Value = 1.6 per BR470 usage.
Value = 1.2 per BR470 usage.
The BR470 method assumes that the unit weight of sandy materials is either dry or submerged, with no intermediate condition considered. The influence zone of groundwater is taken as twice the track width.
Governing (BR470 punching-shear model):
$$ R = R_{\mathrm{sub}} + \frac{D^2}{B}\,\gamma_p\,K_p\,\tan\delta\,s_p \;+\; \frac{2T_d}{B} $$
where \(R_{\mathrm{sub}} = \begin{cases} c_{ud}\,N_c\,s_c & \text{(clay)}\\ 0.5\,\gamma'_s\,B\,N_\gamma\,s_\gamma & \text{(granular)} \end{cases}\), \(T_d = \chi\,T_{\mathrm{ult}}\), and \( \delta \approx \tfrac{2}{3}\phi'_p \).
Design checks per case: ensure \(R \ge \gamma_1 q_{1k}\) and \(R \ge \gamma_2 q_{2k}\).
Additional checks implemented here: (A) bare-subgrade necessity, (B) platform-only adequacy under reduced factors when geotextile is used.
