Method for analyzing dam slope stability when dam slope is broken due to fracture based on limit equilibrium method

Abstract

The application discloses a dam slope stability analysis method for a dam slope caused by a fault, and specifically relates to the following steps: according to the form of the dam body and the fault position, a fault position for analysis is determined on the dam slope; the maximum vertical dislocation amount and the maximum horizontal variation amount of the fault are obtained from existing geological data, and the settlement of the downstream dam slope at the fault position is determined according to the maximum vertical dislocation amount; the dry bulk density and the saturated bulk density of the dam body material are obtained through a density test in a dam material test, and the Φ0 and the △Φ are obtained through a large triaxial test; the shear strength of the dam body material is reduced in the range of the maximum horizontal variation amount at the determined fault position; the dam slope stability at the determined fault position is calculated; and the dam slope stability at the fault position is evaluated according to the calculation result. The method solves the problem that the existing method cannot quickly and preliminarily determine whether the dam slope is stable when the dam body is caused to fault.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy engineering technology, specifically relating to a method for analyzing the slope stability of an earth-rock dam when fracture leads to misalignment, based on the limit equilibrium method. Background Technology

[0002] In hydropower and water conservancy projects, earth-rock dams are among the most widely used dam types due to their advantages such as readily available materials, strong adaptability to foundation deformation, simple structure, low construction difficulty, and ease of maintenance, reinforcement, and expansion. In recent years, pumped storage projects have experienced explosive growth, with a large number of pumped storage power stations entering the preliminary work stage. Due to the inherent characteristics of pumped storage power stations, it is necessary to select two locations with relatively large elevation differences and relatively short horizontal distances (such as a mountaintop and a piedmont area) for the arrangement of upper and lower reservoirs. These types of areas are often also areas with active fault zones, especially in Northwest my country, where many pumped storage power stations face the problem of being relatively close to faults and experiencing high seismic intensity. Therefore, it is crucial to quickly assess the impact of fault zones on the project and to analyze and evaluate the stability of the dam slope when fault zone misalignment leads to corresponding fault dislocation in the earth-rock dam body.

[0003] In past engineering projects, the impact of fault zones on dam bodies has mostly been treated as the effect of earthquakes on the dam body, without considering the impact of fault displacement in the dam slope area on dam stability. For some projects located close to fault zones, the impact of fault displacement on dam slope stability is usually studied through numerical simulations or physical experiments. However, in the early stages of a project, numerical simulations or physical experiments require a large number of parameters and significant investment of manpower, resources, and time, which is not conducive to the initial formulation of schemes and the comparison of different schemes. Therefore, it is necessary to explore a relatively simple method to calculate and analyze the slope stability of earth-rock dams located close to fault zones when fault displacement leads to dam body displacement, quickly obtaining preliminary conclusions on whether the dam slope is stable after dam body displacement, thereby advancing the initial formulation of schemes and the comparison of different schemes. Summary of the Invention

[0004] The purpose of this invention is to provide a method for analyzing the slope stability of an earth-rock dam when fracture leads to misalignment, based on the limit equilibrium method. This solves the problem that existing methods cannot quickly and preliminarily determine whether the dam slope is stable when fracture leads to misalignment in the early stages of a project.

[0005] The technical solution adopted in this invention is a method for analyzing the slope stability of an earth-rock dam when fracture leads to misalignment, based on the limit equilibrium method. Specifically, it is implemented according to the following steps:

[0006] Step 1: Based on the form of the dam body and the location of the fracture, determine the fault location on the dam slope for analysis;

[0007] Step 2: Obtain the maximum vertical displacement and maximum horizontal displacement of the fault from the existing geological data, and determine the settlement of the downstream dam slope at the fault location based on the maximum vertical displacement of the fault.

[0008] Step 3: Obtain the dry unit weight and saturated unit weight of the dam material through density test in the dam material test, and obtain the shear strength index Φ0 and ΔΦ through triaxial test. Based on the fault position determined in Step 1, reduce the shear strength of the dam material within the range of the maximum horizontal variation of the fault position.

[0009] Step 4: Perform dam slope stability calculations for the fault locations identified in Step 1;

[0010] Step 5: Based on the calculation results obtained in Step 4, evaluate the stability of the dam slope when the fracture leads to the misalignment of the dam body.

[0011] The invention is further characterized in that,

[0012] In step 1, the dam body form includes two cases: a single slope to the bottom and a variable slope.

[0013] The specific process of step 1 is as follows:

[0014] (1) When the dam body is a slope to the bottom, the dam slope closest to the fracture location is taken as the dam slope that causes the fault. Let the horizontal length of the dam slope that causes the fault be L and the number of fault locations be N. Then, L / N, 2L / N...NL / N are taken as the fault locations for analysis.

[0015] (2) If the dam body is of variable slope, then the misalignment position needs to be added at the location where the slope ratio changes, in addition to the misalignment position determined in (1).

[0016] If the dam body is located on the hanging wall of a fault, analysis is not required if the distance from the edge of the influence zone of a steep thrust fault is greater than 500m and the distance from the edge of the influence zone of a gentle thrust fault is greater than 600m.

[0017] If the dam body is located on the footwall of the fracture, then analysis is not required if the distance from the fracture exceeds 300m.

[0018] In step 2, the settlement is equal to the maximum vertical dislocation of the fracture.

[0019] In step 3, the reduction of shear strength at the misalignment location is carried out according to the most unfavorable situation. Therefore, Φ0 and ΔΦ at the misalignment location are both taken as 0, the dry unit weight at the misalignment location is taken as the minimum dry unit weight in the dam material, and the saturated unit weight at the misalignment location is taken as the minimum saturated unit weight in the dam material.

[0020] In step 4, the stability calculation of the dam slope adopts the Swedish circular arc method and the simplified Bishop method.

[0021] The dam slope stability calculation includes the following calculation conditions:

[0022] Condition 1: The water level in front of the dam is the normal storage level. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0023] Condition 2: The water level in front of the dam is the normal storage level and the seismic condition is the peak ground acceleration of the earthquake designed for the earth-rock dam. The dam slope stability calculation is performed on the upstream and downstream slopes at the fault locations determined in step 1.

[0024] Condition 3: The water level in front of the dam is the normal storage level and the seismic condition is the peak ground acceleration of the check earthquake of the earth-rock dam. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0025] Condition 4: The water level in front of the dam is the normal storage level and the seismic condition is that the peak ground acceleration of the earth-rock dam check earthquake is increased by 10%. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0026] Condition 5: The water level in front of the dam is the normal storage level and the earthquake condition is that the peak ground acceleration of the earth-rock dam check earthquake is increased by 20%. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location proposed in step 1.

[0027] Step 5 is as follows:

[0028] If the safety factors of the upstream and downstream dam slopes at different fault locations meet the specifications in the calculation results of conditions 1, 2 and 3, it indicates that the dam slopes are still in a stable state. If the calculation results of conditions 4 and 5 are smaller than those of condition 3, but still greater than 1 and higher than the specifications corresponding to conditions 2 and 3, it indicates that the dam slopes have a certain safety reserve.

[0029] The beneficial effect of this invention is that the method for analyzing the stability of the dam slope when fracture leads to misalignment of the earth-rock dam based on the limit equilibrium method uses only the simple limit equilibrium method for calculation and analysis, without the need for complex numerical simulation methods such as finite element and discrete element methods, which greatly improves the speed of determining whether the dam slope is stable when fracture leads to misalignment of the dam body. Attached Figure Description

[0030] Figure 1 This is a flowchart of the slope stability analysis method for earth-rock dams when fracture leads to misalignment based on the limit equilibrium method, according to the present invention.

[0031] Figure 2 This is a schematic diagram showing the fault location determined in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram illustrating the reduction of shear strength according to an embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram illustrating the relationship between dam body misalignment and slip arc in an embodiment of the present invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0035] Example 1

[0036] This invention relates to a method for analyzing the slope stability of earth-rock dams when fracture leads to faulting, based on the limit equilibrium method. Figure 1 As shown, please follow these steps:

[0037] Step 1: Based on the form of the dam body and the location of the fracture, determine the fault location on the dam slope for analysis;

[0038] In step 1, the dam body form includes two cases: a single slope to the bottom and a variable slope.

[0039] The specific process of step 1 is as follows:

[0040] (1) When the dam body is a single slope to the bottom (i.e., a single slope ratio), the dam slope closest to the fracture location is taken as the dam slope that produces the fracture. Let the horizontal length of the dam slope that produces the fracture be L, and the number of fracture locations be N. If N≥3, then L / N, 2L / N...NL / N are taken as the fault locations for analysis. The larger N is, the more accurate the result.

[0041] (2) When the dam body is of variable slope (the slope ratio changes), a fracture location needs to be added at the location where the slope ratio changes, in addition to the fault location determined in (1).

[0042] If the dam body is located on the hanging wall of the fault, analysis is not required if the distance from the edge of the influence zone of the steep thrust fault is greater than 500m and the distance from the edge of the influence zone of the gentle thrust fault is greater than 600m; if the dam body is located on the footwall of the fault, analysis is not required if the distance from the fault is greater than 300m.

[0043] Step 2: Obtain the maximum vertical displacement and maximum horizontal displacement of the fault from the existing geological data. Determine the settlement of the downstream dam slope at the fault location based on the maximum vertical displacement of the fault. The settlement is equal to the maximum vertical displacement of the fault.

[0044] Step 3: Obtain the dry unit weight and saturated unit weight of the dam material through density test in the dam material test, and obtain the shear strength index Φ0 and ΔΦ through triaxial test. Based on the fault position determined in Step 1, reduce the shear strength of the dam material within the range of the maximum horizontal variation of the fault position.

[0045] Wherein, Φ0 represents the effective stress shear strength index friction angle under one atmosphere of pressure; △Φ represents the effective stress shear strength index friction angle of coarse-grained material under σ3 plus one logarithmic period; σ3 represents the effective minor principal stress of the soil.

[0046] The reduction of shear strength at the fault location is based on the most unfavorable case. Therefore, Φ0 and ΔΦ at the fault location are both taken as 0. The dry unit weight at the fault location is taken as the minimum dry unit weight in the dam material, and the saturated unit weight at the fault location is taken as the minimum saturated unit weight in the dam material.

[0047] Step 4: Perform slope stability calculations on the fault locations identified in Step 1. The slope stability calculations employ the Swedish circular arc method and the simplified Bishop method.

[0048] The dam slope stability calculation includes the following calculation conditions:

[0049] Condition 1: The water level in front of the dam is the normal storage level. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0050] Condition 2: The water level in front of the dam is the normal storage level and the seismic condition is the peak ground acceleration of the earthquake designed for the earth-rock dam. The dam slope stability calculation is performed on the upstream and downstream slopes at the fault locations determined in step 1.

[0051] Condition 3: The water level in front of the dam is the normal storage level and the seismic condition is the peak ground acceleration of the check earthquake of the earth-rock dam. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0052] Condition 4: The water level in front of the dam is the normal storage level and the seismic condition is that the peak ground acceleration of the earth-rock dam check earthquake is increased by 10%. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0053] Condition 5: The water level in front of the dam is the normal storage level and the seismic condition is that the peak ground acceleration of the earthquake used to check the earth-rock dam is increased by 20%. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location proposed in step 1.

[0054] Step 5: Based on the calculation results obtained in Step 4, evaluate the stability of the dam slope when the fracture leads to the misalignment of the dam body;

[0055] Step 5 is as follows:

[0056] If the safety factors of the upstream and downstream dam slopes at different fault locations meet the specifications in the calculation results of conditions 1, 2 and 3, it indicates that the dam slopes are still in a stable state. If the calculation results of conditions 4 and 5 are smaller than those of condition 3, but still greater than 1 and higher than the specifications corresponding to conditions 2 and 3, it indicates that the dam slopes have a certain safety reserve.

[0057] Example 2

[0058] Step 1: Based on the form of the dam body and the location of the fracture, determine the fault location on the dam slope for analysis;

[0059] In this embodiment, the dam body is a single slope down to the bottom, with a downstream slope ratio of 1:1.75. The dam body is located on the lower plate of the fault, 300 meters from the fault point, and on the upper plate, less than 500 meters from the edge of the steep thrust fault influence zone. Therefore, the downstream dam slope is analyzed. Figure 2 As shown, if the number of fracture locations is set to N=4, then the downstream dam slope at 1 / 4 ( Figure 2 At point 1-1, i.e., L / N = 1 / 4, and at point 1 / 2 ( Figure 2 At point 2-2, i.e., L / N = 1 / 2, and at point 3 / 4 ( Figure 2 At point 3-3 (i.e., L / N = 3 / 4) and along the dam axis ( Figure 2 (4-4 positions in the middle) are designated as misalignment locations;

[0060] Step 2: Based on existing geological data, it is determined that the fault in this embodiment is an active fault from the Late Pleistocene, with a maximum vertical displacement Vd = 1m and a maximum horizontal displacement Ld = 1m. Therefore, the downstream dam slope at the fault location will settle by 1m along with the foundation.

[0061] Step 3: Obtain the dry unit weight and saturated unit weight of the dam material through density test in the dam material test, and obtain the shear strength index Φ0 and ΔΦ through triaxial test. Based on the fault position determined in Step 1, reduce the shear strength of the dam material within the range of the maximum horizontal variation of the fault position.

[0062] The dam body materials include main rockfill, downstream rockfill, cushion layer material, and transition material.

[0063] like Figure 3 As shown, the reduction of shear strength at the fault location is based on the most unfavorable case. Therefore, the shear strength indices Φ0 and ΔΦ at the fault location are both taken as 0. The dry unit weight at the fault location is taken as the minimum dry unit weight in the dam material, and the saturated unit weight at the fault location is taken as the minimum saturated unit weight in the dam material. See Table 1 for details.

[0064] Table 1 Material parameters for stability calculation of the lower reservoir dam

[0065]

[0066] Step 4: Perform slope stability calculations on the fault locations determined in Step 1. The slope stability calculations use the Swedish circular arc method and the simplified Bishop method.

[0067] The dam slope stability calculation includes the following calculation conditions:

[0068] Condition 1: The water level in front of the dam is the normal storage level. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0069] Condition 2: The water level in front of the dam is the normal storage level and the dam is a Class 1 structure. The design earthquake is taken as the peak ground acceleration of the ground with a 2% exceedance probability within 100 years, which is 0.485g. The dam slope stability calculation is carried out on the upstream slope and downstream slope at the fault location determined in step 1.

[0070] Condition 3: The water level in front of the dam is the normal storage level and the peak ground acceleration of the ground with a 1% exceedance probability within 100 years is 0.671g. The dam slope stability calculation is performed on the upstream slope and downstream slope at the proposed fault location determined in step 1.

[0071] Condition 4: The water level in front of the dam is the normal storage level and the seismic condition is that the peak ground acceleration of the earth-rock dam check earthquake is increased by 10%, i.e., 0.679g. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location proposed in step 1.

[0072] Condition 5: The water level in front of the dam is the normal storage level and the earthquake condition is that the peak ground acceleration of the earth-rock dam check earthquake is increased by 20%, i.e., 0.740g. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1.

[0073] The specific calculation results are shown in Tables 2 and 3;

[0074] Table 2 Summary of dam slope stability calculation results for the lower reservoir (simplified Bishop)

[0075]

[0076] Table 3 Summary of dam slope stability calculation results for the lower reservoir (Swedish circular arc method)

[0077]

[0078] Step 5: Based on the calculation results obtained in Step 4, evaluate the stability of the dam slope when the fracture leads to the misalignment of the dam body;

[0079] (1) If the safety factor of the upstream dam slope is the same at different fault locations and is greater than the specification requirements, it means that the settlement of the downstream dam slope has little impact on the stability of the upstream dam slope and can be ignored.

[0080] (2) If the safety factor of the downstream dam slope meets the requirements of the specification in different fault locations for conditions 1, 2 and 3, while the calculation results of conditions 4 and 5 decrease, but are still greater than 1 and higher than the specification requirements of conditions 2 and 3 (simplified Bishop greater than 1.2, Swedish circular method greater than 1.1), it indicates that the dam slope is still in a stable state and has a certain safety reserve.

[0081] Example 3: As shown above, a comparative analysis of the safety factors of downstream dam slopes at different fault locations reveals the following: ① Whenever a fault occurs in the dam slope, its safety factor is always less than that without fault, indicating that faulting of the dam slope will have a certain impact on the stability of the dam slope, which is consistent with general understanding; ② When faulting occurs at the dam crest, the safety factor is greater than that at the 1 / 4 position, and the safety factor is greater than that at the 2 / 4 and 3 / 4 positions. This indicates that, considering only the fault location and ignoring other variables, the safety factor first decreases and then gradually increases slightly as the fault location moves closer to the upstream dam slope, but it is always less than that without fault. Preliminary analysis suggests this is due to the relative relationship between the fault location and the dam slope slip arc. As the fault location moves closer to the upstream, the proportion of the weak surface generated by the fault within the slip arc range first increases and then decreases until the fault occurs at the dam crest, at which point the proportion of the weak surface generated by the fault within the slip arc range of the downstream dam slope reaches its minimum value. Figure 4 As shown.

[0082] Based on the above preliminary analysis, it can be concluded that even with a 1m vertical displacement, the downstream dam slope remains stable and has a certain safety margin.

[0083] Meanwhile, the limit equilibrium method has limitations in analyzing such problems because it cannot consider the influence of dynamic and other factors. Therefore, as the project's survey and design progresses, it is necessary to consider the influence of dynamic and displacement factors through numerical simulation methods such as finite element and discrete element methods, or to study the impact of fracture on the dam slope through physical experiments. Finally, the analysis results from various methods are compared and analyzed to reach a final conclusion on whether the dam slope is stable after the fracture leads to the faulting of the dam body.

Claims

1. A method for analyzing slope stability in earth-rock dams when fracture leads to slippage, based on the limit equilibrium method, characterized in that... The specific steps are as follows: Step 1: Based on the form of the dam body and the location of the fracture, determine the fault location on the dam slope for analysis; Step 2: Obtain the maximum vertical displacement and maximum horizontal displacement of the fault from the existing geological data, and determine the settlement of the downstream dam slope at the fault location based on the maximum vertical displacement of the fault. Step 3: Obtain the dry unit weight, saturated unit weight, and shear strength indices Φ0 and ΔΦ of the dam material. Reduce the shear strength of the dam material within the range of the maximum horizontal variation of the fault position determined in Step 1. In step 3, the reduction of shear strength at the misalignment location is carried out according to the most unfavorable case. Therefore, Φ0 and ΔΦ at the misalignment location are both taken as 0, the dry unit weight at the misalignment location is taken as the minimum dry unit weight in the dam material, and the saturated unit weight at the misalignment location is taken as the minimum saturated unit weight in the dam material. Step 4: Perform slope stability calculations for the fault locations determined in Step 1; In step 4, the stability calculation of the dam slope adopts the Swedish circular arc method and the simplified Bishop method; The dam slope stability calculation includes the following calculation conditions: Condition 1: The water level in front of the dam is the normal storage level. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1. Condition 2: The water level in front of the dam is the normal storage level and the seismic condition is the peak ground acceleration of the earthquake designed for the earth-rock dam. The dam slope stability calculation is performed on the upstream and downstream slopes at the fault locations determined in step 1. Condition 3: The water level in front of the dam is the normal storage level and the seismic condition is the peak ground acceleration of the check earthquake of the earth-rock dam. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1. Condition 4: The water level in front of the dam is the normal storage level and the seismic condition is that the peak ground acceleration of the earth-rock dam check earthquake is increased by 10%. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1. Condition 5: The water level in front of the dam is the normal storage level and the seismic condition is that the peak ground acceleration of the earth-rock dam check earthquake is increased by 20%. The dam slope stability calculation is performed on the upstream slope and downstream slope at the fault location determined in step 1. Step 5: Based on the calculation results obtained in Step 4, evaluate the stability of the dam slope when the fracture leads to the misalignment of the dam body; Step 5 is as follows: If the safety factors of the upstream and downstream dam slopes at different fault locations meet the specifications in the calculation results of conditions 1, 2 and 3, it indicates that the dam slopes are still in a stable state; if the calculation results of conditions 4 and 5 are smaller than those of condition 3, but still greater than 1 and higher than the specifications corresponding to conditions 2 and 3, it indicates that the dam slopes have a safety reserve.

2. The method for analyzing slope stability of an earth-rock dam when fracture leads to misalignment based on the limit equilibrium method, as described in claim 1, is characterized in that... In step 1, the dam body form includes two cases: a single slope to the bottom and a variable slope.

3. The method for analyzing slope stability of an earth-rock dam when fracture leads to misalignment based on the limit equilibrium method, as described in claim 1, is characterized in that... The specific process of step 1 is as follows: (1) When the dam body is a slope to the bottom, the dam slope closest to the fracture location is taken as the dam slope that causes the fault. Let the horizontal length of the dam slope that causes the fault be L and the number of fracture locations be N. Then, L / N, 2L / N...NL / N are taken as the fault locations for analysis. (2) In the case of a dam with a variable slope, a fracture location needs to be added at the location where the slope ratio changes, in addition to the fault location proposed in (1).

4. The method for analyzing slope stability of an earth-rock dam when fracture leads to misalignment based on the limit equilibrium method, as described in claim 3, is characterized in that... If the dam body is located on the hanging wall of a fault, then the distance from the edge of the influence zone of a steep thrust fault is greater than 500m, and the distance from the edge of the influence zone of a gentle thrust fault is greater than 600m, and no analysis will be performed. If the dam body is located on the footwall of the fracture, then no analysis will be performed if the distance to the fracture exceeds 300m.

5. The method for analyzing slope stability of an earth-rock dam when fracture leads to misalignment based on the limit equilibrium method, as described in claim 1, is characterized in that... In step 2, the settlement is equal to the maximum vertical dislocation of the fracture.

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