Abstract
The effect of incorporating sewage sludge on the compressibility of four Trinidadian agricultural soils was investigated over a range of stresses from 0 to 1000 kPa. Air-dried sewage sludge was applied at four levels (0, 4, 8 and 12% by mass of dry soil) to the soils (two sandy loams, clay loam and clay) and these were tested at their optimum compaction moisture contents. Compression curves (void ratio versus log applied stress) for each soil were almost linear over the range of applied stress. Mean values of void ratio for all soils at four representative stress levels increased with increasing sewage sludge content and decreased with increasing applied stress and clay content. Significant interaction effects were observed between the experimental factors, with the interaction effect between soil type and applied stress being the most significant. Sewage sludge increased soil compressibility in all cases. Soil compressibility was quantified using two compression indices: C cdefined as the slope of void ratio versus log applied stress and Cdefined as the slope of bulk density versus log applied stress. C cand Ctended to increase with increasing sewage and clay contents, but C cwas identified as the more sensitive index, particularly in the 10-100 kPa stress range. An equation was derived to relate C cto initial bulk density before compression (ρ i), particle density (ρ s), strain difference (ε 2-ε 1) and the corresponding applied stresses (σ 1 and σ 2). The equation is C c=( ρ s( ε 2- ε 1))/ (ρ i log (σ 2/ σ 1)) .
Published Version
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