Wang Sijing

Analysis of rainstorm-induced slide-debris flows on natural terrain of Lantau Island, Hong Kong

Abstract Lantau Island, the largest outlying island of the territory of Hong Kong, experienced a severe rainstorm on 4–5 November 1993, which induced >800 slope failures on natural terrain there. Detailed field investigations were carried out to study the failure modes, in relation with various influencing factors. It was found that the occurrence of slide-debris flows has a close relationship with bedrock geology, slope gradient, vegetation cover and micro landform. The failure modes of slide-debris flows may be classified into translational slides and rotational slides, and the former are predominant. Analysis of the hydrological response of colluvial slopes during the rainstorm indicated that the majority of the failures were caused by the development of a perched water table in the thin surface layer of colluvium of volcanic origin due to infiltration during the heavy rain. Undisturbed soil samples from south Lantau have been subjected to anisotropically consolidated undrained compression tests at comparatively low stress levels. Constant deviatoric stress path tests (CQD) simulating the stress path in the field at in situ stress levels have been performed to investigate soil behavior. The CQD test results indicate that the material of slopes at undisturbed state is brought to dilation because of the increase in pore water pressure caused by infiltration of rain water. For a translational slide, the displacement, resulting from dilation, may destroy cohesion along the failure surface and locally within the interior of the slide. The surplus water during the intense rainstorm was able to equilibrate the reduction in pore pressure caused by dilation, and the dilation and displacement may be further increased. The strain-softening after significant strains triggered debris flow mobilization. However, for a rotational slide, the increase in pore water pressure caused by surplus water infiltration during the intense rainstorm could not equilibrate the reduction in pore pressure caused by dilation, much or even all of the sliding block could not mobilize into a debris flow.

Three-dimensional back-analysis of displacements in exploration adits — principles and application

Abstract Back-analysis from displacements has been attracting the interest of the rock engineering profession in recent years. It has been applied since its inception in the 1970’s because of its instinctive practical value to the designer. In this paper we discuss the principles and application of one feasible method, that of Three-dimensional displacement Back-Analysis (TBA), which is used to back analyze the modulus of elasticity ( E ) of the rock mass and the horizontal component ( P ) of rock stress mainly by means of displacements measured during the the excavation of an exploratory geological adit. An attempt is also being made to solve the problem of unique resolution of TBA.

Coupled Damage-Seepage Constitutive Model of Jointed Rock Masses and its Engineering Application

Abstract Based on the principle of energy superposition of liquid diffusion, the permeability tensor of a jointed rock mass is established. By means of the fracture mechanics and damage theory, a constitutive model of jointed rock mass under complex stress and damage states is studied. The damage evolution laws of jointed rock mass under both compression-shear and tension-shear are considered. Furthermore, coupled damage-seepage relationship is derived and programmed into a FEM code. The developed model and FEM code are applied to analyze the stability of high slope of the permanent lock of Three Gorges Project (TGP). Comparing the numerical results with the monitoring results, it can be seen that the model is creditable.