Laboratory investigation on the mechanical behavior of ice-saturated frozen loess
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Abstract:
To investigate the mechanical properties of ice-saturated frozen soil, a series of triaxial tests under various confining pressures(0.5 to 9.0 MPa) on ice-saturated frozen loess with ice content of 23.7% were carried out at a temperature-6 °C, and at 1.25 mm/min of loading rate. The triaxial tests include two loading modes, one with monotonic loading(i.e., triaxial compression), and another with static cycle loading. The test results under triaxial compression show that the strength and deformation behaviors of ice-saturated frozen loess are affected by confining pressure. According to the test results of triaxial loading-unloading cycle test, the elastic modulus evolution with the number of cycles under different confining pressures are analyzed.Keywords:
Overburden pressure
Triaxial shear test
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The paper decscribes an investigation of the effects of confining pressure on the shear strength of frozen soil. Triaxial compression tests were conducted on two ice-saturated frozen soils to a confining pressure of 40 kip/sq.in.at – 10°C. The shear strength was observed to change with increasing mean stress in three distinct regions. At low mean stresses the shear strength remained constant or increased, at intermediate mean stresses the shear strength decreased, and at high mean stresses the shear strength increased. It is suggested that interpatricle friction and particle interlocking, unfrozen water content, pressure melting, and the ice/water phase change are the factors that most influence the triaxial compression behaviour of frozen soils. La communication décrit une recherche relative aux effets de la pression latérale sur la résistance au cisaillement des sols gelés mesurée au triaxial. On a effectué des essais triaxiaux sur deux sols saturés gelés avec une pression latérale de 40 ksi à – 10°C. On a constaté qui'll y a trois possibilités de vaiation de la résistance au cisaillement avec l'augmentation de la contrainte moyenne. Aux faibles valeurs de contrainte moyenne. la réistance au cisaillement reste constante ou augmente, pour les valeurs intermédiatires de la contrainte moyenne, la résistance au cisaillement décroît et pour les grandes valeurs de la contrainte moyenne, la résistance au cisaillement augmente. On estime que les principaux facteurs an qui influencent le comportement des sols gelés en compression triaxiale sont le frottement intergranulaire, l'enchevêtrement des particules, le pourcentage d'eau non gelée, la pression de fusion de la glace et le changement de phase glace-eau.
Overburden pressure
Triaxial shear test
Shear Strength
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Engineers concerned with the development of Alaska and other highly seismic areas underlain by permafrost must have knowledge of dynamic properties of frozen soils under earthquake loading conditions. In response to this need, a cyclic triaxial test system and test methods have been developed to evaluate the dynamic Young's modulus and damping ratio of artificially frozen soils over a range of test conditions which simulate earthquake loadings of permafrost deposits. The test system developed represents a coupling of conventional closed-loop cyclic triaxial equipment to evaluate the dynamic properties of unfrozen soils with conventional temperature control equipment to evaluate static properties of frozen soils. On-line, real-time data processing has been achieved by coupling a minicomputer to the test system. With the test system, the dynamic Young's modulus and damping ratio can be determined over a range of axial strain amplitudes from 3 × 10-3 to 10-1 percent, temperatures from -1 to -10°C (30 to 14°F), frequencies from 0.3 to 5.0 Hz, and confining pressures from 0 to 1400 kN/m2 (200 psi). An extensive laboratory program was undertaken to establish suitable methods of specimen preparation, specimen installation, and testing for artificially frozen specimens of clay, silt, sand, and ice. At present there is no standard test procedure to evaluate dynamic properties of frozen soils under simulated earthquake loading conditions. The material presented provides a basis for the development of a standard test procedure.
Dynamic testing
Damping ratio
Silt
Soil test
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Overburden pressure
Triaxial shear test
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Mechanical tests of frozen soil are essentially a process to obtain the physical and mechanical parameters of frozen soil for engineering design in cold regions and the model parameters in constitutive model of frozen soil.Along with the deepening of research,mechanical behaviors of frozen soil under different loading paths,which are effective approach to verify the existing models,should be investigated more.Thus,precise mechanical tests are fundamental mean to cognize the mechanical properties of frozen soil.For further examining the mechanical properties of frozen soil and increasing the accuracy of mechanical tests,two isotropic consolidation tests and two triaxial shear loading-unloading tests are conducted by using MTS-810 Triaxial Material Test Machine at low temperature.According to the test results,scope of application of the test method is analyzed.A testing program is proposed using the test machine for shear test with constant net mean stress,which is able to examine the effect of equivalent shearing stress on volumetric deformation of frozen soil.
Shearing (physics)
Consolidation
Triaxial shear test
Soil Mechanics
Soil test
Direct shear test
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Six pressuremeter tests and one multistage triaxial creep test were conducted on a prepared frozen sand at −2.5 and −3°C, respectively. The pressuremeter study suggested that the model of incompressible power-law fluid, which is sometimes used in the numerical modelling of frozen-ground geotechnical problems, would not provide a suitable “simplified constitutive relation” on which we could base the design of a new standard pressurementer test for discerning long-term creep properties of warm permafrost. The multistage triaxial creep test showed a correlation between the decreasing or increasing in volume of the specimen and the attenuating or nonattenuating character of its axial creep behavior.
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