Presentation on theme: "4-4. landslide Introduction"— Presentation transcript:
1 4-4. landslide 4-4-1. Introduction Definition: Movement of mass on a slope (due to gravity)Movement can be fast or slowSlide, slip, fall, or creepThe mass can be soil, debries, rocks, and water mixturesJuly 27, 2011 landslide on the slope of Umyeon Mt., Seoul:
2 27 March 2014 - 10:15am, Buynaksk-Gimry road blocked by landslide
4 Types of LandslidesSlides: Blocks of material moving on well-defined shear planesRotational slides: Moving along a concave surfaceTranslational slides: Moving parallel to the ground surfaceFalls: Sudden release of rocks or soils dropping freely through the air with little contact with other surfaces until impactTopples: Similar to falls except that the initial movement involves a forward rotation of the massFlows: Moving entirely by shearing within the transported mass and act like viscous fluidsCreep: Almost imperceptible movement of material down a slopeLateral spreads: Occurring when liquefaction in underlying materials causes surface rocks or soils to move down gentle slopes
8 Factors affecting slope stability (Geological) structure, esp. joints, foliations, bedding and other layered structuresMass on the slopeTypes of the massWaterClimate (esp. T. and pptn.)PlantationTime
9 Joints, faults, bedding planes, or any planar feature that interrupts cohesion is a risk for slope instability. Water will preferentially travel down such features, weakening them by reducing resisting forces and by weathering the minerals therein. Chemical and physical weathering play roles in slope destabilization.
10 Water: small amounts increase cohesion, but add too much and it causes particles to lose contact with one another reducing both friction and cohesion.Angle of repose: this is the maximum angle of a stable slope as determined by the friction, cohesion, and particle shape
11 Vegetation:Roots penetrate regolith and tend to bind particles together as well as absorb water. They are a stabilizing force on slopes.Here we see the result of vegetative loss due to fire and the resultant mass movement
12 4-4-3. Development and Landslide Generally, landslide more frequently occurs upon developmentCauses of more frequent landslideMaking geologic conditions adverseWater seepageArtificial alteration (change) of the slope
13 Landslide caused by the rupture of a water supply pipe. Source: AIR Caused by Abruzzo (Italy) Earthquake 4/23/2009 3:00:00 PM
14 Both natural and artificial processes can alter slope Both natural and artificial processes can alter slope. As streams (or construction) cut into a bank, slope is increased, thereby increasing the downslope forces.Eventually the driving force becomes too great and failure occurs
15 4-4-4. Recognition & Protection Recognition of possible landslide slope fromGeological surveyLandslide history (frequency)Slope stability mapVarious signsFractures on wallsDistortion of the door (window) framesOut of alignment of the fence barsWater leakage at the basement of the slope
16 Slope-stability index distribution for a calibration region on Oahu
17 Fracture on the bottom floor of a building at the event of landscape in 2007. Maine, USA.