Effect of plastic states on tensile and compressive properties of frozen undisturbed clays
The artificial ground freezing method is widely used in underground engineering in soft soil areas and has been rapidly developed.However,the complex stratigraphic distribution in soft soil areas and the rheologi-cal properties of frozen soil materials also bring challenges to the program design and engineering construction of the artificial ground freezing method under large-scale conditions.Based on the field surveys and the context of an estuary access project in Sanya with pipe curtain freezing method construction,considering the complexity of distribution depth on clay with different plastic states,the tensile and compressive properties of frozen fluid-plas-tic clay,hard-plastic clay and plastic-silty clay were studied by radial splitting and uniaxial or triaxial compres-sion tests.The results show that the tensile properties of frozen undisturbed clays with three different plastic states are different under the radial splitting.The fluid-plastic clay and plastic-silty clay display weak strain-hard-en at-5℃,and weak strain-soften at-10℃and-15℃,while hard-plastic clay exhibits strong strain-soften at three negative temperatures.The frozen undisturbed clays with three different plastic states show weak strain-soften under compression tests.For both the tensile and compressive stress-strain behaviors,the weak strain-harden and strain-soften behaviors of the frozen undisturbed clays with three different plastic states can be de-scribed by a modified hyperbola model of deviator stress and axial strain,and the strong strain-soften behavior can be described by a quadratic parabola model.Under the same negative temperature,the tensile strength of the fluid-plastic clay is the weakest and the deformation resistance is the strongest,the plastic-silty clay is second-ary,and the hard-plastic clay has the strongest tensile resistance and the weakest deformation resistance.In the distribution range of initial tangential modulus on the frozen undisturbed clays with three different plastic states,it is largest for the plastic-silty clay,secondary for the fluid-plastic clay and smallest for the hard-plastic clay.However,the initial tangential modulus tends to increase with the decrease of temperature.The failure strain of hard-plastic clay has a tendency to increase with the increase of confining pressure,while the failure strain of flu-id-plastic clay and plastic-silty clay is relatively discrete and irregular.The shear strength of fluid-plastic,hard-plastic clay and plastic-silty clay can be described by the linear Mohr-Coulomb criterion.The cohesion and inter-nal friction angle of the three soils basically increase with the decrease of temperature.At the same temperature,the cohesive force of fluid-plastic clay is the smallest,the cohesive force of plastic-silty clay is close to that of hard-plastic clay,and for the internal friction angle,it is largest for the hard-plastic clay,secondary for the fluid-plastic clay and smallest for the plastic-silty clay.In this paper,the influence of plastic state on the tensile and compressive properties of frozen undisturbed clay is studied so as to provide data support and reference for the de-velopment of underground artificial freezing projects.
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