Design Strategies to Mitigate Slope Instabilities in Structurally Complex Formations

Abstract

Stiff jointed clays (SJC) belong to so-called structurally complex formations in which the macroscale features of the deposit, that is the pattern of discontinuities affecting the soil mass, influence its response at the scale of engineering works. Such peculiar response was largely recognized during the excavation works carried out for the construction of two new road segments in southern Italy, where several structurally conditioned instability processes were triggered during excavation works. These phenomena mainly involved the Plio-Pleistocene marine clayey formation outcropping along the East coast of the Calabria region, where it constitutes most of the hills interested by construction works. Under a geotechnical perspective, the SJC-formation exhibits good mechanical characteristics at the scale of samples but, if considered as a whole, its behaviour is governed by the presence of discontinuities along which strength is typically at residual. Building on the author’s experience of some exemplary failure events, this paper aims at defining possible design strategies to minimize the risk of adverse and unexpected instability phenomena during construction in structurally complex formations. Design strategies oriented at reducing and possibly avoiding stress releases in the zone of influence were found to be most effective at preventing failures or restoring safety after the occurrence of a failure event.

Seismic and Rainfall Induced Displacements of an Existing Landslide: Findings from the Continuous Monitoring

“…This last hypothesis was confirmed by the presence of slickensided discontinuities on the soil coring close to the failure surface. Slickensided discontinuities in clays are typical evidence of the shear zone when experiencing large displacements, and have been observed in other studies on deepseated landslides in complex clayey formations (Scarpelli et al, 2013 [29]; Segato et al, 2015 [30]; Ruggeri et al, 2016 [31]; Ruggeri et al, 2020 [32]; Ruggeri et al, 2020 [33]). It is interesting to observe that, in several case studies, even the presence of a significant granular fraction could not avoid the reaching of residual conditions along the sliding surface when matrix sustained conditions hold, as documented in Ruggeri et al, 2016 [34].…”

Hydraulic Conductivity and Pore Water Pressures in a Clayey Landslide: Experimental Data

“…Recently, Tagarelli and Cotecchia [14] carried out a coupled hydro-mechanical numerical analysis on the influence of discontinuities on the behavior of landslides in intensely tectonized clay formations. Ruggeri et al [15] and Ruggeri et al [16] also considered the role of discontinuities on the overall behavior of landslides.…”