Role of microfabric in matrix suction of residual soils

Residually derived red soils are present in Bangalore District of Karnataka State. The red soils of Bangalore District are generally unsaturated with bulk of the specimens having degree of saturation (Sr) from 20% to 70%. In unsaturated soils, pores with small radii act as capillary tubes and retain water in a state of reduced pressure with respect to atmospheric pressure. The reduced pressure of capillary water is termed as matrix suction. Factors influencing matrix suction of unsaturated soils are water content/degree of saturation, relative compaction and particle size. Besides the above-mentioned factors, the microfabric is expected to influence matrix suction (ua−uw) of unsaturated soils as it determines the relative abundance of different categories of pores in a soil. The study examines the influence of the microfabric on the matrix suction of residual soils from Bangalore District by referencing the matrix suction of undisturbed residual soil specimens to their remolded state. The matrix suction of the undisturbed and remolded soil specimens is determined by the ASTM filter paper method. Information on microfabric of the residual soil specimens is obtained from mercury intrusion porosimetry (MIP) experiments. Experimental results suggest that the matrix suctions of the undisturbed and remolded residual soil specimens are greatly influenced by the relative abundance of the inter-aggregate porosity and intra-aggregate porosity.