Method for determining rock mass disturbance coefficient under freezing-thawing and mining disturbance action

Abstract

The invention belongs to the technical field of geotechnical engineering, and particularly discloses a method for determining a rock mass disturbance coefficient under the action of freezing and thawing and mining disturbance. The method comprises the following steps: selecting rock samples in a high-cold and high-altitude area, and performing ultrasonic screening, grouping and numbering; after the numbered rock samples are dried, the porosity P0 and the uniaxial compressive strength sigma c0 are tested; testing the saturated longitudinal wave velocity Vp0 of the rock sample after vacuum saturation treatment; performing freezing and thawing cycle treatment on the rock sample subjected to vacuum saturation treatment for different times; testing the porosity PN, the longitudinal wave velocity VpN and the uniaxial compressive strength sigma cN of the rock samples with different freezing and thawing cycle times; rock samples with different freezing and thawing cycle times are extracted to be subjected to a true triaxial unloading test, and the confining pressure value sigma d when the rock samples are damaged under different initial confining pressure values sigma 3 and target unloading confining pressure sigma 3'is tested; and defining a rock mass disturbance coefficient D'according to data obtained before and after freezing and thawing and data obtained by an unloading test. The method has the characteristics of small calculation amount, scientific and reasonable process and accurate and reliable result.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering technology, specifically relating to a method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance effects, which involves minimal calculation, a scientifically sound process, and accurate and reliable results. Background Technology

[0002] In cold-region mining, water conservancy, transportation, and municipal engineering projects, rock masses are often subjected to the dual effects of freeze-thaw cycles and mining disturbances, which significantly deteriorates their mechanical properties and integrity. The rock mass disturbance coefficient D, an important parameter in the Hoek-Brown empirical criterion, reflects the degree of disturbance to the rock mass under natural geological conditions caused by engineering activities. It is used to describe the differences in mechanical properties (such as strength and elastic modulus) and structural integrity between disturbed and undisturbed rock masses.

[0003] In the Hoek-Brown empirical criterion, the rock mass disturbance coefficient D The value range of is 0 to 1: where, when D When = 0, it indicates that the rock mass is undisturbed; while when D When the value is 1, it indicates that the rock mass is completely disturbed. Currently, due to the rock mass disturbance coefficient... D The determination of the perturbation coefficient lacks precise theoretical basis and relies solely on limited practical experience. Therefore, how to achieve the perturbation coefficient through relevant experimental methods remains a challenge. D Quantitative characterization of rocks has always been a key focus of research in the field of rock engineering. In particular, rocks in high-altitude and cold regions are more strongly affected by the disturbances caused by engineering activities such as blasting and mechanical vibration during mining after experiencing freeze-thaw cycles.

[0004] In existing technologies, many scholars mainly use the wave velocity of the rock before and after disturbance to define the rock mass disturbance coefficient. D However, since rock is an anisotropic material, the perturbation coefficient cannot be calculated from a single scale. DThe results are highly discrete. To this end, there is a CT image sequence in the freeze-thaw-disturbance coupling test, combined with the black top-hat algorithm to enhance the crack features, to realize the three-dimensional visualization reconstruction of the CT image and three-dimensional reconstruction technology of the internal damage of the rock mass. Although this technology can non-destructively obtain the three-dimensional structure of the rock mass, accurately quantify the porosity, crack opening and other parameters; and can reveal the self-similarity law of damage evolution; and the spatial resolution is as high as micron level, which can identify the initial micro-cracks. However, this technology also has problems such as high equipment cost, limited rock sample size, complex data processing and difficulty in simulating real stress environment. In addition, there is a SHPB coupling test system based on freeze-thaw cycle and dynamic disturbance coupling loading separation type Hopkinson pressure bar, which is formed by freeze-thaw-surrounding pressure loading system, controllable high-frequency pendulum hitting system, two-side oil pressure propulsion system and multi-channel high-speed data acquisition system. The foregoing technology innovatively integrates freeze-thaw, confining pressure, high-frequency disturbance modules, realizes multi-field coupling simulation; and the pendulum hitting system can accurately control the disturbance parameters (frequency, amplitude, times); and can directly output the dynamic stress-strain curve, which is convenient for disturbance coefficient calculation. However, this technology also has problems such as the patent equipment has not been popularized (exclusive of Shenzhen University), the time-consuming of high-frequency test (>10000 times of impact needs to continue for several hours) and the significant noise interference of low-amplitude signal. Secondly, there is an ultrasonic and borehole camera comprehensive observation technology which inverses the rock mass integrity index through the ultrasonic wave speed and identifies the fracture development situation combined with the borehole camera; and a microseismic monitoring technology which captures the acoustic emission signals generated by rock mass failure through a sensor network, locates the damage source and calculates the energy release rate. The above two kinds of in-situ monitoring technologies also have problems such as the ultrasonic and borehole camera comprehensive observation technology cannot distinguish the independent influence of freeze-thaw and mining disturbance, the microseismic monitoring technology is easily disturbed by environmental noise and needs complex data processing. In addition, there is a damage mechanics model numerical simulation technology which introduces damage variable D to describe the crack density, combined with the permeability coefficient evolution equation ( k k 0 e αD ), so as to quantify the damage mechanics model numerical simulation technology of seepage-damage coupling effect. The technology has a rigorous theoretical framework, which can reveal the meso-mechanism; but has the problem of difficult parameter inversion and needs to be verified by test.

[0005] Therefore, at present, there is still lack of a method with accurate results and scientifically reasonable process for determining the disturbance coefficient of rock mass under the coupling action of freeze-thaw and mining in high-cold and high-altitude areas. D SUMMARY

[0006] ​​In order to solve the problems in the prior art, the present application provides a method for determining rock mass disturbance coefficient under the action of freezing and mining disturbance, which has small calculation amount, scientific process and accurate and reliable result.

[0007] The method for determining rock mass disturbance coefficient under the action of freezing and mining disturbance is realized as follows: including the steps of rock sample collection, pre-freezing test, pre-freezing treatment, freezing treatment, post-freezing treatment, unloading test and definition of disturbance coefficient, and the specific contents of each step are as follows: A, rock sample collection: selecting rock samples in high-cold and high-altitude areas, then screening qualified rock samples by using an ultrasonic velocity tester, and then grouping and numbering the qualified rock samples; B, pre-freezing test: drying the numbered rock samples, then cooling to room temperature, and then testing and recording the porosity of the dried rock samples P 0 and uniaxial compressive strength σ c0 ; C, pre-freezing treatment: vacuum saturation treatment is performed on the rock samples, and then the saturated longitudinal wave velocity of the treated rock samples is tested V p0 ; D, freezing treatment: the vacuum saturated rock samples are subjected to different numbers of freezing and thawing cycle treatment; E, post-freezing treatment: the porosity P N , longitudinal wave velocity V pN and uniaxial compressive strength σ cN of the rock samples after different preset freezing and thawing cycle numbers N are tested F, unloading test: the rock samples reaching the preset freezing and thawing cycle number N are extracted for true triaxial unloading test, and the initial confining pressure value σ 3 and the confining pressure value of the rock sample at the time of failure under the target unloading confining pressure value σ 3' are tested σ d ; G, definition of disturbance coefficient: according to the rock sample data obtained by the pre-freezing, post-freezing and true triaxial unloading test, the rock mass disturbance coefficient D ' is defined, and the calculation formula is: In the formula, K is the rock damage coefficient under the action of freezing and mining disturbance, which is determined by the freezing damage factor D f and the unloading damage factor D d wherein:​ wherein: D f1 、 D f2 、 D f3 are the strength damage factor, the wave velocity damage factor and the microstructure damage factor of the freeze-thawed rock, respectively.

[0008] Further, in the F step, the initial confining pressure value of the true triaxial unloading test is set according to the actual stress level of the engineering construction site σ 3 and the target unloading confining pressure value σ 3'. σ 3 under the same initial confining pressure value σ d .

[0009] Further, in the F step, the confining pressure value before the rock unloading is selected as the initial confining pressure value σ 3, and the confining pressure value after the rock unloading is selected as the target unloading confining pressure value σ 3'.

[0010] Further, in the A step, the target rock samples are taken from the same fresh and complete rock in the typical rock stratum of the engineering site in the high-altitude cold region, all the rock samples are cut and polished into the same size and shape along the original rock stratum direction, then the rock samples with visual defects and joint differences are removed, followed by the removal of the rock samples with large density differences, then the rock samples with large wave velocity differences are removed by using the ultrasonic wave velocity detection, and finally the remaining qualified rock samples are grouped and numbered.

[0011] Further, in the A step, the height, diameter and mass of the rock sample are measured to calculate the density of the rock sample, and the rock sample with large density difference is removed; the ultrasonic wave velocity of the rock sample is measured by using the non-metal ultrasonic detector, and the rock sample with large wave velocity difference is removed.

[0012] Further, in the B step, the drying treatment is to place the numbered rock samples in a vacuum drying oven, then constant temperature drying at 105-110℃ for 24-48h and weighing the weight of the rock sample, then continue to dry and weigh the weight of the rock sample every 12h until the weight of the rock sample no longer changes.

[0013] Further, in the B step, at least 3 rock samples after the drying treatment and cooled to room temperature are selected for uniaxial compressive strength test, and the average value of the data obtained by testing the 3 rock samples is calculated as the uniaxial compressive strength σc0 .

[0014] Further, in the C step, the dried rock sample is first placed in a dry vacuum saturation device, then a vacuum pump is used to extract the vacuum in the vacuum saturation device to 0.05-0.20 MPa and maintain the pressure for 5 h, then the water injection valve is slowly opened, the vacuum degree in the device is kept unchanged during the water injection process, the distilled water is pressed into the vacuum saturation device through atmospheric pressure and completely covers the rock sample, then the valve is closed, then the air extraction is stopped and the rock sample is placed for 36 h, and finally the saturation longitudinal wave velocity of the rock sample is tested. V p0 .

[0015] Further, in the D step, first, the freezing temperature and the thawing temperature of the automatic freeze-thaw cycle machine are set according to the average temperature of the winter in the past 20 years and the average temperature of other seasons of the rock sample location, second, the freezing time is determined according to the 'Engineering Rock Mass Test Method Standard GB / T 50266-2013', and finally, the preset freeze-thaw cycle number N is determined according to the importance of the rock engineering.

[0016] Further, in the E step, the rock sample is dried before testing, and the uniaxial compressive strength of the rock sample is calculated by testing the uniaxial compressive strength of at least three rock samples with different freeze-thaw cycle numbers N. σ cN .

[0017] The present application has the following beneficial effects: 1. The present application innovatively introduces multi-dimensional damage factors coupling, and calculates the strength damage factor D σ c0 , σ cN the longitudinal wave velocity damage factor D V p0 , and the microstructure damage factor D V pN , respectively, and comprehensively calculates the freeze-thaw damage factor D P 0 through formula (3) P N ; then combined with the true triaxial unloading test data (initial confining pressure D f1 , failure confining pressure D f2 , and uniaxial compressive strength f3 . D f ; then combined with the true triaxial unloading test data (initial confining pressure σ 3 , failure confining pressureσ d ) calculating unloading damage factor D d , finally coupled as comprehensive damage coefficient K through formula (2), and substituted into formula (1) to obtain rock mass disturbance coefficient D′ . Thus, through multi-parameter collaborative quantification, compared with the determination of rock mass disturbance coefficient by traditional empirical method and single evaluation method, the one-sidedness of single index is avoided, the problem of inaccurate calculation result caused by anisotropy of rock is effectively overcome, the discreteness of result is significantly reduced, the reliability of result is improved, and the rock mass disturbance coefficient D' is more in line with the real damage state of rock mass.

[0018] 2. In view of the problem that the existing in-situ monitoring technology (such as ultrasonic wave and microseism) is difficult to distinguish the separate action of freezing-thawing and mining disturbance, and the physical meaning of disturbance coefficient is ambiguous, the present application realizes decoupling through step-by-step testing and comparative analysis, that is, the damage of rock mass caused by freezing-thawing cycle (different number N) is quantified alone in the freezing-thawing treatment stage D f , and the mining disturbance interference is excluded; and the damage of unloading is quantified alone in the true triaxial unloading test for the rock sample subjected to preset freezing-thawing cycle D d ; and finally, the coupling relationship between D f and D d is determined through formula (2), and the synergistic effect of 'freezing-thawing weakening-mining disturbance aggravation' is revealed. Thus, the independent quantification-coupling analysis of freezing-thawing and mining disturbance is realized for the first time, and a theoretical basis is provided for the targeted prevention and control of a certain type of disturbance in cold region engineering.

[0019] 3. According to the problems existing in the prior art, such as high equipment cost (such as CT three-dimensional reconstruction, SHPB coupling system), patent exclusivity (such as the pendulum system of Shenzhen University) or complex operation (such as microseismic data processing), it is difficult to popularize in ordinary engineering. The core test of the present application only relies on conventional rock mechanics equipment such as vacuum drying box, freezing-thawing cycle machine, uniaxial / triaxial testing machine and ultrasonic detector, without special customization, which reduces the hardware threshold; and the operation process from rock sample collection to unloading test strictly follows 'Engineering Rock Mass Test Method Standard GB / T 50266-2013', and the operation reproducibility is strong, which is easy for engineering personnel to master; and the rock mass disturbance coefficient D′ is directly calculated through the clear formula (1) to (5), avoiding the complex three-dimensional reconstruction of CT technology or the noise filtering of microseismic monitoring, and reducing the dependence on professional data processing ability.

[0020] 4、According to the existing indoor test, the real stress condition (such as freeze-thaw test lacks confining pressure, and SHPB is difficult to simulate the unloading path in the field) is often ignored, resulting in a large deviation between the disturbance coefficient and the engineering practice. The present application optimizes the stress environment through accurate simulation: during the freeze-thaw treatment stage, the freezing / thawing temperature is set according to the temperature data of the engineering site for nearly 20 years, ensuring that the freeze-thaw damage is consistent with the site environment; then, through the true triaxial unloading test, the confining pressure before mining unloading is used as the initial confining pressure σ 3 , and the confining pressure after mining unloading is used as the target unloading confining pressure σ 3′ , accurately reproducing the stress path of the mining process, so that the final result fits the actual stress environment of the site, enhancing the engineering guidance.

[0021] 5、For the high cost of CT three-dimensional reconstruction equipment in the prior art, the time-consuming of SHPB high-frequency test, it is difficult to meet the actual needs of engineering scale test. The present application is designed through a low-cost and efficient process: such as abandoning high-cost equipment and using conventional test instruments, which can effectively reduce the test cost of a single group of rock samples; the freeze-thaw cycle number N can be flexibly set according to the importance of the project (not forced high frequency), and the true triaxial unloading test has a short single time length, thereby greatly shortening the test period; and the rock sample collection and pretreatment are standardized screening (density, wave speed, and appearance defect rejection), which ensures the consistency of the rock sample, thereby reducing repeated tests and further improving efficiency. Ultimately, the test cost and period can be significantly reduced, facilitating large-scale application.

[0022] In summary, the present application combines the rock freeze-thaw damage degree evaluation and the mining unloading damage degree evaluation method, establishes the first freeze-thaw-unloading coupled damage model ( K = D f + D d ), fills the gap in the research of multi-disturbance cooperative mechanism; and through the technical innovation of “multi-dimensional damage coupling, disturbance factor decoupling, field stress simulation, low cost and easy operation”, the problems of result dispersion, mechanism ambiguity, equipment dependence and poor engineering applicability in the prior art are effectively solved, providing a precise, reliable and easy-to-promote technical solution for determining the rock mass disturbance coefficient under the coupling action of freeze-thaw and mining in high-cold and high-altitude areas. It has important guiding significance for the stability evaluation and safety design of mines, tunnels and other engineering in cold regions. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the flow chart of the method for determining the rock mass disturbance coefficient under the action of freeze-thaw and mining disturbance of the present application; In the figure: S100-rock sample collection, S200-test before freeze-thaw, S300-treatment before freeze-thaw, S400-freeze-thaw treatment, S500-treatment after freeze-thaw, S600-unloading test, S700-definition of disturbance coefficient; Figure 2 The rock mass disturbance coefficient under different unloading confining pressures in the examples D and the freeze-thaw cycle number N is fitted. DETAILED DESCRIPTION

[0024] The present application is further described below in conjunction with the accompanying drawings and examples, but in no way limits the present application, any changes or improvements made based on the teaching of the present application are within the protection scope of the present application.

[0025] As shown in Figure 1 , the method for determining the rock mass disturbance coefficient under the action of freeze-thaw and mining disturbance, comprises the steps of rock sample collection, test before freeze-thaw, treatment before freeze-thaw, freeze-thaw treatment, treatment after freeze-thaw, unloading test, and definition of disturbance coefficient, and the specific contents of each step are as follows: A, rock sample collection: selecting rock samples in high-cold and high-altitude areas, then screening qualified rock samples by using an ultrasonic velocity tester, and then grouping and numbering the qualified rock samples; B, test before freeze-thaw: drying the numbered rock samples first, then cooling to room temperature, and then testing and recording the porosity of the dried rock samples P 0 and uniaxial compressive strength σ c0 ; C, treatment before freeze-thaw: vacuum saturation treatment is performed on the rock samples, and then the saturated longitudinal wave velocity of the treated rock samples is tested V p0 ; D, freeze-thaw treatment: the vacuum saturated rock samples are subjected to freeze-thaw cycle treatment of different numbers; E, treatment after freeze-thaw: the porosity P N , longitudinal wave velocity V pN and uniaxial compressive strength σ cN of the rock samples after different preset freeze-thaw cycle numbers N are tested. F, unloading test: the rock samples reaching the preset freeze-thaw cycle number N are extracted for true triaxial unloading test, and the confining pressure values σ 3 and the target unloading confining pressure values σ 3' of the rock samples at the time of failure are tested. σ d ; G, define disturbance coefficient: according to the freeze-thaw, freeze-thaw and true triaxial unloading test data, define rock mass disturbance coefficient D The calculation formula of the freeze-thaw and mining disturbance is as follows: In the formula: K The rock damage coefficient under the action of freeze-thaw and mining disturbance is calculated by freeze-thaw damage factor D f And unloading damage factor D d Determination: Among them: In the formula: D f1 、 D f2 、 D f3 The strength damage factor, wave velocity damage factor and microstructure damage factor of freeze-thaw rock are respectively.

[0026] In the F step, the initial confining pressure value of the true triaxial unloading test is set according to the actual stress level of the engineering construction site σ 3 and the target unloading confining pressure value σ 3', then test the confining pressure value of the rock sample failure under the same initial confining pressure value σ 3 σ d .

[0027] In the F step, the confining pressure value before rock mining unloading is selected as the initial confining pressure value σ 3, and the confining pressure value after rock mining unloading is selected as the target unloading confining pressure value σ 3'.

[0028] In the A step, the target rock sample is taken from the same fresh and complete rock in the typical rock layer of the engineering site in high altitude cold region, and all the rock samples are cut and polished into the same size and shape structure along the original rock layer direction, then the rock samples with visual defects and joint differences are removed, then the rock samples with large density difference are removed, then the rock samples with large wave velocity difference are removed by using ultrasonic wave velocity, and finally the remaining qualified rock samples are grouped and numbered.

[0029] In the A step, all the rock samples are cut and polished into cylinders with a height of 100 mm and a diameter of 50 mm.

[0030] In the A step, the rock sample with a wave velocity of 2700-3100 m / s and no obvious cracks on the surface is selected as the qualified rock sample.

[0031] In the A step, the height, diameter and mass of the rock sample are measured to calculate the density of the rock sample, and the rock sample with large density difference is removed; the ultrasonic velocity of the rock sample is measured by a non-metal ultrasonic detector, and the rock sample with longitudinal wave velocity difference exceeding 400 m / s is removed.

[0032] In the A step, the rock sample with large density difference is removed according to GB / T 50266-2013 “Standard for Engineering Rock Mass Test Method”: removing the test sample with density difference exceeding 5% of the average value or the test sample with coefficient of variation (standard deviation / average value) greater than 3% in the same group of rock samples.

[0033] In the B step, the drying treatment is placing the numbered rock sample in a vacuum drying oven, then drying at 105-110℃ for 24-48h and weighing the rock sample, then continuing to dry and weighing the rock sample every 12h until the weight of the rock sample no longer changes.

[0034] In the B step, at least 3 rock samples after drying treatment and cooling to room temperature are selected for uniaxial compressive strength test, and the average value of the data obtained by testing the 3 rock samples is taken as the uniaxial compressive strength of the rock sample. σ c0 .

[0035] In the C step, the dried rock sample is first placed in a dry vacuum saturation device, then the vacuum saturation device is evacuated to 0.05-0.20MPa by a vacuum pump and the pressure is maintained for 5h, then the water injection valve is slowly opened, the vacuum degree in the device is kept unchanged during the water injection process, the distilled water is pressurized into the vacuum saturation device through atmospheric pressure and completely covers the rock sample, then the valve is closed, then the air is stopped and is placed for 36h, finally the saturated longitudinal wave velocity of the rock sample is tested. V p0 .

[0036] In the D step, first, the freezing temperature and thawing temperature of the automatic freeze-thaw cycle machine are set according to the average temperature of the selected rock sample in the past 20 years and the average temperature of other seasons, second, the freezing time is determined according to “Standard for Engineering Rock Mass Test Method GB / T 50266-2013”, and finally the preset freeze-thaw cycle number N is determined according to the importance of the rock engineering.

[0037] In the D step, the preset freeze-thaw cycle number N is determined according to the importance of the rock engineering: the preset freeze-thaw cycle number is determined according to the engineering safety grade, the severity of the engineering environment and the properties of the rock; when there is no clear requirement for the engineering, the freeze-thaw cycle number for type I rock mass test in GB / T 502013 “Standard for Engineering Rock Mass Test Method” is executed.

[0038] In the E step, the rock sample is dried before testing, and the rock sample reaching the preset freeze-thaw cycle number N is dried; the rock sample after different freeze-thaw cycle numbers N is selected from at least three rock samples after the same freeze-thaw cycle number N for uniaxial compressive strength testing, and then the average value of the data obtained by testing each rock sample is calculated as the uniaxial compressive strength of the rock sample corresponding to the freeze-thaw cycle number N σ cN .

[0039] Embodiment

[0040] The data of the rock mass mining unloading damage evaluation under the action of freezing and thawing in the dissertation of Wang Chengxiang, "Research on Damage Characteristics and Loading and Unloading Mechanical Behavior of Sandstone under Freeze-thaw Action", is taken as an example, the determination method of the rock mass disturbance coefficient under the action of freezing and thawing and mining disturbance of the application is used to determine the disturbance coefficient D' corresponding to the rock mass, and the process is as follows.

[0041] S100: Select a fresh and complete rock in a typical rock layer of a high-altitude cold region engineering site, cut and polish it into a plurality of standard cylindrical rock samples with a bottom surface diameter of 50 mm and a height of 100 mm along the original rock layer direction; then, first, remove the rock samples with visual defects and joint differences; then, measure the mass of the rock sample and calculate the density of the rock sample according to the foregoing size, remove the samples with a density difference exceeding 5% of the average value in the same group of rock samples, or the rock samples with a coefficient of variation (standard deviation / average value) greater than 3%; then, use a non-metal ultrasonic detector to test the ultrasonic velocity of the rock sample, remove the rock samples with a longitudinal wave velocity difference exceeding 400 m / s and obvious surface cracks, and preferably select the rock samples with a wave velocity of 2700-3100 m / s and no obvious surface cracks as qualified rock samples, and finally group and number the qualified rock samples.

[0042] S200: Place the numbered rock samples in a vacuum drying oven, then dry them at a constant temperature of 105-110°C for 24-48h and weigh the rock samples, then continue to dry and weigh the rock samples every 12h until the weight of the rock samples no longer changes (with an accuracy of 0.001g) to complete the drying treatment; then cool to room temperature, then test and record the porosity of the dried rock samples P 0 and the uniaxial compressive strength σ c0 . Among them, at least three rock samples after drying and cooling to room temperature are tested for uniaxial compressive strength, and the average value of the data obtained by testing the three rock samples is calculated as the uniaxial compressive strength of the rock sample σ c0 .

[0043] S300: Put the rock sample after the foregoing drying treatment into a dry vacuum saturation cylinder, then use a vacuum pump to vacuumize the vacuum saturation cylinder to 0.05-0.20 MPa and maintain the pressure for 5 h, then slowly open the water injection valve, keep the vacuum degree in the vacuum saturation cylinder unchanged during the water injection process, press the distilled water into the vacuum saturation cylinder through atmospheric pressure, and close the valve after the distilled water completely covers the rock sample, then stop the air extraction and stand for 36 h, and finally test the saturated longitudinal wave velocity of the rock sample V p0 .

[0044] S400: According to the average temperature of the selected rock sample site in the winter and the average temperature of other seasons in the past 20 years, first set the freezing temperature of the automatic freeze-thaw cycle machine to-30℃ and the thawing temperature to 30℃; then according to the "Standard for Engineering Rock Mass Test Method GB / T 50266-2013", determine the freezing time to be 4h and the thawing time to be 4h; then according to the importance of rock engineering, select the freeze-thaw cycle number to be 0, 20, 40 and 60 times respectively; finally, put the vacuum saturated rock sample into the automatic freeze-thaw cycle machine and perform freeze-thaw cycle treatment according to the foregoing parameters.

[0045] S500: First, dry the rock sample that reaches the preset freeze-thaw cycle number N, then test the porosity of the rock sample after different preset freeze-thaw cycle numbers N P N , the longitudinal wave velocity V pN . Among them, at least 3 rock samples with the same freeze-thaw cycle number N are selected for uniaxial compression test, and then the average value of the uniaxial compressive strength of the 3 rock samples is calculated as the uniaxial compressive strength of the rock sample after freeze-thaw cycle N times σ cN .

[0046] S600: Extract the rock sample that reaches the preset freeze-thaw cycle number N, select the pre-mining unloading confining pressure value 10 MPa as the initial confining pressure value σ 3, the confining pressure value after mining unloading 0 MPa as the target unloading confining pressure value σ 3', perform true triaxial unloading test: The unloading stress path is to unload the confining pressure with constant axial pressure, the axial stress is loaded to 70% of the peak compressive strength of the rock sample under the confining pressure of 10 MPa in a stress control mode, the confining pressure is loaded to the test set value 10 MPa, then the confining pressure is unloaded until the rock sample fails, and the confining pressure value when the rock sample fails is recorded σ d .

[0047] G700: According to the rock sample data obtained before and after freeze-thaw and true triaxial unloading test, define the rock mass disturbance coefficient D The calculation formula of the rock mass disturbance coefficient is: In the formula: K is the rock damage coefficient under the action of freezing-thawing and mining disturbance, and is calculated by the freezing-thawing damage factor D f and the unloading damage factor D d Determination: wherein:

[0048] In the formula: D f1 , D f2 , D f3 are the strength damage factor, the wave velocity damage factor and the microstructure damage factor of the frozen rock, respectively.

[0049] As shown in Figure 1 , according to the foregoing data, the function relationship fitting curve of the rock mass disturbance coefficient D' and the freezing-thawing times N under different unloading confining pressures is drawn.

[0050] The basic parameters in the embodiment are as shown in Table 1, and the calculation data of the rock mass disturbance coefficient D' are as shown in Table 2.

[0051] Table 1 Rock damage data of freezing-unloading test

[0052] Table 2 Calculation data of rock mass disturbance coefficient D'

[0053] Analysis: According to the calculation results of the rock mass disturbance coefficient D' in Table 1 and Table 2, a linear fitting curve diagram as shown in Figure 2 is drawn, and it can be known from Figure 2 that R 2 = 0.99, the linear fitting result is very good, and the feasibility of the method is verified.

[0054] As can be known from Figure 2 , Table 1 and Table 2, the defined rock mass disturbance coefficient D' comprehensively considers the strength damage, wave velocity damage, microstructure damage and unloading damage of the rock in the freezing-thawing cycle and the mining process, can predict the rock mass structure disturbance and damage under the action of freezing-thawing and mining under different cycle times, and has a small error and high accuracy.

[0055] The above merely provides the preferred but not limiting embodiments of the present application, and any modification or substitution within the technical scope of the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance effects, characterized in that: The process includes rock sample collection, pre-freeze-thaw testing, pre-freeze-thaw treatment, freeze-thaw treatment, post-freeze-thaw treatment, unloading test, and definition of disturbance coefficients. The specific details of each step are as follows: A. Rock sample collection: Select rock samples from high-altitude and cold regions, then use an ultrasonic velocity tester to screen qualified rock samples, and then group and number the qualified rock samples. B. Pre-freeze-thaw test: The previously numbered rock samples were first dried, then cooled to room temperature, and the porosity of the dried rock samples was then tested and recorded. P 0 and uniaxial compressive strength σ c0 ; C. Pre-freeze-thaw treatment: The rock sample is subjected to vacuum saturation treatment, and then the saturated P-wave velocity of the treated rock sample is tested. V p0 ; D. Freeze-thaw treatment: The rock samples that have undergone vacuum saturation treatment are subjected to freeze-thaw cycles of different numbers; E. Post-freeze-thaw treatment: Porosity of rock samples after different preset freeze-thaw cycles N was tested. P N Longitudinal wave velocity V pN and uniaxial compressive strength σ cN ; F. Unloading Test: Rock samples that have reached the preset number of freeze-thaw cycles N are subjected to a true triaxial unloading test to measure different initial confining pressure values. σ 3 and target unloading confining pressure value σ Confining pressure at failure of rock sample at 3' σ d ; G. Define the disturbance coefficient: Based on the rock sample data obtained before and after freeze-thaw cycles and from true triaxial unloading tests, define the rock mass disturbance coefficient. D The formula for calculating ' is: In the formula: K The rock damage coefficient under freeze-thaw and mining disturbance is derived from the freeze-thaw damage factor. D f With unloading damage factor D d Sure: in: In the formula: D f1 , D f2 , D f3 These are the strength damage factor, wave velocity damage factor, and microstructure damage factor of freeze-thawed rocks, respectively.

2. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance as described in claim 1, characterized in that: In step F, the initial confining pressure value for the true triaxial unloading test is set according to the actual stress level at the construction site. σ 3. Target unloading confining pressure value σ 3', then test with the same initial confining pressure value. σ 3. Confining pressure values ​​at rock sample failure σ d .

3. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance as described in claim 2, characterized in that: In step F, the confining pressure value before rock mining unloading is selected as the initial confining pressure value. σ 3. Select the confining pressure value after rock mining unloading as the target unloading confining pressure value. σ 3'.

4. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance as described in claim 1, characterized in that: In step A, the target rock sample is taken from the same fresh and intact rock in a typical rock stratum at a high-altitude cold region engineering site. All rock samples are cut and polished into the same size and shape along the original rock stratum direction. Then, rock samples with visual defects or joint differences are first removed, followed by rock samples with large density differences. Then, rock samples with large wave velocity differences are removed by ultrasonic detection. Finally, the remaining qualified rock samples are grouped and numbered.

5. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance as described in claim 4, characterized in that: In step A, the height, diameter, and mass of the rock sample are measured to calculate the density of the rock sample, and rock samples with large density differences are discarded; the ultrasonic velocity of the rock sample is measured using a non-metallic ultrasonic detector, and rock samples with a longitudinal wave velocity difference exceeding 400 m / s are discarded.

6. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance as described in claim 1, characterized in that: In step B, the drying process involves placing the numbered rock samples in a vacuum drying oven, drying them at a constant temperature of 105–110°C for 24–48 hours, and weighing the rock samples. The drying process continues, and the weight of the rock samples is weighed every 12 hours until the weight of the rock samples no longer changes.

7. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance as described in claim 6, characterized in that: In step B, at least three rock samples that have been dried and cooled to room temperature are selected for uniaxial compressive strength testing, and the average value of the data obtained from the three rock sample tests is calculated as the uniaxial compressive strength of the rock sample. σ c0 .

8. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance as described in claim 1, characterized in that: In step C, the dried rock sample is first placed in a dry vacuum saturation device. Then, a vacuum pump is used to evacuate the device to 0.05–0.20 MPa and maintain the pressure for 5 hours. Subsequently, the water injection valve is slowly opened, and the vacuum level inside the device is kept constant during the water injection process. Distilled water is forced into the vacuum saturation device by atmospheric pressure until it completely submerges the rock sample. The valve is then closed, the evacuation is stopped, and the sample is left to stand for 36 hours. Finally, the saturated longitudinal wave velocity of the rock sample is measured. V p0 .

9. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance effects according to claim 1, characterized in that: In step D, firstly, based on the average winter temperature and average temperature of other seasons in the selected rock sample location over the past 20 years, the freezing and thawing temperatures of the automatic freeze-thaw cycler are set. Secondly, the freezing time is determined according to the "Standard for Test Methods of Engineering Rock Mass GB / T50266-2013". Finally, the preset number of freeze-thaw cycles N is determined based on the importance of the rock engineering.

10. The method for determining the rock mass disturbance coefficient under freeze-thaw and mining disturbance effects according to any one of claims 1 to 9, characterized in that: In step E, the rock sample that has reached the preset number of freeze-thaw cycles N is dried before the rock sample is tested. For rock samples subjected to different freeze-thaw cycles N, at least three samples with the same number of freeze-thaw cycles N were selected for uniaxial compressive strength testing. The average value of the data obtained from each rock sample test was then calculated as the uniaxial compressive strength of the rock sample with the corresponding number of freeze-thaw cycles N. σ cN .

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