Centrifuge modeling of rocking foundations on sand improved with soil-cement columns

This study presents a centrifuge modeling investigation of the seismic performance of shallow, rocking-dominated foundations supported by soil-cement columns intended to limit detrimental settlement and rotation, while preserving the beneficial energy dissipation afforded by a rocking foundation. The footings investigated in this study are modeled after shallow foundations supporting a two-span highway bridge, which served as the archetypal bridge in previous centrifuge studies. While earlier studies proved that rocking foundations in sand exhibit good re-centering while dissipating energy, this study aims to broaden the use cases for the rocking foundation concept for heavily loaded foundations in dry sand that may be prone to excessive settlement by incorporating ground improvement in the form of soil-cement columns with different configurations. A baseline case was developed for a rocking footing without ground improvement by subjecting the soil-foundation system to shaking at a level that caused excessive settlement (more than 5% of its length in this study) and permanent rotation. Foundation performance in the baseline case and rocking footings with ground improvement was assessed based on settlement accumulation rate with increasing cumulative rotation demand, and a correlation diagram relating re-centering and energy dissipation. Test results demonstrate that footings without ground improvement dissipate the most energy but experience excessive settlement. In contrast, paired soil-cement columns at either end of the footing's length preserved adequate energy dissipation and re-centering, while minimizing settlement to an acceptable limit.