Device and method for determining the load-bearing capacity of a rock-concrete composite vorsa beam

Abstract

This invention relates to the field of tunnel and underground engineering technology, specifically disclosing a device and method for determining the bearing capacity of a rock-concrete composite Vulza beam. The device includes: a test specimen comprising multiple test blocks arranged side-by-side along its length and a layer of shotcrete covering the test blocks, the contact surfaces between the test blocks forming an interface simulating rock joints; a support platform located below the test specimen for supporting it; a horizontal loading mechanism located at both ends of the test specimen for applying active horizontal restraint forces; a vertical loading mechanism located above the test specimen for applying a uniformly distributed vertical load to the top surface of the test specimen; and a measuring mechanism. The method employs this device. Therefore, a corresponding method for testing the bearing capacity of rock-concrete composite components can be established, thereby accurately assessing and utilizing the reinforcement contribution of shotcrete to hard surrounding rock, optimizing support structures, and improving safety.

Description

Technical Field

[0001] This invention relates to the field of tunnel and underground engineering technology, specifically to a device and method for measuring the bearing capacity of a rock-concrete composite Vulza beam. Background Technology

[0002] After tunnel excavation, the stress redistribution in the surrounding rock can lead to rock failure and even instability. To ensure construction safety, it is necessary to conduct in-depth research on the synergistic mechanism between the support structure and the surrounding rock, and to take targeted reinforcement measures to improve the overall bearing capacity of the support system. Generally speaking, the failure modes of tunnel surrounding rock are mainly divided into two categories: stress-controlled failure and rock mass structure-controlled failure. For hard surrounding rock with good engineering properties, its failure is often controlled by the rock mass structure, mainly manifested as unstable blocks formed by specific structural planes falling off or collapsing. These blocks have the potential to move after being exposed at the excavation face, becoming the main factor leading to rock instability.

[0003] For hard surrounding rock where structural control failure is the primary cause, conventional support designs tend to focus on active reinforcement measures such as rock bolts, while neglecting the combined load-bearing role of shotcrete. In fact, shotcrete support has a dual function: firstly, it directly inhibits the loosening and detachment of rock blocks; secondly, it can bond several surface rock blocks together to form a cohesive "rock-concrete composite structure." In this composite system, pressure can be transferred between rock blocks, while tensile stress is borne by the shotcrete layer attached to the bottom of the rock blocks. Furthermore, loose rock blocks are laterally constrained by the surrounding intact rock mass, limiting overall deformation and further enhancing the load-bearing capacity of the composite structure. Therefore, shotcrete plays an indispensable role in hard surrounding rock support; however, a systematic and in-depth study of its synergistic load-bearing mechanism with the surrounding rock is currently lacking.

[0004] In current technologies, the understanding of the combined action mechanism between shotcrete and surrounding rock remains insufficient. There is a lack of experimental components capable of realistically simulating the synergistic stress characteristics of both, and corresponding testing methods for the load-bearing capacity of rock-concrete composite components have not been established. This makes it difficult to accurately assess and utilize the reinforcement contribution of shotcrete to hard surrounding rock in practical engineering, limiting the optimization of support structure design and the improvement of safety. Therefore, it is necessary to optimize and improve the testing scheme for the load-bearing capacity of rock-concrete composite components to solve the current technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for measuring the load-bearing capacity of rock-concrete composite Vulza beams, in order to solve the problem that the lack of a corresponding test method for the load-bearing capacity of rock-concrete composite components makes it difficult to accurately assess and utilize the reinforcement contribution of shotcrete to hard surrounding rock in actual engineering, thus limiting the optimization of support structure design and the improvement of safety.

[0006] This invention is achieved through the following technical solution:

[0007] A device for determining the bearing capacity of a rock-concrete composite Vulza beam includes:

[0008] The test specimen includes multiple test blocks arranged side by side along the length direction and a sprayed concrete layer covering the test blocks, the contact surfaces between the test blocks forming an interface simulating rock mass joints;

[0009] A support platform is disposed below the test piece to support the test piece;

[0010] A horizontal loading mechanism is disposed at both ends of the test piece and is used to apply an active horizontal constraint force to the test piece;

[0011] A vertical loading mechanism is disposed above the test piece and is used to apply a uniformly distributed vertical load to the top surface of the test piece;

[0012] A measuring mechanism is used to collect the mechanical response data of the test piece during the loading process.

[0013] In one possible design, the vertical loading mechanism includes a loading airbag and a testing machine actuator, wherein the loading airbag is disposed between the top surface of the test piece and the loading head of the testing machine actuator.

[0014] In one possible design, the measuring mechanism includes a contact measuring unit, which comprises:

[0015] A first mechanical sensor is used to measure the vertical uniformly distributed load;

[0016] A second mechanical sensor is used to measure the active horizontal constraint force;

[0017] The third mechanical sensor is used to measure the vertical deflection of the test piece.

[0018] In one possible design, the measuring mechanism further includes a non-contact full-field strain measurement unit, which includes a camera for capturing images of the deformation on the side of the test piece.

[0019] In one possible design, the test block is a precast concrete block, and the interface between adjacent test blocks is filled with a layer for adjusting the coefficient of friction.

[0020] In one possible design, the shotcrete layer is configured as a fiber-reinforced shotcrete layer.

[0021] A method for determining the bearing capacity of a rock-concrete composite Vulza beam, using a rock-concrete composite Vulza beam bearing capacity determination device, includes the following steps:

[0022] S1: Prepare a test specimen, the test specimen comprising a plurality of test blocks arranged side by side along the length direction and a sprayed concrete layer covering the test blocks;

[0023] S2: Place the test piece on the support platform and apply and maintain a constant active horizontal constraint force at both ends using a horizontal loading mechanism;

[0024] S3: Apply a uniformly distributed vertical load to the top surface of the test piece using a vertical loading mechanism;

[0025] S4: The mechanical response data of the test piece during the loading process is collected in real time by a measuring mechanism until the test piece is destroyed.

[0026] In one possible design, step S1 further includes: spraying concrete on the side-by-side test blocks in situ to form a continuous, integral sprayed concrete layer.

[0027] In one possible design, in step S3, the vertical uniformly distributed load is applied by inflating the loading airbag.

[0028] In one possible design, in step S4, a speckle image of the side of the test piece is acquired by a camera and processed to obtain full-field strain field data of the entire failure process of the test piece.

[0029] The advantages of this invention over the prior art are as follows:

[0030] The above technical solution allows for the construction of a physical entity model of an unstable block in hard surrounding rock bonded by shotcrete to form a composite beam (Volsa beam), providing an irreplaceable dedicated test component for in-depth research on its bearing mechanism. The measuring device applies active and controllable horizontal forces through an independent horizontal loading mechanism, effectively simulating for the first time in indoor tests the lateral constraint effect of deep geostress fields or intact rock masses on unstable blocks. By applying a uniformly distributed load to the top surface through a vertical loading mechanism, rather than a concentrated force, the pressure distribution of loose strata borne by the tunnel support structure is more accurately reproduced, avoiding atypical failures caused by stress concentration, and making the test results more representative and reliable.

[0031] The integrated measurement mechanism (mechanical and electrical sensors) can simultaneously acquire macroscopic mechanical response (load-displacement relationship), local deformation, and microscopic strain data while applying complex loads to the test specimen. This ability to acquire multiple parameters simultaneously throughout the entire process allows researchers to accurately analyze the entire process of composite beams, from the elastic stage and crack development to final failure, providing a solid data foundation for quantifying their load-bearing capacity, deformation characteristics, and energy dissipation capacity. This measurement method can accurately measure the full-section strain data of rock-concrete composite Vulza beams throughout the failure process, derive the law of change in the neutral axis position of the member, and provide an abstract theoretical calculation model for rock-concrete composite Vulza beam members, providing theoretical and experimental basis for accurately considering the load-bearing capacity of members under the rock-concrete composite effect. The measurement device ensures the stability and repeatability of the test process, facilitates comparative studies of test specimens with different parameters, and provides a standardized platform for subsequent research (such as changing the interface characteristics of the test block, the performance of shotcrete, and the load level), which is conducive to systematically revealing the influence of various factors on the load-bearing performance of composite beams. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0033] Figure 1 This is a plan view of the strain gauge arrangement in one embodiment of the rock-concrete composite Vulza beam bearing capacity measuring device provided by the present invention;

[0034] Figure 2 This is a test diagram of the bearing capacity of a Vulsa beam test specimen under a rock-concrete composite structure in one embodiment of the rock-concrete composite bearing capacity measuring device provided by the present invention.

[0035] Figure 3 This is a schematic diagram of the high-speed camera position in one embodiment of the rock-concrete composite Vulsa beam bearing capacity measuring device provided by the present invention;

[0036] Figure 4 This invention provides a DDA simulation model of shotcrete support for multiple rock masses in the rock-concrete composite Vulsa beam bearing capacity testing device.

[0037] Figure 5 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 1. In Example 1, C40 shotcrete is used to support multiple rock masses, and the initial strength of the shotcrete is damaged.

[0038] Should Figure 6 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 1. In Example 1, C40 shotcrete is used to support multiple rock masses, and the range of shotcrete strength failure is expanded.

[0039] Figure 7 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 2. In Example 2, C60 shotcrete is used to support multiple rock blocks, and the initial strength of the shotcrete top fails.

[0040] Figure 8 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 2. In Example 2, C60 shotcrete is used to support multiple rock masses, and the range of failure due to shotcrete strength is expanded.

[0041] Figure 9 This is a partial view of the damage to C40 shotcrete material in Example 1;

[0042] Figure 10 This is a partial image of the damage to C60 shotcrete material in Example 2;

[0043] Figure 11 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 3. In Example 3, C80 shotcrete is used to support multiple rock blocks, and the initial interface of the shotcrete debonds.

[0044] Figure 12 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 3. In Example 3, C80 shotcrete is used to support multiple rock blocks, and the debonding of the shotcrete interface leads to tensile failure at the bottom.

[0045] Figure 13 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 3. In Example 3, C80 shotcrete is used to support multiple rock blocks, and the debonding range of the shotcrete interface and the expansion of the tensile failure area are shown.

[0046] Figure 14 This is a partial view of the initial interface debonding of C80 shotcrete material in Example 3;

[0047] Figure 15 This is a partial view of the bottom tensile failure caused by the interface debonding of C80 shotcrete material in Example 3;

[0048] Figure 16 This is a partial view of the debonding range and tensile failure zone expansion of the C80 shotcrete material in Example 3;

[0049] Figure 17 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 4. In Example 4, UC100 shotcrete is used to support multiple rock blocks, and the initial interface of the shotcrete debonds.

[0050] Figure 18 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 4. In Example 4, UC100 shotcrete is used to support multiple rock blocks. Debonding at the shotcrete interface leads to tensile failure at the bottom.

[0051] Figure 19 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 5. In Example 5, UC120 shotcrete is used to support multiple rock blocks, and the initial interface of the shotcrete debonds.

[0052] Figure 20 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 5. In Example 5, UC120 shotcrete is used to support multiple rock blocks, and the debonding range of the shotcrete interface and the expansion of the tensile failure area are shown.

[0053] Figure 21 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 6. In Example 6, UC160 shotcrete is used to support multiple rock blocks, and the initial interface of the shotcrete debonds.

[0054] Figure 22 This is a simulation model diagram of the method for determining the bearing capacity of the rock-concrete composite Vulza beam provided by the present invention in Example 6. In Example 6, UC160 shotcrete is used to support multiple rock blocks, and the debonding range of the shotcrete interface and the expansion of the tensile failure area are shown.

[0055] Figure 23 This is a partial view of the initial interface debonding of UC160 shotcrete material in Example 6;

[0056] Figure 24 This is a partial view of the tensile failure at the bottom caused by the debonding of the UC160 shotcrete material interface in Example 6;

[0057] Figure 25 The load-displacement curves of shotcrete and rock mass simulation analysis are obtained when the bearing capacity determination method of rock-concrete composite Vulsa beam provided by this invention is used for simulation test.

[0058] The attached diagram shows the following markings and corresponding component names: 1-Test piece, 2-Support platform, 3-Horizontal loading mechanism, 4-Vertical loading mechanism, 41-Loading airbag, 51-First mechanical sensor, 52-Second mechanical sensor, 53-Third mechanical sensor, 54-Camera. Detailed Implementation

[0059] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be noted that while the description of these embodiments is intended to aid in understanding the invention, it does not constitute a limitation thereof. The specific structural and functional details disclosed herein are only for describing exemplary embodiments of the invention. However, the invention can be embodied in many alternative forms and should not be construed as being limited to the embodiments described herein.

[0060] According to the first aspect of this disclosure, a device for determining the bearing capacity of a rock-concrete composite Vulza beam is provided. Figures 1 to 25 Specific embodiments thereof are shown.

[0061] See Figures 1 to 25 As shown, the rock-concrete composite Vulza beam bearing capacity testing device includes: a test piece 1, comprising multiple test blocks arranged side by side along the length direction and a sprayed concrete layer covering the test blocks, the contact surfaces between the test blocks forming an interface simulating rock mass joints; a support platform 2, located below the test piece 1, for supporting the test piece 1; a horizontal loading mechanism 3, located at both ends of the test piece 1, for applying active horizontal constraint force to the test piece 1; a vertical loading mechanism 4, located above the test piece 1, for applying a vertical uniformly distributed load to the top surface of the test piece 1; and a measuring mechanism for collecting mechanical response data of the test piece 1 during the loading process.

[0062] The working process of the rock-concrete composite Vulsa beam bearing capacity measuring device is as follows:

[0063] 1. Preparation and Installation of Test Specimen 1. Multiple test blocks are arranged side-by-side along their length, with their contact surfaces simulating joints in the rock mass. Subsequently, shotcrete is sprayed onto the test blocks in situ to form a continuous, integral shotcrete layer, thus creating test specimen 1 of the rock-concrete composite beam. Test specimen 1 is then placed on the foundation 2 to complete its basic positioning.

[0064] 2. Boundary condition simulation and loading, including surrounding rock constraint simulation and load application. During the surrounding rock constraint simulation, the horizontal loading mechanism 3 is activated to apply and maintain a constant active horizontal constraint force from both ends of the test specimen 1. This step aims to simulate the lateral constraint of an unstable block on the surrounding intact rock mass in tunnel engineering. During load application, the vertical loading mechanism 4 is activated to apply a continuous, uniformly increasing vertically distributed load from the top of the test specimen 1 onto its top surface. This load simulates the surrounding rock pressure borne by the tunnel arch or sidewall.

[0065] 3. Synchronous Data Acquisition and Failure Observation. Throughout the loading process, the measuring mechanism synchronously and in real-time acquires the mechanical response data of test specimen 1. This includes recording the load value, the deformation of test specimen 1 (such as deflection), and possibly observing the initiation and propagation of cracks in the shotcrete layer, as well as failure phenomena such as relative misalignment between test specimens, until test specimen 1 ultimately loses its load-bearing capacity.

[0066] The above technical solution allows for the construction of a physical entity representing a load-bearing model where unstable blocks in hard surrounding rock are bonded together by shotcrete to form a composite beam (Volsa beam). This provides an irreplaceable dedicated test component for in-depth research into its load-bearing mechanism. The measuring device applies active and controllable horizontal forces through an independent horizontal loading mechanism 3, effectively simulating for the first time in indoor tests the lateral constraint effect of deep geostress fields or intact rock masses on unstable blocks. By applying a uniformly distributed load to the top surface through the vertical loading mechanism 4, rather than a concentrated force, the distribution of loose strata pressure borne by the tunnel support structure is more accurately reproduced, avoiding atypical failures caused by stress concentration and making the test results more representative and reliable.

[0067] The integrated measurement mechanism can simultaneously acquire macroscopic mechanical response (load-displacement relationship), local deformation, and microscopic strain data while applying complex loads to test specimen 1. Based on this ability to acquire data simultaneously throughout the entire process and with multiple parameters, researchers can accurately analyze the entire process of the composite beam from the elastic stage, crack development, to final failure, providing a solid data foundation for quantifying its load-bearing capacity, deformation characteristics, and energy dissipation capacity. This measurement method can accurately measure the full-section strain data of the rock-concrete composite Vulza beam during the entire failure process, deduce the change law of the neutral axis position of the component, and provide an abstract theoretical calculation model for the rock-concrete composite Vulza beam component, providing theoretical and experimental basis for accurately considering the load-bearing capacity of the component under the rock-concrete composite effect. The measurement device ensures the stability and repeatability of the test process, facilitates comparative studies of test specimen 1 with different parameters, and provides a standardized platform for subsequent research (such as changing the interface characteristics of the test block, the performance of shotcrete, and the load level), which is conducive to systematically revealing the influence of various factors on the load-bearing performance of the composite beam.

[0068] It should be noted that directional terms such as "inner" and "outer" refer to "inner" and "outer" relative to the outline of the component; "inner" refers to the direction towards the component, and "outer" refers to the direction away from it. Furthermore, terms such as "first" and "second" are used to distinguish one element from another and do not indicate sequence or importance. Also, in the accompanying drawings, the same reference numerals in different drawings represent the same element. It should be noted that "and / or" in the text refers to A and / or B, indicating that there are three possible scenarios: only A, only B, or both A and B. Conversely, " / and" in the text refers to A and B, indicating that there are two possible scenarios: only A and both A and B.

[0069] In one embodiment provided in this disclosure, the vertical loading mechanism 4 includes a loading airbag 41 and a testing machine actuator. The loading airbag 41 is disposed between the top surface of the test piece 1 and the loading head of the testing machine actuator. As a flexible force transmission medium, the loading airbag 41 can efficiently and uniformly convert the concentrated force applied by the loading head of the testing machine actuator into a vertically distributed load distributed across the entire top surface of the test piece 1, thereby ensuring the continuity and uniformity of load transmission and thus more realistically simulating the uniform pressure of the overlying rock strata borne by the tunnel support structure.

[0070] Since test specimen 1 is composed of multiple independent test blocks, its top surface inevitably has microscopic unevenness or slight misalignment between the test blocks. The flexibility of the loading airbag 41 can adaptively conform to the slight undulations of the top surface of test specimen 1, ensuring full contact between the load and the surface of test specimen 1, avoiding damage caused by local stress concentration due to poor contact, and improving the accuracy and reliability of the test. By controlling the displacement or pressure of the testing machine actuator, the expansion process of the loading airbag 41 can be precisely controlled, thereby achieving precise and continuous control of the magnitude and rate of the vertical uniformly distributed load applied to test specimen 1. This provides controllable and stable loading conditions for studying the entire process of mechanical response, deformation development, and eventual failure of rock-concrete composite beams under different load levels.

[0071] In one embodiment, the measuring mechanism includes a contact measuring unit, which comprises: a first mechanical sensor 51 for measuring a uniformly distributed vertical load; a second mechanical sensor 52 for measuring an active horizontal constraint force; and a third mechanical sensor 53 for measuring the vertical deflection of the test piece 1. During operation, as the vertical loading mechanism 4 and the horizontal loading mechanism 3 apply loads and constraints to the test piece 1 respectively, the first mechanical sensor 51 monitors and outputs the uniformly distributed vertical load value acting on the top surface of the test piece 1 in real time, the second mechanical sensor 52 synchronously monitors and outputs the active horizontal constraint force values ​​applied to both ends of the test piece 1, and simultaneously, the third mechanical sensor 53 continuously measures the vertical deflection deformation of the test piece 1 under load. The data acquisition of these three sensors is synchronized, thereby completely recording the entire load-displacement response process of the test piece 1 under complex stress conditions.

[0072] The first mechanical sensor 51 and the second mechanical sensor 52 can directly and accurately obtain the precise values ​​of the vertical load and horizontal constraint force, while the third mechanical sensor 53 quantifies the macroscopic deformation response of the test piece 1. The synchronous acquisition of these three types of data provides an indispensable and direct data foundation for accurately establishing the quantitative relationship between load, constraint force and deformation, and for analyzing the stiffness, bearing capacity and internal force transmission mechanism of the component.

[0073] By placing contact sensors directly on the load transfer path (such as the first mechanical sensor 51 and the second mechanical sensor 52) and the deformation part (such as the third mechanical sensor 53), direct and reliable measurement of these mechanical parameters can be achieved, improving the accuracy and reliability of the test data.

[0074] In this embodiment, the first mechanical sensor 51 is a first stress plate, which is arranged on the vertical end face of the split block to fit tightly against the loading airbag 41 of the vertical loading mechanism 4, thereby measuring the vertical uniformly distributed load. The second mechanical sensor 52 also uses a second stress plate, which is arranged on the horizontal side of the split block to fit tightly against the loading head of the horizontal loading mechanism 3, thereby measuring the horizontal constraint force. The third mechanical sensor is a displacement sensor. Specifically, a wire displacement sensor is selected.

[0075] Furthermore, the measurement mechanism also includes a non-contact full-field strain measurement unit, which includes a camera 54 for capturing images of the deformation of the side of the test piece 1. The camera 54 is equipped with an image sensor, thereby acquiring image information through the image sensor.

[0076] During operation, the camera 54 continuously and synchronously captures a series of high-resolution images of the side of the test specimen 1 throughout the loading process. Subsequently, by processing these images using image analysis technology, the full-field displacement and strain distribution of the surface of the test specimen 1 under load can be reconstructed, and the microscopic deformation behaviors such as crack initiation, propagation path, and relative slippage between test blocks can be directly captured.

[0077] The non-contact full-field strain measurement unit can provide high spatial resolution strain cloud maps and displacement vector fields covering the entire observation area, enabling researchers to accurately locate the critical region where cracking first occurs in test piece 1, and intuitively visualize the strain redistribution process, thereby revealing the failure mechanism and damage mode of the composite structure from a global perspective.

[0078] For test specimen 1, which consists of multiple test blocks, failure is often accompanied by discontinuous deformations such as slippage and opening between the blocks. Non-contact image measurement can continuously record the occurrence time, location, and development process of these local discontinuities, which is difficult to achieve with traditional point measurement methods, and provides information for understanding the influence of joint surfaces on the overall stability of composite beams.

[0079] Furthermore, since this measurement method is non-contact, no additional mechanical interference or mass load is applied to the test specimen 1 during the measurement process. This makes it particularly suitable for measuring test specimens 1 with limited stiffness or those in the brittle fracture stage, ensuring the purity of the test conditions and the reliability of the results. Simultaneously, the acquired image data can be permanently saved for subsequent in-depth analysis, enriching the dimensions and value of the test data.

[0080] In one embodiment, the test blocks are precast concrete blocks, and the interfaces between adjacent test blocks are filled with an adjusting layer for the coefficient of friction. During operation, specific materials (such as grease mixed with quartz sand of different particle sizes, low-strength mortar, etc.) can be selected or formulated to form the adjusting layer based on the mechanical properties of the target joint surface, and this layer is applied to the pre-designed contact surfaces of the precast concrete blocks. Subsequently, the treated precast blocks are assembled along their length, with the adjusting layer positioned between adjacent blocks, thereby constructing a joint system with specific interfacial friction properties. In subsequent loading tests, this precast adjusting layer directly determines the magnitude and nature of the resistance when relative sliding tends to occur between the test blocks.

[0081] Using precast concrete blocks with uniform performance instead of natural rock blocks eliminates the interference of the discreteness of natural rock materials on the test results, ensuring the consistency of the base material of test specimen 1. By pre-setting a precisely adjustable adjustment layer at the interface, the friction coefficient of the joint surface can be actively and quantitatively controlled. This allows for the repeatable simulation of different types of structural surfaces, from smooth and weak interlayers to rough and hard contacts, under laboratory conditions. This provides a reliable and flexible physical model basis for systematically studying the influence of the mechanical properties of joint surfaces on the overall stability of rock-concrete composite beams.

[0082] In this way, researchers can easily prepare a series of comparative test specimens with different interfacial friction parameters by simply changing the material ratio or thickness of the adjustment layer, while keeping all other conditions unchanged. This allows the influence of a single variable (joint surface friction coefficient) on the load-bearing mechanism, failure mode and ultimate bearing capacity of the composite beam to be clearly and independently isolated and studied, which promotes a more refined and quantitative understanding of the synergistic mechanism between joint-controlled surrounding rock and shotcrete.

[0083] In one embodiment of this disclosure, the shotcrete layer is configured as a fiber-reinforced shotcrete layer. During the preparation of the rock-concrete composite beam test specimen 1, chopped fibers (e.g., steel fibers, synthetic fibers) are incorporated into the shotcrete mixture as reinforcing materials, and uniformly sprayed onto the specimen using a wet or dry spraying process. After curing, the fiber-reinforced shotcrete layer is formed. In subsequent loading tests, the fibers dispersed in the concrete matrix can effectively bridge microcracks, participating in and improving the load-bearing performance of the structural layer.

[0084] Secondly, the bridging effect of fibers can not only delay the propagation of cracks in the shotcrete layer, but may also affect the crack development mode and the final failure mode. By comparing and analyzing the mechanical response, crack development process, and ultimate bearing capacity of test specimen 1 made of ordinary shotcrete and fiber-reinforced shotcrete under the same load conditions, the effect of fiber reinforcement technology on improving the overall stability, ductility, and energy absorption capacity of composite beams can be evaluated, providing experimental basis for the optimal selection of support materials in engineering.

[0085] According to a second aspect of this disclosure, a method for determining the load-bearing capacity of a rock-concrete composite Vulsa beam is provided, which employs the rock-concrete composite Vulsa beam load-bearing capacity determination device of the first aspect.

[0086] The method for determining the load-bearing capacity of the rock-concrete composite Vulza beam includes the following steps: S1: Prepare test specimen 1, which includes multiple test blocks arranged side by side along the length direction and a sprayed concrete layer covering the test blocks; S2: Place test specimen 1 on the bearing platform 2, and apply and maintain a constant active horizontal constraint force at both ends of it using a horizontal loading mechanism 3; S3: Apply a uniformly distributed vertical load to the top surface of test specimen 1 using a vertical loading mechanism 4; S4: Collect mechanical response data of test specimen 1 in real time during the loading process using a measuring mechanism until test specimen 1 fails.

[0087] Step S1 prepared test specimen 1 physically reproduced the tunnel surface bearing structure, which consisted of rock blocks cut by structural surfaces and bonded with shotcrete. Step S2 innovatively recreated the boundary condition of lateral stress constraint in deep surrounding rock in a laboratory environment by applying and maintaining a constant active horizontal constraint force. Step S3 simulated the uniform pressure of the overlying rock strata using a vertically distributed load. These three steps are interconnected and collaboratively construct a physical model with a clear stress state, well-defined boundary conditions, and a high degree of approximation to engineering reality, thus giving the subsequent test results direct engineering reference value.

[0088] Step S4 requires real-time acquisition of mechanical response data throughout the loading process. This ensures that the test not only obtains the ultimate bearing capacity as the final indicator, but also continuously records information such as the load-displacement relationship and strain field evolution of the composite structure throughout the elastic stage, crack initiation and propagation stage, and ultimately, instability and failure. This dynamic, full-process data acquisition method provides an irreplaceable data foundation for a deeper understanding of the stiffness degradation law, internal force redistribution mechanism, energy absorption and dissipation characteristics, and final failure mode of rock-concrete composite structures.

[0089] The core parameters throughout the process, such as the interface characteristics of the test block (adjustable in step S1), the magnitude of the horizontal constraint force (step S2), the loading rate and path (step S3), and the performance of the shotcrete layer (adjustable in step S1), can all be independently and precisely controlled. This allows the method to serve as a standardized research platform, systematically revealing the influence of factors such as joint surface friction coefficient, surrounding rock stress level, and shotcrete performance on the load-bearing behavior of composite beams through single-variable control. Therefore, this method is not only a tool for evaluating the performance of specific composite structures, but also a powerful experimental means for in-depth exploration of the "rock-concrete" synergistic mechanism and optimization of support design theory.

[0090] Step S1 also includes: spraying concrete in situ onto the side-by-side test blocks to form a continuous, integral sprayed concrete layer. In-situ spraying allows the concrete to bond tightly under high pressure and embed itself into the microscopic undulations of the test block surface. This not only simulates the bonding at the material level but also realistically reproduces the complex mechanical connection formed between the surrounding rock and the support structure through embedding and interlocking. This ensures that the formation mechanism of the test specimen 1, from interface characteristics to structural integrity, is consistent with engineering reality, thus making the failure modes and final bearing capacity revealed by subsequent loading tests more directly valuable for engineering reference.

[0091] Compared to pre-fabricated concrete layers followed by assembly, on-site spraying effectively avoids interface defects caused by assembly gaps, uneven adhesive application, or differences in human compaction, making the initial interface conditions of each test specimen 1 more controllable and consistent. This improves the repeatability of the experiment and the comparability of data between different series of test specimens 1, laying a reliable foundation for parametric comparative studies (such as different concrete strengths, fiber content, etc.).

[0092] The shotcrete process itself places specific requirements on the workability, cohesiveness, and early strength development of concrete. On-site shotcreting allows the shotcrete layer in test specimen 1 to directly reflect the true performance of these materials under specific processes. Therefore, the test results not only evaluate the macroscopic mechanical behavior of the composite structure, but also indirectly verify the rationality of the shotcrete material mix and process, realizing a closed-loop test covering the entire chain from "materials-process-structure-performance".

[0093] In step S3, a uniformly distributed vertical load is applied by inflating the loading airbag 41. As a flexible force transmission medium, the loading airbag 41, during its internal inflation and expansion, automatically transforms the concentrated force applied by the loading head of the testing machine above into a vertical pressure field that is perpendicular to the top surface of the test specimen 1, continuously distributed, and highly uniform. This loading method fundamentally overcomes the problems of stress concentration, edge effects, or uneven load distribution that are easily caused by traditional rigid loading heads or distribution beams, thereby ensuring that the test specimen 1 as a whole is subjected to stress in a load environment that highly replicates the true distribution of formation pressure, thus improving the simulation fidelity of the test.

[0094] Since test specimen 1 is composed of multiple test blocks, minor unevenness or misalignment of joints is inevitable. The flexible nature of the loading airbag 41 allows it to perfectly conform to these micro-undulations during expansion, ensuring that the load is transferred indiscriminately to each test block and the shotcrete layer, eliminating localized stress anomalies or false early failures caused by poor contact.

[0095] By precisely controlling the inflation rate or pressure of the airbag, linear, stable, and continuous control of the magnitude and rate of increase of the vertical uniformly distributed load applied to test specimen 1 can be achieved. This not only facilitates the implementation of standardized loading regimes (such as displacement control or force control) but also provides stable load input conditions for observing and recording the nonlinear response of the composite structure throughout the entire process from elasticity, yielding, to failure. Simultaneously, the flexibility of the airbag avoids the impact on the loading equipment caused by sudden brittle failure of test specimen 1, thus improving the safety of the testing process.

[0096] In step S4, speckle images of the side of test piece 1 are acquired by camera 54, and the full-field strain field data of the entire failure process of test piece 1 is obtained through processing. By processing the sequence of speckle images, the complete displacement field and strain field distribution of the side of test piece 1 at every moment and in every region during the entire loading process until failure can be reconstructed. This allows researchers to see intuitively how strain accumulates and where and how the first microcrack initiates and propagates with extremely high spatial resolution, thereby directly linking the macroscopic mechanical response with the microscopic deformation mechanism and deepening the understanding of the physical process of failure.

[0097] Image-based full-field strain analysis continuously records the timing, precise location, evolution path, and magnitude of these local abrupt changes, fully revealing the dynamic process of joint surfaces from closure and slippage to eventual loss of load-bearing capacity. This provides an irreplaceable observation method for accurately assessing structural surface-controlled failure. Furthermore, no physical contact or additional mass is applied to test specimen 1 during data acquisition, avoiding potential local stiffness enhancement or interference with vulnerable areas caused by sensor installation. This ensures, in particular, the naturalness and authenticity of the deformation behavior of test specimen 1 in the brittle stage near failure. Simultaneously, the acquired image data itself constitutes a complete, traceable, and permanent record, facilitating subsequent multi-angle in-depth analysis and verification.

[0098] To verify the effectiveness of the experimental design, discontinuous deformation analysis (DDA) was used to simulate the failure process of shotcrete support under the action of a single rock block. The full-scale simulation model consisted of the support and multiple rock blocks, with the same dimensions as the experimental model. A layer of shotcrete fiber was closely attached underneath, and the boundary conditions at both ends of the model were contact boundaries to simulate the surrounding intact rock mass, thus forming the Voussoir Beam effect. A uniformly distributed load was applied to the top of the rock blocks, and it was gradually increased during the calculation.

[0099] Figure 4 This is a DDA simulation model diagram of shotcrete supporting multiple rock masses.

[0100] In the DDA simulation calculations, the rock mass and shotcrete material parameters are shown in Tables 1 and 2:

[0101] Table 1 shows the material parameters for the simulation of rock blocks and rock-concrete interfaces.

[0102] Table 2 shows the material parameters for the shotcrete simulation.

[0103] Simulation results show that when C40 shotcrete is used to support multiple rock blocks, failure first occurs at the top of the shotcrete layer, such as... Figure 5 At this point, no obvious debonding occurred at the rock-concrete interface, and the initial failure was shear failure starting from the top of the shotcrete. As the load increased, the number of failure sites at the top of the shotcrete increased, and cracks gradually extended from top to bottom until the load could no longer increase. Figure 6 Therefore, under this calculation model, the failure of C40 shotcrete material precedes the failure of the rock-concrete interface, and increasing the shotcrete grade is an effective means to enhance the support.

[0104] When C60 shotcrete is used to support multiple rock blocks, the initial failure is also shear failure starting from the top of the shotcrete, with cracks extending from top to bottom. The failure mode is basically the same as that of C40 shotcrete support. Figure 7 The range of strength failure in shotcrete expands, such as... Figure 8 As shown.

[0105] Figure 9 This is a partial image showing damage to C40 shotcrete material. Figure 10 This is a partial view of the damage to C60 shotcrete material.

[0106] When C80 shotcrete is used to support multiple rock masses, the first failure to occur is debonding at the rock-concrete interface. At this stage, the shotcrete material has not yet shown significant damage. Figure 11 As the load increases, interfacial debonding occurs, leading to tensile failure at the bottom, such as... Figure 12 As the load continues to increase, the number and extent of debonding at the interface increase, and cracks gradually penetrate the support section from bottom to top. Figure 13 Under this calculation model, the failure of the rock-concrete interface precedes the failure of the C80 shotcrete material.

[0107] Figures 14-16 The image shows a partial view of the damage to C80 shotcrete material. Figure 14 This is a simulation model diagram of the initial interface debonding of multiple rock blocks supported by C80 shotcrete. Figure 15 This is a simulation model diagram of tensile failure at the bottom caused by debonding at the interface of multiple rock blocks supported by C80 shotcrete. Figure 16 This is a simulation model diagram of the debonding range and tensile failure zone expansion of multiple rock blocks supported by C80 shotcrete.

[0108] When UC100 shotcrete is used to support multiple rock blocks, the failure mode is entirely controlled by the rock-concrete interface failure. When the interface debonding has extended to a considerable extent, the shotcrete will experience tensile failure at the base, such as... Figure 17 and Figure 18 As shown.

[0109] When using UC120 shotcrete, or even the stronger UC160, to support multiple rock masses, the form and location of support failure are basically the same as those of UC100 mentioned above. Figure 19-22 As shown, at this point, the bond strength at the rock-concrete interface is the controlling factor for failure, and the high performance of the material itself is not fully utilized. Figure 23 and Figure 24 The image shows a partial view of the damage to UC160 shotcrete material. Figure 23 In the initial interface detached state, Figure 24 It is in a state of tensile failure due to interface debonding.

[0110] Figure 25 This is a load-displacement curve graph of shotcrete and rock mass simulation analysis. As can be seen from the graph, when the shotcrete grade is lower than C80, the support failure is controlled by the material strength. Therefore, the higher the grade, the stronger the support bearing capacity. When the shotcrete grade is higher than UC100, the support failure is controlled by the bond strength at the rock-concrete interface. Further increasing the shotcrete grade has limited effect on strengthening the support. The load-displacement curves of UC100, UC120, and UC160 shotcrete supports are basically consistent.

[0111] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0112] Finally, it should be noted that this invention is not limited to the optional embodiments described above, and anyone can derive other various forms of products under the guidance of this invention. The specific embodiments described above should not be construed as limiting the scope of protection of this invention, which should be determined by the claims, and the specification can be used to interpret the claims.

Claims

1. A device for determining the load-carrying capacity of a rock-concrete composite Vierendeel beam, characterized in that, include: The test specimen includes multiple test blocks arranged side by side along the length direction and a shotcrete layer covering the test blocks, the shotcrete layer being configured as a fiber-reinforced shotcrete layer; the contact surfaces between the test blocks form an interface simulating rock mass joints, and the interfaces between adjacent test blocks are filled with an adjustment layer for the friction coefficient. A support platform is disposed below the test piece to support the test piece; A horizontal loading mechanism is disposed at both ends of the test piece and is used to apply an active horizontal constraint force to the test piece; A vertical loading mechanism is disposed above the test piece and is used to apply a uniformly distributed vertical load to the top surface of the test piece; A measuring mechanism is used to collect the mechanical response data of the test piece during the loading process; The vertical loading mechanism includes a loading airbag and a testing machine actuator, wherein the loading airbag is disposed between the top surface of the test piece and the loading head of the testing machine actuator; the measuring mechanism includes a contact measuring unit, wherein the contact measuring unit includes: A first mechanical sensor is used to measure the vertical uniformly distributed load; A second mechanical sensor is used to measure the active horizontal constraint force; The third mechanical sensor is used to measure the vertical deflection of the test piece; The measuring mechanism also includes a non-contact full-field strain measurement unit, which includes a camera for capturing images of the deformation on the side of the test piece.

2. The rock-concrete composite Vierendeel beam load capacity measuring apparatus according to claim 1, wherein The test block was a precast concrete block.

3. A method for determining the load-carrying capacity of a rock-concrete composite Vierendeel beam, characterized in that, The method for determining the bearing capacity of a rock-concrete composite Vulza beam using the apparatus described in claim 1 or 2 includes the following steps: S1: Prepare a test specimen, the test specimen comprising a plurality of test blocks arranged side by side along the length direction and a sprayed concrete layer covering the test blocks; S2: Place the test piece on the support platform and apply and maintain a constant active horizontal constraint force at both ends using a horizontal loading mechanism; S3: Apply a uniformly distributed vertical load to the top surface of the test piece using a vertical loading mechanism; S4: The mechanical response data of the test piece during the loading process is collected in real time by a measuring mechanism until the test piece is destroyed.

4. The method of load capacity determination of a rock-concrete composite Vierendeel beam according to claim 3, characterized in that, Step S1 further includes: spraying concrete on the side-by-side test blocks to form a continuous and integral sprayed concrete layer.

5. The method for determining the bearing capacity of a rock-concrete composite Vulza beam according to claim 3, characterized in that, In step S3, the vertical uniformly distributed load is applied by inflating the loading airbag.

6. The method for determining the bearing capacity of a rock-concrete composite Vulza beam according to claim 3, characterized in that, In step S4, a speckle image of the side of the test piece is acquired by a camera and processed to obtain full-field strain field data of the entire failure process of the test piece.

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