Effects of the tube diameter, the cutting edge angle and the penetration speed influencing Toyoura sand movement caused by tube penetration during sampling is examined based on the movement of the soil particles caused by the tube penetration. Samplers with tubes having inner diameters of 35 mm, 45 mm and 75 mm, and cutting edge angles of 6%#176 or 90%#176, are used for model tests on Toyoura sand. Physical characteristics and grain size properties of Toyoura sand are similar to those for the Niigata sand samples. Therefore, for the model tests on Toyoura sand, the ground is assumed to be like that of naturally occurring Niigata sand with few alluvial grains. The tube penetration speed (Sp) is in the range of 0.6 cm/sec to 5.8 cm/sec, while the relative density (Dr) is in the range of 30 % to 70 %. The disturbed area was easily formed by the tube cutting edge angle of 90%#176, since the vertical displacement (Dv) of the targets of the tube cutting edge angle of 90%#176 obtained from all Dv, Sp and tube diameter conditions in this test were smaller than those of the tube cutting edge angle of 6%#176.
Sample quality is directly controlled by the pore water pressure/effective stress behavior and the rearrangement of soil particles caused by the tube penetration during sampling. Up to now, no sufficiently demonstrative research has been conducted on this issue despite the information that elucidates the nature of sample disturbance. Baligh, et al. (1987) and Clayton, et al. (1998) studied the effect of sample disturbance on the sample quality due to the tube cutting edge angle and the tube diameter through numerical analyses. They pointed out that the sample quality decreases with a decreasing tube diameter. However, these results cannot explain the quality of the samples obtained by the 45-mm and 75-mm samplers, since the quality of the samples obtained with the 45-mm sampler is similar to or higher than that of the samples obtained with the 75-mm sampler (Shogaki and Sakamoto, 2004; Shogaki, et al. 2006; Shogaki and Nakano, 2010). One reason given for the higher quality of the samples obtained with the 45-mm sampler is the higher penetration speed (Shogaki and Nakano, 2010). However, this opinion is inadequate, since it is based on field sampling and has not been examined by means of a quantitative evaluation for each factor. Horng et al. (2010) also discussed the effect of sampling tube geometry on reconstituted Kasaoka clay prepared in the laboratory under atmospheric conditions, i.e., not under confining stress. The tank used in their 1 g physical model test was also about 30 cm tall.
