This paper describes the development of coefficient of lateral earth pressure at rest, K0 in soft kaolinbentonite mixtures. The presence of montmorillonite in bentonite increases the consistency limits and consequently enhances the activity of the soil mixture. Ko values of a series of reconstituted kaolinbentonite mixtures were observed continuously during one - dimensional consolidation during loading as well as unloading cycles. The samples were consolidated under a constant hydraulic gradient of 0.2 kPa/mm in a purposely built consolidometer and measurements from flush diaphragm transducers gave the total vertical stress and total lateral stress on the sample. The equipment used has previously been described in Ting, Sills and Wijeyesekera (1994). Experimental observations confirm that K0 increase linearly with decreasing void ratio as reported by Ting et al (1994) for soft kaolin soils. The increasing montmorillonite content results in a lowering of the angle of friction, which in turn increases the value of K0. The value of K 0 was observed to initially decrease with time during secondary consolidation. These observations provide an answer to a query raised by Schmertman (1983) which had remained unanswered to date. During unloading, K0 values were observed to increase with increasing over consolidation ratio (OCR).
The coefficient of earth pressure at rest, K0, is an essential design parameter in soil mechanics and its evaluation is important for problems related with foundations, excavations, retaining walls, friction piles and numerical modelling. Therefore the estimation of an incorrect value of Ko can seriously affect the soil deformation parameters (Wijeyesekera, 1994). Donath (1891) defined k0 as the ratio of the total horizontal stress to the total vertical stress (sh/sv) when under a condition of zero lateral strain.
The kaolin used was Speswhite China Clay, marketed by English China Clays Ltd.
