MEASUREMENT OF ANISOTROPIC HYDRAULIC CONDUCTIVITY IN UNCONSOLIDATED SANDS - A CASE-STUDY FROM A SHOREFACE DEPOSIT, OYSTER, VIRGINIA

In this study an integrated held and laboratory method which can be us ed to evaluate the magnitude and distribution of anisotropic hydraulic conductivity at the scale of bedding structures in unconsolidated sed iment is demonstrated. Undisturbed sediment cores 10.16 cm in diameter and 18.25 cm long are obtained using a split-barrel core sampler. Two undisturbed 5.72 cm diameter (7.90 cm long) subcores, oriented parall el and perpendicular to the primary bedding structures, are then obtai ned from each field core; the hydraulic conductivities of the subcores are then measured with a constant-head permeameter. The sampling and experimental procedures are designed to minimize potential sources of error. Sixty-four 10.16 cm cores were sampled in a coastal sand outcro p located similar to 300 m from a subsurface injection experiment near Oyster, Virginia. Four distinct lithologies were sampled in horizonta l transects with a spacing of 0.5 m between core locations. In additio n, iron oxide bands which were prevalent throughout the exposure were sampled from both ends of the outcrop. The average hydraulic conductiv ity values are consistent with the observable geologic features (grain size, sorting, and iron oxide banding). Hydraulic conductivity is gre ater in the parallel-oriented subcore for 90% of the core pairs, and m ean hydraulic conductivity ratios of parallel to perpendicular-oriente d subcores (K-parallel to/K-perpendicular to) for the different lithol ogies ranged from 1.33 to 1.57. The major control on the anisotropy in this sediment is interpreted to be preferential grain orientations re sulting from depositional processes, with additional influences from t he prominence of the bedding structures and secondary features such as hydrous iron oxide banding.