Geotechnical Engineering

The Civil Engineering Department (CED) manages a comprehensive slope safety system, which has successfully brought about substantial improvement in the safety of slopes in Hong Kong by improving slope safety standards and technology, ensuring the safety of new slopes, improving the safety of existing slopes, and providing public warnings, information, education, and community advisory services on slope safety.

    The department audits the adequacy of the design and construction of all geotechnical works by the private sector, public authorities and government departments to ensure their long-term safety. In 2002, it audited 13 966 geotechnical design proposals and inspected 2 747 active construction sites.

    The CED maintains an ongoing Landslip Preventive Measures (LPM) Programme to rectify the safety of existing slopes. In 2002, a total of about $940 million was spent on the LPM Programme. Upgrading works were completed on 266 government slopes, and all were landscaped to blend them with the surrounding environment. In addition, safety screening was completed on 320 private slopes.

    The department inspects hillside squatter villages to identify huts vulnerable to landslides, recommends rehousing of the affected squatters and advises the occupants to seek safe shelter during heavy rain. In 2002, it inspected about 90 squatter villages. Over the past 20 years, more than 74 800 squatters have been rehoused on slope safety grounds.

    With the availability of the Slope Maintenance Responsibility Information System on the Internet, members of the public can have ready access to information on slopes under their responsibility. Other slope-related information is also available in the Slope Information System. A bilingual version of the system has been uploaded on the Internet at the CED's Hong Kong Slope Safety website for free access by the public. The website has become an important source of reference for the public in obtaining slope-related information.

    The CED continues to raise the awareness of slope safety among members of the public through sustained publicity and public education. A two-month special exhibition 'Discover Soil and Slope' was held at the Hong Kong Science Museum to promulgate the slope safety messages. TV broadcasting of Announcements in the Public Interest continues on the issues of private slope maintenance and personal precautionary measures while landslip warnings are in force. To promulgate the important slope-related messages to children, cartoon books and an animated cartoon VCD on slope safety and maintenance have been produced and distributed to the public. The department's Community Advisory Unit continues to provide useful advice to private slope owners to help them maintain and improve the condition and appearance of their slopes. In order to assist private slope owners to improve the living environment, a Layman's Guide to Landscape Treatment of Slopes and Retaining Walls has been published to provide guidance on landscape treatment for slopes.

    The Slope Maintenance Audit Section of the CED continues to assist maintenance departments to improve their performance in discharging their slope maintenance responsibilities. Audits of government slope works indicate a continuous improvement in the overall state of maintenance.

    The department maintains a 24-hour year-round emergency service to provide geotechnical advice to government departments on actions to be taken to protect the public against landslide danger. To further improve the landslip emergency service, it has upgraded its computerised information system and telecommunication facilities to enhance its efficiency in handling landslide information and emergency calls.

    The CED continues with various studies to improve the knowledge and methodology of dealing with natural terrain landslide hazards. Besides the regional study of natural terrain hazards in the Tsing Shan Foothills, which is near completion, the department has commenced a study on dating of natural terrain landslides. Natural terrain hazard studies have been arranged for four sites in developed areas, and design of natural terrain hazard mitigation works are being carried out for five sites. In 2002, technical guidelines for natural terrain hazard studies were produced and distributed to geotechnical practitioners.

    During the year, the department completed a study of non-destructive means for measuring the length of installed soil nails. The findings were documented in a report for dissemination to geotechnical practitioners.

    The Geotechnical Information Unit in the Civil Engineering Library houses the largest collection of geotechnical data in Hong Kong. The library is open to the public, and served more than 37 500 users during 2002.

    The CED also provides construction material testing and ground investigation services to support public works projects. The Public Works Laboratories (PWL) (consisting of the Public Works Central Laboratory at Kowloon Bay and five Public Works Regional Laboratories in various parts of Hong Kong) conduct testing of construction material and calibration tests. During the year, some 700 000 tests were carried out through the PWL under the department's ground investigation term contracts, and the length of soil and rock drilled totalled 27 000 metres.

    The CED continued to provide specialist geotechnical advisory services to government departments, including the provision of ad hoc geotechnical advice and conducting feasibility studies, detailed investigations, design and construction supervision for a wide range of public works projects. The projects handled by the department during the year included road widening and slope works at Lin Tak Road, Lam Tin; road widening and mitigation of natural terrain landslides at Tsing Yi North Coastal Road; design and supervision of geotechnical works for the Shenzhen River Stage III Project; and mitigation of natural terrain landslides affecting Yung Shue Wan Reclamation (Phase 1).

Mining and Quarrying

The CED enforces legislation relating to mining, quarrying and explosives, and administers quarrying contracts. It processes applications for the manufacture, storage, conveyance and use of explosives, and inspects stone quarries, blasting sites and explosives stores.

    Hong Kong consumed 12.5 million tonnes of aggregates and other rock products in 2002. About 40 per cent of its demand for aggregates and rock products was met locally, with the balance imported from the Mainland.

    In 2002, one quarrying contract and three quarry rehabilitation contracts were in force. The rehabilitation contracts require the operators to rehabilitate the quarries within a specified period, in return for the granting of rights to process and sell surplus rock excavated during the course of the works. The rehabilitation works involve recontouring and extensive planting to blend the quarries with the surrounding hillsides.

    The CED manages two government explosives depots (one on Lantau Island and the other at Piper's Hill, Sha Tin) which provide bulk storage facilities for imported explosives. It also undertakes the delivery of explosives from the depots to blasting sites and issues shotfirer certificates.

    The largest use of explosives during the year was for quarrying and site formation works. The overall consumption of explosives was 1 900 tonnes.

    The department also provides technical support to the Home Affairs Bureau and the Marine Department in assessing applications for fireworks displays.

Fill Supply and Mud Disposal

The Marine Fill Committee (MFC) is responsible for identifying and managing the supply of marine fill resources for development projects, and for managing disposal facilities for dredged sediments. The Public Fill Committee (PFC) has the duty to manage construction and demolition (C&D) materials and utilisation of land-based fill reserves. Both committees are responsible to the Secretary for the Environment, Transport and Works.

    In 2002, the amount of marine sand used for reclamation projects has been reduced from 66 million cubic metres in 2001 to about 32 million cubic metres; and about 22 million cubic metres of it were imported from nearby regions in the Mainland. To reduce future use of marine sand and help preserve its limited resources in Hong Kong, more use will be made of inert C&D materials as fill for reclamation.

    About 9.1 million cubic metres of C&D materials were generated by local construction activities in 2002. Of this, about 6.6 million cubic metres of inert materials were re-used as fill in public filling areas including Tseung Kwan O Area 137, Pak Shek Kok, Tuen Mun Area 38, North Tsing Yi and Penny's Bay.

    The PFC continues to explore ways to minimise the generation of C&D materials and reduce their disposal at landfills. The construction industry is encouraged to adopt construction methods and materials that reduce the generation of C&D materials at source. A temporary recycling facility at Tuen Mun Area 38 has started to operate for recycling of suitable C&D materials into aggregates for re-use.

    The MFC maintains a Fill Management Database on fill requirements, mud disposal and surplus excavated materials from major public and private projects. Its purpose is to help the construction industry coordinate sources of fill materials and make the best use of surplus materials. All project data is available on the Internet.

    The CED manages mud disposal facilities. In 2002, about 11 million cubic metres of uncontaminated mud and three million cubic metres of contaminated mud were generated from various works projects. Uncontaminated mud was disposed of at open sea floor disposal grounds or exhausted marine sand borrow pits. Contaminated mud was placed in specially selected and closely monitored exhausted sand borrow pits, which were then capped with uncontaminated mud on completion of filling to isolate the contaminants from the environment. The use of exhausted sand borrow pits for mud disposal is preferred as it has the dual benefits of providing much needed disposal capacity and restoring the seabed to its natural profile and state.

    In connection with the management of Hong Kong's fill resources and mud disposal capacity, the CED, on behalf of the MFC, continues to undertake a series of geotechnical, environmental and ecological studies and monitoring to examine the effect of the dredging and disposal activities, and to investigate possible ways to avoid or minimise the impact on the marine environment.

Hydraulic Studies

Coastal engineering projects may affect the flow of water, sediment transport and wave activity in the harbour. The CED employs sophisticated computer hydraulic models to analyse the likely effects of proposed schemes, both during and after the construction phases, to ensure that their impacts are minimised to within acceptable limits. The models are used for reclamation layout planning, design of marine structures, waterway studies and assessment of future maintenance dredging requirements. A digital tidal stream atlas and a wave atlas were also developed by CED to provide average tidal and extreme wave information.

    Construction of a trial section of wave absorbing seawall at the new waterfront of the West Kowloon Reclamation is substantially completed. It is anticipated that this new type of seawall will help reduce the reflection of waves in the inner part of Victoria Harbour.