PORT WORKS DESIGN MANUAL PART 3 Guide To - The University ...

32Jewell (1987) and Yeo & Woodrow (1992) considered that an embankment on soft clay isessentially a problem of bearing capacity. Due to the loading from the fill, the clay layer atthe bottom of the embankment experiences both vertical stresses due to surcharge loadingand horizontal stresses. Therefore, the loading from an embankment onto the soft soilcreates not just vertical stress but also an outward shear stress. The combined effect ofvertical stress and the outward shear stress is to reduce the resistance of the foundation to theapplied vertical stresses. If the foundation cannot support the lateral shear stresses, it willdeform laterally. The lateral displacement may lead to cracking of the fill, destroyingwhatever contribution the fill strength makes to the overall stability of the embankment.For an embankment constructed on soft clay of uniform strength and limited depth withrespect to the embankment width (see Figure 6), Jewell (1987) derived the followingexpression:FyH__D(3.3)whereFHrDaFactor of safety.Height of embankment fill.Unit weight of embankment fill; for fill underwater, thesubmerged unit weight should be used.Length from the toe to the crest of embankment.Undrained strength of soft clay.Thickness of soft clay.Ratio of the shear stress developed at the base of theembankment to the available c tt .For an unreinforced embankment:awhere K a = Coefficient of active pressure of fill.