Abstract

Mr D. N. Holt, Chairman of the Engineering Group, welcomed the large audience to the Meeting, designed to promote the interchange of ideas between Clay Mineralogists, Engineering Geologists and Geotechnical Engineers. Nine papers were presented and discussed:

Engineering geology of clay minerals: swelling, shrinking and mudrock breakdown by Dr R. K. Taylor of University of Durham who introduced the theme of the Meeting.

Argillaceous sediments make up about 60% of the geological column, clay minerals accounting for about two-thirds of the constituents of over-consolidated clays and mudrocks. In North America, expansive clays are regarded as the principal hazard, whilst in southeast England shrinkage of heavy clays is the main geotechnical problem. Expansive clays are rarer in the older rocks, and in the UK there are virtually none below the Silurian. After summarizing the structure of clay minerals Dr Taylor discussed problems caused by expanding seat earths and roof seams in coal mines. Formation waters are generally saline, creating Na-montmorillonite which is more expansive than the Ca variety, exacerbating the problems. Swelling is divided into mechanical or physicochemical in origin; a mechanical origin is more common in soil mechanics problems, clay minerals may not be involved. Samples recovered from depth with high KQ values may swell in a total stress oedometer because of high suctions generated by stress release on sampling. In long-term excavations mechanical and physicochemical swelling can take place. The swelling process of clays is a function of absorbed water; there is strongly bonded water near the surface of

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