Dredged Material Slump Test

ERDC TN-DOER-D1

August 2004

Another application of the slump test has been to determine the yield stress of mine tailing waste

materials (Pashias et al. 1996). For highly flocculated mineral suspensions, the test was shown to

be an inexpensive method for plant operators to monitor suspension handling and transport.

Especially useful was the ability to rapidly monitor changes in the slurry solids concentration.

The benefits of observing lateral displacement of dredged material samples as a function of time

were first noted during a dredged capping project in the Boston Harbor (Fredette et al. 2000).

Grab samples were openly placed on a flat sheet of plywood and their spread diameters and

height changes were monitored for the purpose of observing dredged material consistency over a

period of time. The height change values showed a better trend than did the spread values, and

this simple test helped to achieve success for the subsequently placed sand cap by revealing

when the dredged material had reached an optimum consistency.

For further application to dredged materials, the proposed cylinder slump test will provide a

means to assess the selected material properties required for input into current and future physi-

cal and numerical models developed for both nearshore and contaminated dredging operations.

As further tests are conducted on dredged materials, parameter correlation and predictability

should be enhanced.

Dredged Material Slump Test. Figure 1 shows the sequence for the proposed dredged mate-

rial cylinder slump test. The remolded material is placed as a thoroughly mixed homogenous

mass into the slump cylinder, leveled off, and allowed to flow outward as the cylinder is slowly

lifted upward with minimum disturbance to the sample. After the outward flow has visually

stopped, the difference in height between the cylinder and the slumped material is noted. The

outward flow spread diameter may also be noted.

Experimental Methods and Applicability. Numerous slump tests were conducted on dif-

ferent types of dredged material soils (coarse and fine-grained) using open-ended polyvinyl chlo-

ride (PVC) cylinders of various heights and diameters. Aspect ratios (cylinder height to cylinder

diameter) of 1, 1.5, and 2 were evaluated, as well as slump/cylinder height, slump/cylinder

diameter, slump/cylinder volume, and spread/cylinder volume ratios.

The slump cylinders were filled with remolded saturated soils at various consistencies. The water

contents were varied to obtain consistencies ranging from viscous slurry to a soft soil. In situ

pore water was removed or added as needed, and each sample was thoroughly mixed by hand to

avoid air entrapment. The slump and spread diameter dimensions were noted, and the ASTM

D2216 water content was taken from the slumped soil center to minimize excess pore pressure

effects after shear failure. The best predictor was found to be the slump/cylinder height, also

referred to as the normalized slump. Its applicability is discussed in more detail below.

Cylinder height dimensions ranged from 5 cm (2 in.) to 20 cm (8 in.), and diameter dimensions

ranged from 5 cm (2 in.) to 15.2 cm (6 in.). Slightly better correlation between water content and

normalized slump was found in cylinders with aspect ratios of 1:1 and 2:1, but many 2:1 samples

had a higher tendency to topple over before slumping. The lateral spread was also measured in

numerous samples, but better correlations were observed using the vertical deformation (slump)

measurement. Deformations were measured to the nearest 0.32 cm (0.125 in.).