Effects of fixed-piston sampler fixity on clay sample quality

This research studied the application of samplers under three fixity conditions during sampling tube penetration and evaluated the quality of the retrieved samples. Original and portable types of oil-operated fixed-piston samplers with identical sampling tubes were employed at a site in the Nakdong River Delta. Suction, shear wave velocity and consolidation tests were conducted to assess sample quality. The soil fabric, including holes, nodules, roots and shells, rather than soil sensitivity (4 to 28) was found to significantly affect sample quality, particularly suction. The sample quality indicators, except for the suction-based values, near the centre of each sampling tube tended to vary depending on the bulk density of the ground. The original type of sampler fixed at the centre of the steel casing produced samples of slightly better quality than those produced by the same sampler freely located in the borehole and those produced by a portable sampler tightly located in the steel casing. This finding was also supported by different qualities of samples obtained using the oil-operated and mechanical samplers at a different site. It is thus concluded that the fixity of samplers is a minor factor that influences sample quality.