Introduction
The Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department (CEDD) is responsible for a wide range of geotechnical engineering activities related to the safe and economic utilisation and development of land.
The GEO operates on the basis of 11 Divisions under the direction of the Head of Geotechnical Engineering Office and provides the following geotechnical engineering services:
Geotechnical Control And Land Use Planning
One of the GEO's major slope safety regulatory functions is to audit the design of geotechnical works to ensure they meet current safety standards. Geotechnical auditing is exercised largely through our 3 District Divisions: Island, Mainland East and Mainland West Divisions. Each District Division is responsible for a geographical region of Hong Kong.
The scope of auditing covers the design of the geotechnical aspects of all building developments and civil engineering works and the standards of site supervision. In particular, the District Divisions audit the site formation works, landslip prevention and mitigation works, deep excavations, tunnelling works, caverns and foundation works in areas with cavernous marble or complex geological conditions that are designed and constructed by the private sector, public authorities and government departments.
In exercising geotechnical control over private sector projects, we operate through the statutory powers of the Buildings Department to approve design submissions made by a developer's agent or an owner's agent before construction proceeds.
The District Divisions also provide an emergency response service in relation to landslide incidents and advice on the clearance of squatter structures on slope safety grounds.
One of the most effective methods for reducing landslide risks is land use planning, in which the potential impact of natural hazards is taken into account in planning new developments as part of a wider risk management strategy.
We provide the Planning Department and the Lands Department with geotechnical input at the early stages of land developments, identifying any geotechnical constraints and advising on the suitability of land for specific purposes.
We also undertake technical studies to promote the enhanced use of rock caverns and urban underground space for more efficient use of land resources.
Implementation of the Landslip Prevention and Mitigation Programme (LPMitP)
The GEO manages projects under the LPMitP, including planning and launching the projects, managing financial resources, monitoring works expenditure and progress, and appointing and managing consultants to undertake the projects. We select potentially substandard man-made slopes and vulnerable natural hillside catchments for inclusion into the LPMitP and provide technical support to other departments with regard to preventive maintenance works.
As part of the LPMitP, studies of high priority man-made slopes, retaining walls and natural hillside catchments are carried out to identify potential danger and the need for preventive and mitigation works. Where preventive, remedial or mitigation measures are needed for man-made slopes or natural hillside catchments that are under Government's maintenance responsibility, detailed design and the necessary works will be carried out to reduce the landslide risk.
In the design of slope upgrading works, innovative design approaches and new techniques are adopted where possible in order to improve quality and enhance cost effectiveness.
We carry out tendering, management and supervision of contracts for LPMit works designed in-house.
Apart from in-house slope studies, we are also responsible for managing consultants, who are engaged in assignments to investigate, design, prepare contracts, manage and supervise the construction of LPMit works.
While our primary objective is to safeguard the public from slope failures, we have always given priority attention to blend in the engineering works with the surrounding environment by making them look as natural as possible. It aims to create a sustainable and biodiversified ecosystem that create habitats for wild lives, reduce susceptibility to pests and diseases, and allow natural plant succession. Every effort is therefore made to establish sustainable slope appearance and ecology and establish suitable vegetation around natural terrain hazard mitigation measures under the LPMitP. As a general rule, a hard surface cover is used only as emergency repairs to landslide scars and as a last resort on slope stability grounds. On average, we plant about 2.7 hundred thousand plants each year in connection with our landslip prevention and mitigation works, and most of the plants are native species.
As for slopes or retaining walls on private land, we manage consultants who are engaged to study and recommend follow-up actions. Where the slope or retaining wall studied is found to be sub-standard, unstable or becoming dangerous, statutory orders will be issued to the responsible private owners by the Buildings Department through the Buildings Ordinance to ensure appropriate follow-up actions to be taken on the sub-standard situations.
In 2022, about $1.0 billion was spent on studies and LPMit works, through which 158 government man-made slopes were upgraded, safety-screening studies for 100 private man-made slopes were completed and mitigation works for 36 natural hillside catchments were implemented.
Natural Terrain Landslide Risk Management
Tsing Shan debris flow in 1990
About 60% of Hong Kong's total land area consists of relatively steep natural terrain. Landslides occurring in natural terrain can be very large and travel long distances, such as those occurred in Tsing Shan in 1990, Sham Tseng San Tsuen in 1999, and western Lantau in 2008. The GEO has carried out numerous research and development activities since the early 1990s to prepare for the risks posed by natural terrain landslides. The natural terrain hazard studies and necessary mitigation works on selected sites with known significant natural terrain hazards are undertaken under the LPMitP.
Over the years, we have made significant advances in applying new digital and information technology and expanded its ability to manage natural terrain landslides. Geographical Information System is used in spatial analysis and 3-D engineering modelling. Some of the new technologies adopted include digital photogrammetry, satellite-based Interferometric Synthetic Aperture Radar, remote sensing using 3-D laser scanning and image processing and air-borne Light Detection and Ranging.
Landslide Investigation
Investigation works under LPMitP
Systematic landslide investigations are carried out as part of the LPMitP. The scope of landslide investigations includes examination of all reported landslide incidents and in-depth studies of selected significant landslides to identify the causes of failure and necessary follow-up actions. The objectives of systematic landslide investigations are to identify slopes in need of early attention and undertake forensic assessments of landslides that involve subsequent coroner inquests or legal actions. Through landslide investigations, the performance of the Government's slope safety system will be reviewed and areas for improvement identified. Landslide investigations will advance the understanding of the causes and mechanisms of landslides and enhance the slope engineering practices and the reliability of landslide preventive or mitigation works.
Standards and Testing
The GEO undertakes technical development work for the production of geotechnical standards. We promulgate technical guidance in our publications. These can be purchased from the Publications Sales Unit of the Information Services Department, or downloaded from the CEDD website. Please refer to the catalogue of GEO publications on the CEDD website for details.
The technical development work is carried out in-house as well as in partnership with universities, consultants and contractors. It provides essential technical support to various aspects of the works for landslip mitigation. This includes technical guidelines on soil nail design and construction, development of prescriptive measures to improve existing man-made slopes and retaining walls, priority ranking system for the selection of slopes for actions, technical guidelines on landscape treatment for slopes, design and construction approaches for landslide debris-resisting barriers and regional seismic microzonation study to assess seismic hazards of natural terrain.
Technical development work was also undertaken on quantitative risk assessment techniques for landslide risk management, assessment of debris mobility for natural terrain landslides, greening techniques, rainfall and landslide relationship, assessment of effects of climate change on landslide risk, and properties of saprolite, loose fill and other construction materials.
Testing services are provided through the Public Works Laboratories (PWL), which comprise the Public Works Central Laboratory and five Public Works Regional Laboratories. The PWL are accredited under the Hong Kong Laboratory Accreditation Scheme for most of the tests as well as a range of calibration services. The PWL provide a wide range of construction material testing services principally for government projects. These include tests on aggregates, bitumen and bituminous materials, cement, concrete, pulverised fuel ash, rubber fender, soil, rock, steel, chemical compositions of construction materials and Time Domain Reflectometry tests on soil nails. In addition, the PWL conduct research and development work related to construction material testing to enhance the quality of service and meet the needs of the construction industry. We manage the List of Approved Suppliers of Materials and Specialist Contractors for Public Works under the category of Soil and Rock Testing. The PWL also provide testing services for other government departments on forensic investigations.
Emergency Services
The GEO Emergency Control Centre in operation
There are around 300 reported landslides in Hong Kong each year. The GEO maintains a 24-hour year-round emergency service to provide geotechnical advice to government departments on actions to be taken to protect public safety in case of danger arising from landslips. Upon request, our geotechnical engineers will carry out site inspections with the responsible government departments and give advice on any necessary mitigation measures and emergency works.
Landslip Warning System
The GEO operates an automatic raingauge system utilising advanced data logging and processing equipment and software. It comprises an extensive network of about 100 automatic raingauges providing real-time rainfall data to the operation of the Landslip Warning System. Based on historical data, we developed a landslide frequency-rainfall model which can estimate the total number of potential landslides for a certain storm. By combining this with the rainfall forecasts from the Hong Kong Observatory, the Government is able to make a decision on the issuing or cancelling of a Landslip Warning.
Public Education and Community Advisory Services
Private owners are responsible for their slopes. The GEO has sustained community education programmes to remind private owners of the importance of slope maintenance in preventing landslides. A dedicated Community Advisory Unit (Tel No.: 2760 5800) has been set up to provide proactive outreach services and advice to help private slope owners discharge their slope maintenance responsibilities.
Apart from providing community services to private slope owners, we have developed a comprehensive proactive strategy to educate the public to take necessary precautions especially when the Landslip Warning is in force. It involves partnership with the community in promoting public awareness of slope safety through education, regular publicity campaigns and information services. Our public education activities include organising slope safety roving exhibitions and talks, broadcasting television and radio announcements of public interest, and promoting slope safety messages through media and electronic platforms, etc.
In addition, we have been proactively assisting the Education Bureau in providing the most updated and suitable information on slope safety for the New Senior Secondary (NSS) Geography Curriculum, with a view to enhancing the understanding of teachers and students on slope safety issues in Hong Kong. For example, we prepared a teaching support materials kit on 2 topics namely Natural Hazards and Earth Sciences for distribution to all secondary schools in Hong Kong. We also regularly organise seminars and visits for geography teachers.
Slope Information System
Hong Kong Slope Safety website
Landslide prevention begins with information. The GEO's work in improving slope safety in Hong Kong is greatly enhanced by the use of information technology to collect and disseminate slope information. Containing information of 60,000 registered man-made slopes and retaining walls, the Slope Information System (SIS) provides engineers as well as the general public with updated slope information through the slope safety website (https://hkss.cedd.gov.hk).
Hong Kong Geological Survey
Geological map of Hong Kong
One of the GEO's most notable technical achievements is the development of improved understanding of the characteristics of weathered rock, which is prerequisite for a successful slope engineering design. Many of the landslide problems that affect Hong Kong are related to weathering processes which gradually change rock into soil.
In 1982, we established the Hong Kong Geological Survey. It maintains the most comprehensive archive of geological information in Hong Kong and provides authoritative advice on Hong Kong's geology to the Government, the engineering profession and the public. It also produces geological maps and relevant publications, and compiles engineering geological and natural terrain database for use by the Government and the private sector. Many of the datasets are stored in the Geographical Information System. An online version of the geology of Hong Kong has been uploaded onto the slope safety website which is accessible via http://hkss.cedd.gov.hk. A mobile version of the Geological Map of Hong Kong can also be downloaded from the Android Play Store and Apple Store.
Advisory and Ground Investigation Services
The GEO undertakes geotechnical feasibility studies, investigations and design for a wide range of government projects. We also provide ad-hoc 'clinic' advice to project departments to deal with geotechnical problems regarding natural terrains, caverns and tunnels during the project implementation. In addition, we render project-based support for works department to enhance the cost-effectiveness of geotechnical works in major capital works projects.
Furthermore, we implement tunnel / cavern related projects in order to develop underground space for different government uses and free up land for better urban developments. We also manage the list of accepted reinforced fill products used in Hong Kong and the list of approved off-site rebar prefabrication yards for public works contracts.
Through the letting of term contracts, we provide ground investigation services and geophysical surveys to government departments. We also manage the List of Approved Suppliers of Materials and Specialist Contractors for Public Works under the category of Ground Investigation Field Work.
Regulatory Control of Explosives and Management of Quarries
Mines Division, on behalf of the Commissioner of Mines, who is the Director of Civil Engineering and Development, is the regulatory authority for the manufacture, storage, conveyance (on land) and use of explosives under the Dangerous Goods Ordinance. It is also responsible for issuing Mines Blasting Certificates under the Mines (Safety) Regulations to shot firers who are permitted to use blasting explosives. As part of its responsibilities, the division manages the Government Explosives Depots, which provide storage for explosives, provides an explosives delivery service from the Depots to blasting sites, carries out audit inspections for blasting sites and explosives stores, and provides technical support to other government departments on matters relating to explosives, including fireworks displays.
Mines Division is responsible for the management and rehabilitation of rock quarries in Hong Kong. These quarries supply aggregates and rock products to the local construction industry. They also process surplus rock generated from local construction projects to produce aggregates. As an ongoing exercise, the division carries out studies related to strategy of rock supply and Hong Kong's rock resources management, including searching for potential quarry sites, research on aggregate suitability and review on supply chain of concrete.
