Landslides
Landslides Describe how the impact of landslides depends on: population density, economic infrastructure, and population preparedness. o Increasing population density higher death rate
Explain why British Columbia has the highest frequency of landslides in Canada and what we should expect as our population expands into the mountains. o Return period of large landslides = 25-70 years, Frequency = 0.01 to 0.04 events / year
Distinguish between the 3 main failure models (falls, flows, and slides) and how they are influenced by geology. o Falls Occur on very steep slopes (usually rock) Material detaches because of weakness Falls due to gravity, very fast
o Slides Vary from slow to fast Usually soil, rock or debris Material moves as a coherent mass along a surface of failure (either curved or straight) If surface is curved: rotational slide (slump), intermediate speed, weak material, curved failure plane, often characterized by curved scarp about the slide If surface is flat: translational slide, sow to fast, usually strong material moving on planes of weakness, cohesive motion of material along a flat surface
o Flows Very slow to very fast Soil, mud, wet debris, (rock) Water is usually very important Fluid or plastic flow of material (chaotic)
o Complex movement Combination of mass movements (a slide that becomes a fall)
Categorize, identify, and name a variety of different landslides. o Classified by type of material, type of movement, rate of movement Type of material: rock, soil/earth, mud, debris Type of motion: falls, slides (cohesive block moves on failure surface) – curved/bowl shaped = rotational, flat/planar failure = translational), flows (fluid motion), complex movements Rate of movement: speed; if the movement is slow or slower, the name will be: creep, soil flow, earth flow
Define angle of repose. o Steepest angle a slope can maintain without collapsing o The exact angle varies depending on material o At the angle of repose, shear stress is exactly balanced by shear strength
Assess the balance between the strength of the scope and the destabilizing forces acting on it (factor of safety). o Driving force Shear stress (parallel to slope) o Resisting force Shear strength (slope’s ability to resist shearing motion) o Fs = shear strength / shear stress o Fs >> 1 = stable slope; Fs < 1 = fail
Explain why British Columbia has the highest frequency of landslides in Canada and what we should expect as our population expands into the mountains. o Return period of large landslides = 25-70 years, Frequency = 0.01 to 0.04 events / year
Distinguish between the 3 main failure models (falls, flows, and slides) and how they are influenced by geology. o Falls Occur on very steep slopes (usually rock) Material detaches because of weakness Falls due to gravity, very fast
o Slides Vary from slow to fast Usually soil, rock or debris Material moves as a coherent mass along a surface of failure (either curved or straight) If surface is curved: rotational slide (slump), intermediate speed, weak material, curved failure plane, often characterized by curved scarp about the slide If surface is flat: translational slide, sow to fast, usually strong material moving on planes of weakness, cohesive motion of material along a flat surface
o Flows Very slow to very fast Soil, mud, wet debris, (rock) Water is usually very important Fluid or plastic flow of material (chaotic)
o Complex movement Combination of mass movements (a slide that becomes a fall)
Categorize, identify, and name a variety of different landslides. o Classified by type of material, type of movement, rate of movement Type of material: rock, soil/earth, mud, debris Type of motion: falls, slides (cohesive block moves on failure surface) – curved/bowl shaped = rotational, flat/planar failure = translational), flows (fluid motion), complex movements Rate of movement: speed; if the movement is slow or slower, the name will be: creep, soil flow, earth flow
Define angle of repose. o Steepest angle a slope can maintain without collapsing o The exact angle varies depending on material o At the angle of repose, shear stress is exactly balanced by shear strength
Assess the balance between the strength of the scope and the destabilizing forces acting on it (factor of safety). o Driving force Shear stress (parallel to slope) o Resisting force Shear strength (slope’s ability to resist shearing motion) o Fs = shear strength / shear stress o Fs >> 1 = stable slope; Fs < 1 = fail
