A $4 \: m$ wide strip footing is founded at a depth of $1.5 \: m$ below the ground surface in a $c-\phi$ soil as shown in the figure. The water table is at a depth of $5.5 \: m$ below ground surface. The soil properties are: $c’=35 \: kN/m^2, \: \phi‘=28.63^{\circ}, \: \gamma_{\text{sat}} = 19 \: kN/m^3, \: \gamma_{\text{bulk}} = 17 \: kN/m^3$ and $\gamma_u =9.81 \: kN/m^3$. The values of bearing capacity factors for different $\phi ‘$ are given below:
$$\begin{array}{|c|c|c|c|} \hline \phi’ & N_c & N_q & N_{\gamma} \\ \hline 15^{\circ} & 12.9 & 4.4 & 2.5 \\ \hline 20^{\circ} & 17.7 & 7.4 & 5.0 \\ \hline 25^{\circ} & 25.1 & 12.7 & 9.7 \\ \hline 30^{\circ} & 37.2 & 22.5 & 19.7 \\ \hline \end{array}$$
Using Terzaghi’s bearing capacity equation and a factor of safety $F_s=2.5$, the net safe bearing capacity (expressed in $kN/m^2$) for local shear failure of the soil is _______