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

41where S pt(residml) = Residual settlement of the soil layer due to primaryconsolidation at time t.S p = Ultimate primary consolidation settlement of the soil layer(see Equation 4.1).S p t = Primary consolidation settlement of the soil layer achieved attime / (see Equation 4.2).4.3.3 Correction for Construction PeriodIn practice, the loading due to fill is not applied to the soil instantaneously but over a periodof time. The calculation of the consolidation settlement achieved within a give timetherefore needs to be corrected for the loading variation during the construction period (t c ).There are several ways of dealing with this but the simplest is the equivalent load method.It may be assumed that the load due to the fill increases uniformly throughout theconstruction period. Thus the degree of consolidation at time t c9 the end of the constructionperiod, is the same as if the total load due to the fill had acted constantly for a period of tJ2.Hence, at any time after the end of construction, the corrected time for the calculation of theconsolidation achieved is equal to the time from the start of fill placement less half theconstruction period (tJ2).Similarly, at any time during the construction period, the consolidation achieved may betaken as being equal to that occurring for instantaneous loading at half that time. Sincefilling is still in progress, the load acting is not the total load of the fill. Hence, the value ofthe consolidation achieved should be reduced in proportion of current load to the total load.Thus, the primary consolidation settlement at any time t after commencement of fillplacement can be determined as follows:(1) At any time t during the construction periodSettlement = (settlement for instantaneous loading, computed using 0.50x (fraction of final fill load in place)(2) At any time t after the construction period of duration t cSettlement = settlement for instantaneous loading (final fill load), computed using t -