DENSITY-MOISTURE RELATIONS OF SOME TRINIDADIAN SOILS INCORPORATED WITH SEWAGE SLUDGE

Abstract

Maximum dry bulk density ( max) and optimum moisture content (Wopt) were measured in the laboratory forfour Trinidadian soils (two sandy loams, clay loam and clay) mixed with cured sewage sludge at four levels (0, 4, 8, and12% by mass) and compacted using 5, 15, and 25 standard Proctor hammer blows. Compaction tests on the soils werecarried out at different moisture contents ranging from 5 to 45%. Mean max decreased significantly (P <0.001) from 1.51to 1.34 Mg m3, while mean Wopt increased from 24.2 to 29.5% as sewage sludge content increased from 0 to 12%. Whilemax increased, Wopt decreased with increasing compaction levels. On the other hand, max declined while Wopt increasedwith increasing clay content of the soils. The values of bulk density for the Proctor compaction curves were predictedusing an equation that involved, max, Wopt and an empirical coefficient, S. The predicted values of bulk density whenregressed on the corresponding measured values, gave a near-perfect fit (R2 = 0.977, regression constant = 1.00 andconstant term = 0.012). Multiple regression equations were developed to relate Wopt and S each to clay, sand, and sewagesludge contents as well as to compaction effort. Two equations, one physically based and the other empirically based,were developed to relate max to Wopt. The procedure described provides a good method for quantifying the effect ofsewage sludge incorporation on soil compaction.