Figure 7. Cumulative grain size distribution (by weight) curves for dredged material samples taken prior to dredging (Mobile Bay Channel) and post-dredged (Hopper Dredge)

ERDC TN-DOER-D2

September 2004

VARIABILITY DUE TO DREDGING OPERATION: In addition to the influence of spatial

variability, there is uncertainty when predicting the geotechnical properties of dredged sediments

during the dredging operation.

Hydraulic Suction Dredging. To observe the changes in properties between pre-dredged

sediment and post-dredged sediment during suction hopper maintenance dredging, grab samples

were taken in the Mobile Bay channel and on a hopper dredge. The Bay samples were taken

within a 50-ft (16.5-m) radius with a hand-operated bottom dredger sampler in the surficial

sediment inside the pre-dredged main navigation channel at water depths of approximately 40 ft

(13.2 m). The hopper dredge sample was a hopper grab sample of material dredged within a

500-ft (165-m) reach of the pre-dredged samples during transport to an ocean disposal site.

Figure 7.

Cumulative grain size distribution (by weight) curves for dredged material samples taken prior

to dredging (Mobile Bay Channel) and post-dredged (Hopper Dredge)

The pre-dredged and post-dredged materials had the same soil type classification, CH, with liq-

uid limits within 7 percent of each other. The as-sampled water content of the pre-dredged mate-

rial was 212 percent, and the as-sampled water content of the post-dredged material was 546 per-

cent, indicating a solids bulking factor of 2 caused by hydraulic dredging (solids bulking = ωfinal

+ 1 / ωinitial + 1).

The median pre-dredged grain size was 0.001 mm, and the post-dredged size was 0.002 mm. The

mean pre-dredged grain size was 0.013 mm, and the post-dredged size was 0.018 mm.