Figure 2. Example criterial failure surfaces for different modes of failure

ERDC TN-DOER-N5

July 2000

Figure 2. Example criterial failure surfaces for different modes of failure (to convert feet to meters,

multiply by 0.3048)

failure modes that has the lowest factor of safety against sliding. The computer program UTEXAS3

searches for the critical surface that gives the lowest factor of safety on a grid that moves the

postulated failure shape up and down the slope. By using different starting failure shapes and

different grid densities, the user can examine a large range of possible failures and identify the ones

with the smallest factor of safety.

The sand cap is usually assumed to be applied instantaneously and uniformly for the analysis.

Realistically, this is impossible. The best stability will be achieved if the sand is placed at the toe

of the slope and then worked up toward the crest of the slope. Achieving this controlled placement

is problematic under actual disposal conditions, and if sand is placed toward the crest of the slope

before the lower portions of the slope are covered, the factor of safety against sliding will generally

be reduced.

Critical failure surfaces with the lowest factor of safety should be located for each mode of slope

failure. These values of factor of safety should be compared; the failure surface with the lowest

factor of safety will be the most likely to fail. Limit equilibrium analysis of this type determines

only if a configuration is stable or unstable. It does not predict postsliding configuration or behavior.

Once a slide occurs, the uphill scarp may be quite steep and subject to further progressive slips.