Deep mixing method for the construction of earth and water retaining walls

In the deep mixing method, the ground is mechanically mixed in place while a binder, often based on cement, is injected. After hardening of the soil-cement mixture, called soil mix material, soil mix elements are formed in the ground. Originally known as a ground improvement technique, the deep mixing is more and more applied for the construction of earth-water retaining structures within the framework of excavation works. After a short introduction to the execution aspects of the method, the authors discuss the hydro-mechanical properties of the soil mix material mainly based on the results of the BBRI Soil Mix project (2009-2013). A design approach dedicated to the soil mix retaining walls and developed in collaboration with the SBRCURnet is then presented. In this methodology, which is in line with the structural Eurocodes, design rules are adapted to the functions of the soil mix wall (earth-water retaining, bearing and cut-off functions) including the temporary or permanent character of the application. Based on the result of large-scale bending tests, the interaction between the soil mix material and the steel reinforcement is considered in the calculations allowing a reduction of the steel section between 10 and 40 %