Experimental Study On Static And Dynamic Deformation Characteristics Of Unsaturated Granite Residual Soil

Granite residual soil is widely distributed in South China.With the development of the economy and the construction of large scale construction projects such as the highway,urban subway,inter-city rail and so on,the engineering problem caused by the granite residual soil is becoming more and more serious,such as the settlement,collapse and other damage caused by the deformation under the load.To meet the need of engineering construction,the engineering characteristics of unsaturated granite residual soil are explored,which is of great significance in engineering.Taking the unsaturated granite residual soil in Hengyang as an example,the soil water characteristic curve test,the three axis shear test and dynamic deformation test with the suction controlled are carried out.The influences of suction and net confining pressure on the deformation characteristics of unsaturated granite residual soil are explored,and the corresponding constitutive relation and model parameters are analyzed.(1)In the same net confining pressure condition,the strength of unsaturated residual granite soil increases with the increase of the suction;under the same suction,the strength increases as the net confining pressure increases.When the net confining pressure is small,the effect of suction on the strength is relatively large,with the increase of the net confining pressure,the influence of the suction is obviously weakened.(2)Duncan-Chang model is used to get the model parameters of nonlinear constitutive equation of unsaturated soil.The initial tangent modulus of deformation increases with the increase of suction,and changes in the quadric curve with the increase of net confining pressure.The model parameters K and n were increased with the increase of the matrix suction and its variation law is similar to the initial deformation modulus.(3)With the increase of granite residual soil dynamic strain,the dynamic stress increases;Suction and net confining pressure of granite residual soil have significant influence on dynamic constitutive relationship and in the same suction condition,the bigger the net confining pressure,the higher the skeleton curves.In the same net confining pressure conditions,the skeleton curves of saturated and unsaturated state have obvious differences.Overall,the effect of suction on the backbone curve is smaller than that of the net confining pressure.(4)Based on the empirical formula of the backbone curve of Hardin hyperbolic model,the constitutive model of unsaturated granite residual soil is established.With the increase of dynamic strain,the dynamic elastic modulus of granite decreases non-linearly.When the dynamic strain is smaller,the change rate of the dynamic elastic modulus is relatively fast.After reaching a certain dynamic strain,the change trend of the dynamic elastic modulus decreases gradually.In the same net confining pressure condition,the bigger the suction,the larger the dynamic elastic modulus and in the same suction condition,the bigger the net confining pressure,the larger the dynamic elastic modulus.Finally,the relationship between the maximum dynamic elastic modulus and damping ratio is obtained.