EVALUATION OF TRUE C-NU AND INSTANTANEOUS C-NU, AND ISOLATION OF SECONDARY CONSOLIDATION

It is shown that the presence of a distinct straight line in the initi al portion of settlement versus the square root of time plot indicates that soil follows theoretical behavior and that there is no initial a nd secondary compression in the straight line portion. If the coeffici ent of consolidation, c(v), is determined using the data of only this portion, it can be regarded as the true c(v). Secondary consolidation essentially starts after 60% consolidation and runs superposed over th e primary consolidation. Its effect is to gradually decrease c(v) so t hat at every instant of time it is a new Terzaghian soil with a new c( v) and other consolidation parameters. Characteristics of linear and s emi-log plots of U versus U, where U is the degree of consolidation an d U is the theoretical velocity, are used for determining true c(v) an d instantaneous c(v), and for isolation of secondary consolidation fro m the experimental consolidation curve.