Strength reduction of till under dynamic pore pressure condition

Abstract

Cuttings in heavily overconsolidated clays are known to be susceptible to progressive deformation caused by creep and fatigue which usually begins at the toe of the slope. The progressive deformation leads to strength reduction with time at constant stress (or called softening) and could be accelerated by fluctuation of groundwater level associated with more extreme rainfall events predicted through climate change. The purpose of this article is to assess the mechanism of progressive deformation due to creep and fatigue using element testing on samples of till. The samples were subjected to fully drained loading and the deviator stresses were held constant at various percentages of the peak failure stress while the pore water pressure was kept static or dynamic (fluctuating ±5 kPa) over a period of time. The results have shown that the samples experienced significant deformation even at higher factor of safety (i.e. the failure deviator stress/ deviator stress at which the pore water pressure was fluctuated) under pore water pressure dynamics.

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

“…Both cyclic and creep tests show that the soil shear strength in addition to the critical state line may be lost by the accumulated strain. Similar results were obtained by Harley et al (2016) in tests with cyclic pore pressure performed on overconsolidated till. They showed that cohesion is lost if the stress state is maintained or cycled beyond the critical state line.…”

“…Time dependent behaviour in CSD triaxial tests conducted in in undisturbed residual soil was also reported by Ng and Petley (2009). Harley et al (2016) showed a reduction of the shear strength in the creep test carried out in overconsolidated till. According to Harley et al (2016), this reduction is related to the stress state conditions between the critical state line and shear strength envelope.…”

The initial, primary and secondary consolidation response of soft clay reinforced with a granular column under isolated loading

“…It is suggested that the reason for this is due to the additional creep associated with shear loading. This hypothesis is supported by recent work carried out on glacial till (Harley et. al.…”

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.…”