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Slope Management and Landslip Preventative Measures Development of the Hong Kong System

Slope Management and Landslip Preventative Measures Development of the Hong Kong System. Major Landslide at Maracas, Trinidad - Late December 2002. Prevention of Landslides. Database of Slopes Type of Slope Condition Consequences. Cut Slopes Fill Slopes Retaining Walls

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Slope Management and Landslip Preventative Measures Development of the Hong Kong System

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  1. Slope Management and Landslip Preventative Measures Development of the Hong Kong System Major Landslide at Maracas, Trinidad - Late December 2002.

  2. Prevention of Landslides • Database of Slopes • Type of Slope • Condition • Consequences • Cut Slopes • Fill Slopes • Retaining Walls • Hybrids: Cut/Retaining Wall / Fill/Retaining Wall • “Natural” Slopes - slopes where there has been no anthropogenic activity, or where such activity is causes small changes to the geometry of the slope so that the Factor of Safety is largely unaffected.

  3. Development of Slope Registration Scheme • Began in late 1970’s based on geographic map area • e.g. 11SW-A • followed by a code • C - Cut Slope : F - Fill Slope • R - Retaining Wall : N - Natural Slope • CR - Cut Slope with Retaining Wall • FR - Fill Slope with Retaining Wall • followed by a number i.e. 11SW-A/R188 refers to Retaining wall 188 in Map area 11SW-A

  4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 NW A NE B SW C SE D Hong Kong Slope Catalogue Map Referencing Scheme 11SW-A

  5. Cut Slope Fill Slope Retaining Wall “Natural” Slope Cut Slopes and Fill Slopes e.g. North Coast Road

  6. Fill Slope Fill Slope

  7. Home Page for Hong Kong Slope Information System http://hkss.ced.gov.hk/hkss/

  8. Main Menu for Slope Information System

  9. Slope Catalogue: Slope 11SW-A/CR175: Po Shan Road Click once on Slope to display data for 11SW-A/CR175

  10. Centred Map for Cut Slope 11SW-A/CR175: Po Shan Road

  11. Photographs of Slope 11SW-A/CR175: Po Shan Road Failure of slope in June 1972 Aerial Photograph of Slopes 11SW-A/CR175and 11SW-A/FR30

  12. Feature Registration Form for Po Shan Road Slope 11SW-A/CR175 Major Disaster in June 1972 Landslide Preventative Measure

  13. Field Observation Form for Po Shan Road Slope 11SW-A/CR175

  14. Example of Fill Slope from Slope Catalogue: Street Reference

  15. Fill Slope 11SW-A/FR 30: Reconstructed slope from lower part of 1972 Po Shan Road Failure

  16. Photographs of Slope 11SW-A/CR175: Po Shan Road Failure of slope in June 1972 Aerial Photograph of Slopes 11SW-A/CR175and 11SW-A/FR30

  17. Example of Retaining Wall from Slope Catalogue: Street Reference

  18. Landslip Preventative Measures Peel Street: Wall: 11SW-A/R188 before LPM in 1984 Same Wall in 1998 - from Slope Catalogue

  19. Po Hing Fong: LPM 33 NK Tovey inspecting Walls 11SW-A/R53 11SW-A/R64 Oct. 15th 1982

  20. LPM: Wing Lee Street (Bridges Street Market) Wall in 1982 prior to LPM Note: N.K. Tovey with assistants Wall in 2001

  21. Landslide Preventative Measures - Step 1 Slope catalogue - data collected quickly - Stage 1 Very Simple Ranking System NOT necessarily accurate BUT gives a Rational Way to move forward. • Evaluate a score system • e.g. (3 * height + drainage factor )* consequence factor • drainage factor say 0 if good > 5 if poor) • consequence factor - say • 1 for little consequence : 2 for minor roads • 3 for major roads : 4 for buildings Slopes with High Rank Number SUGGESTS they are MORE CRITICAL

  22. Landslide Preventative Measures - Step 2 • Limited Financial Resources available in any one year • so • From the thousands of slopes in catalogue, select the 20 with the highest RANK Number for more careful analysis. • e.g. • Check initial catalogue data is correct • probe depth of weep holes in retaining walls • make a thorough check for signs of distress • do a simple slope stability analysis • shortlist (say 6) most critical based on this Stage 2 study for detailed study as Stage 3

  23. Landslide Preventative Measures - Step 3 • Arrange for Site Investigation of shortlisted Slopes • trial pits • soil sampling - shear testing • bore holes • install piezometers • monitor piezometers • Check History of Site • Check responsibility • Full Stability Analysis • If public responsibility move to design Stage - otherwise serve notice on person or authority liable for maintenance.

  24. Landslide Preventative Measures - Step 4 • Design Preventative Measures • Check designs • Working Drawings • Tender Process • Contractors on Site • Preventative Work complete • Begin Step 2 for next group of slopes for next year. • After a number of years, most critical slopes should now be safe.

  25. Some recent Landslides in Trinidad • There is NO proactive system in place • Everything is Reactive

  26. Landslide at Maracas December 2002 December 2004 – note the slide is much more extensive

  27. December 9th Landslide 3 km beyond Las Cuevas as seen on TV half of road blocked Landslide 11th December 2004 at approximately 13:00 1 km before Las Cuevas half of road blocked

  28. Slope before failure at Couva Slope after Landslide Slide by Derek Gay, UWI

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