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Soil mix walls as retaining structures - mechanical characterization.

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Since several decennia, the deep soil mix (DSM) technique has been used for ground improvement (GI) applications. In recent years, soil mix walls (SMW) have become an economical alternative to traditional excavation support systems. The Belgian building market has also witnessed such development with the growing use of the Cutter Soil Mix (CSM), the Tubular Soil Mix (TSM) and the CVR C-mix® systems. Unfortunately, standardized guidelines for SMW are not currently available. For the purpose of developing such guidelines, mechanical characteristics of DSM material must be investigated. Within the framework of a Flemish regional research program (IWT 080736), DSM material from 38 Belgian construction sites, with various soil conditions and for different execution processes, has been tested. In the present paper, results of various tests, performed to determine characteristics of DSM material are firstly described. Porosity, permeability, Unconfined Compressive Strength (UCS) and tensile strength, as well as the modulus of elasticity, the ultrasonic pulse velocity and the adherence between DSM material and steel reinforcement are investigated. In addition, results of petrographic analysis performed using thin section technology are also presented in order to obtain a microscopic view of the material. On the basis of UCS tests performed on core samples, the determination of the 5% quantile characteristic UCS value of the DSM material is then discussed with regard to the influence of unmixed soil inclusions in the material and considering the scale effect.