Failure mode of steep thin slope and anchor length determination method and system

Abstract

The present invention provides a method and system for determining the failure mode and anchoring length of a steeply inclined thin-layer slope. A drilling experiment is carried out in the area where the slope to be supported has been partially excavated to obtain the measured value L of the rock mass relaxation depth M , the average longitudinal wave velocity C of the rock mass within the relaxation range p1 , the average longitudinal wave velocity C of the rock mass outside the range p0 and the bedding thickness δ of the thin-layer rock mass of the slope; a jointed model covering the slope to be supported is established; based on the material constant R, the average longitudinal wave velocity C of the rock mass within the relaxation range p1 , the average longitudinal wave velocity C of the rock mass outside the range p0 and the bedding thickness δ of the thin-layer rock mass of the slope, a damage coefficient D is constructed, and the threshold range of the damage coefficient D is confirmed: based on the measured value L of the rock mass relaxation depth M and the damage coefficient D, the deformation modulus E0, the bedding cohesion c L0 and the bedding internal friction angle φ L0 of the jointed model covering the slope are corrected; the corrected jointed model covering the slope is used to calculate the relaxation depth to determine the failure mode and anchoring length of different anchoring points.

Description

Technical Field

[0001] The invention relates to the technical field of rock mass construction, and in particular to a method and system for determining a failure mode and anchoring length of a steep thin-layer slope. Background Art

[0002] The construction of water conservancy and hydropower projects requires the excavation of a large number of rock slopes. For hydropower projects located in high mountain canyon areas, the geological conditions of the engineering area where the slopes of the hub area are located are complex, the rock formations are variable, and the rock formations are of varying thickness. Thin-layered steep slopes have the characteristics of thin layers, large rock formation dips, and easy deformation and relaxation after excavation unloading. Specifically, according to the relationship between the angle between the rock formation and the slope direction, they can be divided into forward slopes, oblique slopes, and transverse slopes. For forward slopes, thin-layered steep slopes are prone to layer shear slip instability. When the excavation slope angle is greater than the rock formation dip, it is also prone to angle shear failure, resulting in rock mass cracking and then slipping; for reverse slopes, thin-layered steep slopes are prone to layer normal cracking, resulting in rock mass bending and tipping failure; for oblique slopes, it is prone to compound instability failure that couples the above two slope types. For the anchor support design of steep thin slopes, the empirical analogy method or the specification recommendations are currently used to determine the type of anchor support and the length of support measures based on the rock failure mode, which lacks quantitative basis.

[0003] In recent years, the stability analysis of slope rock mass based on numerical analysis has played an increasingly significant role in slope support design. By setting a suitable slope constitutive model and inputting the corresponding rock mass mechanical parameters, the slope deformation field, stress field and rock mass plastic zone distribution under excavation unloading can be obtained. According to the numerical calculation results, the currently commonly used anchor support design practice generally believes that the anchor support length is selected to exceed the plastic zone range of the slope, that is, the far end of the anchor support should generally reach the elastic zone of the slope rock mass. The above idea of ​​determining the length of the slope anchor support is based on the quantitative results of the numerical analysis of the slope excavation unloading process, which can certainly play a role in targeted reinforcement of the slope and effectively improve the stability of the slope.

[0004] However, the rock mass on the slope surface is generally subjected to significant natural weathering, and the original mechanical parameters of the rock mass are not high. Under the action of excavation unloading, the stress disturbance range may be large, resulting in the calculated plastic zone depth being too large. If the anchor support length should be greater than the plastic zone depth, the slope anchor support design will not be implemented. At the same time, it is noted that steep thin-layer slopes have significantly different deformation and failure modes and different failure ranges in different slope sections (i.e., forward slope, reverse slope, transverse slope, etc.). There is currently a lack of effective methods for effectively judging the slope failure mode and reflecting the impact of these factors on the slope anchor support design. It can be seen that there is an urgent need for a method to judge the failure mode of thin steep rock layer slopes and calculate the anchor support length. Summary of the invention

[0005] The present invention proposes a failure mode of a steep thin-layer slope and a method for determining the anchoring length to solve the technical problems that the plastic zone depth obtained by the existing quantitative calculation method is too large, resulting in inaccurate anchoring support design and difficulty in construction, and the slope failure mode cannot be effectively determined.

[0006] In order to solve the above technical problems, the present invention provides a method for determining the anchor support length of a steep thin slope, comprising the following steps:

[0007] Step S1: Conduct a drilling experiment in the area where the slope to be supported has been partially excavated to obtain the rock relaxation depth test value L M , the mean longitudinal wave velocity of the rock mass within the relaxation range C p1 , the average longitudinal wave velocity of the rock mass outside the range C p0 and the thickness of the thin-bedded rock mass on the slope, δ;

[0008] Step S2: establishing a diffuse joint model for the slope to be supported;

[0009] Step S3: Based on the material constant R and the mean longitudinal wave velocity C of the rock mass within the relaxation range p1 , the average longitudinal wave velocity of the rock mass outside the range C p0 and the thickness δ of the thin-layered rock mass of the slope, construct a damage coefficient D, and confirm the threshold range of the damage coefficient D;

[0010] Step S4: Based on the rock relaxation depth test value L M and the damage coefficient D have an influence on the deformation modulus E0, the cohesion c L0 and the internal friction angle φ L0 make corrections;

[0011] Step S5: Calculate the relaxation depth using the modified diffuse joint model to determine the anchor support lengths of different anchor points.

[0012] Preferably, step S1 comprises: in an area where a steep thin-layer slope has been partially excavated, selecting the highest level of horse trail, arranging a geological drill, drilling toward the inside of the slope, and after the drilling is completed, using a geophysical acoustic wave testing method to obtain the variation law of the longitudinal wave velocity of the slope rock mass at different depths from the excavation surface; according to the rock mass acoustic wave velocity and drilling depth curve obtained by drilling, the range corresponding to the wave velocity value lower than the deep rock mass wave velocity value threshold is divided into a rock mass relaxation zone, and the rock mass relaxation depth of the test site is recorded as L M ; According to the distribution of rock mass longitudinal wave velocity along the borehole depth obtained by the test, the mean values ​​of rock mass longitudinal wave velocity within and outside the relaxation range are calculated, which are recorded as C p1 and C p0; Based on the drill core, the thickness δ of the thin-layered rock mass on the slope of this part is obtained.

[0013] Preferably, the borehole has a diameter of not less than 90 mm and a depth of not less than 20 m.

[0014] Preferably, the expression of the damage coefficient D in step S3 is:

[0015]

[0016] In the formula, ε p represents the equivalent plastic strain, and R represents the material constant.

[0017] Preferably, the method for confirming the threshold range of the damage coefficient D in step S3 includes:

[0018] Step S31: According to elastic wave theory, determine the mean value C of the longitudinal wave velocity of the rock mass within the relaxation range. p1 and the mean longitudinal wave velocity of the rock mass outside the range C p0 Theoretical formula of

[0019] Step S32: Based on the theoretical formula, obtain the mean value of the rock mass longitudinal wave velocity C p1 and the mean longitudinal wave velocity of the rock mass outside the range C p0 The ratio formula of

[0020] Step S33: transforming the ratio formula to obtain a relationship between the damage coefficient D and the ratio formula;

[0021] Step S34: Based on the rock relaxation theory, the range of the ratio formula is obtained to obtain the threshold range of the damage coefficient D.

[0022] Preferably, step S4 comprises:

[0023] Step S41: Based on the damage coefficient D, construct the deformation modulus E0 and the cohesion c of the joint model. L0 and the internal friction angle φ L0 The correction equation of

[0024] Step S42: Within the threshold range of the damage coefficient D, the relaxation depth calculated value L obtained by the joint model is adjusted by adjusting the material constant R C Equal to the rock relaxation depth test value L M , and the modified diffuse joint model is obtained.

[0025] Preferably, step S5 includes: comparing the calculated value of the rock relaxation depth obtained by calculating the corrected diffuse joint model with the anchor support length, and when the rock relaxation depth is greater than the anchor support length, increasing the anchor support length until the far end of the anchoring measure enters the non-relaxation zone of the rock; when the rock relaxation depth is less than the anchor support length, the current anchor support length is not adjusted.

[0026] The present invention also provides a method for determining the failure mode of a steep thin-layer slope, which uses the above-mentioned modified diffuse joint model, does not consider anchor support measures, and performs calculation and analysis based on the slope excavation plan; when the slope is excavated, the strength reduction method is used to obtain the deformation and relaxation range distribution of the slope under the limit state; the deformation and relaxation depth of the top area and the bottom area of ​​the slope are compared to determine the failure mode.

[0027] Preferably, the method for determining the failure mode comprises:

[0028] 1) When the deformation and relaxation depth of the top area of ​​the slope are greater than those of the bottom area of ​​the slope and are greater than the set threshold, it is judged that the thin layer steep slope has bent and collapsed;

[0029] 2) When the deformation and relaxation depth of the bottom area of ​​the slope are greater than those of the top area of ​​the slope and less than the set threshold, it is judged that the thin layer steep slope has shear-slip failure;

[0030] 3) When the difference between the deformation and relaxation depth of the top and bottom areas of the slope is within the set threshold range, it is judged that the thin-layer steep slope has undergone bending-toppling / shear-slip composite failure.

[0031] The present invention also provides a failure mode and anchorage length determination system for steep thin-layer slopes, wherein the above method is implemented by comprising a diffuse joint model correction module, an anchorage support length determination module and a failure mode determination module;

[0032] The pervasive joint model correction module is used to test the rock relaxation depth value L M The diffuse joint model is modified by using the damage coefficient D;

[0033] The anchor support length determination module is used to determine the anchor support length through the modified diffuse joint model;

[0034] The failure mode determination module is used to determine the failure mode through the modified diffuse joint model.

[0035] The beneficial effects of the present invention include at least: the present invention proposes a method for judging the failure mode of a thin-layer steep rock stratum slope and calculating the length of anchor support, which can be used as a basis for dividing the failure mode of a steep-layer thin-layer slope and determining the design length of the slope anchor support based on actual geological conditions, field test results of representative stratigraphic areas, calculation results of excavation unloading relaxation of layered rock slopes based on an elastoplastic damage model, based on the distribution law of deformation and relaxation depth, and the relaxation depth of the steep-layer thin-layer slope rock mass under excavation unloading. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The figure is a schematic diagram of a method flow of an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0038] like Figure 1 As shown, an embodiment of the present invention provides a method for determining the anchor support length of a steep thin-layer slope, comprising the following steps:

[0039] Step S1: Conduct a drilling experiment in the area where the slope to be supported has been partially excavated to obtain the rock relaxation depth test value L M , the mean longitudinal wave velocity of the rock mass within the relaxation range C p1 , the average longitudinal wave velocity of the rock mass outside the range C p0 and the thickness δ of the thin-layered rock mass on the slope.

[0040] Specifically, in the embodiment of the present invention, in the area where the steep thin layer slope has been partially excavated, the highest level of horse trail is selected, and the geological drilling machine is arranged to drill holes toward the inside of the slope. The drilling direction is slightly downward from the horizontal, the hole diameter is not less than 90mm, and the hole depth is not less than 20m. After the drilling is completed, the geophysical acoustic wave test method is used to obtain the variation law of the longitudinal wave velocity of the slope rock mass at different depths from the excavation surface.

[0041] According to the rock mass acoustic wave velocity and borehole depth curve obtained by drilling, the range corresponding to the wave velocity value significantly lower than the deep rock mass wave velocity value is divided into the rock mass relaxation zone, and the rock mass relaxation depth of the test site is recorded as L M At the same time, according to the distribution of rock mass longitudinal wave velocity along the borehole depth obtained by the test, the mean values ​​of rock mass longitudinal wave velocity within and outside the relaxation range are calculated and recorded as C p1 and C p0In addition, the thickness of the thin-layered rock mass on the slope at this location was obtained based on the drill core, which was recorded as δ.

[0042] Step S2: Establish a diffuse joint model for the slope to be supported.

[0043] Specifically, in the embodiment of the present invention, a numerical analysis model is established for the slope at this location, and a pervasive joint model considering the influence of the layer is used to simulate the steep thin rock mass. Based on the engineering geological survey data, the initial mechanical parameters of the pervasive joint model are determined, including: deformation modulus E0, rock mass cohesion c R0 、Friction angle of rock mass Layer occurrence (dip, inclination), layer cohesion c L0 , internal friction angle of the layer

[0044] Step S3: Based on the material constant R and the mean longitudinal wave velocity C of the rock mass within the relaxation range p1 , the average longitudinal wave velocity of the rock mass outside the range C p0 and the thickness δ of the thin-layered rock mass on the slope, the damage coefficient D is constructed, and the threshold range of the damage coefficient D is confirmed.

[0045] Specifically, the deformation modulus E0 and the cohesion c of the layer in the diffuse joint model used for the slope are L0 and the internal friction angle of the layer The damage coefficient D is introduced to consider the damage and degradation effect of excavation unloading on the slope rock mass, that is:

[0046]

[0047] E1=(1-D)E0(2)

[0048]

[0049] Where: D is the damage coefficient of the slope rock mass. The smaller the D value is, the smaller the unloading damage of the rock mass is. The unit of the layer thickness δ of the thin-layered rock mass is cm. When δ>10, δ=10, and when δ<1, δ=1. ε p is the equivalent plastic strain; R is the material constant, the initial value can be taken as 10.0, and E0 is the deformation modulus considering the influence of unloading damage. From the deformation instability mode of steep thin rock slopes, the primary factor inducing the instability of such slopes is the significant weakening of the strength of the layer, so the main consideration is the influence of excavation unloading on the strength of the layer.

[0050] In this embodiment, the discontinuous deformation characteristics of thin steep slopes are considered. and Two dimensions are corrected, Based on the continuous medium method, the damage coefficient calculation method does not consider the influence of the rock slope layer; Based on the results of sonic wave velocity tests on steep thin slopes, the relaxation range is obtained and the average wave velocity values ​​inside and outside the relaxation zone are further calculated. A damage coefficient calculation method considering the actual slope characteristics is given, that is, the discontinuous deformation characteristics of thin steep slopes.

[0051] In the embodiment of the present invention, considering that the term "thin rock mass" is still a qualitative expression without quantitative judgment, the above two methods of measuring damage are used, according to the rock mass layer thickness δ, as the weight value, to combine the calculation results of the two damage coefficients. Specifically: According to the engineering geological survey specifications, thin rock mass can be further divided into thin layer and ultra-thin layer rock mass. Thin rock mass refers to a layer with a thickness of 1 to 10 cm, and ultra-thin rock mass refers to a layer with a thickness of less than 1 cm. According to existing engineering knowledge, the thicker the rock mass layer, the closer its deformation characteristics are to a continuous medium, and it is more suitable for use. When the thickness of the rock mass layer is smaller, its deformation characteristics tend to be more discontinuous medium, which is more suitable for Therefore, the rock layer thickness index δ is used as a weight term to determine the contribution weights of the two damage calculation methods to the comprehensive damage coefficient.

[0052] When δ≥10, the above formula becomes That is, when the layer thickness is large, the damage coefficient is calculated according to the continuous medium analysis method; when δ≤1, the above formula becomes That is, when the layer thickness is small, the damage coefficient is determined according to the discontinuous medium analysis method. When δ is between 1 and 10, the comprehensive damage coefficient value is calculated according to the actual layer thickness, reflecting the influence of both at the same time.

[0053] In the embodiment of the present invention, the damage coefficient D threshold value that can be used to judge the rock mass entering the unloading relaxation state is derived by the following method. The longitudinal wave velocity of the rock mass before and after the slope excavation corresponds to the measured longitudinal wave velocity of the rock mass outside the relaxation range and within the relaxation range, which are C p0 and C p1 According to elastic wave theory:

[0054]

[0055] Where E0 is the deformation modulus taking into account the influence of unloading damage, μ represents Poisson's ratio, ρ0 represents the density of the unloaded rock mass before excavation, and ρ1 represents the density of the relaxed rock mass after excavation unloading.

[0056] Since the influence of excavation unloading on the Poisson's ratio μ of the rock mass is small, 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 longitudinal wave velocity, deformation modulus and density of the surrounding rock before and after excavation unloading can be obtained:

[0057]

[0058] According to formula (1), we have:

[0059]

[0060] Since the excavation unloading effect has little effect on the density of the rock mass, ρ1≈ρ2, then equation (7) can be further simplified to:

[0061]

[0062] Generally, a 10% drop in wave velocity is taken as the basis for rock mass relaxation, that is:

[0063] C p1 ≤0.9C p0 (9)

[0064] When the wave velocity of the slope rock mass satisfies the condition of formula (9), it can be considered that the rock mass at this location is relaxed. Then, by substituting formula (9) into formula (8), the range of values ​​of the damage coefficient D of rock mass relaxation is obtained, which is D ≥ 0.19.

[0065] Step S4: Based on the rock relaxation depth test value L M The influence of the damage coefficient D on the deformation modulus E0 and the cohesion c of the joint model L0 and the internal friction angle φ L0 Make corrections.

[0066] Specifically, according to the standard of D ≥ 0.19, the depth of the rock relaxation zone calculated using the initial mechanical parameters of the pervasive joint model is determined, and the calculated value of the rock relaxation depth L corresponding to the on-site drilling acoustic wave test site is extracted. C When the rock relaxation depth test value L M Greater than the calculated value L C When the material constant R in formula (3) is reduced, the calculation is repeated; when the rock relaxation depth test value L M Less than the calculated value L C When the material constant R in formula (3) is increased, the calculation is repeated until the rock relaxation depth test value L M Equal to the calculated value L C Stop and obtain the material constant value for reviewing the current formation characteristics, recorded as R OK .

[0067] Step S5: Calculate the relaxation depth using the modified diffuse joint model to determine the anchor support lengths of different anchor points.

[0068] Specifically, R OK Substituting into formula (3), considering the preliminarily proposed anchor support design scheme, the slope excavation calculation and analysis are performed layer by layer according to the slope excavation scheme. When the calculation of each layer of slope excavation is completed, the calculated rock relaxation depth is determined according to the standard of D ≥ 0.19 and compared with the anchor support length. For the parts where the rock relaxation depth is greater than the anchor support length, the anchor support length should be increased until the far end of the anchoring measure enters the non-relaxation zone of the rock mass; for the parts where the rock relaxation depth is less than the anchor support length, the anchor support length can meet the slope stability requirements, and the current anchor support scheme does not need to be adjusted. In this way, the anchor length of the steep thin rock slope is determined.

[0069] The embodiment of the present invention also provides a method for determining the failure mode of a steep thin-layer slope, using the above-mentioned modified diffuse joint model, and transforming R OK Substituting into formula (3), without considering anchor support measures, the calculation and analysis are performed according to the slope excavation plan. When the slope is excavated, the strength reduction method is used to obtain the deformation and relaxation range distribution of the slope under the limit state, and the following method is used to determine the failure mode of the slope:

[0070] (1) When the deformation and relaxation depth of the top area of ​​the slope are significantly greater than those of the bottom area of ​​the slope, it is judged that the thin layer steep slope has bent and collapsed;

[0071] (2) When the deformation and relaxation depth of the bottom area of ​​the slope are significantly greater than those of the top area of ​​the slope: it is judged that the thin layer steep slope has shear-slip failure;

[0072] (3) When the deformation and relaxation depth of the top and bottom areas of the slope are generally equivalent, it is judged that the thin-layer steep slope has undergone bending-toppling / shear-slip composite failure.

[0073] The embodiment of the present invention also provides a system for determining the failure mode and anchoring length of a steep thin-layer slope, wherein the above method is implemented by comprising a diffuse joint model correction module, an anchoring support length determination module and a failure mode determination module;

[0074] The joint model correction module is used to test the rock relaxation depth value L M The diffuse joint model is modified by using the damage coefficient D;

[0075] An anchor support length determination module, used to determine the anchor support length through the modified diffuse joint model;

[0076] The failure mode determination module is used to determine the failure mode through the modified ubiquitous joint model.

[0077] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. Only the preferred embodiments of the present invention are expressed. The description is more specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. As long as there is no contradiction in the combination of these technical features, they should be considered as the scope recorded in this specification.

[0078] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for determining the anchor support length of a steep thin slope, characterized in that: The following steps are involved: Step S1: Conduct a drilling experiment in the area where the slope to be supported has been partially excavated to obtain the rock relaxation depth test value L M , the mean longitudinal wave velocity of the rock mass within the relaxation range C p1 , the average longitudinal wave velocity of the rock mass outside the range C p0 and the thickness of the thin-bedded rock mass on the slope, δ; Step S2: establishing a diffuse joint model for the slope to be supported; Step S3: Based on the material constant R and the mean longitudinal wave velocity C of the rock mass within the relaxation range p1 , the average longitudinal wave velocity of the rock mass outside the range C p0 and the thickness δ of the thin-layered rock mass on the slope, construct a damage coefficient D, and confirm the threshold range of the damage coefficient D; Step S4: Based on the rock relaxation depth test value L M and the damage coefficient D have an influence on the deformation modulus E0, the cohesion c L0 and the internal friction angle of the layer make corrections; Step S5: Calculate the relaxation depth using the modified diffuse joint model to determine the anchor support lengths at different anchor points; The expression of the damage coefficient D in step S3 is: In the formula, ε p represents the equivalent plastic strain, R represents the material constant, δ represents the thickness of the thin-layered rock mass of the slope, and the unit is cm. When δ>10, δ=10 is taken, and when δ<1, δ=1 is taken.

2. The method for determining the anchor support length of a steep thin slope according to claim 1 is characterized in that: Step S1 includes: in an area where a steep thin-layer slope has been partially excavated, the highest level of horse trail is selected, a geological drill is arranged, and a hole is drilled toward the inside of the slope. After the drilling is completed, a geophysical acoustic wave test method is used to obtain the variation law of the longitudinal wave velocity of the slope rock mass at different depths from the excavation surface; according to the rock mass acoustic wave velocity and drilling depth curve obtained by drilling, the range corresponding to the wave velocity value lower than the deep rock mass wave velocity value threshold is divided into a rock mass relaxation zone, and the rock mass relaxation depth of the test part is recorded as L M ; According to the distribution of rock mass longitudinal wave velocity along the borehole depth obtained by the test, the mean values ​​of rock mass longitudinal wave velocity within and outside the relaxation range are calculated, which are recorded as C p1 and C p0 ; Based on the drill core, the thickness δ of the thin-layered rock mass on the slope of this part is obtained.

3. The method for determining the anchor support length of a steep thin slope according to claim 2 is characterized in that: The diameter of the drill hole is not less than 90 mm, and the depth of the drill hole is not less than 20 m.

4. The method for determining the anchor support length of a steep thin slope according to claim 1 is characterized in that: The method for confirming the threshold range of the damage coefficient D in step S3 includes: Step S31: According to elastic wave theory, determine the mean value C of the longitudinal wave velocity of the rock mass within the relaxation range. p1 and the mean longitudinal wave velocity of the rock mass outside the range C p0 Theoretical formula of Step S32: Based on the theoretical formula, obtain the mean value of the rock mass longitudinal wave velocity C p1 and the mean longitudinal wave velocity of the rock mass outside the range C p0 The ratio formula of Step S33: transforming the ratio formula to obtain a relationship between the damage coefficient D and the ratio formula; Step S34: Based on the rock relaxation theory, the range of the ratio formula is obtained to obtain the threshold range of the damage coefficient D.

5. The method for determining the anchor support length of a steep thin slope according to claim 1, characterized in that: Step S4 includes: Step S41: Based on the damage coefficient D, construct the deformation modulus E0 and the cohesion c of the joint model. L0 and the internal friction angle φ L0 The correction equation of Step S42: Within the threshold range of the damage coefficient D, the relaxation depth calculated value L obtained by the joint model is adjusted by adjusting the material constant R C Equal to the rock relaxation depth test value L M , and the modified diffuse joint model is obtained.

6. The method for determining the anchor support length of a steep thin slope according to claim 1, characterized in that: Step S5 includes: comparing the calculated value of the rock relaxation depth obtained by calculating the corrected diffuse joint model with the anchor support length. When the rock relaxation depth is greater than the anchor support length, the anchor support length is increased until the far end of the anchoring measure enters the non-relaxation zone of the rock; when the rock relaxation depth is less than the anchor support length, the current anchor support length is not adjusted.

7. A method for determining the failure mode of a steep thin slope, characterized by: The modified diffuse joint model of claim 1 is adopted, and the anchor support measures are not considered. The calculation and analysis are performed according to the slope excavation plan; when the slope excavation is completed, the strength reduction method is used to obtain the deformation and relaxation range distribution of the slope under the limit state; the deformation and relaxation depth of the top area of ​​the slope and the bottom area of ​​the slope are compared to determine the failure mode.

8. The method for determining the failure mode of a steep thin-layer slope according to claim 7 is characterized in that: Methods for determining failure modes include: 1) When the deformation and relaxation depth of the top area of ​​the slope are greater than those of the bottom area of ​​the slope and are greater than the set threshold, it is judged that the thin layer steep slope has bent and collapsed; 2) When the deformation and relaxation depth of the bottom area of ​​the slope are greater than those of the top area of ​​the slope and less than the set threshold, it is judged that the thin layer steep slope has shear-slip failure; 3) When the difference between the deformation and relaxation depth of the top and bottom areas of the slope is within the set threshold range, it is judged that the thin-layer steep slope has undergone bending-toppling / shear-slip composite failure.

9. A system for determining the failure mode and anchoring length of a steep thin-layer slope, which is implemented based on the method described in any one of claims 1 to 8, characterized in that: It includes a module for correcting the model of diffuse joints, a module for determining the length of anchor support, and a module for determining the failure mode; The pervasive joint model correction module is used to test the rock relaxation depth value L M The diffuse joint model is modified by using the damage coefficient D; The anchor support length determination module is used to determine the anchor support length through the modified diffuse joint model; The failure mode determination module is used to determine the failure mode through the modified diffuse joint model.

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