Standardization of the molding procedures for stabilized soil specimens as used for QC/QA in Deep Mixing application

An international collaborative research has been undertaken to establish common understanding of the key issues involved in Quality Control/Quality Assurance (QC/QA) of Deep Mixing technique and propose international standards on design, execution and execution control. The aim of the study is to investigate the influence of the laboratory procedures on the mechanical properties of stabilised soil specimens and develop an innovative method to select the appropriate molding technique. A large laboratory testing program was carried out on seven types of heterogeneous natural soils, as found in Rome, and on Kawasaki clay stabilised with Portland cement. Thirty soil-binder mixtures with different workability were prepared using five different molding techniques, varying initial water content of the soils, water to cement ratio and binder amount. Unconfined compression tests have been carried out systematically on over 800 specimens. The applicability of different molding techniques in function of the workability of the mixture has been investigated and from the results it was possible to define an “applicability index” and therefore the range of applicability for each technique in function of the mixture’s workability.