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

Abstract

Constant rate of strain (CRS) consolidation test is an alternative testing method to estimate the consolidation parameters of fine grained soils, which has gained popularity in countries, such as USA, Japan, Hong Kong, and Canada, because of its several merits over conventional incremental loading (IL) method. Constant rate of strain test is also important to study the effect of strain rate on consolidation behavior of soils. Organic soils are considered problematic soils because of their low strength and higher compressibility. In this paper, an attempt has been made to determine consolidation parameters of a number of undisturbed and remolded organic soils in the Kolkata region with organic content 14–45% by testing them at different strain rates (1·2, 0·24, 0·12, 0·048, and 0·012% min−1) using an indigenously built CRS cell. Incremental loading tests were also conducted to verify the dependability of CRS results. Results indicate that 1·2 and 0·24% min−1 strain rates generate high pore pressure ratio (PPR), which are beyond the recommended values. Present investigation revealed that vertical effective stresses, pre-consolidation pressure, coefficient of consolidation, coefficient of volume change, hydraulic conductivity, etc., are strain-rate dependent. Higher strain rate is found to produce higher effective stress and consolidation parameters. Constant rate of strain test results obtained from undisturbed organic clays (OCs) and a number of remolded organic and inorganic soils particularly at 0·12, 0·048, and 0·012% min−1 strain rates are in line with that of IL tests.