A field unloading shear test method for gravel soil and strongly weathered rock

Abstract

The present invention discloses a field unloading shear test method for crushed stone soil and highly weathered rock. The method comprises the following steps: Step 1: Select a test site on site; Step 2: Excavate a test pit to measure the density of the crushed stone soil or highly weathered rock on site; Step 3: Measure the topographic cross section of the measured slope along the slope; Step 4: Excavate a dividing groove along both sides of the topographic cross section, leaving a rectangular specimen; Step 5: Excavate a leading-edge unloading groove; Step 6: Measure the shear sliding surface within the dividing groove; Step 7: Draw a cross-sectional diagram of the sliding body based on the measured topographic cross section and the shear sliding surface, dividing the sliding body into several strips; Step 8: Repeat the above steps at an adjacent location on the test site to draw another cross-sectional diagram of the sliding body; Step 9: Determine the shear strength parameters of the specimen based on the two cross-sectional diagrams of the sliding body obtained in the above steps. The method simulates the instability mode of the rock and soil mass on site and has the advantages of high reliability and high accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of geotechnical engineering testing, and more particularly to a field unloading shear test method for crushed stone soil and strongly weathered rock. Background Art

[0002] Gravel soil and strongly weathered rock are often encountered during geotechnical engineering surveys in mountainous areas. Gravel soil is primarily formed by residual accumulation, slope accumulation, collapse, flooding, alluvial deposits, and glacial accumulation. Its composition is mostly non-cohesive gravel, crushed stone (pebbles), and boulders (drift stones). It is difficult to obtain soil samples with their original structure, so in indoor tests, artificially reshaped samples are used to conduct shear tests on gravel soil. However, the particle sizes of crushed stone, pebbles, and other materials often encountered in engineering projects range from 60mm to 500mm, or even over 1000mm. The determination of their shear strength is beyond the capabilities of existing large-scale shear testers. Strongly weathered rock is usually mostly discontinuous skeletons or core stones, with a small portion decomposed into soil or sand. In terms of testing difficulty, it has similar characteristics to gravel soil.

[0003] Field in-situ shear tests, in which the specimen structure remains intact, are a promising method. Currently, the primary in-situ shear test method for gravel soils is the horizontal push method. This test involves excavating a test pit, creating a rectangular test soil volume with three sides open to the air, and then applying a horizontal thrust until shear failure occurs. The horizontal push method is simple and offers significant advantages for sample preparation for larger-particle gravel soils and strongly weathered rock. However, its theoretical basis is insufficient, resulting in low reliability and precision in test results.

[0004] In summary, mechanical testing of crushed stone soil and highly weathered rock is difficult due to their unique composition and structure. However, these are often the rock masses for which mechanical parameters need to be obtained in order to evaluate and utilize them in engineering construction. Therefore, it is necessary to further develop shear testing methods for crushed stone soil and highly weathered rock with high reliability and precision. Summary of the Invention

[0005] The purpose of the present invention is to provide a field unloading shear test method for crushed stone soil and strongly weathered rock. It is a field unloading shear test method based on the instability mode and stability calculation method of crushed stone soil and strongly weathered rock slopes. It simulates the instability mode of the on-site rock and soil body and has the characteristics of high reliability and high precision.

[0006] In order to achieve the above object, the technical solution of the present invention is: a field unloading shear test method for crushed stone soil and strongly weathered rock, characterized by comprising the following steps:

[0007] Step 1: Select a slope with an open area and a gentle-steep-gentle or gentle-steep slope from top to bottom as the test site to excavate the test pit. Gentle slopes are convenient for construction, while steep slopes are conducive to sample preparation.

[0008] Step 2: Excavate a test pit and use the water filling method or sand filling method to measure the γ density of the gravel soil or strongly weathered rock on site;

[0009] Step 3: Topographic cross section along the measured slope;

[0010] Step 4: Dig a split groove along both sides of the terrain section, leaving a cuboid as a specimen;

[0011] Step 5: Excavate the front edge unloading groove and observe the dividing grooves on both sides at the same time. When the specimen produces a through shear surface and slides, stop excavating the front edge unloading groove;

[0012] Step 6: Measure the shear sliding surface in the dividing groove;

[0013] Step 7: Draw a sliding body cross-section diagram based on the measured topographic cross-section and shear sliding surface, and divide the sliding rock and soil on the sample into several strips and blocks;

[0014] Step 8: Repeat steps 3-7 above at a location adjacent to the previous specimen in the test site to draw another sliding body cross-section diagram;

[0015] Step 9: Based on the two sliding body cross-sectional views obtained in the above steps, the strip method of slope stability calculation is used to establish equations respectively, and then the equation group is solved to obtain the shear strength parameters of the sample.

[0016] In the above technical solution, in step 4, in order to control the sliding path, the size of the sample should meet the following requirements: length along the slope > height > width across the slope > maximum particle size.

[0017] In the above technical solution, in step 4, the dividing groove includes a left dividing groove and a right dividing groove; the sample is located between the left dividing groove and the right dividing groove; the front edge unloading groove is located at the front lower part of the sample and between the left dividing groove and the right dividing groove;

[0018] In step 6, the shear sliding surface is measured in the left dividing groove or the right dividing groove.

[0019] In the above technical solution, in step 7, the sliding body is divided into a number of strips and blocks according to the turning points or equal distances of the sliding surface.

[0020] In the above technical solution, according to the sample strip formed in step 7, in step 9, the shear strength parameter is derived as follows:

[0021] The stress analysis of the first specimen block i is as follows:

[0022] N 1i =W 1i cosa 1i

[0023] T 1i =W 1i sinα 1i

[0024]

[0025]

[0026] where τ 1i =T 1i

[0027] Right now

[0028] Where c represents the cohesion of the sample, kPa; Indicates the internal friction angle of the sample, degrees; W 1i represents the gravity of the first sample block i, kN / m; T 1i represents the tangential force on the sliding surface of the first sample block i; N1i represents the normal force on the sliding surface of the first sample block i, kN; τ 1i Indicates the shear strength of the first specimen strip i on the sliding surface, kPa; l 1i represents the length of the sliding surface of the first sample block i, m; α 1i represents the angle between the normal line of the sliding surface of the first specimen strip i and the vertical line, in degrees;

[0029] According to the force balance on the sliding surface, the equation for the first specimen is established:

[0030]

[0031] Among them, W 1i =γA 1i ②

[0032] Substituting equation ② into equation ①, we get:

[0033]

[0034] Among them, c, γ is an invariant, we get:

[0035]

[0036] Where: c represents the cohesion of the sample, kPa; represents the internal friction angle of the sample, degrees; γ represents the density of the sample, kN / m 3 ; l 1i represents the length of the sliding surface of the first sample block i, m; α 1i W represents the angle between the normal line of the sliding surface of the first sample block i and the vertical line, degrees;1i A represents the weight of the first sample block i, kN / m; 1i Represents the area of ​​the first sample block i, m 2 ;

[0037] According to the above method of establishing the equation of the first sample, establish the equation of the second sample:

[0038]

[0039] Where: c represents the cohesion of the sample, kPa; represents the internal friction angle of the sample, degrees; γ represents the density of the sample, kN / m 3 ; l 2i represents the length of the sliding surface of the second sample block i, m; α 2i A represents the angle between the normal line of the sliding surface of the second sample block i and the vertical line, degrees; 2i Represents the area of ​​the second sample block i, m 2 ;

[0040] Combining equations ④ and ⑤ to form a system of linear equations with two variables, we get:

[0041]

[0042] Solving the system of equations, we get:

[0043]

[0044]

[0045] Where: c represents the cohesion of the sample, kPa; represents the internal friction angle of the sample, degrees; γ represents the density of the sample, kN / m 3 ; l 1i 、l 2i are the lengths of the sliding surface of the first and second specimen strip i, m; α 1i , α 2i The angles between the normal line of the sliding surface of the first and second specimen blocks i and the vertical line, degrees; A 1i 、A 2i The area of ​​the first and second sample blocks i, m 2 ; Among them, c, is an unknown number, and the remaining parameters can be measured directly.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The method provided by the present invention fully simulates the instability mode of field gravel soil and strongly weathered rock slopes, can reflect the actual geological conditions on site, has high accuracy, simple procedures, low costs, and strong applicability;

[0048] (2) In the method provided by the present invention, the calculation method of the shear strength parameters of crushed stone soil and strongly weathered rock is the inverse process of slope stability calculation, which has sufficient theoretical basis and the reliability of the calculated shear strength parameters is high;

[0049] (3) The method provided by the present invention not only solves the problem that it is difficult to obtain shear strength parameters close to the actual ones for gravel soil and strongly weathered rock, but also can observe the instability mode of the slope during the test, which is also of beneficial value for the study of the instability mechanism of the slope. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a diagram of the field unloading shear test device of the present invention.

[0051] Figure 2 It is a cross-sectional view of the sliding body of the present invention.

[0052] Figure 3 Schematic diagram of the force applied to the bar i in the present invention.

[0053] Figure 4 Flowchart of the present invention.

[0054] exist Figure 2 In the figure, A1 is the topographic line; A2 is the sliding body; A3 is the sliding surface; and A4 is the leading edge unloading groove.

[0055] exist Figure 3 In, W i is the gravity of bar i; T i is the tangential force on the sliding surface of block i; N i is the normal force on the sliding surface of block i; τ i is the shear strength on the sliding surface of strip i; l i is the length of the sliding surface of block i; α i is the angle between the normal line of the sliding surface of block i and the vertical line.

[0056] Among them, 1-topography contour line and elevation value, 2-sample, 3-left dividing groove, 4-right dividing groove, 5-front edge unloading groove. DETAILED DESCRIPTION

[0057] The following detailed description of the embodiments of the present invention is given in conjunction with the accompanying drawings, which do not limit the present invention but are merely examples. The description makes the advantages of the present invention clearer and easier to understand.

[0058] Referring to the accompanying drawings, a field unloading shear test method for crushed stone soil and strongly weathered rock is characterized by comprising the following steps:

[0059] Step 1: Select a slope with a gentle-steep-gentle or gentle-steep slope from top to bottom and an open area around it as the test site (e.g. Figure 1 As shown in the figure, steep slopes with large slope angles and close to the critical stability state should be selected as the specimen locations in the engineering area, while gentle slopes and open areas can ensure the safety and controllability of the test;

[0060] Step 2: Excavate a test pit and use the water or sand filling method to measure the γ density of the gravel soil or strongly weathered rock on site. A representative area should be selected in the vicinity for measurement.

[0061] Step 3: Follow the slope to the topographic section of the measured slope. The topographic section line should be the center line of the proposed sample.

[0062] Step 4: Dig the split groove along both sides of the terrain section (such as Figure 1 As shown), set aside a rectangular specimen (as Figure 1 The size of the sample should meet the following requirements: along-slope length L> height H> transverse-slope width B> maximum particle size D;

[0063] Step 5: Excavate the front edge unloading groove (such as Figure 1 As shown), while splitting the grooves on both sides (as Figure 1 When the specimen produces a through shear surface and slides, the excavation is stopped;

[0064] Step 6: In the split slot (such as Figure 1 The measured shear sliding surface in (shown);

[0065] Step 7: Draw a cross-section of the sliding body based on the measured topographic cross-section and shear sliding surface, and divide the sliding body into several blocks (such as Figure 2 shown);

[0066] Step 8: Repeat steps 3-7 above at the adjacent location to draw another sliding body cross-section diagram;

[0067] Step 9: Based on the two sliding body cross-sectional views obtained in the above steps, the strip method of slope stability calculation is used to establish equations respectively, and then the equation group is solved to obtain the shear strength parameters of the sample.

[0068] In the above technical solution, in step 9, the shear strength parameter derivation formula is as follows:

[0069] 1) The stress analysis of the first specimen block i is as follows (e.g. Figure 3 shown):

[0070] N 1i=W 1i cosα 1i

[0071] T 1i =W 1i Sinα 1i

[0072]

[0073]

[0074] where τ 1i =T 1i

[0075] Right now

[0076] Where, c-cohesion of the specimen; - internal friction angle of the specimen; W 1i - the weight of the first sample block i; T 1i - tangential force on the sliding surface of the first specimen strip i; N1i - normal force on the sliding surface of the first specimen strip i; τ 1i - Shear strength of the first specimen strip i on the sliding surface; l 1i - the length of the sliding surface of the first specimen strip i; α 1i -The angle between the normal line of the sliding surface of the first specimen strip i and the vertical line.

[0077] 2) According to the force balance on the sliding surface, establish the equation for the first specimen

[0078]

[0079] Among them, W 1i =γA 1i ②

[0080] Substituting equation ② into equation ①, we get

[0081]

[0082] Among them, c, γ is an invariant, we get

[0083]

[0084] Where, c-cohesion of the sample, kPa; -Internal friction angle of the sample, degrees; γ-density of the sample, kN / m 3 ; l 1i -The length of the sliding surface of the first specimen block i, m; α 1i -The angle between the normal line of the sliding surface of the first specimen block i and the vertical line, degrees; W1i -The weight of the first sample block i, kN / m; A 1i -Area of ​​the first sample block i, m 2 .

[0085] 3) Similarly, establish the equation for the second sample

[0086]

[0087] Where, c-specimen cohesion, kPa; -Internal friction angle of the sample, degrees; γ-density of the sample, kN / m 3 ; l 2i -The length of the sliding surface of the second specimen block i, m; α 2i - Angle between the normal line of the sliding surface of the second specimen block i and the vertical line, degrees; A 2i -Area of ​​the second sample block i, m 2 .

[0088] 4) Combine equations ④ and ⑤ to form a system of linear equations with two variables, and we get

[0089]

[0090] Solving the system of equations, we get

[0091]

[0092]

[0093] Where, c-specimen cohesion, kPa; -Internal friction angle of the sample, degrees; γ-weight of the sample, kN / m 3 ; l 1i 、l 2i - is the length of the sliding surface of the first and second sample blocks i, m; α 1i , α 2i - is the angle between the normal line of the sliding surface of the first and second sample blocks i and the vertical line, degrees; A 1i 、A 2i -areas of the first and second sample blocks i, m 2 .

[0094] In formula ⑦ and formula ⑧, only c, is an unknown number, and the remaining parameters can be measured directly.

[0095] In the method provided by the present invention, one group of tests requires two specimens. By completing the number of test groups specified in the specification within the project area and then performing statistical analysis, representative parameters of the shear strength of gravel soil and strongly weathered rock can be obtained, thereby acquiring mechanical test data.

[0096] The method provided by this invention fully simulates the instability patterns of field-tested gravel soil and strongly weathered rock slopes. It is generally easy to select a field site that meets the test requirements. The process is simple, safe, and controllable, with low costs and strong applicability. Furthermore, during the test, various mechanical test data can be obtained by applying loads to the slope or immersing the specimen in water, meeting the requirements for shear strength parameters under different working conditions.

[0097] In actual operation, the slope instability mode observed in the test can be used to perform inverse analysis of shear strength parameters with the help of computer technology. The calculation process is convenient and the calculation accuracy is high.

[0098] Other parts not described belong to the prior art.

Claims

1. A field unloading shear test method for gravel soil and strongly weathered rock, characterized by: The following steps are involved: Step 1: Select a slope with an open area as the test site. Step 2: Excavate a test pit and use the water filling method or sand filling method to measure the γ density of the gravel soil or strongly weathered rock on site; Step 3: Topographic cross section along the measured slope; Step 4: Dig a split groove along both sides of the terrain section, leaving a rectangular parallelepiped as the specimen (2); Step 5: excavate the front edge unloading groove (5), and observe the dividing grooves on both sides at the same time. When the specimen (2) produces a through shear surface and slides, stop excavating the front edge unloading groove (5); Step 6: Measure the shear sliding surface in the dividing groove; Step 7: Draw a sliding body cross-section diagram based on the measured topographic cross-section and shear sliding surface, and divide the sliding rock and soil body on the sample (2) into several strips and blocks; Step 8: Repeat steps 3-7 above at a location adjacent to the previous specimen in the test site to draw another sliding body cross-section diagram; Step 9: Based on the two sliding body cross-sections obtained in the above steps, the slice method of slope stability calculation is used to establish equations respectively, and then solve the equation system to obtain the shear strength parameters of the specimen; In step 4, the dividing groove includes a left dividing groove (3) and a right dividing groove (4); the sample (2) is located between the left dividing groove (3) and the right dividing groove (4); the leading edge unloading groove (5) is located in front of the sample (2) and between the left dividing groove (3) and the right dividing groove (4); In step 6, the shear sliding surface is measured in the left dividing groove (3) or the right dividing groove (4).

2. The field unloading shear test method for crushed stone soil and strongly weathered rock according to claim 1, characterized in that: In step 4, the size of the sample meets the following requirements: length along the slope > height > width across the slope > maximum particle size.

3. The field unloading shear test method for crushed stone soil and strongly weathered rock according to claim 1, characterized in that: In step 7, the sliding body is divided into several strips and blocks according to the turning points or equal distances of the sliding surface.

4. The field unloading shear test method for crushed stone soil and strongly weathered rock according to claim 2, characterized in that: Based on the sample strips formed in step 7, in step 9, the shear strength parameter is derived as follows: The stress analysis of the first specimen block i is as follows: N 1i =W 1i cosα 1i T 1i =W 1i sinα 1i where τ 1i =T 1i Right now Where c represents the cohesion of the sample, kPa; Indicates the internal friction angle of the sample, degrees; W 1i represents the gravity of the first sample block i, kN / m; T 1i Indicates the tangential force on the sliding surface of the first specimen strip i; N 1i represents the normal force on the sliding surface of the first specimen strip i, kN; τ 1i Indicates the shear strength of the first specimen strip i on the sliding surface, kPa; l 1i represents the length of the sliding surface of the first sample block i, m; α 1i represents the angle between the normal line of the sliding surface of the first specimen strip i and the vertical line, in degrees; According to the force balance on the sliding surface, the equation for the first specimen is established: Among them, W 1i =γA 1i ② Substituting equation ② into equation ①, we get: Among them, c, γ is an invariant, we get: Where: c represents the cohesion of the sample, kPa; represents the internal friction angle of the sample, degrees; γ represents the density of the sample, kN / m 3 ; l 1i represents the length of the sliding surface of the first sample block i, m; α 1i W represents the angle between the normal line of the sliding surface of the first sample block i and the vertical line, degrees; 1i A represents the weight of the first sample block i, kN / m; 1i Represents the area of ​​the first sample block i, m 2 ; According to the above method of establishing the equation of the first sample, establish the equation of the second sample: Where: c represents the cohesion of the sample, kPa; represents the internal friction angle of the sample, degrees; γ represents the density of the sample, kN / m 3 ; l 2i represents the length of the sliding surface of the second sample block i, m; α 2i A represents the angle between the normal line of the sliding surface of the second sample block i and the vertical line, degrees; 2i Represents the area of ​​the second sample block i, m 2 ; Combining equations ④ and ⑤ to form a system of linear equations with two variables, we get: Solving the system of equations, we get: Where: c represents the cohesion of the sample, kPa; represents the internal friction angle of the sample, degrees; γ represents the density of the sample, kN / m 3 ; l 1i 、l 2i are the lengths of the sliding surface of the first and second specimen strip i, m; α 1i , α 2i The angles between the normal line of the sliding surface of the first and second specimen blocks i and the vertical line, degrees; A 1i 、A 2i The area of ​​the first and second sample blocks i, m 2 .

Images