Study Of The Freeze-thaw Effects On Physical And Mechanical Properties Of Subgrade Soils

The physical and mechanical properties of the subgrade change due to cryogenic actions in the freeze-thaw cycling. Chose some representative clays from Harbin as main research object to study the physical changes in which there will be different temperature and freezing velocity, mechanical changes in which there will be different water content and density and freeze-thaw cycles. The test result indicated that,The freezing and thawing function Mother Earth has the heave amount of deformity to be bigger than sinks friendly the amount of deformity, the earth dry weight density reduces; In the low freezing temperatures (- 20~-10°C) under, the earth mainly has the home position freeze, can appear the phenomenon in the melted initial period which the amount of deformity increases suddenly; Many is higher than the unidirectional freeze way to the freeze way freeze speed, the effective freezing depth is small, the heave and sinks the distortion all to be smaller than friendly much to the freeze way under distortion; After the freezing and thawing function, the earth snapping back module and the shearing strength reduce, along with the thaw-freeze cycle number of times increase, the freezing and thawing function is not obvious to two mechanics target influence. Chose four experimental road from Harbin city road network and tested vertical water content of subgrade twice a year, at the same time monitoring the temperature of the subgrade to get the water content and temperature changes of soils in the freeze-thaw cycling. The result shows that the stage of freezing is more longer than that of thawing; water aggregates between 1.2～1.4 meters under the pavements in the thawing of subgrade, so more water stay at this level and can not penetrate to other levels of soils, so compressive strength reduces, which will be destroyed by the actions of vehicles. When there is high water content in soils, subgrade is instable which is the main reason that cause the subgrade damage. Freeze-thaw cycling has a conspicuous effect on physical and mechanical properties of subgrade. The result can provide parameters for road design and maintenance and there will be positive significance in improving the quality of road construction in frozen area.