The shrinkage and swelling behaviour of UK soils : the clays of the Lambeth Group

The report describes work carried out in the geotechnical laboratories of the BGS at Keyworth. A limited number of undisturbed samples were collected from outcrops of the Reading and Woolwich formations of the Lambeth Group at locations in England by taking hand-prepared block samples and tube samples. A variety of geotechnical laboratory tests, measuring shrinkage and swelling both directly and indirectly, were carried out. These included both standard tests and new methods, based on experimental research work, and included tests on both undisturbed and remoulded specimens. The report describes the results of these tests, compares them with the results of geotechnical index tests and mineralogical analyses, and examines the shrink/swell classification of formations within the Lambeth Group. Where appropriate, comparisons are made with data obtained for the Gault Formation and Mercia Mudstone Group previously reported on. Swelling and shrinkage are two mechanical properties of a soil, which though driven by related physico-chemical mechanisms, are usually treated separately in the laboratory. Swelling sensu stricto is mainly a function of the clay minerals present in the soil or rock. The engineering phenomena of heave and subsidence may be caused by factors other than swelling and shrinkage of clays, respectively, for example, by stress relief, dissolution etc. The geological processes affecting swelling and shrinkage were reviewed by Gostelow (1995). Usually, the assessment of swelling and shrinkage does not involve direct measurement, but rather indirect estimation of volume change potential from index tests on reworked samples. There has been little change over the years to the shrink/swell tests that are described in British Standards. Three shrinkage tests are described in BS1377 (BSI, 1990), two for shrinkage limit and one for linear shrinkage. Both shrinkage limit tests make use of mercury. The two simple swelling tests in BS1377 (BSI, 1990) are based on the oedometer apparatus and measure swelling pressure (surcharge) and swelling strain (no surcharge). A swelling test is also incorporated in the compaction test procedure.