Strain-rate effect on consolidation behaviour of Ariake clay

Abstract

A total of 114 constant rate of strain (CRS) consolidation tests and 15 incremental loading (IL) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in the Saga Plain, Kyushu, Japan, to systematically investigate the strain-rate effect on the consolidation behaviour of Ariake clay. The test results show that the consolidation yield stress (p c ) of Ariake clays increased by about 15-16% with a tenfold increase in strain rate, and no clear correlation exists between the strain-rate effect and the clay content or plasticity index I p of the samples. For a given strain level, the strain rate does not influence the compression index C c , which implies that an isotach model is applicable to Ariake clay. It has been newly found that, under a given effective vertical stress, the coefficient of consolidation c v increases with increase of the strain rate, resulting mainly from the increase of hydraulic conductivity k with strain rate. Linear regression gives about a 33% increase in c v with a tenfold increase in the strain rate. For the Ariake clay tested, the p c and c v values of CRS tests with a strain rate of 0 . 02%/min are comparable with those of IL tests.void ratio e t void ratio of sample at time t e t þ˜t void ratio of sample at time t +˜t H thickness of samplẽ H change of sample thickness in time interval˜t H t thickness of sample at time t H t þ˜t thickness of sample at time t +˜t H average thickness of sample between t and t +˜t i hydraulic gradient i av average hydraulic gradient i c threshold hydraulic gradient k hydraulic conductivity m v coefficient of volume compressibility p c_ å consolidation yield stress for a given strain rate _ å p c0 : 02%=min consolidation yield stress under strain rate of 0 . 02%/min q flow rate RPC ratio of consolidation yield stress SRE strain-rate effect u b excess pore water pressure at the bottom of the sample u b, t excess pore water pressure at bottom of sample at time t u b, t þ˜t excess pore water pressure at bottom of sample at time t +˜t u b average excess pore water pressure at bottom of sample between t and t +˜t w L

Constant rate of strain consolidation of organic clay: in Kolkata region

“…Pore pressure ratio values obtained for strain rates 0?12, 0?048, and 0?012% min 21 more or less fall within the recommended range of 0?03-0?15 and stress-strain curves are also following the established trend, i.e. the higher the strain rate the higher is the effective stress (Leroueil, Kabbaj, Tavenas, and Bouchard 1985;Cheng and Yin 2005;Jia, Chai, Hino, and Hong 2010).…”

“…Generally, stress-strain curves of higher strain rates give higher effective stresses and locate at the top; as the strain rate decreases, the effective stress also decreases and the corresponding stress-strain curves locate below that of the higher strain rates (Leroueil, Kabbaj, Tavenas, and Bouchard 1985;Cheng andYin 2005, Jia, Chai, Hino, andHong 2010). The vertical effective stress-vertical strain relationships for undisturbed Jadavpur and Howrah OC soils as obtained in the present investigation are presented in Figs.…”

“…This may be understood as SRE. Jia, Chai, Hino, and Hong (2010) investigated SRE, choosing the effective stress at 15% strain level and expressed SRE as the ratio of effective stresses at 0?2 and 0?02% min 21 strain rates. In this study, SRE is expressed as percentage increase in effective stress for a given increase in strain rate at 5, 15, and 25% strains.…”

“…Slowest strain rate 0?012% min 21 recorded very less maximum values, 43 and 30 kPa for undisturbed Jadavpur and Howrah OCs, respectively. From the literature, the recorded maximum excess base pore pressures at comparable strain rate are 50 kPa for Hong Kong marine deposit (Cheng and Yin 2005), 7 kPa for Ariake clay (Jia, Chai, Hino, and Hong 2010), and 70 kPa for Lindberg Road (LR) soil (Santagata, Bobet, Cliff, and Hwang 2008). The mechanism and magnitude of pore pressure in organic soils appear to be an intricate aspect because of their dependence on complex factors, like fiber content, degree of decomposition, degree of saturation, and partial drying of intact samples.…”

Editorial

“…In contrast to the papers which relate to field behaviour, Jia et al (2010) present a laboratory study on the one-dimensional consolidation characteristics of the Ariake Clay. This study is based on a large number of constant rate of strain (CRS) and incrementally loaded (IL) oedometer tests; it reminds us of the high rate of dependency of many soft clays and highlights the importance of selecting appropriate testing regimes when designing a programme of laboratory testing.…”