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Landslide and erosion problems in glacio-fluvial soil escarpments, Greater VancouverOldrich Hungr, Geological Engineering, UBC
15 000 years ago, Vancouver was covered by as much as 2 km of ice
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Glacier retreat
Elevation relative to the present sea level
Eustatic sea level depression
Deglaciation 11 000 years ago
The unloaded land rose by ~100 m relative to the sea level
Meltwater deposited large quantities of sand and gravel in front of the glacier fronts. The sand deposits were raised ~100 m high to form glacio-fluvial terraces (“uplands”)
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Glacio-fluvial uplands in Greater Vancouver
Westwood Plateau
Sand and Gravel Escarpments
Reference: Eisbacher, G.H. and Clague, J.J., 1981, Urban landslides in the vicinity of Vancouver, B.C., with special reference to the December, 1979 rainstorm. Canadian Geotechnical Journal, 1*:205-216
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Rain!December, 1979
1997
Landslides!
January 19, 2005, Spanish Banks
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December 17, 1979
Riverside Drive
December 14, 1979,
Port Moody
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December, 1981, White Rock
c 1990
Chilliwack
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Riverside Drive
January 19, 2005
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DENSE SAND
GLACIAL TILL
SILT
SEEP
EROSION
20-120 m
Escarpment: original configuration (active toe erosion)
Escarpment: long-term natural slope profile
LOOSE SAND VENEER
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Escarpment: development
LOOSE SAND VENEER
Escarpment: natural slide (“debris avalanche”)
House may be damaged
House OK, if on dense soil
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Escarpment: development with random fill
LOOSE SAND VENEER
FILL
PERCHED WATER
Escarpment: fill failure (“flow slide”)
House destroyed
High pore pressure (undrained loading)
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Remedial measures
FILL
2) “TRAVEL ANGLE”
3)“SETBACK”
1) PULL BACK OR STABILIZE FILLS
4) CONTROL DRAINAGE
5) MINIMIZE DEFORESTATION
6) MONITOR SLOPES
1972 Po Shan Road, Hong Kong, 67 dead
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1972 Sau Mau Ping Hong Kong
79 dead
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Erosion problems:
Backward erosion
plunge pool
waterfall
Chilliwack landfillGully created in several hours, due to diversion of a stream. 10 000 m3
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Seepage erosion
Concentrated seepage, cave
Debris flow removes soil
Coquitlam gravel pits, 1985
100 m
A
20 m contours:beforeafter 2 days
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Coquitlam gravel pits and Westwood Plateau
The Grand Campus Washout, UBCJanuary 24 to 26, 1935Rain on snowmelt, total eroded 70 000 m3, rate 3 m/hour
1990 washout
truck
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