CN111624070A - Test sample and method for measuring external friction angle of saturated soil and structure by utilizing triaxial apparatus - Google Patents

Test sample and method for measuring external friction angle of saturated soil and structure by utilizing triaxial apparatus Download PDF

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CN111624070A
CN111624070A CN202010510594.6A CN202010510594A CN111624070A CN 111624070 A CN111624070 A CN 111624070A CN 202010510594 A CN202010510594 A CN 202010510594A CN 111624070 A CN111624070 A CN 111624070A
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sample
soil
test
soil body
stress
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CN111624070B (en
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廖晨聪
刘世奥
苏新斌
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Shanghai Jiaotong University
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Shanghai Jiaotong University
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N1/00Sampling; Preparing specimens for investigation
    • G01N1/28Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/02Details
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/24Investigating strength properties of solid materials by application of mechanical stress by applying steady shearing forces

Abstract

The invention provides a test sample and a method for measuring saturated soil and a structural external friction angle by using a triaxial apparatus, wherein the test sample is integrally cylindrical and consists of a structural sample and a soil body sample, and the method for measuring the structural sample which is a chamfered semi-cylinder comprises the following steps: carrying out a triaxial shear test on the soil body and obtaining an internal friction angle of the soil body; according to the internal friction angle of the soil body, determining the inclination angle between the structural sample and the soil sample, and manufacturing the structural sample according to the structural inclination angle and the roughness corresponding to the actual engineering; and combining the structural sample and the soil sample into a test sample, and carrying out a triaxial shear test after saturation and consolidation to obtain an external friction angle of the saturated soil body and the structure. The invention can more accurately control the drainage condition, better accords with the engineering practice and is more suitable for the engineering and design requirements; according to the mechanical characteristics of the interface, the structure is customized according to the needs, and the influence factors of the external friction angle can be further discussed; the test principle is simple, the operation is convenient, and the realization is easy.

Description

Test sample and method for measuring external friction angle of saturated soil and structure by utilizing triaxial apparatus
Technical Field
The invention belongs to the technical field of civil engineering, and particularly relates to a test sample and a method for measuring the external friction angle of saturated soil and a structure by using a triaxial apparatus.
Background
The contact surface of the soil body and the structure is an important medium for mutual transmission of stress and deformation between the soil and the structure, and is ubiquitous in engineering such as civil engineering, water conservancy, construction, traffic, municipal engineering, ocean and the like. The friction property of the contact surface of the soil body and the structure has important significance in practical engineering, and the external friction angle and the corresponding friction coefficient of the soil body and the structure are important strength indexes in engineering application. The contact problem of the soil body and the structure is involved, and the external friction angle of the soil body and the structure is a vital parameter for practical engineering design and numerical simulation analysis. The correct selection of soil and the external friction angle of the structure can reduce the engineering risk, reduce the occurrence of engineering accidents, save the economic cost and have important engineering significance.
At present, methods for measuring the external friction angle of the soil body and the structure mainly comprise direct shear tests and single shear tests, and some researchers also use a drawing test or a ring shear test to measure the external friction angle of the soil body and the structure. However, the drawing test is generally directed at the determination of the friction angle and the friction coefficient between the soil body and the geosynthetic material, and is not suitable for the determination of the external friction angle between the soil body and the structure, while the ring shear test is complex in operation and uneven in stress distribution in the test process, so that the direct shear test and the single shear test are widely applied to determine the external friction angle between the soil and the structure.
The prior art documents are searched to find that:
application No.: 201811335513.2, title of the invention: a method of determining a sand-structure interface friction coefficient, publication no: CN109459381A, published 2019.03.12, discloses a method for determining a sand-structure interface friction coefficient, which can determine two friction coefficients, one is the interface friction coefficient in a normal volume state, and the other is the interface friction coefficient corresponding to a phase change line. The core principle of the patent still utilizes the interface shear apparatus based on the direct shear apparatus to perform a plurality of groups of tests to obtain corresponding external friction coefficients. However, the direct shear apparatus or the single shear apparatus can only simulate different drainage conditions approximately through the shear rate, and cannot accurately control the drainage state in the actual test process; due to the lack of devices such as latex films and the like, the pore pressure change in the shearing process cannot be accurately measured, the measured external friction angle cannot accurately reflect the actual working condition, larger errors are caused, and design risks may be brought by the direct application to the actual engineering. In summary, it is very important to provide a safe and reliable method for determining the external friction angle between the soil body and the structure.
Disclosure of Invention
The invention provides a test sample and a method for measuring the external friction angle of saturated soil and a structure by using a triaxial apparatus, aiming at the defect of the existing test device in measuring the external friction angle of the soil and the structure.
The invention is realized by the following technical scheme.
According to one aspect of the invention, a test sample for measuring the external friction angle of saturated soil and a structure by using a triaxial apparatus is provided, which comprises a structure sample and a soil mass sample, wherein the structure sample and the soil mass sample respectively adopt a chamfered semi-cylinder structure; under the working state, the soil body sample and the structure sample are contacted and combined up and down to form a test sample, and a contact surface between the soil body sample and the structure sample is an elliptical plane.
Preferably, the test sample adopts any one of the following sizes:
-a diameter of 39.1mm and a height of 80 mm;
-a diameter of 61.8mm and a height of 120 mm;
diameter 101mm and height 200 mm.
Preferably, the structural sample is prepared from concrete or steel according to engineering practice.
According to another aspect of the present invention, there is provided a method for determining an external friction angle of saturated soil and a structure by using a triaxial apparatus, comprising:
s1, obtaining a soil body researched by the test through practical engineering, carrying out a triaxial shear test on the soil body, and obtaining the soil body according to the test data in combination with a molar coulomb strength criterion:obtaining the internal friction angle of the soilWherein, taufThe shear strength of the soil body, the cohesive strength and the normal stress on a failure surface are shown as c and sigma respectively;
s2, according to the obtained internal friction angle of the soil bodyDetermining a structural inclination angle theta between the structural sample and the soil mass sample by utilizing the stress Mohr circle; manufacturing a structural sample according to the structural inclination angle theta and the roughness corresponding to the actual engineering;
and S3, preparing a soil body sample according to the structure inclination angle theta and the soil body attribute, forming a test sample with the structure sample prepared in the S2, installing the test sample in a triaxial pressure chamber according to the operation specification of an adopted triaxial apparatus, carrying out a triaxial shear test after the test sample is saturated and solidified under certain initial confining pressure, and obtaining the soil body and structure external friction angle alpha according to the test data.
Preferably, the S1 includes the following steps:
s11, preparing, loading and saturating according to the triaxial test specification and according to the required confining pressure sigma3Carrying out equidirectional consolidation;
s12, selecting a strain control or stress control mode to apply load according to the test instrument, performing triaxial compression test, and obtaining a group of confining pressure sigma during failure3And axial pressure σ1The data of (a);
s13, repeating S11 and S12 to obtain at least three groups of data during damage, drawing a stress Moire circle under the same coordinate system, fitting common tangents of different Moire circles, and obtaining the stress Moire circle and the fitting result according to the Moire coulomb intensity criterionThe dip angle of the common tangent is the internal friction angle
Preferably, in S2, the stress moire circle is used to determine the structural sample and the soil body testThe method of the structural dip angle theta between the samples is as follows: according to the molar coulomb strength criterion, combining with a stress Morel circle; when the shear strength envelope is tangent to the stress Mohr circle, soil body destruction occurs, and the included angle between the destruction surface and the large main stress surface isThe included angle is the structure inclination angle theta of the structure sample and represents the included angle between the inclined plane and the bottom surface of the cylinder.
Preferably, in S2, the method for manufacturing the structural sample includes: according to the property of the contact surface of the structure and the soil body in the engineering practice, determining the roughness parameter of the inclined surface of the structure sample on the basis of a specific inclination angle, and manufacturing the concrete or steel structure sample.
Preferably, in S3, when the soil attribute is cohesive soil, the method for composing the test sample is as follows:
taking out the undisturbed or remolded cohesive soil sample, and cutting the soil sample into cylinders with required size;
according to the inclination angle theta of the structural sample, the soil sample cylinder is obliquely cut into two parts with equal volume from the center of the soil sample cylinder according to the inclination angle theta, and then the soil sample is obtained;
and placing the soil body sample on the prefabricated structure sample to obtain a test sample.
Preferably, in S3, when the soil attribute is sandy soil, the method for composing the test sample is as follows:
putting a permeable stone on a triaxial apparatus base, and sticking filter paper; putting a prefabricated structural sample, and sleeving a rubber film on the film bearing cylinder;
installing a split mold outside the rubber film, turning the top of the rubber film, sleeving the split mold into the split mold and fixing the split mold;
weighing dry sand with a certain mass according to a preset compactness, and adding a little distilled water into the dry sand to generate pseudo-cohesion and form a sand sample;
pouring the sand sample into a split mold for three times, compacting the sand sample to the required compactness through compacting blocks with different inclination angles to form a soil body sample;
after the soil body sample is loaded, putting a permeable stone and a sample cap on the upper part, turning up the rubber film, fastening the rubber film on the sample cap, and removing the split mold to obtain the test sample.
Preferably, filter paper strips are applied to both sides of the prefabricated structural sample to increase the sidewall permeability coefficient.
Preferably, for the test sample with the soil body attribute of cohesive soil, a water head saturation and/or back pressure saturation mode is adopted.
Preferably, for the test sample with soil body attribute of sandy soil, a water head saturation mode, a carbon dioxide introducing saturation mode and/or a back pressure saturation mode are adopted.
Preferably, in S3, the stress path in the triaxial shear test is performed by using a normal direction stress shear test; wherein:
the relationship between the stress path K and the structure tilt angle θ is:
in the formula, m is a calculation parameter:
preferably, in S3, the contact surface between the soil sample and the structure sample is a fracture surface in the case of shear fracture; the inclination angle of the contact surface is a structure inclination angle theta, and is an included angle between the maximum shear stress surface and the large main stress surface in the soil body sample; and when the soil body does not slide on the contact surface, increasing the structure inclination angle theta, and preparing a sample again to perform a triaxial shear test.
Preferably, in S3, the method for obtaining the external friction angle α between the soil body and the structure according to the test data includes:
according to the triaxial shear test, obtaining experimental data comprises: confining pressure sigma during breakdown3To axial pressure sigma1
From the resulting confining pressure σ at failure3To axial pressure sigma1And the normal stress sigma on the contact surface of the soil body sample and the structural sample is obtained through conversionnAnd shear stress τn
According to the coulomb's law of friction, the external friction coefficient μ satisfies the following relationship,
the external friction angle alpha satisfies:
α=arctanμ
changing initial confining pressure, namely consolidation pressure, repeating the triaxial shear test, obtaining at least three groups of test data, and averaging the obtained external friction angle alpha to obtain the required soil body and structure external friction angle alpha.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
according to the test sample and the method for measuring the external friction angle of the saturated soil and the structure by using the triaxial apparatus, the external friction angle of the soil body and the structure is measured by using the triaxial apparatus, so that the drainage condition can be controlled more accurately, the engineering practice is better met, and the engineering and design requirements are better met; moreover, the structure can be customized according to the interface mechanical property and requirements, and the influence factors of the external friction angle can be further discussed; the test principle is simple, the operation is convenient, the realization is easy, and the instrument is not required to be modified on the basis of the existing triaxial test.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic structural diagram of a testing apparatus used in a preferred embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a test sample composed of a soil sample and a structural sample according to a preferred embodiment of the present invention;
fig. 3 is a schematic view of the analysis of the force applied to the contact surface between the soil sample and the structural sample according to a preferred embodiment of the present invention.
Detailed Description
The following examples illustrate the invention in detail: the embodiment is implemented on the premise of the technical scheme of the invention, and a detailed implementation mode and a specific operation process are given. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.
An embodiment of the present invention provides a test sample for measuring the external friction angle of saturated soil and a structure by using a triaxial apparatus, as shown in fig. 1 and 2, the test sample is composed of a structure sample and a soil body sample. Wherein:
the structure sample and the soil mass sample respectively adopt a chamfered semi-cylinder structure; under the working state, the soil body sample and the structure sample are contacted and combined up and down to form a test sample, and the contact surface between the soil body sample and the structure sample is an elliptical plane.
As a preferred embodiment, the test sample is consistent with the size of a general triaxial test sample, and any one of the following sizes can be adopted:
-a diameter of 39.1mm and a height of 80 mm;
-a diameter of 61.8mm and a height of 120 mm;
diameter 101mm and height 200 mm.
As a preferred embodiment, the structural sample is prepared from concrete or steel according to the actual engineering practice.
Another embodiment of the present invention provides a method for determining an external friction angle between saturated soil and a structure by using a triaxial apparatus, including:
s1: the soil body researched by the actual engineering test is subjected to a triaxial shear test, and more than three groups of different confining pressure sigma are selected as test working conditions3(e.g., 50KPa, 100KPa, 200KPa), based on experimental data in combination with molar coulombic intensity criteria:obtaining internal friction angle of soil body by using stress Morse circleWherein, taufThe shear strength of the soil body, the cohesive strength and the normal stress on a failure surface are shown as c and sigma respectively;
as a preferred embodiment, the specific test procedure of S1 is as follows:
s11: preparing a sample, filling the sample, saturating the sample according to the three-axis test specification and according to the required confining pressure sigma3Carrying out equidirectional consolidation;
s12: selecting a strain control or stress control mode to apply load according to a test instrument, performing a triaxial compression test, and obtaining a group of confining pressure sigma during failure3And axial pressure σ1The data of (a);
s13: repeating S11 and S12 to obtain at least three groups of damage data, drawing a stress Moire circle under the same coordinate system, fitting common tangents of different Moire circles, and obtaining the damage data according to the Moire coulomb intensity criterionThe dip angle of the common tangent is the internal friction angle
S2: according to the obtained internal friction angle of the soil bodyAnd determining a structure inclination angle theta between the structure sample and the soil mass sample, and manufacturing the structure sample according to the structure inclination angle theta and the roughness actually required by the engineering.
As a preferred embodiment, the structural inclination angle θ in S2 is obtained by combining the stress moire circle according to the molar coulomb strength criterion; when the shear strength envelope is tangent to the stress Mohr circle, the damage surface, i.e. the maximum shear stress surface in the soil body, and the included angle between the maximum shear stress surface and the major main stress surface areThe angle is the structure inclination angle theta of the structure sample, namely the included angle between the inclined plane and the bottom surface of the cylinder.
In S2, according to the nature of the contact surface between the structure and the soil body in the engineering practice, the parameters such as the roughness of the inclined surface of the structure sample can be determined based on the specific inclination angle, and then the concrete or steel structure sample is made.
S3: preparing a soil body sample according to the structure inclination angle theta and the soil body attribute, combining the soil body sample with the structure sample to form a test sample, installing the test sample in a triaxial pressure chamber according to the operation specification of an adopted triaxial apparatus, carrying out a shear test after the test sample is saturated and solidified, and obtaining the external friction angle alpha of the soil body and the structure according to test data.
As a preferred embodiment, the specific test procedure of S3 is as follows:
s31: and (5) manufacturing a soil body sample. Different sample preparation methods are needed according to the soil property of cohesive soil or sandy soil.
Wherein:
when the soil attribute is cohesive soil, the soil sample preparation method comprises the following steps:
(1) taking out the undisturbed or remolded cohesive soil sample, and cutting the soil sample into a cylinder with required size by using a soil cutter and a soil cutter;
(2) according to the inclination angle theta of the structural sample, cutting the soil column into two parts with equal volume from the center of the soil sample cylinder according to the inclination angle theta to obtain a soil sample;
in some embodiments, the method of continuing to assemble the test sample is:
(3) slowly placing the soil sample on the structural sample, reducing disturbance of the soil sample as much as possible, and combining the soil sample into a test sample.
And finally, placing the whole sample on a base of a pressure chamber of the triaxial apparatus, and loading the sample according to a common triaxial test sample preparation method.
When the soil attribute is sandy soil, the sample preparation method of the soil sample comprises the following steps:
(1) putting a permeable stone on the base of the triaxial apparatus, and sticking filter paper. Then, a prefabricated structure is put in, and a rubber membrane is sleeved on the membrane bearing cylinder. In order to improve the permeability coefficient of the side wall, filter paper strips can be attached to two sides of the prefabricated structure;
(2) installing a split mold outside the rubber film, turning the top of the rubber film to be sleeved on the split mold, and fixing the split mold by using a rubber ring;
(3) weighing dry sand with a certain mass according to a preset compactness, and adding a little distilled water into the dry sand to generate a certain pseudo-cohesion.
(4) And then slowly pouring the weighed sand sample into the split mold for three times, and compacting the sand sample to the required compactness through compaction blocks with different inclination angles to obtain a soil body sample. Because the lower part of the compaction block contains a structure with an inclination angle, the traditional compaction method can cause the compaction situation near the contact surface to be uneven, and the compaction degree at the edge is lower, so that compaction blocks with different inclination angles are manufactured to ensure the success of sample preparation. The following two points should be noted during the sample preparation process: firstly, the compaction force avoids the sand from breaking the rubber film, thereby causing the test failure; secondly, care was taken to avoid sand particles entering between the rubber membrane and the structure in order to avoid puncture of the rubber membrane during the test.
In some embodiments, the method of continuing to assemble the test sample is:
(5) after the sand sample is filled, the permeable stone and the sample cap are placed on the upper part, the rubber film is turned up and is tightly tied on the sample cap, and then the split mold is removed.
S32: saturating the test specimen, wherein:
for a test sample with soil body attribute as cohesive soil, adopting a water head saturation and/or back pressure saturation mode;
for a test sample with soil body attribute of sandy soil, a water head saturation mode, a carbon dioxide introducing saturation mode and/or a back pressure saturation mode are adopted.
As a preferred embodiment, the test sample saturation method for soil with sand as soil attribute comprises the following saturation steps:
(1) after sample preparation and sample loading, a pressure chamber is arranged, and after the airless water is injected, the confining pressure of 15KPa is applied.
(2) And connecting a vacuum pump with an upper drainage pipeline of the triaxial apparatus, opening the vacuum pump, applying negative pressure on the top of the sample, introducing carbon dioxide into the lower drainage pipeline at the bottom of the sample, and regulating a carbon dioxide valve to control the air inlet rate according to the back pressure of the sample so as to enable the back pressure to be about 10 KPa. Since the lower part of the sample is a water-tight structure, carbon dioxide generally enters the sand on the upper part through the side wall, and filter paper is attached to the periphery of the sample in order to improve the permeability coefficient of the side wall.
(3) And after the introduction of the carbon dioxide is stopped, continuously applying negative pressure on the top of the sample, then applying pressure of 15KPa to the backpressure groove, injecting airless water from the bottom of the sample, when the water discharging pipe is discharged without bubbles, determining that the sample is filled with the airless water, continuously discharging the water, diluting and replacing carbonic acid generated by dissolving the carbon dioxide, and generally pumping the water with the volume 3-4 times of the volume of the sample. The change of the pore pressure gauge is also noticed at any moment when the water head is saturated, as when carbon dioxide is saturated.
(4) And carrying out back pressure saturation after the water head is saturated, and carrying out B value detection after the saturation is finished to ensure that the saturation of the sample reaches over 95 percent.
S33: the samples were tested for consolidation and shear. For consolidation drainage and consolidation non-drainage tests, the sample consolidation is generally carried out by adopting equidirectional consolidation, namely confining pressure sigma3And axial pressure σ1Equal; for the no consolidation and no drainage test, consolidation may not be performed. In the shear test, the actual working condition can be simulated more accurately according to different stress paths in the shear test. For the traditional strain triaxial apparatus, the confining pressure sigma in the general shearing process3The slope of the total stress path (or effective stress path in drainage shear) remains unchanged at 3. For the triaxial apparatus capable of controlling stress path loading, a normal confining pressure shear test and a normal direction stress shear test can be carried out. The shearing stage can be generally divided into two modes of stress control and strain control to apply loads, and different shearing modes can be adopted according to the difference of the triaxial test instrument: the shearing mode is normal compression shearing, i.e. controlling confining pressure sigma during shearing3Unchanged, axial pressure σ1Gradually increasing until destruction; for the triaxial apparatus capable of controlling the stress path, the stress path can be controlled to be loaded according to the actual engineering requirement, and the stress path can also be controlled to be loadedThe normal stress on the contact surface is constant, and normal stress shearing is realized.
S34: and analyzing and determining the structure and the soil body external friction angle according to the test result. After the triaxial shear test, the confining pressure sigma at the time of failure is obtained3To axial pressure sigma1By confining pressure σ at the time of failure3To axial pressure sigma1The normal stress sigma on the contact surface of the soil and the structure can be obtained through conversionnAnd shear stress τnAccording to the coefficient of external friction mu τnnAnd the external friction angle α is arctan mu, and the external friction angle α can be obtained, the initial confining pressure, namely consolidation pressure (such as 50KPa, 100KPa and 200KPa) is changed, the test is repeated, at least three groups of test data are obtained, and the external friction angle α obtained by each group is averaged, so that the external friction angle α of the saturated soil body and the structure can be obtained.
As a preferred embodiment, when the sample of S33 reaches the failure state, the contact surface of the soil sample and the structure is the failure surface during shearing failure. The inclination angle of the contact surface is the included angle between the maximum shear stress surface in the soil body and the large main stress surfaceAccording to engineering experience, the external friction angle is generally smaller than the internal friction angle of the soil body, the contact surface is a weak surface in the sample, the soil body slides along the contact surface in the shearing process, if special conditions are met, the soil body does not slide on the contact surface, the structure inclination angle theta can be properly increased, and the sample is rebuilt for testing.
As a preferred embodiment, the S33 normal direction stress shear test is to control the normal direction stress on the contact surface to be constant by selecting a proper stress path according to different structure inclination angles. The stress state of the cylinder in the triaxial test can be generally simplified into two-dimensional state analysis, and the normal stress and the shear stress of any inclined plane can be obtained. However, the normal stress and shear stress obtained by the method have larger error than the actual stress, so the normal stress and shear stress on the contact surface of the soil and the structure are deduced according to the actual stress situation, and the process is as follows:
(1) when the test piece is subjected to stress analysis, as shown in fig. 3, the confining pressure applied to the left portion (portion C) and the confining pressure applied to the right portion (portion D) of the test piece partially cancel each other. And due to the symmetry of the two parts A and B, the part A can be directly calculated when the horizontal resultant force generated by the confining pressure is calculated. The force analysis is carried out on the wedge body formed by the four parts of the ABCD, the height of the wedge body is h, the radius of the bottom surface is r, and the inclination angle of the inclined plane is theta:
horizontal direction stress analysis:
vertical force analysis:
finishing can obtain:
(2) if the normal stress sigma is to be maintainednIf not, the following requirements are met:
Δσn=0
namely:
the following can be obtained:
therefore, in the triaxial test, according to different structure inclination angles, a proper stress path is selected, and the constant normal stress on the contact surface can be controlled. In a normal stress shear test, the relation between a stress path K and an inclination angle theta is as follows:
as a preferred embodiment, S34 is based on the confining pressure σ at break3To axial pressure sigma1The normal stress sigma on the contact surface of the soil and the structure can be obtained through conversionnAnd shear stress τnAccording to the coefficient of external friction mu τnnAnd the external friction angle α ═ arctan μ, the external friction angle α can be obtained as follows:
(1) normal stress sigma on the contact surface of soil and structurenAnd shear stress τn
(2) According to the coulomb's law of friction, the external friction coefficient μ satisfies the following relationship,
(3) and the external friction angle alpha is satisfied,
α=arctanμ
the external friction angle alpha of the soil body and the structure can be obtained.
The method provided in the above embodiment of the present invention is further described below with reference to a specific application example as follows:
s1: obtaining the internal friction angle of the soil bodyThe soil body researched by the test is determined by engineering practice, and through carrying out a triaxial shear test on the soil body, more than three groups of different confining pressure sigma are selected according to test working conditions3(e.g., 50KPa, 100KPa, 200KPa), based on experimental data in combination with molar coulombic strength criteriaObtaining the internal friction angle of the soil
S11: preparing a sample, filling the sample, saturating the sample according to the three-axis test specification and according to the required confining pressure sigma3And (4) carrying out equidirectional consolidation.
(1) In the concrete test, soil is selected as Fujian standard sand, and the maximum and minimum dry density and the grading curve of the soil are determined through the soil test. Control of soil parameters such as initial compaction to determine dry density ρ of sampledAccording to the volume V of the triaxial standard sample, according to M-V × rhodWeighing a certain mass of sandy soil.
(2) According to the relevant regulations in geotechnical test regulations (SL237-1999), a sandy soil sample is manufactured and is arranged on a base of a triaxial pressure chamber, and the sample is saturated by carbon dioxide, saturated by a water head and saturated by back pressure to reach the saturation requirement (generally B is more than or equal to 0.95).
(3) After the test is saturated, the test platform is loaded step by step, the effective confining pressure is increased to the confining pressure required by the test, and the test sample is subjected to equidirectional consolidation (the operation is not required in the unconsolidated and non-drainage test).
S12: selecting a strain control or stress control mode to apply load according to a test instrument, performing a triaxial compression test, and obtaining a group of confining pressure sigma during failure3And axial pressure σ1The data of (1).
(4) The triaxial apparatus adopted in the present case is a strain control type triaxial apparatus, and the consolidation drainage test is carried out at the required effective confining pressure sigma3Then, a triaxial compression test was carried out at a shear rate of 0.011mm/min to obtain σ at failure3And σ1And the standard reference test specification is destroyed.
(5)σ3Taking 50KPa, 100KPa and 200KPa respectively, performing three tests to obtain three groups of failure data, drawing stress Mohr circle under the same coordinate system with normal stress as abscissa and shear stress as ordinate, fitting common tangent lines of different Mohr circles, and obtaining the final product according to Mohr coulomb intensity criterionThe dip angle of the common tangent line is the consolidation drainage strength index: internal friction angleIn this caseApproximately 30.
S2: and determining the inclination angle theta of the structural sample according to the internal friction angle of the soil body and the stress Mohr circle, and manufacturing the structural sample according to the structural inclination angle and the roughness actually required by the engineering.
(6) At the inner friction angleThen, determining the inclination angle theta of the structure by the stress Mohr circle, wherein theta is the included angle between the maximum shear stress surface in the soil body and the large main stress surfaceTake 60 deg. According to engineering experience, the external friction angle is generally smaller than the internal friction angle of the soil body, the contact surface is a weak surface in the sample, and the soil body can slide along the contact surface in the shearing process.
(7) According to the inclination angle theta of the structure, a stainless steel structure with the diameter of 39.1mm is manufactured, the structure sample is a chamfered semi-cylinder which is made of concrete or steel and other materials according to the actual engineering, and the volume of the structure sample is the whole volume of the standard 39.1mm × 80mm sample
S3: the method comprises the steps of combining a structural sample and a soil body sample into a test sample, installing the test sample in a triaxial pressure chamber according to the operation specification of an adopted triaxial apparatus, carrying out a shear test, and obtaining a soil body and structure external friction angle alpha according to test data.
S31: preparation of triaxial test specimens (test specimens) containing structures.
(8) Making a sandy soil sample containing a structure, and determining the sandy soil volume V, root according to half of the volume of a triaxial standard sampleAccording to M-V × rhodAnd weighing a certain mass of sandy soil, wherein the sample preparation process is as before.
S32: saturation of triaxial samples containing structure.
(9) And (3) saturating the sample after the sample is installed, wherein the saturation process is as before, the saturation modes are carbon dioxide saturation, water head saturation and back pressure saturation, and detecting the B value of the sample after the saturation is finished, so that the B value is ensured to be more than or equal to 0.95 to meet the saturation requirement.
S33: consolidation and shear of the three-axis test specimen containing the structure (test specimen).
(10) Performing consolidation and shearing according to the steps (3), (4) and (5), ensuring that the front consolidation mode and the rear consolidation mode are consistent with the shearing mode, performing consolidation drainage shearing on the sand sample containing the structure, and performing a test on confining pressure sigma3Respectively taking 50KPa, 100KPa and 200KPa, and the shear rate is 0.011mm/min to obtain the axial pressure sigma when the failure is reached1
S34: and analyzing and determining the structure and the soil body external friction angle according to the test result.
(11) After the triaxial shear test, the confining pressure sigma at the time of failure is obtained3To axial pressure sigma1By confining pressure σ at the time of failure3To axial pressure sigma1The normal stress sigma on the contact surface of the soil and the structure can be obtained through conversionnAnd shear stress τnAccording to the coefficient of external friction mu τnnAnd the external friction angle α is arctan mu, and the external friction angle α can be obtained, the initial confining pressure, namely consolidation pressure (such as 50KPa, 100KPa and 200KPa) is changed, the test is repeated, at least three groups of test data are obtained, and the external friction angle α obtained by each group is averaged, so that the external friction angle α of the saturated soil body and the structure can be obtained.
According to the test sample and the method for measuring the external friction angle of the saturated soil and the structure by using the triaxial apparatus, provided by the embodiment of the invention, the external friction angle of the saturated soil and the structure under different working conditions can be measured by controlling test conditions such as drainage conditions, the roughness of the structure sample, a shear stress path and the like, and the test sample and the method are used for geotechnical engineering design and construction. The test sample is a cylinder integrally and consists of a structure sample and a soil body sample, and the size of the test sample is consistent with that of a common triaxial test sample. The structural sample is a quiltThe cylinder material is determined by a structure needing to measure the external friction angle and is made of concrete or steel and the like. The determination step comprises: firstly, the soil body researched by the test is obtained by the actual engineering, the internal friction angle of the soil body is obtained by carrying out the triaxial shear test on the soil body and combining the result with the molar coulomb strength criterionThen, according to the internal friction angle of the soil bodyThe method comprises the steps of determining an inclination angle theta between a structural sample and a soil sample by using a stress Mohr circle, manufacturing the structural sample according to the structural inclination angle and the roughness corresponding to an actual project, finally combining the structural sample and the soil sample into a triaxial test sample, carrying out a triaxial shear test after saturation and consolidation, and processing test data to obtain an external friction angle α of a saturated soil body and a saturated structure.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (10)

1. A test sample for measuring the external friction angle of saturated soil and a structure by using a triaxial apparatus is characterized by comprising a structure sample and a soil body sample, wherein the structure sample and the soil body sample respectively adopt a chamfered semi-cylinder structure; under the working state, the soil body sample and the structure sample are contacted and combined up and down to form a test sample, and a contact surface between the soil body sample and the structure sample is an elliptical plane.
2. The test specimen for measuring the external friction angle of saturated soil and structure using the triaxial apparatus according to claim 1, wherein the test specimen has any one of the following dimensions:
-a diameter of 39.1mm and a height of 80 mm;
-a diameter of 61.8mm and a height of 120 mm;
diameter 101mm and height 200 mm.
3. The test specimen for measuring the external friction angle of saturated soil and structure by using the triaxial apparatus according to claim 1, wherein the structural specimen is prepared by concrete or steel according to actual engineering.
4. A method for measuring the external friction angle of saturated soil and a structure by using a triaxial apparatus is characterized by comprising the following steps:
s1, obtaining a soil body researched by the test through practical engineering, carrying out a triaxial shear test on the soil body, and obtaining the soil body according to the test data in combination with a molar coulomb strength criterion:obtaining the internal friction angle of the soilWherein, taufThe shear strength of the soil body, the cohesive strength and the normal stress on a failure surface are respectively α;
s2, according to the obtained internal friction angle of the soil bodyDetermining a structural inclination angle theta between the structural sample and the soil mass sample by utilizing the stress Mohr circle; manufacturing a structural sample according to the structural inclination angle theta and the roughness corresponding to the actual engineering;
and S3, preparing a soil body sample according to the structure inclination angle theta and the soil body attribute, forming a test sample with the structure sample prepared in the S2, installing the test sample in a triaxial pressure chamber according to the operation specification of an adopted triaxial apparatus, carrying out a triaxial shear test after the test sample is saturated and solidified under certain initial confining pressure, and obtaining the soil body and structure external friction angle alpha according to the test data.
5. The method for measuring the external friction angle of saturated soil and structure using a triaxial apparatus according to claim 4, wherein the S1 comprises the steps of:
s11, preparing, loading and saturating according to the triaxial test specification and according to the required confining pressure sigma3Carrying out equidirectional consolidation;
s12, selecting a strain control or stress control mode to apply load according to the test instrument, performing triaxial compression test, and obtaining a group of confining pressure sigma during failure3And axial pressure σ1The data of (a);
s13, repeating S11 and S12 to obtain at least three groups of data during damage, drawing a stress Moire circle under the same coordinate system, fitting common tangents of different Moire circles, and obtaining the stress Moire circle and the fitting result according to the Moire coulomb intensity criterionThe dip angle of the common tangent is the internal friction angle
6. The method for determining the external friction angle of saturated soil and structure using three-axis apparatus according to claim 4, wherein in said S2:
the method for determining the structure inclination angle theta between the structure sample and the soil mass sample by utilizing the stress Mohr circle comprises the following steps: according to the molar coulomb strength criterion, combining with a stress Morel circle; when the shear strength envelope is tangent to the stress Mohr circle, soil body destruction occurs, and the included angle between the destruction surface and the large main stress surface isThe included angle is a structural inclination angle theta of the structural sample and represents the included angle between the inclined plane and the bottom surface of the cylinder;
and/or
The method for manufacturing the structural sample comprises the following steps: according to the property of the contact surface of the structure and the soil body in the engineering practice, determining the roughness parameter of the inclined surface of the structure sample on the basis of a specific inclination angle, and manufacturing the concrete or steel structure sample.
7. The method for determining the external friction angle of saturated soil and structure using three-axis apparatus according to claim 4, wherein in said S3:
when the soil property is cohesive soil, the method for composing the test sample is as follows:
taking out the undisturbed or remolded cohesive soil sample, and cutting the soil sample into cylinders with required size;
according to the inclination angle theta of the structural sample, the soil sample cylinder is obliquely cut into two parts with equal volume from the center of the soil sample cylinder according to the inclination angle theta, and then the soil sample is obtained;
placing a soil body sample on a prefabricated structure sample to obtain a test sample;
when the soil body attribute is sandy soil, the method for composing the test sample is as follows:
putting a permeable stone on a triaxial apparatus base, and sticking filter paper; putting a prefabricated structural sample, and sleeving a rubber film on the film bearing cylinder;
installing a split mold outside the rubber film, turning the top of the rubber film, sleeving the split mold into the split mold and fixing the split mold;
weighing dry sand with a certain mass according to a preset compactness, and adding a little distilled water into the dry sand to generate pseudo-cohesion and form a sand sample;
pouring the sand sample into a split mold for three times, compacting the sand sample to the required compactness through compacting blocks with different inclination angles to form a soil body sample;
after the soil body sample is loaded, putting a permeable stone and a sample cap on the upper part, turning up the rubber film, fastening the rubber film on the sample cap, and removing the split mold to obtain the test sample.
8. The method for determining the external friction angle of saturated soil and structure by using a triaxial apparatus according to claim 7, wherein the S3 further comprises any one or more of the following items:
-applying filter paper strips on both sides of the prefabricated structural sample to increase the side wall permeability coefficient;
-for a test sample with soil body properties of cohesive soil, adopting a water head saturation and/or back pressure saturation mode;
for test samples with soil properties of sandy soil, a water head saturation, carbon dioxide saturation and/or back pressure saturation mode is adopted.
9. The method for determining the external friction angle of saturated soil and structure by using a triaxial apparatus according to claim 4, wherein in the step S3, the stress path in the triaxial shear test is performed by using a normal direction stress shear test; wherein:
the relationship between the stress path K and the structure tilt angle θ is:
in the formula, m is a calculation parameter:
and/or
The contact surface between the soil body sample and the structure sample is a damaged surface during shearing damage; the inclination angle of the contact surface is a structure inclination angle theta, and is an included angle between the maximum shear stress surface and the large main stress surface in the soil body sample; and when the soil body does not slide on the contact surface, increasing the structure inclination angle theta, and preparing a sample again to perform a triaxial shear test.
10. The method for determining the external friction angle α of the saturated soil and the structure by using the triaxial apparatus according to claim 4, wherein in step S3, the method for obtaining the external friction angle α of the soil and the structure according to the test data comprises:
according to the triaxial shear test, obtaining experimental data comprises: confining pressure sigma during breakdown3To axial pressure sigma1
From the resulting confining pressure σ at failure3To axial pressure sigma1And the normal stress sigma on the contact surface of the soil body sample and the structural sample is obtained through conversionnAnd shear stress τn
According to the coulomb's law of friction, the external friction coefficient μ satisfies the following relationship,
the external friction angle alpha satisfies:
α=arctanμ
changing initial confining pressure, namely consolidation pressure, repeating the triaxial shear test, obtaining at least three groups of test data, and averaging the obtained external friction angle alpha to obtain the required soil body and structure external friction angle alpha.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112557168A (en) * 2020-11-06 2021-03-26 清华大学 Stacked ring type hollow torsional shear equipment and pressure compensation method thereof
CN113218735A (en) * 2021-05-10 2021-08-06 昆明理工大学 Triaxial test saturated sample loading method for soil
CN113533034A (en) * 2021-08-30 2021-10-22 石家庄铁道大学 Soil body tensile test device and soil body tensile test method
CN113916739A (en) * 2021-08-24 2022-01-11 河海大学 Soil-concrete contact seepage test device and method considering contact surface shearing

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU1541470A1 (en) * 1987-05-22 1990-02-07 Всесоюзный научно-исследовательский институт зерна и продуктов его переработки Method of integrating priority and production-dependent streams of loose materials
CN1916359A (en) * 2005-11-28 2007-02-21 长庆石油勘探局 Method for building new slot to implement refracturing
CN101986130A (en) * 2010-09-06 2011-03-16 水利部交通运输部国家能源局南京水利科学研究院 Triaxial test method for shear strength property of weak layer
CN104034608A (en) * 2014-06-20 2014-09-10 中国水电顾问集团华东勘测设计研究院有限公司 Vertical pull-type bidirectional contact surface shearing strength parameter testing device and testing method
CN109211688A (en) * 2018-09-19 2019-01-15 华北水利水电大学 A kind of quick method for judging whether to destroy after unsaturated soil stress
CN110004991A (en) * 2019-04-29 2019-07-12 中铁第一勘察设计院集团有限公司 Underground structure anti-floating system and construction method based on raised type tangs plate

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SU1541470A1 (en) * 1987-05-22 1990-02-07 Всесоюзный научно-исследовательский институт зерна и продуктов его переработки Method of integrating priority and production-dependent streams of loose materials
CN1916359A (en) * 2005-11-28 2007-02-21 长庆石油勘探局 Method for building new slot to implement refracturing
CN101986130A (en) * 2010-09-06 2011-03-16 水利部交通运输部国家能源局南京水利科学研究院 Triaxial test method for shear strength property of weak layer
CN104034608A (en) * 2014-06-20 2014-09-10 中国水电顾问集团华东勘测设计研究院有限公司 Vertical pull-type bidirectional contact surface shearing strength parameter testing device and testing method
CN109211688A (en) * 2018-09-19 2019-01-15 华北水利水电大学 A kind of quick method for judging whether to destroy after unsaturated soil stress
CN110004991A (en) * 2019-04-29 2019-07-12 中铁第一勘察设计院集团有限公司 Underground structure anti-floating system and construction method based on raised type tangs plate

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
张骞: "岩石三轴压缩峰后曲线与抗剪强度参数关系探讨", 《地下空间与工程学报》 *
黄吉龙: "大口径管顶进过程的数值模拟分析", 《地下空间与工程学报》 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112557168A (en) * 2020-11-06 2021-03-26 清华大学 Stacked ring type hollow torsional shear equipment and pressure compensation method thereof
CN113218735A (en) * 2021-05-10 2021-08-06 昆明理工大学 Triaxial test saturated sample loading method for soil
CN113916739A (en) * 2021-08-24 2022-01-11 河海大学 Soil-concrete contact seepage test device and method considering contact surface shearing
CN113533034A (en) * 2021-08-30 2021-10-22 石家庄铁道大学 Soil body tensile test device and soil body tensile test method

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