Hydromechanical Behavior of Bamboo Biochar–Amended Soils under Various Environmental Conditions

Biochar is a carbon-rich material whose properties vary depending on the feedstock, pyrolysis condition, and heating rate. It possesses high water-retention properties, making it suitable for amending natural soil in landfill cover for green and sustainable development. The landfill cover may also undergo uneven settlements in the long term due to several loading and environmental conditions. Therefore, it is important to carry out a detailed study on the compressibility, hydraulic conductivity, and compressive strength of landfill cover layers considering long-term effects such as prolonged curing and wetting–drying cycles. Hence, in the current study, these hydromechanical properties of bamboo biochar–amended soil (BAS) were investigated. Series of one-dimensional oedometer and unconfined compressive strength (UCS) tests were performed on bamboo biochar (BB) mixed with low plastic clay (CL) and silty sand (SM) in five proportions (i.e., 0, 1, 2, 3.5, and 5%). Mercury intrusion porosimetry (MIP) and field emission scanning electron microscopy (FESEM) tests were carried out to find out microstructural changes in the samples. In CL soil, the addition of up to 2% BB reduced compressibility and hydraulic conductivity while enhancing UCS values; however, higher dosages led to reverse outcomes. In contrast, BB addition (1–5%) in SM soil resulted in a continuous increase in compressibility and hydraulic conductivity, along with a decrease in UCS values. The UCS values increased with an increasing curing period and decreased with wetting–drying cycles in both soils amended with biochar. MIP and FESEM analysis revealed efficient filling of pores and reduction of void space in CL soil up to 2% BB addition. Thus, CL soil amended with BB ensures enhanced material stability, suggesting its potential suitability for landfill cover applications.