Laboratory shear strength parameters of cohesive soils: variability and potential effects on slope stability

The study quantified laboratory geotechnical variability by analyzing compacted alluvial fine-grained soils commonly used to backfill exhausted quarries in Central Italy. Repeating the test 4 times and combining the relevant results, 256 pairs of friction angle and cohesion values were obtained, with mean values of 27.0° ± 0.8° and 19.22 ± 4.08 kPa, respectively in the shear stress range 100–250 kPa. The influence of the variability of laboratory drained shear strength parameters on the long-term stability of artificial saturated slopes was examined, taking into account both deterministic and probabilistic approaches. In many cases, when the deterministic approach indicates stability, the probabilistic one indicates a certain probability of instability, even for the lowest slope height (5 m) and a slope angle higher than 15°.