Estimating settlements in dry sands during earthquakes

Abstract

An analytical method for predicting the settlement of a horizontal stratum of dry sand subjected to earthquake excitation is presented. An equivalent linear viscoelastic dynamic analysis is used to determine the time-history of shear strains at various levels within the stratum. The vertical strains caused by these shear strains are calculated by an empirical relationship shown to be in close agreement with laboratory test data over a wide range of relative densities. This allows the settlement distribution with depth to be calculated as a function of time.The method was applied to a 50 ft (15 m) stratum of sand. A base acceleration corresponding to 0–10 s of the N–S component of El Centro earthquake was used. Settlement distribution vs. depth, as well as surface settlements for various relative densities and earthquake scaling factors are shown. The effect of surcharge loading on settlements is investigated in an approximate manner.The results may be used to estimate differential settlement of a structure due to an earthquake. The results show that while the compaction of the upper layers may be sufficient to reduce the settlements due to static loads to tolerable amounts, deep-seated settlements will still occur during an earthquake.