Presentation on theme: "4-4. LANDSLIDE 4-4-1. Introduction Definition: Movement of mass on a slope (due to gravity) Movement can be fast or slow Slide, slip, fall, or creep The."— Presentation transcript:
4-4. LANDSLIDE Introduction Definition: Movement of mass on a slope (due to gravity) Movement can be fast or slow Slide, slip, fall, or creep The mass can be soil, debries, rocks, and water mixtures July 27, 2011 landslide on the slope of Umyeon Mt., Seoul:
27 March :15am, Buynaksk-Gimry road blocked by landslide
Types of Landslides Slides: Blocks of material moving on well-defined shear planes Rotational slides: Moving along a concave surface Translational slides: Moving parallel to the ground surface Falls: Sudden release of rocks or soils dropping freely through the air with little contact with other surfaces until impact Topples: Similar to falls except that the initial movement involves a forward rotation of the mass Flows: Moving entirely by shearing within the transported mass and act like viscous fluids Creep: Almost imperceptible movement of material down a slope Lateral spreads: Occurring when liquefaction in underlying materials causes surface rocks or soils to move down gentle slopes
Slope Stability m
Factors affecting slope stability (Geological) structure, esp. joints, foliations, bedding and other layered structures Mass on the slope Types of the mass Water Climate (esp. T. and pptn.) Plantation Time
Joints, faults, bedding planes, or any planar feature that interrupts cohesion is a risk for slo pe instability. Water will preferentially travel down such features, weakening them by reduci ng resisting forces and by weathering the minerals therein. Chemical and physical weather ing play roles in slope destabilization.
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
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
Development and Landslide Generally, landslide more frequently occurs upon development Causes of more frequent landslide Making geologic conditions adverse Water seepage Artificial alteration (change) of the slope
Landslide caused by the rupture of a water supply pipe. Source: AIR Caused by Abruzzo (Italy) Earthquake 4/23/2009 3:00:00 PM
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
Recognition & Protection Recognition of possible landslide slope from Geological survey Landslide history (frequency) Slope stability map Various signs Fractures on walls Distortion of the door (window) frames Out of alignment of the fence bars Water leakage at the basement of the slope
Slope-stability index distribution for a calibration region on Oahu
Fracture on the bottom floor of a building at the event of landscape in Maine, USA.
Reducing the risk by Drainage improvement Decreasing slope angle Construction of retaining walls Rock bolting