Structural surface shear failure model under cooperative influence of freeze-thaw cycle and compression-shear load

Abstract

The invention provides a structural plane shear failure model under the cooperative influence of freeze-thaw cycle and compression-shear load. In the formula, the stress is normal stress; the friction angle is a basic friction angle; the angle is a characteristic angle; the uniaxial compressive strength of the number of freezing and thawing cycles is considered; the parameters are fitting parameters; the characteristic angle represents a corresponding critical apparent inclination angle when the contact area ratio of the shear side is 1 / e. According to the method, the feature angle lambda is mainly adopted to measure the rough features of the structural surface, a new model based on the feature angle lambda is provided, and the relation between the critical apparent dip angle and the potential contact area can be well represented; compared with a Grassselli model and a JRC-JCS model, the new model has remarkable advantages in the aspects of prediction precision and simplicity. Compared with a Grassselli morphology characterization method, the new model gathers the potential contact area of the shear facing side, the maximum apparent dip angle with unstable value is removed, a better fitting effect is achieved, and the problem of multi-parameter combination is avoided.

Description

Technical Field

[0001] This application relates to the field of rock mass structural surface shear strength prediction technology, and in particular to a structural surface shear failure model under the combined influence of freeze-thaw cycle and compressive shear load. Background Technology

[0002] Structural plane slip-type disasters frequently occur in cold-region rock masses, causing severe casualties and economic losses. Understanding the compressive-shear failure mechanism of structural planes under freeze-thaw cycles is crucial for effectively preventing this type of disaster. The JRC-JCS model (Barton and Choubey 1977) and the Grasselli model (Grasselli 2006) are two classic models for studying the mechanical properties of rock mass structural planes and have received widespread attention from scholars both domestically and internationally. However, they have the following shortcomings in predicting the shear strength of structural planes in cold regions: (1) Most of the key parameters are obtained based on normal temperature drying or water saturation conditions, without being associated with the deterioration law of the parameters by the number of freeze-thaw cycles; for example, in the RC-JCS model, JCS is taken by default as the uniaxial compressive strength of the unfrozen rock mass.

[0003] (2) Model parameters are difficult to obtain in practice. For example, the Grasselli model requires the maximum contact area ratio. Maximum viewing angle and fitting parameters To measure the relationship between the tilt angle of the micro-protrusion and the potential contact area, but Small range of variation The high level of noise from scanning makes it difficult to obtain parameters and results in high prediction errors in engineering applications.

[0004] (3) The characterization of the potential contact area does not conform to the actual shear mechanism. For example, the JRC-JCS model assumes that the roughness is uniformly distributed, but in reality, the structural surface damage is mainly concentrated on the shear side, and the relatively rough micro-protrusions on the shear side bear the main shear load.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology, a new model that can fit the freeze-thaw scenario of cold-region rock masses and the actual freeze-thaw deterioration law of cold-region rock masses, and whose key parameters are easy to obtain. Summary of the Invention

[0006] The purpose of this application is to provide a structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads, so as to solve or alleviate the problems existing in the prior art.

[0007] To achieve the above objectives, this application provides the following technical solution: This application provides a structural shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads, considering the structural shear strength under the influence of freeze-thaw cycle count. for: ; In the above formula, Normal stress; This is the basic friction angle; For characteristic angles; Uniaxial compressive strength considering the number of freeze-thaw cycles; These are the fitting parameters; Feature angle In the quantitative model of the critical apparent tilt angle-shear side contact area ratio of the structural surface constructed based on the Weibull distribution function, the critical apparent tilt angle is the angle corresponding to the shear side contact area ratio of 1 / e, where e is a natural constant.

[0008] Furthermore, feature angles The calculation formula is: ; In the above formula, This indicates the ratio of the contact area on the shear side of the structural surface; The fitting parameters represent the shape parameters of the Weibull distribution and control the type of decay. Indicates the critical apparent tilt angle.

[0009] Furthermore, the fitting parameter k ranges from 1.21 to 1.39.

[0010] Furthermore, The function for calculating the uniaxial compressive strength of rock walls after considering the number of freeze-thaw cycles is as follows: ; In the above formula, N represents the number of freeze-thaw cycles; This refers to the uniaxial compressive strength of the rock wall before it has undergone freeze-thaw cycles, i.e., the uniaxial compressive strength in its natural state.

[0011] Furthermore, the construction of the structural shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads includes the following steps: Step 1: Prepare several sets of structural surface samples with consistent morphology; use three-dimensional laser scanning technology to obtain at least 30 sets of structural surface point clouds with different roughness, convert the micro-protrusions into triangular mesh units, obtain the mesh tilt angle, area, and structural surface contact area ratio data under different critical tilt angles, and construct a critical tilt angle-contact area ratio quantization model based on the Weibull distribution function. Step 2: Conduct freeze-thaw cycle tests on these structural surface specimens, with a minimum of 30 freeze-thaw cycles; and conduct uniaxial compression, Brazilian splitting, triaxial compression, and direct shear tests on the same specimen after 0, 10, 20, and 30 freeze-thaw cycles, respectively, to obtain measurement data of uniaxial compressive strength, internal friction angle, peak shear strength of the structural surface, and normal stress under different freeze-thaw cycle numbers; Step 3: Based on the critical apparent tilt angle-contact area ratio quantification model constructed in Step 1, define and solve for the characteristic angle. ; Step 4: Analyze the relationships between the above data based on the Patton model. The incremental term i is determined to be of the form of nonlinear fitting. , The fitting parameters are used; substituting them into the Patton model yields the final model. .

[0012] Furthermore, the critical apparent tilt angle-contact area ratio quantification model constructed in step one is as follows: ; In the above formula, This indicates the contact area ratio on the shear side; The characteristic angle represents the contact area ratio. The critical angle corresponding to the time; The scale parameter of the Weibull distribution controls the rate of decay. The fitting parameters represent the shape parameters of the Weibull distribution and control the type of decay. Represents the critical tilt angle; ln is the operator for the natural logarithm.

[0013] Furthermore, in step one, the steps for preparing the structural surface sample are as follows: First, a rock mechanics testing system was used to conduct splitting tests on cubic rock samples with dimensions of 100mm×100mm×100mm, from which four groups of rock samples with significant differences in roughness were selected. According to the different roughness, the samples were numbered JA, JB, JC and JD, representing flat, relatively smooth, relatively rough and very rough structural surface samples, respectively. Then, a 3D scanner was used to perform 3D laser scanning on the four rock samples, and the obtained point cloud data was used to construct a 3D geometric model. Finally, a carving path program was written based on the three-dimensional geometric model, and structural surface samples with four roughnesses were made using a CNC carving machine.

[0014] Furthermore, in step two, the freeze-thaw cycle test includes the following steps: The first step is to dry the structural surface sample in a constant temperature forced-air drying oven at 105°C for 24 hours until constant weight is achieved; The second step is to place the dried sample in a vacuum pressure saturation device, evacuate for 4-6 hours, and then pressurize for 24 hours. The pressure value is set to 0.1 MPa, and distilled water is used as the saturation solution to obtain the pressurized saturated sample. The third step is to seal the pressurized and saturated sample with plastic wrap and place it in a TMS9012-160 high and low temperature test chamber for freeze-thaw cycles. The freeze-thaw cycle cycle is 8 hours. One freeze-thaw cycle process is as follows: (1) Cooling stage, from the initial temperature of 20℃ to -20℃ in 1.5h; (2) Freezing stage, maintained at -20℃ for 2.5h; (3) Heating stage, from -20℃ to 20℃ in 1.5h; (4) Melting stage, maintained at 20℃ for 2.5h.

[0015] Furthermore, the validation method for this model includes the following steps: Select at least 10 independent structural surface specimens and repeat the freeze-thaw cycle and uniaxial compression, Brazilian splitting, triaxial compression and direct shear tests in step two to obtain the measurement data of uniaxial compressive strength, internal friction angle, and normal stress under different freeze-thaw cycle numbers, as well as the measured value of the peak shear strength of the structural surface for verification. Substitute the above data into the structural shear failure model under the combined influence of freeze-thaw cycle and compression-shear load, and calculate the predicted value of the peak shear strength of the structural surface. Compare the measured values ​​of the peak shear strength of the structural surface with the predicted values, using the index average relative error and the coefficient of determination R. 2 To conduct evaluation and analysis.

[0016] The principle of calculating the contact area ratio: Rock mass structural planes can be considered as a series of micro-protrusions (i.e. Figure 1 The micro-protrusions are composed of triangular mesh elements, and their tilt angles are shown in the following formula. During shearing, the micro-protrusions on the shear-facing side gradually undergo mechanical behaviors such as slippage, abrasion, and shearing, while the micro-protrusions on the back-shear side gradually separate. When analyzing the behavior of the micro-protrusions on the shear-facing side, the tilt angle has a significant impact on the shearing process. When the tilt angle is small, the micro-protrusions on the shear-facing side fail to make effective contact during shearing and therefore cannot resist the shear force; however, when the tilt angle increases, the micro-protrusions come into close contact with each other and break down during shearing. As the tilt angle further increases, the degree of fracture of the micro-protrusions also intensifies, manifesting as a significant damaged area after shearing.

[0017] ; in, Indicates the apparent tilt angle. Indicates the geometric inclination angle. This represents the angle between the projection vector n1 of the outer normal of the triangular element onto the shear plane and the shear direction S.

[0018] When structural surface specimens are subjected to compressive and shear loads, their damage and strength characteristics are closely related to the potential contact area during shearing. This potential contact area is typically located in a steeper region on the shear-facing side. Therefore, a critical inclination angle is assumed; when the inclination angle of the micro-protrusions exceeds this critical value, they will be within the potential contact area. The potential contact area bears the majority of the shear force during shearing and may lead to significant damage. Since the potential contact area is mainly concentrated on the shear-facing side, its characteristics can be quantitatively described using the shear-facing side contact area ratio formula (below), thus providing a basis for further analysis of the quantitative relationship between the potential damage of the structural surface and the critical inclination angle of the micro-protrusions.

[0019] ; in, This indicates the contact area ratio on the shear side. This represents the potential contact area (i.e., the area of ​​all triangular units with an inclination angle greater than the critical value). This represents the total area of ​​the micro-convex body on the shear side.

[0020] Principle of constructing structural shear strength model: The Patton bilinear model is a classic theoretical model describing the shear strength of structural surfaces. The shear strength of rock mass structural surfaces can be considered to consist of two parts: (1) the frictional force between straight structural surfaces ( (2) The shear strength increment caused by the roughness of the structural surface ( ), this part of the load is subjected to the combined action of normal stress and basic friction angle; This portion of the load is affected by normal stress and the roughness of the structural surface. The increase in shear strength can be measured by the peak expansion angle. To represent this, see the following formula.

[0021] ; The main influencing factors on the shear mechanical properties of rock mass structural surfaces include normal stress, fundamental friction angle, surface roughness characteristics, and rock wall strength. Under compressive-shear loading, rock mass structural surfaces primarily experience shear slip and shear fracture, while tensile fracture failure is less common. In engineering practice, structural surfaces mainly experience shear failure rather than tensile failure. Therefore, the uniaxial compressive strength of the rock wall... It is commonly used as a key indicator for measuring rock wall strength. In addition to rock wall strength, the fundamental friction angle of the structural surface is calculated using direct shear tests on a straight structural surface. Using characteristic angles The roughness characteristics of the structural surface are measured. Therefore, the key parameters of the structural surface shear mechanics properties used in this application include normal stress. Basic friction angle Feature angle and uniaxial compressive strength .

[0022] The technical solution of this application has the following beneficial effects: This application mainly uses characteristic angles. To measure the roughness of structural surfaces, a feature angle-based approach is proposed. The new model effectively characterizes the relationship between the critical apparent tilt angle and the potential contact area. Compared to the Grasselli and JRC-JCS models, the new model demonstrates significant advantages in prediction accuracy and simplicity. Compared to the Grasselli topography method, the new model focuses on the potential contact area on the shear side, eliminates the maximum apparent tilt angle with unstable values, achieves better fitting results, and avoids the challenges of multi-parameter combinations. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein: Figure 1 This is a schematic diagram of the three-dimensional joint surface morphology characteristics in the calculation principle of the contact area ratio.

[0024] Figure 2 The critical apparent tilt angle obtained from the JB sample in the embodiments of the present invention. and their corresponding contact area ratio The curve graph.

[0025] Figure 3 The critical apparent tilt angle obtained from the JC sample in the embodiments of the present invention. and their corresponding contact area ratio The curve graph.

[0026] Figure 4 This is a scatter plot of the polar coordinate error of the new model in this embodiment of the invention.

[0027] Figure 5 This is a schematic diagram of the fitting function of equation (5) in an embodiment of the present invention.

[0028] Figure 6 The embodiment of the present invention is a freeze-thaw cycle control curve.

[0029] Figure 7 To verify the comparison results of the three models in the example.

[0030] Figure 8 The results of the basic friction angle of the structural surface specimen obtained by direct shear test on a straight structural surface in this embodiment of the invention are shown.

[0031] Figure 9 This refers to the basic friction angle of the structural surface specimen measured by tilting test in this embodiment of the invention. Detailed Implementation

[0032] The model of this application and its construction process will be described in detail below.

[0033] The construction of the structural shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads includes the following steps: Step 1: Use 3D laser scanning technology to obtain at least 30 sets of structural surface point clouds with different roughness, convert the micro-convex body into triangular mesh elements, obtain the mesh tilt angle, area, and structural surface contact area ratio data under different critical tilt angles, and construct a critical tilt angle-contact area ratio quantization model based on the Weibull distribution function.

[0034] Step one involves selecting natural rock samples and artificially preparing structural surface samples. The red sandstone used in this embodiment was obtained from a mine in Zigong, Sichuan. Uniaxial compression, conventional triaxial compression, and Brazilian splitting specimens were prepared according to the "Standard for Engineering Rock Mass Testing Methods." During the specimen preparation process, the specimens were manually screened to remove those with surface defects, cracks, or significant differences in diameter and height due to processing errors. Subsequently, structural surface specimens with consistent morphology were fabricated using 3D scanning and CNC engraving techniques. First, a splitting test was conducted on 100mm×100mm×100mm cubic rock specimens using an RMT-150C rock mechanics testing system, from which four groups of specimens with significant differences in roughness were selected. Based on the degree of roughness, the specimens were numbered JA, JB, JC, and JD, representing flat, relatively smooth, relatively rough, and very rough structural surface specimens, respectively. Then, a FreeScan Combo metrology-grade dual-light source handheld 3D scanner was used to perform 3D laser scanning on these four types of structural surface specimens, and the obtained point cloud data was used to construct a 3D geometric model. Finally, an engraving path program was written based on the 3D geometric model, and the structural surface specimens were fabricated using a DS-4040 three-axis CNC engraving machine. The engraving substrate was a 100mm×100mm×50mm flat rock specimen. During the engraving process, the spindle speed was set to 22,000 rpm, the feed rate to 1300, the step size to 0.1mm, and the tool diameter to 1mm. The steps for constructing the critical apparent tilt angle-contact area ratio quantification model in step one are as follows: First, analyze the data, specifically the critical tilt angles obtained from measuring the JA, JB, JC, and JD samples. and their corresponding contact area ratio Plotting a curve and observing the data characteristics reveals the following: (1) Gradual decay: In the initial stage, the value is high and decreases rapidly, while in the later stage it gradually decreases; (2) Exponential decay: As the value increases, the value decreases gradually. As the value gradually increases, the rate of decrease gradually slows down, showing a stable state close to 0; (3) Stable state: After the value approaches the minimum value, the change almost disappears and enters a stable state; - The dataset requires the following boundary conditions: when When it approaches 0, Approaching 1; when When approaching 90°, Approaching 0; Because the Weibull distribution has significant advantages in modeling decay processes, especially in effectively describing the rapid decay of data in the initial stage and its gradual stabilization over time, a quantitative relationship between the two can be established using the Weibull distribution function, as shown in equation (1) and Figure 2 , Figure 3 As shown by the red curve in the middle. Figure 2 , Figure 3 Critical tilt angles obtained for JB and JC samples, respectively. and their corresponding contact area ratio A curve graph; (1); In the formula, This indicates the contact area ratio on the shear side; The characteristic angle represents the contact area ratio. The critical angle corresponding to the time; The scale parameter of the Weibull distribution controls the rate of decay. The fitting parameters represent the shape parameters of the Weibull distribution, controlling the type of decay; ln is the operator for the natural logarithm. Indicates the critical apparent tilt angle.

[0035] Figure 2 This is the fitted curve for parameter k with deviations of 20% and 30%. Figure 3 For characteristic angle Fitting curves at deviations of 20% and 30%.

[0036] The fitted curve fits the data points extremely well, R0 2 The values ​​generally exceed 0.99, indicating that the model can accurately capture the changing trends of the data. This excellent fitting effect shows that equation (1) based on the Weibull distribution function is effective in describing the data. and It has good applicability and high accuracy when dealing with the relationship between them.

[0037] Furthermore, after constructing the critical apparent tilt angle-contact area ratio quantification model in step one, the inventors also further refined the characteristic angle... and fitting parameters Sensitivity analysis was conducted to study the effect of slight fluctuations in these two indicators on the contact area ratio. (1) The characteristic angle was adjusted to 70%, 80%, 120% and 130% of the initial value, and the new contact area ratio was calculated using equation (1). As the deviation of the characteristic angle increased, the calculated value gradually deviated from the experimental value. The minimum, average and maximum values ​​of the correlation coefficients of each calculation result were 0.9425, 0.9624 and 0.98, respectively. The minimum, average and maximum values ​​of the mean absolute error of each calculation result were 0.0119, 0.0204 and 0.0398, respectively. (2) The fitting parameters were adjusted to 70%, 80%, 120% and 130% of the initial value, and the new contact area ratio was calculated using equation (1). The values ​​were adjusted to 70%, 80%, 120%, and 130% of the initial values, and the new contact area ratio was calculated using equation (1). With the fitted parameters... As the deviation increases, the calculated values ​​gradually deviate from the experimental values. Ultimately, the average deviation of all calculated results is 20%, and the maximum deviation is 30%. These results indicate that the fitted parameters... The effect of adjusting the feature angle on the results is relatively small, with minimal changes; however, the effect of adjusting the feature angle is significant, indicating that it plays a crucial role in data fitting. Therefore, the inventors propose an ideal fitting parameter. This allows for a perfect fit across all data points, simplifying the model. Morphological quantitative analysis was performed on 30 groups of structural surface specimens. - The dataset is fitted to obtain the fitting parameters. The minimum value is 1.21, the maximum value is 1.39, the mean is 1.3, and the median is 1.27, exhibiting high stability and low fluctuation. The data mostly concentrate between 1.24 and 1.34, and the mean and median are close, indicating a relatively uniform data distribution. Therefore, this application preferably uses a mean of 1.3 as the ideal fitting parameter. At this point, equation (1) can be transformed into equation (2). Substituting k=1.3 into equation (2), the fitting curves of all 30 groups of structural surface specimens show extremely high consistency with the data points, R 2 The values ​​generally exceed 0.99. Therefore, equation (2) is suitable for measuring... - The connection between them.

[0038] (2).

[0039] Step 2: Conduct freeze-thaw cycle tests on these structural surface specimens, with a minimum of 30 freeze-thaw cycles; and conduct uniaxial compression, Brazilian splitting, triaxial compression, and direct shear tests on the same specimen after 0, 10, 20, and 30 freeze-thaw cycles, respectively, to obtain measurement data of uniaxial compressive strength, internal friction angle, peak shear strength of the structural surface, and normal stress under different freeze-thaw cycle numbers.

[0040] Step 3: Based on the critical apparent tilt angle-contact area ratio quantification model (2) constructed in Step 1, define and solve for the characteristic angle. ,get: (3); In the above formula, This indicates the ratio of the contact area on the shear side of the structural surface; The fitting parameter is set to 1.3 in this embodiment; Indicates the critical apparent tilt angle.

[0041] Step 4: Analyze the relationships between the above data. The following relationships exist between the main controlling factors of the structural surface, the peak expansion angle, and the peak strength: (1) The above key parameters of the shear mechanical properties of the structural surface are positively correlated with the peak shear strength. (2) The actual contact area during the shearing process accounts for only a small part of the total area of ​​the structural surface, and the actual contact area is positively correlated with the ratio of the rock wall compressive strength to the normal stress. (3) When the normal stress is close to 0, the peak expansion angle is equal to the initial expansion angle, and its value is completely determined by the surface morphology; while when the normal stress approaches infinity, the peak expansion angle is close to 0, and the influence of the surface morphology can be almost ignored. (4) The current peak expansion angle function expressions mainly include exponential functions, hyperbolic functions, power functions, and logarithmic functions. Taking into account the above factors and combining the test results of structural surface specimens JA, JB, JC, and JD, the Patton model is used. The incremental term i is determined to be of the form of nonlinear fitting. , The fitting parameters are substituted into the Patton model to obtain the final model, as shown in equation (4), which is referred to as the new model: (4); In the formula, The peak shear strength of the structural surface; The normal stress on the structural surface; The basic friction angle of the structural surface; For characteristic angles; Uniaxial compressive strength considering the number of freeze-thaw cycles; The fitting parameters are obtained by nonlinear fitting; in this embodiment, the fitting parameters are... The results were obtained through nonlinear fitting of experimental data from 30 sets of structural surface specimens.

[0042] The prediction results and biases of the new model are as follows: Figure 4 As shown, the maximum error, minimum error, and average error are 0.117, 0.038, and 0, respectively, all within acceptable limits. Therefore, the new model demonstrates good predictive performance.

[0043] In equation (4), the basic friction angle It may be related to the number of freeze-thaw cycles, so it can be written as The form. For the test results of the 30 sets of structural surface samples in this embodiment, the basic friction angle... In the direct shear test (test results are shown in...) Figure 8 ) and tilt test (test results see Figure 9 The former also exhibited stability, with deviations of 5.06%, 5.62%, and 2.81% under varying freeze-thaw cycles; the latter showed deviations of -0.84%, 3.88%, and 1.53%, all with variations below 4%. That is, the basic friction angle of the structural surface specimen in this embodiment... No significant changes were observed under different freeze-thaw cycles. In all data, the fluctuation of the basic friction angle under different freeze-thaw cycles was even lower than that under the same number of freeze-thaw cycles. This is because while freeze-thaw cycles have a significant impact on rock bonding, their impact on friction is very limited. Therefore, in this embodiment, the basic friction angle... The basic friction angle of the structural surface is calculated by direct shear test on a straight structural surface.

[0044] In equation (4), uniaxial compressive strength This may be related to the number of freeze-thaw cycles. In previous experiments, the uniaxial compressive strength of the aforementioned 30 groups of structural surface specimens was measured through uniaxial compression tests. The results show that as the number of freeze-thaw cycles gradually increases, the uniaxial compressive strength decreases, and the corresponding fitting function is shown in equation (5). Figure 5 As shown.

[0045] (5); In the formula, N is the number of freeze-thaw cycles; This refers to the uniaxial compressive strength of the rock wall before it has undergone freeze-thaw cycles, i.e., the uniaxial compressive strength in its natural state. A function for calculating the uniaxial compressive strength of rock walls after considering the number of freeze-thaw cycles.

[0046] Furthermore, in step one, the ratio of the contact area of ​​the structural surfaces under different critical apparent tilt angles... The method of obtaining it is: (1) Use three-dimensional laser scanning technology to perform fine scanning of the structural surface to obtain high-precision point cloud data; (2) Import the original point cloud data into Geomagic software for noise reduction to ensure data quality; (3) Import four ASC format point cloud files, namely the structural surface, bottom surface, right side surface and front side surface, into MATLAB for coordinate system reconstruction, structural surface point cloud reconstruction and homogenization processing, and finally generate homogenized point cloud data with a sampling interval of 0.25mm; (4) Import the homogenized point cloud data into Geomagic software, use the triangular meshing method to reconstruct the structural surface image, and export the STL file format to provide data support for subsequent geometric analysis and calculation; (5) Identify the coordinates of the triangular mesh points in the STL file in MATLAB, obtain the basic geometric parameters such as the mesh tilt angle and area, and thus evaluate the structural surface contact area ratio under different critical tilt angles.

[0047] In step two, the freeze-thaw cycle test steps are as follows: Place the sample in a DHG-9036A electric thermostatic drying oven, set the temperature to 105℃, and dry for 24 hours until constant weight. After drying, place the sample in an NM-V vacuum pressure saturation device, evacuate for 4-6 hours, and then pressurize for 24 hours. Set the pressure value to 0.1MPa, and use distilled water as the saturation solution. Seal the pressurized and saturated sample with plastic wrap and place it in a TMS9012-160 high and low temperature test chamber. Set the temperature range to -20℃ to +20℃. The freeze-thaw cycle period is 8 hours. One freeze-thaw cycle process is as follows: (1) Cooling stage, from the initial temperature of 20℃ to -20℃ in 1.5h; (2) Freezing stage, maintain at -20℃ for 2.5h; (3) Heating stage, from -20℃ to 20℃ in 1.5h; (4) Melting stage, maintain at 20℃ for 2.5h. The freeze-thaw cycle process is automatically controlled by a computer, and the programmed curve and the actual operating curve are as follows: Figure 6 As shown.

[0048] Verification Example In the verification example, the structural shear failure model under the combined influence of freeze-thaw cycle and compression-shear load of this application is compared with two classical models—the JRC-JCS model and the Grasselli model.

[0049] At least 10 independent structural surface specimens were selected as test subjects. Then, the freeze-thaw cycle and uniaxial compression, Brazilian splitting, triaxial compression and direct shear tests in step two were repeated to obtain the measurement data of uniaxial compressive strength, internal friction angle, and normal stress under different freeze-thaw cycles, as well as the measured value of the peak shear strength of the structural surface for verification.

[0050] The JRC-JCS model is: (6); (7); Where JCS represents the rock wall strength of the structural surface, and JRC represents the roughness coefficient of the structural surface. The root mean square of the first derivative of the contour line is given. For a natural, unweathered structural surface, the JCS can be considered as the uniaxial compressive strength, and the uniaxial compressive strength under different freeze-thaw cycles can be calculated according to equation (6). Ten contour lines are extracted at equal intervals on the structural surface, and the values ​​of each contour line are calculated. The JRC value of the profile is calculated using equation (7), and the average JRC value of all profiles is the JRC value of the sample.

[0051] The Grasselli model is: (8); in, Indicates tensile strength. This represents the angle between the foliated surface and the normal plane of the plane containing the structural surface. The tensile strength under different freeze-thaw cycles is calculated according to equation (8). The specimen used in this verification example does not have foliated surfaces, therefore... It equals 0.

[0052] Figure 7 The comparison results of three models are shown in the figure. The new model in the figure is the structural shear failure model under the combined influence of freeze-thaw cycle and compressive-shear load of this application. The results show that the predicted values ​​of the JRC-JCS model are generally lower than the experimental values, and the prediction error gradually increases with the increase of peak intensity. The maximum error, average error, and minimum error of the JRC-JCS model are 0.329, 0.713, and 0, respectively. Since the Grasselli model is not applicable to flat structural surfaces, only the experimental data of rough structural surfaces are compared. The prediction results of the Grasselli model are better than those of the JRC-JCS model, and its predicted values ​​are slightly lower than the experimental values. The maximum error, average error, and minimum error of the Grasselli model are 0.197, 0.079, and 0.003, respectively. The maximum error, minimum error, and average error of the new model (structural shear failure model under the combined influence of freeze-thaw cycle and compressive-shear load) are 0.117, 0.038, and 0, respectively; it is in high agreement with the experimental data and has the best fitting effect among the three models.

[0053] Of the two classic models, the Grasselli model performs better. Grasselli (2001) proposed using the maximum contact area ratio... Maximum viewing angle and fitting parameters To measure the relationship between the tilt angle of the micro-protrusion and the potential contact area, see equation (9). (9); in, It represents the contact area ratio (i.e., the ratio of the total area of ​​the micro-protrusions that make contact to the total area of ​​the structural surface). Indicates the maximum contact area ratio. Indicates the maximum apparent tilt angle. This represents the fitted parameters.

[0054] The main differences between the new model in this application and the Grasselli model are as follows: (1) Focus on the contact area on the shear side.

[0055] This study focuses on the shear-facing structural surface, not all structural surfaces. Existing research indicates that the maximum contact area ratio... The relationship between this parameter and the surface roughness, damage characteristics, and mechanical properties is unclear, and its variation range is small, essentially negligible and insufficient as an effective parameter for morphology evaluation. Therefore, this paper uses the shear-side contact area ratio. To replace the Grasselli method .

[0056] (2) The maximum apparent tilt angle with unstable values ​​was eliminated.

[0057] During 3D laser scanning, noise and outliers inevitably appear in point cloud data due to environmental factors such as temperature and vibration, causing fluctuations in the maximum apparent tilt angle of the structural surface specimen. Analysis of multiple scans of the same specimen revealed instability in the maximum apparent tilt angle, with some specimens exhibiting deviations exceeding 10%. Therefore, this paper no longer uses the maximum apparent tilt angle as a morphological parameter.

[0058] (3) Better fitting effect.

[0059] Equation (4) of the new model in this application all show good fitting results, and the fit between each fitting curve and the actual data points is high. From the fitting results, the fitting effect of Equation (4) is generally better than that of Equation (9) of the Grasselli model, and its corresponding R... 2 The values ​​are generally high, indicating that equation (4) can better capture the trends and changes in the data.

[0060] (4) It avoids the problem of multi-parameter combination.

[0061] The Grasselli method measures the roughness of a structural surface using three parameters. Based on this, researchers have proposed various combinations of these parameters. , , However, these combined parameters lack sufficient theoretical support, and their physical meaning is unclear. In the quantitative model proposed in this paper, the roughness characteristics of the structural surface are determined by only one key parameter—the feature angle. This method of characterization not only simplifies model construction but also effectively avoids the interpretation difficulties that may arise from multi-parameter quantization.

[0062] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A structural shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads, characterized in that: Structural shear strength considering freeze-thaw cycles for: ； In the above formula, Normal stress; This is the basic friction angle; For characteristic angles; Uniaxial compressive strength considering the number of freeze-thaw cycles; These are the fitting parameters; Feature angle In the quantitative model of the critical apparent tilt angle-shear side contact area ratio of the structural surface constructed based on the Weibull distribution function, the critical apparent tilt angle is the angle corresponding to the shear side contact area ratio of 1 / e, where e is a natural constant.

2. The structural shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 1, characterized in that: Feature angle The calculation formula is: ； In the above formula, This indicates the ratio of the contact area on the shear side of the structural surface; The fitting parameters represent the shape parameters of the Weibull distribution and control the type of decay. Indicates the critical apparent tilt angle.

3. The structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 1, characterized in that: The fitting parameter k ranges from 1.21 to 1.

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4. The structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 1, characterized in that: The function for calculating the uniaxial compressive strength of rock walls after considering the number of freeze-thaw cycles is as follows: ； In the above formula, N represents the number of freeze-thaw cycles; This refers to the uniaxial compressive strength of the rock wall before it has undergone freeze-thaw cycles, i.e., the uniaxial compressive strength in its natural state.

5. The structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 1, characterized in that: The construction of the structural shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads includes the following steps: Step 1: Prepare several sets of structural surface samples with consistent morphology; use three-dimensional laser scanning technology to obtain at least 30 sets of structural surface point clouds with different roughness, convert the micro-protrusions into triangular mesh units, obtain the mesh tilt angle, area, and structural surface contact area ratio data under different critical tilt angles, and construct a critical tilt angle-contact area ratio quantization model based on the Weibull distribution function. Step 2: Conduct freeze-thaw cycle tests on these structural surface specimens, with a minimum of 30 freeze-thaw cycles; and conduct uniaxial compression, Brazilian splitting, triaxial compression, and direct shear tests on the same specimen after 0, 10, 20, and 30 freeze-thaw cycles, respectively, to obtain measurement data of uniaxial compressive strength, internal friction angle, peak shear strength of the structural surface, and normal stress under different freeze-thaw cycle numbers; Step 3: Based on the critical apparent tilt angle-contact area ratio quantification model constructed in Step 1, define and solve for the characteristic angle. ; Step 4: Analyze the relationships between the above data based on the Patton model. The incremental term i is determined to be of the form of nonlinear fitting. , The fitting parameters are used; substituting them into the Patton model yields the final model. .

6. The structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 5, characterized in that: The critical apparent tilt angle-contact area ratio quantification model constructed in step one is as follows: ； In the above formula, This indicates the contact area ratio on the shear side; The characteristic angle represents the contact area ratio. The critical angle corresponding to the time; The scale parameter of the Weibull distribution controls the rate of decay. The fitting parameters represent the shape parameters of the Weibull distribution and control the type of decay. Represents the critical tilt angle; ln is the operator for the natural logarithm.

7. The structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 5, characterized in that: In step one, the steps for preparing the structural surface specimen are as follows: First, a rock mechanics testing system was used to conduct splitting tests on cubic rock samples with dimensions of 100mm×100mm×100mm, from which four groups of rock samples with significant differences in roughness were selected. According to the different roughness, the samples were numbered JA, JB, JC and JD, representing flat, relatively smooth, relatively rough and very rough structural surface samples, respectively. Then, a 3D scanner was used to perform 3D laser scanning on the four rock samples, and the obtained point cloud data was used to construct a 3D geometric model. Finally, a carving path program was written based on the three-dimensional geometric model, and structural surface samples with four roughnesses were made using a CNC carving machine.

8. The structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 5, characterized in that: Step two, the freeze-thaw cycle test includes the following steps: The first step is to dry the structural surface sample in a constant temperature forced-air drying oven at 105°C for 24 hours until constant weight is achieved; The second step is to place the dried sample in a vacuum pressure saturation device, evacuate for 4-6 hours, and then pressurize for 24 hours. The pressure value is set to 0.1 MPa, and distilled water is used as the saturation solution to obtain the pressurized saturated sample. The third step is to seal the pressurized and saturated sample with plastic wrap and place it in a high and low temperature test chamber for freeze-thaw cycles. The freeze-thaw cycle cycle is 8 hours. One freeze-thaw cycle process is as follows: (1) Cooling stage, from the initial temperature of 20℃ to -20℃ in 1.5h; (2) Freezing stage, maintained at -20℃ for 2.5h; (3) Heating stage, from -20℃ to 20℃ in 1.5h; (4) Melting stage, maintained at 20℃ for 2.5h.

9. The structural surface shear failure model under the combined influence of freeze-thaw cycles and compressive-shear loads as described in claim 5, characterized in that: The validation method for this model includes the following steps: Select at least 10 independent structural surface specimens and repeat the freeze-thaw cycle and uniaxial compression, Brazilian splitting, triaxial compression and direct shear tests in step two to obtain the measurement data of uniaxial compressive strength, internal friction angle, and normal stress under different freeze-thaw cycle numbers, as well as the measured value of the peak shear strength of the structural surface for verification. Substitute the above data into the structural shear failure model under the combined influence of freeze-thaw cycle and compression-shear load, and calculate the predicted value of the peak shear strength of the structural surface. Compare the measured values ​​of the peak shear strength of the structural surface with the predicted values, using the index average relative error and the coefficient of determination R. 2 To conduct evaluation and analysis.

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