) / dt represent the axial force growth rates for the shallow and deep anchorage sections, respectively; a1~a3, b1~b5, and c1~c3 are non-negative weighting coefficients determined by indoor calibration tests, numerical simulations, or field initial stabilization period data; Qs and Q d Q f The section that achieves the maximum value is determined to be the section where the hidden hard structural surface intersects with the gradually decoupled anchor or the section with the strongest activity influence; when two adjacent activity scores increase simultaneously and exceed the preset threshold, it is determined that the hidden hard structural surface is located near the boundary of adjacent segments or its extended leading edge is migrating across segments.

9. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 8, characterized in that: In step S7, the active states of the hidden hard structural surface are divided into stable state, micro-activated state, extended state, and slip or penetration risk state, and identified according to the following rules: when |ΔN s (t)|、|ΔN d (t)|、|ΔN f (t)|、D sd (t), D df When both (t) are below the stability threshold, it is determined to be a stable state; when D sd (t), D df (t) or its growth rate exceeds the micro-activation threshold, and the decoupling allows for plastic elongation Δl in the compression section. p,d (t) When no sustained growth is observed, it is determined to be in a micro-activation state; When the difference in axial force between sections continues to increase, the ratio of axial force between deep and shallow anchorage sections R sf (t) When a sustained shift occurs, or when the segment corresponding to the maximum activity score migrates over time, it is determined to be in an extended state; when the load sharing rate η of the decoupling segment... d (t) exceeds the preset threshold, and the plastic elongation Δl of the decoupling section is reduced. p,d When (t) or its growth rate continues to increase, it is determined to be a slip or breakthrough risk state.

10. The method for segmented axial force measurement and structural surface early warning of an external ultrasonic decoupled anchor bolt according to claim 9, characterized in that: In step S8, a patrol-style ultrasonic measurement is performed on multiple progressively decoupled anchor bolts with passive impedance mismatch rings on the roadway cross-section or roadway direction. The structural surface section, activity score, and activity status output by each anchor bolt are mapped to spatial coordinates. Interpolation, clustering, or surface fitting methods are used to reconstruct the expansion leading edge, expansion direction, and activity intensity distribution of the hidden hard structural surface.

Images