Constant Stress Ratio Loading Test Of Frozen Sand And Study Of Strength Criterion

The artificial ground freezing refers to artificially freezing the water-containing rock and soil layer to form a stable freezing curtain to resist the ground pressure and isolate the groundwater.It is widely used in geotechnical engineering such as urban underground transportation,underground mining roadways,and deep foundation pits.At present,more researches had been made on the mechanical properties of frozen soils under symmetric stress conditions,while the researches on stress-strain relationships,strength characteristics,deformation characteristics and constitutive models in three-dimensional unequal stress conditions has been less.Based on the true triaxial apparatus for frozen soil,we conducted a series of constant stress ratio three-dimensional compression tests.Five intermediate principal stress coefficients and three initial confining pressures were measured at-5,10 and-15? with artificially frozen sand.And the effects of temperature,confining pressure and intermediate principal stress on the mechanical properties of artificially frozen sand were researched.Meanwhile,a three-dimensional strength criterion considering unequal tensile and compressive strength of geotechnical materials and temperature effects was proposed.The main research contents and results are as follows:(1)The stress-strain relationship can be divided into four stages:compaction stage,elastic stage,strain hardening stage and yield stage.In response to increases of either the intermediate principal stress coefficient or the confining pressure or to decreases of temperature,the strength typically increased,and it has a linear relationship with the confining pressure and temperature.The failure strain decreases with the increase of the intermediate principal stress coefficient,then increases and then decreases.When the confining pressure is low,the failure strain increases linearly with the decrease of temperature.(2)The internal friction angle increases with the increase of the intermediate principal stress coefficient,which increases faster when the intermediate principal stress coefficient is small,and gradually decreases as the intermediate principal stress coefficient increases.When the intermediate principal stress coefficient is less than 0.5,the cohesive gradually decreases as the intermediate principal stress coefficient increases,and when the intermediate principal stress coefficient is greater than 0.5,the cohesive gradually increases again.As the confining pressure increases,the failure stress ratio gradually decreases and keeps constant.Parabola can be used to describe the relationship between the failure stress ratio and intermediate principal stress coefficient.(3)The volume change shows a trend of shear shrinkage followed by dilatation When the intermediate principal stress coefficient is small,the intermediate principal stress direction exhibits an expansion trend,and as the intermediate principal stress increases,it exhibits a compression trend.While the minor principal stress direction always expands.As the strength of the specimen increases,the failure shear dilation rate and critical generalized shear strain of the specimen increase gradually.(4)At low confining pressure,the intensity on the p-q plane can be described by a linear relationship,and the slope and intercept of the straight line change linearly with temperature.The existing three-dimensional strength criterion applicable to conventional geotechnical materials is not suitable for describing the strength envelope of artificial frozen sand on the ? plane.(5)A three-dimensional strength criterion for frozen sand under low confining pressure was established.The results of tests on different geotechnical materials show that the tensile strength of the soil is not equal to the compressive strength.Based on the relationship between the stress invariants of geotechnical materials,a strength criterion considering the unequal characteristics of tension and compression of the material is proposed.At the same time,the influence of temperature on the parameters of the criterion is considered,and the analytical solution of the angular function is given.The verification results show that the criterion can describe the strength characteristics of artificial frozen sand under low confining pressure.Figure[62]table[5]reference[85]...