Warnings

These are the warnings a retaining wall’s result can carry, and what each one means.

• Tension crack. The cohesion of the backfill makes the active pressure negative near the surface. The warning gives the depth of the crack, which is taken full of water; the soil beside it doesn’t pull on the wall. It also gives the soil’s thrust with that tension counted, the textbook value before the crack opens, next to the design one.
• Passive resistance relied on. The wall is embedded, so the sliding resistance includes the passive resistance in front of it. The warning gives how much, and the factor of safety without it: that soil must not be dug out or eroded.
• Base lift-off ($B/6 \lt e \lt B/2$). The resultant is outside the middle third: $q_{min}$ is negative, and that edge of the base loses contact with the soil.
• Resultant outside the base ($e \ge B/2$). The wall overturns, and there is no contact pressure to compute.
• Linear uplift. The water under the base has a different head at the heel than at the toe. The uplift is taken as linear between them, with no seepage analysis; where seepage under the wall matters, check it with one.
• Bearing stratum. The base rests on a stratum below the top one. The base friction and the bearing capacity use that stratum; the ones above only add overburden.
• Unusual friction angle. A stratum has $\phi$ above 45°, possible in rock fill but rare in soil. The calculation runs, and the warning points at the stratum.