In situ ground freezing and sampling of a Pleistocene sand deposit in the South Carolina Coastal Plain.

摘要

The procedures used to freeze and sample a Pleistocene sand deposit at the Coastal Research and Education Center near Charleston, South Carolina to preserve and study the effects of diagenesis are presented in this thesis. An initial feasibility study was conducted to target a layer of clean sand at the CREC site with little to no frost heave potential. To freeze the sand deposit, a ground freezing system with a central freezing pipe was installed to target a column of sand 1-m in radius and 2.3-m long. Liquid nitrogen was continuously supplied to the large steel freezing pipe, which was fabricated to isolate and radially freeze between depths of 1.8 m and 3.8 m below the ground surface, for 270 hours. Frozen sand cores taken from five locations 0.65 m to 0.7 m away from the central freeze pipe indicate the ground around the freeze pipe was frozen between depths of 1.8 m and 3.8 m below the ground surface at all but one location. A total length of core equal to 8 m with no indication of frost heave was retrieved from the site. Results of the ground freezing system including ground temperature measurements, growth of the frozen zone, and the amount of liquid nitrogen consumed are presented and compared with predicted values.;Temperatures recorded during ground freezing indicate that the rate of freezing at CREC was influenced by the direction of groundwater flow, flow rate of liquid nitrogen, and the location and type of liquid nitrogen inlet. The frozen zone estimated with temperature measurements was shown to be tapered with the largest growth at the same elevation as the liquid nitrogen inlet. The frozen zone also appeared to extend in the direction of groundwater flow and contract in the upstream direction. To reduce the time required to freeze the soil surrounding the freeze pipe, the flow rate of liquid nitrogen was increased. While temperatures decreased as predicted when the liquid nitrogen flow rate was high, the volume of liquid nitrogen consumed was much higher than predicted.;Frozen samples obtained from the CREC site were transported to Clemson University and the University of South Carolina following ground freezing. The samples will be used in high quality static and cyclic triaxial tests.