DETERMINATION OF IN-SITU UNDRAINED STRENGTH OF SOFT CLAY DEPOSITS

Abstract

Determination of in-situ undrained strength of soft clay deposits is discussed based on their stress history (engineering geological history). First, classification of soft clay deposits is shown and the importance of understanding the stress history for evaluating undrained strength characteristics of soft clay deposits is demonstrated for an alluvial marine clay. The method for obtaining in-situ undrained strength of soft clay deposits are then discussed for each clay classified with brief review on past studies. A method for obtaining in-situ undrained strength is proposed for normally consolidated aged clay which is the most common type of soft clay deposits and its validity is proved by various tests results. Characteristics of unconfined compression and in-situ vane strengths are also discussed based on their comparison with the in-situ undrained strength obtained from the proposed method. Further, field behaviour and stability analysis of five embankments constructed on a normally consolidated aged clay under very low factor of safety are shown. The results of stability analysis strongly demonstrated the efficiency of the method proposed in this paper.