The Change Rule Of Frozen Loess Long-term Strength Under Freeze-thaw Cycle

As the global third largest frozen soil country, the distribution area of permafrost and seasonal frozen soil accounts for two-thirds of the total land area in our country. With the development of national development strategy planning, frozen engineering construction is increasing. However, the periodical change of atmospheric temperature makes the property of soil change, which has direct affected the stability of frozen soil engineering foundation. Since long-term strength of frozen soil is the essential basis for determining foundation bearing capacity and stability of frozen soil engineering, then research on the change rule of frozen soil long-term strength under the freeze-thaw cycle and its related influencing factors has very important significance on practical engineering construction in frozen soil region.In this paper, through laboratory test, the research had taken remolded loess as the study object of freeze-thaw cycle test, tested the composition, structure, physical properties and the long-term strength of loess which had experienced different freeze-thaw cycles, respectively. To get the key factors has a principal effect on the change of the long-term strength, and the correlation analysis is performed between related parameters and mechanical properties. Experimental results show that:after repeated freeze-thaw cycles, quantity of sand particles in the sample increased while silt and clay particles reduced, at the same time, small pores among fine particles are gradually transformed into large pores among coarse particles, the particle composition, arrangement and coupling of soil sample has changed significantly. The changes of composition and structure directly affected its physical properties, and the void ratio of loess increased while density, liquid limit, plastic limit and plasticity index all decreased; The long-term strength of frozen soil increased first and decreased then after increasing freeze-thaw cycles, and the change of strength in the first 10 cycles was unstable; The long-term strength reached its peak after only 8 freeze-thaw cycles, and then the strength decreased slow; Through the correlation analysis, the correlation of particle composition and long-term strength is more closely than pore structure, especially the clay percentage composition, has significant negative correlation with long-term strength. So the clay content is the key factor to determine the long-term strength of the frozen soil.