The Buildings Ordnance Office of the Hong Kong Public Works Department stipulates minimum requirements for site formation plans submitted where rock slopes are involved. In particular, design assumptions and evidence upon which they are based must be clearly stated and verified during excavation by means of engineering geological drawings, showing salient features and details of proposed support and drainage measures.
Examples from rock slope construction records for a residential development at Tsuen Wan, Hong Kong, are presented. The site formation involved excavation of benches into an existing hillside, resulting in the formation of rock faces up to 15 m in height in slightly weathered granodiorite, both beneath and behind the residential blocks.
A rapid system of logging the rock faces by means of subjective surveys using photographic overlays is outlined, and remedial measures employed after final scaling are briefly described.
A potentially unstable rock face was identified at an early stage, and geological conditions are presented in the form of a detailed Face Log. A further investigation of this slope by orientated rotary drilling was carried out, and design parameters are assessed by a combination of back-analysis and laboratory testing. A method of designing active support systems using a computer program is outlined, and ‘as-built’ construction records are presented.