Shaking-Induced Sublayer Vertical Strains of Saturated Sands Estimated from Partially Drained Dynamic Centrifuge Tests

Earthquake-induced free-field settlement of coarse-grained soils has historically been assessed using laboratory element tests under drained or undrained conditions. However, in saturated sands, dynamic centrifuge and lg shaking table tests illustrate that excess porewater pressure generation/dissipation and settlement occur simultaneously during shaking under partially drained conditions. The average vertical strains computed from measured surface settlements in these tests neglect (1) the impact of effective stress on compressibility and (2) settlements that occur in denser and potentially nonliquefiable sands present in the centrifuge models. Here, the authors employ a simple procedure that uses measured porewater pressure and surface settlement time histories from partially drained centrifuge and lg shaking table tests to properly distribute vertical strain throughout the coarse-grained soil profiles, thereby incorporating variations of effective stress and relative density on vertical strain. The vertical strains are resolved into a shaking-induced component and a post-shaking reconsolidation component, and the procedure yields computed surface settlement time histories that reasonably match the rate and magnitude of measured settlements both during and after shaking. Using this procedure, we interpreted 151 individual (sublayer) estimates of vertical strain from 34 shaking events applied in dynamic centrifuge and lg shaking table tests. Combined with the sublayer shaking intensities, the 151 vertical strain values constitute a new database that can be used to develop shaking-induced settlement correlations for realistic partially drained conditions.