Density-moisture relations of some Trinidadian soils incorporated with sewage sludge.
Ekwue E.I. | Stone R.J.
Maximum dry bulk density (rhomax) and optimum moisture content (Wopt) were measured in the laboratory for four Trinidadian soils (two sandy loams, clay loam and clay) mixed with cured sewage sludge at four levels (0, 4, 8, and 12% by mass) and compacted using 5, 15, and 25 standard Proctor hammer blows. Compaction tests on the soils were carried out at different moisture contents ranging from 5 to 45%. Mean rhomax decreased significantly (P <0.001) from 1.51 to 1.34 Mg m-3, while mean Wopt increased from 24.2 to 29.5% as sewage sludge content increased from 0 to 12%. While rhomax increased, Wopt decreased with increasing compaction levels. On the other hand, rhomax declined while Wopt increased with increasing clay content of the soils. The values of bulk density for the Proctor compaction curves were predicted using an equation that involved, rhomax, Wopt and an empirical coefficient, S. The predicted values of bulk density when regressed on the corresponding measured values, gave a near-perfect fit (R2 = 0.977, regression constant = 1.00 and constant term = 0.012). Multiple regression equations were developed to relate Wopt and S each to clay, sand, and sewage sludge contents as well as to compaction effort. Two equations, one physically based and the other empirically based, were developed to relate rhomax to Wopt. The procedure described provides a good method for quantifying the effect of sewage sludge incorporation on soil compaction.
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