Seismic Response Evaluation of an Onshore Building Site Improved by Deep Mixed Foundation System

This study presents the seismic response of a deep mixed (DM) treated foundation under the fourteen-story Oriental Hotel building in Japan using a simplified method proposed by Siddharthan and Porbaha (2008). This hotel was subjected to intensive shaking during the 1995 Hyogoken-Nanbu (Kobe) Earthquake (M = 6.9) and extensive liquefaction and ground movement at locations near the building have been observed. The hotel that was retrofitted with grid type deep mixing method survived the earthquake with little or no damage. The proposed simplified approach showed clearly the effectiveness of treated columns in reducing the pore water pressure response at locations closer to DM treated zone. The effectiveness of treatment is significant, especially near the surface. Absence of liquefaction within the cells and at locations within up to 2.7 m from the edge column would have played a positive role relative to the accepted performance of the Oriental Hotel during the 1995 Hyogoken-Nanbu earthquake. Accordingly, the proposed simplified approach can be effectively used to analyse various DM configurations, site and excitation conditions. The soil responses are needed within and around the DM columns to ascertain the effectiveness of DM treatment and obtain an optimum design.