ABSTRACT

To investigate whether chemical additives could be effective at accelerating the strength regain of a clay slurry, a series of laboratory tests were undertaken at the University of Glasgow using a range of additives. Bothkennar clay was used in the test programme, with a small addition of bentonite to replicate the plasticity of the Witch Ground clays found in an area of the North Sea. To produce the slurry, water was added to the samples to increase the water content to 1.5 and 2.0 times the liquid limit. The results of the test programme found that calcium hydroxide can significantly improve the strength of the soil over 1-day, 3-day, 7-day, 30- day and 1-year time periods, for a range of dosing concentrations of 1–5%. This paper presents the laboratory test results and highlights the potential use of calcium hydroxide offshore.

1. Introduction

Clay slurries can loosely be defined as cohesive soils with moisture contents in excess of their liquid limit (LL). The use of additives to increase the strength of such weak slurries has received relatively little attention, although there is an increasing commercial imperative, associated with offshore developments, for pursuing this ground-strengthening technique. For example, clay slurry is produced offshore during jet trenching in clay soils where near rectangular trenches are formed, which generally are partially filled with slurry. The slurry provides little resistance to the uplift movement of trenched pipelines and is typically removed and replaced with either rock dump, or more competent in situ material obtained by destabilising the side walls of the trench. This paper presents the results from laboratory tests undertaken at the University of Glasgow to investigate the influence of a range of chemical additives on accelerating the strength improvement of clay slurries.

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