It is important to excavation in the ground and the behavior of the ground by the construction of the structure accurately. Especially, it might have a hard influence on the structure around the ground in the surrounding by the excavating work of the adjoining land board of the existing structure in the soft ground. The consideration here examines from the process from the behavior of the effective stress in the saturated clay soil to destruction, and moreover an examination of the process from the behavior of the mean effective stress to destruction. The mean effective stress path obtained from the mean effective stress requests from the effective axis difference stress and the mean effective stress. And this critical line is called Roscoe's critical state line and the angle of this line is shown in M. Obtains the angle of effective shear resistance from this, and evaluates strength. Here, the difference of a mechanical characteristic by the restraint pressure constancy examination, the average main stress constancy examination, and the axis pressure constancy examination was considered by Consolidated Undrained shear test (CU) by using the normally consolidated clay sample by preloading that obtained the route to the strength change and destruction in the soft ground by Omits while changing a maximum and a minimum main stress