Table 6. Physical Properties of Ocean-Placed Sediment Samples

ERDC TN-DOER-D2

September 2004

Table 6

Physical Properties of Ocean-Placed Sediment Samples

Sample

% sand

% silt

% clay

Class

Pre-

2.73

156

Post-

2.65

Figure 10. Frequency grain size distribution (by weight) curves for pre-dredged and post-placed material

samples

The two curves have similar particle size frequency distributions in the coarse sand and fine silt

ranges, but vary in the fine sand and fine clay ranges. The variation in the fine sand percentage is

likely due to mixing with the native sandy sediment, which has a mean size of 0.21 mm as

reported by Davis et al. (1999). The variation in the fine clay percentage is likely due to loss in

the water column during placement, or from surficial erosion as reported by Gailani et al. (2001).

Confined Aquatic Placement. Property variability has also been observed in pre-dredged

and post-placed sediments placed in a contained subaqueous pit. For the previously referenced

Boston Harbor project, the subaqueous cell M2 received material from the Mystic River channel

mechanically dredged in the relative vicinity of surficial grab samples MRA, MRB, and MRC.

The dredged material was placed using split-hull scows dumping through approximately 25 ft

(8.2 m) of water to the top of the subaqueous cell surface. Figures 11 and 12 compare composite

samples MRA, MRB, and MRC to the dredged material subsequently placed in subaqueous cell

M2.