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 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.

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

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

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

Fill Slope Fill Slope

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

Main Menu for Slope Information System

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

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

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

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

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

Example of Fill Slope from Slope Catalogue: Street Reference

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

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

Example of Retaining Wall from Slope Catalogue: Street Reference

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

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

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

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

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

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.

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.

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

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

3 km beyond Las Cuevas as seen on TV half of road blocked 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

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