Comparing the quality of samples obtained by three types of fixed-piston samplers for soft sensitive clay

Three types of fixed-piston samplers were employed at Nakdong River Delta. The retrieved samples were equally divided into 100 mm long pieces. Quality was evaluated using suction, shear wave velocity, and consolidation tests. The constant rate of strain consolidation test, rather than the incremental loading test, produces a better correlation with the nondestructive test results. The sample quality progressively degrades from the near-center to both ends of each sampling tube. The sample quality measured using the three methods on samples at the near-center of the sampling tubes consistently varies with the in-situ void ratio in the upper clay; however, such a trend is not observed in the lower clay. This may be attributed to the effect of total stress relief on the clay. The sample quality evaluated deteriorates in the following order: oil-operated type, mechanical type, and hydraulic type. The results suggest that the difference in sample quality is principally caused by the mechanical disturbance attributed to the different penetration mechanisms (methods) of the sampling tubes. The tip angle of sampling tubes significantly affects sample quality, whereas the length-to-diameter ratio has a relatively insignificant effect.