Effects of pore fluid salinity on desiccation cracking and microstructural behaviors of biochar-amended red clay

Biochar-amended clay materials have been utilized as the cover or liner layers in waste containment systems. The desiccation cracking behaviors of clay-based cover layer have been widely studied, but related studies considering effects of pore fluid salinity are rarely conducted. In this study, a series of desiccation-cracking tests were performed on biochar-amended red clay to examine the effects of salt solution concentration and biochar dosage on its cracking patterns. The results indicated that the evaporation curves of red clay could be approximately divided into three stages: constant-rate decreasing stage, decelerating decreasing stage, and stable stage. The drying-induced cracks within the soils primarily occurred in the decelerating decreasing stage. The addition of biochar was able to effectively inhibit desiccation cracking of red clay at the low biochar dosage (< 5%); on the contrary, biochar increased the crack number and ratio at the high biochar dosage (> 5%). Compared to the biochar, pore fluid salinity showed more obvious influences on improving the water-holding capacity and inhibiting the desiccation cracking, especially in the high-concentration salt solution. Microscopic observations implied that biochar could effectively fill the pores between clay aggregates and improve the soil absorption capacity. Meanwhile, NaCl solution could lead to the inter-particle aggregation by changing the fabric association modes of clay particles. The obtained findings provide valuable insights into the assessment of long-term performance of the biochar-amended clay cover layer.