Publication Abstract

Proceedings of the Deep Mixing 2015 Conference, (DFI)

Soft Deep Mixing for the Mitigation of Seismic Risk
A. Flora, University of Napoli Federico II, Italy; E. Bilotta, University of Napoli Federico II, Italy; F. Foria, University of Napoli Federico II, Italy; V. Nappa, University of Napoli Federico II, Italy

All the typical applications of deep mixing rely on the good mechanical properties of the improved columns to strengthen or stiffen the ground for a number of geotechnical applications. This paper focuses on a completely different kind of deep mixing, carried out in order to obtain columns much softer than the surrounding soil. This kind of deep mixing, named Soft Deep Mixing (SDM), is introduced as an original means to tackle seismic risk, and can be convenient when the existing structure to be protected has a historic relevance that cannot be altered with structural modifications. The idea is that properly assembled layers made of partially overlapped SDM columns, with dynamic impedance much smaller than that of the surrounding soil, will filter and reflect most of the seismic energy. The paper presents the results of some 2D parametric numerical analyses aimed to investigate the seismic performance of this innovative approach. Simplified dynamic inputs (Ricker wavelets, having only one largely predominant frequency) were adopted to better understand the effect of signal frequency. The analyses show that the effectiveness of the soft grouted isolating barrier depends on soil and SDM geometrical, physical and mechanical properties, as well as on the frequency content of the seismic input.

 article #2022; publication #1013 (DM-2015)