A simple method to account for non-uniform initial excess pore water pressures in settlement computations

Abstract

The variation in percentage consolidation with time within a clay layer subjected to a non-uniform initial excess pore water pressure distribution can be difficult to evaluate, and as a result, often a uniform initial distribution is assumed in most analyses. However, by utilizing some of the key features of consolidation in terms of excess pore water pressure dissipation, it is possible to simply adjust the uniform case to account for any number of non-uniform initial excess pore pressure distributions. By observing the decay of excess pore water pressure with time resulting from various non-uniform initial distributions, it is clear that any initial asymmetry or skewness is quickly dispersed, and the distribution of excess pore pressure with depth becomes sinusoidal (or half-sinusoidal if singly drained) shortly after consolidation has commenced. In other words, once the pore pressure decay due to a non-uniform initial distribution has become sinusoidal, it will actually decay at the same rate as the uniform case – however, it will be “ahead” or “behind” the uniform case by some constant factor. Once this factor has been determined, it is possible to simply adjust the rate of consolidation resulting from a uniform initial pore pressure distribution (the values of which are widely available in literature) to account for any number of realistic non-uniform initial excess pore pressure distributions.