Experimental Study On Non-coaxial Deformation Behavior Of Sands Under Reciprocating Cyclic Rotation Of Principal Stress Axes

Foundation soil induced by traffic, wave and earthquake load, often occurs principal stress rotation, resulting in that principal strain increment direction is inconsistent with principal stress direction,namely the non-coaxiality behavior. Although the non-coaxial deformation characteristics under conditions of principal stress rotation of sand have been noticed and valued, the real situation stress state and stress path of soil is extremely complex, which has not formed a comprehensive system of sand non -coaxial deformation characteristics and the influence factors. In view of this, using HCA of Tongji University carried out a series of experiments about Wenhe river fine sand to further and systematically research on the relationship between stress and strain, the non-coaxial characteristics and the influence factor. The major study and achievements are as following:The monotonic loading tests were performed on the fine sand samples. The results showed that:(1) The principal stress direction a under monotonic loading has a significant effect on the shear strength of fine sand.(2) Each direction strain components showed a clear Nonlinearity at different principal stress direction angles and the variation law of fine sand strain was different,which showed obvious anisotropy of fine sand.(3)The fine sand sample volume strain showed the tendency from shear contraction to shear dilation with the increase of principal stress direction a.(4) The monotonic loading tests of different principal stress direction a showed that fine sand samples exist obvious non-coaxial angle.which can not be ignored and the shearing stress q and principal stress direction a have an obvious impact on the degree of non-coaxiality.The reciprocating cyclic rotation tests of principal stress axes were conducted to the fine sand. The results showed that:(1)The strain components of the fine sand produced obvious plastic deformation and the plastic deformation gradually accumulated with the increase in number of reciprocating cycle rotation. (2) when b=0,the fine sand samples were in plane stress state and when b=0.5,the fine sand samples were in triaxial stress states, thus when b=0.5, the variations of the strain components were more complicated.(3) Due to the fine sand has obvious anisotropy, compression and extension loading state of the fine sand had great difference, so the different cyclic rotation starting angle of the fine sand has a significant impact on strain components (4) with the increase in number of reciprocating cycle rotation, the strain component variation of reverse rotation was unaffected by the positive rotation, and since that was not affected by the stress history.(5)During the reciprocating cyclic rotation tests of principal stress axes, the fine sand samples existed obvious non-coaxial angles, which present definite regularity as reciprocating cycles increased and were almost not influenced by reciprocating cycles.(6)The non-coaxial angle ? showed significant differences with different b,which appeared to gradually decreasing tendency with the b increasing and the different cyclic rotation starting angle of the fine sand had a significant impact on non-coaxial angles(7)When the principal stress direction was positive rotation and reversed rotation, the non-coaxial angle ? had abrupt changes about 90°...