Effects of Cyclic Variations of Pore Pressure on the Behaviour of a Gneiss Residual Soil

Abstract

Many slope failures in residual soils have been attributed to increased soil pore pressure. During the rainy season, water infiltration occurs, which can lead the slope to rupture by increasing the pore pressure. However, some landslides have been observed with pore pressures below those required for failure. Hypotheses for such ruptures include the occurrence of creep or fatigue due to cyclic variations in the piezometric level on the slope. This paper presents a study on the effect of pore pressure on the behaviour of the residual soil of the Soberbo hillside in Rio de Janeiro, Brazil, subjected to monotonic and cyclic pore pressure. Triaxial tests that simulate the increasing piezometric level (constant shear drained-CSD tests), drained creep (DC-CSD tests) and cyclic pore pressure variation (CPP tests) in slopes were carried out. The CSD test results showed that the failure due to increasing pore pressure is essentially dilatant and confirmed the peak strength obtained from conventional drained triaxial tests. Sudden failure was observed in all CSD tests at the end of the pore pressure increase phase. The results show that the failure of the slope may occur due to drained creep and the loss of soil shear strength under cycling pore pressure.

Theory and Implementation of Constitutive Models for Geomaterials

“…This behavior can be explained considering destructuration during the shearing phase, which implies shear strength degradation. Similar results have been presented by Santos et al (2020), who attributed this kind of behavior to the structure inherited from the parent rock.…”

Creep behavior of cemented sand investigated under cyclic loading

“…The mean stress evaluated in the test program is considered as a total mean stress, which is also equivalent to an effective mean stress, since the pore water pressure within the test specimens is zero. The stress paths and stress states evaluated in this study are similar to those of an underground geomaterial that is subjected to cyclic fluctuations of groundwater table or pore water pressure (Chang and Huang 2015;Harley et al 2016;Chen et al 2018;Santos et al 2020). Ground subsidence has been being a serious problem in southwestern Taiwan.…”

“…Evaluation of creep in geomaterials typically involves uniaxial compression test, triaxial test, or direct shear test to determine time-dependent strain subjected to constant deviator stress or shear stress (Nedjar and Le Roy 2013;Aydan et al 2014;Rybacki et al 2017). The time needed to reach creep failure is long, and multiple years may be needed to show meaningful results; for example, a creep test that lasted 20 years for tuff under uniaxial compression has been reported by Hashiba and Fukui (2020).…”