Slope failures and boulder falls are common in Hong Kong, and preventive and remedial works are constantly being undertaken. The paper reviews the history of rock slope engineering in Hong Kong, outlines the present investigation and design practice, and describes the methods employed to stabilize rock slopes and boulders.
Les glissements de terrain et les chutes de caillasses sont courants à Hong Kong et l'on entreprend constamment des travaux de confortement et de reparation. Cet article donne un aperçu de l'historique des etudes de stabilisation des talus rocheux à Hong Kong, esquisse la pratique courante en matière de reconnaissance et de conception de travaux et decrit les methodes de confortement des coteaux et des caillasses.
Böschungsbrueche und Felsstuerze kommen in Hong Kong haufig vor und vorbeugende und Ausbesserungsarbeiten sind standig im Gange. Die nachfolgende Abhandlung gibt einen Überblick ueber die Untersuchung und Gestaltung von Felshangen in Hong Kong sowohl in der Vergangenheit als auch nach dem gegenwartigen Stand, und beschreibt die zur Sicherung von Böschungen und Felsblöcken angewandten Methoden.
The object of this Paper is to provide a general review of rock engineering practice in Hong Kong as related to the design and performance of slopes. No such review has been made to-date, although there are several publications which provide useful information. The Territory of Hong Kong, with a land area of only 1 050 sq. km, is situated on the southern coastline of China (Fig.l). The population of more than 5 million is concentrated largely in the urban areas of Hong Kong Island and Kowloon, and increasingly in the new towns now under construction in the New Territories. The economical development and use of land is of prime importance, and land values are very high. The terrain of Hong Kong is extremely hilly, with the land rising to over 500 m on Hong Kong Island in a distance of less than 2 km from the sea. Most of the Kowloon peninsular has now been levelled to provide fill for reclamation, but isolated hills of up to 100 m still eixst. Little low lying land exists in the New Territories, with peaks of 550 m being common. Natural slopes throughout the Territory are steep, typically with upper slopes greater than 35 degrees, midslopes of 25 to 30 degrees and foots lopes of about 15 degrees. Undeveloped slopes are often densely vegetated. The majority of the slope failures in Hong Kong are caused by rainfall, which averages about 2 200 mm annually, the majority of which falls between May and September. Intensities of 50 mm per hour are not uncommon, and intensities of more than 100 mm per hour are sometimes recorded. Daily rainfalls can exceed 400 mm in extreme cases. Many slope failures therefore occur each year, both in natural slopes and cut slopes, and some of these have been disastrous (So, 1971; Lumb, 1975). The rainstorm that occurred on 28 to 31 May 1982 will serve to illustrate the extreme conditions that can prevail in Hong Kong. During the four day period, the rainfall recorded at the Royal Observatory was 654 mm, of which 437 mm fell on the first two days. The maximum intensities recorded at particular locations were III mm per hour and 394 mm per 24 hours. Widespread landslides and flooding were caused throughout the territory, with a loss of 28 lives. The Geotechnical Control Office gave advice and assistance at 533 landslide 'incidents' that resulted from the rains, but a quick review of aerial photographs taken after the event revealed that well in excess of 1 000 separate slope failures had occurred. Although the majority of the failures were in 'soil' slopes, there were some notable 'rock' slope failures and boulder falls. Examples of typical rock slope failures are given in Figs.2 and 3. It should be mentioned that the climate of Hong Kong is such that frost is virtually unknown and plays no part in engineering design considerations. Neither are earthquake forces considered, since the Hong Kong area is of low seismicity.
The geology of Hong Kong has been described by Ruxton (1960) and Allen & Stephens (1971). The predominant rock types are granite and volcanic rocks (Fig.l), the main difference between the two from a rock slope stability viewpoint being their joint patterns. The granite joint spacing is typically 2 to 10 m, while the volcanics usually have a blocky structure as a result of joint spacings of only 0.2 to 1 m. Extensive sheeting joints can occur in the granite and more rarely in the volcanics, and these often govern the engineering behaviour of the rock mass (see below). These zones of highly and completely weathered rock commonly contain corestones of less weathered material, and are often overlain by colluvium.
