A detailed study is presented of the effect of weathering on the undrained and effective stress strengths of London Clay from a site at South Ockendon, Essex. A limited investigation of the chemistry and clay mineralogy was also carried out.
It is concluded that the effect of weathering is to reduce the apparent degree of overconsolidation. This effect is seen in the undrained strength-water content relationship of the most weathered clay, which shows a 4% higher water content at a given strength than the unweathered clay. There is a corresponding reduction of the overconsolidation ratio from about 40 to about 20. In effective stress terms the corresponding strength change is given by a reduction of c′ from 28 kPa to a minimum value of about 9 kPa, assuming that ø′ (= 20°) remains unchanged by the weathering.