Geotechnical characteristics of fine-grained soil with wood ash

The study investigates the effect of wood ash (WA) on the geotechnical behavior of low-plasticity clay (CL) soil with the aim of improving soil properties while minimizing environmental impact. Various WA ratios (0 %, 8 %, 16 %, 24 %, and 32 % by the dry weight of the soil) were added to the natural soil and then tested for their Atterberg limits, specific gravity, standard compaction, unconfined compression strength (UCS), California bearing ratio (CBR), direct shear strength, consolidation settlement, and permeability. Results showed that a higher WA content increases the plastic limit (PL) and liquid limit (LL). However, the plasticity index (PI), linear shrinkage (LS), specific gravity, free swelling, compression index, and hydraulic conductivity decrease as the WA content increases up to 32 %. Incorporating WA into the CL results in an increasing trend in the optimum moisture content (OMC), while a decreasing trend is observed in the maximum dry density (MDD). The UCS and CBR exhibit remarkable enhancement with the addition of WA up to 24 %; beyond that limit, a subsequent decrease occurs in both parameters. In addition, the enhancement of the subgrade with a WA content of 24 % leads to a reduction in the thickness of the subbase layer by about 46 %. Moreover, a higher content of WA increases cohesion and friction angle significantly. Consequently, the optimal improvement of clay soil can be achieved by incorporating 24 % WA.