Water infiltration in cracked soils for landslide study (Sponsor: RGC-CERG; PI: Prof. LM Zhang; Co-Is: Prof. DG Fredlund and Y Wang; PhD student: Ms Li JH and Mr. Ben Kwong)

Many large-scale landslides have been caused by water infiltration during rainstorms or reservoir level changes; therefore, the study of water infiltration into soil is essential for landslides investigation and mitigation. Most soil deposits contain cracks and other geological discontinuities near the ground surface. Field studies indicate that to describe the infiltration process for slope engineering design purposes, a model based on the assumption of uniform porous media is inadequate. Ignoring cracks near the ground surface will underestimate water infiltration and possibly lead to incorrect interpretation of the causes of landslides and insufficient slope design. The objectives of this project are to characterize the geometrical features of soil cracks, study the permeability tensors of cracked soils under saturated and unsaturated conditions, and investigate the scale effect and anisotropy of cracked soils. Six exploration pits, three in Hong Kong and another three in the Three-Gorge Reservoir Zone, will be used for the field study in selected natural terrain landslide areas in order to build three-dimensional prototypes of the crack networks in soils. Sophisticated laboratory tests will be devised to further characterize cracks in soils and test the anisotropic permeability of cracked soils. Based on these experiments, models for stochastic crack networks will be established and permeability tensors under saturated and unsaturated conditions will be determined based on characteristics of the cracks and the soil matrix. These models will then be implemented into a numerical code to analyze various water infiltration problems. The results from the study will improve our ability to deal with a class of important problems involving the mitigation of landslides in natural terrain, generation of floods, long-distance water transfer and pollutant transport.