Experimental Investigation On The Long-term Properties Of Expansive Soils Subjected To Freeze-thaw Cycling

As a typical high cold and deep seasonal frozen soil area,northeast China is seriously affected by the strong freeze-thaw cycle that threatens long-term safety and working performance of various geotextiles structures.In the engineering practice of the seasonal frost area,it is found that expansive soil,which is widely distributed in the warm-moist climate region is also developed in the seasonal freezing zone.Considering that the long-term freeze-thaw cycle may trigger landslides easily,in order to improve the long-term safety of geotechnical engineering in cold regions,it is necessary to study the long-term performance of expansive soil under freeze-thaw cycles.With the support of the high-speed railway project in cold region,combined with the study of soil rheology at home and abroad,a series of tests were carried out on the expansive soil in Binxi and two other expansive soils.Including the basic physical properties test,the non-load swelling ratio test under the freeze-thaw cycles,the triaxial creep tests and the stress relaxation test under non-freezing and freeze-thaw cycle conditionsConsidering the influence of different water content,different confining pressure or vertical pressure and the number of freeze-thaw cycles,the triaxial creep test and the direct shear stress relaxation test were carried out on the spice expansive soil,and the experimental results are compared with the results of the Jiamusi expansive soil and Yanji expansive soil,which were obtained under the same condition.Based on the concept of disturbance state,an improved Nishihara model is established according to the experimental data.Through parameter fitting,it is proved that the model can consider the effect of freeze-thaw cycles on the long-term performance of expansive soil.To sum up,the research contents and results in this paper are as follows:Firstly,the basic physical and mechanical parameters of expansive soil were obtained,including mineral composition,swelling mineral content,particle gradation,boundary water content,free expansion rate and non-load expansion rate etc.And nonload expansion tests were carried out to study the change rules of expansive soil in Binxi,Jiamusi and Yanji under different water content,dry density and freeze-thaw cycles.Secondly,creep and stress relaxation tests of expansive soil with non freezing and freeze-thaw cycles condition were carried out.The laws of creep and stress relaxation properties of expansive soil under different water content,confining pressure or vertical pressure and freeze-thaw cycles were investigated.Then,the rheological properties of the expansive soil are compared with those of Yanji and Jiamusi.The rheological test results show that the increase of water content will have a significant effect on the long-term performance of expansive soil,and the confining pressure and vertical pressure will inhibit the rheological properties of the expansive soil,and the freeze-thaw cycle has an obvious adverse effect on the long-term performance of expansive soil.Finally,considering the effect of freezing and thawing cycles,the improved Nishihara model based on the concept of disturbed state is established.The disturbance function D takes into account the rheological properties of expansive soil with the variation of freeze-thaw cycles.On the basis of the Nishihara model,the effect of the freeze-thaw cycles on the long-term performance of expansive soil is reflected by the disturbance function.The model can effectively consider the creep and stress relaxation characteristics of expansive soil under different freeze-thaw cycles.