1、8.6 Coulombs earth pressure theoryC. A. Coulomb (1736 - 1806)Basic assumptions of Coulombs earth pressure theoryIn the 1770s, Coulomb， a Frenchengineer investigated the static conditionsin limit equilibrium of the sliding soilwedge behind the retaining wall. Thecalculation method of earth pressure i
2、sproposed, which is named Coulombsearth pressure theory. Another name issliding wedge soil pressure theory.土力学Soil MechanicsProf. H.J.LiaoThe influence of friction between the wall and theearth-fill and the inclined wall can be taken intoaccount in this theory. It is suitable for various earth-fill
3、surface and different wall back conditions, and thecalculation method is simple. So it is a widely usedearth pressure theory.土力学Soil MechanicsProf. H.J.Liao Basic assumptions1. The earth-fill behind the wall is granular material, such as sand, the cohesion c=0.Calculation diagram of Coulombs earth p
4、ressure theoryRetaining wallGranularmaterialBasic assumptions土力学Soil MechanicsProf. H.J.Liao2. The wall moves forward or backward and reaches the active orpassive limit equilibrium state, a sliding split oblique plane will beyielded through the back and the heel of the wall. The earth-fillbehind the
5、 wall slides along the wall back AB, and it will also slidealong the sliding surface AM inside the soil. A triangular wedge-shaped soil ABM is yielded. It is assumed that the stress-strain stateinside the triangular wedge soil ABM is neglected.Coulombs earth pressure theory calculation diagramRetain
6、ing wallEarth-fillTriangular wedge soil土力学Soil MechanicsProf. H.J.Liao3. Assuming that the triangular wedge soil ABM under the limitequilibrium state, the force equilibrium relationship is analyzedaccording to the rigid body equilibrium method of theoreticalmechanics, i. e., the force polygon method
7、.Calculation diagram of Coulombs earth pressure theoryRetaining wallEarth-fill 土力学Soil MechanicsProf. H.J.LiaoTriangular wedge soilCoulombs earth pressure theory calculation diagramApplicable conditions 1. The inclined angle of wall is ;2. The wall back is rough and the friction angle between the wa
8、ll back and the soil is .3. The backfill of the wall has an inclined surface, the slope angle is .土力学Soil MechanicsProf. H.J.LiaoBThe active and passive limit equilibrium states of Coulombs earth pressure theory are shown in the figure.Active limit equilibrium state Passive limit equilibrium state土力学Soil MechanicsProf. H.J.LiaoStatement: Thanks for some pictures and materials fromthe Internet used in this courseware only for teaching.
