Self-Weight Consolidation Test

material mounds are generally stiffer than dredged sediments, they are usually

still categorized as soft soils within the geotechnical community. Therefore, it is

prudent to test the foundation soils in the fixed ring device, although the standard

loading sequence may be used.

A representative sample of the fine-grained (minus No. 40 sieve) portion of

sediments to be dredged should be used for the standard oedometer test. Since

sediments have typically been remolded during the dredging process and any

internal structure existing in situ in the channel has been destroyed, a remolded

sample can be used for this test. The samples of foundation soils for consolida-

tion testing, however, should be undisturbed.

When soft disturbed sediment samples are used, they are often spooned into

the consolidation device. In this case, the dredged material must be placed

carefully into the consolidometer to prevent inclusion of air bubbles that would

invalidate the test results. After the sample is placed in the consolidation ring in

the oedometer, the initial load is applied. The seating load consisting of the

porous stone, loading plate, and ball bearings plus the compression load caused

by the dial indicator is considered as the initial load increment for the test. This

load should not exceed 0.005 tsf. If the sample consistency is extremely fluid-

like, a lower initial load may be necessary to prevent extrusion of the soft mate-

rial from the consolidation ring.

Succeeding load increments may be placed using the normal beam and weight

or pneumatic loading devices. The following loading schedule is typically used

for dredged material testing: 0.005, 0.01, 0.02, 0.05, 0.10, 0.25, 0.50, and 1.0 tsf.

A maximum load of 1.0 tsf should be adequate for most applications. However,

the maximum effective stress anticipated to occur at the bottom of the dredged

material deposit during its existence should be estimated and the loading

sequence extended, if necessary, to cover the full range of potential effective

stresses.

Time-consolidation data should be examined while the test is in progress to

ensure that 100-percent primary consolidation is reached for each load incre-

ment. In some cases, it may be necessary to allow each load increment to remain

for a period of several days. Rebound loadings are not normally required since

the dredged material will not typically be excavated after placement at a disposal

site (USACE 1987).

Self-Weight Consolidation Test

A test device and testing procedure were developed by Cargill (1985 and

1986) to allow determination of the compressibility characteristics of dredged

material at high void ratios. This test represents a modification to a testing

procedure developed by Bromwell and Carrier (1979) for use in analyzing

phosphate mining wastes. It is used to supplement the standard consolidation

test in order to provide e- and e-k data over the full range of anticipated void

ratios and is especially useful for hopper or hydraulically dredged materials.

Appendix I Consolidation Testing