A method for determining soil shear strength index based on side pressure test
By using a pressuremeter test-based method to obtain soil shear strength indices, the problems of stress environment changes after soil sample extraction and equipment complexity are solved. This method enables rapid, accurate, and low-cost determination of soil shear strength indices, is applicable to various soil types, and provides reliable data for engineering construction.
Patent Information
- Application Number
- CN202210808566.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-07-11
- Publication Date
- 2025-11-21
- Estimated Expiration
- 2042-07-11
AI Technical Summary
Existing technologies for determining soil shear strength parameters suffer from several problems, including changes in the stress environment after soil sample extraction, cumbersome operations, complex and expensive equipment, and difficulty in accurately obtaining shear strength parameters for cohesionless soils.
The method based on pressuremeter test is adopted. The geological conditions of the soil are to be studied through exploration. Pressuremeter test is designed and test boreholes are drilled. The test is conducted using a pressuremeter device to obtain at least two sets of test data. The data are then substituted into the expression for soil shear strength index to calculate the shear strength index.
It enables rapid, accurate, and low-cost acquisition of soil shear strength indices, and is applicable to cohesive, low-cohesive, and non-cohesive soils, improving testing efficiency and accuracy and providing reliable data support for engineering construction.
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Figure CN115165589B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of geotechnical engineering, and particularly relates to a method for determining soil shear strength index based on a side pressure test. BACKGROUND
[0002] With the rapid development of China's social economy, the construction industry, as one of the important driving forces for the rapid development of social economy, has gradually shown a faster growth trend with the rapid development of social economy. The overall development growth rate of the construction industry. The technology of foundation pit support and slope support is a key technical field in the construction industry, and whether the related design is accurate and reasonable directly affects the stability and reliability of the building support protection measures.
[0003] In the field of foundation pit support and slope support technology, soil shear strength index is a key design parameter essential in the design process of foundation pit support and slope support. The accuracy of the soil shear strength index directly affects the safety and quality of the project. For example, if the soil shear strength index is too high, it may cause safety hazards during construction; if the soil shear strength index is too low, it may increase the project investment and waste social resources.
[0004] In the prior art, the soil shear strength index is usually tested by sampling for indoor soil test or in-situ test. When sampling for indoor soil test, undisturbed soil samples are taken during the survey and transported to the laboratory for testing. This approach has the following main drawbacks: (1) Undisturbed soil samples are taken during the survey, and the stress environment of the soil samples changes after they are taken out. The physical and mechanical properties of the soil also change from the original state. In addition, the soil samples may be disturbed during sampling, storage, transportation, and handling. Furthermore, the soil test operation process is complex, and the proficiency of the operator affects the performance of the prepared soil samples. (2) During indoor testing, the stress path of the soil samples is different from the original state. The soil samples undergo unloading rebound and recompression shear processes, and the confining pressure conditions, drainage conditions, and actual shear surface conditions are all conducted under ideal indoor conditions, which are different from the actual conditions on the construction site. (3) For non-cohesive or less cohesive soils such as fill, sand, and gravel, it is difficult to take undisturbed soil samples during the survey. Even if undisturbed soil samples are taken through strict means, large-scale direct shear or large-scale triaxial shear tests are required for coarse-grained soils. Such experimental operations are more complex and require more stringent conditions. Moreover, general geotechnical laboratories often lack large-scale direct shear or large-scale triaxial instruments, making it difficult to conduct indoor shear tests on coarse-grained soils, and it is difficult to obtain the shear strength index through this approach.
[0005] In-situ testing generally employs vane shear tests and in-situ direct shear tests, which are conducted in situ, essentially maintaining the natural state of the soil and providing stronger representativeness than laboratory tests. However, certain shortcomings remain: (1) The control of shear displacement often uses mechanical systems, resulting in a high failure rate. (2) The stress environment of the soil near the shear probe is complex, and the area of the soil being sheared is greatly affected by different soil types, making it impossible to determine precisely. Furthermore, the probe is affected by the passive earth pressure of the soil in front in the shear direction. (3) Vane shear tests are often only applicable to determining the shear strength index of saturated soft clay under undrained conditions. In-situ direct shear tests are applicable to rock masses and general soils, but their applicability to soft clay and loose soil needs improvement. In addition, the equipment used in these tests is large, the operation is complex, manual excavation or leveling is required to form test pits, the test cycle is long, and the test cost is high, so they are not commonly used in general engineering projects. Summary of the Invention
[0006] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for determining the shear strength index of soil based on pressuremeter test. This method can directly and accurately obtain the relevant parameters of the soil to be studied, and the accuracy of the soil parameters will not be affected by changes in the geological conditions of the soil to be studied. Furthermore, the shear strength index of the soil to be studied can be reasonably obtained through these relevant parameters.
[0007] To achieve the above objectives, the present invention provides a method for determining the shear strength index of soil based on pressuremeter tests, comprising the following steps:
[0008] The exploration aims to study the geological conditions of the soil.
[0009] Based on the geological conditions, a pressure meter test was designed and a test borehole was drilled.
[0010] Insert the pressure gauge into the test borehole to conduct a pressure gauge test and obtain at least two sets of test data for the soil to be studied.
[0011] Substitute the at least two sets of test data into the expression for soil shear strength index to calculate the shear strength index of the soil to be studied.
[0012] As a further preferred embodiment of the present invention, the expression for the soil shear strength index is derived based on Rankine's passive earth pressure theory.
[0013] As a further preferred embodiment of the present invention, the expression for the soil shear strength index is as follows:
[0014]
[0015] In the formula, ρ is the internal friction angle; c is the cohesion; K pKp is the passive earth pressure coefficient; z is the depth when collecting the test data, z1 and z2 are the first group of test data collection depth and the second group of test data collection depth respectively; σ p Kp is the passive earth pressure coefficient; z is the depth when collecting the test data, z1 and z2 are the first group of test data collection depth and the second group of test data collection depth respectively; σ p1 Kp is the passive earth pressure coefficient; z is the depth when collecting the test data, z1 and z2 are the first group of test data collection depth and the second group of test data collection depth respectively; σ p2 Kp is the passive earth pressure coefficient; z is the depth when collecting the test data, z1 and z2 are the first group of test data collection depth and the second group of test data collection depth respectively; σ
[0016] As a further preferred embodiment of the present application, the passive earth pressure coefficient is represented as And z1>z2, σ p1 >σ p2 , σ p1 -σ p2 >γ(z1-z2), γ is the specific gravity of the soil to be studied.
[0017] As a further preferred embodiment of the present application, any two groups of test data are selected from the test data and brought into the soil shear strength index expression to obtain multiple groups of soil shear strength indexes.
[0018] As a further preferred embodiment of the present application, the number of groups of test data is not less than 4 groups, and the number of groups of soil shear strength indexes that can be obtained is not less than 6 groups at most.
[0019] As a further preferred embodiment of the present application, when the number of groups of shear strength indexes is less than 6 groups, the shear strength index of the soil to be studied is the average value of each group of shear strength indexes; when the number of groups of shear strength indexes is greater than or equal to 6 groups, the shear strength index of the soil to be studied is the standard value of each group of shear strength indexes.
[0020] As a further preferred embodiment of the present application, the test data at least includes the lateral pressure test depth, the limit pressure at the corresponding depth, and the limit pressure is equal to the passive earth pressure.
[0021] As a further preferred embodiment of the present application, when the soil to be studied is cohesionless soil layer, the soil shear strength index expression is:
[0022]
[0023] In the formula, is the internal friction angle; c is the cohesion; σ p is the passive earth pressure; z is the depth when collecting the test data; γ is the specific gravity of the soil to be studied.
[0024] As a further preferred embodiment of the present application, the specific gravity of the soil to be studied is determined by any one of the following methods: on-site determination by sand pouring method, sampling for indoor test, and estimation by engineering experience analogy.
[0025] The above technical features can be combined with each other as long as they do not conflict with each other.
[0026] Overall, compared with the prior art, the above technical solutions conceived by the present application have the beneficial effects including:
[0027] (1) The method for determining soil shear strength index based on lateral pressure test of the present application accurately obtains the geological conditions of the soil to be studied by field exploration. The test process of the lateral pressure test is accurately designed based on the geological conditions of the soil to be studied, and the test drilling is started at the corresponding position of the soil to be studied based on the test process of the lateral pressure test, so as to improve the test efficiency of the subsequent lateral pressure test. Then, the lateral pressure test is performed by placing the lateral pressure device into the test drilling, and the test data of the soil to be studied are obtained. The test data are substituted into the soil shear strength index relationship expression, effectively solving the problem of judging the shear strength index of cohesive soil, less cohesive soil, and non-cohesive soil, and having the characteristics of wide applicability, simple operation, high test efficiency, and low use cost.
[0028] (2) The method for determining soil shear strength index based on lateral pressure test of the present application can quickly calculate the soil shear strength index corresponding to the two groups of test data by selecting any two groups of test data from at least two groups of test data and substituting them into the soil shear strength index expression. By flexibly selecting multiple data sets composed of any two groups of test data from at least two groups of test data and substituting them into the soil shear strength index expression, the soil shear strength index of the soil to be studied in all directions and with high accuracy can be accurately calculated, providing accurate and reliable basis for engineering construction.
[0029] (3) The method for determining soil shear strength index based on lateral pressure test of the present application divides the soil to be studied into cohesive soil layer and non-cohesive soil layer by exploring the geological conditions of the soil to be studied, flexibly selects soil shear strength index expressions with different expression forms based on the geological conditions of the soil to be studied, and accurately designs the drilling position, test depth, etc. in the lateral pressure test according to the geological conditions of the soil to be studied, so as to ensure that the limit pressure of all positions of the soil to be studied can be accurately and comprehensively collected.
[0030] (4) The method for determining the soil shear strength index based on the lateral pressure test has the advantages of simple operation, high applicability, accurate collection of at least two groups of test data containing the limit pressure of the soil to be studied by using the lateral pressure test, equivalent of the limit pressure to the passive earth pressure in the expression of the soil shear strength index, and accurate acquisition of the soil shear strength index of the soil to be studied by substituting the test data into the expression of the soil shear strength index, so that the operator can accurately and quickly acquire the soil shear strength index of the soil to be studied after completing the lateral pressure test on site, accurate engineering guidance is provided for engineering construction, and excellent economic benefits and popularization value are achieved. BRIEF DESCRIPTION OF DRAWINGS
[0031] Figure 1 is a flow chart of the method for determining the soil shear strength index based on the lateral pressure test in the application. DETAILED DESCRIPTION
[0032] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.
[0033] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.
[0034] In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features limited by "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically limited.
[0035] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.
[0037] Example:
[0038] like Figure 1 As shown in the preferred embodiment of this application, the method for determining the soil shear strength index based on pressuremeter test is mainly used to obtain the soil shear strength index of the soil under different geological conditions in the field in an accurate, rapid and low-cost manner, so as to provide accurate and reliable data support for engineering construction design, and avoid useless increase in engineering investment and waste of social resources while ensuring the stability of the engineering construction structure.
[0039] Specifically, the method for determining the soil shear strength index based on the pressuremeter test in the preferred embodiment of the present invention includes the following steps:
[0040] S1. Explore the geological conditions of the soil to be studied;
[0041] S2. Based on the geological conditions, design a pressure meter test and drill a test borehole;
[0042] S3. Place the pressure gauge into the corresponding test borehole, conduct the pressure gauge test, and obtain at least two sets of test data for the soil to be studied.
[0043] S4. Substitute at least two sets of test data into the expression for soil shear strength index to calculate the shear strength index of the soil to be studied.
[0044] The soil body to be studied is preferably obtained by drilling on site, and the geological condition of the soil body to be studied is obtained by analyzing the sample. Further preferably, the geological condition of the soil body to be studied is divided into three types of soil properties, i.e., clay layer, less cohesive soil layer, or non-cohesive soil layer, and the unit weight of the soil body to be studied is determined at the same time. Preferably, the unit weight of the soil body to be studied is determined by any one of the following methods: sand filling method on site, indoor test by sampling, and engineering experience analogy estimation, so as to facilitate the calculation of the shear strength index of the soil body.
[0045] Further, in a preferred embodiment of the present application, the test steps of the lateral pressure test are designed according to the geological condition under the premise that the geological condition of the soil body to be studied is determined, and the key parameters of the test borehole, such as the borehole distribution and the borehole depth, required for the lateral pressure test are divided. For example, when the soil body to be studied is a non-cohesive soil layer, the test position needs to be adaptively increased during the lateral pressure test to avoid the influence between adjacent two lateral pressure tests.
[0046] Preferably, the test borehole can be uniformly arranged with several test boreholes in the soil body to be studied, so as to ensure that the lateral pressure test can cover all strata of the soil body to be studied, and thus the shear strength index of the soil body to be studied is comprehensive and accurate.
[0047] Further, after the test borehole is drilled, the lateral pressure tester is sequentially placed into the test borehole, the lateral pressure test is sequentially performed at different depths of the test borehole, and at least two groups of test data of the soil body to be studied at different test boreholes and different depths are recorded.
[0048] Preferably, the test data at least include the lateral pressure test depth and the ultimate pressure of the soil body to be studied at the corresponding depth, and the ultimate pressure of the soil body to be studied in the lateral pressure test is equal to the passive earth pressure of the soil body to be studied under the limit equilibrium condition (i.e., the major principal stress of the soil body to be studied under the critical state of passive pressure and shear failure), so that the at least two groups of test data obtained by the lateral pressure test can also be considered to at least include the lateral pressure test depth and the passive earth pressure of the soil body to be studied at the corresponding depth, so as to facilitate the subsequent calculation of the shear strength index of the soil body to be studied based on the test data.
[0049] Further, in a preferred embodiment of the present application, the at least two groups of test data obtained by the lateral pressure test are substituted into the expression of the shear strength index of the soil body to be studied, and the shear strength index of the soil body to be studied is calculated. Preferably, the expression of the shear strength index of the soil body to be studied is as follows:
[0050]
[0051] In the formula, φ is the internal friction angle, c is the cohesion, K is the pressure coefficient, and P is the ultimate pressure of the soil body to be studied. p K is the passive earth pressure coefficient; z is the depth when collecting the test data, z1 and z2 are the first group of test data collection depth and the second group of test data collection depth respectively; σ p is the passive earth pressure, σ p1 p2 is the passive earth pressure of the first group of test data collection and the passive earth pressure of the second group of test data collection respectively.
[0052] The soil shear strength index expression is derived from the Rankine passive earth pressure calculation formula. Specifically, the Rankine passive earth pressure calculation formula is derived from the passive earth pressure σ p , cohesion c and internal friction angle of the soil under the limit equilibrium condition.
[0053]
[0054] The passive earth pressure coefficient formula is:
[0055]
[0056] The specific gravity γ of the soil to be studied has been obtained through relevant tests during the geological survey stage. In the specific derivation process, first, select any two groups of test data from the oedometer test to substitute into formula (2) to construct an equation group with only K p and c as unknowns. By solving the equation group, the expressions of K p and c can be obtained. Then, the expression of is calculated by formula (3), and the expressions of c and are combined to construct the soil shear strength index formula (1) of the soil to be studied.
[0057] Further preferably, in the above formula, the expression of K p can be obtained by solving the equation group about K p :
[0058]
[0059] When selecting any two groups of test data from the oedometer test, the selected test data satisfies the parameter selection requirements of z1>z2, σ p1 >σ p2 , σ p1 -σ p2 >γ(z1-z2) to ensure that the internal friction angle obtained by the soil shear strength index expression is greater than 0, so that the solved internal friction angle satisfies the basic mechanical properties and mechanical logic.
[0060] In order to ensure the accuracy of the calculation of the shear strength index of the soil to be studied, in another preferred embodiment of the present application, when calculating the shear strength index of the soil to be studied, any two groups of test data are selected from the test data and brought into the expression of the shear strength index of the soil to be studied, and a plurality of groups of shear strength indexes of the soil to be studied are obtained, so as to more comprehensively determine the shear strength index of the soil to be studied. Preferably, the test data can be preferably not less than 4 groups according to the geological conditions of the soil to be studied, so as to ensure that not less than 6 groups of shear strength indexes can be obtained when calculating the shear strength index.
[0061] Further preferably, when the number of groups of shear strength indexes X is less than 6 groups, the average value of the internal friction angle and the average value of the cohesion of the soil to be studied are obtained by adding the internal friction angle and the cohesion in the plurality of groups of shear strength indexes and dividing by the number of groups, and the average value of the internal friction angle and the average value of the cohesion are the shear strength indexes of the soil to be studied; and when the number of groups of shear strength indexes X is greater than or equal to 6 groups, the shear strength indexes of the soil to be studied are obtained by calculating the standard values of the internal friction angle and the cohesion in the plurality of groups of shear strength indexes, and the calculated standard values are the shear strength indexes of the soil to be studied, thereby distinguishing the accuracy of the calculation of the shear strength index of the soil to be studied. Of course, the number of groups of shear strength indexes X can be any one of 5 groups or 7 groups, and the number of groups of shear strength indexes X is obtained according to the geological conditions of the soil to be studied, for example, according to the range of the soil to be studied, the soil layer condition, the research depth and other parameters.
[0062] In addition, in another preferred embodiment of the present application, when it is determined through geological exploration that the geological conditions of the soil to be studied are non-cohesive soil layer, since the cohesion c of the non-cohesive soil layer is zero, at this time, the expression of the shear strength index of the soil to be studied is:
[0063]
[0064] The test data and the unit weight of the soil to be studied can be directly brought into the above formula (5) to directly obtain the shear strength index of the soil to be studied.
[0065] Further, in a preferred embodiment of the present application, after the determination of the shear strength index of the soil to be studied is completed each time, the geological exploration parameters used in the determination of the shear strength index, the test parameters of the lateral pressure test, the test data obtained by the lateral pressure test, and the shear strength index of the soil to be studied are collected and constructed into a lateral pressure test database. Preferably, after the database is completed, the related parameters in the calculation of the shear strength index each time are compared with the database, and when there is a difference between the actual calculation of the shear strength index and the data stored in the database, it can be determined whether the calculation of the shear strength index of the soil to be studied is correct through the traditional method, and when it is found that there is an error in the data in the database, the data is updated in time.
[0066] Further preferably, a shear strength index calculation standard program is constructed based on the database, and in actual use, the test data obtained from the lateral pressure test of the soil to be studied is input into the program to directly obtain the shear strength index of the soil to be studied.
[0067] Of course, in a preferred embodiment of the present application, the database and the shear strength index calculation standard program can also be improved by monitoring data obtained during the actual use of foundation pit support or slope support, to realize automatic iteration of the lateral pressure test-based soil shear strength index determination method.
[0068] A lateral pressure test-based soil shear strength index determination method in the present application is simple to operate and highly applicable, accurately collects at least two groups of test data containing limit pressure of the soil to be studied using a lateral pressure test, and equivalent the limit pressure to passive earth pressure in the expression of the soil shear strength index, then substitutes the test data into the expression of the soil shear strength index to accurately obtain the shear strength index of the soil to be studied, so that the operator can accurately and quickly obtain the soil shear strength index of the soil to be studied after completing the lateral pressure test on site, to provide accurate engineering guidance for engineering construction, and has excellent economic benefits and promotional value.
[0069] Those skilled in the art will readily understand that the above description is only a preferred embodiment of the present application and is not intended to limit the present application, and any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.
Claims
1. A method for determining the shear strength index of a soil mass based on a side pressure test, characterized in that, The method comprises the following steps: Exploring the geological condition of the soil to be studied; The geological condition of the soil to be studied includes clay layer, little clay layer or no clay layer; Based on the geological condition, a lateral pressure test is designed and a test borehole is drilled; The lateral pressure test is performed by extending a lateral pressure device into the test borehole, and at least two groups of test data of the soil to be studied are obtained; The at least two groups of test data are substituted into the expression of the soil shear strength index to calculate the shear strength index of the soil to be studied; The expression of the soil shear strength index is derived according to the Rankine passive earth pressure theory. From the test data, any two groups of test data are selected to be substituted into the expression of the soil shear strength index to obtain a plurality of groups of soil shear strength indexes. wherein is the internal friction angle; c is the cohesion; K p is the passive earth pressure coefficient; z is the depth at which the test data is collected, z1 and z2 are the first and second set of test data collection depths, respectively; σ p is the passive earth pressure, σ p1 , σ p2 are the passive earth pressures collected from the first and second set of test data, respectively; The passive earth pressure coefficient is expressed as and z1>z2, σ p1 >σ p2 ,σ p1 -σ p2 >γ(z1-z2), γ is the specific weight of the soil under study.
2. The method for determining the soil shear strength index based on the side pressure test according to claim 1, wherein, The number of the test data groups is not less than 4, and the number of the soil shear strength index groups is not less than 6.
3. The method for determining the soil shear strength index based on the side pressure test according to claim 2, wherein, When the number of the soil shear strength index groups is less than 6, the shear strength index of the soil to be studied is the average value of the shear strength indexes of the groups; when the number of the soil shear strength index groups is greater than or equal to 6, the shear strength index of the soil to be studied is the standard value of the shear strength indexes of the groups.
4. The method for determining soil shear strength index based on side pressure test according to claim 3, wherein, The test data at least include the lateral pressure test depth and the limit pressure at the corresponding depth, and the limit pressure is equal to the passive earth pressure.
5. The method for determining the soil shear strength index based on the side pressure test according to claim 1, wherein, When the soil to be studied is a no clay layer, the expression of the soil shear strength index is:
6. The method for determining the soil shear strength index based on the side pressure test according to claim 1, wherein, The specific gravity of the soil to be studied is determined by any one of the following methods: in-situ sand filling method, indoor test by sampling, and engineering experience analogy estimation. wherein C is the cohesion; and p z is the depth at which the test data is collected; and γ is the unit weight of the soil under investigation.
7. The method for determining the soil shear strength index based on the side pressure test according to claim 1 or 6, wherein,