Performance of an innovative direct-push piston sampler in soft clay

An innovative direct-push sampler has been developed to maximize sample retention and reduce disturbance. The stainless steel sampler has an outer diameter of 63mm, a wall thickness of 1.6mm and a toe cutting angle of 5 degrees. The sampler is inserted into the ground by direct push methods, then operates as a conventional fixed-piston sampler until it is about to be withdrawn from the ground. Prior to withdrawal a very brief "shot" of pressurized nitrogen is injected horizontally at the base of the sample, just above the cutting edge, to cut the soil. Then, during withdrawal, low pressure air or water is injected into the void that develops below the sampler to overcome the suction that otherwise would develop as it is pulled out of the ground. Sample quality is investigated in this paper, using CAT scans performed on each of the samples prior to extrusion, constant rate of strain compression and triaxial tests.