Simulation of Crack Propagation under Controllable Confining Pressure and Fiber Optic Testing Instrument and its Application Methods

Abstract

This invention belongs to the field of contaminated soil remediation technology and relates to a confining pressure-controlled crack propagation simulation and fiber optic testing instrument and its application method. The technical solution includes a confining pressure control module, a crack propagation module, a pull-out test module, a distributed fiber optic sensing module, and a centralized control system. The crack propagation module and the pull-out test module are mounted on the confining pressure control module. The confining pressure control module, crack propagation module, and pull-out test module are integrated into a single structure. A long, narrow soil box is divided into two parts, forming a fixed soil box and a sliding soil box. The crack propagation module provides three different forms of crack propagation devices: soil box pull-out crack initiation, internal airbag expansion crack initiation, and steel plate crack initiation, to simulate different soil crack propagation conditions. This invention solves the problem that existing laboratory dimensional model test modules lack the ability to simultaneously perform fiber optic pull-out tests and simulate soil crack propagation.

Description

Technical Field

[0001] This invention relates to the field of contaminated soil remediation technology, specifically to a crack propagation simulation and fiber optic testing instrument with controllable confining pressure and its application method. Background Technology

[0002] In-situ oxidation technology is used for low-permeability soil strata (generally with a permeability coefficient ≤ 1×10⁻⁶). -6 In-situ oxidation technology is suitable for contaminated sites with a flow rate of m / s, and some removal rates can reach over 80% in a short period. However, the remediation effect of in-situ oxidation technology is limited by many factors, such as dominant seepage in heterogeneous strata, difficulty in contacting pollutants with oxidants, quenching and consumption of oxidants due to the natural oxygen demand of the site, backflow of slurry on the wellbore caused by high-pressure injection into low-permeability layers, and severe tailing phenomena in remediation. To overcome the limitations of traditional oxidants, some researchers have adopted new technologies and materials to improve in-situ oxidation technology, such as heating enhancement and soil fracturing to enhance permeability. Fracturing and permeability enhancement synergistic remediation technology forms a fracture network through high-pressure injection of gas and liquid, which helps to improve the local permeability of low-permeability soil, shorten the oxidant transport distance, and improve the applicability of in-situ oxidation technology. Therefore, it is very necessary to accurately monitor the generation and propagation process of hydraulic fracturing fractures, which is of great significance for evaluating the fracturing effect and optimizing the synergistic remediation process parameters.

[0003] Distributed optical fiber sensing technology, in which the sensor uses optical fiber itself as the sensing medium, can simultaneously measure physical quantities such as temperature, strain, and vibration at multiple continuous measurement points along the fiber, and acquire information on the distribution of these physical quantities with the length or position of the fiber. It has the advantages of high monitoring accuracy and strong anti-interference performance, providing a reliable means to monitor the formation and propagation of soil cracks. The most critical aspect of accurately monitoring soil cracks using distributed optical fiber is to ensure the coupling effect between the optical fiber and the soil. The optical fiber pull-out test is the most direct and effective way to explore the coupling deformation between the optical fiber and the soil. At the same time, since the crack width generated by hydraulic fracturing is difficult to measure, a fracturing crack simulation instrument is needed to simulate the generation of soil cracks.

[0004] Existing fiber optic pull-out instruments have limited functionality and cannot simulate the propagation of soil cracks. Therefore, it is necessary to invent an instrument that combines fiber optic pull-out and crack propagation simulation functions to better study the monitoring of the generation and propagation process of hydraulic fracturing cracks in soil by distributed optical fibers. Summary of the Invention

[0005] The purpose of this invention is to provide a controlled-pressure crack propagation simulation and fiber optic testing instrument and its application method. It aims to address the lack of existing laboratory-scale model testing modules capable of simultaneously performing fiber optic pull-out tests and simulating soil crack propagation.

[0006] The technical solution of the present invention is: a confining pressure controllable crack propagation simulation and optical fiber testing instrument, including a confining pressure control module, a crack propagation module, a pull-out test module, a distributed optical fiber sensing module, and a centralized control system.

[0007] The confining pressure control module consists of a long strip soil box divided into two parts, forming a fixed soil box and a sliding soil box. Each fixed soil box and the sliding soil box is equipped with a set of loading reaction components. Each set of loading reaction components includes a reaction frame, a hydraulic cylinder, a loading plate, and a pressure sensor. The pressure sensor monitors the confining pressure value in real time. The fixed soil box and the sliding soil box can be combined into a whole or separated. Both the fixed soil box and the sliding soil box are equipped with a drainage system.

[0008] The crack propagation module includes a fixed soil box, a sliding soil box, and a crack propagation device; the crack propagation device is placed in the soil sample between the fixed soil box and the sliding soil box.

[0009] The pull-out test module includes a displacement control motor, a displacement gauge, and a replaceable tie rod; the replaceable tie rod is located between the displacement control motor and the sliding soil box; a tension sensor is installed on the replaceable tie rod; and the displacement gauge is installed on the displacement control motor.

[0010] The distributed optical fiber sensing module includes an optical fiber, an optical fiber demodulator, and a computer. The optical fiber is buried in the soil sample; the optical fiber demodulator is connected to the optical fiber and outputs optical fiber strain data; the computer presents and stores the optical fiber strain data monitored by the optical fiber demodulator in real time.

[0011] The centralized control system sets the displacement value of the displacement control motor, controls the forward and backward movement of the displacement control motor, and can also adjust the pulling speed of the displacement control motor; the centralized control system sets the confining pressure value in the confining pressure control module, and controls the loading and unloading of the hydraulic cylinder; the centralized control system has a data acquisition unit to collect confining pressure, tension, and displacement data transmitted by pressure sensors, tension sensors, and displacement gauges.

[0012] Based on the above technical features: the reaction frames of the two sets of loading reaction components share the same reaction frame base; the reaction frame is a portal frame structure, and its bottom is rigidly connected to the shared reaction frame base; the hydraulic cylinder is set below the crossbeam of the reaction frame, and the loading rod of the hydraulic cylinder applies vertical loading pressure to the loading plate; the loading plate covers the surface of the soil sample, and the pressure sensor is set between the loading plate and the loading rod.

[0013] The dual-box switching connector is located at the connection between the fixed soil box and the sliding soil box, allowing the fixed soil box and the sliding soil box to be integrated or separated.

[0014] The bottom of the sliding soil box is equipped with pulleys and is placed on a track on one side of the reaction frame base. The track is horizontal, allowing the sliding soil box to move along the track.

[0015] The drainage system for the fixed soil box and the sliding soil box consists of drainage holes at the bottom of the fixed soil box and the drainage trough connected to the water collection trough; the water collection trough is set on the reaction frame base.

[0016] Based on the above technical features: the replaceable pull rod is a soil box pull rod and an optical fiber clamping pull rod; the soil box pull rod and the optical fiber clamping pull rod are interchangeable; one end of the soil box pull rod is installed on the displacement control motor, and the other end is connected to the sliding soil box; one end of the optical fiber clamping pull rod is installed on the displacement control motor, and the other end clamps the optical fiber passing through the sliding soil box.

[0017] Based on the above technical features: the crack propagation device is an airbag, and the center of the airbag has an airbag fiber optic hole, so that the fiber optic can pass through the airbag.

[0018] Based on the above technical features: the crack propagation device consists of two steel plates stacked vertically, with a horizontally inserted anchor rod on the top of one of the steel plates. By tightening the anchor rod, the two steel plates are separated; a fiber optic hole is reserved in the middle of the two steel plates so that the fiber optic cable can pass through the two steel plates.

[0019] Based on the above technical features: one end of the soil box pull rod is equipped with a hexagonal buckle, and the overlapping buckle is set on the outer protruding support plate at the bottom of the sliding soil box. The hexagonal buckle locks the overlapping buckle, so that the soil box pull rod is fixedly connected to the sliding soil box; the other end of the soil box pull rod is inserted horizontally into the installation port of the displacement control motor; one end of the fiber optic clamping pull rod used to replace the soil box pull rod is equipped with two pressure plates, one upper and one lower. There are silicone gaskets on the inner side of the two pressure plates. The two pressure plates are tightened with screws to clamp the fiber optic cable that passes horizontally out of the sliding soil box. The other end of the fiber optic clamping pull rod is bent downwards to the height of the installation port of the displacement control motor, and then horizontally inserted into the installation port of the displacement control motor to complete the connection with the displacement control motor.

[0020] Based on the above technical characteristics, the following steps are included when conducting fiber optic pull-out tests:

[0021] Step 1: Turn on the centralized control system and select the fiber optic pull-out test mode.

[0022] Step 2: Clean the fixed soil box and the sliding soil box, install the fiber optic clamping rod on the displacement control motor, operate the centralized control system to place the loading rod of the hydraulic cylinder and the fiber optic clamping rod in the initial position, and fasten the dual-box switching connector to merge the fixed soil box and the sliding soil box into a whole soil box.

[0023] Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the overall soil box height. After each layer of soil is filled, the soil sample is compacted by applying pressure with a hydraulic cylinder.

[0024] Step 4: When the soil is compacted to half the height of the overall soil box, place the optical fiber for the test on the soil layer and pass it out through the optical fiber holes on both sides of the overall soil box. On the side of the fixed soil box, clamp the end of the optical fiber with the optical fiber clamp, and pass the other end through the side of the sliding soil box and clamp it on the optical fiber clamping rod. Then connect the optical fiber to the optical fiber demodulator.

[0025] Step 5: Turn on the fiber optic demodulator and computer, open the demodulation program on the computer, monitor the remaining backfilling process, and ensure that the fiber optic cable remains in a working state throughout the remaining backfilling process.

[0026] Step 6: Use a displacement control motor to apply pre-tension to the optical fiber, making the optical fiber taut, continue to fill and compact the soil, and consolidate the soil sample.

[0027] Step 7: Set the confining pressure value on the centralized control system according to the confining pressure required for the test, and operate the hydraulic cylinder to apply the confining pressure to the loading plate.

[0028] Step 8: Set the required pull-out displacement value on the centralized control system and control the displacement control motor to drive the fiber clamping rod to apply the set pull-out displacement to the fiber; at the same time, use the centralized control system to record the displacement and tension changes during the pull-out process, and use the demodulation program in the computer to record the strain data along the fiber during the pull-out process.

[0029] Step 9: After the test is completed, shut down the centralized control system.

[0030] Based on the above technical features, the following steps are included when conducting a soil box pull-out cracking test:

[0031] Step 1: Open the centralized control system and select the soil box cracking test mode.

[0032] Step 2: Clean the fixed soil box and the sliding soil box, install the fiber optic clamping rod on the displacement control motor, operate the centralized control system to place the loading rod of the hydraulic cylinder and the fiber optic clamping rod in the initial position, and open the dual-box switching connector so that the sliding soil box can be controlled by the displacement control motor to slide.

[0033] Step 3: Fill the fixed soil box and the sliding soil box with soil in layers. The thickness of each layer should not exceed 1 / 3 of the height of the soil box. After each layer of soil is filled, the soil sample is compacted by applying pressure with a hydraulic cylinder.

[0034] Step 4: When the soil is compacted to half the height of the soil box, place the optical fiber for the test on the soil layer and pass it out through the optical fiber holes on both sides of the fixed soil box and the sliding soil box. On the side of the fixed soil box, one end of the optical fiber is clamped with an optical fiber clamp, and on the side of the sliding soil box, the other end of the optical fiber is clamped on the optical fiber clamping rod. Then connect the optical fiber to the optical fiber demodulator.

[0035] Step 5: Turn on the fiber optic demodulator and computer, open the demodulation program on the computer, monitor the remaining backfilling process, and ensure that the fiber optic cable remains in a working state throughout the remaining backfilling process.

[0036] Step 6: Use a displacement control motor to apply pre-tension to the optical fiber, making the optical fiber taut, continue to fill and compact the soil, and consolidate the soil sample.

[0037] Step 7: Set the confining pressure value on the centralized control system according to the required confining pressure for the test, and control the hydraulic cylinder to apply the set confining pressure to the loading plate.

[0038] Step 8: Replace the fiber optic clamping rod with a soil box rod. Based on the crack width value required for the test, set the displacement value on the centralized control system. Control the displacement control motor to drive the soil box rod to apply the set displacement to the sliding soil box. At the same time, use the centralized control system to record the displacement and tension changes during the test, and use the demodulation program in the computer to record the strain data along the fiber optic cable during the test.

[0039] Step 9: After the test is completed, shut down the centralized control system.

[0040] Based on the above technical features, the following steps are included when conducting an airbag inflation and cracking test:

[0041] Step 1: Turn on the centralized control system and select the airbag initiation test mode.

[0042] Step 2: Clean the fixed soil box and the sliding soil box, install the fiber optic clamping rod on the displacement control motor, operate the centralized control system to place the loading rod of the hydraulic cylinder and the fiber optic clamping rod in the initial position, and place the airbag between the fixed soil box and the sliding soil box; then fasten the dual-box switching connector to merge the fixed soil box and the sliding soil box into a whole soil box.

[0043] Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the overall soil box height. After each layer of soil is filled, the soil sample is compacted by applying pressure with a hydraulic cylinder.

[0044] Step 4: When the soil is compacted to half the height of the overall soil box, place the optical fiber for the test on the soil layer. The optical fiber passes through the optical fiber hole in the middle of the air bag and comes out from the optical fiber holes on both sides of the overall soil box. On the side of the fixed soil box, one end of the optical fiber is clamped with an optical fiber clamp. On the side of the sliding soil box, the other end of the optical fiber is clamped on the optical fiber clamping rod. Then connect the optical fiber to the optical fiber demodulator.

[0045] Step 5: Turn on the fiber optic demodulator and computer, open the demodulation program on the computer, monitor the remaining backfilling process, and ensure that the fiber optic cable remains in a working state throughout the remaining backfilling process.

[0046] Step 6: Use a displacement control motor to apply pre-tension to the optical fiber, making the optical fiber taut, continue to fill and compact the soil, and consolidate the soil sample.

[0047] Step 7: Set the confining pressure value on the centralized control system according to the required confining pressure for the test, and control the hydraulic cylinder to apply the set confining pressure to the loading plate.

[0048] Step 8: Simulate crack propagation; Inject 50kPa-400kPa high-pressure gas into the airbag. The airbag expands and causes cracks to form in the soil sample. Record the expansion height of the airbag during the test to calculate the crack width of the soil. Use the demodulation program in the computer to record the strain data along the optical fiber during the test.

[0049] Step 9: After the test is completed, shut down the centralized control system.

[0050] Based on the above technical features, the following steps are included when conducting a steel plate crack initiation test:

[0051] Step 1: Open the centralized control system and select the steel plate crack initiation test mode.

[0052] Step 2: Clean the fixed soil box and the sliding soil box, install the fiber optic clamping rod on the displacement control motor, operate the centralized control system to place the loading rod of the hydraulic cylinder and the fiber optic clamping rod in the initial position, insert the two overlapping steel plates between the fixed soil box and the sliding soil box; then fasten the dual-box switching connector to merge the fixed soil box and the sliding soil box into a whole soil box.

[0053] Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the overall soil box height. After each layer of soil is filled, the soil sample is compacted by applying pressure with a hydraulic cylinder.

[0054] Step 4: When the soil is compacted to half the height of the overall soil box, place the optical fiber for the test on the soil layer. The optical fiber passes through the optical fiber hole in the steel plate between the two steel plates and comes out from the optical fiber holes on both sides of the overall soil box. On the side of the fixed soil box, one end of the optical fiber is clamped with an optical fiber clamp. On the side of the sliding soil box, the other end of the optical fiber is clamped on the optical fiber clamping rod. Then connect the optical fiber to the optical fiber demodulator.

[0055] Step 5: Turn on the fiber optic demodulator and computer, open the demodulation program on the computer, monitor the remaining backfilling process, and ensure that the fiber optic cable remains in a conductive state throughout the remaining backfilling process.

[0056] Step 6: Use a displacement control motor to apply pre-tension to the optical fiber, making the optical fiber taut, continue filling and compacting the soil, and consolidate the soil sample;

[0057] Step 7: Set the confining pressure value on the centralized control system according to the confining pressure required for the test, and control the hydraulic cylinder to apply the set confining pressure to the loading plate;

[0058] Step 8: Simulate crack propagation; One of the two steel plates has a horizontally inserted anchor rod at its top; Tighten the anchor rod to open the upper part of the two steel plates, causing cracks in the soil sample. Record the opening distance of the top of the steel plate during the test to calculate the crack width of the soil; Use the demodulation program in the computer to record the strain data along the optical fiber during the test.

[0059] Step 9: After the test is completed, shut down the centralized control system.

[0060] This invention achieves a breakthrough in multimodal technology integration, organically combining fiber optic pull-out testing technology, which focuses on interfacial mechanical properties, with soil crack propagation simulation and distributed fiber optic monitoring technology, which focuses on monitoring applications. By sharing a testing platform, it achieves complementary and synergistic technical approaches, which strongly promotes the development of indoor testing instruments for the coordinated remediation of low-permeability contaminated soil through fracturing and permeability enhancement.

[0061] The beneficial effects of this invention are: its simplicity and sophistication meet the needs of laboratory-scale testing, and its core value lies in organically integrating fiber optic pull-out tests and soil crack propagation simulation experiments onto a single platform. This design allows researchers to simultaneously study the mechanical behavior of the fiber-soil interface and simulate and monitor the initiation and propagation morphology of internal cracks in a single experimental setup, avoiding the need for separate instruments in traditional methods, thus improving experimental efficiency and data acquisition consistency while reducing costs. The multimodal technology integration achieved by this invention directly addresses the indoor simulation and verification needs of fracturing and permeability enhancement synergistic remediation technologies for low-permeability contaminated soils. It provides a crucial prototype experimental platform for studying the formation law of crack networks during fracturing and the tracking and monitoring capabilities of distributed optical fibers during this process, significantly advancing the development of indoor experimental instruments for fracturing and permeability enhancement synergistic remediation of low-permeability contaminated soils. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the overall three-dimensional structure of the instrument of the present invention.

[0063] Figure 2 A schematic diagram illustrating the installation of optical fibers and the movement of sliding soil boxes.

[0064] Figure 3 A schematic diagram showing cracks that occur after fiber optic cable installation and the movement of a sliding soil box.

[0065] Figure 4 This is a diagram showing the initial state of two steel plates vertically stacked and inserted into a soil sample.

[0066] Figure 5 This is a schematic diagram showing the top of the two steel plates being opened.

[0067] Figure 6 This is a schematic diagram of the fiber optic holes in a steel plate.

[0068] Figure 7 This is a schematic diagram of an optical fiber passing through two steel plates.

[0069] Figure 8 This is a planar schematic diagram of the airbag and the airbag fiber optic port.

[0070] Figure 9 A schematic diagram of the air supply port for the airbag.

[0071] Figure 10 This is a schematic diagram of an optical fiber passing through an airbag.

[0072] Figure 11 This is a schematic diagram of airbag inflation.

[0073] Figure 12 This is a schematic diagram of the soil box tie rod.

[0074] Figure 13 This is a schematic diagram of a fiber optic clamping rod.

[0075] Figure 14 This is a schematic diagram of the control panel for a centralized control system.

[0076] Figure 15 This is a schematic diagram showing the connection between the soil box tie rod, the displacement control motor, and the sliding soil box.

[0077] Figure 16 A schematic diagram showing the connection between the fiber optic clamping rod and the displacement control motor, as well as the fiber optic clamping mechanism.

[0078] Reference numerals: reaction frame 101; hydraulic cylinder 102; loading plate 103; pressure sensor 104; reaction frame base 105; track 106;

[0079] Fixed soil box 201; Sliding soil box 202; Pulley 203; Crack propagation device 204; Water collection trough 205; Dual-box switching connector 206; Overlap buckle 207; Fiber optic hole 208;

[0080] Displacement control motor 301; displacement gauge 302; replaceable tie rod 303; soil box tie rod 303a; fiber optic clamping tie rod 303b; centralized control system 304; tension sensor 305;

[0081] Fiber optic demodulator 401; Computer 402; Fiber optic cable 403;

[0082] Steel plate 501; Anchor bolt 502; Soil sample 503; Fiber optic hole in steel plate 504; Anchor bolt hole 505;

[0083] Airbag 601; Airbag fiber optic hole 602; Air inlet 603. Detailed Implementation

[0084] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0085] In the description of this invention, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0086] A confining pressure-controlled crack propagation simulation and fiber optic testing instrument includes: a confining pressure control module, a crack propagation module, a pull-out test module, a distributed fiber optic sensing module, and a centralized control system 304. The crack propagation module and the pull-out test module are mounted on the confining pressure control module. The confining pressure control module, crack propagation module, and pull-out test module are integrated into a single structure.

[0087] The confining pressure control module is mainly used to load and control the pressure of soil sample 503. It can provide confining pressure of different ranges for soil sample 503, with a pressure range of 0-0.8 MPa, to simulate the formation pressure conditions at different depths and to build the framework of the entire instrument.

[0088] The crack propagation module offers three different types of crack propagation devices: soil box pull-out cracking, built-in airbag expansion cracking, and steel plate cracking, to simulate different soil crack propagation scenarios.

[0089] The pull-out test module is used to provide the power for the pull-out of the optical fiber 403 and the propagation of tensile cracks in the soil, and is equipped with a tension sensor 305 and a displacement meter 302 to monitor the mechanical displacement characteristics of the pull-out process in real time.

[0090] The distributed fiber optic sensing module is used to sense the strain distribution along the axial direction of fiber 403 and visualize the monitoring results on a computer.

[0091] The following section provides a detailed description of each module, in conjunction with the diagrams.

[0092] I. Confining Pressure Control Module

[0093] like Figure 1 As shown, the confining pressure control module is: a long strip soil box is divided into two parts to form a fixed soil box 201 and a sliding soil box 202. That is, the fixed soil box 201 and the sliding soil box 202 are boxes enclosed on three sides, and there are no side panels at the connection surface of the fixed soil box 201 and the sliding soil box 202.

[0094] A set of loading reaction components is configured above both the fixed soil box 201 and the sliding soil box 202. Each set of loading reaction components includes a reaction frame 101, a hydraulic cylinder 102, a loading plate 103, and a pressure sensor 104. The reaction frames 101 of the fixed soil box 201 and the sliding soil box 202 share the same reaction frame base 105. The reaction frame 101 is a portal frame structure, and its bottom is rigidly connected to the shared reaction frame base 105. The hydraulic cylinder 102 is located below the crossbeam of the reaction frame 101, and the loading rod of the hydraulic cylinder 102 applies vertical loading pressure to the loading plate 103. The loading plate 103 covers the surface of the soil sample 503, and the pressure sensor 104 is located between the loading plate 103 and the loading rod. The pressure sensor 104 monitors the confining pressure value in real time.

[0095] The dual-box switching connector 206 is installed at the connection between the fixed soil box 201 and the sliding soil box 202. The dual-box switching connector 206 can be a pin or a latch, allowing the fixed soil box 201 and the sliding soil box 202 to be either integrated or separate. The dual-box switching connector 206 can be installed at the side wall connection between the fixed soil box 201 and the sliding soil box 202, or as shown below. Figure 1 As shown, it is set on the plate surface of the protruding plate at the bottom of the fixed soil box 201 and the sliding soil box 202.

[0096] The bottom of the fixed soil box 201 and the sliding soil box 202 is provided with drainage holes and is connected to the water collection trough 205; the water collection trough 205 is set on the reaction frame base 105. The function of the drainage holes is to allow water in the soil sample 503 to flow into the water collection trough 205 when the soil sample 503 consolidates.

[0097] The bottom of the sliding soil box 202 is equipped with pulleys 203 and placed on a track 106 on one side of the reaction frame base 105. The track 106 is horizontal, so that the sliding soil box 202 can move along the track 106.

[0098] The hydraulic cylinder 102 of the confining pressure control module adopts a hydraulic servo control system, which can provide pressure of 0-0.8 MPa, pressure application accuracy ≤1 kPa, and the measurement accuracy of the pressure sensor 104 ≤0.1 kPa.

[0099] The fixed soil box 201 and the sliding soil box 202 can be made of stainless steel.

[0100] II. Crack Expansion Module

[0101] The crack propagation module includes the aforementioned fixed soil box 201, the aforementioned sliding soil box 202, and the crack propagation device 204.

[0102] The crack propagation device 204 is placed in the soil sample 503 between the fixed soil box 201 and the sliding soil box 202. The crack propagation device 204 is an airbag or steel plate crack initiation structure.

[0103] Crack propagation occurs in three ways: cracking initiation through the opening of the soil box, cracking initiation through the steel plate, and cracking initiation through the expansion of the built-in airbag.

[0104] like Figure 2 and Figure 3 As shown, when simulating the cracking of soil sample 503 by pulling open the soil box, the sliding soil box 202 can be pulled open to cause cracks in the soil.

[0105] like Figures 4 to 7 As shown, when simulating soil cracking by using steel plates, two steel plates 501 are placed side by side between two soil boxes. One of the steel plates 501 has an anchor bolt hole 505 at its top. Anchor bolts 502 are screwed into the anchor bolt hole 505, causing the upper parts of the two steel plates 501 to open and simulate cracks in the soil. A fiber optic hole 504 is provided in the middle of the steel plate 501.

[0106] like Figures 8 to 11 As shown, when simulating soil cracking by inflating the built-in airbag, the airbag 601 is placed between two soil boxes. Figure 9 The air inlet 603 shown is inflated, causing the airbag 601 to expand and simulate cracks in the soil. An airbag fiber optic hole 602 is located in the center of the airbag 601. Figure 10 The optical fiber 403 can pass through the airbag optical fiber hole 602. Figure 11 This is a schematic diagram of airbag inflation.

[0107] III. Pull-out Test Module

[0108] like Figure 1 As shown, the pull-out test module includes a displacement control motor 301, a displacement gauge 302, and a replaceable pull rod 303. The displacement control motor 301 is a servo motor with a displacement control accuracy of ≤0.1mm, a maximum tensile force of 20kN, and a measurement accuracy of 0.1mm.

[0109] A replaceable tie rod 303 is positioned between the displacement control motor 301 and the sliding soil box 202; a tension sensor 305 is mounted on the replaceable tie rod 303; a displacement gauge 302 is mounted on the displacement control motor 301. The pull-out test module can be mounted on the reaction frame base 105.

[0110] The replaceable pull rod 303 comes in two forms: soil box pull rod 303a and fiber optic clamping pull rod 303b. The soil box pull rod 303a and the fiber optic clamping pull rod 303b are interchangeable.

[0111] like Figure 12 and Figure 15As shown, the left end of the soil box pull rod 303a is equipped with a hexagonal buckle, and the overlapping buckle 207 is set on the outer protruding support plate at the bottom of the sliding soil box 202. The hexagonal buckle can lock the overlapping buckle 207, so that the soil box pull rod 303a is fixedly connected to the sliding soil box 202. The right end of the soil box pull rod 303a is horizontally inserted into the mounting port of the displacement control motor 301. In addition, the tension sensor 305 is set on the soil box pull rod 303a.

[0112] like Figure 13 and Figure 16 As shown, the left end of the fiber optic clamping rod 303b has two pressure plates, one upper and one lower. Silicone gaskets are located inside the two pressure plates. Screws are used to tighten the two pressure plates to clamp the fiber optic cable 403, which horizontally exits from the sliding soil box 202. Since the installation height of the displacement control motor 301 matches the height of the soil box rod 303a, and is lower than the horizontal exit height of the fiber optic cable 403, the right end of the fiber optic clamping rod 303b is bent downwards to the height of the installation port of the displacement control motor 301, and then horizontally bent and inserted into the installation port of the displacement control motor 301, completing the connection with the displacement control motor 301. This facilitates the replacement of the soil box rod 303a and the fiber optic clamping rod 303b.

[0113] In addition, the tension sensor 305 is mounted on the fiber optic clamping rod 303b.

[0114] The above is merely an example of the interchangeable use of the soil box pull rod 303a and the fiber optic clamping pull rod 303b. When the installation height of the displacement control motor 301 matches the height at which the fiber optic cable 403 extends horizontally from the sliding soil box 202, the right end of the fiber optic clamping pull rod 303b does not need to be bent and can be directly inserted into the installation port of the displacement control motor 301. However, the right end of the soil box pull rod 303a needs to be bent upwards and then horizontally inserted into the installation port of the displacement control motor 301. If the installation height of the displacement control motor 301 does not match the left ends of both the soil box pull rod 303a and the fiber optic clamping pull rod 303b, both the soil box pull rod 303a and the fiber optic clamping pull rod 303b can be bent at their right ends and then horizontally inserted into the installation port of the displacement control motor 301.

[0115] IV. Distributed Fiber Optic Sensing Module

[0116] like Figure 1 As shown, the distributed optical fiber sensing module includes an optical fiber 403, an optical fiber demodulator 401, and a computer 402. The optical fiber 403 is buried in the soil sample 503. The optical fiber demodulator 401 is connected to the optical fiber 403 and outputs optical fiber strain signal data. The computer 402 displays and stores the optical fiber strain data monitored by the optical fiber demodulator 401 in real time.

[0117] The distributed fiber optic sensing module can use ODFR (Optical Frequency Reflection) technology, achieving a spatial resolution of 1 mm and a strain measurement accuracy of ±1 με.

[0118] V. Centralized Control System

[0119] The centralized control system 304 sets the displacement value of the displacement control motor 301, controls the forward and backward movement of the displacement control motor 301, and can also adjust the pulling speed of the displacement control motor 301; the centralized control system 304 sets the confining pressure value in the confining pressure control module, and controls the loading and unloading of the hydraulic cylinder 102; the centralized control system 304 has a data acquisition unit that collects the confining pressure, tension, and displacement data transmitted by the pressure sensor 104, tension sensor 305, and displacement gauge 302.

[0120] The pressure sensor 104 is placed between the loading plate 103 and the loading rod of the cylinder 102 to measure the pressure applied to the soil. The tension sensor 305 and the replaceable tie rod 303 are integrated. When it is the soil box tie rod 303a, it measures the tension applied to the sliding soil box by the displacement control motor 301. When it is the fiber optic clamping tie rod 303b, it can measure the tension applied to the fiber optic cable 403. The displacement gauge 302 is placed on the displacement control motor 301 to measure the tensile length of the fiber optic cable 403 or the moving distance of the sliding soil box 202.

[0121] like Figure 14 The diagram shown is a schematic of the display panel of the centralized control system 304. It includes a power switch, and options for four test modes, as described below. Figure 14 As shown, there are four buttons: fiber optic pull-out, soil box cracking, steel plate cracking, and airbag cracking. Simultaneously, the confining pressure control allows input of specific values, zeroing, and confirmation; the loading rod's raising and lowering control buttons; the pull-out displacement control allows input of specific displacement values, zeroing, and confirmation; and the forward and backward movement of the pull rod allows for changing the forward and backward movement of pull rod 303.

[0122] The centralized control system 304 also displays schematic diagrams of displacement curves, confining pressure curves, and tensile force curves.

[0123] The specific methods for the four experimental modes of this invention are described below.

[0124] I. Conduct fiber pull-out test:

[0125] Step 1: Open the centralized control system 304 and select the fiber optic pull-out test mode.

[0126] Step 2: Clean the fixed soil box 201 and the sliding soil box 202, install the fiber optic clamping rod 303b on the displacement control motor 301, operate the centralized control system 304 to place the loading rod of the hydraulic cylinder 102 and the fiber optic clamping rod 303b in the initial position, and fasten the dual-box switching connector 206 to merge the fixed soil box 201 and the sliding soil box 202 into a whole soil box.

[0127] Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the overall soil box height. After each layer of soil is filled, the soil sample 503 is compacted by applying pressure with hydraulic cylinder 102.

[0128] Step 4: When the soil is compacted to half the height of the overall soil box, place the test optical fiber 403 on the soil layer and pass it out through the optical fiber holes 208 on both sides of the overall soil box. On the side of the fixed soil box 201, the end of the optical fiber is clamped with an optical fiber clamp, and the other end passes through the side of the sliding soil box 202 and is clamped on the optical fiber clamping rod 303b. Then connect the optical fiber 403 to the optical fiber demodulator 401.

[0129] Step 5: Turn on the fiber optic demodulator 401 and the computer 402. Open the demodulation program on the computer 402 and monitor the remaining backfilling process to ensure that the fiber optic cable 403 remains in a conductive state throughout the remaining backfilling process.

[0130] Step 6: Use displacement control motor 301 to apply pre-tension to optical fiber 403, making optical fiber 403 taut, continue filling and compacting soil, and consolidate soil sample 503.

[0131] Step 7: According to the confining pressure required for the test, set the confining pressure value on the centralized control system 304, and operate the hydraulic cylinder 102 to apply the confining pressure to the loading plate 103.

[0132] Step 8: Set the required pull-out displacement value on the centralized control system 304 and control the displacement control motor 301 to drive the fiber clamping rod 303b to apply the set pull-out displacement to the fiber 403; at the same time, use the centralized control system 304 to record the displacement and tension changes during the pull-out process, and use the demodulation program in the computer 402 to record the strain data along the fiber 403 during the pull-out process.

[0133] Step 9: After the test, shut down the centralized control system 304.

[0134] II. Conduct a soil box pull-out cracking test.

[0135] Step 1: Open the centralized control system 304 and select the soil box cracking test mode.

[0136] Step 2: Clean the fixed soil box 201 and the sliding soil box 202, install the fiber optic clamping rod 303b on the displacement control motor 301, operate the centralized control system 304 to place the loading rod of the hydraulic cylinder 102 and the fiber optic clamping rod 303b in the initial position, and open the dual box switching connector 206 so that the sliding soil box 202 can be controlled to slide by the displacement control motor 301.

[0137] Step 3: Fill soil into the fixed soil box 201 and the sliding soil box 202 in layers. The thickness of each layer should not exceed 1 / 3 of the height of the soil box. After each layer of soil is filled, the soil sample 503 is compacted by applying pressure with the hydraulic cylinder 102.

[0138] Step 4: When the soil is compacted to half the height of the soil box, place the test optical fiber 403 on the soil layer and pass it through the optical fiber holes 208 on both sides of the fixed soil box 201 and the sliding soil box 202. On the side of the fixed soil box 201, one end of the optical fiber 403 is clamped with an optical fiber clamp, and on the side of the sliding soil box 202, the other end of the optical fiber 403 is clamped on the optical fiber clamping rod 303b. Then connect the optical fiber 403 to the optical fiber demodulator 401.

[0139] Step 5: Turn on the fiber optic demodulator 401 and the computer 402. Open the demodulation program on the computer 402 and monitor the remaining backfilling process to ensure that the fiber optic cable 403 remains in a conductive state throughout the remaining backfilling process.

[0140] Step 6: Use displacement control motor 301 to apply pre-tension to optical fiber 403, making optical fiber 403 taut, continue filling and compacting soil, and consolidate soil sample 503.

[0141] Step 7: Set the confining pressure value on the centralized control system 304 according to the confining pressure required for the test, and control the hydraulic cylinder 102 to apply the set confining pressure to the loading plate 103.

[0142] Step 8: Replace the fiber clamping rod 303b with the soil box rod 303a. Based on the crack width value required for the test, set the displacement value on the centralized control system 304. Control the displacement control motor 301 to drive the soil box rod 303a to apply the set displacement to the sliding soil box 202. At the same time, use the centralized control system 304 to record the displacement and tension changes during the test, and use the demodulation program in the computer 402 to record the strain data along the fiber optic cable 403 during the test.

[0143] Step 9: After the test, shut down the centralized control system 304.

[0144] III. Conduct an airbag inflation and cracking test.

[0145] Step 1: Open the centralized control system 304 and select the airbag initiation test mode.

[0146] Step 2: Clean the fixed soil box 201 and the sliding soil box 202, install the fiber optic clamping rod 303b on the displacement control motor 301, operate the centralized control system 304 to place the loading rod of the hydraulic cylinder 102 and the fiber optic clamping rod 303b in the initial position, and place the airbag between the fixed soil box 201 and the sliding soil box 202; then fasten the dual-box switching connector 206 to merge the fixed soil box 201 and the sliding soil box 202 into a whole soil box.

[0147] Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the overall soil box height. After each layer of soil is filled, the soil sample 503 is compacted by applying pressure with hydraulic cylinder 102.

[0148] Step 4: When the soil is compacted to half the height of the overall soil box, place the optical fiber 403 for the test on the soil layer. The optical fiber 403 passes through the optical fiber hole 602 in the middle of the air bag and comes out from the optical fiber holes 208 on both sides of the overall soil box. On the side of the fixed soil box 201, one end of the optical fiber 403 is clamped with an optical fiber clamp. On the side of the sliding soil box 202, the other end of the optical fiber 403 is clamped on the optical fiber clamping rod 303b. Then connect the optical fiber 403 to the optical fiber demodulator 401.

[0149] Step 5: Turn on the fiber optic demodulator 401 and the computer 402. Open the demodulation program on the computer 402 and monitor the remaining backfilling process to ensure that the fiber optic cable 403 remains in a conductive state throughout the remaining backfilling process.

[0150] Step 6: Use displacement control motor 301 to apply pre-tension to optical fiber 403, making optical fiber 403 taut, continue filling and compacting soil, and consolidate soil sample 503.

[0151] Step 7: Set the confining pressure value on the centralized control system 304 according to the confining pressure required for the test, and control the hydraulic cylinder 102 to apply the set confining pressure to the loading plate 103.

[0152] Step 8: Simulate crack propagation; Inject 50kPa-400kPa high-pressure gas into the airbag. The expansion of the airbag causes cracks to form in the soil sample 503. Record the expansion height of the airbag during the test to calculate the crack width of the soil. Use the demodulation program in the computer 402 to record the strain data along the optical fiber 403 during the test.

[0153] Step 9: After the test, shut down the centralized control system 304.

[0154] IV. Conducting steel plate cracking tests

[0155] Step 1: Open the centralized control system 304 and select the steel plate crack initiation test mode.

[0156] Step 2: Clean the fixed soil box 201 and the sliding soil box 202, install the fiber optic clamping rod 303b on the displacement control motor 301, operate the centralized control system 304 to place the loading rod of the hydraulic cylinder 102 and the fiber optic clamping rod 303b in the initial position, insert the two overlapping steel plates 501 between the fixed soil box 201 and the sliding soil box 202; then fasten the dual-box switching connector 206 to merge the fixed soil box 201 and the sliding soil box 202 into a whole soil box.

[0157] Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the overall soil box height. After each layer of soil is filled, the soil sample 503 is compacted by applying pressure with hydraulic cylinder 102.

[0158] Step 4: When the soil is compacted to half the height of the overall soil box, place the test optical fiber 403 on the soil layer. The optical fiber 403 passes through the optical fiber hole 504 in the middle of the two steel plates 501 and comes out from the optical fiber holes 208 on both sides of the overall soil box. On the side of the fixed soil box 201, one end of the optical fiber 403 is clamped with an optical fiber clamp. On the side of the sliding soil box 202, the other end of the optical fiber 403 is clamped on the optical fiber clamping rod 303b. Then connect the optical fiber 403 to the optical fiber demodulator 401.

[0159] Step 5: Turn on the fiber optic demodulator 401 and the computer 402. Open the demodulation program on the computer 402 and monitor the remaining backfilling process to ensure that the fiber optic cable 403 remains in a conductive state throughout the remaining backfilling process.

[0160] Step 6: Use displacement control motor 301 to apply pre-tension to optical fiber 403, making optical fiber 403 taut, continue filling and compacting soil, and consolidate soil sample 503.

[0161] Step 7: Set the confining pressure value on the centralized control system 304 according to the confining pressure required for the test, and control the hydraulic cylinder 102 to apply the set confining pressure to the loading plate 103.

[0162] Step 8: Simulate crack propagation; One of the two steel plates 501 has a horizontally inserted anchor rod 502 at its top; Tighten the anchor rod 502 to push open the upper part of the two steel plates 501, causing cracks to appear in the soil sample 503. Record the opening distance of the top of the steel plate 501 during the test to calculate the crack width of the soil; Use the demodulation program in the computer 402 to record the strain data along the optical fiber 403 during the test.

[0163] Step 9: After the test, shut down the centralized control system 304.

[0164] The above description of the embodiments is intended to enable those skilled in the art to understand and use the present invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art based on the principles of the present invention, without departing from the scope of the invention, should be within the protection scope of the present invention.

Claims

1. A crack propagation simulation and fiber optic testing instrument with controllable confining pressure, characterized in that: It includes a confining pressure control module, a crack propagation module, a pull-out test module, a distributed fiber optic sensing module, and a centralized control system (304). The confining pressure control module is composed of a long strip soil box divided into two parts, forming a fixed soil box (201) and a sliding soil box (202); a set of loading reaction components is correspondingly configured on the top of the fixed soil box (201) and the sliding soil box (202), and each set of loading reaction components includes a reaction frame (101), a hydraulic cylinder (102), a loading plate (103) and a pressure sensor (104); the pressure sensor (104) monitors the confining pressure value in real time; the fixed soil box (201) and the sliding soil box (202) can be combined into a whole or separated; the fixed soil box (201) and the sliding soil box (202) are equipped with a drainage system; The crack propagation module includes the fixed soil box (201), the sliding soil box (202), and the crack propagation device (204); the crack propagation device (204) is disposed in the soil sample (503) between the fixed soil box (201) and the sliding soil box (202); The pull-out test module includes a displacement control motor (301), a displacement gauge (302), and a replaceable tie rod (303); the replaceable tie rod (303) is disposed between the displacement control motor (301) and the sliding soil box (202); a tension sensor (305) is provided on the replaceable tie rod (303); the displacement gauge (302) is disposed on the displacement control motor (301); The distributed optical fiber sensing module includes an optical fiber (403), an optical fiber demodulator (401), and a computer (402). The optical fiber (403) is buried in the soil sample (503). The optical fiber demodulator (401) is connected to the optical fiber (403) and outputs optical fiber strain data. The computer (402) displays and stores the optical fiber strain data monitored by the optical fiber demodulator (401) in real time. The centralized control system (304) sets the displacement value of the displacement control motor (301), controls the forward and backward movement of the displacement control motor (301), and can also adjust the pulling speed of the displacement control motor (301); the centralized control system (304) sets the confining pressure value in the confining pressure control module, and controls the loading and unloading of the oil cylinder (102); the centralized control system (304) has a data acquisition unit that collects the confining pressure, tension and displacement data transmitted by the pressure sensor (104), the tension sensor (305) and the displacement gauge (302).

2. The confining pressure controllable crack propagation simulation and fiber optic testing apparatus according to claim 1, characterized in that: The reaction frames (101) of the two sets of loading reaction components share the same reaction frame base (105); the reaction frame (101) is a portal frame structure, and its bottom is rigidly connected to the shared reaction frame base (105); the hydraulic cylinder (102) is located below the crossbeam of the reaction frame (101), and the loading rod of the hydraulic cylinder (102) vertically loads and presses against the loading plate (103); the loading plate (103) covers the surface of the soil sample (503), and the pressure sensor (104) is located between the loading plate (103) and the loading rod; A dual-box switching connector (206) is provided at the connection between the fixed soil box (201) and the sliding soil box (202), so that the fixed soil box (201) and the sliding soil box (202) can be integrated or separated; The sliding soil box (202) is equipped with pulleys (203) at the bottom and is placed on a track (106) on one side of the reaction frame base (105). The track (106) is horizontal, so that the sliding soil box (202) can move along the track (106). The drainage system of the fixed soil box (201) and the sliding soil box (202) is provided with drainage holes at the bottom of the fixed soil box (201) and the sliding soil box (202) and connected to the water collection trough (205); the water collection trough (205) is set on the reaction frame base (105).

3. The confining pressure controllable crack propagation simulation and fiber optic testing instrument according to claim 2, characterized in that: The replaceable pull rod (303) is a soil box pull rod (303a) and an optical fiber clamping pull rod (303b); the soil box pull rod (303a) and the optical fiber clamping pull rod (303b) are interchangeable; one end of the soil box pull rod (303a) is installed on the displacement control motor (301), and the other end is connected to the sliding soil box (202); one end of the optical fiber clamping pull rod (303b) is installed on the displacement control motor (301), and the other end clamps the optical fiber (403) passing through the sliding soil box (202).

4. The confining pressure controllable crack propagation simulation and fiber optic testing instrument according to claim 3, characterized in that: The crack propagation device (204) is an airbag, and the center of the airbag is provided with an airbag fiber optic hole (602) so that the fiber optic cable (403) can pass through the airbag.

5. The confining pressure controllable crack propagation simulation and fiber optic testing instrument according to claim 3, characterized in that: The crack propagation device (204) consists of two steel plates (501) stacked vertically. One of the steel plates (501) has a horizontally inserted anchor rod (502) on its top. By tightening the anchor rod (502), the two steel plates (501) are separated. A steel plate fiber optic hole (504) is reserved in the middle of the two steel plates (501) so that the optical fiber (403) can pass through the two steel plates (501).

6. The confining pressure controllable crack propagation simulation and fiber optic testing instrument according to claim 3, characterized in that: One end of the soil box pull rod (303a) is provided with a hexagonal buckle, and an overlap buckle (207) is provided on the outer protruding support plate at the bottom of the sliding soil box (202). The hexagonal buckle locks the overlap buckle (207) to fix the soil box pull rod (303a) to the sliding soil box (202). The other end of the soil box pull rod (303a) is inserted horizontally into the mounting port of the displacement control motor (301). The fiber optic clamp is used to replace the soil box pull rod (303a). One end of the pull rod (303b) is provided with two pressure plates, one above the other. The inner side of the two pressure plates has a silicone gasket. The two pressure plates are tightened with screws to clamp the optical fiber (403) that passes horizontally out of the sliding soil box (202). The other end of the optical fiber clamping pull rod (303b) is bent downwards to the height of the installation port of the displacement control motor (301), and then horizontally inserted into the installation port of the displacement control motor (301) to complete the connection with the displacement control motor (301).

7. An application method of the crack propagation simulation and fiber optic testing instrument with controllable confining pressure as described in claim 3, characterized in that: The following steps are included when performing an optical fiber pull-out test. Step 1: Turn on the centralized control system (304) and select the fiber optic pull-out test mode; Step 2: Clean the fixed soil box (201) and the sliding soil box (202), install the fiber optic clamping rod (303b) on the displacement control motor (301), operate the centralized control system (304) to place the loading rod of the hydraulic cylinder (102) and the fiber optic clamping rod (303b) in the initial position, and fasten the dual-box switching connector (206) so that the fixed soil box (201) and the sliding soil box (202) are combined into a whole soil box; Step 3: Fill the integral soil box with soil in layers. The thickness of each layer shall not exceed 1 / 3 of the height of the integral soil box. After each layer of soil is filled, the soil sample (503) shall be compacted by applying pressure through the oil cylinder (102). Step 4: When the soil is compacted to half the height of the overall soil box, place the test optical fiber (403) on the soil layer and pass it out from the optical fiber holes (208) on both sides of the overall soil box. On the side of the fixed soil box (201), the end of the optical fiber is clamped with an optical fiber clamp, and the other end passes through the side of the sliding soil box (202) and is clamped on the optical fiber clamping rod (303b). Then connect the optical fiber (403) to the optical fiber demodulator (401). Step 5: Turn on the fiber optic demodulator (401) and the computer (402), open the demodulation program in the computer (402), monitor the remaining backfilling process, and ensure that the fiber optic cable (403) is always in the path state during the remaining backfilling process; Step 6: Use the displacement control motor (301) to apply pre-tension to the optical fiber (403) to make the optical fiber (403) taut, continue to fill and compact the soil, and consolidate the soil sample (503); Step 7: According to the confining pressure required for the test, set the confining pressure value on the centralized control system (304) and operate the oil cylinder (102) to apply the confining pressure to the loading plate (103); Step 8: Set the required pull-out displacement value on the centralized control system (304) according to the test, and control the displacement control motor (301) to drive the fiber clamping rod (303b) to apply the set pull-out displacement to the fiber (403); at the same time, use the centralized control system (304) to record the displacement change and tension change during the pull-out process, and use the demodulation program in the computer (402) to record the strain data along the fiber (403) during the pull-out process; Step 9: After the test is completed, shut down the centralized control system (304).

8. An application method of the crack propagation simulation and fiber optic testing instrument with controllable confining pressure as described in claim 3, characterized in that: The following steps are included when conducting a soil box pull-out cracking test. Step 1: Turn on the centralized control system (304) and select the soil box cracking test mode; Step 2: Clean the fixed soil box (201) and the sliding soil box (202), install the fiber optic clamping rod (303b) on the displacement control motor (301), operate the centralized control system (304) to place the loading rod of the hydraulic cylinder (102) and the fiber optic clamping rod (303b) in the initial position, and open the dual-box switching connector (206) so that the sliding soil box (202) can be controlled to slide by the displacement control motor (301); Step 3: Fill soil into the fixed soil box (201) and the sliding soil box (202) in layers. The thickness of each layer shall not exceed 1 / 3 of the height of the soil box. After each layer of soil is filled, the soil sample (503) shall be compacted by applying pressure through the oil cylinder (102). Step 4: When the soil is compacted to half the height of the soil box, place the optical fiber (403) for the test on the soil layer and pass it out from the optical fiber holes (208) on both sides of the fixed soil box (201) and the sliding soil box (202). On the side of the fixed soil box (201), one end of the optical fiber (403) is clamped with an optical fiber clamp, and on the side of the sliding soil box (202), the other end of the optical fiber (403) is clamped on the optical fiber clamping rod (303b). Then connect the optical fiber (403) to the optical fiber demodulator (401). Step 5: Turn on the fiber optic demodulator (401) and the computer (402), open the demodulation program in the computer (402), monitor the remaining backfilling process, and ensure that the fiber optic cable (403) is always in the path state during the remaining backfilling process; Step 6: Use the displacement control motor (301) to apply pre-tension to the optical fiber (403) to make the optical fiber (403) taut, continue to fill and compact the soil, and consolidate the soil sample (503); Step 7: According to the confining pressure required for the test, set the confining pressure value on the centralized control system (304), and operate the oil cylinder (102) to apply the set confining pressure to the loading plate (103); Step 8: Replace the fiber clamping rod (303b) with the soil box rod (303a). According to the crack width value required for the test, set the displacement value on the centralized control system (304) and control the displacement control motor (301) to drive the soil box rod (303a) to apply the set displacement to the sliding soil box (202). At the same time, use the centralized control system (304) to record the displacement and tension changes during the test, and use the demodulation program in the computer (402) to record the strain data along the fiber (403) during the test. Step 9: After the test is completed, shut down the centralized control system (304).

9. An application method of the crack propagation simulation and fiber optic testing instrument with controllable confining pressure as described in claim 4, characterized in that: The following steps are included when conducting an airbag inflation and cracking test. Step 1: Turn on the centralized control system (304) and select the airbag initiation test mode; Step 2: Clean the fixed soil box (201) and the sliding soil box (202), install the fiber optic clamping rod (303b) on the displacement control motor (301), operate the centralized control system (304) to place the loading rod of the cylinder (102) and the fiber optic clamping rod (303b) in the initial position, place the airbag between the fixed soil box (201) and the sliding soil box (202); then fasten the dual-box switching connector (206) to merge the fixed soil box (201) and the sliding soil box (202) into a whole soil box; Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the height of the overall soil box. After each layer of soil is filled, the soil sample (503) is compacted by applying pressure through the oil cylinder (102). Step 4: When the soil is compacted to half the height of the overall soil box, place the optical fiber (403) for the test on the soil layer. The optical fiber (403) passes through the optical fiber hole (602) in the middle of the air bag and comes out from the optical fiber holes (208) on both sides of the overall soil box. On the side of the fixed soil box (201), one end of the optical fiber (403) is clamped with an optical fiber clamp. On the side of the sliding soil box (202), the other end of the optical fiber (403) is clamped on the optical fiber clamping rod (303b). Then connect the optical fiber (403) to the optical fiber demodulator (401). Step 5: Turn on the fiber optic demodulator (401) and the computer (402), open the demodulation program in the computer (402), monitor the remaining backfilling process, and ensure that the fiber optic cable (403) is always in the path state during the remaining backfilling process; Step 6: Use the displacement control motor (301) to apply pre-tension to the optical fiber (403) to make the optical fiber (403) taut, continue to fill and compact the soil, and consolidate the soil sample (503); Step 7: According to the confining pressure required for the test, set the confining pressure value on the centralized control system (304), and operate the oil cylinder (102) to apply the set confining pressure to the loading plate (103); Step 8: Simulate crack propagation; inject 50kPa-400kPa high-pressure gas into the airbag, the airbag expands and causes cracks to appear in the soil sample (503), record the expansion height of the airbag during the test to calculate the crack width of the soil, and use the demodulation program in the computer (402) to record the strain data along the optical fiber (403) during the test. Step 9: After the test is completed, shut down the centralized control system (304).

10. An application method of the crack propagation simulation and fiber optic testing instrument with controllable confining pressure as described in claim 5, characterized in that: The following steps are included when conducting a crack initiation test on a steel plate. Step 1: Turn on the centralized control system (304) and select the steel plate crack initiation test mode; Step 2: Clean the fixed soil box (201) and the sliding soil box (202), install the fiber optic clamping rod (303b) on the displacement control motor (301), operate the centralized control system (304) to place the loading rod of the cylinder (102) and the fiber optic clamping rod (303b) in the initial position, insert the two overlapping steel plates (501) between the fixed soil box (201) and the sliding soil box (202); then fasten the dual-box switching connector (206) to merge the fixed soil box (201) and the sliding soil box (202) into a whole soil box; Step 3: Fill the soil into the overall soil box in layers. The thickness of each layer should not exceed 1 / 3 of the height of the overall soil box. After each layer of soil is filled, the soil sample (503) is compacted by applying pressure through the oil cylinder (102). Step 4: When the soil is compacted to half the height of the overall soil box, place the optical fiber (403) for testing on the soil layer. The optical fiber (403) passes through the optical fiber hole (504) in the middle of the two steel plates (501) and comes out from the optical fiber holes (208) on both sides of the overall soil box. On the side of the fixed soil box (201), one end of the optical fiber (403) is clamped with an optical fiber clamp. On the side of the sliding soil box (202), the other end of the optical fiber (403) is clamped on the optical fiber clamping rod (303b). Then connect the optical fiber (403) to the optical fiber demodulator (401). Step 5: Turn on the fiber optic demodulator (401) and the computer (402), open the demodulation program in the computer (402), monitor the remaining backfilling process, and ensure that the fiber optic cable (403) is always in the path state during the remaining backfilling process; Step 6: Use the displacement control motor (301) to apply pre-tension to the optical fiber (403) to make the optical fiber (403) taut, continue to fill and compact the soil, and consolidate the soil sample (503); Step 7: According to the confining pressure required for the test, set the confining pressure value on the centralized control system (304), and operate the oil cylinder (102) to apply the set confining pressure to the loading plate (103); Step 8: Simulate crack propagation; One of the two steel plates (501) is provided with a horizontally inserted anchor rod (502) at the top; by tightening the anchor rod (502), the upper part of the two steel plates (501) is pushed open, causing cracks to appear in the soil sample (503). During the test, the opening distance of the top of the steel plate is recorded to calculate the crack width of the soil. The strain data along the optical fiber (403) during the experiment were recorded using the demodulation program in the computer (402); Step 9: After the test is completed, shut down the centralized control system (304).

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