Draft:Landslip Prevention and Mitigation Programme

Due to Hong Kong's unique terrain, which has many hills and limited flat land, along with the impact of seasonal heavy rains, the risk of landslides has always been a significant challenge for urban development. Since 1977, the Geotechnical Engineering Office under the Civil Engineering and Development Department has carried out a series of studies and engineering measures aimed at reducing the threat of landslides to Hong Kong. Up until 2010, the focus was on addressing Hong Kong's highest-risk, substandard man-made slopes. However, as urbanization accelerates, more development or redevelopment projects are located near steep natural slopes, increasing the landslide risk from these natural terrains as well.

In light of this, the Geotechnical Engineering Office launched the 'Landslip Prevention and Mitigation Programme (LPMitP)' in 2010, aiming to systematically address the landslide risks from both man-made slopes and natural terrains. The LPMitP annually selects the most risky man-made slopes and natural hillsides to study, based on a risk-based priority system. Slopes maintained by the government will undergo necessary landslip prevention and mitigation works under this programme. For dangerous private slopes, the Buildings Department will issue dangerous hillside orders for repairs according to the Buildings Ordinance, requiring the relevant private owners to ensure slope safety. To further push the LPMitP, the Geotechnical Engineering Office does not only use in-house resources but also hires consultants for related study and manages engineering contracts. As of March 31, 2023, around 27.9 billion HKD has been invested in landslide prevention study and works, reinforcing about 6,562 government man-made slopes, completing studies on around 6,431 private man-made slopes, and implementing mitigation measures on 422 natural hillside catchments.

The Geotechnical Engineering Office is committed not only to ensuring that all man-made and natural slopes under the LPMitP plan meet the highest safety standards but also to beautifying these slopes. During the landscaping process, existing trees will be preserved as much as possible, and vegetation will be used to cover the slopes and mitigation measures. If hard surfacing is required, corresponding landscaping measures will be taken to minimize visual impact. To improve techniques for greening slopes, the Geotechnical Engineering Office continues to research how to use plants in landslip prevention and mitigation works and constantly experiments with new techniques in erosion control measures and vegetation on steep slopes. The research outcomes will contribute to the preventive and mitigation works on both man-made and natural slopes.

Background
In the 1960s and early 1970s, Hong Kong was in a period of rapid development and underwent extensive site formation works. However, due to lack of professional geotechnical engineers involvement at the time, many substandard man-made slopes were built.

In 1977, the Geotechnical Engineering Office was established, specifically responsible for overseeing new geotechnical engineering projects, and also began planning strategies for dealing with a large number of potentially substandard man-made slopes. From that time on, the design of newly constructed slopes had to be reviewed by the Geotechnical Engineering Office to ensure that they met the necessary safety standards. Prior to 2010, the Geotechnical Engineering Office systematically upgraded government slopes that did not meet standards under a Landslip Preventive Measures Programme. Starting from 2010, the Geotechnical Engineering Office launched the 'Landslip Prevention and Mitigation Programme (LPMitP)' expanding its scope of work to include risk mitigation works for natural hillsides as well.

The 'Landslip Prevention and Mitigation Programme (LPMitP)' follows the previous 'Landslip Preventive Measures Programme' and focuses on addressing landslide risks caused by man-made slopes and natural hillsides. The annual goals are as follows:"


 * 1) Upgrade 150 government man-made slopes
 * 2) Conduct safety-screening studies for 100 private man-made slopes
 * 3) Implement studies and necessary risk mitigation work for 30 natural hillside catchments.

Man-made slope
To effectively manage the considerable risk posed by man-made slopes, the Geotechnical Engineering Office has complied the "Catalogue of Slopes". This Catalogue comprehensively records relevant information about sizeable man-made slopes in Hong Kong. This Catalogue details data on approximately 60,000 slopes throughout Hong Kong, which have undergone preliminary assessments and studies. These studies primarily include on-site inspections, assessments of the possible impacts should a collapse occur, and determinations of whether further studies are needed. Although the main goal of the preliminary studies is to establish the priority order for detailed studies, the Geotechnical Engineering Office can also use this data to promptly identify slopes that pose obvious and immediate dangers. This allows for the necessary upgrading works to be conducted to ensure public safety.

The detailed studies of man-made slopes includes conducting stability assessments on existing slopes to determine whether upgrading works are needed. These studies involve meticulous examination of slope data, analysis of aerial photographs, on-site inspections, stability analyses, and site surveys as required. The purpose of these studies is to understand the current condition and potential risks of the slopes, and to provide detailed information for the formulation of appropriate upgrading measures. Through these studies, we can better understand the safety of man-made slopes and take the necessary actions to ensure both the stability of the slopes and public safety.

Natural Hillside
The Geotechnical Engineering Office has successfully identified approximately 3,300 natural hillsides with potential risks by analyzing aerial photographs. These hillsides are located near existing buildings and important transportation corridors and have a potential risk of failure. Compared to man-made slopes, natural hillsides are generally not suitable for large-scale upgrading works because they are neither practical nor cost-effective, and are also detrimental to the environment. Therefore, risk mitigation methods are usually adopted to reduce the risk of landslides on natural hillsides in a more cost-effective manner. This includes the use of measures commonly found overseas, such as check dams and flexible barriers.

Related departments

 * Civil Engineering and Development Department
 * Lands Department
 * Buildings Department