Experimental Study On Mechanical Properties Of Silty Soil Subjected To Repeated Freeze-thaw

In permafrost areas deep season, due to the change of external climaticconditions, station roadbed freezing in winter and thawing in spring, freeze thawcycles repeated leads to the decrease of subgrade soil strength, resulting in largedeformation of subgrade soil. In the strong freezing and melting under subgrade,prone to mud pumping, settlement, strength weakening disease phenomenon, whichwill have great influence on the normal use of the station track, road and building,seriously affecting the normal operation of railway and road safety. The station ofQinghai Tibet Railway Naqu logistics center field as the project background, thetechnical route of theoretical analysis and laboratory test combination, the repeatedfreezing and thawing effects influence on mechanical properties of subgrade filler.By indoor test to determine the basic physical properties of silty soil subgradefiller, drawing the particle analysis grading curve, determine the particle density ofsilty soil, the compaction characteristic curve, change trend with the void ratio ofmaximum dry density and optimum moisture content and permeability coefficient.Through the cycle of freezing and thawing and static three triaxial test, foundthat the stress-strain relationship is work hardening of silty soil, and its failure toplastic failure, shear strength and elastic modulus and the freeze-thaw cycle and watercontent was negatively correlated with silt, confining pressure and compaction degreeshowed a positive correlation; Silty soil cohesive force decreases gradually with theincrease of the number of freezing and thawing, and the internal friction Angleincreases with the increase of number of freezing and thawing first decreases, andafter curve downward trend in general.By freezing thawing cycle and dynamic triaxial tests on three levels, that thesame as strain, the dynamic stress size and thawing, moisture content was negativelycorrelated, and confining pressure, loading frequency, positive correlation with thedegree of compaction; dynamic strain level, dynamic modulus and damping ratiodecreases exponentially with the increase; increase in the number of freeze-thaw cycle, dynamic modulus and damping ratio decreased and increased, after6freezingthawing cycles have tended to be stable; dynamic modulus and confining pressureand compaction degree increase and decrease, the damping ratio increases withconfining pressure and compaction degree decreased; the change of water content haslittle effect on the damping ratio, when the soil is saturated, the dynamic modulusdecreased greatly; the loading frequency has great influence on the damping ratio,and decreases rapidly with increasing frequency.