Method for selecting strength parameters of expansive soil slope by zoning

Abstract

The present invention discloses a method for taking values ​​of strength parameters of an expansive soil slope by zoning, comprising the following steps: 1) Zoning: dividing the engineering geological structure of the expansive soil slope into three zones according to soil-related indicators, namely, an atmospheric influence zone, a transition zone, and a non-influence zone; 2) taking values ​​of the strength parameters of the expansive soil in each zone according to the zoning of the expansive soil on the slope. The present invention performs zoning analysis on the expansive soil slope based on the vertical engineering geological structural characteristics of the expansive soil, and adopts different strength parameter value analysis methods according to the structural characteristics of each zoning zone, and finally obtains a strength parameter zoning value method for this type of slope. The method of the present invention provides support for the geological survey, analysis, and determination of support schemes of this type of slope, and finally achieves the purpose of improving the accuracy of slope stability analysis and providing a reasonable basis for the support design of this type of slope.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering, and in particular to a method for taking values ​​of strength parameters of an expansive soil slope by zones. Background Art

[0002] As a special type of soil, expansive soil (rock) is rich in hydrophilic clay minerals. Its physical properties such as clay content, liquid (plastic) limit and porosity are different from those of general clay soil (rock). Expansive soil has multiple fissures, and the development of fissures is random. The occurrence of fissures is variable, the scale of fissures varies greatly, the soil strength varies greatly, and it is more complex than general clay soil. Under the natural ground, the structure of expansive soil is vertically zonal. Usually, it is divided into atmospheric influence zone, transition zone and non-influence zone from the ground downward. The soil failure mode of each zone is different, and the soil strength is also different. At present, there is no mature technology for zoning strength parameters based on the engineering geological structure characteristics of expansive soil.

[0003] Relevant data show that the expansive soil in the atmospheric influence zone has been subjected to repeated dry-wet cycles, and the expansion and contraction cracks have developed, the integrity of the soil has been destroyed, and the surface layer is often divided into loose particles by tiny cracks. The color of the soil is mostly gray-brown, yellow-brown or gray, and large cracks are not developed. The moisture content of the soil varies greatly with rainfall. The pores are developed and the pores are relatively large. Most of them are weak-medium expansive soils. The mechanical strength of the soil is high in the non-rainy season, and the mechanical strength decreases rapidly when it rains or after being saturated with water. The soil in the atmospheric influence zone is mainly distributed with microcracks (less than 10cm in length) and small cracks (10cm to 50cm). After rain, creep-collapse deformation and damage due to the expansion and contraction cracks in the shallow surface layer are prone to occur.

[0004] The transition zone is a relative aquifer in the expansive soil layer, in which stagnant water is distributed in the upper layer. Groundwater generally moves along the open cracks and root holes under the action of gravity. The water volume of this layer is limited, and the annual fluctuation of the water level is generally 2m to 3m. The thickness of this layer is about 0m to 4m, the soil saturation is generally high, the annual fluctuation of water content is small, the color of the soil is generally yellow-brown, light brown, etc., the groundwater replacement effect is obvious, large cracks and long cracks are developed, and the cracks are mostly filled with gray-white to gray-green clay. The soil moisture content is generally above 24%. The strength of the transition zone is mainly controlled by large cracks (50cm to 200cm), and the failure mode is mostly controlled by the gently inclined structural surface.

[0005] The expansive soil in the non-influence zone is generally unsaturated, and the microcracks in the soil are mostly closed and mirror-smooth. There are many iron-manganese films on the crack surface. The soil permeability is weak, the porosity ratio is often less than 0.7, the pores are not developed, the soil is dense, and the atmospheric influence is slight. The strength of the soil in the non-influence zone is controlled by the randomly distributed long cracks (greater than 200cm), the crack-intensive zone and the soil. The non-influence zone mainly suffers from deep sliding failure controlled by the gently inclined structural surface.

[0006] For expansive soil slopes, the instability type is closely related to the engineering geological structure of the expansive soil, and different zones reflect different strength characteristics of the expansive soil.

[0007] The existing slope strength parameter selection methods usually adopt a unified selection method, which does not fully consider the structural zoning characteristics of expansive soil, affecting the rationality and accuracy of slope stability analysis results. Summary of the invention

[0008] The purpose of the present invention is to provide a method for taking strength parameters of expansive soil slopes in different zones in view of the deficiencies of the above-mentioned prior art, so as to provide a basis for taking strength parameters of engineering slopes in expansive soil areas, provide support for slope stability analysis, etc., and also provide a basis for the design of expansive soil slope management.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] A method for determining the strength parameters of an expansive soil slope by zone, comprising the following steps:

[0011] 1) Zoning: Vertically downward from the ground, the engineering geological structure of the expansive soil slope is divided into the atmospheric influence zone, transition zone and non-influence zone;

[0012] 2) The strength parameters of the expansive soil in the atmospheric influence zone, transition zone and non-influence zone are respectively determined; the strength parameters of the expansive soil are cohesion and internal friction angle.

[0013] Preferably, in step 2), the strength parameters of the expansive soil in the atmosphere-affected zone are determined based on the results of an in-situ large shear test or an indoor shear test of the soil.

[0014] Preferably, the method for determining the strength parameters of the expansive soil in the atmospheric influence zone is as follows:

[0015] If an in-situ large shear test is used, the soil cohesion C obtained by the in-situ large shear test is y and the soil internal friction angle φ y Cohesion C of expansive soil in atmospheric influence zone d and internal friction angle φ d ;

[0016] If indoor shear test is used, the cohesion C of the atmospheric influence zone expansive soil is d and internal friction angle φ d They are:

[0017] C d =α1·C s ,;

[0018] φ d =β1·φ s ;

[0019] Among them, C s is the residual strength and cohesion of soil obtained from indoor shear test, s is the internal friction angle of residual strength of soil obtained from indoor shear test; α1 and β1 are reduction coefficients, α1 is 0.55~0.68, and β1 is 0.53~0.69.

[0020] Preferably, the values ​​of α1 and β1 are adjusted within their value ranges according to the different swelling potentials of the expansive soil in the atmospheric influence zone. The stronger the swelling potential of the expansive soil, the larger the values ​​of α1 and β1.

[0021] Preferably, the in-situ large shear test is specifically to select soil 0.5m to 1.0m below the ground to carry out the in-situ large shear test under saturated state.

[0022] Preferably, the calculation of the strength parameters of the transition zone expansive soil is divided into the following two cases according to the different expansion potentials of the expansive soil:

[0023] If the transition zone is medium expansive soil or strong expansive soil, the expansive soil strength parameter is the shear strength parameter of the transition zone crack surface;

[0024] If the transition zone is weak expansive soil, the strength parameter of the expansive soil shall be taken as a comprehensive value based on the connectivity rate of the cracks with a gentle inclination angle in the soil.

[0025] Preferably, if the transition zone is weak expansive soil, the strength parameter of the expansive soil can also be obtained by using the strength reduction method: C g =α2×C 平均 ,φ g =β2×φ 平均 ; where C g is the cohesion of the expansive soil in the transition zone, φ g is the internal friction angle of the expansive soil in the transition zone; α2 is 0.7-0.8, β2 is 0.8-0.9; the soil index is the indoor saturated consolidation quick shear test value, where C 平均 and φ 平均 are the average values ​​of strength parameters obtained from the tests.

[0026] Preferably, the calculation of the strength parameters of the non-impact zone expansive soil is divided into the following four cases:

[0027] a. If the non-affected zone is strong expansive soil, the strength parameters of the expansive soil are comprehensively determined based on the connectivity rate of the cracks at the gentle inclination angle of the soil;

[0028] b. If the non-affected zone is medium expansive soil, when the soil develops large cracks or a zone with dense cracks, the strength parameter of the expansive soil is the crack surface strength. In other cases, the comprehensive value is taken according to the crack connectivity rate of the soil with a gentle inclination angle;

[0029] c. If the non-affected zone is weak expansive soil, the strength parameter of the expansive soil shall be the value of the indoor saturated consolidation quick shear test;

[0030] d. When there are stratum-lithology interfaces in the non-influence zone, the smaller strength parameter between the fracture surface and the stratum-lithology interface is taken as the controlling parameter for slope stability calculation.

[0031] Preferably, the method for comprehensively determining the value of the crack connectivity rate at a gentle inclination angle of the soil is as follows:

[0032] The shear strength parameters cohesion C and internal friction angle φ are calculated comprehensively according to the results of the shear test of the crack surface and the soil block. The calculation formula is as follows:

[0033] C=C J ×k+C R ×(1-k);

[0034] φ=tan -1 [tanφ J ×k+tanφ R ×(1-k)]

[0035] Among them C J C is the crack surface cohesion; R It is the cohesion of soil clod; is the internal friction angle of the crack surface; is the internal friction angle of the soil block; k is the connectivity rate of the gently inclined cracks calculated based on the broadband projection method.

[0036] Preferably, the calculation formula of the gentle angle crack connectivity rate k is as follows:

[0037]

[0038] Among them, ∑PBR and ∑JL represent the lengths of the soil and structural surface on the shear path, respectively.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention conducts zone analysis on the expansive soil slope based on the vertical engineering geological structure characteristics of the expansive soil, and adopts different strength parameter value analysis methods according to the structural characteristics of each zone, and finally obtains the strength parameter zone value method of this type of slope. The method of the present invention provides support for the geological survey, analysis and determination of the support scheme of this type of slope, and finally achieves the purpose of improving the accuracy of slope stability analysis and providing a reasonable basis for the support design of this type of slope. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the engineering geological structure of expansive soil slope. DETAILED DESCRIPTION

[0042] The following is a detailed description of the implementation of the present invention in conjunction with the accompanying drawings, but they do not constitute a limitation of the present invention and are only given as examples. At the same time, the advantages of the present invention will become clearer and easier to understand through the description.

[0043] The method for taking values ​​of the strength parameters of expansive soil by zoning is provided by the present invention. Based on the engineering geological structure characteristics, hydrogeological environment and slope instability mechanism of expansive soil, different testing methods and taking values ​​of the strength parameters of expansive soil are adopted according to the zoning characteristics, wherein the strength parameters refer to the shear strength parameters of the rock and soil mass, which are cohesion C and internal friction angle φ respectively.

[0044] The above method mainly comprises the following steps:

[0045] 1) Vertically downward from the ground, the expansive soil is divided into three zones, such as Figure 1 As shown in the figure, they are the atmospheric influence zone, transition zone and non-influence zone, and the judgment basis can refer to Table 1. The burial depth of each zone is determined according to the swelling and shrinkage of the soil, the local meteorological and hydrological environment, or according to exploration and testing.

[0046] Table 1: Vertical structural zoning of expansive soil

[0047]

[0048]

[0049] 2) According to the zoning of expansive soil in the slope, the strength parameters of the expansive soil in each zone are calculated and assigned.

[0050] ① Atmospheric influence zone: micro cracks are developed, and the soil may tend to be saturated during the rainy season. The strength parameters of the expansive soil in the atmospheric influence zone are determined by the test results of the in-situ large shear test or indoor shear test of the soil: cohesion C d and internal friction angle

[0051] a. If the in-situ large shear test is used, the soil cohesion C obtained by the in-situ large shear test is y and soil internal friction angle That is, the cohesion C of the expansive soil in the atmospheric influence zone d and internal friction angle The in-situ large shear test specifically selects soil 0.5m to 1.0m below the ground for an in-situ large shear test under saturated conditions.

[0052] b. If indoor shear test is adopted, according to the relationship between the residual strength of the expansive soil in the indoor test and the strength value of the in-situ large shear test, the cohesion C of the expansive soil in the atmospheric influence zone can be obtained by optimizing the indoor shear test results through the following optimization formula: d and internal friction angle

[0053] C d =α1·C s , α1=0.55~0.68

[0054] β1=0.53~0.69

[0055] Among them, the values ​​of reduction coefficients α1 and β1 are adjusted within their value range according to the different expansion potentials of the expansive soils in the atmospheric influence zone. The stronger the expansion potential of the expansive soil, the larger the values ​​of α1 and β1. Specifically, if the atmospheric influence zone is weak expansive soil, α1 and β1 take small values; if the atmospheric influence zone is strong expansive soil, α1 and β1 take large values; if the atmospheric influence zone is medium expansive soil, α1 and β1 take interval values. s is the residual strength and cohesion of soil obtained from indoor shear test. is the internal friction angle of soil residual strength obtained from indoor shear test.

[0056] ② Transition zone: According to the different expansion potential of expansive soil, the value of expansive soil strength parameter is divided into the following two cases:

[0057] a. If the transition zone is medium expansive soil or strong expansive soil, the expansive soil strength parameter is taken as the shear strength parameter of the transition zone crack surface according to the most unfavorable situation;

[0058] b. If the transition zone is weak expansive soil, the expansive soil strength parameter is preferably a comprehensive value based on the connectivity rate of the cracks at the gentle inclination angle of the soil body;

[0059] If the transition zone is weak expansive soil, the strength parameter of the expansive soil can also be obtained by the strength reduction method: C g =α2×C 平均 , C g The cohesion of the expansive soil in the transition zone, is the internal friction angle of the transition zone expansive soil; α2 and β2 are reduction coefficients; α2 can be 0.7-0.8, and β2 can be 0.8-0.9. The soil index is the indoor saturated consolidation quick shear test value, where C 平均 and are the average values ​​of strength parameters obtained from the tests.

[0060] ③ Non-impact zone: divided into the following four situations:

[0061] a. If the non-affected zone is a strong expansive soil with long and large structural surfaces, the strength parameters of the expansive soil are comprehensively determined based on the connectivity rate of the cracks with a gentle inclination angle of the soil;

[0062] b. If the non-affected zone is medium expansive soil, when the soil develops large cracks or a zone with dense cracks, the strength parameter of the expansive soil is the crack surface strength. In other cases, the comprehensive value is taken according to the crack connectivity rate of the soil with a gentle inclination angle;

[0063] c. If the non-affected zone is weak expansive soil, the strength parameter of the expansive soil shall be the value of the indoor saturated consolidation quick shear test;

[0064] d. When there are stratum-lithology interfaces in the non-affected zone, the smaller strength parameter between the fracture surface and the stratum-lithology interface is taken as the controlling parameter for slope stability calculation, and this structural surface is taken as the potential bottom sliding surface.

[0065] In the above method, the value of the expansive soil strength parameter is determined by the comprehensive value of the crack connectivity rate of the soil body with a gentle inclination angle as follows:

[0066] When the expansive soil is damaged by shear, the structural surface and the expansive soil between the structural surfaces jointly provide comprehensive shear strength. The shear strength parameters cohesion C and internal friction angle φ are calculated comprehensively according to the results of the shear test of the crack surface and the soil block. The calculation formula is as follows:

[0067] C=C J ×k+C R ×(1-k);

[0068]

[0069] Among them C J —crack surface cohesion; C R - soil cohesion; —Internal friction angle of crack surface; —internal friction angle of soil block; k—connectivity of gently inclined cracks obtained based on broadband projection method;

[0070] The fracture surface and soil block shear tests were carried out using the same method.

[0071] The calculation formula of the connectivity rate k of the gently inclined fracture is as follows:

[0072]

[0073] In the formula, ∑PBR and ∑JL represent the lengths of the soil and structural surface on the shear path, respectively;

[0074] In step 1), the engineering geological structure of the expansive soil is analyzed by zoning based on the field macroscopic indicators and test indicators of the expansive soil.

[0075] In step 1), the expansive soil is divided into an atmospheric influence zone, a transition zone and a non-influence zone according to the engineering geological structure characteristics of the expansive soil.

[0076] In step 1), the reference basis for zoning the engineering geological structure of the expansive soil slope includes: color, groundwater, degree of development of cracks and filling conditions, degree of development of holes, soil structure, general burial depth of soil, water content, and porosity.

[0077] Other parts not described belong to the prior art.

Claims

1. A method for determining the strength parameters of an expansive soil slope by zoning, characterized in that: The following steps are involved: 1) Zoning: Vertically downward from the ground, the engineering geological structure of the expansive soil slope is divided into the atmospheric influence zone, transition zone and non-influence zone; 2) respectively taking values ​​of the expansive soil strength parameters of the atmospheric influence zone, transition zone and non-influence zone; the expansive soil strength parameters are cohesion and internal friction angle; The method for determining the strength parameters of the expansive soil in the atmospheric influence zone is specifically as follows: If an in-situ large shear test is used, the soil cohesion C obtained by the in-situ large shear test is y and soil internal friction angle Cohesion C of expansive soil in atmospheric influence zone d and internal friction angle If indoor shear test is used, the cohesion C of the atmospheric influence zone expansive soil is d and internal friction angle They are: C d =α1·C s ; Among them, C s is the residual strength and cohesion of soil obtained from indoor shear test. is the internal friction angle of soil residual strength obtained from indoor shear test; α1 and β1 are reduction coefficients; The calculation of the strength parameters of the transition zone expansive soil is divided into the following two cases according to the different expansion potentials of the expansive soil: If the transition zone is medium expansive soil or strong expansive soil, the expansive soil strength parameter is the shear strength parameter of the transition zone crack surface; If the transition zone is weak expansive soil, the expansive soil strength parameter is taken based on the comprehensive value of the soil body's gentle angle crack connectivity or the strength reduction method: C g =α2×C 平均 , Among them C g The cohesion of the expansive soil in the transition zone, is the internal friction angle of the expansive soil in the transition zone; α2 and β2 are reduction coefficients; the soil index is taken from the indoor saturated consolidation quick shear test value, where C 平均 and are the average values ​​of strength parameters obtained from the tests; The calculation of the strength parameters of the non-influence zone expansive soil is divided into the following four cases: a. If the non-affected zone is strong expansive soil, the strength parameters of the expansive soil are comprehensively determined based on the connectivity rate of the cracks at the gentle inclination angle of the soil; b. If the non-affected zone is medium expansive soil, when the soil develops large cracks or crack-intensive zones, the strength parameter of the expansive soil is the crack surface strength. In other cases, the comprehensive value is taken according to the crack connectivity rate of the soil with a gentle inclination angle; c. If the non-affected zone is weak expansive soil, the strength parameter of the expansive soil shall be the value of the indoor saturated consolidation quick shear test; d. When there are stratum-lithology interfaces in the non-influence zone, the smaller strength parameter between the fracture surface and the stratum-lithology interface is taken as the controlling parameter for slope stability calculation.

2. The method for determining the strength parameters of expansive soil slopes according to claim 1 is characterized in that: In the step 2), the strength parameters of the expansive soil in the atmosphere-affected zone are determined based on the results of an in-situ large shear test or an indoor shear test of the soil.

3. The method for determining the strength parameters of expansive soil slope according to claim 1, characterized in that: The value of α1 is 0.55-0.68, and the value of β1 is 0.53-0.

69.

4. The method for determining the strength parameters of expansive soil slopes according to claim 3 is characterized in that: The values ​​of α1 and β1 are adjusted within their value range according to the different swelling potentials of the expansive soil in the atmospheric influence zone. The stronger the swelling potential of the expansive soil, the larger the values ​​of α1 and β1.

5. The method for determining the strength parameters of expansive soil slopes according to claim 3 is characterized in that: The in-situ large shear test specifically selects soil 0.5m to 1.0m below the ground to carry out the in-situ large shear test under saturated state.

6. The method for determining the strength parameters of expansive soil slopes according to claim 1 is characterized in that: The value of α2 is 0.7-0.8, and the value of β2 is 0.8-0.

9.

7. The method for determining the strength parameters of expansive soil slopes according to claim 1, characterized in that: The method for comprehensively determining the value of the crack connectivity rate according to the gentle inclination angle of the soil is as follows: Shear strength parameters such as cohesion C and internal friction angle are calculated comprehensively based on the results of shear tests on crack surface and soil block. The calculation formula is as follows: C=C J ×k+C R ×(1-k); Among them C J C is the crack surface cohesion; R It is the cohesion of soil clod; is the internal friction angle of the crack surface; is the internal friction angle of the soil block; k is the connectivity rate of the gently inclined cracks calculated based on the broadband projection method.

8. The method for determining the strength parameters of expansive soil slopes according to claim 7 is characterized in that: The calculation formula of the gentle angle crack connectivity rate k is as follows: Among them, ∑PBR and ∑JL represent the lengths of the soil and structural surface on the shear path, respectively.

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