Determination of the shrinking and swelling properties of the Lias Clay : laboratory report

The behaviour of clay rich geological formations in response to a change in moisture content is often exhibited as shrinking or swelling. The material is able to change volume with a change in effective stress causing a geological hazard for engineering construction. These changes vary with clay content and composition and hence geological formation. The work described in this report comprises the fourth stage of a study of the swelling and shrinkage behaviour of major UK clay formations. It deals with the testing of undisturbed and disturbed samples of the clay in a variety of ways, most of which follow internationally recognised British or American soil mechanics standards. The test methods applied can be broadly grouped into three categories: a) direct swelling tests, b) direct shrinkage tests, c) index tests. The measured moisture content of the natural state and at certain defined test conditions can provide an extremely useful method of classifying cohesive soils and assessing their engineering behaviour. These tests are Index Properties but are also known as the Atterberg Limits. The Atterberg Limits are related to the combined effects of particle size and mineral composition. The liquid limit and plastic limit provide the most useful way of identifying and classifying fine-grained soils. Particle Size provides quantitative data on the range of sizes of particles and the % of clay size particles present. Further information is provided by the particle density test. The purpose of the index tests is to classify the soils and also to investigate correlations between index properties and direct swelling and shrinkage tests. The report describes the test methodologies for the above geotechnical tests used to determine the characteristics of sampled Lias Group formations. Also presented are the results for the suite of tests carried out on samples taken from thirty sites along the outcrop of the Lias clay, from the south of England to the coastal Durham, North Yorkshire border. The locations of the sample sites are given in table 1 and details on the sites can be found in BGs internal reports (Rowlands and Jones, 2003; Freeborough and Jones, 2004). The tests resulting from the collection of these samples were carried out in the Engineering Geology Group (EGG) laboratories at the British Geological Survey (BGS) on samples obtained by the authors. Oedometer consolidation tests were also carried out and are reported in an internal report by Nelder and Jones (2004). In addition to the test results reported here, research was also undertaken into the mineralogical and geochemical properties of the samples. Scanning electron microscopy has also been carried out at BGS on the same samples as reported in Bouch 2003. The mineralogical data are complete and are referenced in this report.