Study on the influence of different temperature modes on the freezing characteristics of silty clay in seasonally frozen area under unidirectional freezing
In order to study the freezing characteristics of soil under different temperature modes,the unidirec-tional freezing test of silty clay in Changchun area was carried out by using the freezing test device.By changing the temperature and temperature change rate of the roof of the test device,the temperature change of the soil dur-ing the test,the water content change of the soil before and after the test,the cold structure and vertical frost heave displacement of the sample after the test were studied and analyzed.The test results show that the soil tem-perature change is roughly divided into four stages:sudden drop,rebound or slow drop,continuous cooling,constant.At the same cooling rate,the greater the temperature gradient of the roof and floor,the greater the tem-perature recovery in the second stage;When the temperature gradient of the roof and floor is the same,the great-er the cooling rate,the smaller the temperature recovery in the second stage.After the test,reticular cracks ap-peared on the outer surface of the soil and widened along the depth direction.The width of the reticular structure was proportional to the temperature gradient.There is obvious water crystallization inside the soil,and the con-tinuous segregated ice wraps the soil to form a honeycomb-like structure,in which there is a certain amount of unfrozen water visible to the naked eye,and the smaller the cooling rate,the less the unfrozen water content visi-ble to the naked eye.The water content of the soil near the temperature control roof(cold end)increases signifi-cantly,and the water content of the soil near the temperature control floor(warm end)decreases or remains basi-cally unchanged,and the cooling rate is the same,The greater the temperature gradient,the more obvious the in-crease of soil moisture content near the cold end.At the same freezing temperature,the lower the cooling rate,the greater the water content increment near the cold end.The vertical frost heave of the soil is proportional to the temperature gradient.Under the condition of 30 min cooling time,the cold end temperature decreases from 0 ℃ to-15 ℃,and the frost heave increases greatly.When the cooling time is 60 min,the frost heave in the temperature range of-10～-15 ℃ has the largest change trend.
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