Effect of Soil Layering on Shorter-Term Pile Setup

Abstract

Four medium-scale experiments were conducted in a laboratory setting to better understand the effect of soil layering on the increase in pile resistance as a function of time known as pile setup. Each experiment entailed compacting a soil profile consisting of cohesionless and/or cohesive soil in a large manhole and driving a steel pile model instrumented with strain gauges and pile driving monitoring system sensors. Piezometers were placed in selected soil layers to monitor pore-water pressure. Two experiments performed were entirely cohesive and cohesionless soil, and the other two experiments were conducted with mixed soil profiles simulating single- and double-drainage conditions. Time-dependent pile resistances were estimated by pile restrikes using the monitoring system with subsequent signal matching analyses. Static load tests (SLT) were also performed at the end of the last restrike. Cone penetration tests (CPT) were performed before pile installation and after the static load test. This study showed that pile setup occurred in cohesive soil layers, followed the logarithmic time scale, and is contributed mainly from the gain in shaft resistance. No pile setup was experienced in cohesionless layers, regardless of their locations along a test pile and the soil stratigraphy. The presence of a double-drained condition in an intermediate cohesive soil facilitates the dissipation of excess pore-water pressure and pile setup. The pile setup trend follows the pattern of pore-water pressure dissipation in a cohesive soil.