The Impact of Biosolids on the Geotechnical Properties of Some Soils of the Niger Delta Sub-region, Nigeria

摘要

The production of biosolids (human wastes) in the Niger Delta of Nigeria has been taking place since man inhabited the sub-region. One of the negative impacts of biosolids is the changes to the geo-environmental conditions of the soils of the sub-region. Studies carried out on the effects of biosolids in the Niger Delta Sub-region over the last sixteen years indicate that the conventional geo-environmental engineering properties of the soils have been altered significantly. Biosolids have been found to affect both the grain size distribution patterns, the Atterberg Limits (Liquid Limits (LL), Plasticity indices (PI), California Bearing Rations (CBRs), Proctor Compaction indices such as Maximum Dry Densities (MDD); Optimum Moisture Contents (OMC), Soil friction angles (Φ) & cohesion values (c) and to an extent Ultimate Bearing Capacities (q_(ult). & q_(allow)). Biosolids applied on two types of tropical soils classified as slightly to medium plastic (lateritic (CL) and Sandy (SP) soils) batched and mixed at four different percentage levels of 5%, 10%, 15% and 20% by weight of sample indicated that % biosolids in the soils positively correlated with the Total Organic Contents (TOC) while inversely correlating with the Moisture content in the lateritic soils to a limiting value at 15%, while in the basically sandy soil it was at the 20% biosolids treatment. The infiltration rate increased to a peak at 13.5% biosolids content and thereafter decreased, while in the basically sandy soil, addition of biosolids caused the infiltration rate to fluctuate. It has also been observed that 100kN is the critical stress under which high volume reduction is recorded in all cases of biosolids treatments. The 5 to 10% biosolids treatment range experienced minimum volume change (Δv) compared to the 15 to 20% biosolids treatment range. The wide gap observed existing between 15 - 20% and 0 - 10% biosolids treatment ranges tends to suggest the existence of two groups of biosolids-treated lateritic soils namely: the Low and High Compressible Lateritic soils.