The Study On Strength Weakening Of Residual Soil Under The Action Of Moisture And Temperature

The granite residual soil is widely distributed in the coastal area of Fujian province.The external factors,for example the temperature stress caused by the temperature difference between day and night and the seasonal alternation,wet dry cycling process in the rainy season and dry season,are of great importance on the physical and mechanical properties of the residual soil.The shear strength of residual soil is one of the most important factor in mechanical properties.The weathering of the external environment will make the shear strength parameters of residual soil gradually deteriorated,and then affects the stability of the slope and other geotechnical engineering.It's of important theoretical and practical significance for revealing the deterioration law of shear strength parameters of granite residual soil and anti weathering design of geotechnical soil slope that studying on the mechanism of strength deterioration of granite residual soil in the weathering environment.In this thesis,the residual soil samples were tested by direct shear test to explore the deterioration rule of shear strength parameters in the case of different water content,dry density,different times of wet and dry cycles,the weathering of heating and cooling,and the weathering humid and hot.The main research works and conclusions are as follows:(1)When the value of dry density value is certain,the cohesion and internal friction angle of the granite residual soil increases with the water content firstly and then decreases.And the maximum value is obtained at the optimum water content WOP = 20%,When moisture content is constant,the cohesion and internal friction angle increase linearly with the increase of dry density.(2)The value of cohesion and internal friction angle of granite residual soil showed an exponential decay trend with the increase of dry and wet cycles.Attenuation mainly occurs in the first to two cycles of wet and dry cycles.After 5 cycles of wetting and drying cycles,when the moisture content is in the optimum water content,the attenuation amplitude of cohesion was the minimum.And it decreases with the increase of dry density.(3)In the weathering of the action of temperature rising,the value of cohesion decreases exponentially with the increase of temperature,and the internal friction angle degrees between 21.29°and 27.97°.In the weathering of cooling,the relationship between cohesion and temperature is in accordance with the three order polynomial.And the value of internal friction angle decreases significantly when the temperature decreases from 5?to-5?.Under the effect of damp and hot weather,the value of cohesion begins to decline in the zeroth to second time of the humid and hot weather.And it increases in the second to fourth times.And it is exponential decay in the fourth to tenth times.The value of the internal friction angle increases with the increase of the times of damp and hot weather firstly,and then decreases.The minimum value is obtained in the eighth times.(4)The safety factor of slope obtained the maximum value at optimum moisture content.And it increased with the increase of dry density.The safety factor of slope decrease with the increase of the times of the dry wet cycles with the law of the exponential attenuation.The value of attenuation gets minimum value at the optimum moisture content.And it decreases with the increase of dry density.The safety factor of the slope floats between 1.064 to 1.292 under the action of the weathering of temperature rising.And the safety factor of the slope increases first and then decreases at 25? under the action of the weathering of cooling.As the increase of the times of the weathering of humid and hot,it decreases with the law of exponential decay.Under the action of the weathering of humid and hot,the safety factor of the slope decreases in the zeroth times to second times,and increases in the second to fourth times.It is exponential decay in the fourth to tenth times.