Deep Mixing Method: Equipment and Field of Applications

Abstract The purpose of this chapter is to introduce the reader to the deep mixing method. In the deep mixing process, the ground is mixed in place while a binder is injected with the help of a mixing tool. After hardening, soil mix elements with improved mechanical and hydraulic characteristics are realized. This technology, originally developed in the 1960s for ground improvement works, has seen amazing growth in the past few decades. Today, the deep mixing method is used for a large scope of engineering projects, such as soil reinforcement, slope stabilization, support of embankment, and liquefaction mitigation. In addition, the soil mix elements are being increasingly used as structural elements, for the construction of earth–water retaining walls and cutoff walls, and even as an alternative to the classical foundation solution. Geo-environmental applications are also performed with the soil mixing remediation technology with the containment or the treatment of the contaminants directly into the ground. In this chapter, the construction principles and the equipment allowing the execution of the deep mixing method are presented first. Although most of the existing deep mixing systems are mentioned in this chapter, the focus is on recent advances in the development of new mixing tools available today on the international market. Different ground improvement patterns can be designed with these various systems: soil–cement columns, rectangular soil mix panels, continuous barriers, or global mass stabilization offering a broad range of applications. The core of the chapter is dedicated to the description of the field of applications of the method with the help of several case histories that are briefly described. Finally, a detailed case history is highlighted. It concerns the realization of a retaining wall for the construction of a three-story underground car park (12-m depth) in downtown Aalst, Belgium. This chapter presents the main advantages and disadvantages of the technique, and it highlights the importance of the clear definition of the field of applications of the deep mixing method and the durability aspects of this particular material, taking into account the envisaged lifetime. It is important that the design and the imposed quality control carefully consider these two aspects.