To investigate the effect of sampling method in sample quality, six types of samplers were used and three boring methods were employed to retrieve coastal clays of Japan (Ariake), Thailand (Bangkok), and United Kingdom (Bothkennar). Unconfined compression tests and residual effective stress measurements were carried out in soil samples taken by the various types of samplers and sampling methods. It has been found that the sample quality from the Japanese sampler is equivalent to that of the large diameter Laval sampler and Sherbrooke sampler. Sample quality of Japanese sampler is significantly influenced by the method of boring.
Geotechnical engineers have recognized the importance of sample quality in evaluating reliable design parameters. However, although some countries or organizations have developed their own sampling methods suitable for their soil conditions and characteristics, still there is no international standard for collecting undisturbed soils. Similarly, although the measurement methods of residual effective stress of soil is getting easier and more precise than before due to the advancement of technology, there is no internationally accepted standard method for suction measurement and for the evaluation of the sample quality. In this paper influences of samplers and sampling techniques in sample quality have been investigated using six types of samplers and the corresponding sampling techniques for several clay deposits. Some researchers (e. g. Hight et at., 1992) have claimed that residual effective stress of a soil reduces with storage time. We have checked the phenomenaof residual effective stress, and compared our results with the data available in literature. Some researchers (e. g. Shogaki, 1995) have been insisting that the residual effective stress of samples can be estimated, even if the samples are disturbed, and therefore, shear strength of a ground can be estimated from it.
