Study On Engineering Characteristics Of Expansive Soil Under Freeze-thaw Cycles

The distribution of expansive soil overlaps with the seasonal frozen regions in large area in China,After the winter frezing and spring thawing,there are many problems such as suspension and expansion cracks in the slope retaining structure,and significantly increase the difficulty of construction of the high-speed railway subgrade project and the risk of safe and smooth operation in the frozen quarter.so it is important to clarify the change rules of engineering characteristics of expansive soil under freeze-thaw cycles.Through the combination of theoretical analysis and laboratory tests,this paper discusses the influence of freeze-thaw cycles on the engineering characteristics of expansive soil in different initial conditions.The main research results of this dissertation are as follows:(1)In the freeze-thaw cycle,the volume of expansive soil sample with the initial state of moisture content 26%/compactness 0.9/freezing temperature-15? is frost expanding and thawing shrinking.But the volume of expansive soil sample with the initial state of moisture content 20% and 23%/compactness 0.90/freezing temperature-15? shows freeze-shrinkage and thaw-expansion.(2)In the first freeze-thaw cycle,unconfined stress-strain relation curve of the expansive soil sample with the initial state of moisture content 23% and 26%/compactness 0.90/freezing temperature-15? shows a significant decrease.With the increase of freeze-thaw cycles,the unconfined compressive stress strain curves of the expansive soil samples with the initial state of compactness 0.85?0.90?0.95/moisture content 20%/freezing temperature-15? are composed of the scattered small stress drop curves.This proves that the lower the freezing temperature,the greater the influence on the unconfined compressive strength.(3)With the increase of freeze-thaw cycles,the internal structure of the sample changes,impaired cementation between particles,so the unconfined compressive strength,cohesion,shear strength and elastic modulus of expansive soil show a decreasing trend in general,about 0.5 to 0.7 lower to the initial value.Although the internal friction angle fluctuates,However,due to the increase in the area of bite contact between particles,it presents an increasing regularity in general(4)This paper establishes the functional relationship between the engineering characteristics parameters of expansive soils and the number of freeze-thaw cycles,which is an exponential attenuation function.Secondly,it further establishes the binary function expression of the unconfined compressive strength,cohesion,freeze-thaw cycles and initial state of expansive soil.To some extent,it can quantitatively reflect the influence of the coupling effect of freeze-thaw cycle and initial state on engineering properties of expansive soil.