SAMPLE DISTURBANCE IN LONDON CLAY

Mechanical disturbance caused by open-tube (U100) drive sampling has been investigated at two London Clay sites by examining the suctions measured in tube and block samples taken from identical depths. The suctions were measured using the filter paper method. It is assumed that the block samples were affected only by the changes in stress from the in situ values, and that as a consequence the mechanical disturbance during tube sampling is directly related to the difference between the suctions recorded in the tube and block samples. The results show that drive-sampling increases the suction in U100 samples of stiff clay. This increase becomes greater as the stiffness of the clay increases. These observations have important implications if tube samples are to be used for the measurement of undrained strength, or for the estimation of the magnitude of the coefficient of earth pressure at rest from suction measurements.