Experimental Study On The Effect Of Freezing And Thawing Cycles On The Mechanical Properties Of Loess

The freeze-thaw cycle of loess is a natural phenomenon that occurs continuously in seasonal frozen soil area of our country.The influence of freeze-thaw cycle on foundation can not be avoided in the construction and use stage of various buildings based on Loess in Northwest China.In the process of continuous freeze-thaw cycles,the structure of the soil will be changed obviously,and the loess will be deteriorated,which will cause the mechanical properties of the loess to be greatly attenuated.The freeze-thaw cycle is also one of the main reasons for the quality problems of loess-based buildings in Northwest China,which affects the stability and service life of structures.Therefore,it is very meaningful to study the freeze-thaw cycle of loess.Although there are many related research results,the effect of freeze-thaw cycle on the strength of loess is lack of systematic research,lack of comprehensive and unified results.In this paper,soil samples from Changan District are taken as research objects,and the soil samples used in the tests are unsaturated remolded soil.After testing the physical parameters,three axis tests were carried out and the following conclusions were drawn based on the test data.(1)The strength of the soil decreases with the increase of the number of freeze-thaw cycles,and the first freeze-thaw cycles have the greatest impact on the strength of the soil,and with the increase of the number of freeze-thaw cycles on its strength gradually weakened.When the freeze-thaw cycles reach 30 times,the strength of the loess is basically in a stable state.(2)According to the test data,it is found that the axial compressive strength of loess is slightly greater than that of the Loess except 20%-25% water content,which proves that the pore of loess changed greatly after the freeze-thaw cycles in this water content range,and the structure of Loess changed,leading to the change of loess particles and grains.The connection between grains decreases,and the intensity change is more significant.(3)With the increase of confining pressure,the peak value of soil strength will increase.When the freeze-thaw cycles and water content do not change,the larger the confining pressure,the higher the peak value of soil strength.But with the increase of confining pressure,the peak value of loess strength decreases.(4)When the water content is constant,the cohesion of loess decreases gradually with the increase of freeze-thaw cycles,and the decreasing extent will be weakened with the increase of freeze-thaw cycles.The first five freeze-thaw cycles decrease more,and when the freeze-thaw cycles approach 30,the cohesion of loess basically reaches a stable state.(5)When the moisture content is constant,the internal friction angle of loess will decrease with the increase of freeze-thaw cycles.But the influence of moisture content on internal friction angle is not obvious.But when the water content is close to the saturated water content of the soil,the internal friction angle is basically stable in the range of 3 degrees.(6)When the freeze-thaw cycles are the same and the water content increases gradually,although the effect on the internal friction angle is not obvious,the cohesion will decrease with the increase of water content.Therefore,considering the combined effect of the two on the shear strength of soil,the shear strength will still decrease with the increase of water content.