Compressibility of Artificially Sedimented Clays

ADOLPH GEORGE ALTSCHAEFFL, Purdue University

Abstract

This investigation attempts to clarify the suitability of labora- tory consolidation testing for ascertaining the in-situ compressibility of natural clay sediments. It comprises the study of effects of stress history, rate of loading, and sampling on the compressibility of artificially sedimented clays.A residual clay soil derived from limestone was disaggregated and sedimented in the laboratory in a special apparatus. Continuous loadings were applied to the sediments at rates varying from 0.01 to 0.0001 kg./sq.cm./day. A steel frame 9 ft by 6 ft by 16 ft was con- structed to permit sedimentation of eight samples simultaneously. The soil was sedimented in special lucite tube-brass (or lucite) base assemblies of two types: a flat base to facilitate sediment sampling and a depressed center base to permit in-place tests.Various combinations of continuous loading, secondary compression, continuous rebound, and continuous reloading were applied to seven sediments, after which increment type tests were performed, either in- place or on sampled specimens, using conventional or reduced load increment ratios.The principal conclusions are:1) A "quasi-preconsolidation pressure" develops in natural clay sediments due to sustained loads from the weight of overburden even if no other changes in environmental conditions take place.2) Reduced load increment tests produce compression curves similar to those produced by continuous loading at approximately the same rate.3) A change in the rate of continuous loading produces a changein the sedimentation-compression curve.4) The effects of stress release during sampling may not be as significant as previously conjectured. The sampling procedures used in this study appear to have little influence on compressibility other than reducing slightly the magnitude of the deduced quasi- preconsolidation pressure.

Degree

Ph.D.

Subject Area

Civil engineering

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