Philip WK CHUNG, Chief Geotechnical Engineer Becky L S LUI, Geotechnical Engineer
Geotechnical Engineering Office Civil Engineering & Development Department
Ir Ms Becky L S LUI Geotechnical Engineer Geotechnical Engineering Office Civil Engineering & Development Department HK SAR Government
1
• Landslide History of Hong Kong
2
• Causes of Landslides
3
• Hong Kong Slope Safety System
4
• New Challenges and Initiatives
5
• Conclusion
Outline of Presentation Outline of Presentation
1
• Landslide History of Hong Kong
2
• Causes of Landslides
3
• Hong Kong Slope Safety System
4
• New Challenges and Initiatives
5
• Conclusion
Outline of Presentation
Outline of Presentation
• In old days, there was very limited regulatory control of geotechnical engineering and slope formation.
• So in 1970s, many tragic historical landslideshappened.
Landslide History of Hong Kong
木ul程-of-thumb 總n slop程 d程s總gn 木ap總d d程v程lopm程nt aft程處 WW師師
Landslide at Po Shan Road on 18 June 1972
• Volume = 20,000 m3
• 67 Fatalities
土程fo處程
Aft程處
Landslide Computer Animation Landslide Computer Animation
Before Before
After After
The fill slope
Landslide at Sau Mau Ping on 18 Jun 1972
• Volume = 6,000 m3
• 71 Fatalities
Landslide Computer Animation Landslide Computer Animation Landslide at Sau Mau Ping on 25 Aug 1976
• Volume = 5,000 m3
• 18 Fatalities
- Exercise geotechnical checking of new development works
- Retrofit large number of existing man-made slopes through the “Landslip Preventive Measures (LPM) Programme (防止山泥傾瀉計劃)”
• Set up in 1977 as HK’s geotechnical control authority:
About 300 reported landslides each year !!
1994 Kwun Lung Lau
1992 Baguio Villas
1995 Shum Wan Road
1997 Ching Cheung Road
1999 Shek Kip Mei 1999 Shum
Tseng
•Hourly rainfall = 145.5 mm Historical record!!
•24-hour cumulative rainfall = 622.5 mm
7 June 2008 Rainstorm
Max. rolling 4-hr rainfall : 384 mm Return period: ~ 1,100 years!!
Max. rolling 4-hr rainfall : 384 mm Return period: ~ 1,100 years!!
North Lantau Highway
Video from YouTube
Yu Tung Road in Tung Chung, North Lantau
•Source Volume ~ 2,350 m3
•Debris Volume Reaching Road >3,000 m3
•Runout Distance ~ 600 m
•Vertical Fall ~ 230 m
•Max Velocity ~ 15 m/sec
南涌村 大澳新村 石仔埗 吉慶後街橫坑村
Tai O
山道 深屈道
昂坪 昂坪路
Lantau
Keung Shan
1
• Landslide History of Hong Kong
2
• Causes of Landslides
3
• Hong Kong Slope Safety System
4
• New Challenges and Initiatives
5
• Conclusion
Outline of Presentation Outline of Presentation
Terrain of HK
60% of HK’s total land area is hilly terrain
Hilly Terrain, but with dense population
Wet summers with typhoons and rainstorms
Many slopes formed to provide platforms for building development and roads
Buildings & Infrastructures built on or very near to slopes
60,000 Registered Man-made Slopes
Gov程處nm程nt: 40,000 P處總vat程: 20,000
Boulder 孤石 孤石 孤石 孤石
Rock 岩石岩石岩石岩石
Rock Cut Slope 切削石 切削石 切削石 切削石坡坡坡坡
Soil Cut Slope 切削土坡切削土坡 切削土坡切削土坡 Natural Terrain 天然
天然 天然 天然山坡山坡山坡山坡
Platform 平台平台平台平台
Fill Slope 填土坡 填土坡 填土坡 填土坡
How to categorize slopes?
Soil 泥土 泥土 泥土 泥土
Retaining Wall 擋土牆 擋土牆擋土牆 擋土牆
Causes of Landslides (Natural Factors) Causes of Landslides (Natural Factors)
Heavy Rainfall
• Damage to slope surface protection
• Erosion of soil
• Infiltration of water into soil or rock
• Rise in groundwater table
Causes of Landslides (Natural Factors) Causes of Landslides (Natural Factors)
Adverse Geological Features
• Weathered Soil (Can be as deep as 100 m)
• Exposed boulders
• Weak weathered seam
Weak seam Steeply sloping
joints
Discontinuity Exposed boulders
Causes of Landslides (Natural Factors) Causes of Landslides (Natural Factors)
Adverse Geological Features
• Weak weathered seam
Kaolinite-infill on the seam
Causes of Landslides (Human Factors) Causes of Landslides (Human Factors)
Inadequate support during trench excavation
Inadequate Design or Construction
• Slope design not up to safety standards
• Slope works not properly constructed
Causes of Landslides (Human Factors) Causes of Landslides (Human Factors)
Leaking Drains
• Leakage from buried water pipes or sewers could contribute to slope failures
Causes of Landslides (Human Factors) Causes of Landslides (Human Factors)
Lack of Maintenance
• Poorly maintained slopes will deteriorate and fail
• Regular maintenance is needed
1
• Landslide History of Hong Kong
2
• Causes of Landslides
3
• Hong Kong Slope Safety System
4
• New Challenges and Initiatives
5
• Conclusion
Outline of Presentation
Outline of Presentation
Geotechnical Engineering Office Geotechnical Engineering Office
土力工程處 土力工程處 土力工程處 土力工程處 土力工程處 土力工程處 土力工程處 土力工程處
Hong Kong Slope Safety System – Major Strategies
1977
Slope Safety System set up by GEO Landslide
risk in HK
1.Check new slopes 2.Plan land use
Contain the increased risk
1950 1960 1970 1990 2010
Reduce risk by improving slope stability
Reduce risk by reducing landslide consequence 2000
3.Upgrade & maintain government slopes 4.Promote private
slope maintenance
5.Clear squatters on hilly terrain 6.Educate the public
to take precaution
Checking Designs
Site Audits
1. Check New Slopes
• GEO exercises geotechnical control over both private and public developments to ensure that they conform with the required safety standards.
1. Check New Slopes
• GEO exercises geotechnical control also by carrying out geotechnical studies and publish standards and guidelines for the practitioners.
Tuen Mun Area 19 proposed for residential use
1990 Tsing Shan Landslide
2. Plan Land Use
• GEO identifies geotechnical constraints at early stages of land developments
New Tuen Mun Centre
Land use changed to Golf Driving Range & Road
Tuen Mun Golf Driving Range Lung Fu Road
2. Plan Land Use
3. Upgrade and Maintain Government Man-made Slopes
• Starting from 1977, the GEO has begun to implement the
“Landslip Preventive Measures (LPM)” to upgrade old man- made slopes
• Details to be covered:
Priority with respect to consequence to life
Methods of upgrading man-made slopes
Slope Greening
Priority with respect to consequence to life
Major Road Residential Buildings
School
Hospital
Soil Cut Slopes
• Cutting back
• Using retaining wall
• Soil Nails
Fill Slopes
• Recompaction
• Soil Nails
Retaining Wall
• Thickening
• Soil Nails
Methods of upgrading man-made slopes
• Cutting Back to a flatter slope angle –not often used today
Before After
Soil Cut Slopes
1. A lot of trees will have to be felled
2. A large amount of soil and rock will be generated
Soil Cut Slopes
• Using Hand-dug caissons or piles as retaining walls to retain the cut slopes –not often used today
1. Hand-dug caissons lead to a lot of fatal accidents banned!
2. Piles expensive
• Soil nails
Soil Cut Slopes
Soil Nail
Potential Slip Surface
Mechanism of how soil nails work
Interaction between soil and soil nails
Internal Force of Soil Nails
PLASTIC GROUT TUBE
32∅∅∅∅GALVANIZED HIGH YIELD STEEL BAR
Typical layout of a Soil Nail
•Length from 8 m to 20 m
•Hole diameter normally 100 mm
Construction of Soil Nails – Hole Drilling
• Steel bar diameter either 25 mm or 32 mm
• Steel bar with corrosion protection
Construction of Soil Nails – Insertion of Steel Bars
Construction of Soil Nails – Grouting
Construction of Soil Nails – Soil Nail Head Construction
Construction of Soil Nails in progress
Completed Soil Nailed Slopes
