Retaining walls · Rischio

What Rischio checks in a retaining wall: overturning, sliding, bearing capacity, eccentricity and gabion levels, and how a model is built.

Rischio checks a retaining wall’s external stability under static loads: overturning, sliding, bearing capacity, the eccentricity of the resultant and, in a gabion wall, each level on the one below. The design of the reinforcement, seismic loads and the global stability of the slope are outside it.

What it checks

Check	Rule	Limit
Overturning The wall rotating about its toe $FS = \frac{\Sigma M_R}{\Sigma M_O}$	$FS = \frac{\Sigma M_R}{\Sigma M_O}$	$\ge 2.0$
Sliding The wall pushed along its base $FS = \frac{R}{\Sigma H}$	$FS = \frac{R}{\Sigma H}$	$\ge 1.5$
Bearing capacity The ground under the base giving way $FS = \frac{q_u}{q_{max}}$	$FS = \frac{q_u}{q_{max}}$	$\ge 3.0$
Eccentricity The resultant inside the middle third of the base $e$	$e$	$\le \frac{B}{6}$
Gabion levels Each level overturning or sliding on the one below $FS = \frac{\Sigma M_R}{\Sigma M_O},\; \frac{R}{\Sigma H}$	$FS = \frac{\Sigma M_R}{\Sigma M_O},\; \frac{R}{\Sigma H}$	$\ge 2.0,\; \ge 1.5$

The limits are Rischio’s defaults; each result shows its margin to the limit, and the check with the smallest margin governs.

How a model is built

A model has these parts; strata below a water table need their $\gamma_{sat}$ .

Wall. Rectangles and trapezoids, stacked from the base up and placed by their distance $x$ from the toe. $H$ is the sum of their heights; $B$ runs from the toe to the end of the heel. Concrete or masonry is solid, with unit weight $\gamma_c$ ; gabions have their unit weight, voids included, and a friction angle between levels.
Embedment. $D_f$ , the depth of the base below the ground in front of the toe.
Backfill. Strata from the crest down to the base, whose thicknesses add up to $H$ ; the slope $\beta$ ; and, unless it is drained, a water table below the crest.
Foundation. Strata from the ground in front of the toe down, and a water table, which may stand above the ground. The base rests on the stratum at depth $D_f$ (at a boundary, the lower one), whose $c$ and $\phi$ give the base friction and the bearing capacity.
Loads. Uniform surcharges $q$ on the backfill, added together.

Inputs describes each of them in full.

In these pages

Inputs: every input of a model.
Method and assumptions: the units and conventions, the key assumptions and the method, in order. Each part of the method has its own page:
- Earth pressure: the active thrust on the virtual back, the tension crack, the water and the passive resistance.
- Stability: weights and uplift, overturning, sliding and the eccentricity of the resultant.
- Bearing capacity: the base as a strip footing.
- Gabion walls: each level on the one below.
Equations: every step of the calculation, in the order of the calculation report.
Warnings: what each warning means.
Verified examples: worked examples from Das & Sivakugan that Rischio reproduces, with the book’s answer beside its own.