211.%20Landslides

211.%20Landslides - Landslides Lecture 21 Rarely do we...

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Unformatted text preview: Landslides Lecture 21 Rarely do we appreciate the Impact of Geology. Impact Graduate Assistant Field Trip Leader Lecture 21: Landslides Page 1 of 34 Lecture 21: Landslides “Not only that, George is no longer an atheist” Lecture 21: Landslides Page 2 of 34 Lecture 21: Landslides “And the Earth Moved!” “And the Earth Moved!” Lecture 21: Landslides Page 3 of 34 Lecture 21: Landslides “And the Earth Moved!” “And the Earth Moved!” Lecture 21: Landslides Page 4 of 34 Lecture 21: Landslides “And the Earth Moved!” “And the Earth Moved!” Lecture 21: Landslides Page 5 of 34 Lecture 21: Landslides Landslide Characteristics Mass movement of Earth materials Mass Variable velocities Variable Variable materials Variable Controlled by Controlled – material strength – moisture conditions – secondary features (rock discontinuities) Classification – Failure Mode Lecture 21: Landslides Page 6 of 34 Lecture 21: Landslides Rock Fall Irregular failure and Irregular rapid fall from a fractured/bedded steep slope Often influenced by Often freeze-thaw and moisture conditions Difficult to predict Difficult Lecture 21: Landslides Page 7 of 34 Lecture 21: Landslides Rock fall from the upper cliff leads to a talus slope that represents a potential risk to people below. Lecture 21: Landslides Page 8 of 34 Lecture 21: Landslides Topple Vertically oriented, Vertically closely spaced fractures Hard rock Hard Steep slope angle Steep Similar to a deck of Similar cards set on end Lecture 21: Landslides Page 9 of 34 Lecture 21: Landslides Photo by Jack Vitek Photos by Jack Vitek Lecture 21: Landslides Page 10 of 34 Lecture 21: Landslides Photos by Jack Vitek Spread Failure Weak rock Weak sandwiched between more competent rock Load from above Load causes weak unit to squeeze out Failure of soft unit Failure causes failure of overlying competent unit Lecture 21: Landslides Page 11 of 34 Lecture 21: Landslides Spread Failure Limestone Soft Shale Lecture 21: Landslides Page 12 of 34 Lecture 21: Landslides Spread Failure results in stress on the building rear wall. Excavation of moving material allows reconstruction of the building. Flow Failure Types Soil Creep Soil Rock Creep Rock Flow Failures Flow – Avalanche – Debris Flow – Mud Flow Lecture 21: Landslides Page 13 of 34 Lecture 21: Landslides Creep in Sedimentary Rocks • Slow process • Often associated with freeze-thaw or wet-dry cycles • Does not require steep slopes Surface Creep Lecture 21: Landslides Page 14 of 34 Lecture 21: Landslides Flow Type Processes Fluid properties Fluid Very low shear strength Very Failure surface may be a “normal” landslide with Failure post-failure liquifaction of the material Avalanche Slope failure in mountain snow becomes liquefied when mixed with air Lecture 21: Landslides Page 15 of 34 Lecture 21: Landslides “Riding a Debris Flow – Utah” Lecture 21: Landslides Page 16 of 34 Lecture 21: Landslides Flood or Mud Flow? Mud Flow Mud Flood Lecture 21: Landslides Page 17 of 34 Lecture 21: Landslides Rotational/Circular Landslides Low strength materials Low No existing structural No (rock mass) control Failure surface is Failure circular in form Lecture 21: Landslides Page 18 of 34 Lecture 21: Landslides Components of Rotational Slide Analysis of Rotational Slide Balance the forces Driving Force: Driving D = d (weight) Resisting Force: Resisting R = r (Shear Strength) Factor of Safety (FS) Factor FS = R/D No obvious failure surface exists Lecture 21: Landslides Page 19 of 34 Lecture 21: Landslides Rotational Slide - Waco Riding the Slide One of nine homes destroyed - Colorado Lecture 21: Landslides Page 20 of 34 Lecture 21: Landslides Head Scarp Damages Retaining Wall Failure Lecture 21: Landslides Page 21 of 34 Lecture 21: Landslides Translational Slide Variable strength Variable materials Steep bedding/fracture Steep orientated toward open slope Strong structural (rock Strong mass) control Components Lecture 21: Landslides Page 22 of 34 Lecture 21: Landslides Analysis of Translational Slide Identify potential Identify failure surface from rock mass Driving force is vector Driving component of weight along failure plain Resisting force is Resisting shear strength of failure plain Obvious failure surface(s) Head Scarp Lecture 21: Landslides Page 23 of 34 Lecture 21: Landslides Translational Slides Texas Colorado Hope Slide - Canada Lecture 21: Landslides Page 24 of 34 Lecture 21: Landslides Wedge Slide - Colorado Permafrost/Frost Translational Slide Lecture 21: Landslides Page 25 of 34 Lecture 21: Landslides Sliding on Ice Frozen Ground New York Permafrost - Arctic Compound Landslides Most common Most Processes change as slide mass moves Processes Often solid failure followed by liquefaction Often and flow failure Lecture 21: Landslides Page 26 of 34 Lecture 21: Landslides Compound Landslide Compound Slide - Colorado Lecture 21: Landslides Page 27 of 34 Lecture 21: Landslides Stability Analysis Reinforcement Lecture 21: Landslides Page 28 of 34 Lecture 21: Landslides Retaining Walls Rock Reinforcement Lecture 21: Landslides Page 29 of 34 Lecture 21: Landslides Warning Signs Lecture 21: Landslides Page 30 of 34 Lecture 21: Landslides Lecture 21: Landslides Page 31 of 34 Lecture 21: Landslides Lecture 21: Landslides Page 32 of 34 Lecture 21: Landslides Flow Diversion Lecture 21: Landslides Page 33 of 34 Lecture 21: Landslides Break Lecture 21: Landslides Page 34 of 34 Lecture 21: Landslides ...
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This note was uploaded on 04/16/2011 for the course GEOL 320 taught by Professor Mathewson during the Spring '11 term at Texas A&M.

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