Mechanical Properties And Constitutive Models Of Frozen Clay Under Different States Of Intermediate Principal Stress

With the rapid development of economic construction,urban underground engineering construction in complex hydrogeological environment is increasing,which provides a broad space for the application of artificial freezing method.Therefore,it is of great significance to study the mechanical properties of artificial frozen soil.Based on frozen clay as the research object,this paper use the permafrost true triaxial test apparatus,carried out in different initial moisture content,negative moderate small primary stress under the condition of true triaxial compression test,in principal stress strength of frozen clay are studied and the influence of the deformation characteristics,based on the Duncan-chang model is established on the effect of the principal stress frozen clay constitutive model.The main research contents are as follows:(1)The unconfined compressive strength tests were carried out under different negative temperatures(-5℃,-10℃,-15℃)and different water content(8%,12%,16%,20%,24%,28%).The results show that the compressive strength of frozen clay increases with the decrease of negative temperature when the water content is the same.Under different negative temperature conditions,the compressive strength first increased and then decreased with the increase of water content.When the temperature is-5℃ and-10℃,the frozen clay with 12% moisture content has the highest strength,and when the temperature is-15℃,the frozen clay with 16% moisture content has the highest strength.There is a positive correlation between deformation modulus and unconfined compressive strength.With the increase of water content,the failure mode changes from brittle failure to plastic failure.(2)The effects of medium principal stress on the mechanical properties of frozen clay at different negative temperatures(-5℃,-10℃,-15℃)and small principal stresses(0.8MPa,1.6MPa,2.4MPa)were investigated.The results show that the stress-strain curves of frozen clay show strain hardening type under different test conditions.The influence of middle principal stress on the deformation of frozen clay is significant.With the increase of middle principal stress,the deformation difference between middle principal stress and small principal stress direction gradually increases,while the deformation difference between middle principal stress and large principal stress direction gradually decreases.The medium principal stress has both strengthening and weakening effects on the mechanical properties of frozen clay.There is a critical value of medium principal stress,and the critical value varies with temperature and small principal stress.When the medium principal stress is less than the critical value,the strengthening effect is dominant,and when the medium principal stress is more than the critical value,the weakening effect is dominant.With the increase of middle principal stress,the deformation in this direction changes from expansion to compression,and the expansion deformation in the direction of small principal stress increases significantly.In addition,the strength of frozen clay increases with the decrease of negative temperature and the increase of small principal stress under different medium principal stress states.(3)Based on the Duncan-Zhang model,a constitutive model of frozen clay affected by medium principal stress is established.The theoretical values of the model are compared with the experimental values.The results show that the model can reflect the strength and deformation characteristics of frozen clay under different medium principal stress states,which provides a reference for the artificial freezing method.Figure [32] table [11] references [103]...