4-4. LANDSLIDE4-4-1. Introduction

• Definition: Movement of mass on a slope (due to gravity)• Movement can be fast or slow• Slide, slip, fall, or creep• The mass can be soil, debries, rocks, and water

mixtures• July 27, 2011 landslide on the slope of Umyeon Mt.,

Seoul: http://www.youtube.com/embed/J2vkhY7gqQM

27 March 2014 - 10:15am, Buynaksk-Gimry road blocked by landslide

http://vestnikkavkaza.net/news/society/53205.html

http://www.idahogeology.org/DrawOnePage.asp?PageID=83

4-4-2. 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

http://www.idahogeology.org/DrawOnePage.asp?PageID=83

http://academic.emporia.edu/aberjame/struc_geo/primary/prim32.jpg

4-4-3. Slope Stability

http://www.fao.org/docrep/006/T0099E/T0099e01.htm

• 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 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.

http://gomyclass.com/geology10/files/lecture15/html/web_data/file37contents.htm

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 fric-tion, cohesion, and particle shape

http://gomyclass.com/geology10/files/lecture15/html/web_data/file35contents.htm

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

http://gomyclass.com/geology10/files/lecture15/html/web_data/file38contents.htm

4-4-3. Development and LandslideGenerally, 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

http://alert.air-worldwide.com/EventSummary.aspx?e=460&tp=68&c=1

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

http://gomyclass.com/geology10/files/lecture15/html/web_data/file36contents.htm

4-4-4. 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

http://www.soest.hawaii.edu/GG/FACULTY/aly/slide.html

Fracture on the bottom floor of a building at the event of landscape in 2007. Maine, USA.

http://www.maine.gov/doc/nrimc/mgs/explore/hazards/landslide/facts/nov07.htm

http://www.wjgl.com/sites/default/files/imagecache/photo/photos/sand_and_water_slope_instability.jpg

• Reducing the risk by• Drainage improvement• Decreasing slope angle• Construction of retaining walls• Rock bolting

http://www.rawell.co.uk/landscaping_solutions_product_applications/stabilisation_of_cover_soil.php

http://www.evansvillebasementrepair.com/foundation-repair/foundation-problems/collapsing-retaining-wall.html

http://westernhps.com/gallery.htm