Department of Civil Engineering, N-W.F.P UET, Peshawar
Design of Retaining Walls
To safeguard the wall against bodily displacements, i.e., to ensure its external stability, requires special consideration. Consistent with current practice in geotechnical engineering, the stability investigation is based on actual earth pressures (as nearly as they may be determined) and on computed or estimated service dead and live loads, all without load factors. Computed bearing pressures are compared with allowable values, and overall factors of safety evaluated by comparing resisting forces to maximum loads acting under service conditions. Factor of safety against overturning: (FOS)OT = Stabilizing moment / overturning moment = Rva / Py ≥1.5 Factor of safety against sliding: (FOS)S = µRv / P ≥1.5
P GL
R v = ΣW
a
R
y
µRv = µ(ΣW)
Figure 4: Rv = Summation of vertical forces acting on wall, P = Earth pressure, R = Resultant of P and Rv. Next, it is necessary to ensure that the pressure under the footing does not exceed the permissible bearing pressure for the particular soil.
Prof Dr. Qaisar Ali (http://www.eec.edu.pk)
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