Mechanical and hydraulic properties of residual dolomite and wad found in the Malmani Subgroup in South Africa

Abstract

Dolomitic land is known for subsidence and sinkhole formation, making development such as housing unsafe, especially when wad is found. Wad and residual dolomite are usually found at the bedrock-soil interface and in grykes, in an unsaturated, non- to highly-reworked, state. These are critical areas for ground stability of a dolomite site (Buttrick, 1986). This research aims to better understand the geotechnical properties and hydrological behaviour of unsaturated wad and residual dolomite in relation to the grading, fabric and geochemical composition and the microstructure of the particles of the material, and how the reworking processes alter these characteristic properties. The fabric of the residuum is inherent to the structure of the parent rock, which is determined by the stress history of the rock. The fabric influences the unsaturated behavioural characteristics and water holding capacity of the material. The high and variable liquid limits is dependent on the overall fine grading, and the nanoparticle structure and large reactive surfaces exhibited by the metal oxides in the material. The residuum is typically non-dispersive, possess a low density, when not reworked, that can be below that of water, mostly grades in the silt fraction and has hydraulic conductivities in the order of 1x10-6 m/s. The mobilisation potential is dependent on the presence of the fabric, variance of sorting of the material’s grain sizes and the disparity of the degree of saturation above and below the wetting front moving through the material. The material is considered reworked when mechanical processes destroy the structured or nonstructured inherent fabric and foreign material is introduced into the soil matrix. The factors influencing the consequential broad potential behavioural and characteristic properties of the material are the type and degree of reworking and the environment of reworking.