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

81B ASSESSMENT OFOF CONSOLIDATIONB.IGeneralThis appendix gives guidance on the principles of calculating the average degree ofconsolidation for a homogeneous soil stratum with or without vertical drains. When avertical load is applied, an initial uniform excess pore pressure is assumed generatedinstantaneously throughout the soil stratum. This excess pore pressure will dissipategradually or almost instantaneously, depending on the permeability of the soil and thedrainage conditions at the boundaries of the stratum, by vertical drainage through the soil tothe horizontal boundaries and/or by radial drainage into pre-installed vertical drains. Theaverage degree of consolidation indicates how much of the imposed load is transferred to theeffective stress in the soil (with 100% meaning full transfer), defined by:IT, =-xlOO%u.(Bl)where U t = Average degree of consolidation of a homogeneous soil stratum at aparticular time.Uf = Initial excess pore pressure upon application of a vertical load.u t = Average excess pore pressure at a particular time.B.2 Consolidation without Vertical DrainsTerzaghi's theory of one-dimensional consolidation predicts the excess pore pressure undervertical drainage alone. Based on Equation Bl, Terzaghi's theory gives the following termfor the average degree of consolidation due to vertical drainage:(B2 >where U v = Average degree of consolidation due to vertical drainage alone.M = -(2m + 1)d .= Length of longest drainage path.