Study On Shear Modulus Of Thawing Soils By Side-mounted Bender Elements

Thaw of frozen soil results in deterioration of its stiffness and strength,which is not conducive to the stability of the engineering structure.It is of great significance to understand the variation of mechanical parameters of frozen soil during the thaw,and to the structural health assessment and prevention of thaw disasters in cold area engineering and artificial freezing engineering.In order to obtain the variation of shear modulus of thawing soil,a freeze-thaw bender element test system was set up to test characteristics study on shear modulus of thawing clay ang sand under loaded and unloaded conditions.The analysis of the test results showed that:(1)A freeze-thaw bender element test device was developed,the sample tube of the device was a double-layered structure,the side of the cylinder was opened and the bender element probe was installed.The outer layer of the cylinder was a steel structure and the inner,layer was a PTFE material,which meets high pressure and vibration isolation requirements.The maximum pressure of the device is 10 MPa,which can realize single and two-way temperature control.(2)The bender element testing method of frozen soil was studied.The method of judging the arrival time was analyzed using standard plexiglass test pieces,the results show that the initial wave method has the highest test accuracy.The natural frequency of the test system was measured under the conditions of unfrozen soil,frozen soil and soilless conditions,and the frequency range of the excitation signal was determined from 3 kHz to 7 kHz.By testing different excitation waveforms,it was found that square wave waveforms were selected and the test results were less discrete.(3)The bender element test results of shear modulus of thawing soil under no-load condition show that the shear modulus of thawing clay and sand decreases with increasing temperature when the temperature is-25°C~-1°C,and the relationship between the shear modulus and the temperature can be expressed by logarithmic function.(4)Under no-load conditions,the shear modulus of thawing clay and sand increases with the increase of dry density.The lower the initial freezing temperature,the smaller the shear modulus of the thawing clay under the same temperature and density conditions.The shear modulus of thawing sand increases with the increase of water content,while the shear modulus of sand-saturated soil at positive temperature decreases with the increase of water content.(5)The initial thaw temperature of frozen clay is about-5 °C under load,and the shear modulus of thawing clay decreases with increasing temperature when the temperature is-25 °C ~-5 °C.The greater the axial load at the same temperature,the greater the shear modulus.Under the same load conditions,the thawing coefficient decreases with the increase of shear modulus.(6)Under the same experimental conditions,the shear modulus of the undisturbed soil is higher than that of the remolded soil,and the change of the void ratio of the undisturbed soil is smaller than that of the remolded soil.(7)In general,the shear modulus of sand is greater than that of clay.When the temperature is-25°C,the difference between them is about 3500 MPa.When the temperature is 20°C,the difference between the two is about 70 MPa.The degree of variation gradually decreases as the frozen soil thaws.(8)Under the same experimental conditions,the shear modulus measured in the load conditions is much higher than the shear modulus measured under no-load conditions,and their difference increases with the thaw of the frozen soil.