ENG-1990 — Page 273

LAND, PUBLIC WORKS AND UTILITIES

Geotechnical Control

The Geotechnical Control Office (GCO) of the Civil Engineering Services Department was established after the landslip disasters of the 1970s, and the control of geotechnical aspects of construction works in the interest of public safety continues to be its foremost duty. Checks were made on 6 009 design proposals in 1990. Prior approval systems were introduced for prestressed ground anchors and reinforced fill structures which will reduce the work involved in approvals for individual projects in the future. Landslip preventive work was carried out on 36 slopes and stabilisation work completed on four networks of disused air-raid precaution tunnels, requiring the expenditure of $100 million in the Landslip Preventive Measures Programme.

In addition, the office designed and is undertaking work for improvement of the stability and reduction of environmental hazards of the old sanitary landfill at Sai Tso Wan. This work to improve stability and control landfill gas migration is the first of its kind in Hong Kong.

The presence of cavernous marble beneath sites in the North-west New Territories has posed problems for development. Geological mapping to identify buried marble has been completed and ten 1:5 000 scale geological maps were published for the areas around Yuen Long. New legislation was enacted in July 1990 to empower the Building Authority with additional geotechnical controls to ensure safe development in the area.

The Geotechnical Control Office operates the Landslip Warning System and a 24-hour emergency service to provide advice on landslips. During the year, site investigation worth $58 million was carried out on land and offshore by the office. The Geotechnical Information Unit (GIU), which houses the largest collection of data on ground conditions in Hong Kong, serves as an important reference centre for geotechnical information. The GIU received more than 1 125 enquiries during the year.

The Hong Kong Geological Survey continues to publish 1:20 000 scale geological maps and memoirs for the land and marine areas of the territory. During 1990, geological maps for Sai Kung and the Waglan Island area were published, together with a geological memoir for Sai Kung and Clear Water Bay. New geological maps at a scale of 1:20 000 are now available for more than 70 per cent of the territory. Large scale (1:5.000) geological survey work was commenced in the Ma On Shan district and in the development areas of North Lantau. The Ma On Shan mapping followed confirmation of buried marble deposits beneath an area of new reclamation.

The office's work on the use of underground space continued in 1990, with detailed feasibility studies being completed for a government warehouse at Siu Sai Wan, and for a refuse transfer station at Mount Davis. A number of preliminary engineering geological studies for cavern usage were also completed, and arrangements were established for in- cluding underground space in the government town planning system.

A new Marine Geotechnology Section was formed to provide advice and to carry out research and development work on the marine geotechnical aspects of Port and Airport Development Strategy projects. The section completed a study on gas in marine sediments during 1990, and the office carried out a comprehensive technical investigation for the possible extension area for the new airport covering fill supply and mud disposal and potential use of underground space at Chek Lap Kok.

During 1990, Hong Kong's construction industry consumed some 19 million tonnes of crushed rock aggregates and natural sand, of which about 50 per cent was imported from

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