Appendix I: Consolidation Testing

Appendix I

Consolidation Testing

Consolidation Testing Procedures

Consolidation analysis of soft dredged material requires that laboratory

compressiblity data be obtained across the entire, wide range of void ratios that

are commonly encountered in these soft materials as they consolidate. Void

ratios in dredged materials can vary much more than those of normal soils. In

typical (nonsediment) soils in the natural state, void ratios normally vary

between 0.25 and 2.0, with some soft organic clays reaching 3.0. Recently

deposited in situ sediments often have void ratios as high as 5 or 6, double or

triple the values of most soils. When dredged by hopper or hydraulic dredges,

the initial void ratios after disposal may reach as high as 10 to 12; in a few

clayey sediments; the maximum values may reach even higher. Mechanical

dredging does not dramatically alter the void ratio of the mass of dredged mate-

rial; however, there will be clumps of material at about the in situ void ratio with

much softer (slurry consistency) material between the clumps.

Laboratory consolidation testing of soft materials often requires use of at

least two types of consolidation tests. Both a modified version of the standard

oedometer consolidation test and a self-weight consolidation test must normally

be conducted; these tests provide data for the low and high ends of the antici-

pated range of void ratios, respectively. However, on relatively firm dredged

materials that are mechanically dredged, use of oedometer testing alone may

suffice.

Several additional consolidation test devices and procedures have been

developed and evaluated in recent years, but none are currently available or

recommended for routine dredged material testing. Some of these devices were

intended to supplement the self-weight and oedometer test by providing more

continuous void ratio-effective stress (e- ) and void ratio-permeability (e-k)

throughout the middle ranges of interest, while some devices were intended to

provide all of the necessary data, thus eliminating the need for any other tests

(e.g., Poindexter 1988). Because of continued widespread interest in slurry

consolidation in the dredging, mining, and phosphate industries, it is anticipated

that the American Society for Testing and Materials (ASTM) will develop a

Appendix I Consolidation Testing