METHODS FOR REDUCING UNDRAINED SHEAR STRENGTH OF SOFT CLAY

Observations from failures of slopes and embankments, and loading tests show that the shear strength measured in field vane tests and fall-cone tests in organic and plactic clay has to be reduced in order to correspond to the real shear strength of the clay. In Sweden a gradual shear strength reduction has been made on the basis of the cone liquid limit, as soon as this exceeds 80%. In recent years several new methods have been proposed for the shear strength reduction. Some observations indicate that the reduction used today has been in certain cases insufficient. A comparison between different reduction methods and the corresponding risks of failure has therefore been made. The risk of failure has been analysed according to the scatter of the case records used by Bjerrum for deduction of his reduction factor and also according to the variations of the ratio of vane shear strength and effective overburden pressure in different types of clay. /Author/