GGU-TRENCH: Safety against groundwater ingress into the trench

The program calculates the pressure exerted by the slurry p_s and the pressure exerted by the groundwater p_w at the toe of the diaphragm wall. The FOS, eta(gw), is then

eta(gw) = p_s / p_w.

The old DIN 4126, (9.1.1) and DIN 4126:2013 (6.1) require a safety factor of 1.05.