True triaxial test device and method for rock heat conduction parameter in-situ measurement under controllable temperature-stress coupling condition

Abstract

The invention discloses a true triaxial test device for rock heat conduction parameter in-situ measurement under a controllable temperature-stress coupling condition. The device comprises a triaxial pressure chamber, a temperature adjusting system, a double-electric servo loading system and an automatic control unit, the temperature adjusting system tightly surrounds the outer side wall of the triaxial pressure chamber, and the temperature applying value of the temperature adjusting system ranges from 10 DEG C to 150 DEG C; an upper seat and a base are arranged at the upper end and the lower end of the triaxial pressure chamber respectively, and a test space is defined by the triaxial pressure chamber, the upper seat and the base; the upper end of the side wall of the testing space is provided with an exhaust channel and a temperature sensor channel which are communicated with the outside from inside to outside, and the lower end of the testing space is provided with an oil conveying pipeline and a flat cable channel. The device has the advantages of being simple in structure, convenient to use and high in precision. The invention further discloses a method of the true triaxial test device for in-situ measurement of the heat conduction parameters of the rock under the controllable temperature-stress coupling condition.

Description

Technical Field

[0001] This invention relates to the field of testing instruments, and more specifically to a true triaxial testing apparatus for in-situ determination of thermal conductivity parameters of rocks under controlled temperature-stress coupling conditions. This invention also relates to a method for using this true triaxial testing apparatus for in-situ determination of thermal conductivity parameters of rocks under controlled temperature-stress coupling conditions. Background Technology

[0002] Thermal conductivity is an important thermal parameter of rocks. In projects such as underground nuclear waste disposal, CO2 sequestration, and natural gas and shale gas storage, it is often necessary to test the thermal conductivity of rocks. Accurate measurement of rock thermal conductivity is crucial for the study of multi-field coupling in rock mass engineering. During diagenesis and long-term geological processes, the actual environment of deep rock masses is extremely complex, subjected to various external loads and temperature changes. Changes in stress state and internal damage significantly impact the thermal conductivity of rocks. Currently, research on rock thermal conductivity under conditions of simultaneous temperature and stress variations is extremely limited, far from meeting the needs of current engineering applications. With the rapid development of underground space technology in my country, the standards and requirements for rock mass engineering are becoming increasingly stringent.

[0003] If the thermal conductivity of rocks under stress variation conditions is not considered, it is impossible to know whether and how much the temperature change in the actual environment affects the rock sample; the experimental conditions cannot be made closer to reality, and therefore the true state of the rock mass in actual engineering cannot be more accurately reflected.

[0004] Therefore, it is necessary to design a true triaxial test fixture that is simple in structure, easy to use, and highly accurate in testing the thermal conductivity of rocks under temperature and stress changes. Summary of the Invention

[0005] This invention provides a true triaxial test device for in-situ determination of thermal conductivity parameters of rocks under controllable temperature-stress coupling conditions. It can perform true triaxial tests on the thermal conductivity of rocks under temperature and stress changes, solving the problem of testing the thermal conductivity of rocks under different stress states and temperature changes in three phases, and can more accurately reflect the condition of rocks in actual engineering environments.

[0006] The present invention also provides a method for in-situ determination of the thermal conductivity parameters of rocks under controlled temperature-stress coupling conditions, as described above.

[0007] The present invention can be implemented as follows: a true triaxial test device for in-situ measurement of rock thermal conductivity parameters under controllable temperature-stress coupling conditions, including a triaxial pressure chamber 4, a temperature control system 20, a dual electric servo loading system and an automated control unit;

[0008] The temperature regulation system 20 is tightly surrounded by the outer wall of the triaxial pressure chamber 4, and the temperature regulation range is -50℃ to 300℃. It is electrically connected to the automatic control unit.

[0009] The triaxial pressure chamber 4 has an upper seat 1 and a base 3 at its upper and lower ends, respectively, which together with the triaxial pressure chamber 4 form a test space 21. The upper seat 1 is equipped with a vertical loading piston 2. The lower middle part of the upper seat 1 is provided with an upper seat bottom port 1.1. The upper horizontal ends of the vertical loading piston 2 are slidably connected to the upper seat 1, and the lower end extends axially out of the upper seat bottom port 1.1. A pressure sensor is provided between the vertical loading piston 2 and the upper pressure head 12.

[0010] The dual electric servo loading system includes a left shaft 7, a right shaft 8, and an electric servo drive module 5. One end of the left shaft 7 and the right shaft 8 are connected to the electric servo drive module 5, and the other end passes through the side wall of the triaxial pressure chamber 4 and is located directly above the side of the horizontal pressure head 13. Displacement sensors 6 are provided on both the left and right shafts.

[0011] An upper pressure head 12 and a rock sample 15 are disposed in the test space 21. The upper pressure head 12 and the first step 3.1 are respectively disposed at the upper and lower ends of the rock sample 15, and the horizontal pressure head 13 is respectively disposed at the left and right ends of the rock sample 15. A rubber sleeve 14 is disposed on the outside of the rock sample 15. The lower end of the rock sample 15 is provided with an axially upward extending mounting hole 17, and a thermal probe 16 is disposed in the mounting hole 17. The lower end of the thermal probe 16 is fixed in the flat groove 18.

[0012] The upper side wall of the test space 21 is provided with an exhaust channel 9 and a temperature sensor channel 19 that communicate with the outside from the inside. The lower end of the test space 21 is provided with an oil pipeline 11 and a cable channel 10. The oil pipeline 11 and the cable channel 10 extend downward from the upper end of the second step 3.2 and bend at 90° to the outer side wall of the second step 3.2. A data cable is connected to the lower end of the thermal probe 16 and passes through the cable channel 10 to connect with the external data control and acquisition system.

[0013] The automation control unit is a PLC controller, which is electrically connected to the temperature control system and the dual electric servo loading system to realize parameter setting, automatic control and data processing.

[0014] Furthermore, when the measured temperature deviates from the set value by more than ±1℃, the automated control unit automatically adjusts the heating power or cooling intensity; the electric servo drive module forms a closed-loop control with the displacement sensor and pressure sensor, the horizontal force loading accuracy is ≤±0.1MPa, and the loading rate can be steplessly adjusted within the range of 0.01MPa / s to 1MPa / s.

[0015] Furthermore, a sealing ring is provided on the contact surface between the vertical loading piston 2 and the upper seat bottom port 1.1, a sealing ring is provided on the contact surface between the left shaft 7 and the side wall of the triaxial pressure chamber 4, a sealing ring is provided on the contact surface between the right shaft 8 and the side wall of the triaxial pressure chamber 4, and a sealing ring is provided on the contact surface between the lower end of the triaxial pressure chamber 4 and the base 3.

[0016] Furthermore, the rock sample 15 is a rectangular body with a square base and a height of 100mm. The mounting holes 17 extend upward along the axial direction, and the hole spacing is ≥20mm. The rubber sleeve 14 has a length of 140mm and a thickness of 5mm. The contact surfaces of the upper pressure head 12 and the horizontal pressure head 13 are both coated with silicon nitride ceramic coating, with a friction coefficient ≤0.03. The bottom dimensions of the upper pressure head 12 are the same as the bottom dimensions of the rock sample 15.

[0017] Furthermore, the vertical loading piston 2, upper pressure head 12, rock sample 15, and base 3 are coaxially arranged; the inner diameter of the upper pressure head 12, rubber sleeve 14, rock sample 15, and first step 3.1 are the same, with a fit tolerance ≤ ±0.02mm; the triaxial pressure chamber 4 is integrally forged from 40CrNiMoA alloy steel, with a wall thickness increased by 10% compared to the original structure, and a compressive strength ≥800MPa.

[0018] Furthermore, the automated control unit supports a synchronous temperature and stress loading mode, can preset the linkage ratio between the heating rate and the stress loading rate, and has an abnormal alarm function.

[0019] Another objective of this invention is to provide a method for testing the thermal conductivity of rocks under temperature and stress changes using a true triaxial test apparatus for in-situ measurement of rock thermal conductivity parameters under controlled temperature-stress coupling conditions, comprising the following steps:

[0020] S1: Prepare a rock sample 15; set an axially upward mounting hole 17 at the bottom of the rock sample 15, attach strain gauges to the side of the rock sample, place a thermal probe 16 in the center hole 17 of the rock sample 15, and lead the data line of the thermal probe 16 out from the flat groove 18, and connect it together with the data line of the side strain gauge through the cable channel 10 to the data control and acquisition system; use a rubber sleeve 14 to cover the outside of the rock sample 15 and the lower end of the upper pressure head 12 and the upper end of the first step 3.1, and clamp it with a clamping ring 22; axial strain sensors are set on both sides of the upper pressure head 12.

[0021] S2: Place the vertically loaded piston 2 into the upper seat 1. The upper seat 1, together with the triaxial pressure chamber 4, is placed on the base 3 and connected by a nut. The left shaft 7 and the right shaft 8 are respectively connected to the pump-driven loading part 5 and the manual loading part 6 and pass through the side wall of the triaxial pressure chamber 4.

[0022] S3: Connect the oil supply pipeline 11 to the hydraulic servo pump. Before the test begins, close the exhaust channel 9 and the oil supply channel 11.

[0023] S4: Apply horizontal force σ2, set the target value of σ2 and the loading rate, the PLC controller controls the dual electric servo loading system to drive the left and right shafts to advance synchronously, the displacement sensor provides real-time feedback, and the pressure sensor stops loading when it detects that the actual force value has reached the set value;

[0024] S5: Apply horizontal force σ3, open exhaust channel 9 and oil pipeline 11, the hydraulic servo pump delivers hydraulic oil to oil pipeline 11 until the hydraulic oil flows out from exhaust channel 9, then close exhaust channel 9 and continue pressurizing to the set value of σ3;

[0025] S6: Apply axial force σ1. The axial loading system applies axial force to the vertical loading piston 2. The pressure sensor monitors the force value in real time until the set value of σ1 is reached. If synchronous loading is required, the temperature-stress synchronization mode is activated through the automatic control unit, and the temperature and stress are adjusted according to the preset ratio.

[0026] S7: Test thermal conductivity, stop loading and maintain stress state, temperature control system raise temperature to predetermined value, distributed temperature sensor monitors multiple point temperature deviation ≤±1℃ and lasts for 5 minutes, multi-channel thermal conductivity measurement system synchronously collects data from 4 thermal probes 16, and calculates average thermal conductivity after removing outliers.

[0027] S8: After the test is completed and the temperature has cooled to room temperature, remove the axial force σ1, horizontal force σ2, and horizontal force σ3 in sequence, remove the loading components, disassemble the device, and take out the rock sample 15 and the thermal probe 16.

[0028] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0029] 1. This invention solves the problem of testing the thermal conductivity of rocks under different stress states and temperature changes in three phases, enabling true triaxial tests of thermal conductivity of rocks under temperature and stress changes; it can more accurately reflect the condition of rocks in actual engineering environments.

[0030] 2. Simple structure, easy to use, and high precision;

[0031] 3. A thermometer located on the upper side wall of the triaxial pressure chamber can measure the temperature inside the triaxial pressure chamber, ensuring precise control of the test temperature;

[0032] 4. The upper and lower ends of the rubber sleeve are respectively fitted onto the lower end of the upper pressure head and the upper end of the first step, and a clamping ring is set on the outside of the rubber sleeve to prevent hydraulic oil from entering the rock sample and the mounting hole, ensuring the sealing of the rock sample; a sealing ring is set on the contact surface between the vertical loading piston and the bottom port of the upper seat, a sealing ring is set on the contact surface between the left shaft and the side wall of the triaxial pressure chamber, a sealing ring is set on the contact surface between the right shaft and the side wall of the triaxial pressure chamber, and a sealing ring is set on the contact surface between the lower end of the triaxial pressure chamber and the base, ensuring the sealing of the entire test device;

[0033] 5. Consider the influence of temperature and understand the impact and magnitude of temperature changes on rock samples in actual environments; improve the multi-field coupling effect in rock mass engineering to include the influence of temperature on rock mass; make experimental conditions closer to reality and better reflect the true state of rock mass in actual engineering.

[0034] 6. Expanded application scope: The temperature range covers -50℃ to 300℃, and the stress loading accuracy is improved to ±0.1MPa, which can meet the testing needs of multiple scenarios such as frozen soil, high-temperature thermal reservoirs, and deep mines.

[0035] 7. Optimized operational efficiency: Automated control replaces manual operation, reducing testing time by 30% and minimizing human error; automatic data processing and export functions improve the efficiency of scientific research.

[0036] 8. Improved test realism: The stress-temperature synchronous loading mode and uniform stress application are closer to the actual stress and heat process of deep rock masses, providing more reliable data support for multi-field coupling research in rock mass engineering.

[0037] The technical solution of this invention solves a technical problem that people have long desired to solve but have never been able to achieve: conventional triaxial instruments can only load at ≤200℃ and cannot apply true triaxial stress synchronously, which leads to the failure of thermal conductivity testing of deep (>200℃) rock samples. This device adopts a true triaxial high-temperature loading system (300℃, 600MPa), and realizes synchronous loading and unloading of temperature and triaxial stress through electro-hydraulic servo closed-loop control. The heating-holding-cooling cycle is fully coupled with the stress cycle. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of the present invention.

[0039] Figure 2 This is a schematic diagram of the cross-sectional structure of the flat groove of the present invention.

[0040] Figure 3 This is a schematic diagram of the rock sample encapsulation structure of the present invention.

[0041] Figure 4 This is a schematic diagram of the structure of the automated control unit of the present invention.

[0042] Figure 5 This is a flowchart of the method for testing the thermal conductivity of rocks under temperature and stress changes according to the present invention.

[0043] In the diagram, 1-upper seat, 1.1-bottom port of upper seat, 2-vertical loading piston, 3-base, 3.1-first step, 3.2-second step

[0044] Step, 3.3-Third step, 4-Triaxial pressure chamber, 5-Electric servo drive module, 6-Pressure sensor, 7-Left shaft, 8-Right shaft, 9-Exhaust channel, 10-Cable channel, 11-Oil pipeline, 12-Upper pressure head, 13-Horizontal pressure head, 14-Rubber sleeve, 15-Rock sample, 16-Thermal probe, 17-Mounting hole, 18-Flat groove, 19-Temperature sensor channel, 20-Temperature control system, 21-Test space, 22-Clamping ring, 23-Automatic control unit. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] like Figure 1 , Figure 2 As shown, embodiments of the present invention provide a true triaxial test apparatus for in-situ determination of thermal conductivity parameters of rocks under controllable temperature-stress coupling conditions, including a triaxial pressure chamber 4, and further including a temperature control system 20, a dual electric servo loading system and an automatic control unit 23;

[0047] The temperature regulation system 20 is tightly surrounded by the outer wall of the triaxial pressure chamber 4, and the temperature regulation range is -50℃ to 300℃. It is electrically connected to the automatic control unit 23.

[0048] The triaxial pressure chamber 4 has an upper seat 1 and a base 3 at its upper and lower ends, respectively, which together with the triaxial pressure chamber 4 form a test space 21. The upper seat 1 is equipped with a vertical loading piston 2. The lower middle part of the upper seat 1 is provided with an upper seat bottom port 1.1. The upper horizontal ends of the vertical loading piston 2 are slidably connected to the upper seat 1, and the lower end extends axially out of the upper seat bottom port 1.1. A pressure sensor is provided between the vertical loading piston 2 and the upper pressure head 12.

[0049] The dual electric servo loading system includes a left shaft 7, a right shaft 8, and an electric servo drive module 5. One end of the left shaft 7 and the right shaft 8 are connected to the electric servo drive module 5, and the other end passes through the side wall of the triaxial pressure chamber 4 and is located directly above the side of the horizontal pressure head 13. Displacement sensors 6 are provided on both the left and right shafts.

[0050] An upper pressure head 12 and a rock sample 15 are disposed within the test space 21. The upper pressure head 12 and the first step 3.1 are respectively disposed at the upper and lower ends of the rock sample 15, and the horizontal pressure head 13 is respectively disposed at the left and right ends of the rock sample 15. A rubber sleeve 14 is disposed on the outside of the rock sample 15. The lower end of the rock sample 15 is provided with an axially upward extending mounting hole 17, and a thermal probe 16 is disposed in the mounting hole 17, with the lower end of the thermal probe 16 fixed in the flat groove 18. Figure 2 As shown

[0051] The upper sidewall of the test space 21 is provided with an exhaust channel 9 and a temperature sensor channel 19 that communicate with the outside from the inside. The lower sidewall of the test space 21 is provided with an oil delivery pipe 11 and a wiring channel 10. The oil delivery pipe 11 and the wiring channel 10 extend downward from the upper end of the second step 3.2 and bend at 90° to the outer sidewall of the second step 3.2. Figure 1 As shown, a data cable is connected to the lower end of the thermal probe 16, and the data cable passes through the cable channel 10 to connect to an external data control and acquisition system.

[0052] The automation control unit 23 is a PLC controller, which is electrically connected to the temperature regulation system 20 and the dual electric servo loading system to realize parameter setting, automatic control and data processing.

[0053] When the measured temperature deviates from the set value by more than ±1℃, the automatic control unit 23 automatically adjusts the heating power or cooling intensity; the electric servo drive module forms a closed-loop control with the displacement sensor and pressure sensor, the horizontal force loading accuracy is ≤±0.1MPa, and the loading rate can be steplessly adjusted within the range of 0.01MPa / s to 1MPa / s.

[0054] A sealing ring is provided on the contact surface between the vertical loading piston 2 and the upper seat bottom port 1.1; a sealing ring is provided on the contact surface between the left shaft 7 and the side wall of the triaxial pressure chamber 4; a sealing ring is provided on the contact surface between the right shaft 8 and the side wall of the triaxial pressure chamber 4; and a sealing ring is provided on the contact surface between the lower end of the triaxial pressure chamber 4 and the base 3.

[0055] The rock sample 15 is a rectangular body with a square base and a height of 100mm. The mounting holes 17 extend axially upwards, with a hole spacing ≥20mm. The rubber sleeve 14 is 140mm long and 5mm thick. The contact surfaces of the upper pressure head 12 and the horizontal pressure head 13 are coated with a silicon nitride ceramic coating, with a friction coefficient ≤0.03. The bottom dimensions of the upper pressure head 12 are the same as the bottom dimensions of the rock sample 15. Figure 3 As shown

[0056] The vertical loading piston 2, upper pressure head 12, rock sample 15, and base 3 are coaxially arranged; the inner diameter of the upper pressure head 12, rubber sleeve 14, rock sample 15, and first step 3.1 are the same, with a fit tolerance of ≤±0.02mm; the triaxial pressure chamber 4 is integrally forged from 40CrNiMoA alloy steel, with a wall thickness increased by 10% compared to the original structure, and a compressive strength ≥800MPa.

[0057] This experimental apparatus consists of an upper seat 1, a triaxial pressure chamber 4, and a base 3, which are coaxially fixed from top to bottom to form a closed loading chamber. The bottom end of the upper seat has an upper seat bottom port 1.1, through which the vertical loading piston 2 passes from top to bottom and slides axially. The base 3 has a first step 3.1, a second step 3.2, and a third step 3.3 to support the rock sample 15 and the internal wires and oil passages. The side walls of the triaxial pressure chamber 4 are arranged in a ring shape, and the temperature regulation system 20 tightly covers its outer perimeter to achieve isothermal heating or cooling of the entire experimental chamber. The upper pressure head 12 abuts against the lower end of the vertical loading piston 2 and applies force from top to bottom. The rock sample 15 is located below it. The left shaft 7 and the right shaft 8 pass horizontally from both sides of the triaxial pressure chamber 4 and are in contact with the horizontal pressure head 13 to apply bidirectional confining pressure. Thus, the upper, lower, left, and right sides together form a true triaxial loading condition.

[0058] The left shaft 7 and right shaft 8 are connected at one end to the electric servo drive module 5 to achieve horizontal stress σ2 loading. Both are equipped with sealing rings at the side walls of the triaxial pressure chamber 4 to prevent oil leakage. A pressure sensor 6 is installed at the contact surface between the lower end of the vertical loading piston 2 and the upper pressure head 12 to detect changes in axial force σ1 in real time. The cable channel 10 and the oil pipeline 11 extend downward along the second step 3.2 and bend at 90 degrees to the outer wall at the bottom, so that the data line of the thermal probe 16 and the hydraulic oil pipe are led out of the device through the shortest path, improving measurement stability. The exhaust channel 9 and the temperature sensor channel 19 are symmetrically arranged at the upper edge of the test space 21 to ensure that the gas in the cavity can be discharged in time during temperature control and to allow temperature distribution monitoring to enter the sealed cavity.

[0059] Before operation, the rock sample 15 is placed in the center of the first step 3.1, and the rubber sleeve 14 is fitted in, ensuring that its upper end fits against the lower end of the upper pressure head 12 and its lower end is fully pressed against the step. Then, a clamping ring 22 is used to lock it in a circumferential manner to form a sealed enclosure. The mounting hole 17 at the bottom of the sample extends upward and connects with the flat groove 18. The thermal probe 16 is inserted from the bottom upward and anchored in the flat groove 18. Its data line is led out from the cable channel 10 to the external acquisition module. Subsequently, the upper seat 1 is installed and the vertical loading piston 2 is inserted into the bottom port 1.1 of the upper seat. The nut and the base 3 are used to fix the entire enclosure. During loading, the dual electric servo units advance the horizontal pressure head 13 synchronously through the left shaft 7 and the right shaft 8. The piston 2 moves downward in the vertical direction to generate σ1 compression on the sample. After the three-dimensional pressure is formed, the temperature regulation system 20 is activated to achieve uniform temperature conduction in the closed cavity.

[0060] After the test loading is completed, the automated control unit 23 enters the constant temperature stage. By comparing the set temperature with the sensing results in real time, the heating or cooling power is adjusted when the deviation exceeds ±1 degree Celsius to keep the temperature of the confining pressure oil chamber and the sample body stable. The thermal probe 16 forms a stable heat flow path from the axial center of the sample outward. The temperature field diffuses from the inside to the outside through the rock sample 15. The distributed temperature monitoring is fed back by the temperature difference gradient through the temperature sensing network introduced by channel 19. The data control module calculates the heat transfer curve in real time. When the temperature difference between the inside and outside of the sample is stable and lasts for more than five minutes, the system collects the probe heat change rate and calculates the thermal conductivity by combining the sample geometry and temperature gradient, realizing the in-situ thermal conductivity measurement under stress-temperature coupling. During unloading, the axial and horizontal loads are removed in sequence, the sealing structure is released, and finally the sample and thermal probe are taken out to complete the cyclic test.

[0061] like Figure 4 As shown, the automated control unit 23 supports a synchronous temperature and stress loading mode, can preset the linkage ratio between the heating rate and the stress loading rate, and has an abnormal alarm function.

[0062] like Figure 5As shown, this embodiment of the invention provides a method for testing the thermal conductivity of rock under temperature and stress changes using a true triaxial test apparatus for in-situ measurement of rock thermal conductivity parameters under controlled temperature-stress coupling conditions, comprising the following steps:

[0063] Step 1: Prepare rock sample 15; Set an axially upward extending mounting hole 17 at the bottom of rock sample 15, attach strain gauges to the side of rock sample, place thermal probe 16 in the center hole 17 of rock sample 15, and lead the data line of thermal probe 16 out from the flat groove 18, and connect it together with the data line of the side strain gauge through the cable channel 10 to the data control and acquisition system; Cover the outside of rock sample 15 and the lower end of upper pressure head 12 and the upper end of first step 3.1 with rubber sleeve 14, and clamp it with clamping ring 22; Axial strain sensors are set on both sides of upper pressure head 12;

[0064] Step 2: Place the vertically loaded piston 2 into the upper seat 1. The upper seat 1, together with the triaxial pressure chamber 4, is placed on the base 3 and connected by nuts. The left shaft 7 and the right shaft 8 are respectively connected to the pump-driven loading part 5 and the manual loading part 6 and pass through the side wall of the triaxial pressure chamber 4.

[0065] Step 3: Connect the oil supply pipeline 11 to the hydraulic servo pump. Before the test begins, close the exhaust channel 9 and the oil supply channel 11.

[0066] Step 4: Apply horizontal force σ2, set the target value of σ2 and the loading rate, the PLC controller controls the dual electric servo loading system to drive the left and right shafts to advance synchronously, the displacement sensor provides real-time feedback, and the pressure sensor stops loading when it detects that the actual force value has reached the set value;

[0067] Step 5: Apply horizontal force σ3, open exhaust channel 9 and oil supply pipeline 11, and the hydraulic servo pump delivers hydraulic oil to the oil supply pipeline 11 until the hydraulic oil flows out from exhaust channel 9. Then close exhaust channel 9 and continue pressurizing to the set value of σ3.

[0068] Step 6: Apply axial force σ1. The axial loading system applies axial force to the vertical loading piston 2. The pressure sensor monitors the force value in real time until the set value of σ1 is reached. If synchronous loading is required, the temperature-stress synchronization mode is activated through the automatic control unit, and the temperature and stress are adjusted according to the preset ratio.

[0069] Step 7: Test the thermal conductivity, stop loading and maintain the stress state, the temperature control system raises the temperature to the predetermined value, the distributed temperature sensor monitors the temperature deviation at multiple points ≤±1℃ and lasts for 5 minutes, the multi-channel thermal conductivity measurement system simultaneously collects data from 4 thermal probes, removes outliers and calculates the average thermal conductivity.

[0070] Step 8: After the test is completed and the temperature has cooled to room temperature, remove the axial force σ1, horizontal force σ2, and horizontal force σ3 in sequence, remove the loading components, disassemble the device, and take out the rock sample 15 and the thermal probe 16.

[0071] The controllable temperature-stress coupled true triaxial thermal conductivity parameter in-situ measurement device of the present invention achieves real-time acquisition of the thermal conductivity of rock materials under multi-field coupling by precisely superimposing the temperature field and the triaxial stress field. Its core principle lies in: independently achieving triaxial stress loading of σ1, σ2, and σ3 through a dual-electric servo loading system and a vertical loading piston, while a temperature control system forms a closed and controllable temperature environment around the test space; under stable temperature-stress coupling conditions, a quantitative thermal pulse is applied to the interior of the rock by a thermal probe, and the thermal conductivity of the rock under different loading states is obtained by measuring the temperature response data and retrieving the thermal conductivity.

[0072] Before the test, the rock sample was sealed with a rubber sleeve to prevent the infiltration of hydraulic media from interfering with temperature measurement and heat conduction paths, ensuring that the heat transfer behavior of the sample was dominated solely by the rock itself. A thermal probe was placed in the central mounting hole of the sample, ensuring close contact between the probe and the rock, allowing heat to diffuse into the sample in an approximately radial manner. Distributed temperature sensors were deployed along the sample and the test space to monitor temperature uniformity in real time and provide feedback to the automated control unit, achieving closed-loop temperature regulation control. The temperature control deviation was stabilized within ±1℃, providing a steady-state thermal field basis for characterizing thermal conductivity.

[0073] During stress loading, the left and right servo shafts apply σ2 to both sides of the specimen. Strain and displacement sensors form a feedback closed loop, allowing for precise control of the loading rate and final value. The hydraulic servo system injects oil into the test space through oil pipelines. Once the cavity is full of oil and discharged from the exhaust channel, σ3 is effectively loaded. The axial load σ1 is applied to the rock by the vertical servo loading column, causing the specimen to form a complete triaxial stress state. Pressure, displacement, and temperature signals are all input to the PLC control unit to achieve synchronous loading, proportional linkage, and dynamic adjustment of temperature and stress. This allows the thermal field and stress field to evolve collaboratively according to a set rhythm, simulating the actual confining pressure and geothermal environment of deep underground rocks.

[0074] Once the temperature and stress stabilize, the thermal probe generates controlled thermal disturbances, and the temperature change within the rock over time conforms to the thermal conductivity equation. The system simultaneously acquires temperature response curves at multiple points, and by analyzing the temperature rise rate, heat diffusion pattern, and steady-state temperature gradient, the thermal conductivity and its relationship with temperature-stress coupling are determined. Multi-channel measurements enable comparison and anomaly removal, ensuring the accuracy and reliability of the experimental data.

[0075] In summary, this invention constructs an experimental system that can simulate the deep earth environment through true triaxial loading, full temperature range control, embedded thermal probe heat transfer measurement, and automatic closed-loop synchronous control. It enables in-situ determination of rock thermal conductivity parameters under real stress conditions, providing key testing methods for geothermal extraction, deep well engineering, oil and gas reservoir evaluation, and geophysical thermal reservoir analysis.

[0076] It should be noted that embodiments of the present invention can be implemented using hardware, software, or a combination of both. The hardware portion can be implemented using dedicated logic; the software portion can be stored in memory and executed by a suitable instruction execution system, such as a microprocessor or dedicated-design hardware. Those skilled in the art will understand that the above-described devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory firmware, or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented using hardware circuitry such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field-programmable gate arrays, programmable logic devices, etc., or using software executed by various types of processors, or using a combination of the above-described hardware circuitry and software, such as firmware.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A true triaxial testing apparatus for in-situ measurement of thermal conductivity parameters of rocks under controlled temperature and stress coupling conditions, characterized in that, It includes a triaxial pressure chamber, a temperature control system, a dual-servo horizontal loading unit, a vertical loading unit, a thermal probe measurement structure, and an automated control unit, among which: The triaxial pressure chamber has an upper seat and a base to form a test space. The vertical loading piston passes through the upper seat axially and contacts the upper pressure head. The left and right servo loading shafts pass through the side walls of the pressure chamber horizontally and are positioned opposite the horizontal pressure head. The rock sample is placed in the test space and covered with a rubber sleeve. The bottom of the sample has an upward-extending mounting hole. The thermal probe is inserted into the mounting hole and led out to the data acquisition module through a cable channel. The temperature control system tightly covers the triaxial pressure chamber and is bidirectionally electrically connected to the automatic control unit, which can implement wide-range heating and cooling of the test environment. The automatic control unit is used for loading control, temperature control and data processing to realize in-situ measurement of thermal conductivity.

2. The apparatus according to claim 1, characterized in that, The temperature control system has a temperature range of -50 to 300 degrees Celsius, and the automatic control unit triggers heating or cooling correction based on the temperature deviation.

3. The apparatus according to claim 1, characterized in that, Both the dual-servo horizontal loading unit and the vertical loading piston are equipped with pressure sensors and displacement sensors to form a closed-loop control. The horizontal loading accuracy is ±0.1 MPa, and the loading rate is continuously adjustable from 0.01 to 1 MPa per second.

4. The apparatus according to claim 1, characterized in that, The three-axis pressure chamber, the left and right shafts, and the vertical piston are equipped with sealing ring structures, and the base mating surface is equipped with circumferential seals to achieve oil pressure isolation and high-pressure stable support.

5. A sample measuring assembly suitable for determining the thermal conductivity of rocks under true triaxial coupling conditions, characterized in that, It includes a rock sample, a rubber sleeve, a thermal probe, and a wire lead-out unit. The rock sample is rectangular and has an axially extending mounting hole. The thermal probe is inserted into and fixed to a flat groove structure at the lower end of the mounting hole and is connected to an external data system through a wiring channel. The rubber sleeve covers the outer periphery of the sample and fits tightly against the upper pressure head and step to isolate the confining pressure medium and form a constant thermal conductivity test envelope.

6. The component according to claim 5, characterized in that, The sample height is 100 mm, and the center distance between the mounting holes is not less than 20 mm.

7. The component according to claim 5, characterized in that, The rubber sleeve is 140 mm long and 5 mm thick. The contact surface between the upper pressure head and the horizontal pressure head is coated with a silicon nitride ceramic coating, and its coefficient of friction is not higher than 0.

03.

8. The component according to claim 5, characterized in that, The upper pressure head is coaxially arranged with the sample, and the fit gap tolerance is no higher than ±0.02 mm. The triaxial pressure chamber is forged from 40CrNiMoA and the wall thickness is increased by 10% compared with the original wall thickness. The pressure bearing strength is no less than 800 MPa.

9. A method for in-situ testing of the thermal conductivity of rock based on the apparatus described in any one of claims 1 to 8, characterized in that, The process includes steps such as sample preparation, assembly of measurement components, simultaneous application of triaxial stress, establishment of a temperature control field, acquisition of temperature transfer curves, and calculation of thermal conductivity. Its characteristic is that: After applying horizontal stress σ2, the closed-loop adjustment is made to the set value. Then, oil is injected to apply horizontal stress σ3 to the stable point. Subsequently, axial stress σ1 is applied and the temperature control stage is entered. When the temperature of the test space reaches the set value and the temperature difference at multiple points is not higher than ±1 degree Celsius for 5 minutes, the multi-channel acquisition of thermal probe data is started and the heat flux and temperature gradient are calculated to obtain the thermal conductivity.

10. The method according to claim 9, characterized in that, The automated control unit executes a synchronous temperature and stress loading mode, coordinating the heating rate and stress loading rate through a preset ratio, and supporting abnormal deviation alarms and test shutdown protection.

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