Method for evaluating stability of steeply inclined bedding soft and hard interbedded and fault coupled rock slope

Abstract

This invention discloses a method for assessing the stability of steeply dipping, bedding-parallel soft-hard interbedded and fault-coupled rock slopes, relating to the field of geotechnical engineering. The aim is to accurately evaluate slope stability based on the instability patterns following excavation and unloading. The technical solution employed in this invention is as follows: Before slope excavation and unloading, a geological survey is conducted to determine if the slope meets the applicable conditions. Then, for slopes meeting the applicable conditions, geological exploration is carried out to obtain quantitative parameters, including the crack penetration rate η and the rock mass integrity coefficient K. v Fault shear strength τ p The tangential component of the self-weight of the layered rock mass above the fault, σ τ Next, the deformation stage after slope excavation and unloading is determined, and the stability level is identified. Finally, after slope excavation and unloading, the slope is treated based on its stability level. This invention is used for slope stability assessment and treatment design.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering, and more particularly to the field of slope stability evaluation, specifically a method for evaluating the stability of steeply dipping, bedding, interbedded soft and hard rock slopes coupled with faults. Background Technology

[0002] Interbedded rock masses typically consist of hard rock layers interspersed with weak rock layers, such as the sandstone-mudstone interbedded layers in the Sichuan Basin and the limestone-shale interbedded layers in South China. The compressive strength of the weak rock layers generally does not exceed 15 MPa, and there is a significant difference in compressive strength between the hard and weak rock layers. These rock masses are characterized by low rock mass strength, inconsistent deformation modulus, and weak weathering resistance, resulting in significant stability risks for slopes constructed from them.

[0003] Deformation and failure mechanisms are central to slope stability analysis and evaluation. Current slope stability assessment techniques primarily target slopes with single lithology, relying on qualitative descriptions (such as rock mass integrity and crack development) and lacking corresponding quantitative evaluation indicators. This approach is limited and highly subjective. For steeply dipping, bedding-parallel soft-hard interbedded rock slopes coupled with faults, the complex instability mechanism of "lower rock mass bending and pulling upper rock mass sliding" is not considered, making it difficult to explain the instability of steeply dipping, soft-hard interbedded slopes without significant toe uplift.

[0004] Patent 1 (authorization announcement number CN104360411B, authorization announcement date 2017-01-25) discloses a method for evaluating the stability of a leading edge gently dipping slope. It proposes the slope structure type of the leading edge gently dipping slope and establishes a three-stage deformation and failure mechanism of "unloading tensile cracking - sliding tensile cracking - shearing". It is applicable to hard rock slopes with gently dipping leading edges (dip angle ≤ 30°) but not applicable to the stability evaluation of steeply dipping rock slopes with bedding soft and hard interbedded layers and fault coupling.

[0005] Patent 2 (Publication No. CN118858588A, Publication Date: 2024-10-29) discloses a method for analyzing the stability of bedding rock landslides. It first divides the bedding rock landslide into three segments: the rear edge (A1), the front edge (A2), and the middle-rear edge (A3). Then, it determines the deformation level of each segment based on the slope structure, the development of structural surfaces, and the rock mass integrity coefficient. Next, it determines the deformation stage of the landslide based on the deformation level, and finally, it determines the stability state of the landslide based on the deformation stage. This patent proposes a deformation instability mechanism of "tensile cracking and pushing - floating and sliding - locking and shearing," focusing on water-soaked, hard-interbedded soft slopes at the front edge. It does not address the bending creep failure of steeply dipping bedding rock slopes with interbedded hard and soft layers and fault coupling.

[0006] Scholars have proposed six basic failure modes for slopes: creep-tensile cracking, slip-tensile cracking, slip-compression-tensile cracking, bending-tensile cracking, plastic flow-tensile cracking, and slip-bending. Patents 1 and 2 modify or combine these six basic failure modes, effectively addressing most natural slope instability issues. For example, steeply dipping rock slopes are primarily affected by bending-tensile cracking, while gently dipping, bedding rock slopes with weak layers are primarily affected by slip-bending. For steeply dipping, bedding rock slopes with alternating hard and soft layers and fault coupling, the rock structure and deformation mechanism are unique under conditions of top loading and toe unloading, making it difficult to evaluate using the aforementioned six basic failure modes. Summary of the Invention

[0007] This invention provides a method for evaluating the stability of steeply dipping, bedding, soft and hard interbedded rock slopes coupled with faults. The purpose is to accurately evaluate the slope stability based on the instability pattern after slope excavation and unloading.

[0008] The technical solution adopted in this invention is: a method for assessing the stability of steeply dipping, bedding, soft and hard interbedded rock slopes coupled with faults, comprising the following steps.

[0009] S1. Before slope excavation and unloading, a geological survey of the slope is conducted to determine whether the slope meets the applicable conditions. The applicable conditions are: the slope is a layered rock mass with alternating layers of hard rock and soft rock, the dip of the layered rock mass is opposite to the dip of the fault, and the slope excavation range covers part of the fault.

[0010] Specifically: the dip angle α of the layered rock mass is ≥60°, the angle between the strike of the layered rock mass and the strike of the slope is ≤30°, and the compressive strength σ of the weak rock layer... n ≤15MPa, weathering grade is strong weathering to complete weathering, the angle σ between the bedding plane of the layered rock mass and the bedding plane of the fault is <90°, and the thickness of the fault is not less than 0.5m.

[0011] S2. Conduct geological exploration on slopes that meet the applicable conditions to obtain quantitative parameters, including: crack penetration rate η and rock mass integrity coefficient K. v Fault shear strength τ p The tangential component of the self-weight of the layered rock mass above the fault, σ τ Among them, the fault shear strength τ p The shear strength τ of the fault structure surface p1 The shear strength τ of the material within the fault p2 The smaller of the two.

[0012] To facilitate geological surveys and explorations, further steps S1 and S2 involve arranging exploration adits at intervals along the slope direction and dip within the bending influence area of ​​the fault, with the exploration adits completely covering the bending influence area of ​​the fault in the length direction.

[0013] To ensure the accuracy of the quantitative parameters, specifically: the length of the exploration adit shall not be less than 10m, and the diameter of the exploration adit shall be ≥90mm.

[0014] Specifically, the tangential component σ τ The calculation formula is: σ τ =γHsinβ, where γ is the average unit weight of the layered rock mass, H is the average depth of the layered rock mass above the fault, and β is the dip angle of the fault.

[0015] S3. Determine the deformation stage after slope excavation and unloading, and determine the stability level.

[0016] If η≤30%, K v ≥0.75, σ τ <τ p If the slope is in the rebound bending stage, the stability level is considered stable.

[0017] If 30% ≤ η < 60%, then 0.75 > K v If the value is ≥0.5, the slope is judged to be in the stable creep stage, and the stability level is basically stable.

[0018] If 60%≤η<90%, K v <0.5, σ τ ≥τ p If the slope is in the accelerated creep stage, its stability level is considered unstable.

[0019] If η≥90%, the slope is judged to be in a critical state of instability, and the stability level is unstable.

[0020] S4. After the slope is excavated and unloaded, the slope is treated according to the slope stability level.

[0021] Specifically: for stable slopes, unloading control at the toe of the slope is implemented, and surface drainage is carried out; for basically stable slopes, grouting reinforcement is carried out on the fault, and anchor bolts are installed on the slope surface after unloading during slope excavation; for under-stable slopes, the layered rock mass above the fault is reduced in load by slope cutting, and the layered rock mass above the fault is supported by prestressed anchor cables; for unstable slopes, the slope is reinforced as a whole.

[0022] The beneficial effects of this invention are: this invention uses the fracture penetration rate η and the rock mass integrity coefficient K. v and fault shear strength τ p The tangential component σ of the self-weight of the layered rock mass above the fault in the fault. τThe magnitude relationship is used as a core quantitative parameter to determine the deformation stage of slopes after excavation and unloading, and to determine the stability level. This method boasts a high degree of quantification, repeatable and verifiable evaluation results, and strong engineering operability, making it easy to implement. This invention proposes three deformation stages: "rebound bending - traction creep - shear instability." Traction creep is further divided into two stages: stable creep and accelerated creep. It precisely adapts to geological conditions of steeply dipping, bedding-type soft-hard interbedded layers and fault coupling, achieving accurate assessment of the stability level. Furthermore, by focusing on the deformation and instability modes after slope excavation and unloading, it effectively explains instability phenomena that existing models cannot cover, providing precise targets for slope treatment. This invention can be applied to slope stability assessment and treatment design in fields such as highways, railways, water conservancy and hydropower, and mining engineering. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the slope in the springback bending stage after excavation and unloading in this invention.

[0024] Figure 2 This is a schematic diagram of the slope in the stable creep stage in this invention.

[0025] Figure 3 This is a schematic diagram of the slope in the accelerated creep stage in this invention.

[0026] Figure 4 and Figure 5 This is a schematic diagram of the slope in the shear instability stage in this invention.

[0027] Attached figures: 1. Hard rock layer; 2. Soft rock layer; 3. Fault; 4. Excavation area of ​​slope; 5. Area affected by bending; 6. Accumulation at the top of slope. Detailed Implementation

[0028] The invention will now be further described with reference to the accompanying drawings.

[0029] This invention relates to a method for assessing the stability of steeply dipping, bedding-parallel, interbedded hard and soft rock slopes coupled with faults. It is applicable to layered rock masses where the slope consists of interbedded hard rock layer 1 and soft rock layer 2, and the dip direction of the layered rock mass is opposite to the dip direction of fault 3. The slope excavation range 4 covers a portion of fault 3, meaning a portion of fault 3 is located within the slope excavation range 4. In the title of this invention, "steeply dipping" refers to a large dip angle α of the layered rock mass, generally α ≥ 60°. "Bedding-parallel" means that the dip direction of the layered rock mass is consistent with the dip direction of the slope or the angle between them is less than 30°, i.e., the angle between the strike of the layered rock mass and the strike of the slope is ≤ 30°. "Soft rock layer 2" refers to the compressive strength σ... n≤15MPa, weathering grade is strongly weathered to completely weathered interlayer, generally soft rock with a natural water content (mass water content) ≥20%. The thickness of fault 3 is generally not less than 0.5m, and the material in the fault is mainly argillaceous and gravelly. Coupled between layered rock mass and fault refers to the dip of the layered rock mass being opposite to the dip of fault 3, that is, the layered rock mass and fault are oppositely intersected, and the angle σ between the bedding plane of the layered rock mass and the bedding plane of fault 3 is <90°, such as... Figure 1 As shown.

[0030] The stability assessment method for steeply dipping, bedding-parallel soft-hard interbedded and fault-coupled rock slopes includes the following steps.

[0031] S1. Before slope excavation and unloading, a geological survey of the slope is conducted to determine whether the slope meets the applicable conditions. If it does, proceed to the next step; otherwise, existing methods are used to evaluate slope stability. The geological survey includes collecting data on the occurrence of layered rock masses and faults.

[0032] When conducting surface geological surveys, a total station can be used to measure the dip angle α of the layered rock mass (with ≥3 measuring points and the average value), and the angle σ between the bedding plane of the layered rock mass and the bedding plane of fault 3 (with ≥2 measuring points and the average value). The relationship between the layered rock mass and the slope direction can be determined by a geological compass, and the spatial position of fault 3 and the slope surface can be determined by the outcrop of fault 3, so as to facilitate the layout of subsequent exploration adits.

[0033] S2. Conduct geological exploration on slopes that meet the applicable conditions to obtain quantitative parameters.

[0034] Quantitative parameters include: fracture penetration rate η and rock mass integrity coefficient K. v Fault shear strength τ p The tangential component of the self-weight of the layered rock mass above fault 3 in fault 3, σ τ Fault shear strength τ p The shear strength τ of the fault 3 structural plane p1 The shear strength τ of the material within fault 3 p2 The smaller of the two, where the shear strength τ p1 This refers to the shear strength of fault 3 as a whole, specifically the shear strength τ. p2 This refers to the shear strength of the material within fault 3. A direct shear test was conducted on the structural plane of fault 3 to obtain the shear strength τ. p1 A direct shear test was conducted on the material within fault 3 to obtain the shear strength τ. p2 Shear strength τ p2 This represents the peak intensity.

[0035] The quantification parameters are obtained through testing, or through a combination of testing and calculation, both of which are performed according to existing techniques. The self-weight of the layered rock mass above fault 3 can be decomposed into a tangential component force σ at fault 3.τ (Along the structural plane of fault 3) and normal component (perpendicular to the structural plane of fault 3). Tangential component σ τ The impact on slope stability depends on factors such as the roughness of the structural surface and the physical and mechanical properties of the materials within the structural surface. The normal component is manifested in the thrust of the upper layered rock mass of fault 3 on the lower layered rock mass of fault 3. This is also the most important factor causing the bending deformation of the lower layered rock mass of fault 3. Moreover, the steeper the dip angle of the layered rock mass, the more obvious the thrust. That is, the smaller the angle σ between the bedding plane of the layered rock mass and the bedding plane of fault 3, the greater the thrust.

[0036] To facilitate geological surveys and explorations and accurately obtain quantitative parameters, steps S1 and S2 generally involve arranging exploration adits at intervals along the slope strike and dip within the bending influence zone 5 of fault 3. For example, one exploration adit is arranged every 30m to 50m along the slope strike and dip. The exploration adits completely cover the bending influence zone 5 of fault 3 in the length direction, and the bending influence zone 5 includes the creep influence zone. The length of the exploration adits is generally not less than 10m. The exploration adits can be boreholes, for example, boreholes with a diameter ≥90mm.

[0037] After setting up the exploration adit, the interbedded conditions of hard rock layer 1 and weak rock layer 2, the thickness of the layered rock mass, the dip angle of the rock layers, the angle σ between the fault and the rock layers, and the attitude of fault 3 were investigated. The fracture penetration rate of tensile fractures and the distribution of confined water in the bending influence zone 5 were also investigated. At least two sets of materials were collected from each of the hard rock layer 1, weak rock layer 2, and fault 3, and their density was measured. Acoustic wave testing was also conducted, and the rock mass integrity coefficient K was calculated. v Direct shear tests were conducted on the structural plane of fault 3 and the material within fault 3. The shear strength τ of the fault was obtained by comparison. p .

[0038] The fracture penetration rate η is calculated using existing methods. For example, the penetration length L1 and the total surveyed fracture length L2 are first recorded by observing and recording the fractures in the exploration adit, and then the fracture penetration rate η is calculated as (L1 / L2) × 100%. Rock mass integrity coefficient K v The calculation is performed using existing methods, such as first using acoustic wave testing to obtain the longitudinal wave velocity v of the layered rock mass. p And the longitudinal wave velocity of rocks (the longitudinal wave velocity of fresh hard rock layers in a layered rock mass) v p0 Then calculate the rock mass integrity factor K. v =(v p / v p0 )².

[0039] Calculate the tangential component σ of the self-weight of the layered rock mass above fault 3 within fault 3. τ First, calculate the self-weight of the layered rock mass above fault 3. Tangential component σ τ The calculation formula is: στ =γHsinβ, where γ is the average unit weight of the layered rock mass, H is the average depth of the layered rock mass above fault 3, and β is the dip angle of fault 3. The average unit weight γ of the layered rock mass can be calculated by weighting the unit weight of hard rock layer 1 and soft rock layer 2. The weight of hard rock layer 1 is the total thickness of hard rock layer 1, and the weight of soft rock layer 2 is the total thickness of soft rock layer 2.

[0040] S3. Determine the deformation stage after slope excavation and unloading, and determine the stability level.

[0041] After slope excavation and unloading, the layered rock mass undergoes unloading rebound deformation. If η≤30%, K v ≥0.75, σ τ <τ p If the slope is in the rebound bending stage, the stability level is considered stable. Figure 1 As shown.

[0042] If 30% ≤ η < 60%, then 0.75 > K v If the value is ≥0.5, the slope is judged to be in the stable creep stage, and the stability level is basically stable. For example... Figure 2 As shown, the lower layered rock mass of fault 3, under the thrust of the upper layered rock mass of fault 3, is initially in the elastic deformation stage. When the tangential component force σ τ The shear strength τ of the material within fault 3 is greater than p2 This means that bending deformation begins, and the layered rock mass near the contact surface will develop compression and tensile cracks.

[0043] Under the weight of the upper rock mass of fault 3, the lower rock mass of fault 3 undergoes accelerated bending deformation, resulting in tensile cracks on its back side. Within the bending-affected area 5, the center of gravity of the rock mass shifts outwards from the slope, intensifying the bending of the lower rock mass of fault 3. This leads to compressional failure on the compression side and the development of tensile cracks on the tension side. Under the traction of the lower rock mass of fault 3, the upper rock mass of fault 3 creeps downwards along the weaker rock plane, such as… Figure 3 As shown.

[0044] If 60%≤η<90%, K v <0.5, σ τ ≥τ p If η ≥ 90%, the slope is judged to be in the accelerated creep stage, and the stability level is understability. If η ≥ 90%, the slope is judged to be in the critical state of instability, and the stability level is unstable. Under the gravity of the layered rock mass above fault 3, the tensile side cracks of the rock mass below fault 3 develop to penetrate, the rock mass is sheared, the rock mass above fault 3 loses its lower support, and slides down the weak rock layer 2, causing slope instability and failure. Figure 4 As shown. Ultimately, the slope reaches a new equilibrium, as... Figure 5 As shown.

[0045] S4. After the slope is excavated and unloaded, the slope is treated according to the slope stability level.

[0046] Slope treatment involves corresponding engineering measures. For stable slopes, unloading control at the toe is implemented, with an unloading depth generally ≤3m, and surface drainage is carried out. For basically stable slopes, fault 3 is reinforced by grouting, with a grouting pressure generally between 1.5MPa and 2.0MPa. Anchor bolts are installed on the slope surface after unloading through excavation, with a spacing of generally 2m to 3m. For unstable slopes, the layered rock mass above fault 3 is reduced in thickness, generally ≥5m, for example, by removing the top deposit 6. In addition, prestressed anchor cables are used to support the layered rock mass above fault 3, with an anchoring force generally ≥100kN. For unstable slopes, personnel and equipment are evacuated, and the slope is reinforced as a whole, for example, by combining anti-slide piles with anchor cables.

Claims

1. A method for assessing the stability of steeply dipping, bedding-parallel soft-hard interbedded rock slopes coupled with faults, characterized in that... Includes the following steps: S1. Before the slope is excavated and unloaded, a geological survey is conducted on the slope to determine whether the slope meets the applicable conditions. The applicable conditions are: the slope is a layered rock mass with alternating layers of hard rock (1) and soft rock (2), the dip of the layered rock mass is opposite to the dip of the fault (3), and the slope excavation range (4) covers part of the fault (3). S2. Conduct geological exploration on slopes that meet the applicable conditions to obtain quantitative parameters, including: crack penetration rate η and rock mass integrity coefficient K. v Fault shear strength τ p The tangential component σ of the self-weight of the layered rock mass above fault (3) in fault (3) τ Among them, the fault shear strength τ p The shear strength τ of the fault (3) structural plane p1 The shear strength τ of the material within the fault (3) p2 The smaller of the two; S3. Determine the deformation stage after slope excavation and unloading, and determine the stability level; If η≤30%, K v ≥0.75, σ τ <τ p If so, the slope is judged to be in the rebound bending stage, and the stability level is stable; If 30% ≤ η < 60%, then 0.75 > K v If the value is ≥0.5, the slope is judged to be in the stable creep stage, and the stability level is basically stable. If 60%≤η<90%, K v <0.5, σ τ ≥τ p If so, the slope is judged to be in the accelerated creep stage, and the stability level is understability; If η≥90%, the slope is judged to be in a critical state of instability, and the stability level is unstable. S4. After the slope is excavated and unloaded, the slope is treated according to the slope stability level.

2. The method for assessing the stability of steeply dipping, bedding-parallel soft-hard interbedded and fault-coupled rock slopes as described in claim 1, characterized in that, In step S1, the applicable conditions also include: the dip angle α of the layered rock mass ≥ 60°, the angle between the strike of the layered rock mass and the strike of the slope ≤ 30°, and the compressive strength σ of the weak rock layer (2) n ≤15MPa, weathering grade is strong weathering to complete weathering, the angle σ between the layer of the layered rock mass and the layer of the fault (3) is less than 90°, and the thickness of the fault (3) is not less than 0.5m.

3. The method for assessing the stability of steeply dipping, bedding-parallel soft-hard interbedded and fault-coupled rock slopes as described in claim 1, characterized in that: In steps S1 and S2, exploration adits are arranged at intervals along the slope direction and dip within the bending influence area (5) of the fault (3), and the exploration adits completely cover the bending influence area (5) of the fault (3) in the length direction.

4. The method for assessing the stability of steeply dipping, bedding-parallel soft-hard interbedded and fault-coupled rock slopes as described in claim 3, characterized in that: The length of the exploration adit shall not be less than 10m, and the diameter of the exploration adit shall be ≥90mm.

5. The method for assessing the stability of steeply dipping, bedding-parallel soft-hard interbedded and fault-coupled rock slopes as described in claim 1, characterized in that: Tangential component σ τ The calculation formula is: σ τ =γHsinβ, where γ is the average unit weight of the layered rock mass, H is the average depth of the layered rock mass above the fault (3), and β is the dip angle of the fault (3).

6. The method for assessing the stability of steeply dipping, bedding-parallel soft-hard interbedded and fault-coupled rock slopes as described in any one of claims 1 to 5, characterized in that: In step S4, for stable slopes, unloading control is carried out at the toe of the slope and surface drainage is carried out; for basically stable slopes, grouting reinforcement is carried out on the fault (3) and anchor rods are installed on the slope surface after the slope is excavated and unloaded; for unstable slopes, the upper layered rock mass of the fault (3) is reduced by cutting the slope and the upper layered rock mass of the fault (3) is supported by prestressed anchor cables; for unstable slopes, the slope is reinforced as a whole.

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