ABSTRACT: The applicability of the SHANSEP method was examined for six different natural clays, namely Louiseville (Quebec, Canada), Bothkennar (Scotland, UK), Yamashita (Yokohama, Japan), Amagasaki (Japan), Rakusai (Kyoto, Japan) and Singapore. All of these clays are somewhat overconsolidated and their OCR range between 1.9 and 5.0. It was confirmed that post-depositional stress change had taken place for the latter three clays, although their OCRs could not be fully explained only by the stress history. Some or all parts of the overconsolidation for the objective clays may have been created by reasons other than the stress change, such as ageing or Cementation. The undrained shear strength (s_u) of these Clays was examined using the SHANSEP method and compared with that obtained using the recompression method. All the soil samples were recovered using the Japanese standard fix piston or equivalent samplers, and strength evaluation was done using the triaxial and the direct shear apparatuses. It was found that the stress-strain relations as well as stress paths are somewhat different between the SHANSEP and the recompression methods: that is, larger strain and smaller internal friction angle at failure for the SHANSEP method. However, difference in s_u measured by the two methods was surprisingly small, the ratio ranging between 0.9 and 1.1. This research has led us to the conclusion that considering the variation in sample quality in practical soil investigation, the SHANSEP method is a quite useful method in evaluating the design undrained shear strength of a soil, which is free from sample disturbance. It should be noted, however, that the yield consolidation stress, which is an important soil parameter in SHANSEP method, is affected by sample quality.

Key words: natural clays, overconsolidation, recompression, sample quality, SHANSEP, soil investigation, undrained shear strength (IGC: D6)