Method for calculating and evaluating stability of engineering slope containing karst structure

Abstract

The invention belongs to the technical field of slope stability calculation, and particularly provides a method for calculating and evaluating the stability of an engineering slope containing a karst structure. Comprising the following steps: finding out geological conditions of a side slope and a karst structure by adopting a field investigation method, finding out the unloading relaxation depth of the excavated side slope above the elevation of the karst structure by adopting a drilling test method, and representing the excavation unloading relaxation depth of the karst structure and the rock side slope by adopting computational analysis based on a damage concept. The local stability degree of the side slope affected by the karst structure is quantitatively evaluated by adopting the relaxation depth of rock masses around the karst and side slope excavation face and the strength-stress ratio of unrelaxed rock masses, and the overall stability degree of the side slope is obtained by adopting a strength reduction method. Through the method, on the basis of obtaining the quantitative evaluation result of the overall stability of the slope, the quantitative evaluation of the karst structure on the local stability of the slope can be further obtained, so that calculation analysis, stability evaluation and support measure design of the karst-containing engineering slope are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of slope stability calculation, and in particular relates to a method for calculating and evaluating the stability of an engineering slope containing a karst structure. Background Art

[0002] The stability evaluation of the slope containing adverse geological structures, especially karst structures, is not only not involved in the current specifications, but also rarely analyzed in the research. Karst structures are located in strata such as limestone, and are generally filled with blocks, gravel, clay or sand and gravel. The overall strength is low. When used as a resistance body and a force transmission body, it may face the problem of insufficient bearing capacity and inability to effectively transmit the arch dam body load. In actual engineering, the treatment of karst structures is generally to excavate the fillings and then backfill. Therefore, affected by the karst structure, the mechanical response and unloading characteristics of the dam shoulder slope during the excavation process will significantly affect the local stability of the slope at a relatively close distance. When the slope contains a karst structure close to the slope surface, the stability evolution caused by the excavation of the dam shoulder groove slope containing the adverse karst geological structure is affected by the superposition of the karst excavation effect, which is not conducive to the local stability of the slope. For engineering slopes containing karst, although the existing methods can still be used to analyze the overall stability of the slope, there are few targeted methods for the calculation, analysis and evaluation of the influence of karst structure on the local stability of the slope. The present invention proposes a calculation and evaluation method for the stability of engineering slopes containing karst structure. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for calculating and evaluating the stability of an engineering slope containing a karst structure, so as to realize calculation analysis and stability evaluation of an engineering slope containing a karst structure.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for calculating and evaluating the stability of an engineering slope containing a karst structure, comprising the following steps: Step 1: Identify the karst structure distribution and engineering geological conditions of the slope through exploration; Step 2: Drill holes in the excavated slope area above the identified karst structure elevation, and use geophysical acoustic wave testing methods to obtain the variation law of the longitudinal wave velocity of the slope rock mass at different depths from the excavation surface, that is, to obtain the curve of rock mass acoustic wave velocity and drilling depth; Step 3: Based on the obtained rock mass acoustic wave velocity and borehole depth curve, the range corresponding to the velocity value significantly lower than the deep rock mass velocity value is divided into the rock mass relaxation zone, and the rock mass relaxation depth test value is obtained. L M ; Step 4: Based on the identified karst structure and engineering geological conditions of the slope, a numerical analysis model of the slope containing the karst structure is established, and the initial mechanical parameters of the numerical analysis model of the slope are determined based on the engineering geological survey data; Step 5: Introduce damage coefficient for mechanical parameters D , numerical analysis model of slope with mechanical parameters, damage coefficient D and material constants R related; Step 6: Derive the damage coefficient that can be used to determine whether the rock mass has entered the unloading relaxation state D The threshold value of Step 7: According to the damage coefficient D The threshold value is used to determine the calculated rock relaxation zone depth and extract the calculated rock relaxation depth value corresponding to the on-site drilling acoustic wave test site. L C , the rock relaxation depth test value L M Calculated value of rock relaxation depth L C Make a comparison; based on the comparison results, adjust the material constants in step 5 R , recalculate the damage coefficient D , and then recalculate the rock relaxation depth calculation value L C , until the rock relaxation depth test value L M Equal to the calculated value of rock relaxation depth L C Stop and obtain the material constant value for verifying the current formation characteristics, recorded as R OK ; Step 8: Obtain one of the quantitative evaluation indicators for quantitatively evaluating the impact of karst structure on local slope stability F 1; Step 9: Quantitative evaluation indicators obtained according to step 8 F 1. Determine whether the rock mass between the karst structure and the slope is penetrated by the relaxation zone. If the rock mass between the karst structure and the slope is penetrated by the relaxation zone, adopt a response strategy and recalculate the quantitative evaluation index. F 1; For the area that is not penetrated by the relaxation zone, calculate the strength stress ratio of the rock mass in the relaxation zone. S , as another quantitative evaluation index to quantify the impact of karst structure on local slope stability; Step 10: Based on quantitative evaluation indicators F 1 and S , determine the impact of karst structure on local slope stability and adopt different coping strategies; Step 11: Use the strength reduction method to obtain the overall safety factor of the slope containing karst structures F 2, according to the safety factor [ Fos ]Evaluate the overall stability of the slope. F2<[ Fos ], indicating that the overall stability of the slope does not meet the requirements, then after targeted reinforcement according to the instability mode, repeat steps 8 to 11 until F 2≥[ Fos ].

[0005] In a preferred embodiment, in step 2, the drilling depth is not less than 20 m.

[0006] In the preferred embodiment, in step 4, the initial mechanical parameters of the slope numerical analysis model include deformation modulus E 0. Cohesion c 0. Internal friction angle f 0.

[0007] In the preferred embodiment, in step 5, the damage coefficient D The calculation formula is: (1); Where: D is the damage coefficient of the slope rock mass, D The smaller the value, the smaller the unloading damage of the rock mass; is the equivalent plastic strain; R is the material constant.

[0008] In a preferred solution, in step 5, the calculation formula of the slope numerical analysis model of mechanical parameters is as follows: (2); (3); Where: E 1 is the deformation modulus considering the effect of unloading damage; c 1 and f 1 is the cohesion and internal friction angle of the layer considering the influence of unloading damage.

[0009] In the preferred embodiment, in step 6, the damage coefficient D The derivation process of the threshold is as follows: The longitudinal wave velocities of the rock mass before and after slope excavation correspond to the longitudinal wave velocities of the rock mass outside and within the relaxation range measured in step 3, respectively. C p0 and C p1 , according to elastic wave theory, the calculation formula is: (4); (5); Where: C p0 is the longitudinal wave velocity of the rock mass before slope excavation, Cp1 is the longitudinal wave velocity of the rock mass after slope excavation; The relationship between the change in the longitudinal wave velocity of the surrounding rock before and after excavation unloading and the deformation modulus and density is expressed as follows: (6); According to formula (1), we can get: (7); Since the excavation unloading effect has little effect on the density of the rock mass, r 1≈ r 2, then formula (6) can be further simplified as: (8); The 10% drop in wave velocity is taken as the basis for rock mass relaxation, that is: C p1 ≤0.9 C p0 (9); When the wave velocity of the slope rock mass satisfies the condition of formula (9), it is considered that the rock mass at this location is relaxed. Then, by substituting formula (9) into formula (8), the range of the damage coefficient for rock mass relaxation is obtained, which is D ≥ 0.19.

[0010] In the preferred embodiment, in step 7, the material constants in step 5 are adjusted according to the comparison results. R The adjustment rule for the value of is as follows: when the rock relaxation depth test value L M Greater than the calculated rock relaxation depth L C When the material constant is reduced R value, recalculate; when the rock relaxation depth test value L M Less than the calculated rock relaxation depth L C When the material constant is increased R value, recalculate until the rock relaxation depth test value L M Equal to the calculated value of rock relaxation depth L C stop.

[0011] In the preferred embodiment, in step 8, the quantitative evaluation index F The calculation formula for 1 is: (10); Where: P S and P K are the relaxation depths of slope and karst, respectively. PIt is the shortest distance from the karst structure wall to the excavation slope surface.

[0012] In the preferred embodiment, in step 9, the strength stress ratio S The calculation formula is: S = F 1 K v R b / s m (11); Where: K v is the slope rock mass integrity coefficient of the area, s m is the maximum compressive stress in the unrelaxed rock mass area between the karst structure and the slope, R b is the uniaxial compressive strength of rock.

[0013] In a preferred embodiment, step 8 further includes obtaining a qualitative index: the material constant value of the current formation characteristic obtained in step 7 is converted into R OK Substitute the mechanical parameters into the slope numerical analysis model, and perform calculations and analysis based on the karst structure and the slope excavation and support scheme; then, when the slope excavation is completed, cut the section of the karst structure closest to the slope surface, and first measure the shortest distance from the karst structure wall to the excavated slope surface in the slope numerical analysis model. P , and then, within the section, the distribution range of the plastic zones of the slope and karst is determined based on the calculation and analysis results, and it is judged whether the rock mass between the karst and the slope is penetrated by the plastic zone, which serves as a qualitative indicator for evaluating the impact of the karst structure on the local stability of the slope.

[0014] The present invention provides a method for calculating and evaluating the stability of an engineering slope containing a karst structure, which has the following beneficial effects: 1. In the past, slope stability evaluation mainly used the plastic zone index to evaluate the range of unloading disturbance of slope excavation, and the safety factor method to evaluate the overall stability of the slope. There is no calculation analysis and stability analysis method for the presence of karst structure in the slope.

[0015] The present invention proposes an evaluation method for the influence of karst structure on the local stability of slope, including using the relaxation depth of rock mass around karst and slope excavation surface and the strength stress ratio of unrelaxed rock mass to quantitatively evaluate the local stability of slope affected by karst structure.

[0016] 2. In terms of evaluation indicators, for rock excavation projects that are close to each other, the degree of mutual influence is generally determined by whether the plastic zone penetrates the rock mass between adjacent excavated buildings. For example: for underground cavern projects, if the rock pillars between caverns that are close to each other are penetrated by the plastic zone after excavation, it is considered that the stability of the rock pillars is significantly affected, and it is necessary to consider adjusting the design plan or adding support measures. Although the plastic zone indicator can quantify the disturbance of excavation unloading on the rock mass to a certain extent, it actually exaggerates the impact of excavation unloading. This is because after the rock mass enters the plastic state, it still has a certain bearing capacity. Using the plastic zone penetrating the rock pillar as a standard for affecting the local stability of the rock mass is too strict and underestimates the bearing capacity of the rock mass after entering the plastic state.

[0017] Therefore, the present invention adopts the rock mass unloading relaxation zone to evaluate the influence of excavation unloading on the rock mass, takes the unloading relaxation of the rock mass as the basis for the rock mass being unable to continue to bear the load, and takes whether the unloading relaxation zone is connected as the indicator for judging the local stability of the slope, which is more in line with the mechanical properties of the rock mass after excavation unloading.

[0018] 3. Based on the use of unloading relaxation zone as an indicator, the quantitative index of the influence of karst structure on local slope stability is further defined. F 1. When F When 1=1, the rock mass between the karst structure and the slope surface is penetrated by the relaxation zone. It can be seen that the karst structure has a significant impact on the local stability of the slope, and additional cross-link anchor cables or anchor rod support measures should be added; when F When 1>1, it can be seen that the rock mass between the karst structure and the slope surface is not penetrated by the relaxation zone, and F The larger the value of 1, the smaller the impact of karst structure on the local stability of the slope.

[0019] 4. In order to further analyze the stability of the rock mass that is not penetrated by the unloading relaxation zone, the rock strength stress ratio of the unpenetrated area is used to determine the degree of influence of the karst structure on the local stability of the slope. This index is calculated using the uniaxial compressive strength of the rock, the rock integrity coefficient, and the maximum compressive stress of the part. First, the uniaxial compressive strength index of the rock just reflects the actual state of the rock mass under the unloading relaxation conditions on both sides, and the stress state gradually tends from triaxial to uniaxial; secondly, the rock integrity coefficient characterizes the degree to which the rock mass in this part is affected by the rock structure; finally, the maximum compressive stress data of this part characterizes the stress state of the regional rock mass. Then, the existing specifications for the classification standard of rock stress-type failure can be used to quantitatively analyze the stability of the rock column that is not penetrated by the relaxation zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 is a flow chart of the present invention; Figure 2 It is the relationship curve between the acoustic wave velocity of rock mass and the drilling depth; Figure 3 It is a schematic diagram when the slope is not penetrated by the relaxation zone. DETAILED DESCRIPTION

[0021] A method for calculating and evaluating the stability of an engineering slope containing a karst structure specifically includes using a field survey method to ascertain the geological conditions of the slope and the karst structure, using a drilling test method to ascertain the unloading relaxation depth of the excavated slope above the karst structure elevation, using a damage concept-based calculation and analysis to characterize the unloading relaxation depth of the karst structure and the rock slope excavation, using the relaxation depth of the rock mass around the karst and slope excavation surface and the strength-stress ratio of the unrelaxed rock mass to quantitatively evaluate the local stability of the slope affected by the karst structure, and using a strength reduction method to obtain the overall stability of the slope. Through the above analysis, on the basis of obtaining the quantitative evaluation results of the overall stability of the slope, a quantitative evaluation of the karst structure on the local stability of the slope can be further obtained, thereby realizing the calculation and analysis of the engineering slope containing karst, stability evaluation and support measures design.

[0022] like Figure 1 As shown, the specific steps include: Step 1: Use drilling and other exploration methods to identify the distribution of karst structures in the slope and the engineering geological conditions of the slope. For karst structures, further identify their boundaries, scale, and filling materials.

[0023] Step 2: Drill holes in the excavated slope area above the identified karst structure elevation. The drilling depth is not less than 20m. Use the geophysical acoustic wave test method to obtain the variation law of the longitudinal wave velocity of the slope rock mass at different depths from the excavation surface, that is, to obtain the rock mass acoustic wave velocity V p With drilling depth L The relationship curve, such as Figure 2 shown.

[0024] The geophysical acoustic wave testing method is a common geophysical testing method. First, a hole is drilled in the rock mass, and then the acoustic wave probe is placed in the hole to test the wave velocity of the corresponding part, and then the variation law of the longitudinal wave velocity at different depths from the excavation surface is obtained.

[0025] Step 3: Based on the obtained rock mass acoustic wave velocity and borehole depth curve, the range corresponding to the velocity value significantly lower than the deep rock mass velocity value is divided into the rock mass relaxation zone, and the rock mass relaxation depth test value is obtained. L M .

[0026] Step 4: According to the identified karst structure and engineering geological conditions of the slope, a numerical analysis model of the slope containing karst structure is established, and the initial mechanical parameters of the slope numerical analysis model are determined based on the engineering geological survey data.

[0027] The slope numerical analysis model is a finite element mesh model that reflects the actual spatial position relationship between the karst structure and the excavated slope. The initial mechanical parameters of the slope numerical analysis model include the deformation modulus E 0. Cohesion c 0. Internal friction angle f 0.

[0028] Step 5: Deformation modulus of slope rock mass E 0. Cohesion c 0 and internal friction angle f 0, introduce damage coefficient D , to consider the damage and degradation effect of excavation unloading on karst structure and slope rock mass, and obtain the slope numerical analysis model of mechanical parameters, damage coefficient D and material constants R related, Damage coefficient D The calculation formula is: (1); Where: D is the damage coefficient of the slope rock mass, D The smaller the value, the smaller the unloading damage of the rock mass; is the equivalent plastic strain; R is a material constant. In this embodiment, the initial value is selected as 10.0.

[0029] The calculation formula of the slope numerical analysis model of mechanical parameters is as follows: (2); (3); Where: E 1 is the deformation modulus considering the effect of unloading damage; c 1 and f 1 is the cohesion and internal friction angle of the layer considering the influence of unloading damage.

[0030] Step 6: Derive the damage coefficient that can be used to determine whether the rock mass has entered the unloading relaxation state D The threshold value.

[0031] Damage coefficient D The derivation process of the threshold is as follows: The longitudinal wave velocities of the rock mass before and after slope excavation correspond to the longitudinal wave velocities of the rock mass outside and within the relaxation range measured in step 3, respectively. Cp0 and C p1 , according to elastic wave theory, the calculation formula is: (4); (5); Where: C p0 is the longitudinal wave velocity of the rock mass before slope excavation, C p1 It is the longitudinal wave velocity of the rock mass after slope excavation.

[0032] Poisson's ratio of rock mass due to excavation unloading m The influence of is small, so only the influence on the elastic modulus and density of the rock mass is considered. From equations (4) and (5), the relationship between the change of the longitudinal wave velocity of the surrounding rock before and after excavation unloading and the deformation modulus and density can be obtained as follows: (6); According to formula (1), we can get: (7); Since the excavation unloading effect has little effect on the density of the rock mass, r 1≈ r 2, then formula (6) can be further simplified as: (8); The 10% drop in wave velocity is taken as the basis for rock mass relaxation, that is: C p1 ≤0.9 C p0 (9); When the wave velocity of the slope rock mass satisfies the condition of formula (9), it is considered that the rock mass at this location is relaxed. Then, by substituting formula (9) into formula (8), the range of the damage coefficient for rock mass relaxation is obtained, which is D ≥ 0.19.

[0033] Step 7: According to D ≥0.19 standard, determine the calculated rock relaxation zone depth, and extract the calculated rock relaxation depth value corresponding to the on-site drilling sonic test site L C , the rock relaxation depth test value L M Calculated value of rock relaxation depth L C Make a comparison; based on the comparison results, adjust the material constants in step 5 R , recalculate the damage coefficient D , and then recalculate the rock relaxation depth calculation value L C, until the rock relaxation depth test value L M Equal to the calculated value of rock relaxation depth L C Stop and obtain the material constant value for verifying the current formation characteristics, recorded as R OK .

[0034] According to the comparison results, adjust the material constants in step 5 R The adjustment rule for the value of is as follows: when the rock relaxation depth test value L M Greater than the calculated rock relaxation depth L C When the material constant is reduced R value, recalculate; when the rock relaxation depth test value L M Less than the calculated rock relaxation depth L C When the material constant is increased R value, recalculate until the rock relaxation depth test value L M Equal to the calculated value of rock relaxation depth L C stop.

[0035] The above steps 1 to 7 realize the calibration of model parameters.

[0036] Step 8: Obtain one of the quantitative evaluation indicators for quantitatively evaluating the impact of karst structure on local slope stability F 1.

[0037] The material constant values ​​of the current formation properties obtained in step 7 are R OK Substitute the mechanical parameters into the slope numerical analysis model, and perform calculations and analysis based on the karst structure and the slope excavation and support scheme; then, when the slope excavation is completed, cut the section of the karst structure closest to the slope surface, and first measure the shortest distance from the karst structure wall to the excavated slope surface in the slope numerical analysis model. P , and then, within the section, the distribution range of the plastic zones of the slope and karst is determined based on the calculation and analysis results, and it is judged whether the rock mass between the karst and the slope is penetrated by the plastic zone, which serves as a qualitative indicator for evaluating the impact of the karst structure on the local stability of the slope.

[0038] use D ≥0.19, the relaxation depth of slope and karst is determined and recorded as P S and P K , when the relaxation range of slope and karst is connected, takeP S + P K = P .

[0039] Quantitative evaluation indicators F The calculation formula for 1 is: (10); Where: P S and P K are the relaxation depths of slope and karst, respectively. P It is the shortest distance from the karst structure wall to the excavation slope surface.

[0040] Step 9: Quantitative evaluation indicators obtained according to step 8 F 1. Determine whether the rock mass between the karst structure and the slope is penetrated by the relaxation zone. If the rock mass between the karst structure and the slope is penetrated by the relaxation zone, take countermeasures, such as adding cross-penetrating anchor cables or anchor rods, and then recalculate the quantitative evaluation index. F 1.

[0041] For the area not penetrated by the relaxation zone, that is, F 1>1, such as Figure 3 As shown, the strength stress ratio of the rock mass in the unrelaxed zone is calculated S , as another quantitative evaluation index for quantitatively evaluating the impact of karst structure on local stability of slope.

[0042] Strength stress ratio S The calculation formula is: S = F 1 K v R b / s m (11); Where: K v is the slope rock mass integrity coefficient of the area, which is taken according to Table 1; s m is the maximum compressive stress in the unrelaxed rock mass area between the karst structure and the slope; R b is the uniaxial compressive strength of rock.

[0043]

[0044] Defined quantitative indicators of the impact of karst structure on local slope stability F 1, the shortest distance from the karst structure wall to the excavation slope surfaceP Depth of relaxation with slope and karst P S + P K When F When 1=1, the rock mass between the karst structure and the slope surface is penetrated by the relaxation zone. It can be seen that the karst structure has a significant impact on the local stability of the slope, and additional cross-link anchor cables or anchor rod support measures should be added; when F When 1>1, it can be seen that the rock mass between the karst structure and the slope surface is not penetrated by the relaxation zone, and F The larger the value of 1, the smaller the impact of karst structure on the local stability of the slope.

[0045] Step 10: Based on quantitative evaluation indicators F 1 and S , determine the impact of karst structure on local slope stability, and adopt different coping strategies, as shown in Table 2.

[0046]

[0047] The rock strength-stress ratio of the unpenetrated area is used to determine the degree of influence of the karst structure on the local stability of the slope. This index is calculated using the uniaxial compressive strength of the rock, the rock integrity coefficient, and the maximum compressive stress of the site. First, the uniaxial compressive strength index of the rock just reflects the actual state of the rock mass under the conditions of unloading and relaxation on both sides, and the stress state gradually tends from triaxial to uniaxial; secondly, the rock integrity coefficient characterizes the degree to which the rock mass in this area is affected by the rock structure; finally, the maximum compressive stress data of this site characterizes the stress state of the regional rock mass. In addition, the existing specifications for the classification standard of rock stress-type failure can be used to quantitatively analyze the stability of the rock column that is not penetrated by the relaxation zone, as shown in Table 3.

[0048]

[0049] In the above steps 8 to 10, numerical analysis is used to determine the effect of karst structure on the local stability of the slope.

[0050] Step 11: Use the strength reduction method to obtain the overall safety factor of the slope containing karst structures F 2. Obtain the failure mode of the slope, and according to the safety factor specified in Table 4.0.5 of the "Specification for Slope Design of Hydropower Engineering NBT10512" [ Fos ] to evaluate the overall stability of the slope. F 2<[ Fos ], indicating that the overall stability of the slope does not meet the requirements, then after targeted reinforcement according to the instability mode, repeat steps 8 to 11 until F 2≥[ Fos ].

[0051] The basic principle of the strength reduction method is to reduce the shear strength parameters (cohesion and internal friction angle) of the rock mass at a certain ratio until the slope reaches a critical failure state. In this process, the reduction factor is the safety factor of the slope. The formula is: c m = c / F 2; f m =arctan(tan f / F 2), where c m and f m is the reduced cohesion and internal friction angle, F 2 is the reduction factor (also known as the safety factor), c and f It is the original shear strength parameter of the rock mass. When the reduction coefficient is small, the calculation is easy to converge. As the reduction coefficient increases, when the slope approaches or reaches the limit equilibrium state, the calculated slope deformation gradually increases and develops towards a non-convergent trend. The reduction coefficient corresponding to the sudden change in slope deformation is recorded as the overall safety factor. F 2.

[0052] Step 11, evaluate the overall stability of the slope through numerical analysis.

[0053] The present invention studies the distribution of geological conditions of slopes and karst structures, obtains the unloading relaxation depth of excavated slopes above the elevation of karst structures, characterizes the unloading relaxation depth of karst combination and rock slope excavation, quantitatively evaluates the influence of karst on the local stability of slopes, and quantitatively evaluates the overall stability of slopes, and finally realizes the calculation analysis and stability evaluation of engineering slopes containing karst structures.

[0054] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for calculating and evaluating the stability of an engineering slope containing a karst structure, characterized in that: The following steps are involved: Step 1: Identify the karst structure distribution and engineering geological conditions of the slope through exploration; Step 2: Drill holes in the excavated slope area above the identified karst structure elevation, and use geophysical acoustic wave testing methods to obtain the variation law of the longitudinal wave velocity of the slope rock mass at different depths from the excavation surface, that is, to obtain the curve of rock mass acoustic wave velocity and drilling depth; Step 3: Based on the obtained rock mass acoustic wave velocity and borehole depth curve, the range corresponding to the velocity value significantly lower than the deep rock mass velocity value is divided into the rock mass relaxation zone, and the rock mass relaxation depth test value is obtained. L M ; Step 4: Based on the identified karst structure and engineering geological conditions of the slope, a numerical analysis model of the slope containing the karst structure is established, and the initial mechanical parameters of the numerical analysis model of the slope are determined based on the engineering geological survey data; Step 5: Introduce damage coefficient for mechanical parameters D , numerical analysis model of slope with mechanical parameters, damage coefficient D and material constants R related; Step 6: Derive the damage coefficient that can be used to determine whether the rock mass has entered the unloading relaxation state D The threshold value of Step 7: According to the damage coefficient D The threshold value is used to determine the calculated rock relaxation zone depth and extract the calculated rock relaxation depth value corresponding to the on-site drilling acoustic wave test site. L C , the rock relaxation depth test value L M Calculated value of rock relaxation depth L C Make a comparison; based on the comparison results, adjust the material constants in step 5 R , recalculate the damage coefficient D , and then recalculate the rock relaxation depth calculation value L C , until the rock relaxation depth test value L M Equal to the calculated value of rock relaxation depth L C Stop and obtain the material constant value for verifying the current formation characteristics, recorded as R OK ; Step 8: Obtain one of the quantitative evaluation indicators for quantitatively evaluating the impact of karst structure on local slope stability F 1; Step 9: Quantitative evaluation indicators obtained according to step 8 F 1. Determine whether the rock mass between the karst structure and the slope is penetrated by the relaxation zone. If the rock mass between the karst structure and the slope is penetrated by the relaxation zone, adopt a response strategy and recalculate the quantitative evaluation index. F 1; For the area that is not penetrated by the relaxation zone, calculate the strength stress ratio of the rock mass in the relaxation zone. S , as another quantitative evaluation index to quantify the impact of karst structure on local slope stability; Step 10: Based on quantitative evaluation indicators F 1 and S , determine the impact of karst structure on local slope stability and adopt different coping strategies; Step 11: Use the strength reduction method to obtain the overall safety factor of the slope containing karst structures F 2, according to the safety factor [ Fos ]Evaluate the overall stability of the slope. F 2<[ Fos ], indicating that the overall stability of the slope does not meet the requirements, then after targeted reinforcement according to the instability mode, repeat steps 8 to 11 until F 2≥[ Fos ].

2. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 1, characterized in that: In step 2, the drilling depth is not less than 20m.

3. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 1, characterized in that: In step 4, the initial mechanical parameters of the slope numerical analysis model include deformation modulus E 0. Cohesion c 0. Internal friction angle φ 0.

4. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 1 or 3, characterized in that: In step 5, the damage coefficient D The calculation formula is: （1）； Where: D is the damage coefficient of the slope rock mass, D The smaller the value, the smaller the unloading damage of the rock mass; is the equivalent plastic strain; R is the material constant.

5. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 3 is characterized in that: In step 5, the calculation formula of the slope numerical analysis model of mechanical parameters is as follows: （2）； （3）； Where: E 1 is the deformation modulus considering the effect of unloading damage; c 1 and φ 1 is the cohesion and internal friction angle of the layer considering the influence of unloading damage.

6. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 4, characterized in that: In step 6, the damage coefficient D The derivation process of the threshold is as follows: The longitudinal wave velocities of the rock mass before and after slope excavation correspond to the longitudinal wave velocities of the rock mass outside and within the relaxation range measured in step 3, respectively. C p0 and C p1 , according to elastic wave theory, the calculation formula is: （4）； （5）； Where: C p0 is the longitudinal wave velocity of the rock mass before slope excavation, C p1 is the longitudinal wave velocity of the rock mass after slope excavation; The relationship between the change in the longitudinal wave velocity of the surrounding rock before and after excavation unloading and the deformation modulus and density is expressed as follows: （6）； According to formula (1), we can get: （7）； Since the excavation unloading effect has little effect on the density of the rock mass, ρ 1≈ ρ 2, then formula (6) can be further simplified as: （8）； The 10% drop in wave velocity is taken as the basis for rock mass relaxation, that is: C p1 ≤0.9 C p0 （9）； When the wave velocity of the slope rock mass satisfies the condition of formula (9), it is considered that the rock mass at this location is relaxed. Then, by substituting formula (9) into formula (8), the range of the damage coefficient for rock mass relaxation is obtained, which is D ≥ 0.

19.

7. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 1, characterized in that: In step 7, the material constants in step 5 are adjusted according to the comparison results. R The adjustment rule for the value of is as follows: when the rock relaxation depth test value L M Greater than the calculated rock relaxation depth L C When the material constant is reduced R value, recalculate; when the rock relaxation depth test value L M Less than the calculated rock relaxation depth L C When the material constant is increased R value, recalculate until the rock relaxation depth test value L M Equal to the calculated value of rock relaxation depth L C stop.

8. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 1, characterized in that: In step 8, the quantitative evaluation index F The calculation formula for 1 is: （10）； Where: P S and P K are the relaxation depths of slope and karst, respectively. P It is the shortest distance from the karst structure wall to the excavation slope surface.

9. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 1, characterized in that: In step 9, the strength stress ratio S The calculation formula is: S = F 1 K v R b / σ m （11）； Where: K v is the slope rock mass integrity coefficient of the area, σ m is the maximum compressive stress in the unrelaxed rock mass area between the karst structure and the slope, R b is the uniaxial compressive strength of rock.

10. The method for calculating and evaluating the stability of an engineering slope containing a karst structure according to claim 5, characterized in that: The step 8 also includes obtaining a qualitative index: the material constant value of the current formation characteristic obtained in step 7 is converted into R OK Substitute the mechanical parameters into the slope numerical analysis model, and perform calculations and analysis based on the karst structure and the slope excavation and support scheme; then, when the slope excavation is completed, cut the section of the karst structure closest to the slope surface, and first measure the shortest distance from the karst structure wall to the excavated slope surface in the slope numerical analysis model. P , and then, within the section, the distribution range of the plastic zones of the slope and karst is determined based on the calculation and analysis results, and it is judged whether the rock mass between the karst and the slope is penetrated by the plastic zone, which serves as a qualitative indicator for evaluating the impact of the karst structure on the local stability of the slope.

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