Jung Man Lee

This study presents an enhanced hydraulic fixed-piston (HNS-N) sampler that reflects a local practice. This sampler was employed at a deltaic site along with two other types of samplers: a similar hydraulic (HNS-K) type with no vacuum breaker and an oil-operated (ONS) sampler that is equipped with a vacuum breaker and is fixed at the center of a casing. The generation of a slowly but erratically increasing pressure in the hydraulic samplers often does not ensure constant speed and full penetration; thus, the pressure in these samplers was increased rapidly after the drill rods were filled with water. By contrast, the pressure in the ONS sampler was increased instantaneously. The hydraulic samplers exhibited slightly discrete penetration behavior, whereas the ONS sampler induced constant penetration. The sample qualities of the samplers are ordered based on an evaluation via two nondestructive methods and a consolidation test, as follows: ONS > HNS–N > HNS–K. The sample quality was affected signifi...