Hong Kong has a hilly terrain with substantial urban development near hillsides. Coupled with torrential summer rainfall, landslide is a long-term threat that we have to face. Since 2010, the Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department (CEDD) has launched the Landslip Prevention and Mitigation Programme (LPMitP) to systematically deal with the landslide risk associated with both natural hillside and man-made slopes. As last year marked the 10th Anniversary of the LPMitP, the GEO specially held the Sustainable Slope Excellence Award to recognise the contribution of the engineering sector in improving slope safety while maintaining the sustainability of the natural ecology. This time, I have invited a colleague from the GEO and two representatives of the consultants to talk to us about the details of their award-winning projects.

Slope works blending in well with the surrounding environment

Geotechnical Engineer of the GEO, Ms TAM Wing-man, Grace, says that apart from its commitment to maintaining slope stability for public safety, the GEO also pays attention to the appearance of slopes with a view to integrating slope works with the surrounding environment and providing a safe and ecologically sustainable slope environment for the public. The GEO will continue to study and improve sustainable development technology for landslip prevention and mitigation works, and encourage owners of private slopes to incorporate landscaping elements into their slopes when planning for improvement and new works, in order to make Hong Kong a greener, safer and more ecologically diverse city.

Terraced planter walls built beside a dam

The 2020 Sustainable Slope Excellence Award is divided into two categories, namely Man-made Slope/Retaining Wall Category and Natural Terrain Catchment Category. The Project manager and representative of the consultancy firm which is the champion of the Man-made Slope/Retaining Wall Category, Mr LEE Tsz-leung, Chris, says that the award-winning project has adopted the concept of terraced planter walls to stabilise the slope. Apart from installation of soil nails to reinforce the slope at its toe, trial pit excavation with backfilling of concrete was carried out from the middle to the top of the slope. Such slope stabilisation method could provide space for planting and enhance the biodiversity of the slope at the same time.

Sharing with us the project challenges, he says that the slope is right next to the dam of Kowloon Byewash Reservoir, a Grade 2 Historic Building with a history of 90 years, adopting the method of terraced planter walls could minimise the impact on the dam during construction. Besides, the planter walls and adjacent areas are paved with masonry blocks to integrate the slope with the dam in their appearance.

Avoiding plants that attract monkeys

According to Mr Chris LEE, since a considerable number of monkeys often appear in Kam Shan Country Park, where the slope is located, the project team was very careful in selecting plants for the slope. Besides excluding climbing plants that could grow into the dam, the team also avoided species that might attract monkeys. In designing the planter walls, the vertical posts of handrailing were specially designed to embed into the planter wall to prevent the monkeys from shaking and loosening the connections. Mr Chris LEE is very pleased that the green environment can still be maintained after the completion of the slope works for almost five years.

Removal of shotcrete scars from the site

Senior Geologist Miss Kitty CHAN, a representative of the consultancy firm which is the champion of the Natural Terrain Catchment Category, tells us that the award-winning project has adopted soil bioengineering measures to design and improve the natural terrain. Due to emergency slope stabilisation works conducted after a number of landslides at the natural slope of Upper Keung Shan in West Lantau, shotcrete scars of about 4 500 square metres were left in the natural terrain. Therefore, the project team had to remove the shotcrete scars on the terrain first and then adopt various measures to mitigate the risk of landslide according to the geological conditions of the slope.

Adopting soil bioengineering measures

Miss Kitty CHAN says that the use of “soil bioengineering” is not simply about growing plants, but also about assessing biodiversity, and it is a self-sustaining, natural and aesthetically unobtrusive terrain management approach. For example, different kinds of plants are grown on the slope to help boost biodiversity and further enhance slope stability together with the surrounding plants. In the steeper slope area, live crib walls are built to reduce surface erosion, which can help restore the natural terrain to its original appearance and mitigate the landslide risk in the future.

Besides, the works project has innovative sustainable features, such as upcycling the broken-up shotcrete surface to integrate it with rock drains to avoid the generation of construction and demolition materials. She says, now that a year has passed since the completion of the project, the original sullen grey terrain has returned to its natural green glory.

The public should maintain vigilant

Landslide risks will increase with the more frequent extreme rainfall events brought about by climate change. I appreciate the GEO’s efforts in slope safety for more than 40 years in the past. Meanwhile, people should maintain vigilant against landslides, and particularly when the landslip warning is in force, they should stay away from slopes. Moreover, private slope owners are responsible for regular maintenance of their slopes or retaining walls to keep hazards at bay.

Construction sector’s anti-epidemic measures

Furthermore, in response to the volatile COVID-19 epidemic situation, the construction sector has spared no efforts to prevent and fight the virus. With support from the Development Bureau (DEVB), the Construction Industry Council (CIC) and the Hong Kong Construction Association (HKCA) jointly launched a scheme in the end of December last year to arrange for professional testing agencies to provide free voluntary testing services to workers and resident site staff on public and private construction sites. As of last Thursday, 4 February, over 29 000 workers at 125 sites had been tested and 99.99 per cent of their test results were negative. A total of four confirmed cases identified so far were handled by the Centre for Health Protection of the Department of Health under the mechanism. The contractors concerned were also notified promptly that there were confirmed cases on the sites and arranged follow-up work accordingly, including suspension of work on site for disinfection and arrangement of testing for the related workers.

The HKCA and the CIC are working at full stream to examine ways to enhance anti-epidemic measures by requiring workers and staff to present a negative result proof of a nucleic acid test for COVID-19 before entering their construction sites. The Airport Authority has announced that similar measures will begin from this Tuesday on the construction site at the airport's three-runway system. Given the large number of employees in the construction sector with some 100 000 to 200 000 site workers across the industry, the industry needs some time to formulate the plan, details of which are expected to be announced this week and we are confident that it will be implemented within this month. The DEVB will fully support the industry and workers to fight the virus together.