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Unformatted text preview: Coulombs Method Failure mechanism In Coulombs method a mechanism of failure has to be assumed Assumed failure plane wall movement soil movement Failure mechanism In Coulombs method a mechanism of failure has to be assumed If this is the failure mechanism then the MohrCoulomb failure criterion must be satisfied on the assumed failure planes Assumed failure plane wall movement soil movement The application of the failure criterion to assumed mechanisms of failure is widely used in geotechnical engineering. This is generally known as the limit equilibrium method. It is not a rigorous theoretical method but is used because it gives simple and reasonable estimates of collapse. The method has advantages over Rankines method it can cope with any geometry it can cope with applied loads friction between soil and retaining walls (and other structural elements) can be accounted for Limit equilibrium method Failure criterion For any point on the failure plane we have = c + tan Failure criterion For any point on the failure plane we have = c + tan If analysis is of undrained stability then the failure criterion must be expressed in terms of total stress using undrained parameters c u and u = c + u u tan Failure criterion For any point on the failure plane we have = c + tan If analysis is of undrained stability then the failure criterion must be expressed in terms of total stress using undrained parameters c u and u = c + u u tan If the pore pressures are known or the soil is dry an effective stress analysis can be conducted and the failure criterion must be expressed in terms of effective stress and effective strength parameters c, = c + tan direction of soil movement Assumed failure plane Failure criterion direction of soil movement Assumed failure plane Failure criterion Forces on the failure plane Shear Force T = ds direction of soil movement Assumed failure plane Failure criterion Forces on the failure plane Shear Force T = Normal Force N = ds ds direction of soil movement Assumed failure plane Failure criterion Forces on the failure plane Shear Force T = Normal Force N = Cohesive Force C = ds ds cds Failure criterion T = C + N tan If the soil properties are constant Failure criterion T = C + N tan If the soil properties are constant T N The forces acting on the failure plane are Failure criterion T = C + N tan If the soil properties are constant C T N R The forces acting on the failure plane are which may be more convieniently represented by Failure criterion For a wedge of soil failing as shown below there has to be relative movement between the wall and the soil, and the soil must be failing on this plane....
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 Three '11
 DAirey

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