Two identical soil specimen $4$ cm diameter, $8$ cm height are tested in a triaxial shear test under undrained condition. The $1$st specimen failed at an axial load of $720$ N under the cell pressure of $100$kpa. The $2$nd specimen failed at an axial load of $915$ N under a cell pressure of $200$ kpa. The $1$st sample is shortened by $0\mathrm{.}8$ cm$,$ at failure point. $2$nd sample is shortened by $0\mathrm{.}1$ cm$.$ calculate the shear strength of soil.