A recent paper by Pierson (1983) provided sound evidence of the contribution of soil pipes to landslides. Whereas the existence of pipes has been documented in a good number of publications, their importance in the context of slope stability has not generally been appreciated. Attention is now focusing on pipes in Hong Kong as a major contributory factor to frequent landsliding.
Pipes in Hong Kong
The hilly terrain of Hong Kong is prone to landslides brought about by the heavy seasonal rainfall (Lumb 1975; Brand 1984, 1985). The granites and volcanic rocks are weathered to considerable depths, the surface residual soil often being overlain by a mantle of colluvium. Until recently, it was not realized that the existence of pipes was an important factor in the overall stability of some of Hong Kong's hillsides, and that they have undoubtedly been the main cause of some of the failures that have occurred in Hong Kong cut slopes (Premchitt et al., 1985).
The pipes in the residual soils and colluvium of Hong Kong cover the range of types described in the Paper and discussed previously by Crouch (1976) and Jones (1981). They vary considerably in diameter, in length and in depth in the soil profile. In some cases, they are suspected of comprising anastomosing networks which cover large areas (Nash & Dale 1983).
Pipes in Hong Kong are most commonly exposed in shallow excavations in A and B soil horizons, as described by Crouch (1976). These are most commonly attributed to