Abstract

The photograph shows part of a trench excavated in weathered rock for the construction of a retaining wall along the northern boundary of the Tin Hau Temple Road site in Hong Kong (Fig. 1).

In 1978 the Client purchased a piece of land to construct three blocks of flats. The site, shown in Fig. 2, consists of the north western corner of a steep spur composed of granite in various stages of decomposition and containing a number of large sub-rounded residual boulders.

The flats are to be at least 21 storeys high and, because of the height restrictions imposed by the proximity of the site to the approach path of the airport, the formation level had to be some 35 m down into the spur. Excavation to this formation level posed the problem of the stability of the cut slopes and, as no permanent excavation was allowed outside the limit of the site and temporary incursion was strictly limited, the cuts had to be near-vertical to provide sufficient foundation area to accommodate the apartments. The general rock profile on the site consists of 10 m grade V/VI weathered granite overlying 14 m of grade IV/V and about 8 m of grade III/IV materials above grade II to I fresh granite.

The site is bounded in the north by a private development with a steep slope down to a comparable formation level. The owners would not allow the removal of the part of the slope on their property and it was

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