Microstructural Characterization of Alluvial Sand Containing Cohesive Soil Lumps During Loading and Inundating

Cohesive soil, as soil lumps within the sand matrix of the Gangetic alluvial plain, exerts a significant influence on the dynamic properties of sand deposits, as extensively documented in prior research. This study aimed to describe the intricacies of microstructural changes and re-distribution of pore sizes resulting from the effects of loading and wetting. To gain a comprehensive understanding, microstructural characterization of Indo-Gangetic alluvial soil was performed using two advanced analytical techniques, mercury intrusion porosimetry and scanning electron microscopy. The collapse behavior of Sone river sand samples mixed with varying proportions of soil lumps was studied using a series of oedometer test. A decrease in the collapse potential (CP) trend was observed with each increase in the sand percentage. The CPs were estimated as 16.39% and 10.07% for alluvial sand containing 70% and 40% collapsible lumps, respectively. The micrographs and differentiation in pore morphology were used to describe the microstructural evolution of lump-sand mixture due to saturation and loading. This study highlights the pivotal role played by the collapsible soil lumps within the sand matrix. Initially, these lumps possess an open structure, characterized by cementation bonds that interconnect clay-coated silts and sand aggregates. However, these cemented bonds are susceptible to disintegration under the influences of loading and wetting, ultimately triggering collapse in the soil matrix. After the collapse, soil particle re-arrangement occurs, and the initial open structure in soil lumps transforms into a dense structure. Microstructural change is dependent on stress levels. With increasing stress levels, higher inter-aggregate pores or macro-pores evolve into small sized intra-aggregate pores or micro-pores. This study contributes to the literature by providing both qualitative and quantitative insights into soil collapse and valuable guidelines for comprehending the intricate microstructural alterations that occur within alluvial sand containing these unique lumps.