172_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

172_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 -...

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SL1 STABILITY OF EARTH SLOPES Types Of Slopes o Open Cuts o Embankments o Levees o Earth Dams o Natural Slopes Failed / Failure may occur suddenly without warning, or may get warning cracks and settlements. ·F-allure occurs when the shear.:Stress exceeds the-shear:§trength along a continuous surface This sUrlace IS ermed the failure surla ,slip surface, or surla.ce of rupture. Estimated cost of landslide damage in the U.s (direct and indirect) - $1.5 billion Causes of Slope Failures (Landslides) _- i' .' , .." iii , ... New loading t t , . Temporary or permanenl excavation for conslruclion project (pipeline, bUilding basement) High ground waler lovel causes seepage ~ '" forces in the ..... ....... :.-.,:-. ........ : direclion of ~ potential slope movement ~-=---- SUSCeptible'.'••- .. ;;;::--- layer or zone weakoned from continual exposure to ground water Of chemical waste leachate New forces resulting _-;:. ~.,::~~h,:om seismic activity Dashed arrow' '\ indicates '" tendency
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Unformatted text preview: ...... for movement W normal o.f earth mass ra'vity force In lho slope g acting A. Increased Shear Stress o External loads (buildings, roads) o Unit wt. increase due to water content increase o Water pressure in tension crack a Seepage forces o Seismic forces (earthquakes, vibrations) B. Decreased Resistance o Removal of lateral support at toe (stream erosion, excavation) o Undermining caused by tunneling, collapse of caverns or seepage o Tension cracks C. Decreased shear strength o t = C + (cr - u ) tan ~ o Increased pore water pressure, uj o Deterioration of cementing material, cJ. . " Originallopography Loss of capillary tension '. .../ Planned tinal grade a ".' lorprojectarea on drying, d and out '. "_ ' ---, o Swelling of clays by 'o", adsorption of water, ct ..-o Earthquakes reduce shear strength of sensitive silts and clays, d and ~t...
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