CN108375505A - A kind of high-precision straight line stress path tests method of frozen soil - Google Patents

A kind of high-precision straight line stress path tests method of frozen soil Download PDF

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CN108375505A
CN108375505A CN201810169833.9A CN201810169833A CN108375505A CN 108375505 A CN108375505 A CN 108375505A CN 201810169833 A CN201810169833 A CN 201810169833A CN 108375505 A CN108375505 A CN 108375505A
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stress path
slope
experiment
frozen soil
stress
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CN108375505B (en
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徐湘田
白瑞强
王永涛
曹阳
杨宗维
何扬
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Inner Mongolia University
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Inner Mongolia University
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    • 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
    • G01N3/08Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • 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
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014Type of force applied
    • G01N2203/0016Tensile or compressive
    • G01N2203/0019Compressive
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058Kind of property studied
    • G01N2203/0069Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0075Strain-stress relations or elastic constants
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02Details not specific for a particular testing method
    • G01N2203/06Indicating or recording means; Sensing means
    • G01N2203/067Parameter measured for estimating the property
    • G01N2203/0682Spatial dimension, e.g. length, area, angle

Abstract

The invention discloses a kind of high-precision straight line stress path tests methods of frozen soil comprising following steps:(1) bulk strain is disregarded when specimen cross sectional area is corrected, and carries out near linear stress path tests;(2) according to step (1) test result, actual volume strains during calculating experiment, corrects specimen cross sectional area with this, obtains actual stress path slope k '.The straight line stress path of arbitrary slope may be implemented in the method for the present invention, has filled up in frozen soil and has been difficult to carry out the vacancy of complicated stress environment experiment;Modified specimen cross sectional area is applied when calculating axial stress, has been included in bulk strain, when correcting specimen cross sectional area, using the axial strain ε of last time experiment1It is modified with the relationship of cross-sectional area A, the problem of bulk strain cannot be considered when overcoming current load;The present invention is that new stress path tests method is developed on existing frozen soil triaxial apparatus, does not increase optional equipment, substantially increases the service efficiency etc. of existing experimental rig.

Description

A kind of high-precision straight line stress path tests method of frozen soil
Technical field:
The present invention relates to a kind of frozen soil mechanics test methods, more particularly to a kind of high-precision straight line stress path of frozen soil Test method.
Background technology:
Straight line stress path tests refer to keeping dq/dp=k for the experiment of constant in Geotechnical materials triaxial test, should Experiment can be used for investigating the mechanical characteristics of frozen soil material under different k values, can be used for determining yield surface and the hardening of frozen soil material Law, it can also be used to the verification of Constitutive Model of Frozen Soil.It is special that frozen soil does not freeze one kind that water, soil particle and gas form by ice, The soil body, group structure complexity, mechanical behavior are influenced by many factors such as temperature, loading speed, stress conditions.Currently, freezing In the research of soil mechanical properties, uniaxial compression test and conventional triaxial compression test are mainly applied, both experiments are actually only It is the straight line stress path of slope k=3.Single shaft can be realized with ordinary triaxial test by strain controlling pattern, i.e. axial pressure Plunger at the uniform velocity loads, without calculating bulk strain during experiment, without calculating correction area, therefore, uniaxial compression Experiment and conventional triaxial compression test, can not investigate deformation and failure rule of the frozen soil under other straight line stress paths.And it is real In the engineering of border, the stress path for undergoing various complexity is known from experience as the frozen soil of works ground or structures, only uses slope k=3 The obtained frozen soil mechanics property of straight line stress path tests instruct engineering design then can and actual condition deviation occurs.
Uniaxial compression test and conventional triaxial compression test are only capable of mechanical deformation row of reflection frozen soil in the case of k=3 For, and arbitrary line stress path tests can reflect the mechanical deformation behavior of frozen soil under arbitrary line stress path, can obtain Frozen soil mechanics property under more stress paths, makes the Constitutive Model of Frozen Soil thereby determined that for the prediction of frozen soil mechanics deformational behavior It is more accurate.It investigates frozen soil mechanics under different stress paths to respond and carry out engineering design accordingly, then needs to develop more jellies The stress path tests method of soil, to investigate the mechanical property of frozen soil comprehensively and establish rational Constitutive Model of Frozen Soil.
Arbitrary line stress path can not be realized by strain controlling pattern, need to be realized, tried by Stress Control pattern It needs to be gone to correct load-carrying area with bulk strain during testing, solves required load actual axial force.Currently, applying low temperature three When axis instrument carries out the stress path tests of frozen soil, confining pressure increment Delta σ in practical operation3Can directly it be applied by confining pressure loading system, But domestic and international existing frozen soil triaxial apparatus axial loading system can only control axle power increment Delta F, axial stress increment Delta σ1=Δ F/A It then needs that (cross-sectional area that A is sample) is obtained by calculation, in test frozen soil sample is axially compressed, and cross-sectional area A is not It is disconnected to become larger, the cross-sectional area A of sample when the Δ F that each step applies must just calculate each step load in advance is accurately calculated, it is horizontal Sectional area A is according to A=A0(1-εv)/(1-εa) calculate (A0For the original area of sample), experiment cannot calculate body when not completing Product strain stressvValue, A when also being loaded you can't get each step and Δ F.Therefore, there is presently no application low temperature triaxial apparatus into The method of the arbitrary line stress path tests of row frozen soil.
Invention content:
The present invention lacks the present situation of complicated stress environment experiment in order to change in frozen soil mechanics test method, using existing low Warm triaxial apparatus provides a kind of high-precision straight line stress path tests method of frozen soil.
The present invention is implemented by following technical solution:A kind of high-precision straight line stress path tests method of frozen soil comprising Following steps:(1) bulk strain is disregarded when specimen cross sectional area is corrected, and carries out near linear stress path tests;(2) according to step Suddenly (1) test result, actual volume strains during calculating experiment, corrects specimen cross sectional area with this, obtains actual stress road Diameter slope k ';
(1) bulk strain is disregarded when specimen cross sectional area is corrected, and carries out near linear stress path tests:
Step 1 makes frozen soil sample;
Frozen soil sample is put into the balancing gate pit of frozen soil triaxial apparatus by step 2, and pressure room temperature is maintained at targeted test temperature Degree;
Step 3 applies confining pressure to the starting point of stress path;
Step 4, sets target stress path slope k, and setting often walks confining pressure increment Delta σ3
Step 5, according to axial strain ε1Typically much deeper than bulk strain εvThe fact, set each step axial strain increment No more than 0.1%, amendment of the bulk strain to specimen cross sectional area is disregarded first, with A '=A0/(1-ε1) replace A=A0(1- εv)/(1-ε1) come calculate frozen soil sample approximate cross-section accumulate A ';When disregarding amendment of the bulk strain to specimen cross sectional area, Suitable each step axial strain increment can be set according to the property of different frozen soil itself, reduce iterative test number.
Wherein:A0For frozen soil sample original cross-sectional area, εvFor bulk strain, ε1For axial strain;
Step 6 is used according to step 4 and step 5 in step (1)It calculates and sets each step Axle power incrementThen, the straight line stress path tests of approximation k slopes are carried out;
(2) according to step (1) test result, actual volume strains during calculating experiment, and sample cross is corrected with this Product, obtains actual stress path slope k ':
Step 1, step (1) after the test, measure the Z during step (1) experimentdAnd Cd, (1-1) formula is utilized to calculate Bulk strain ε during experimentv,
Wherein, ZdAnd Z0The respectively current location of triaxial apparatus axial pressure plunger and initial position;V0For on-test when Frozen soil sample initial volume, ShFor the cross-sectional area of confining pressure loading system piston, CdThe present bit of piston is loaded for confining pressure in experiment It sets, C0For on-test when confining pressure load piston initial position;
Step 2, each step bulk strain ε that will be calculatedvε in being tested with step (1)1Substitute into A=A0(1-εv)/ (1-ε1) in, each step sample real cross-section product A is calculated;
Step 3, each step sample real cross-section product A and step (1) obtained according to step 2 in step (2) are tested In each step actual axial stress increment Delta σ of the practical axle power incremental computations of each step1=Δ F/A;
Step 4 calculates each step actual axial stress increment Delta σ of gained using step 3 in step (2)1With it is preset Each step confining pressure increment Delta σ3, actual stress path slope k ' is calculated according to (1-2) formula,
If the relative error of the actual stress path slope k ' value calculated and setting target stress path slope k value Allow in accuracy rating in experiment, it is proposed that relative error 5%, the then experiment in step (1) can be used as that meet precision k slopes straight It tests in uniaxial stress path.
Further, in the step (2), actual stress path slope k ' value and setting target stress path slope k value Relative error be more than experiment allow precision, then according to the test result of the step (1), by step 2 in the step (2) The each step sample real cross-section for calculating gained accumulates A, with axial strain stress in high-precision Function Fitting step (1)1With sample cross The relationship of sectional area A is denoted as A=f (ε1);
A, target stress path slope k is set, setting often walks confining pressure increment Delta σ3
B, it sets each step axial strain increment and is not more than 0.1%, utilize function A=f (ε1) calculate the close of frozen soil sample Like cross-sectional area A ';
C, according to step A and step B as a result, withIt calculates and sets each step axle power incrementThen, the straight line stress path tests of approximation k slopes are carried out;
After the test, repeating said steps (2) step, calculates sample real cross-section product A and actual stress path is oblique Rate k ', if experiment gained actual stress path slope k ' value and the relative error of setting target stress path slope k value are being tested Allow in accuracy rating, then this experiment, which can be used as, meets precision k slope straight line stress path tests;
If experiment gained actual stress path slope k ' value and the relative error of setting target stress path slope k value are more than Experiment allows precision, then according to new ε1- A functional relation A=f (ε1), step A, step B and step C are repeated, then carry out close It tests, iterates like k slopes path, until actual stress path slope k ' value and setting target stress path slope k value For relative error until experiment allows in accuracy rating, last time experiment can be used as the enough k slope stress paths examinations of precision It tests.By this step can realize the bulk strain for being included in last experiment in the specimen cross sectional area amendment tested next time, Actual stress path slope k ' value constantly approaches setting target stress path slope k value.
Specifically, the triaxial apparatus is currently generally with the low of Stress Control, strain controlling and multi-way contral pattern Warm triaxial apparatus.
Specifically, stress path starting point σ3, it can be achieved that slope k is the arbitrary line stress road in (0 ,+∞) range when being 0 Diameter is tested;Stress path starting point σ3, it can be achieved that slope k is the arbitrary line stress path examination in (- ∞ ,+∞) range when more than 0 It tests.
The principle and test procedure of the method for the present invention can be applied to required precision it is high melt native straight line stress path tests.
Straight line stress path tests method of the present invention is based on following calculating formula in experiment is arranged:
(1-k/3)Δσ1=(1+2k/3) Δ σ3 (1-4)
P is mean stress in formula, and q is deviatoric stress, σ1For axial stress, σ3For confining pressure;Δp、Δσ1With Δ σ3Respectively For mean stress increment, Deviation stress increment, axial stress increment and confining pressure increment, k is stress path slope.
By (1-4) formula it is found that after given slope k and setting confining pressure increment, can be calculated in frozen soil low temperature three by (1-5) formula The axial stress increment that should be arranged on axis instrument realizes various straight line stress path tests.
Confining pressure increment Delta σ in practical operation3Can directly it be applied by confining pressure loading system and control.However, existing both at home and abroad Frozen soil triaxial apparatus axial loading system can not carry out axial stress increment directly to apply and control, and can only control axle power increment Delta F, axial stress increment are then needed through Δ σ1(cross-sectional area that A is sample) is calculated in=Δ F/A, freezes during the test Axial strain occurs for soil sample and bulk strain, cross-sectional area A change with deformation, accurately to calculate the axis that each step applies The cross-sectional area A of sample when power increment Delta F must just calculate the load of each step in advance, and test the when of being not finished can not calculate it is each The cross-sectional area A of sample when step load, it is transversal during experiment to correct that the present invention proposes a kind of method similar to iterative method Area A and control axle power increment Delta F.
Advantages of the present invention:
(1) present invention proposes a kind of high-precision straight line stress path tests method of frozen soil, and this method can be to frozen soil reality The straight line stress path of incumbent meaning slope provides test hand to investigate deformation failure behavior of the frozen soil under complicated stress environment Section;
(2) present invention has been included in axial strain and bulk strain simultaneously in the final stress path test result of frozen soil, Mechanical characteristic of the frozen soil under true stress path can be obtained;
(3) present invention applies modified specimen cross sectional area when calculating axial stress, has been included in bulk strain, has corrected When specimen cross sectional area, using the axial strain ε of last time experiment1It is modified, overcomes with the relationship of cross-sectional area A The problem of bulk strain cannot be considered when current load;
(4) present invention controls the essence of arbitrary slope straight line stress path frozen soil experiment by the method similar to iteration Degree, the area correction of each iteration all contain the bulk strain factor of last experiment, so that result is constantly tended to be accurate, can lead to The straight line stress path tests achievement of arbitrary accuracy is obtained after iteration several times;
(5) present invention takes each step axial strain step delta ε during experiment for the first time1No more than 0.1%, make each step Approximate cross-section product A ' variations it is little, when being not yet included in bulk strain obtained by k value errors it is little, it is secondary to reduce iterative test Number improves test efficiency;
(6) present invention is that new straight line stress path tests method is developed on traditional frozen soil triaxial apparatus, is not increased Add optional equipment, improves the service efficiency of existing experimental rig.
Description of the drawings:
Fig. 1 is a kind of high-precision straight line stress path tests method flow diagram of frozen soil;
Fig. 2 is that straight line stress path tests slope k value calculates schematic diagram;
Fig. 3 is the straight line stress path tests value figure of 1 slope k of embodiment=3;
Fig. 4 is the straight line stress path tests value of 2 slope k of embodiment=2 and preset value comparison diagram;
Fig. 5 is 3 slope k of embodiment=5 straight line stress path, 2 test values and preset value comparison diagram;
Specific implementation mode:
Embodiment 1-3 be all made of water content be 16%, dry density 1.5g/cm3Root river clay make frozen soil sample and come The straight line stress path tests for carrying out frozen soil, prepare frozen soil sample and are as follows:
Soil is first configured to the scattered soil body of target water content, and about 6h is kept in the case where limiting evaporation conditions, makes moisture in soil In body uniformly, it is then layered die-filling, by the dry density of test requirements document by rammed earth densification, the circle of high 100mm, diameter 50mm is made Cylinder sample.Sample gang mould tool is put into togerther refrigeration case, and the quick freezing in -30 DEG C of environment takes off sample after freezing about 48h Mould, then by sample be placed under test temperature constant temperature for 24 hours more than, be made and freeze root river clay sample.
Embodiment 1:Frozen soil sample obtained is put into low temperature triaxial apparatus to have set in the balancing gate pit of test temperature, waits for temperature After stabilization, apply confining pressure to the stress path starting point of 2MPa, keeps after five minutes, carrying out frozen soil conventional triaxial compression test, such as scheming Shown in 3, conventional triaxial compression test path can be accurately obtained the frozen soil straight line stress path tests result of slope k=3.
Embodiment 2:A kind of high-precision straight line stress path tests method of frozen soil, includes the following steps:(1) sample is transversal Bulk strain is disregarded when area correction, carries out near linear stress path tests;(2) according to step (1) test result, examination is calculated Actual volume strains during testing, and corrects specimen cross sectional area with this, obtains actual stress path slope k ';Wherein,
(1) bulk strain is disregarded when specimen cross sectional area is corrected, and carries out near linear stress path tests:
Step 1 makes frozen soil sample, the constant temperature 24 hours at a temperature of -10 DEG C of targeted test;
Frozen soil sample is put into the balancing gate pit of frozen soil triaxial apparatus by step 2, and pressure room temperature is maintained at -10 DEG C of target examinations Test temperature;
Step 3 applies confining pressure 3MPa to the starting point of stress path, is kept for 5 minutes;
Step 4, setting target stress path slope k=2, setting often walk confining pressure increment Delta σ3=0.02MPa/min;
Step 5, according to axial strain ε1Typically much deeper than bulk strain εvThe fact, set each step axial strain increment It is 0.1%, disregards amendment of the bulk strain to specimen cross sectional area first, with A '=A0/(1-ε1) replace A=A0(1-εv)/ (1-ε1) come calculate frozen soil sample approximate cross-section accumulate A ';
Wherein:A0For frozen soil sample original cross-sectional area, εvFor bulk strain, ε1For axial strain;
Step 6 is used according to step 4 and step 5 in step (1)It calculates and sets each step Axle power incrementThen, the straight line stress path tests of approximation k slopes are carried out;
(2) according to step (1) test result, actual volume strains during calculating experiment, and sample cross is corrected with this Product, obtains actual stress path slope k ':
Step 1, step (1) after the test, measure the Z during step (1) experimentdAnd Cd, (1-1) formula is utilized to calculate Bulk strain ε during experimentv,
Wherein, ZdAnd Z0The respectively current location of triaxial apparatus axial pressure plunger and initial position;V0For on-test when Frozen soil sample initial volume, ShFor the cross-sectional area of confining pressure loading system piston, CdThe present bit of piston is loaded for confining pressure in experiment It sets, C0For on-test when confining pressure load piston initial position;
Step 2, each step bulk strain ε that will be calculatedvε in being tested with step (1)1Substitute into A=A0(1-εv)/ (1-ε1) in, each step sample real cross-section product A is calculated;
Step 3, each step sample real cross-section product A and step (1) obtained according to step 2 in step (2) are tested In each step actual axial stress increment Delta σ of the practical axle power incremental computations of each step1=Δ F/A;
Step 4 calculates each step actual axial stress increment Delta σ of gained using step 3 in step (2)1With it is preset Each step confining pressure increment Delta σ3, actual stress path slope k ' is calculated according to (1-2) formula,
Test result is as shown in figure 3, be calculated actual stress path slope k '=2.07, actual stress path slope k ' Value with set the relative error of target stress path slope k value as 3.5%, without departing from the relative error 5% of setting, then step (1) experiment in can be used as the enough k slope stress path tests of precision.
Embodiment 3:A kind of high-precision straight line stress path tests method of frozen soil, includes the following steps:(1) sample is transversal Bulk strain is disregarded when area correction, carries out near linear stress path tests;(2) according to step (1) test result, examination is calculated Actual volume strains during testing, and corrects specimen cross sectional area with this, obtains actual stress path slope k ';Wherein,
(1) bulk strain is disregarded when specimen cross sectional area is corrected, and carries out near linear stress path tests:
Step 1 makes frozen soil sample, the constant temperature 24 hours at a temperature of -10 DEG C of targeted test;
Frozen soil sample is put into the balancing gate pit of frozen soil triaxial apparatus by step 2, and pressure room temperature is maintained at -10 DEG C of target examinations Test temperature;
Step 3 applies confining pressure 1MPa to the starting point of stress path, is kept for 5 minutes;
Step 4, setting target stress path slope k=5, setting often walk confining pressure increment Delta σ3=0.002MPa/min;
Step 5, according to axial strain ε1Typically much deeper than bulk strain εvThe fact, set each step axial strain increment It is 0.1%, disregards amendment of the bulk strain to specimen cross sectional area first, with A '=A0/(1-ε1) replace A=A0(1-εv)/ (1-ε1) come calculate frozen soil sample approximate cross-section accumulate A ';
Wherein:A0For frozen soil sample original cross-sectional area, εvFor bulk strain, ε1For axial strain;
Step 6 is used according to step 4 and step 5 in step (1)It calculates and sets each step Axle power incrementThen, the straight line stress path tests of approximation k slopes are carried out;
(2) according to step (1) test result, actual volume strains during calculating experiment, and sample cross is corrected with this Product, obtains actual stress path slope k ':
Step 1, step (1) after the test, measure the Z during step (1) experimentdAnd Cd, (1-1) formula is utilized to calculate Bulk strain ε during experimentv,
Wherein, ZdAnd Z0The respectively current location of triaxial apparatus axial pressure plunger and initial position;V0For on-test when Frozen soil sample initial volume, ShFor the cross-sectional area of confining pressure loading system piston, CdThe present bit of piston is loaded for confining pressure in experiment It sets, C0For on-test when confining pressure load piston initial position;
Step 2, each step bulk strain ε that will be calculatedvε in being tested with step (1)1Substitute into A=A0(1-εv)/ (1-ε1) in, each step sample real cross-section product A is calculated;
Step 3, each step sample real cross-section product A and step (1) obtained according to step 2 in step (2) are tested In each step actual axial stress increment Delta σ of the practical axle power incremental computations of each step1=Δ F/A;
Step 4 calculates each step actual axial stress increment Delta σ of gained using step 3 in step (2)1With it is preset Each step confining pressure increment Delta σ3, actual stress path slope k ' is calculated according to (1-2) formula,
Actual stress path slope k '=4.5785, actual stress path slope k ' value and setting target stress is calculated The relative error of path slope k values is 8.43%, the relative error 5% beyond setting, therefore, according to the examination of the step (1) It tests as a result, by each step sample real cross-section product A of step 2 calculating gained in the step (2), is intended with high-precision function Close axial strain stress in step (1)1With the relationship of specimen cross sectional area A, it is denoted as A=f (ε1);
A, setting target stress path slope k=5, setting often walk confining pressure increment Delta σ3=0.002MPa/min;
B, each step axial strain increment is set as 0.1%, utilizes function A=f (ε1) calculate the approximate horizontal of frozen soil sample Sectional area A ';
C, according to step A and step B as a result, withIt calculates and sets each step axle power incrementThen, the straight line stress path tests of approximation k slopes are carried out;
After the test, repeating said steps (2) step, calculates sample real cross-section product A and actual stress path is oblique Rate k '=4.7815, after an iteration, experiment gained actual stress path slope k ' value and setting target stress path are oblique The relative error of rate k values is 4.37%, and without departing from the relative error 5% of setting, it is enough to show that this experiment can be used as precision K slope stress path tests.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all essences in the present invention With within principle, any modification, equivalent replacement, improvement and so on should all be included in the protection scope of the present invention god.

Claims (4)

1. a kind of high-precision straight line stress path tests method of frozen soil, it is characterised in that:It includes the following steps:(1) sample Cross-sectional area disregards bulk strain when correcting, carry out near linear stress path tests;(2) according to step (1) test result, meter Actual volume strains during calculating experiment, corrects specimen cross sectional area with this, obtains actual stress path slope k ';
(1) bulk strain is disregarded when specimen cross sectional area is corrected, and carries out near linear stress path tests:
Step 1 makes frozen soil sample;
Frozen soil sample is put into the balancing gate pit of frozen soil triaxial apparatus by step 2, and pressure room temperature is maintained at targeted test temperature;
Step 3 applies confining pressure to the starting point of stress path;
Step 4, sets target stress path slope k, and setting often walks confining pressure increment Delta σ3
Step 5, according to axial strain ε1Typically much deeper than bulk strain εvThe fact, it is little to set each step axial strain increment In 0.1%, amendment of the bulk strain to specimen cross sectional area is disregarded first, with A '=A0/(1-ε1) replace A=A0(1-εv)/ (1-ε1) come calculate frozen soil sample approximate cross-section accumulate A ';
Wherein:A0For frozen soil sample original cross-sectional area, εvFor bulk strain, ε1For axial strain;
Step 6 is used according to step 4 and step 5 in step (1)It calculates and sets each step axle power IncrementThen, the straight line stress path tests of approximation k slopes are carried out;
(2) according to step (1) test result, actual volume strains during calculating experiment, corrects specimen cross sectional area with this, obtains To actual stress path slope k ':
Step 1, step (1) after the test, measure the Z during step (1) experimentdAnd Cd, (1-1) formula is utilized to calculate experiment Bulk strain ε in the processv,
Wherein, ZdAnd Z0The respectively current location of triaxial apparatus axial pressure plunger and initial position;V0For on-test when frozen soil Sample initial volume, ShFor the cross-sectional area of confining pressure loading system piston, CdThe current location of piston is loaded for confining pressure in experiment, C0For on-test when confining pressure load piston initial position;
Step 2, each step bulk strain ε that will be calculatedvε in being tested with step (1)1Substitute into A=A0(1-εv)/(1- ε1) in, each step sample real cross-section product A is calculated;
Step 3, during each step sample real cross-section product A and step (1) obtained according to step 2 in step (2) is tested The each step actual axial stress increment Delta σ of each practical axle power incremental computations of step1=Δ F/A;
Step 4 calculates each step actual axial stress increment Delta σ of gained using step 3 in step (2)1With preset each step Confining pressure increment Delta σ3, actual stress path slope k ' is calculated according to (1-2) formula,
If the relative error of the actual stress path slope k ' values calculated and setting target stress path slope k value is being tried Testing allows in accuracy rating, then the experiment in step (1), which can be used as, meets precision k slope straight line stress path tests.
2. a kind of high-precision straight line stress path tests method of frozen soil according to claim 1, it is characterised in that:It is described In step (2), the relative error of actual stress path slope k ' values and setting target stress path slope k value, which is more than experiment, to be allowed Precision, then according to the test result of the step (1), each step sample that step 2 in the step (2) is calculated to gained is true Real cross-sectional area A, with axial strain stress in high-precision Function Fitting step (1)1With the relationship of specimen cross sectional area A, it is denoted as A=f (ε1);
A, target stress path slope k is set, setting often walks confining pressure increment Delta σ3
B, it sets each step axial strain increment and is not more than 0.1%, utilize function A=f (ε1) calculate the approximate transversal of frozen soil sample Area A ';
C, according to step A and step B as a result, withIt calculates and sets each step axle power incrementThen, the straight line stress path tests of approximation k slopes are carried out;
After the test, repeating said steps (2) step calculates sample real cross-section and accumulates A and actual stress path slope k ', If experiment gained actual stress path slope k ' values and the relative error of setting target stress path slope k value allow essence in experiment It spends in range, then this experiment, which can be used as, meets precision k slope straight line stress path tests;
If the relative error of experiment gained actual stress path slope k ' values and setting target stress path slope k value is more than experiment Allow precision, then according to new ε1- A functional relation A=f (ε1), step A, step B and step C are repeated, then to carry out approximate k oblique The experiment of rate path, iterates, and is missed until actual stress path slope k ' values are opposite with setting target stress path slope k value For difference until experiment allows in accuracy rating, last time experiment can be used as the enough k slope stress path tests of precision.
3. a kind of high-precision straight line stress path tests method of frozen soil according to claim 1 or 2, it is characterised in that: The triaxial apparatus is current generally with Stress Control, the low temperature triaxial apparatus of strain controlling and multi-way contral pattern.
4. a kind of high-precision straight line stress path tests method of frozen soil according to claim 1 or 2, it is characterised in that: Stress path starting point σ3, it can be achieved that slope k is the arbitrary line stress path tests in (0 ,+∞) range when being 0;Stress path Starting point σ3, it can be achieved that slope k is the arbitrary line stress path tests in (- ∞ ,+∞) range when more than 0.
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