In order to construct buildings resistant against earthquake in seismic area, the use of dampers is necessary to reduce the damaging effects of earthquakes on structures by decreasing shear force applied to the foot of the column, rotation, subsidence and horizontal motions of the foundation and structure. In this research, it is tried to evaluate the rotation, subsidence and horizontal motions of the foundation by putting a layer of soft sand under the singular foundation of a part of a six-storey building and by performing El Center Accelerogram and the rate of effect of soft layer on reducing the effect of shear force of columns foot and compare and study this case with the corresponding values without the presence of sand. Also the effects of changes of parameters such as shear modulus and internal friction angle of the soil and shear modulus, thickness and angle of internal friction of sand were investigated. The results show that the use of soft sand reduces the considerable amount of shear force applied to the foot of the columns and the structure relative displacement to foundation. Due to creating the possibility of slipping between foundation and the bed, the values of relative displacements and rotation between the bed and foundation are increased comparing to values of relative displacements and rotation without the presence of sand.
