Spatial variability of saprolitic soil properties and relationship with joint set orientation of parent rock: Insights from cases in Hong Kong

Geomaterials are known to be associated with significant heterogeneity, and the natural variations in properties can affect the occurrence of landslides and failure of engineering structures. While these variations are often observed to be spatially correlated, the correlation patterns and their relationships with the geological origins of the materials are not well understood. This study utilizes a three-dimensional spatial variability model to investigate the correlation features in mechanical properties of saprolitic soils, which are products of chemical weathering of granite. Rigorous geostatistical analyses are performed for soil test data at four locations in Hong Kong, each also consisting of extensive rock joint survey information. The analyses show that the principal directions of spatial variability in saprolitic soils correlate well with joint set orientations in the parent rock, providing quantitative evidence that soil heterogeneity partly arises from the different rates of weathering along various directions relative to the rock discontinuities.