| A unique device, similar to the direct simple shear device of the Norwegian Geotechnical Institute, is described. The device was employed to establish a relationship between void ratio and contant volume undrained direct simple shear strength of a silty sand.; The device is used in conjunction with a specimen mold, a frost cabinet, and auxiliary instrumentation to establish a relationship between void ratio and post-thaw undrained direct simple shear strength of the same soil. The mold consists of twenty removable interlocking split discs so that shear testing can be performed at various elevations within the previously frozen specimen. The post-thaw sample allows for shear strength determination at locations of high moisture content due to prior ice lensing during freeze. The freeze phase is well controlled and automatically monitored by the auxiliary instrumentation. Field conditions are simulated.; The resulting relationship between void ratio and post-thaw undrained shear strength indicates the soil has weakened due to freeze and thaw. The causes of weakening are increased void ratio due to moisture migration during freeze and weakened planes at the location of previous ice lenses. Because of problems controlling a stationary thaw-freeze interface during shear and suspected flexibility of the reinforced membranes, it cannot be categorically stated that the post-thaw shear strength is, in fact, less than the prefreeze strength at all magnitudes of void ratio.; However, as shown in this report, the utilization of this device shows great promise for quantitative assessment of thaw-weakening. This pioneering study employs the direct simple shear test mode to investigate the anisotropic shear strength versus depth profile of a previously frozen soil column. |
