As shown in Figure 1, an earth retaining wall is installed on the ground and comprises a clay layer and a sand layer. It is planned to excavate the ground on the left side of the earth retaining wall up to 5 m in depth. The water table at the end of the excavation is located at the top of the clay layer. It is assumed that there is no frictional force between the earth retaining wall and the ground. The clay layer is considered to have failed in the undrained condition because the construction period is short. For simplicity, the unit weight of water is assumed to be 10 kN/m³. (1) Cohesion of the sand layer c and the internal friction angle & are 0 kN/m² and 30°, respectively. Find the coefficient of active earth pressure of the sand layer. (2) Undrained shear strength of the clay layer cu is 35 kN/m² regardless of depth. Vertical effective stress o', applying at the point of the clay layer is 90 kN/m². Draw two Mohr's stress circles corresponding to the active and passive failure states of the clay. Indicate the stress values at the intersection of Mohr's stress circle and the axis of the diagram. (3) Draw the lateral pressure profile per unit width through the depth (sum of water pressure and soil pressure) acting on the back side of the retaining wall (right side of the retaining wall in the figure) at which the active failure state is reached. In addition, find the resultant force of the lateral pressure per unit width and indicate the position of the resultant force measured from the bottom of the earth retaining wall. (4) Draw the lateral pressure profile per unit width through the depth (sum of water pressure and soil pressure) acting on the front side of the retaining wall (left side of the retaining wall in the figure) at which the passive failure state is reached. In addition, find the resultant force of the lateral pressure per unit width and indicate the position of resultant force measured from the bottom of the earth retaining wall. (5) Investigate the stability of the retaining wall, considering the bottom of the retaining wall as the center of rotation. INI Retaining wall Sand layer Wet unit weight 18kN/m³ 5m INT 1.5m Clay layer Saturated unit weight 18kN/m³ Figure 1