Compound Deep Soil Mixing Columns for Retaining Structures in Excavations

Abstract

Deep soil mixing (DSM) columns as a retaining structure for deep excavations in soft soil areas has been widely used because, in addition to its low cost, it has fewer environmental hazards and no need of dewatering. However, due to its low tensile strength, this system usually requires a very thick wall cross section and is generally impractical for use as a retaining structure for very deep excavations. In an attempt to extend the use of DSM columns for deeper excavations, this paper introduces a so-called compound DSM retaining wall system that combines DSM columns with reinforced concrete bored piles. As shown in the paper, both the compressive strength of soil-cement mixtures and the bending moment capacity of concrete piles are developed to their full advantage in this hybrid soil-retaining system. The paper also presents the detail design methodology for the proposed compound DSM wall as a retaining structure for deep excavation. Finally, the benefits of this hybrid retaining system are further demonstrated through a case study completed in Shanghai, China.