Cryogenic rock mechanics response monitoring method, system and device

Abstract

The application discloses a kind of super-low temperature rock mechanics response monitoring method, system and equipment, and the super-low temperature rock mechanics response monitoring method includes: the rock sample with strain-temperature sensitive grating array and temperature reference grating array being mutually connected in series is placed in super-low temperature environment loading system;Start super-low temperature environment loading system, and the wavelength shift of each grating and the wavelength shift of each grating are measured in real time;The wavelength shift of one of temperature reference grating measured in temperature reference grating array is used to calculate the real temperature of rock sample corresponding grating measuring point;The physical model of strain-temperature sensitive grating center wavelength shift in strain-temperature sensitive grating array is established, and the total strain of rock sample grating measuring point is calculated according to real temperature and the physical model;According to the total strain of rock sample and the natural freeze shrinkage strain of rock sample, the mechanical strain generated by the ice expansion of pore water of rock sample is calculated, and frost heaving stress.

Description

Technical Field

[0001] This application relates to the field of rock mechanics testing and geotechnical engineering monitoring technology, specifically to a method, system and equipment for monitoring rock mechanics response at ultra-low temperatures. Background Technology

[0002] With the rapid development of engineering fields such as polar resource development, underground liquefied natural gas (LNG) storage, and deep space exploration, the study of the mechanical behavior of rocks under ultra-low temperature conditions has become increasingly important. Rocks are porous media that undergo two diametrically opposed mechanical responses simultaneously in low-temperature environments: one is the thermal contraction (freezing contraction) of the rock's mineral framework due to temperature decrease; the other is the frost heave force generated by the phase change and freezing of pore water, resulting in increased volume. These two effects are coupled within the rock, leading to an extremely complex stress state.

[0003] Currently, when measuring the mechanical response of rocks at extremely low temperatures, traditional resistance strain gauges are usually attached to the periphery of the rock sample. However, the resistivity of resistance strain gauges changes drastically at extremely low temperatures, which can easily lead to distorted measurement data or sensor failure. It is difficult to distinguish whether the change in sensor readings is due to material shrinkage caused by temperature or expansion stress caused by icing, resulting in the inability to accurately obtain the true mechanical response value. Summary of the Invention

[0004] This application provides a method, system, and device for monitoring the mechanical response of rocks at ultra-low temperatures. It can solve the technical problem in the prior art that when traditional resistance strain gauges are pasted on the periphery of rock samples, the resistivity of the resistance strain gauges changes drastically in ultra-low temperature environments, which can easily lead to distorted measurement data or sensor failure. It is also difficult to distinguish whether the change in sensor readings is due to material shrinkage caused by temperature or expansion stress caused by icing, thus making it impossible to accurately obtain the true mechanical response value.

[0005] In a first aspect, embodiments of this application provide a method for monitoring the mechanical response of rock at ultra-low temperatures. The method includes: placing a rock sample with an internally embedded strain-temperature sensitive grating array and a series-connected temperature reference grating array into an ultra-low temperature environment loading system; activating the ultra-low temperature environment loading system and measuring the wavelength drift of each grating in the strain-temperature sensitive grating array and the wavelength drift of each grating in the temperature reference grating array in real time; calculating the true temperature at the corresponding grating measurement point of the rock sample using the wavelength drift of one of the temperature reference gratings measured in the temperature reference grating array; establishing a physical model of the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array, and calculating the total strain of the rock sample at the grating measurement point based on the true temperature and the physical model; calculating the mechanical strain of the rock sample at the grating measurement point caused by the expansion of pore water freezing at the grating measurement point based on the total strain of the rock sample at the grating measurement point and the natural freezing and shrinkage strain of the rock sample itself; and calculating the frost heave stress at the grating measurement point using the mechanical strain of the rock sample at the grating measurement point caused by the expansion of pore water freezing at the grating measurement point.

[0006] In conjunction with the first aspect, in one embodiment, calculating the true temperature of the rock sample at the corresponding grating measurement point using the wavelength drift of one of the temperature reference gratings in the temperature reference grating array includes: calibrating the temperature reference gratings in the temperature reference grating array within a selected temperature range; and fitting the wavelength drift of the temperature reference grating. and temperature changes The relationship is denoted as ,in, The center wavelength of the temperature reference grating at the initial temperature. , , The nonlinear temperature sensitivity coefficient obtained from the calibration;

[0007] The true temperature at the corresponding grating measurement point of the rock sample is calculated using the nonlinear temperature sensitivity coefficient obtained from calibration and the wavelength drift of the measured temperature reference grating.

[0008] In conjunction with the first aspect, in one embodiment, before calculating the total strain of the rock sample at the grating measurement point based on the actual temperature and the physical model, the method includes: selecting a dry sample of the same material as the rock sample, cooling the dry sample within a selected temperature range, and measuring the linear expansion coefficient function of the dry sample, denoted as... Using the measured linear expansion coefficient function of the dried sample, the theoretical freeze-shrinkage strain curve of the dried sample at the selected temperature is calculated, denoted as... ,in, This represents the natural shrinkage strain caused by the temperature drop in the dried sample.

[0009] In conjunction with the first aspect, in one embodiment, the center wavelength drift of the strain-temperature sensitive grating includes the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted from the rock sample to the strain-temperature sensitive grating. Establishing a physical model for the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array includes: establishing a physical model of the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted from the rock sample to the strain-temperature sensitive grating, denoted as... ;in, The center wavelength of the strain-temperature sensitive grating at the initial temperature; This refers to the center wavelength shift of the strain-temperature sensitive grating. The effective photoelastic coefficient of the strain-temperature sensitive grating; The total strain transferred from the rock sample to the strain-temperature sensitive grating; This refers to the nonlinear temperature response term of the strain-temperature sensitive grating itself.

[0010] In conjunction with the first aspect, in one embodiment, after calculating the true temperature at the corresponding grating measurement point of the rock sample using the calibrated nonlinear temperature sensitivity coefficient and the measured wavelength shift of the temperature reference grating, the method includes: using the true temperature and a physical model of the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted from the rock sample to the strain-temperature sensitive grating, calculating the total strain transmitted from the rock sample to the strain-temperature sensitive grating. .

[0011] In conjunction with the first aspect, in one embodiment, the total strain transmitted from the rock sample to the strain-temperature sensitive grating Including the natural frost-shrinkage strain of rocks caused by temperature drops Mechanical strain caused by the expansion of pore water upon freezing After the cryogenic loading system is activated, the process includes: recording the number of acoustic emission impacts, acoustic emission energy, and acoustic emission arrival time inside the rock sample; and calculating the total strain transferred from the rock sample to the strain-temperature sensitive grating. Next, this includes: determining whether the rock sample is in the mineral skeleton freeze-shrinkage stage or the pore water phase transformation freeze-swelling and microcrack initiation stage; if If the value is negative and the acoustic emission signal is quiet, then the rock sample is in the mineral framework shrinkage stage; if If the value is positive and the acoustic emission signal is high-frequency and high-energy, then the rock sample is in the stage of pore water phase transformation frost heave and microcrack initiation.

[0012] In conjunction with the first aspect, in one embodiment, calculating the frost heave stress at the grating measuring point includes: using the mechanical strain at the grating measuring point caused by the expansion of pore water due to freezing as the frost heave strain of the rock sample; and applying the generalized Hooke's law, combined with the dynamic elastic modulus of the rock sample at low temperature. The frost heave strain of the rock sample is converted into frost heave stress of the rock sample. The conversion formula is .

[0013] In conjunction with the first aspect, in one embodiment, the frost heave strain of the rock sample is converted into frost heave stress of the rock sample. Next, this includes: calculating the frost heave stress based on each grating measurement point. Based on the coordinates of the corresponding measuring points, an interpolation algorithm is used to generate a three-dimensional stress cloud map inside the rock sample.

[0014] Secondly, this application provides a cryogenic rock mechanical response monitoring system, comprising: a loading module for placing a rock sample containing a series-connected strain-temperature sensitive grating array and a series-connected temperature reference grating array into a cryogenic environment loading system; the loading module for activating the cryogenic environment loading system and measuring the wavelength drift of each grating in the strain-temperature sensitive grating array and the wavelength drift of each grating in the temperature reference grating array in real time; and a measurement module for calculating the wavelength drift of the rock sample at the corresponding grating measurement point using the wavelength drift of one of the temperature reference gratings in the temperature reference grating array. The system comprises: a true temperature; a first calculation module, which establishes a physical model of the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array, and calculates the total strain of the rock sample at the grating measuring point based on the true temperature and the physical model; a second calculation module, which calculates the mechanical strain of the rock sample at the grating measuring point caused by the expansion of pore water due to freezing at the grating measuring point based on the total strain of the rock sample at the grating measuring point and the natural frost-shrinkage strain of the rock sample itself; and a third calculation module, which calculates the frost heave stress at the grating measuring point using the mechanical strain of the rock sample at the grating measuring point caused by the expansion of pore water due to freezing at the grating measuring point.

[0015] Thirdly, this application provides a cryogenic rock mechanical response monitoring device, which includes a processor, a memory, and a cryogenic rock mechanical response monitoring program stored in the memory and executable by the processor. When the cryogenic rock mechanical response monitoring program is executed by the processor, it implements the steps of the cryogenic rock mechanical response monitoring method as described above.

[0016] The beneficial effects of the technical solutions provided in this application include:

[0017] By embedding a series of strain-temperature sensitive grating arrays and temperature reference grating arrays inside a rock sample, the fiber optic array can overcome the limitations of traditional single-point measurements. Furthermore, the combination of the strain-temperature sensitive grating array and the temperature reference grating array allows for the separate monitoring of temperature and strain at the same measurement point. Moreover, based on the grating measurement points in the rock sample, the total strain at multiple grating measurement points can be calculated separately. By combining the total strain at the corresponding grating measurement points with the natural freeze-shrinkage strain of the rock sample itself, it is possible to accurately distinguish whether the rock is in a state of freeze-shrinkage or freeze-swelling, eliminating the significant measurement errors caused by temperature changes. In addition, the magnitude of freeze-swelling stress at the corresponding grating measurement points can be calculated based on the mechanical strain generated by the expansion of pore water upon freezing at the grating measurement points. This solves the technical problem that traditional resistance strain gauges cannot accurately obtain the true mechanical response value in related technologies. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating an embodiment of the ultra-low temperature rock mechanical response monitoring method of this application;

[0019] Figure 2 This is a schematic diagram of the cryogenic environment loading system of this application;

[0020] Figure 3 This is a schematic diagram of the hardware structure of the cryogenic rock mechanical response monitoring device involved in the embodiments of this application.

[0021] In the picture:

[0022] 1. Rock sample; 2. Intelligent rock core sensor array; 3. Atomizing nozzle; 4. Acoustic emission sensor; 5. Double-layer vacuum insulated environment chamber; 6. Liquid nitrogen Dewar flask; 7. Cryogenic solenoid valve; 8. Anti-frost device; 9. Industrial-grade nitrogen tank; 10. Vaporization heater. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0024] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0025] In a first aspect, embodiments of this application provide a method for monitoring the mechanical response of rocks at ultra-low temperatures.

[0026] In one embodiment, reference is made to Figure 1 , Figure 1 This is a flowchart illustrating the first embodiment of the ultra-low temperature rock mechanical response monitoring method of this application. Figure 1 As shown, the method for monitoring the mechanical response of ultra-low temperature rocks may include:

[0027] S1: Place the rock sample 1, which contains an array of strain-temperature sensitive gratings and an array of temperature reference gratings embedded in series, into the cryogenic loading system. It should be understood that the strain-temperature sensitive grating array may include multiple strain-temperature sensitive gratings, and the temperature reference grating array may also include multiple temperature reference gratings. Each strain-temperature sensitive grating and each temperature reference grating corresponds one-to-one with a monitoring point within the rock sample 1, and each monitoring point is also a grating measurement point. It should be understood that the array of strain-temperature sensitive gratings and the array of temperature reference gratings connected in series can be considered as a series-connected dual-grating differential sensing unit.

[0028] S2: Start the cryogenic environment loading system and measure the wavelength drift of each grating in the strain-temperature sensitive grating array and the wavelength drift of each grating in the temperature reference grating array in real time. In this embodiment, the cryogenic temperature loading system can provide a controllable variable temperature environment from room temperature to -196°C.

[0029] S3: Calculate the true temperature at the corresponding grating measurement point of rock sample 1 using the wavelength shift of one of the temperature reference gratings measured in the temperature reference grating array. The grating measurement point described here is the monitoring point mentioned above, and the true temperature can be calculated using... express.

[0030] S4: Establish a physical model for the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array, and calculate the total strain of rock sample 1 at the grating measuring point based on the actual temperature and the physical model. It should be understood that the total strain of rock sample 1 at the corresponding grating measuring point... This can include the natural frost shrinkage strain caused by a decrease in temperature in rock sample 1, denoted as […]. The mechanical strain caused by the expansion of pore water upon freezing is denoted as... , that is .

[0031] S5: Based on the total strain of rock sample 1 at the grating measuring point and the natural freeze-thaw strain of rock sample 1, calculate the mechanical strain of rock sample 1 at the grating measuring point caused by the expansion of pore water due to freezing. That is, after calculating the total strain of rock sample 1 at the grating measuring point, based on... The mechanical strain of rock sample 1 caused by the expansion of pore water due to freezing at the grating measuring point can be calculated.

[0032] S6: Calculate the frost heave stress at the grating measuring point using the mechanical strain generated by the expansion of pore water due to freezing at the grating measuring point of the rock sample 1.

[0033] In this embodiment, by implanting a strain-temperature sensitive grating array and a temperature reference grating array connected in series inside the rock sample 1, the fiber optic array can overcome the limitations of traditional single-point measurement. Furthermore, the combination of the strain-temperature sensitive grating array and the temperature reference grating array allows for the separation of temperature and strain monitoring at the same measurement point. Further, based on the grating measurement points in the rock sample 1, the total strain at multiple grating measurement points can be calculated separately. And based on the total strain at the corresponding grating measurement points and the natural freezing and contraction strain of the rock sample 1 itself, it is possible to accurately distinguish whether the rock is in a state of freezing and contraction or freezing and swelling, eliminating the huge measurement error caused by temperature changes. In addition, the magnitude of the freezing and swelling stress at the corresponding grating measurement points can be calculated based on the mechanical strain generated by the expansion of pore water due to freezing at the grating measurement points, solving the technical problem in related technologies where the measurement method using traditional resistance strain gauges cannot accurately obtain the true mechanical response value.

[0034] Furthermore, in one embodiment, the method of embedding the interconnected strain-temperature sensitive grating array and temperature reference grating array into the rock sample 1 can be as follows: micropores are drilled in the rock sample 1, and then the interconnected dual-grating differential sensing unit array is implanted through the micropores, followed by backfilling with a cementing material matching the rock properties; or a rock-like sample 1 containing pre-embedded optical fibers is prepared using 3D printing technology. In this embodiment, the strain-temperature sensitive grating can be designated as FBG1, which is directly and tightly coupled to the rock sample 1 to simultaneously sense the mechanical strain of the rock and the ambient temperature; the temperature reference grating is designated as FBG2, which is located adjacent to FBG1, encapsulated in a microcapillary steel tube, and is in a free-floating state, without mechanical coupling to the rock matrix, only sensing the ambient temperature. Furthermore, the center wavelengths of FBG1 and FBG2 have a preset interval to ensure that the spectra do not overlap across the entire temperature range. Compared to traditional resistance strain gauges used in related technologies, which exhibit drastic changes in resistivity at extremely low temperatures (such as -100℃ to -196℃) and whose adhesives are prone to embrittlement and detachment, leading to distorted measurement data or sensor failure, the fiber Bragg grating (FBG) in this application embodiment possesses excellent resistance to ultra-low temperatures and anti-interference capabilities, thereby ensuring stable and reliable monitoring signals in ultra-low temperature environments and providing a hardware foundation for accurate measurement of rock mechanical response.

[0035] Furthermore, in one embodiment, the cryogenic environment loading system can employ a double-layer vacuum insulation structure and a gas-liquid mixing spray temperature control mechanism, specifically including: a double-layer vacuum insulation environment chamber 5, a gas-liquid two-phase intelligent temperature control unit, and an anti-frost drying and purging device. The double-layer vacuum insulation environment chamber 5 is made of stainless steel and has a double-wall structure, with the interlayer vacuumed to 10°C. -3 The pressure chamber is measured in Pa and filled with multiple layers of insulation material to minimize external heat radiation interference. Low thermal conductivity loading flange interfaces are located at the top and bottom of the chamber, with zirconia ceramic insulating gaskets at the interfaces to block heat conduction between the external loading press and the internal low-temperature environment, ensuring the uniformity of the temperature field of rock sample 1 under pressure. The gas-liquid two-phase intelligent temperature control unit may include a liquid nitrogen Dewar flask 6, a set of low-temperature solenoid valves 7, a vaporization heater 10, and an array of atomizing nozzles 3. When cooling is required, the opening of the solenoid valve is adjusted by a PID controller, spraying liquid nitrogen through the array of atomizing nozzles 3 surrounding the rock sample 1. The liquid nitrogen vaporizes and absorbs heat upon spraying, forming a uniform low-temperature nitrogen gas flow that envelops the rock, preventing thermal shock cracking caused by direct contact between liquid nitrogen and the rock. A resistance heating wire with a microsecond-level response is connected in series in the nitrogen circulation pipeline. When precise temperature control (accuracy ±0.1℃) or simulation of temperature rise and freeze-thaw cycles is required, the controller controls the heating wire power through pulse width modulation to achieve dynamic thermal balance with the liquid nitrogen cold source. The environmental chamber is equipped with an independent dry nitrogen purging inlet. Before cooling and throughout the testing process, dry nitrogen with a dew point below -70°C is continuously injected into the chamber to maintain a slight positive pressure. This design aims to prevent water vapor in the air from condensing into frost on the surface of the acoustic emission sensor 4 or at the fiber optic interface, thereby eliminating the attenuation of the acoustic signal by frost and the physical damage to the fiber optic connector.

[0036] Further, in one embodiment, calculating the true temperature at the corresponding grating measurement point of rock sample 1 using the wavelength shift of one of the temperature reference gratings measured in the temperature reference grating array may include:

[0037] S31: The temperature reference grating in the temperature reference grating array is calibrated to select a temperature range. In this embodiment of the application, before implanting the temperature reference grating into the rock sample 1, the temperature reference grating can be calibrated to select a temperature range. The selected temperature range can refer to the entire temperature range. Taking room temperature of 20°C as an example, the entire temperature range is 20°C to -196°C.

[0038] S32: Wavelength shift of the fitted temperature reference grating and temperature changes The relationship is denoted as ,in, The center wavelength of the temperature reference grating at the initial temperature. , , The nonlinear temperature sensitivity coefficient obtained during calibration. Due to the nonlinearity of material properties at low temperatures, a third-order polynomial can be used to fit the relationship between the wavelength shift of the temperature reference grating and the temperature change. Preferably, Records can be made before the temperature changes.

[0039] S33: Calculate the true temperature at the corresponding grating measurement point of rock sample 1 using the calibrated nonlinear temperature sensitivity coefficient and the measured wavelength drift of the temperature reference grating. During the experiment, the temperature is measured in real time... By performing the inverse operation of the above formula, the true temperature of the current grating measurement point can be accurately calculated. Preferred, The values ​​can be recorded in real time using an optical demodulator after the ultra-low temperature environment loading is started.

[0040] Further, in one embodiment, before calculating the total strain of rock sample 1 at the grating measuring point based on the actual temperature and the physical model, the following steps may be included: selecting a dry sample of the same material as rock sample 1, cooling the dry sample within a selected temperature range, and measuring the linear expansion coefficient function of the dry sample, denoted as... Using the measured linear expansion coefficient function of the dried sample, the theoretical freeze-shrinkage strain curve of the dried sample at the selected temperature is calculated, denoted as... ,in, This represents the natural freeze-shrinkage strain of the dried sample due to temperature reduction. It should be understood that T0 is the initial temperature, and T is the final target temperature. When cooling the dried sample within the selected temperature range, the same cooling process as for the temperature reference grating (FBG2) is performed, with the selected temperature range also being 20°C to -196°C. In this embodiment, the natural freeze-shrinkage strain of the dried sample is calculated in this way. When it is necessary to subsequently calculate the mechanical strain of rock sample 1 caused by the expansion of pore water due to freezing at the grating measurement point, the natural freeze-shrinkage strain of the dried sample can be directly used as the natural freeze-shrinkage strain of rock sample 1.

[0041] Further, in one embodiment, the center wavelength drift of the strain-temperature sensitive grating includes the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted to the strain-temperature sensitive grating by the rock sample 1. The physical model for establishing the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array may include:

[0042] A physical model is established for the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted from the rock sample 1 to the strain-temperature sensitive grating, denoted as . ;

[0043] in, The center wavelength of the strain-temperature sensitive grating at the initial temperature can be recorded using an optical modulator before the temperature changes.

[0044] The value of the center wavelength shift of the strain-temperature sensitive grating can also be recorded in real time using an optical demodulator after the ultra-low temperature environment loading is started.

[0045] The effective photoelastic coefficient of the strain-temperature sensitive grating;

[0046] The total strain transmitted to the strain-temperature sensitive grating for rock sample 1;

[0047] This represents the nonlinear temperature response term of the strain-temperature sensitive grating itself. It should be understood that the strain-temperature sensitive grating is in close contact with rock sample 1, and its center wavelength shift... It consists of two parts: the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted from the rock to the strain-temperature sensitive grating. Furthermore, The nonlinear temperature response term of the strain-temperature sensitive grating (FBG1) can be compensated and eliminated based on the temperature measured by the temperature reference grating (FBG2).

[0048] Further, in one embodiment, after calculating the true temperature at the corresponding grating measurement point of the rock sample 1 using the calibrated nonlinear temperature sensitivity coefficient and the measured wavelength drift of the temperature reference grating, the method may include: using the true temperature and a physical model of the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted from the rock sample 1 to the strain-temperature sensitive grating, calculating the total strain transmitted from the rock sample 1 to the strain-temperature sensitive grating. In other words, after calculating the true temperature at the grating measurement point, the obtained true temperature is input into the established physical model to calculate the total strain transmitted to the strain-temperature sensitive grating from rock sample 1. .

[0049] Furthermore, in one embodiment, the total strain transmitted from the rock sample 1 to the strain-temperature sensitive grating Including the natural frost-shrinkage strain of rocks caused by temperature drops Mechanical strain caused by the expansion of pore water upon freezing After the cryogenic environment loading system is started, it may include:

[0050] Record the number of acoustic emission impacts, acoustic emission energy, and acoustic emission arrival time inside the rock sample. It should be understood that after starting the cryogenic loading system, the optical modulator can simultaneously record the number of acoustic emission impacts, acoustic emission energy, and acoustic emission arrival time inside the rock sample using the acoustic emission instrument while recording the wavelength shift of FBG1 and FBG2.

[0051] The total strain transferred to the strain-temperature sensitive grating in the calculation of rock sample 1 Next, this includes: determining whether rock sample 1 is in the mineral skeleton freeze-shrinkage stage or the pore water phase transformation freeze-swelling and microcrack initiation stage; if If the value is negative and the acoustic emission signal is quiet, then rock sample 1 is in the mineral skeleton shrinkage stage; if If the acoustic emission signal is positive and has high frequency and high energy, then rock sample 1 is in the stage of pore water phase transformation frost heave and microcrack initiation. That is, a deep decoupling of the frost heave or frost contraction mechanical response of rock sample 1 can be performed. It should be understood that... Usually a negative value. Typically a positive value, the mechanical strain generated by the expansion of pore water during freezing can be obtained by subtracting from the baseline of dry rock. That is, utilizing the linear expansion coefficient function of the dried sample. Calculate the theoretical freeze-shrinkage strain curve at the currently selected temperature T. To determine the true strain of rock sample 1 caused by the ice phase transition: .

[0052] In this embodiment of the application, when determining the state of rock sample 1, the calculated value is used... And combine the acoustic emission signal to make a judgment, if If the value is negative (shrinkage) and the acoustic emission signal is calm, then rock sample 1 is judged to be in the mineral skeleton freeze-shrinkage stage; if If the value is positive (expansion) and has a high-frequency, high-energy acoustic emission signal, then rock sample 1 is in the stage of pore water phase transformation frost heave and microcrack initiation.

[0053] Further, in one embodiment, calculating the frost heave stress at the grating measuring point includes: using the mechanical strain generated by the expansion of pore water upon freezing at the grating measuring point as the frost heave strain of the rock sample 1; and applying the generalized Hooke's law, combined with the dynamic elastic modulus of the rock sample 1 at low temperature. The frost heave strain of rock sample 1 is converted into frost heave stress of rock sample 1. The conversion formula is That is, stress transformation can be performed, converting the frost heave strain of rock sample 1 into frost heave stress. .

[0054] Furthermore, in one embodiment, the frost heave strain of rock sample 1 is converted into frost heave stress of rock sample 1. This can then include: the frost heave stress calculated based on each grating measurement point. Based on the coordinates of the corresponding measuring points, an interpolation algorithm is used to generate a three-dimensional stress cloud map inside the rock sample 1. That is, based on the coordinates of each monitoring point in the array and the calculated stress values, a three-dimensional reconstruction can be performed to generate a three-dimensional stress cloud map inside the rock sample 1, which can dynamically display the advancement of the freezing front. In this embodiment, high-precision measurement at ultra-low temperatures is achieved. Gas-liquid two-phase atomization avoids the thermal shock caused by direct liquid nitrogen spray, causing the rock to swell under a uniform cooling field. Utilizing the stable physical properties and lack of electromagnetic interference of fiber optic grating material at low temperatures, the problem of failure of traditional electrical sensors in the liquid nitrogen temperature range is solved, achieving long-term stable monitoring at -196 °C. Furthermore, true internal stress decoupling is achieved, with the dual-grating differential sensing unit realizing complete separation of temperature and strain at the same measuring point. This enables the system to accurately distinguish whether rocks are in a state of freezing-shrinkage or freezing-swelling, eliminating huge measurement errors caused by temperature changes. In addition, by integrating fiber optic sensing with acoustic emission technology, it can not only measure the magnitude of force, but also determine the freezing-swelling and freezing-shrinking state of minerals based on acoustic emission signals. Furthermore, by deploying fiber optics in an array, it can overcome the limitations of traditional single-point measurement and reconstruct the three-dimensional stress field inside the rock, which has important scientific research and engineering value for understanding stress concentration and crack propagation paths in heterogeneous rocks during the freezing process.

[0055] This embodiment takes the freezing experiment of a water-bearing sandstone sample in the liquid nitrogen temperature range (-196 °C) as an example to explain in detail the construction of the system, the identification and calculation of frost heave and frost contraction forces, and the reconstruction process of the three-dimensional stress field.

[0056] See Figure 2 As shown, the monitoring system constructed in this embodiment includes an ultra-low temperature environment loading system, which consists of a double-layer vacuum insulated environment chamber 5, a gas-liquid two-phase intelligent temperature control unit, and an anti-frost device 8. The anti-frost device 8 is connected to an industrial-grade nitrogen tank 9. The double-layer vacuum insulated environment chamber 5 is made of 304 stainless steel, and the space between the double-layer walls is evacuated to 10°C. -3 The enclosure is reinforced with multiple layers of aluminum foil and fiberglass insulation paper. The internal dimensions are designed to be 400×400×600 mm. 3A liquid nitrogen Dewar flask 6 is configured and connected to eight atomizing nozzles 3 surrounding the sample inside the chamber via a cryogenic solenoid valve 7. The nozzles are designed with micron-level atomization apertures to ensure that the liquid nitrogen vaporizes immediately upon ejection. A pulse-controlled heating wire is installed in the circulating air duct. An anti-frost device 8 is connected to an industrial-grade dry nitrogen source with a dew point of -75°C, which purges the chamber at a constant flow rate to maintain a slightly positive pressure environment inside the chamber. The monitoring system also includes an intelligent core sensing array 2, namely a dual-grating differential sensing unit. Specifically, a 3mm diameter microhole is drilled on the central axis of a 50mm×100mm saturated sandstone sample, and a fiber grating array containing 5 measuring points is implanted. Each measuring point includes a strain-temperature sensitive grating and a temperature reference grating. The monitoring system also includes an acoustic emission monitoring system, which uses 4 low-temperature resistant broadband acoustic emission sensors 4, symmetrically arranged on the side surface of the cylindrical sample using a low-temperature coupling agent, and connected to the host through a preamplifier. The monitoring system also includes a data acquisition and processing terminal, which uses a high-speed fiber grating demodulator and an acoustic emission acquisition card, and achieves time axis alignment through a synchronous trigger line.

[0057] Further testing may include the following steps:

[0058] First, baseline calibration and parameter acquisition were performed. Before implantation, the FBG2 was placed in a temperature-controlled chamber and cooled from 20°C to -196°C, and the wavelength changes were recorded. The temperature sensitivity coefficient was obtained using third-order polynomial fitting. , , Take dry sandstone samples of the same material, perform the same cooling process, and measure their linear expansion coefficient function. And calculate the theoretical freeze-shrinkage strain curve. At room temperature of 20°C, record the initial center wavelengths of FBG1 and FBG2 at each measuring point.

[0059] Secondly, synchronous data acquisition and temperature inversion are performed. Specifically, a cooling program is initiated (e.g., cooling at a rate of 2°C / min), and data is acquired in real time. For the i-th measurement point in the array, the wavelength shift of FBG2 is first utilized. Invert the true temperature at that point. :

[0060]

[0061] Solve the above equation to obtain the true temperature at that location inside the rock at the current moment. .

[0062] Furthermore, to achieve deep decoupling of frost heave or frost contraction strain, the dual-grating differential principle can be used, combined with a dry rock baseline, to calculate the actual frost heave or frost contraction mechanical strain caused by pore water freezing. The calculation formula is as follows:

[0063]

[0064] In the above formula, the first term is the total strain of the rock after removing the optical fiber thermal effect, and the second term represents the shrinkage that rock sample 1 should have due to cooling alone. T represents the sensor monitoring temperature.

[0065] Next, the frost heave stress transformation is carried out. Specifically, based on the current actual temperature and the generalized Hooke's law, combined with the dynamic elastic modulus of the rock at low temperatures, Transforming frost heave strain into frost heave stress :

[0066]

[0067] Subsequently, the frost heave and contraction state of the rock was determined by multiphysics field fusion. In the initial stage of cooling, such as from 0°C to -5°C, the calculated values ​​were... Furthermore, the acoustic emission signal is extremely small, which can be considered as the supercooled liquid phase stage.

[0068] During the sudden phase transition period, such as around -5°C, The sudden and rapid increase, coupled with the detection of high-amplitude burst signals by acoustic emission, can be considered as the pore water phase change freeze-swell stage.

[0069] During periods of extreme cold, such as -20°C to -196°C, if If the acoustic emission remains stable and positive, it is considered a stable freeze; if... The continued surge accompanied by sustained high-energy acoustic emission impacts can be considered as a stage of frost heave-induced cracking or microcrack propagation.

[0070] Finally, the three-dimensional stress field of the rock under cryogenic conditions is reconstructed. Based on multi-point data acquired by the intelligent rock core sensor array 2, the three-dimensional stress field of the rock under cryogenic conditions can be reconstructed.

[0071] A cylindrical coordinate system (r, θ, z) is established with the fiber array as the axis to represent the coordinates of different fiber measurement points. This system utilizes the coordinates of different measurement points... Using the data as axial control points, and combining the rock thermal conductivity equation and thermoelasticity model, the stress distribution at non-axial locations inside the specimen is derived using Kriging interpolation. Furthermore, since freezing conduction often proceeds from the surface inwards, a stress evolution function f(r, z, t) can be constructed by incorporating the time axis t.

[0072] Through the above embodiments, this system can distinguish between the freezing and shrinking or freezing and swelling states of rocks in an ultra-low temperature environment of -196°C, and can quantify the internal destructive force, thus filling the current gap in ultra-low temperature rock monitoring.

[0073] Secondly, embodiments of this application also provide a cryogenic rock mechanical response monitoring system.

[0074] In one embodiment, the cryogenic rock mechanical response monitoring system includes: a loading module for placing a rock sample 1, internally containing a strain-temperature sensitive grating array and a temperature reference grating array connected in series, into a cryogenic environment loading system; the loading module is used to activate the cryogenic environment loading system and measure the wavelength drift of each grating in the strain-temperature sensitive grating array and the wavelength drift of each grating in the temperature reference grating array in real time; a measurement module for calculating the true temperature at the corresponding grating measurement point of the rock sample 1 using the wavelength drift of one of the temperature reference gratings measured in the temperature reference grating array; and a first calculation module. The first calculation module is used to establish a physical model of the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array, and calculate the total strain of the rock sample 1 at the grating measuring point based on the actual temperature and the physical model; the second calculation module is used to calculate the mechanical strain of the rock sample 1 at the grating measuring point caused by the expansion of pore water due to freezing at the grating measuring point based on the total strain of the rock sample 1 at the grating measuring point and the natural frost contraction strain of the rock sample 1 itself; the third calculation module is used to calculate the frost heave stress at the grating measuring point using the mechanical strain of the rock sample 1 at the grating measuring point caused by the expansion of pore water due to freezing at the grating measuring point.

[0075] Reference Figure 3 , Figure 3 This is a schematic diagram of the hardware structure of the cryogenic rock mechanical response monitoring device involved in the embodiments of this application. In this embodiment, the cryogenic rock mechanical response monitoring device may include a processor, a memory, a communication interface, and a communication bus.

[0076] The communication bus can be of any type and is used to interconnect the processor, memory, and communication interface.

[0077] The communication interface includes input / output (I / O) interfaces, physical interfaces, and logical interfaces used for interconnecting internal components of the cryogenic rock mechanics response monitoring equipment, as well as interfaces used for interconnecting the equipment with other devices (such as other computing devices or user equipment). Physical interfaces can be Ethernet interfaces, fiber optic interfaces, ATM interfaces, etc.; user equipment can be displays, keyboards, etc.

[0078] Memory can be various types of storage media, such as random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), flash memory, optical storage, hard disk, programmable ROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM), etc.

[0079] The processor can be a general-purpose processor, which can call the cryogenic rock mechanical response monitoring program stored in the memory and execute the cryogenic rock mechanical response monitoring method provided in the embodiments of this application. For example, the general-purpose processor can be a central processing unit (CPU). The method executed when the cryogenic rock mechanical response monitoring program is called can be referred to the various embodiments of the cryogenic rock mechanical response monitoring method of this application, and will not be repeated here.

[0080] Those skilled in the art will understand that Figure 3 The hardware structure shown does not constitute a limitation of this application and may include more or fewer components than shown, or combine certain components, or have different component arrangements.

[0081] Fourthly, embodiments of this application also provide a computer-readable storage medium.

[0082] The present application has a computer-readable storage medium storing a cryogenic rock mechanical response monitoring program, wherein when the cryogenic rock mechanical response monitoring program is executed by a processor, it implements the steps of the cryogenic rock mechanical response monitoring method described above.

[0083] The method implemented when the ultra-low temperature rock mechanical response monitoring program is executed can be referred to in the various embodiments of the ultra-low temperature rock mechanical response monitoring method of this application, and will not be repeated here.

[0084] It should be noted that the sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0085] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus. The terms "first," "second," and "third," etc., are used to distinguish different objects, etc., and do not indicate a sequence, nor do they limit "first," "second," and "third" to different types.

[0086] In the description of the embodiments of this application, terms such as "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a concrete manner.

[0087] In the description of the embodiments of this application, unless otherwise stated, " / " means "or". For example, A / B can mean A or B. The "and / or" in the text is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of this application, "multiple" means two or more.

[0088] In some processes described in the embodiments of this application, multiple operations or steps are included in a specific order. However, it should be understood that these operations or steps may not be executed in the order they appear in the embodiments of this application, or they may be executed in parallel. The sequence number of the operation is only used to distinguish different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed sequentially or in parallel, and these operations or steps may be combined.

[0089] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes several instructions to cause a terminal device to execute the methods described in the various embodiments of this application.

[0090] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for monitoring the mechanical response of rock at ultra-low temperatures, characterized in that, The ultra-low temperature rock mechanical response monitoring method includes: A rock sample with an internally embedded strain-temperature sensitive grating array and an internally embedded temperature reference grating array was placed in an ultra-low temperature environment loading system. The cryogenic environment loading system was activated, and the wavelength drift of each grating in the strain-temperature sensitive grating array and the wavelength drift of each grating in the temperature reference grating array were measured in real time. The true temperature at the corresponding grating measurement point of the rock sample is calculated using the wavelength drift of one of the temperature reference gratings in the temperature reference grating array. A physical model for the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array is established, and the total strain of the rock sample at the grating measuring point is calculated based on the actual temperature and the physical model. Based on the total strain of the rock sample at the grating measuring point and the natural freeze-shrinkage strain of the rock sample itself, the mechanical strain of the rock sample at the grating measuring point caused by the expansion of pore water due to freezing is calculated. The frost heave stress at the grating measuring point is calculated using the mechanical strain generated by the expansion of pore water due to freezing at the grating measuring point on the rock sample. The calculation of the true temperature at the corresponding grating measurement point of the rock sample using the wavelength drift of one of the temperature reference gratings measured in the temperature reference grating array includes: The temperature reference grating in the temperature reference grating array is calibrated within a selected temperature range; Wavelength shift of the fitted temperature reference grating and temperature changes The relationship is denoted as ,in, The center wavelength of the temperature reference grating at the initial temperature. , , The nonlinear temperature sensitivity coefficient obtained from the calibration; The true temperature at the corresponding grating measurement point of the rock sample is calculated using the nonlinear temperature sensitivity coefficient obtained from calibration and the wavelength drift of the measured temperature reference grating. The center wavelength drift of the strain-temperature sensitive grating includes the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted to the strain-temperature sensitive grating by the rock sample. The physical model for establishing the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array includes: A physical model is established for the thermal effect of the strain-temperature sensitive grating itself and the mechanical strain transmitted from the rock sample to the strain-temperature sensitive grating, denoted as . ; in, The center wavelength of the strain-temperature sensitive grating at the initial temperature; This refers to the center wavelength shift of the strain-temperature sensitive grating. The effective photoelastic coefficient of the strain-temperature sensitive grating; The total strain transferred from the rock sample to the strain-temperature sensitive grating; This refers to the nonlinear temperature response term of the strain-temperature sensitive grating itself.

2. The method for monitoring the mechanical response of ultra-low temperature rocks as described in claim 1, characterized in that, Before calculating the total strain of the rock sample at the grating measuring point based on the actual temperature and the physical model, the following steps are included: A dry sample of the same material as the rock sample was selected, and the sample was cooled within a selected temperature range. The linear expansion coefficient function of the dry sample was measured and denoted as . ; Using the measured linear expansion coefficient function of the dried sample, the theoretical freeze-shrinkage strain curve of the dried sample at the selected temperature is calculated, denoted as... ,in, This represents the natural shrinkage strain caused by the temperature drop in the dried sample.

3. The method for monitoring the mechanical response of ultra-low temperature rocks as described in claim 2, characterized in that, After calculating the true temperature of the rock sample at the corresponding grating measurement point using the calibrated nonlinear temperature sensitivity coefficient and the measured wavelength shift of the temperature reference grating, the process includes: Using the physical model of the actual temperature, the thermal effect of the strain-temperature sensitive grating itself, and the mechanical strain transmitted from the rock sample to the strain-temperature sensitive grating, the total strain transmitted from the rock sample to the strain-temperature sensitive grating is calculated. .

4. The method for monitoring the mechanical response of ultra-low temperature rocks as described in claim 3, characterized in that, The total strain transferred from the rock sample to the strain-temperature sensitive grating Including the natural frost-shrinkage strain of rocks caused by temperature drops Mechanical strain caused by the expansion of pore water upon freezing After the cryogenic environment loading system is started, the following is included: Record the number of acoustic emission impacts, acoustic emission energy, and acoustic emission arrival time inside the rock sample; The total strain transferred to the strain-temperature sensitive grating from the calculated rock sample is described. After that, including: To determine whether the rock sample is in the mineral skeleton freeze-shrinkage stage or the pore water phase transformation freeze-swelling and microcrack initiation stage. like If the value is negative and the acoustic emission signal is quiet, then the rock sample is in the mineral skeleton shrinkage stage. like If the value is positive and the acoustic emission signal is high-frequency and high-energy, then the rock sample is in the stage of pore water phase transformation frost heave and microcrack initiation.

5. The method for monitoring the mechanical response of ultra-low temperature rocks as described in claim 3, characterized in that, The calculation of the frost heave stress at the grating measuring point includes: The mechanical strain generated by the expansion of pore water upon freezing at the grating measurement point is taken as the frost heave strain of the rock sample. Based on the generalized Hooke's law, and combined with the dynamic elastic modulus of rock samples at low temperatures The frost heave strain of the rock sample is converted into frost heave stress of the rock sample. The conversion formula is .

6. The method for monitoring the mechanical response of ultra-low temperature rocks as described in claim 5, characterized in that, In the process of converting the frost heave strain of the rock sample into the frost heave stress of the rock sample... After that, including: The frost heave stress calculated based on each grating measuring point Based on the coordinates of the corresponding measuring points, an interpolation algorithm is used to generate a three-dimensional stress cloud map inside the rock sample.

7. A cryogenic rock mechanical response monitoring system for implementing the method as described in claim 1, characterized in that, The cryogenic rock mechanical response monitoring system includes: The loading module places a rock sample containing a series-connected strain-temperature sensitive grating array and a series-connected temperature reference grating array into an ultra-low temperature environment loading system. The loading module is used to start the ultra-low temperature environment loading system and measure the wavelength drift of each grating in the strain-temperature sensitive grating array and the wavelength drift of each grating in the temperature reference grating array in real time. The measurement module is used to calculate the true temperature of the rock sample at the corresponding grating measurement point by using the wavelength drift of one of the temperature reference gratings in the temperature reference grating array. The first calculation module is used to establish a physical model of the center wavelength drift of the strain-temperature sensitive grating in the strain-temperature sensitive grating array, and to calculate the total strain of the rock sample at the grating measuring point based on the actual temperature and the physical model. The second calculation module is used to calculate the mechanical strain of the rock sample at the grating measuring point caused by the expansion of pore water freezing at the grating measuring point, based on the total strain of the rock sample at the grating measuring point and the natural freezing and shrinkage strain of the rock sample itself. The third calculation module is used to calculate the frost heave stress at the grating measuring point by utilizing the mechanical strain generated by the expansion of pore water due to freezing at the grating measuring point of the rock sample.

8. A cryogenic rock mechanical response monitoring device, characterized in that, The cryogenic rock mechanical response monitoring device includes a processor, a memory, and a cryogenic rock mechanical response monitoring program stored in the memory and executable by the processor, wherein when the cryogenic rock mechanical response monitoring program is executed by the processor, it implements the steps of the cryogenic rock mechanical response monitoring method as described in any one of claims 1 to 6.

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