Low-frequency excitation and high-frequency impact coupling void lining test device and method

Abstract

The present invention provides a device and method for testing a debonded lining by coupling low-frequency excitation with high-frequency impact, which belongs to the technical field of tunnel instability monitoring and includes a lining loading system, a low-frequency excitation system, and a high-frequency impact system. The loading mechanism simulates the surrounding rock load borne by the lining in the circumferential direction, and can simulate the surrounding rock load borne by the lining by adjusting parameters such as the magnitude and direction of the loading force. The exciter, in conjunction with the power amplifier, can generate low-frequency and high-amplitude vibrations that match the axle load characteristics of the train, simulating the fatigue damage to the lining caused by long-term operation of the train. When the electric unhooker controls the drop hammer to detach from the truss and fall freely, a high-frequency transient impact force can be generated to simulate the transient load effect of falling rocks hitting the lining. The test device solves the difficult problems of unclear destruction mechanism and lack of prediction means of debonded linings through multi-physical field coupled loading, providing a complete technical chain for the structural safety of railway tunnels, with both academic value and engineering promotion significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel instability monitoring, and more specifically, relates to a hollow lining test device and method coupled with low-frequency excitation and high-frequency impact. Background Art

[0002] Due to the early construction period and the limitations of existing technology, some railways in my country suffer from the high shrinkage of No. 200 concrete and inadequate construction techniques. This results in insufficient compaction of the contact surface with the surrounding rock after pouring, ultimately leading to void defects. The void linings in railway tunnels are constantly subjected to the low-frequency, high-amplitude excitation of large axle loads and long train formations, as well as the high-frequency impact of falling rocks. This deteriorates the lining structure, leading to cracking in the voids and the potential for further collapse. Such sudden collapse can not only cause partial collapse of the tunnel, destabilizing the overall structure, but can also cause trains in operation to skid, threatening the lives of passengers.

[0003] Lining cracking is a gradual process. Repeated stresses, environmental changes, or other external loads accumulate until a critical point is reached, leading to sudden lining failure. When there is a void in the lining, the combined effects of low-frequency train excitation, surrounding rock pressure, and high-frequency rockfall can cause initially small cracks or loose areas to rapidly expand, leading to severe, sudden lining failure. The timing and extent of the failure are difficult to predict. Summary of the Invention

[0004] The purpose of the present invention is to provide a void lining test device that couples low-frequency excitation and high-frequency impact, simulating the combined effects of low-frequency train excitation, surrounding rock pressure and high-frequency impact of falling rocks to achieve the purpose of predicting lining response characteristics.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is to provide a void lining test device coupled with low-frequency excitation and high-frequency impact, comprising:

[0006] The lining loading system includes a main frame, a lining ring, and a loading mechanism. The lining ring and the loading mechanism are both arranged inside the main frame. The loading mechanism is arranged circumferentially of the lining ring to simulate the surrounding rock load in the circumferential direction of the lining.

[0007] A low-frequency excitation system, comprising a support beam, an exciter, and a power amplifier, wherein the support beam axially passes through the lining ring, the exciter is connected to the support beam, and the power amplifier is electrically connected to the exciter, for simulating low-frequency excitation of a train passing through the lining;

[0008] The high-frequency impact system includes a top frame body, a truss, an electric unhooker and a drop hammer. The top frame body is fixed to the top of the main frame body. The truss is set on the top of the top frame body through the electric unhooker. The drop hammer is set at the bottom of the truss and is located directly above the lining ring. The drop hammer is separated from the truss to impact the lining ring, which is used to simulate the high-frequency impact of falling rocks on the lining.

[0009] In a possible implementation, a monitoring system is further included, and the monitoring system includes:

[0010] A plurality of three-axis accelerometers are respectively arranged on the circumference of the inner wall of the lining ring, and the three-axis accelerometers are used to detect vibration signals of the lining ring in three directions;

[0011] A vibration analyzer is electrically connected to the plurality of three-axis accelerometers and is used to convert vibration signals into time-frequency domain signals to simulate the main frequency and main eigenvalue of the lining ring.

[0012] In a possible implementation, a plurality of jacks are sequentially provided at the bottom of the main frame along the length direction, and the lining ring is provided on the plurality of jacks.

[0013] In a possible implementation, the loading mechanism includes:

[0014] Multiple servo electric cylinders are arranged in the circumference of the lining ring, the outer end of the servo electric cylinder is fixed on the main frame, and the inner end of the servo electric cylinder is fixed with a rigid plate. The inner side surface of the rigid plate is provided with a nylon gasket pressed against the outer wall of the lining ring, and the inner side surface of the nylon gasket has a conformal surface adapted to the outer wall of the lining ring.

[0015] In a possible implementation, the vibration exciter is suspended at the lower end of the support beam through an elastic member, and the vibration exciter is located inside the lining ring and in the longitudinal projection area of ​​the lining ring.

[0016] In a possible implementation, sliding rods are longitudinally provided on both sides of the top frame body, sliding sleeves are respectively provided on both sides of the truss, the sliding sleeves slide in cooperation with the sliding rods on the same side, and the electric unhooking device is used to drive the truss to rise and fall.

[0017] The beneficial effects of the low-frequency excitation and high-frequency impact coupled debonding lining test device provided by the present invention are as follows: Compared with the prior art, the lining loading system's main frame is equipped with a lining ring and a loading mechanism. The loading mechanism is arranged circumferentially around the lining ring, simulating the surrounding rock load borne by the lining. By adjusting parameters such as the magnitude and direction of the loading force, the surrounding rock load borne by the lining can be simulated. In the low-frequency excitation system, a support beam axially extends through the lining ring. The exciter is connected to the support beam and, in conjunction with a power amplifier, can generate low-frequency, high-amplitude vibrations that match the train axle load characteristics, simulating the fatigue damage caused by long-term train operation to the lining. In the high-frequency impact system, the top frame is fixed to the top of the main frame, and the truss is installed at the top of the top frame via an electric unhooker. The drop hammer is located at the bottom of the truss and directly above the lining ring. When the electric unhooker controls the drop hammer to detach from the truss and freely fall, it generates a high-frequency transient impact force, simulating the transient load effect of falling rocks impacting the lining. These three systems work together to realize the multi-physical field coupling of "static loading of surrounding rock pressure + low-frequency excitation of train + high-frequency impact of falling rocks", highly restoring the complex stress environment faced by the lining in actual operation.

[0018] This test device, through the collaborative operation of multiple systems, can highly reproduce the actual complex stress environment of the lining. The lining loading system simulates surrounding rock pressure, the low-frequency excitation system generates low-frequency excitation from trains, and the high-frequency impact system simulates high-frequency impact from falling rocks. These three systems work together to achieve multi-physics field coupling of "static loading of surrounding rock pressure + low-frequency excitation from trains + high-frequency impact from falling rocks." This breaks through the limitations of traditional testing, achieves coordinated loading of low-frequency and high-frequency loads, fills a gap in coupling research, quantifies the effects of load time-series coupling, reduces operational safety risks, and reveals the probability distribution of lining block loss. Through multi-physics field coupled loading, this test device solves the problems of unclear failure mechanisms and lack of predictive methods for debonding linings, providing a complete technical chain for railway tunnel structural safety, with both academic value and engineering promotion significance.

[0019] The present invention also provides a method for testing hollow linings by coupling low-frequency excitation with high-frequency impact, which uses the hollow lining testing device coupled with low-frequency excitation with high-frequency impact, and includes the following steps:

[0020] S1. Make a steel mold in proportion, use the steel mold to cast the lining ring and install it in the main frame;

[0021] S2. Install a loading mechanism inside the main frame, which circumferentially compresses the lining ring to simulate the surrounding rock load around the lining.

[0022] S3. Install a vibration exciter on the support beam, the support beam axially penetrates the lining ring, and the vibration exciter is located inside the lining ring, and the vibration exciter is electrically connected to the power amplifier;

[0023] S4: Install the truss on the electric unhooking device on the top of the top frame body and install the drop hammer at the bottom of the truss;

[0024] S5: Turn on the vibrator to simulate the low-frequency excitation of a train passing through the lining, and disconnect the electric uncoupler to allow the inertia of the falling hammer to separate from the truss and impact the lining ring to simulate the high-frequency impact of falling rocks on the lining;

[0025] S6: Obtain single-factor data of low-frequency excitation or high-frequency shock, or obtain coupled data of low-frequency excitation and high-frequency shock.

[0026] In one possible implementation, in step S1, a 1:10 steel mold is produced through on-site measurement or actual drawings. According to the scaled model test, the elastic modulus is taken as 1 / 10 of the prototype concrete. After the lining ring is poured, it is cured indoors for 28 days to reach the standard compressive strength, and then the steel mold is removed.

[0027] In a possible implementation, in step S3, the power amplifier is connected to a digital signal source, the digital signal source is connected to a computer control device, and the output mode is two-channel synchronous output.

[0028] In a possible implementation, in step S4, the electric unhooker controls the truss to be raised and lowered in the top frame body, and replaces drop hammers of different masses to simulate impact forces of different magnitudes to erode the lining ring.

[0029] The beneficial effect of the debonding lining test method coupled with low-frequency excitation and high-frequency impact provided by the present invention is that: compared with the existing technology, the debonding lining test method coupled with low-frequency excitation and high-frequency impact uses the above-mentioned test device, and therefore has the same beneficial effects as the above-mentioned test device, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 A schematic structural diagram of a void lining test device coupled with low-frequency excitation and high-frequency impact provided by an embodiment of the present invention;

[0032] Figure 2 for Figure 1 A local enlarged view of point M in the middle.

[0033] In the picture:

[0034] 1. Main frame; 2. Lining ring; 3. Servo electric cylinder; 4. Rigid plate; 5. Nylon gasket; 6. Support beam; 7. Vibrator; 8. Power amplifier; 9. Top frame; 10. Truss; 11. Electric unhooker; 12. Drop hammer; 13. Slide rod; 14. Slide sleeve; 15. Power supply; 16. Three-axis accelerometer; 17. Vibration analyzer; 18. Jack. DETAILED DESCRIPTION

[0035] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] Unless otherwise explicitly defined, the use of terms such as "first," "second," or "third," etc., are intended to distinguish different objects rather than to describe a specific order.

[0037] Unless otherwise expressly defined, directional words such as the terms "center", "lateral", "longitudinal", "horizontal", "vertical", "top", "bottom", "inside", "outside", "up", "down", "front", "back", "left", "right", "clockwise", "counterclockwise", "high", "low" and the like indicating directions or positional relationships are based on the directions and positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction, so they cannot be understood as limiting the specific scope of protection of the present invention.

[0038] See also Figure 1, the debonding lining test device coupled with low-frequency excitation and high-frequency impact provided by the present invention is now described. The debonding lining test device coupled with low-frequency excitation and high-frequency impact includes a lining loading system, a low-frequency excitation system and a high-frequency impact system. The lining loading system includes a main frame 1, a lining ring 2 and a loading mechanism. The lining ring 2 and the loading mechanism are both arranged inside the main frame 1. The loading mechanism is arranged in the circumference of the lining ring 2 to simulate the surrounding rock load in the circumference of the lining; the low-frequency excitation system includes a support beam 6, an exciter 7 and a power amplifier 8. The support beam 6 axially passes through the lining ring 2, the exciter 7 is connected to the support beam 6, and the power amplifier 8 is electrically connected to the exciter 7 to simulate Low-frequency excitation of the train passing through the lining; the high-frequency impact system includes a top frame body 9, a truss 10, an electric uncoupler 11 and a drop hammer 12. The top frame body 9 is fixed to the top of the main frame body 1, and the truss 10 is set on the top of the top frame body 9 through the electric uncoupler 11. The drop hammer 12 is set at the bottom of the truss 10 and is located directly above the lining ring 2. The drop hammer 12 is separated from the truss 10 to impact the lining ring 2, which is used to simulate the high-frequency impact of falling rocks on the lining.

[0039] Compared to existing technologies, the present invention's debonding lining test device, which couples low-frequency excitation with high-frequency impact, features a lining ring 2 and a loading mechanism within the main frame 1 of the lining loading system. The loading mechanism is arranged circumferentially around the lining ring 2, simulating the surrounding rock loads borne by the lining. By adjusting parameters such as the loading force and direction, the surrounding rock loads borne by the lining can be simulated. In the low-frequency excitation system, a support beam 6 axially extends through the lining ring 2. An exciter 7 is connected to the support beam 6 and, in conjunction with a power amplifier 8, generates low-frequency, high-amplitude vibrations that match the characteristics of a train's axle load, simulating the fatigue damage to the lining caused by long-term train operation. In the high-frequency impact system, top frame 9 is fixed to the top of main frame 1, truss 10 is mounted on top of top frame 9 via electric unhooker 11, and drop hammer 12 is located at the bottom of truss 10, directly above lining ring 2. When electric unhooker 11 controls drop hammer 12 to free fall from truss 10, it generates a high-frequency transient impact force, simulating the instantaneous load effect of falling rocks impacting the lining. These three systems work together to achieve a multi-physics coupling of "static loading of surrounding rock pressure + low-frequency excitation by trains + high-frequency impact of falling rocks," highly recreating the complex stress environment faced by the lining in actual operation.

[0040] This test device, through the collaborative operation of multiple systems, can highly reproduce the actual complex stress environment of the lining. The lining loading system simulates surrounding rock pressure, the low-frequency excitation system generates low-frequency excitation from trains, and the high-frequency impact system simulates high-frequency impact from falling rocks. These three systems work together to achieve multi-physics field coupling of "static loading of surrounding rock pressure + low-frequency excitation from trains + high-frequency impact from falling rocks." This breaks through the limitations of traditional testing, achieves coordinated loading of low-frequency and high-frequency loads, fills a gap in coupling research, quantifies the effects of load time-series coupling, reduces operational safety risks, and reveals the probability distribution of lining block loss. Through multi-physics field coupled loading, this test device solves the problems of unclear failure mechanisms and lack of predictive methods for debonding linings, providing a complete technical chain for railway tunnel structural safety, with both academic value and engineering promotion significance.

[0041] See also Figure 1 The test device also includes a monitoring system, which includes multiple three-axis accelerometers 16 and a vibration analyzer 17. Multiple three-axis accelerometers 16 are arranged circumferentially along the inner wall of the lining ring 2. Multiple three-axis accelerometers 16 are connected in series in sequence and electrically connected to a power supply 15, which is fixed to the bottom of the inner wall of the lining ring 2. The vibration signals of the lining ring 2 in the horizontal, longitudinal, and vertical directions can be synchronously detected. The vibration analyzer 17 is electrically connected to the accelerometers. After receiving the signal, it uses Fourier transform to convert it into a time-frequency domain signal, separates the vibration energy distribution of different frequency components, and then obtains the main frequency and main eigenvalue of the lining ring 2. At the same time, a multi-dimensional database is constructed by combining the pressure value of the loading system and the output parameters of the exciter 7. The circumferentially distributed three-axis accelerometers 16 can cover areas with high incidence of air loss, accurately capture the vibration characteristics of the entire space, and avoid the limitations of single-point monitoring and the omission of one-way monitoring information. The time-frequency domain signal separation technology of the vibration analyzer 17 can quantitatively analyze the multi-physical field coupling response, and determine the degree of structural stability degradation by comparing it with the complete lining benchmark data; real-time tracking of changes in parameters such as main frequency and damping ratio can provide early warning of crack propagation, and identify signal mutations at the moment of block falling to trigger an alarm; monitoring data can also verify numerical models, correct parameters, and migrate the correspondence between vibration characteristics and disease severity established indoors to on-site monitoring, thereby realizing remote real-time monitoring of the risk of block falling in the void lining, reducing inspection costs and improving early warning efficiency.

[0042] Among them, the core function of Fourier transform is to decompose the time domain signal into the superposition of different frequency components. Its mathematical expression is: ;

[0043] f ( t ) is the time domain signal, F ( ω) is a frequency domain signal. Regarding the actual vibration signal, the triaxial accelerometer 16 collects the vibration displacement, velocity, or acceleration data of the lining ring 2 in the time dimension (time domain signal), which can be converted into energy distribution in the frequency dimension (frequency domain signal) by Fourier transform.

[0044] A triaxial accelerometer 16 monitors the lining ring 2's vibration signals in real time in the horizontal, vertical, and horizontal directions, generating time-domain waveforms (e.g., displacement-time curves). A vibration analyzer 17 first pre-processes the raw signals through filtering and denoising to eliminate environmental interference and high-frequency noise, ensuring signal accuracy.

[0045] The vibration analyzer 17 performs mathematical transformation on the time domain signal through discrete Fourier transform or fast Fourier transform FFT algorithm:

[0046] Time domain characteristics: reflect the changes in the instantaneous amplitude and waveform period of the vibration of lining ring 2 over time, such as the transient response to low-frequency excitation of a train or the impact of falling rocks.

[0047] Frequency domain characteristics: Decompose the time domain signal into sine / cosine components of different frequencies. Each frequency component corresponds to a specific amplitude and phase, thereby obtaining the frequency distribution of the signal (such as primary frequency, secondary frequency) and energy proportion.

[0048] Strictly speaking, the Fourier transform directly generates a frequency domain signal, but the vibration analyzer 17 can achieve a comprehensive display of "time-frequency domain signals" in the following way: combining the short-time Fourier transform (STFT) or wavelet transform, introducing the time dimension on the basis of frequency domain analysis, and generating a time-frequency diagram (such as the change of the spectrum over time), thereby simultaneously reflecting the frequency characteristics and time distribution of the signal. The main frequency (the frequency with the highest energy share) and the main eigenvalue (such as the damping ratio, resonant frequency) are extracted from the frequency domain signal, and their occurrence time in the time domain are associated to form multi-dimensional data of "time-frequency-energy". Using the Fourier transform to convert it into a time-frequency domain signal is essentially to obtain the frequency domain characteristics through the Fourier transform, and combine it with time series analysis to achieve the time-frequency coupled expression of the signal, that is, to obtain the "time-frequency domain signal" mentioned above.

[0049] See also Figure 1The bottom of the main frame 1 is equipped with multiple jacks 18 along its length, and the lining ring 2 is mounted on these jacks 18 to support and position the lining ring 2 and simulate boundary conditions. The lining ring 2 is placed on these jacks 18. By adjusting the height of the jacks 18, the horizontality and installation position of the lining ring 2 can be precisely adjusted to ensure that its axis remains coaxially aligned with the support beam 6 of the low-frequency excitation system and the impact point of the drop hammer 12 of the high-frequency impact system. The jacks 18 use a spiral or hydraulic drive method to provide stable vertical support force, simulating the contact state between the tunnel lining and the base rock in actual engineering. Similarly, the upper ends of the jacks 18 are also equipped with rigid plates 4 and nylon gaskets 5, so that the pressure of the jacks 18 acts on the nylon gaskets 5 through the rigid plates 4, and then evenly acts on the bottom of the lining ring 2. The fine-tuning function of the jacks 18 can eliminate installation errors of the lining ring 2, avoid uneven load transfer, and ensure the reliability of the test data. The influence of different base rock conditions on the vibration response of the lining ring 2 can be simulated by adjusting the support stiffness, such as simulating base degassing or weak surrounding rock scenarios. By controlling the lifting and lowering amplitudes of the jacks 18 at different positions, the uneven longitudinal stress of the lining ring 2 can be simulated, asymmetric support boundary conditions can be constructed, and the simulation capabilities of complex engineering scenarios can be expanded. The rigid support of the jacks 18 can stabilize the lining ring 2 to prevent it from displacement or overturning due to vibration or impact, while facilitating the rapid installation and disassembly of the lining ring 2 and improving test efficiency. In short, the jacks 18 ensure installation accuracy and test safety through precise adjustment and stable support, enhance the device's ability to reproduce the complex stress environment of the actual tunnel, and provide key support for studying the dynamic response of degassing linings under different base constraints.

[0050] The main frame 1 consists of two longitudinal beams, a bottom crossbeam, a top crossbeam, and two diagonal braces. The two longitudinal beams are arranged symmetrically. The bottom crossbeam is installed horizontally at the bottom of the two longitudinal beams, with the lining ring 2 installed above the bottom crossbeam. The top crossbeam is installed horizontally at the top of the two longitudinal beams, with an escape notch in the middle. The top frame 9 is installed at the upper end of the top crossbeam and located above the escape notch. The two diagonal braces are installed on the inner side of the top of the two longitudinal beams and connected obliquely to the lower end face of the top crossbeam. This structure adopts a symmetrical rigid frame design, with the bottom crossbeam supporting the lining ring 2 and the jack 18 system. The top crossbeam integrates the high-frequency impact system and ensures that the impact path of the drop hammer 12 is unobstructed through the avoidance gap. The diagonal brace, longitudinal beam and top crossbeam form a triangular support system, which enhances the torsional stiffness and overall stability of the top of the main frame 1, evenly distributes vertical and horizontal loads, suppresses structural torsion caused by eccentric loads, ensures that the loads of the loading mechanism, low-frequency excitation system and high-frequency impact system are accurately transferred to the lining ring 2, avoids the deformation of the main frame 1 itself interfering with the test results, and provides a high-strength and high-stability support system for the test device.

[0051] See also Figure 1 and Figure 2 The loading mechanism includes multiple servo electric cylinders 3. Multiple servo electric cylinders 3 are arranged on the circumference of the lining ring 2. The outer end of the servo electric cylinder 3 is fixed to the main frame 1, and the inner end of the servo electric cylinder 3 is fixed with a rigid plate 4. The inner side of the rigid plate 4 is provided with a nylon gasket 5 pressed against the outer wall of the lining ring 2. The inner side of the nylon gasket 5 has a conformal surface adapted to the outer wall of the lining ring 2. During the test, the servo electric cylinder 3 drives the piston rod to move axially through the computer control system, pushing the rigid plate 4 and the nylon gasket 5 to apply pressure to the lining ring 2 to simulate the annular load of the surrounding rock. The elastic compression characteristics of the nylon gasket 5 can convert the thrust into continuously distributed surrounding rock pressure. The compression amount is linearly related to the load. The pressure size and distribution pattern can be accurately controlled by real-time monitoring of the cylinder displacement and output force. The circumferential servo electric cylinders 3 can be loaded synchronously or independently, simulating uniform constraint in intact surrounding rock, as well as simulating voiding behind the lining by reducing local pressure. Pressure ratios can also be adjusted to simulate formation resistance coefficients of varying surrounding rock grades. The conformal surface of the nylon gasket 5 conforms to the lining ring 2, avoiding stress concentration associated with rigid loading. Its elastic deformation absorbs vibration and ensures uniform load transfer. The servo electric cylinders 3 feature high-precision displacement control and force feedback, recording pressure-displacement curves in real time and calibrating load parameters based on regulatory standards to ensure the engineering relevance of the test conditions. Furthermore, by removing portions of the servo electric cylinders 3 or reducing the loading force, local voiding zones can be created. This can be combined with other systems to study stress concentration effects under coupled loading. By replacing gasket materials with varying stiffness, the effects of varying surrounding rock stiffness can be simulated. This loading mechanism, through its rigid drive and flexible transmission mechanism, achieves precise control and diverse simulation of surrounding rock pressure, providing reliable support for studying the mechanical behavior of voided linings under multi-physics coupling, enhancing the engineering applicability and scientific value of the test results.

[0052] See also Figure 1The exciter 7 is suspended from the lower end of the support beam 6 by elastic members. The exciter 7 is located within the lining ring 2 and within its longitudinal projection. Two sets of elastic springs serve as the dynamic coil suspension device to maintain the exciter 7 in a suspended position. The support beam 6 axially extends through the lining ring 2 to form a rigid support axis, ensuring that the excitation direction is aligned with the axis of the lining ring 2. During operation, the power amplifier 8 drives the exciter 7 to vibrate. The excitation force is transmitted to the lining ring 2 through the elastic springs and support beam 6, simulating the low-frequency excitation of the train load. The elastic springs filter high-frequency noise, ensuring the purity of the low-frequency signal. The excitation force amplitude (maximum 200N) and frequency (covering the 0.1-10Hz train load frequency range) can be precisely adjusted using the digital signal source and power amplifier 8. The exciter 7 is located at the center of the longitudinal projection of the lining ring 2. The vibration energy is uniformly transmitted radially to all points on the inner wall, avoiding stress deviation caused by eccentric excitation. It also couples to generate a longitudinal vibration component, reproducing the three-dimensional vibration characteristics of the train. Elastic springs provide cushioning during startup and shutdown, preventing mechanical shock damage to the structure. The connecting rod nut and spring limiter suppress lateral deflection and ensure stability. The internal layout of the exciter 7 reduces energy transfer attenuation, making the micro-motion monitoring system more sensitive to low-frequency responses. The excitation timing can be independently controlled, facilitating the separation of multiple load influences. Through elastic suspension and central layout, this design achieves high purity, uniformity, and precise controllability of low-frequency excitation, providing reliable support for research on fatigue damage and coupling effects in debonded linings.

[0053] Specifically, support legs are fixedly connected at both ends of the support beam 6, and diagonal ribs are fixed between the support legs and the support beam 6, forming a rigid triangular frame structure of beams, legs, and ribs. The support beam 6 axially penetrates the lining ring 2 and is fixed to the main frame 1 through the support legs. The diagonal ribs are made of the same steel material as the support beam 6 and are welded or bolted to form triangular reinforcement ribs, which can enhance the rigidity and stability of the support system. This structure uses the triangular frame effect to quickly transmit the vibration load generated by the exciter 7 through the support beam 6, diagonal ribs, and support legs to the main frame 1, shortening the force transmission path and reducing vibration energy loss. At the same time, it suppresses the bending deformation, shear slip, and lateral swing of the support beam 6 under the action of the exciting force, ensuring that the excitation direction is consistent with the axis of the lining ring 2, and improving the vibration transmission efficiency and directional accuracy. The diagonal reinforcement can also share the stress concentration at the end of the support beam 6, reduce the risk of fatigue cracking, extend the fatigue life of the support system, and cooperate with the high-precision installation of the support legs to ensure the coaxiality of the support beam 6 and the axis of the lining ring 2, improve the consistency and repeatability of multiple sets of test data, and allow the support beam 6 to be quickly disassembled and reassembled, shortening the test preparation time.

[0054] See also Figure 1Slide rods 13 are longitudinally arranged on both sides of the top frame body 9, and sliding sleeves 14 are respectively arranged on both sides of the truss 10. The sliding sleeves 14 slide in conjunction with the slide rods 13 on the same side, and the electric unhooker 11 is used to drive the truss 10 up and down. In this structure, the slide rods 13 and the sliding sleeves 14 form a vertical sliding pair. The steel cable of the electric unhooker 11 is driven by a motor to drive the truss 10 up and down along the slide rods 13, and the vertical distance between the drop hammer 12 and the arch of the lining ring 2 can be adjusted. The rigid guidance of the slide rods 13 and the sliding sleeves 14 ensures that the lateral displacement error of the truss 10 is smaller when it is raised and lowered, and the impact point does not deviate too much from the center of the arch, ensuring the vertical transmission of the impact load. By adjusting the mass and drop height of the drop hammer 12, the impact energy gradient can be precisely controlled to simulate rockfall impacts of different scales; the electric unhooker 11 supports the truss 10 to stay at any position within a specific stroke, which can simulate rockfalls at different rock formation heights.

[0055] Specifically, the electric unhooker 11 includes a motor and a pulley assembly. The controller sends instructions to control the forward and reverse rotation of the motor, which drives the pulley assembly to retract and release the steel cable. The steel cable connects to the top of the truss 10 and then pulls the truss 10 up and down along the slide rod 13, precisely adjusting the vertical distance between the drop hammer 12 and the arch of the lining ring 2. Remote control avoids the risks of manual operation, and supports computer-preset multiple sets of height parameters to achieve one-click working mode switching, improving test efficiency. The electric unhooker 11 can control drop hammers 12 of different masses to impact from different heights. Through automated control and precise transmission, it provides a reliable height adjustment method for the high-frequency impact system, enhancing the test device's ability to simulate impact loads in multiple scenarios.

[0056] Preferably, a mounting slot is provided at the upper end of the drop hammer 12, a mounting column is fixedly provided at the middle part of the lower end of the truss 10, an elastic end is provided at the end of the mounting column, and the elastic end is interference fit in the mounting slot. When the truss 10 is separated from the electric unhooker 11 and descends to the bottom, it stops instantly, while the drop hammer 12 continues to move downward due to inertia. At this time, the mounting slot of the drop hammer 12 generates a downward shear force on the elastic end. When the force exceeds the friction force of the interference fit, the drop hammer 12 is separated from the elastic end and impacts the arch of the lining ring 2 in a free fall state.

[0057] Based on the same inventive concept, the present invention also provides a hollow lining test method coupled with low-frequency excitation and high-frequency impact, which uses the above-mentioned hollow lining test device coupled with low-frequency excitation and high-frequency impact, including the following steps:

[0058] S1. Make a steel mold in proportion, use the steel mold to cast the lining ring 2 and install it in the main frame 1.

[0059] A 1:10 scale steel mold is made according to on-site measurements or design drawings, a mixture of cement and gravel is prepared in a certain proportion, and the lining ring 2 model is cast. After 28 days of indoor curing, the lining ring 2 reaches the standard compressive strength. The steel mold is removed and the lining ring 2 is installed on the jack 18 of the bottom beam of the main frame 1. The horizontality and installation height are adjusted by the jack 18 to ensure that the axis of the lining ring 2 is coaxial with the support beam 6 and the impact point of the drop hammer 12.

[0060] Scaled models, combined with similarity ratio theory (parameters such as elastic modulus and load are scaled proportionally), significantly reduce the labor and material costs of prototype testing while ensuring test accuracy. For example, the load on vibrator 7 was reduced from 1kN in the prototype to 200N. Standardized molds and curing processes ensured the consistency of the lining ring 2 model and improved the comparability of multiple test data.

[0061] S2. A loading mechanism is installed in the main frame 1. The loading mechanism presses the lining ring 2 circumferentially to simulate the surrounding rock load in the circumferential direction of the lining.

[0062] Multiple servo electric cylinders 3 are circumferentially mounted on the main frame 1. Nylon gaskets 5 with conformal surfaces compress the outer wall of the lining ring 2 from the inside. These servo electric cylinders 3 integrate high-precision pressure sensors, enabling real-time pressure data collection from the object or equipment being measured. Complex algorithms are employed to rapidly and accurately analyze and process the massive amounts of collected data, automatically calculating key pressure measurement indicators such as peak pressure, average pressure, and pressure fluctuation range. A computer control system drives the servo electric cylinders 3 axially. The compression of the nylon gaskets 5 is adjusted based on the formation resistance coefficients for Grades III to V surrounding rock, as specified in the "Code for the Design of Railway Tunnels." For example, a compression of 0.5 to 5 mm corresponds to different rock grades. This simulates the circumferential rock pressure distribution of the lining, ensuring uniform or localized degassing. The nylon gaskets 5 have a tensile modulus of 25.5-27.5 MPa and a flexural modulus of 2000-3000 MPa.

[0063] The flexible nylon gasket 5 and conformal surface design ensure uniform load transfer, avoiding stress concentration caused by rigid loading and faithfully recreating the contact characteristics between the surrounding rock and the lining. Independently controlled servo electric cylinders 3 can quickly simulate localized voiding scenarios, such as unloading a 60° range within the vault, providing a foundation for studying stress concentration in voiding areas under coupled loading.

[0064] S3. Install the vibrator 7 on the support beam 6. The support beam 6 axially penetrates the lining ring 2 and positions the vibrator 7 inside the lining ring 2. The vibrator 7 is electrically connected to the power amplifier 8.

[0065] Vibrator 7 is suspended by elastic springs from the lower end of support beam 6, located at the center of the longitudinal projection of lining ring 2. Support beam 6 is secured at both ends by support legs with diagonal reinforcement to ensure that the vibration direction of vibrator 7 is aligned with the axis of lining ring 2. Vibrator 7 is connected to a power amplifier 8 and a digital signal source. It can input signals such as sine waves and on-site train vibration waveforms, with frequencies of 0.1 to 10 Hz and amplitudes of 0 to 200 N.

[0066] The elastic suspension system filters high-frequency noise (purity >80dB) and ensures the accuracy of low-frequency excitation. The centrally symmetrical layout ensures uniform vibration of lining ring 2 around its entire circumference, simulating the three-dimensional vibration characteristics of train loads. The excitation frequency and amplitude can be independently adjusted to isolate the effects of different train operating conditions (e.g., low-speed freight and high-speed passenger) on lining fatigue damage.

[0067] S4: Install the truss 10 on the electric unhooking device 11 on the top of the top frame body 9, and install the drop hammer 12 at the bottom of the truss 10.

[0068] The truss 10 is mounted on the sliding rods 13 on both sides of the top frame 9 through sliding sleeves 14, and a drop hammer 12 with replaceable mass is installed at the bottom. The electric unhooker 11 is connected to the truss 10 through a steel cable. The controller remotely controls the truss 10 to rise and fall to the target height, ensuring that the impact point of the drop hammer 12 is aligned with the dome of the lining ring 2.

[0069] The high-precision control of the guide system of the slide rod 13 and the slide sleeve 14 and the electric unhooker 11 ensures that the drop hammer 12 has a vertical impact with controllable energy. The impact simulation of the drop hammer 12 reproduces the high-frequency load scenario of rock group falling in an actual tunnel.

[0070] S5: Turn on the vibrator 7 to simulate the low-frequency excitation of a train passing through the lining, and disconnect the electric uncoupler 11 to allow the drop hammer 12 to inertially separate from the truss 10 and impact the lining ring 2 to simulate the high-frequency impact of falling rocks on the lining.

[0071] First, static surrounding rock pressure is applied through the loading mechanism, and then the exciter 7 is started to output a low-frequency signal to simulate the train load; after the low-frequency excitation is stable, the electric uncoupler 11 releases the steel cable to allow the drop hammer 12 to fall freely, realizing the multi-physical field coupling of "static surrounding rock pressure + low-frequency excitation + high-frequency impact".

[0072] Time-controlled coupled loading can separate the effects of different load types, revealing the critical conditions for the progression of microcracks into sudden block collapse in the lining. Dynamic adjustment of loading sequences and parameters can simulate the cumulative effects of loads over long-term tunnel operation.

[0073] S6: Obtain single-factor data of low-frequency excitation or high-frequency shock, or obtain coupled data of low-frequency excitation and high-frequency shock.

[0074] A circumferentially arranged triaxial accelerometer 16 collects vibration signals from the lining ring 2 in real time. A vibration analyzer 17 converts the signals into time-frequency data through Fourier transform, extracting characteristic parameters such as dominant frequency, amplitude, and damping ratio. The vibration characteristics of the intact lining and the voided lining are compared to establish a load-deformation-damage relationship.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. The hollow lining test device with low-frequency excitation and high-frequency impact coupling is characterized by: include: A lining loading system comprises a main frame (1), a lining ring (2) and a loading mechanism, wherein the lining ring (2) and the loading mechanism are both arranged inside the main frame (1), and the loading mechanism is arranged circumferentially of the lining ring (2) for simulating the surrounding rock load in the circumferential direction of the lining; a low-frequency excitation system comprises a support beam (6), an exciter (7) and a power amplifier (8), wherein the support beam (6) axially penetrates the lining ring (2), the exciter (7) is connected to the support beam (6), and the power amplifier (8) is electrically connected to the exciter (7) for simulating the low-frequency excitation of a train passing through the lining; The high-frequency impact system comprises a top frame (9), a truss (10), an electric decoupler (11) and a drop hammer (12), wherein the top frame (9) is fixed to the top of the main frame (1), the truss (10) is arranged on the top of the top frame (9) through the electric decoupler (11), the drop hammer (12) is arranged at the bottom of the truss (10) and is located directly above the lining ring (2), and the drop hammer (12) is separated from the truss (10). ) to impact the lining ring (2) to simulate the high-frequency impact of falling rocks on the lining; the vibrator (7) is suspended at the lower end of the support beam (6) through an elastic member, and the vibrator (7) is located inside the lining ring (2) and in the longitudinal projection area of ​​the lining ring (2); two groups of elastic springs serve as dynamic coil suspension devices to keep the vibrator (7) in a suspended state, and the support beam (6) axially penetrates the lining ring (2) to form a rigid support shaft, ensuring that the excitation direction is consistent with the axis of the lining ring (2).

2. The hollow lining test device coupled with low-frequency excitation and high-frequency impact according to claim 1 is characterized in that: The invention also includes a monitoring system, which includes: a plurality of three-axis accelerometers (16), respectively arranged on the inner wall circumference of the lining ring (2), and the three-axis accelerometers (16) are used to detect vibration signals of the lining ring (2) in three directions; a vibration analyzer (17), electrically connected to the plurality of three-axis accelerometers (16), and used to convert the vibration signal into a time-frequency domain signal to simulate the main frequency and main eigenvalue of the lining ring (2).

3. The hollow lining test device coupled with low-frequency excitation and high-frequency impact according to claim 1 or 2, characterized in that: A plurality of jacks (18) are sequentially arranged at the bottom of the main frame (1) along the length direction, and the lining ring (2) is arranged on the plurality of jacks (18).

4. The hollow lining test device coupled with low-frequency excitation and high-frequency impact according to claim 3 is characterized in that: The loading mechanism includes: a plurality of servo electric cylinders (3) arranged in the circumference of the lining ring (2), the outer end of the servo electric cylinder (3) is fixed to the main frame (1), the inner end of the servo electric cylinder (3) is fixed with a rigid plate (4), the inner side surface of the rigid plate (4) is provided with a nylon gasket (5) pressed against the outer wall of the lining ring (2), and the inner side surface of the nylon gasket (5) has a conformal surface adapted to the outer wall of the lining ring (2).

5. The hollow lining test device coupled with low-frequency excitation and high-frequency impact according to claim 1 or 2, characterized in that: The exciter (7) is suspended at the lower end of the support beam (6) through an elastic member. The exciter (7) is located inside the lining ring (2) and in the longitudinal projection area of ​​the lining ring (2).

6. The hollow lining test device coupled with low-frequency excitation and high-frequency impact according to claim 1 or 2, characterized in that: Sliding rods (13) are longitudinally arranged on both sides of the top frame body (9), and sliding sleeves (14) are respectively arranged on both sides of the truss (10). The sliding sleeves (14) are slidably matched with the sliding rods (13) on the same side, and the electric unhooking device (11) is used to drive the truss (10) to rise and fall.

7. A method for testing hollow linings by coupling low-frequency excitation and high-frequency impact, using the hollow lining testing device by coupling low-frequency excitation and high-frequency impact as described in any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Make a steel mold in proportion, use the steel mold to cast the lining ring (2) and install it in the main frame (1); S2. Install a loading mechanism in the main frame (1), the loading mechanism presses the lining ring (2) circumferentially to simulate the surrounding rock load in the circumferential direction of the lining; S3. Install an exciter (7) on the support beam (6), the support beam (6) axially passes through the lining ring (2) and the exciter (7) is located inside the lining ring (2), and the exciter (7) is electrically connected to the power amplifier (8); S4: Install the truss (10) on the electric decoupler (11) at the top of the top frame (9), and install a drop hammer (12) at the bottom of the truss (10); S5: Turn on the exciter (7) to simulate the low-frequency excitation of the train passing through the lining, and disconnect the electric decoupler (11) to allow the drop hammer (12) to inertially separate from the truss (10) and impact the lining ring (2) to simulate the high-frequency impact of falling rocks on the lining; S6: Obtain single-factor data of low-frequency excitation or high-frequency shock, or obtain coupled data of low-frequency excitation and high-frequency shock.

8. The hollow lining test method coupled with low-frequency excitation and high-frequency impact as claimed in claim 7 is characterized in that: In step S1, a 1:10 steel mold is made by on-site measurement or actual drawings. According to the scaled model test, the elastic modulus is taken as 1 / 10 of the prototype concrete. After the lining ring (2) is poured, it is cured indoors for 28 days to reach the standard compressive strength, and the steel mold is removed.

9. The hollow lining test method coupled with low-frequency excitation and high-frequency impact according to claim 7 is characterized in that: In step S3, the power amplifier (8) is connected to the digital signal source, the digital signal source is connected to the computer control device, and the output mode is two-channel synchronous output.

10. The hollow lining test method coupled with low-frequency excitation and high-frequency impact according to claim 7 is characterized in that: In step S4, the electric unhooker (11) controls the truss (10) to be raised and lowered in the top frame (9), and replaces the drop weights (12) of different masses to simulate the impact forces of different magnitudes to erode the lining ring (2).

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