Location: Near No. 14, Po Shan Road, Mid-level
Co-ordinates: 815750N, 832650E
Summary: A devastating landslide occurred on 18 June 1972 near No. 14 Po Shan Road, Mid-levels (see Location plan). Approximately 40 000 m3 of debris travelled some 270 m down slope and resulted in 67 fatalities, 20 injuries, 2 buildings destroyed and 1 building severely damaged.
Urban development of the Mid-levels area extended progressively upslope into the natural terrain during the late 1800s and early 1900s; Conduit Road and Po Shan Road were constructed in 1910 and 1925 respectively. The slope gradient above Po Shan Road was about 35o. Downslope between Po Shan Road and Conduit Road the slope gradient was more gentle. A construction site above Conduit Road, where the major part of the landslide was located, was being redeveloped at the time of the landslide. In late 1971 two landslides occurred on the construction site. Most of the failed area is underlain by weathered rock of volcanic origin blanketed with 5 m - 10 m thick colluvium and locally fill (see Cross-section).
¡§Cracks were noted in Po Shan Road (in the area of the 1972 landslide site)¡¨ following Typhoon Rose about 11 months prior to the June 1972 fatal incident. Inspection at Po Shan Road on 16 June 1972 reported ¡§cracks¡¨ and that attempts to seal these had failed. On 17 June 1972, a landslip occurred the construction site above Conduit Road resulting in a 30o rotation of steel piling, and settlement of the garden terrace upslope. On 18 June 1972, the deterioration continued; the previously failed slip surface showed signs of creep and the sheet piling was creaking. A major detachment occurred at about 8:50 pm on 18 June 1972. The landslide started from the hillside above Po Shan Road, landslide debris travelling some 270 m downslope to below Kotewall Road. On 19 and 20 June 1972, two minor failures were reported after the major landslide. A large relict joint was exposed on the western flank of the failure.
Site formation work on the construction site above Conduit Road, together with the exceptional heavy rainfall in early 1972, caused the landslide. About 1400 mm of rainfall was recorded between May and June 1972 and in particular more than 650 mm of rainfall was recorded from 16 to 18 June 1972.
The information given in this simplified account is extracted from a report prepared by the Geotechnical Engineering Office (GEO) of the Government of the Hong Kong Special Administrative Region following its detailed investigation into the cause of the landslide (GEO, 1992, see References).
