A method for assessing the risk of freeze-thaw damage in rock mass fractures based on surface temperature

Abstract

This invention discloses a method for assessing the freeze-thaw damage risk of rock mass fissures based on surface temperature, comprising the following steps: S1, using a UAV platform equipped with multi-source sensors to collect data on the target area, obtaining fissure geometric parameters, daily minimum surface temperature, daily maximum surface temperature, daily temperature difference, and fissure moisture conditions; S2, based on the fissure geometric parameters, constructing an analytical model of fissure frost heave force; obtaining the quantitative relationship between stress intensity factor and ambient temperature; S3, determining the type I fracture toughness of the target rock mass, determining the critical initiation temperature of the rock mass; determining the critical number of freeze-thaw cycles; S4, based on the daily minimum surface temperature, daily temperature difference, fissure moisture conditions, and critical initiation temperature, obtaining the annual cumulative effective number of freeze-thaw cycles; calculating the freeze-thaw damage ratio, and quantifying and classifying the risk. This invention solves the problem of inaccurate assessments caused by existing technologies being limited to local monitoring and lacking an integrated assessment framework for environmental factors and material parameters.

Description

Technical Field

[0001] This invention relates to the field of rock mass engineering safety technology in cold regions, and in particular to a method for assessing the risk of freeze-thaw damage to rock mass fissures based on surface temperature. Background Technology

[0002] Rock mass engineering projects such as tunnels, slopes, railways, and highways are widely distributed in high-altitude and cold regions. Under low-temperature conditions, water in rock fissures undergoes a water-to-ice phase transition during freeze-thaw cycles. Under the constraint of fissures, this generates frost heave forces, which in turn lead to fissure propagation, loosening of the rock mass structure, and deterioration of mechanical strength, seriously affecting the long-term stability and durability of engineering structures. In particular, under frequent freeze-thaw cycles, the repeated phase transitions of fissure water will cause cumulative damage to the rock mass structure, potentially inducing engineering defects such as slope slippage and tunnel lining cracking.

[0003] Currently, assessment methods for the risk of freeze-thaw damage to rock masses in cold regions largely rely on local monitoring or empirical judgment, lacking a quantitative and systematic evaluation framework that integrates multi-source information such as ambient temperature, rock mass parameters, and fracture conditions. Existing technologies struggle to accurately predict the risk of frost heave cracking based on readily available parameters such as surface temperature, lack unified quantitative indicators to support graded prevention and control of engineering risks, and especially lack quantitative assessment models that integrate environmental factors and material parameters for unified analysis. Consequently, assessment results fail to fully reflect the actual freeze-thaw damage risk. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for assessing the risk of freeze-thaw damage to rock fissures based on surface temperature. This method can comprehensively consider the risk of freeze-thaw cracking of rock fissures under the influence of material properties and freeze-thaw environment, and perform quantitative assessment, thereby achieving standardization and intelligentization of safety evaluation for cold region engineering.

[0005] Therefore, the present invention adopts the following technical solution:

[0006] A method for assessing the risk of freeze-thaw damage to rock mass fractures based on surface temperature includes the following steps:

[0007] S1, collect data from the target area to obtain the geometric parameters of rock mass fractures and the lowest daily surface temperature. Daily maximum surface temperature Daily temperature difference and fissure moisture conditions ;

[0008] S2, based on the geometric parameters obtained in S1, constructs an analytical model of crack frost heave force considering constraint pressure correction. And establish stress intensity factor With ambient temperature Quantitative relationship;

[0009] S3, Calculate the type I fracture toughness of the rock mass And based on the stress intensity factor Determine the critical crack initiation temperature of the rock mass The critical number of freeze-thaw cycles for rock mass fractures was determined by testing the critical point of freeze-thaw propagation. ;

[0010] S4, the lowest daily surface temperature obtained based on S1. Daily temperature difference Fissure moisture conditions The critical crack initiation temperature of the rock mass obtained from S3 The effective freeze-thaw cycles are determined and counted to obtain the annual cumulative number of effective freeze-thaw cycles. Based on the aforementioned annual cumulative effective freeze-thaw cycles. and the critical number of freeze-thaw cycles Calculate the freeze-thaw damage ratio and quantify and classify the risk accordingly.

[0011] In the above method, the specific steps of step S1 are as follows:

[0012] (1) Collect original images of the target area, extract the location, length, width, dip angle and spatial distribution characteristics of the fractures, and simplify the fractures in the rock mass into ideal elliptical fractures to obtain the geometric parameters of the rock mass fractures: major axis length minor axis length ,high , << ;

[0013] (2) During a set time period, acquire thermal infrared images of the target area and record precise timestamps. The thermal infrared images carry brightness temperature data. The set time period is: 04:00 to 06:00 and 13:00 to 15:00. Obtain the effective area in the target area that contains only bare rock pixels. Perform radiometric calibration and emissivity correction on the brightness temperature data carried by the thermal infrared images containing bare rock pixels to invert the surface temperature field. Take the surface temperature from 04:00 to 06:00 as the daily minimum surface temperature. The surface temperature from 13:00 to 15:00 As the highest surface temperature of the day Daily temperature difference ;

[0014] (3) Obtain thermal infrared images of the target area for half an hour before and after 18:00, and extract low-temperature patches; install frequency domain / time domain reflectance moisture content sensors in layers at the center of the low-temperature patches and along their normal direction; set up control monitoring points in patches of the same lithology that exhibit dry characteristics; obtain the moisture content data of the low-temperature patches and dry characteristic patches to determine whether the low-temperature patches are high-moisture patches; use the moisture content data of the high-moisture patches collected by the moisture content sensors as the fracture moisture condition. .

[0015] In step S2 above, the method for constructing an analytical model of crack frost heave force considering constraint pressure correction is as follows:

[0016] Considering the volume expansion rate when water freezes Volume increase caused by water-ice phase transition The calculation formula is:

[0017] ,

[0018] in, The ice content is calculated using the following formula:

[0019] ,

[0020] Among them, unfrozen water content The empirical calculation formula is:

[0021] ,

[0022] in, This is the actual freezing temperature. For ambient temperature, and These are empirical constants related to lithology;

[0023] To obtain the actual freezing temperature, pressure correction is applied. Relative to frost heave instantaneous rate of change Taking the reciprocal of the Clapeyron equation, its expression is:

[0024] ,

[0025] in, For latent heat of phase transition, For volume change, This is the freezing temperature of pure water under standard atmospheric pressure.

[0026] Considering frost heave For the actual freezing temperature Impact:

[0027] ,

[0028] in, This is the initial freezing temperature under standard atmospheric pressure.

[0029] frost heave Under the influence of frost heave, based on the theory of elasticity, the volumetric deformation of cracks caused by frost heave... The calculation formula is:

[0030] ,

[0031] in, For rock shear modulus, , These are the rock elastic modulus and Poisson's ratio, which are related to temperature.

[0032] Based on the principle of volume conservation, the volumetric deformation of cracks caused by frost heave. Equal to the volume and weight caused by the phase transition of water and ice Solve the volume conservation equations simultaneously ( Based on the above calculation formulas, the frost heave force is obtained. With ambient temperature Functional relationship:

[0033] ,

[0034] Therefore, an analytical model of crack frost heave force considering constraint pressure correction was established:

[0035] .

[0036] In step S2 above, for sandstone samples with visible fracture structures, nuclear magnetic resonance (NMR) technology is used to measure the unfrozen water content as a function of temperature. And using unfrozen water content The empirical calculation formulas are fitted to obtain empirical constants related to lithology. , The value of .

[0037] In step S2 above, the stress intensity factor is established. With ambient temperature The specific method for quantitatively determining the relationship between them is as follows: Simultaneously formulate the expression for the stress intensity factor at the crack tip. Analytical model of frost heave force in cracks Establish stress intensity factor With ambient temperature Quantitative relationship between them:

[0038] .

[0039] In step S3 above, the method for calculating the type I fracture toughness of the rock mass is as follows:

[0040] Through on-site geological surveys and drilling, the target rock mass type was identified and samples were taken. Standard fractures were prefabricated on the samples from the target rock mass. After vacuum saturation with water, the samples were placed in a -20℃ low-temperature chamber for 3-4 hours to simulate the low-temperature saturation conditions on-site, resulting in prefabricated water-saturated rock samples. Three-point bending tests were performed on the prefabricated water-saturated rock samples, load-crack tip strain curves were collected, outliers were removed, and the average effective maximum load was taken to calculate the type I fracture toughness of the rock mass. :

[0041] ,

[0042] in, The effective maximum load is the average value; For span; The width of the sample; For sample height; geometric factor function The calculation formula is as follows:

[0043] ,

[0044] in, The length of the standard crack in the specimen.

[0045] In step S3 above, the critical crack initiation temperature is determined. The method is as follows: Under critical conditions, the rock mass fissures are in a limit equilibrium state on the verge of cracking. ,at this time, To obtain information about the ambient temperature The equation:

[0046] ,

[0047] Solving this equation yields the unique unknown quantity. The value is the critical crack initiation temperature. .

[0048] In step S3 above, the method for determining the critical number of freeze-thaw cycles is as follows: a pre-prepared water-saturated rock sample is placed in a freeze-thaw cycle test chamber to simulate the diurnal fluctuations in a cold region; the amount of crack propagation is monitored using resistance strain gauges, and a crack propagation-freeze-thaw cycle number curve is plotted; the position where the second derivative of the crack propagation-freeze-thaw cycle number curve is zero is taken as the critical point for the freeze-thaw propagation of rock mass cracks, and the corresponding number of freeze-thaw cycles is taken as the critical number of freeze-thaw cycles. .

[0049] In step S4 above, the annual cumulative effective freeze-thaw cycle count is obtained. The method is as follows: A valid freeze-thaw cycle is counted if all of the following conditions are met:

[0050] Lowest surface temperature of the day Rock mass crack initiation temperature ;

[0051] Daily temperature difference ≥5℃;

[0052] Fissure Moisture Conditions ≥50%;

[0053] Based on the above conditions, the annual cumulative effective freeze-thaw cycle count was obtained on-site. ;

[0054] The freeze-thaw damage ratio The calculation formula is:

[0055] .

[0056] In step S4 above, A value ≥0.8 indicates extremely high risk; 0.5≤ <0.8 indicates high risk; 0.2≤ A value less than 0.5 indicates a medium risk. A value less than 0.2 indicates low risk.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] 1. This invention effectively improves the calculation accuracy of crack frost heave force by introducing an analytical model that considers constraint pressure correction, and transforms macroscopic environmental parameters such as ambient temperature into a quantitatively describable stress intensity factor, thus laying a solid physical mechanism foundation for risk assessment.

[0059] 2. This invention solves for the critical crack initiation temperature by combining the stress intensity factor and the fracture toughness of the rock mass, and combines the on-site surface temperature and the critical number of freeze-thaw cycles to construct a joint criterion based on on-site parameters and rock material thresholds, thereby realizing the assessment of crack initiation risk.

[0060] 3. The risk classification mechanism of this invention significantly improves the scientificity and completeness of the assessment system, providing a direct and reliable decision-making basis for the differentiated formulation of prevention and control measures such as heat preservation, drainage, and reinforcement in cold-region rock mass engineering, thereby achieving precise control over the engineering protection effect and effectively avoiding insufficient or excessive protection. Attached Figure Description

[0061] Figure 1 This is a flowchart of the evaluation method in an embodiment of the present invention;

[0062] Figure 2A planar diagram of an ideal elliptical crack;

[0063] Figure 3 This is a fitted curve of unfrozen water content versus temperature in an embodiment of the present invention;

[0064] Figure 4 This is a comparison chart of the model-predicted and measured values ​​of the frost heave force-temperature curve for rock sample A-1 in an embodiment of the present invention.

[0065] Figure 5 This is a comparison chart of the model-predicted and measured values ​​of the frost heave force-temperature curve for rock sample A-2 in an embodiment of the present invention.

[0066] Figure 6 This is a comparison chart of the model-predicted and measured values ​​of the frost heave force-temperature curve for rock samples A-3 / B-1 in the embodiments of the present invention.

[0067] Figure 7 This is a comparison chart of the predicted and measured values ​​of the frost heave force-temperature curve for rock sample B-2 in an embodiment of the present invention.

[0068] Figure 8 This is a comparison chart of the predicted and measured values ​​of the frost heave force-temperature curve for rock sample B-3 in an embodiment of the present invention. Detailed Implementation

[0069] The technical solution of the invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the following embodiments are only some embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0070] Example

[0071] This invention provides a method for assessing the risk of freeze-thaw damage to rock mass fissures based on surface temperature, such as... Figure 1 As shown, it includes the following steps:

[0072] S1 is based on an unmanned aerial vehicle platform equipped with multi-source sensors to collect data on the target area.

[0073] In this embodiment, the sensor configuration on the UAV platform includes an oblique photography camera and a thermal infrared imager. Key parameters for UAV aerial surveying are set as follows: flight altitude 80-150 meters, flight speed 8-16 meters per second, and lateral and lateral overlap of no less than 75%, ensuring that the ground resolution of both visible light and thermal infrared images reaches approximately 2 centimeters per pixel. The flight altitude and lateral overlap are configured based on the requirement that the ground resolution is no greater than 10 centimeters. The oblique photography camera has an effective pixel count of no less than 20 million and supports five-view or equivalent multi-view imaging.

[0074] The data collection includes:

[0075] (1) Obtain the geometric parameters of rock mass fractures.

[0076] The oblique photography camera acquires raw images (visible light images) of the target area. Image recognition algorithms automatically process these raw images to extract the location, length, width, dip angle, and spatial distribution characteristics of rock mass fissures. The rock mass fissures are then simplified as follows: Figure 2 The ideal elliptical crack shown is given, where the major axis of the crack is... The minor axis is The height is , << , These are the geometric parameters of the crack.

[0077] (2) Obtaining surface temperature With fissure moisture conditions .

[0078] The thermal infrared imager operates in the 8-14μm band, has an equivalent temperature difference noise value of no more than 50mK@25℃, a temperature measurement range of -20-150℃, and outputs a thermal infrared image with brightness temperature data.

[0079] To accurately obtain the daily minimum surface temperature used for determining effective freeze-thaw cycles Daily maximum surface temperature and daily temperature difference A set time period was planned for thermal infrared data acquisition. Precise timestamps were recorded simultaneously with the acquisition of thermal infrared images during this period to facilitate subsequent calculations of temperature extremes and daily temperature differences, ensuring time alignment. The set time periods were: 04:00 to 06:00 and 13:00 to 15:00 local time. While acquiring visible light thermal infrared images of the target area at different time periods, visible light images of the target area were also acquired. Masks for vegetation, shadows, and highly reflective areas were generated through image segmentation, and these non-target pixels were removed to obtain effective areas containing only bare rock pixels. Based on these effective areas, radiometric calibration was performed on the brightness temperature data carried by the thermal infrared images containing only bare rock pixels, and emissivity correction was applied according to the effective surface type. This resulted in the inversion of a high-precision surface temperature field, allowing the acquisition of surface temperatures for each time period. Among them, the surface temperature from 04:00 to 06:00 The lowest surface temperature of the day Surface temperature from 13:00 to 15:00 The highest surface temperature of the day Calculate the daily temperature range : .

[0080] (3) Obtaining the conditions for fissure moisture .

[0081] Thermal infrared images of the target area were acquired by the thermal infrared imager half an hour before and after 18:00. Low-temperature patches were extracted by local statistics or by setting percentile thresholds. Based on this, frequency domain / time domain reflectance (FDR / TDR) moisture content sensors were layered and buried at the center of the low-temperature patches and along their normal direction. Simultaneously, control monitoring points were set up within patches of the same lithology exhibiting dry characteristics to characterize the moisture content level and temperature response characteristics under dry background conditions, serving as a benchmark for comparative analysis of high-moisture patches. The moisture content sensors acquired moisture content data for low-temperature patches and dry characteristic patches at a sampling frequency of once every 6 hours. The acquired moisture content data from the control monitoring points were used to provide reference values ​​for moisture content under dry background conditions to determine whether low-temperature patches were high-moisture patches. The moisture content data of high-moisture patches acquired by the moisture content sensors represented fracture moisture conditions. .

[0082] S2. Construct an analytical model of crack frost heave force considering constraint pressure correction, and obtain the quantitative relationship between stress intensity factor and ambient temperature. The specific steps are as follows:

[0083] S21. Based on the geometric parameters obtained in S1, an analytical model of crack frost heave force considering constraint pressure correction is constructed. .

[0084] Make the following assumptions: the rock matrix and fissures are initially saturated with water, there is no external load, no salinity, the environment is closed and the temperature is uniform, there is no water migration, the friction between ice and fissures is ignored, the frost heave force is uniformly distributed, and both ice and rock are homogeneous isotropic elastic bodies.

[0085] Volume expansion rate of water when it freezes The volume increase caused by the phase transition of water and ice The calculation formula is:

[0086] ,

[0087] in, The formula for calculating the fracture ice content is:

[0088] ,

[0089] Among them, unfrozen water content The empirical calculation formula is:

[0090] ,

[0091] in, This is the actual freezing temperature. For ambient temperature, and These are empirical constants related to lithology.

[0092] The lithology-related empirical constants and The value of is determined based on the following experiments:

[0093] For the sandstone sample with visible fractures in this embodiment, the unfrozen water content as a function of temperature was measured using nuclear magnetic resonance (NMR) technology. And using unfrozen water content The empirical formula is fitted to obtain the empirical constants. and The value of . In this embodiment, the fitting result is as follows: Figure 3 As shown, the goodness of fit reaches 0.93, proving the applicability of the formula. Based on this, the empirical constant... Set to 53.946, an empirical constant. The value was set to -0.581. For other types of rock samples, the same method was used to apply the empirical constant. and The value of .

[0094] To obtain the actual freezing temperature, pressure correction is applied. Relative to frost heave instantaneous rate of change Taking the reciprocal of the Clapeyron equation, its expression is:

[0095] ,

[0096] in, For latent heat of phase transition, For volume change, This is the freezing temperature of pure water under standard atmospheric pressure.

[0097] In this embodiment, , , ,at this time K / Pa (or -0.074℃ / MPa) indicates that for every 1 MPa increase in pressure, the freezing temperature of water decreases by approximately [amount missing]. .

[0098] Considering frost heave For the actual freezing temperature The effects include:

[0099] ,

[0100] in, This is the initial freezing temperature under standard atmospheric pressure.

[0101] frost heave Under the influence of frost heave, based on the theory of elasticity, the volumetric deformation of cracks caused by frost heave... The calculation formula is:

[0102] ,

[0103] in, , where is the rock shear modulus; , These are the rock elastic modulus and Poisson's ratio, which are related to temperature, respectively.

[0104] Based on the principle of volume conservation, the volumetric deformation of cracks caused by frost heave. Equal to the volume and weight caused by the phase transition of water and ice Solve the volume conservation equations simultaneously ( Based on the above calculation formulas, the frost heave force is obtained. With ambient temperature Functional relationship:

[0105] ,

[0106] Therefore, an analytical model of crack frost heave force considering constraint pressure correction is established:

[0107] .

[0108] The analytical model of frost heave force in the crack Ice content in the cracks as a function of temperature Rock elastic modulus Poisson's ratio of rocks and fracture geometry parameters It fully depicts the evolution of frost heave force in cracks under temperature changes.

[0109] S22, Establishing the relationship between stress intensity factor and ambient temperature The quantitative relationship between them.

[0110] Stress intensity factor at the crack tip The expression is: Jointly Analytical model of frost heave force in cracks established with S21 Establish stress intensity factor With ambient temperature Quantitative relationship between them:

[0111] .

[0112] To verify the analytical model of frost heave force in cracks proposed in this invention To ensure accuracy and applicability, two groups of rock samples, A and B, with different geometric parameters, were selected as comparison objects for frost heave force testing. The crack size and lithology-related empirical constants of each group of samples were determined. , As shown in Table 1.

[0113] Table 1

[0114]

[0115] During the experiment, the system collected data on the frost heave force-temperature change of each group of samples during the cooling process, and compared and analyzed the measured data with the prediction results of the theoretical model. The comparison results are as follows: Figures 4-8 As shown in the figure, the model prediction curve and the measured data curve generally match the trend of change throughout the temperature range; especially in the middle and late stages of freezing, their trends are almost identical, indicating that the model can effectively reflect the development law of frost heave caused by fissure water freezing under low temperature conditions. Further comparison shows that in the initial freezing stage, the model prediction value is slightly higher than the measured value. This is because at this time, a complete ice plug structure has not yet formed inside the fissure, and the frost heave force is insufficient, resulting in the measured value being lower than the theoretical prediction value.

[0116] S3, determine the type I fracture toughness and critical freeze-thaw cycle count of the target rock mass, and determine the critical crack initiation temperature. The specific steps are as follows:

[0117] S31, Calculate the Type I fracture toughness of the rock mass .

[0118] Through on-site geological surveys and drilling, the target rock mass type was identified and samples were taken. In this embodiment, the target rock mass was processed into specimens with dimensions of 24mm×80mm×50mm in the laboratory, and standard fractures (20mm×3mm±0.2mm) were prefabricated. After vacuum saturation with water, the specimens were placed in a -20℃ low-temperature chamber for 3-4 hours to simulate the low-temperature saturation conditions in the field, thus obtaining prefabricated water-saturated rock specimens. Three-point bending tests were performed on the prefabricated water-saturated rock specimens, load-crack tip strain curves were collected, outliers were removed, and the average effective maximum load was taken. The Type I fracture toughness of the rock mass was calculated according to the formula in ASTM E399 standard. :

[0119] ,

[0120] in, The effective maximum load is the average value; For span; The width of the sample; For sample height; geometric factor function Calculated by the following formula:

[0121] ,

[0122] in, The length of the standard crack in the sample.

[0123] Substitute the measured parameters into The calculation formula is used to obtain the Type I fracture toughness of the target rock mass (such as frozen saturated red sandstone). .

[0124] S32, based on the stress intensity factor Determine the critical crack initiation temperature .

[0125] The critical mechanical condition for the unstable propagation (cracking) of rock mass fractures is the stress intensity factor at the crack tip. Reaching or exceeding the Type I fracture toughness of the rock material itself ,Right now: Under critical conditions (i.e., when the crack is in a state of limit equilibrium on the verge of cracking), ,at this time, To obtain information about the ambient temperature The equation:

[0126]

[0127] Solving this equation will yield the unique unknown quantity. The value of this value is the critical crack initiation temperature of the rock mass. This temperature value is the core threshold for subsequent freeze-thaw risk assessment based on surface temperature monitoring data.

[0128] S33, determine the critical number of freeze-thaw cycles.

[0129] To quantitatively characterize the critical state of rock mass fracture propagation under freeze-thaw cycles, saturated rock samples with pre-fabricated standard fractures were placed in a freeze-thaw cycle test chamber ranging from -20℃ (4h) to +15℃ (2h) to simulate diurnal fluctuations in cold regions. The fracture propagation was monitored using resistance strain gauges attached to both sides of the fracture, and a fracture propagation-freeze-thaw cycle count curve was plotted. In the initial stage, the ice expansion force and microcrack growth caused by the freeze-thaw cycle were small, and the displacement was slow. When the freeze-thaw damage accumulated to a critical level, the fracture began to propagate rapidly. The point where the second derivative of the fracture propagation-freeze-thaw cycle count curve was zero was taken as the turning point from the slow stage to the rapid stage of fracture propagation, which is the critical point of rock mass fracture freeze-thaw propagation. Its physical meaning is the moment when the accumulated freeze-thaw damage reached a critical level. Based on this, the number of freeze-thaw cycles corresponding to the accelerated fracture propagation was determined, which is the critical number of freeze-thaw cycles for rock mass fractures. .

[0130] In this embodiment, three resistance strain gauges (accuracy 0.1μm) are attached to each side of the crack.

[0131] S4. Effective freeze-thaw cycles are determined and counted, the freeze-thaw damage ratio is calculated, and then risk quantification and classification are performed, including the following steps:

[0132] S41, based on the data collected in S1, determines and counts the effective freeze-thaw cycles.

[0133] A valid freeze-thaw cycle is counted if all of the following conditions are met:

[0134] Lowest surface temperature Critical crack initiation temperature ;

[0135] Daily temperature difference ≥5℃;

[0136] Fissure Moisture Conditions ≥50%.

[0137] Based on the above conditions, the annual cumulative effective freeze-thaw cycle count was obtained on-site. .

[0138] S42, based on the annual cumulative effective freeze-thaw cycle count and critical freeze-thaw cycles Calculate the freeze-thaw damage ratio Risk is quantified and classified based on the freeze-thaw damage ratio.

[0139] freeze-thaw damage ratio The calculation formula is: ,

[0140] according to The magnitude of the value determines the differentiated risk level, and establishes the correspondence between different risk levels and engineering control measures, forming a complete closed loop from monitoring data to risk classification decision-making, and outputting specific engineering decision-making recommendations.

[0141] In this embodiment, the correspondence between risk level and engineering control measures is shown in Table 2:

[0142] Table 2

[0143] .

Claims

1. A method for assessing the risk of freeze-thaw damage to rock mass fissures based on surface temperature, characterized in that, Includes the following steps: S1, collect data from the target area to obtain the geometric parameters of rock mass fractures and the lowest daily surface temperature. Daily maximum surface temperature Daily temperature difference and fissure moisture conditions The geometric parameters of the rock mass fracture include the length of its major axis. minor axis length and height , << ; S2, based on the geometric parameters obtained in S1, constructs an analytical model of crack frost heave force considering constraint pressure correction. And establish stress intensity factor With ambient temperature Quantitative relationship; S3, Calculate the type I fracture toughness of the rock mass And based on the stress intensity factor Determine the critical crack initiation temperature of the rock mass The critical number of freeze-thaw cycles for rock mass fractures was determined by testing the critical point of freeze-thaw propagation. ; S4, the lowest daily surface temperature obtained based on S1. Daily temperature difference Fissure moisture conditions The critical crack initiation temperature of the rock mass obtained from S3 The effective freeze-thaw cycles are determined and counted to obtain the annual cumulative number of effective freeze-thaw cycles. Based on the aforementioned annual cumulative effective freeze-thaw cycles. and the critical number of freeze-thaw cycles Calculate the freeze-thaw damage ratio and quantify and classify the risk accordingly; The method for constructing the analytical model of crack frost heave force considering constraint pressure correction in S2 is as follows: Considering the volume expansion rate when water freezes Volume increase caused by water-ice phase transition The calculation formula is: ， in, The ice content is calculated using the following formula: ， Among them, unfrozen water content The empirical calculation formula is: ， in, This is the actual freezing temperature. For ambient temperature, and These are empirical constants related to lithology; To obtain the actual freezing temperature, pressure correction is applied. Relative to frost heave instantaneous rate of change Taking the reciprocal of the Clapeyron equation, its expression is: ， in, For latent heat of phase transition, For volume change, This is the freezing temperature of pure water under standard atmospheric pressure. Considering frost heave For actual freezing temperature Impact: ， in, This is the initial freezing temperature under standard atmospheric pressure; frost heave Under the influence of frost heave, based on the theory of elasticity, the volumetric deformation of cracks caused by frost heave... The calculation formula is: ， in, For rock shear modulus, , These are the rock elastic modulus and Poisson's ratio, which are related to temperature. Based on the principle of volume conservation, the volumetric deformation of cracks caused by frost heave. Equal to the volume and weight caused by the phase transition of water and ice Solve the volume conservation equations simultaneously And from the above calculation formulas, the frost heave force is obtained. With ambient temperature Functional relationship: ， Therefore, an analytical model of crack frost heave force considering constraint pressure correction was established: 。 2. The method according to claim 1, characterized in that, The specific steps of step S1 are as follows: (1) Collect the original image of the target area, extract the location, length, width, dip angle and spatial distribution characteristics of the cracks, and simplify the cracks in the rock mass into ideal elliptical cracks to obtain the geometric parameters of the rock mass cracks; (2) During a set time period, acquire thermal infrared images of the target area and record precise timestamps. The thermal infrared images carry brightness temperature data. The set time period is: 04:00 to 06:00 and 13:00 to 15:

00. Obtain the effective area in the target area that contains only bare rock pixels. Perform radiometric calibration and emissivity correction on the brightness temperature data carried by the thermal infrared images containing bare rock pixels to invert the surface temperature field. Take the surface temperature from 04:00 to 06:00 as the daily minimum surface temperature. The surface temperature from 13:00 to 15:00 As the highest surface temperature of the day Daily temperature difference ; (3) Obtain thermal infrared images of the target area for half an hour before and after 18:00, and extract low-temperature patches; install frequency domain / time domain reflectance moisture content sensors in layers at the center of the low-temperature patches and along their normal direction; set up control monitoring points in patches of the same lithology that exhibit dry characteristics; obtain the moisture content data of the low-temperature patches and dry characteristic patches to determine whether the low-temperature patches are high-moisture patches; use the moisture content data of the high-moisture patches collected by the moisture content sensors as the fracture moisture condition. .

3. The method according to claim 2, characterized in that: In S2, nuclear magnetic resonance (NMR) technology was used to measure the unfrozen water content of the target rock mass sample as a function of temperature. And using unfrozen water content The empirical calculation formulas are fitted to obtain empirical constants related to lithology. , The value of .

4. The method according to claim 3, characterized in that, Establish stress intensity factor in S2 With ambient temperature The specific method for quantitatively determining the relationship between them is as follows: Simultaneously formulate the expression for the stress intensity factor at the crack tip. Analytical model of frost heave force in cracks Establish stress intensity factor With ambient temperature Quantitative relationship between them: 。 5. The method according to claim 4, characterized in that, The method for calculating the Type I fracture toughness of rock mass in S3 is as follows: Identify the target rock mass type and take samples through on-site geological surveys and drilling; prefabricate standard fractures on the target rock mass samples; vacuum saturate the samples with water and freeze them in a -20℃ low-temperature chamber for 3-4 hours to simulate on-site low-temperature saturation conditions, obtaining prefabricated water-saturated rock samples; conduct three-point bending tests on the prefabricated water-saturated rock samples, collect load-crack tip strain curves and remove outliers, take the average of the effective maximum load, and calculate the Type I fracture toughness of the rock mass. : ， in, The effective maximum load is the average value; For span; The width of the sample; For sample height; geometric factor function The calculation formula is as follows: ， in, The length of the standard crack in the specimen.

6. The method according to claim 5, characterized in that, Determine the critical crack initiation temperature in S3. The method is as follows: Under critical conditions, the rock mass fissures are in a limit equilibrium state on the verge of cracking. ,at this time, To obtain information about the ambient temperature The equation: ， Solving this equation yields the unique unknown. The value is the critical crack initiation temperature. .

7. The method according to claim 6, characterized in that, The method for determining the critical number of freeze-thaw cycles in S3 is as follows: A pre-fabricated water-saturated rock sample is placed in a freeze-thaw cycle test chamber to simulate diurnal fluctuations in cold regions; the amount of fracture propagation is monitored using resistance strain gauges, and a fracture propagation-freeze-thaw cycle number curve is plotted; the position where the second derivative of the fracture propagation-freeze-thaw cycle number curve is zero is taken as the critical point for the freeze-thaw propagation of rock fractures, and the corresponding number of freeze-thaw cycles is taken as the critical number of freeze-thaw cycles. .

8. The method according to claim 7, characterized in that: In step S4, the annual cumulative effective freeze-thaw cycle count is obtained. The method is as follows: A valid freeze-thaw cycle is counted if all of the following conditions are met: Lowest surface temperature of the day Rock mass crack initiation temperature ; Daily temperature difference ≥5℃; Fissure Moisture Conditions ≥50%; Based on the above conditions, obtain the annual cumulative effective freeze-thaw cycle count at the site. ; The freeze-thaw damage ratio The calculation formula is: 。 9. The method according to claim 8, characterized in that, In step S4: A value ≥0.8 indicates extremely high risk; 0.5≤ <0.8 indicates high risk; 0.2≤ A value less than 0.5 indicates a medium risk. A value less than 0.2 indicates low risk.

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