Uncertainty and Reliability Analysis in Gully Slope Stability Prediction: A Case Study of Iguosa Gully, Benin City

Abstract

Slope stability analysis is an essential tool in gully erosion risk
assessment and modelling. The reliability of a gully wall slope
stability analysis depends on many factors. These factors are: the
uncertainties due to the varying geotechnical parameters within the
site, uncertainties due to the slope stability modelling methods and
soil sampling procedures. In this study, various properties of the soil
and slope were analyzed in order to depict the risk associated with the
gullying process at the Iguosa gully in Benin City. Based on the
samples obtained from the gully walls, a large number of random
slope stability parameters were generated by combining various
geotechnical properties obtained from collected samples. The slope
stability parameters – i.e. factors of safety (FOS) against slope failure
– were analyzed statistically to obtain standard deviations,
distributions, and probability density functions (PDF). Based on the
statistical distribution of the numerous slope stability parameters, a
probable and conservative slope stability index was calculated for the
gully. The results of the analysis gave an average reliability index (RI)
of 0.84 for the stability of the gully wall slope. The RI, which indicates
the stability of the slope, can also be related to the likelihood of slope
failure. The results obtained from this investigation implies that the
likelihood of slope failure of the Iguosa gully is relatively high and
that the current wall formation could lead to a major slope failure