PRediction of jet grouting efficiency e average columns diameter

The result of a jet-grouting treatment is a cemented soil body of quasi-cylindrical shape, commonly termed jet grouted column. Even though technology has noticeably progressed since first applications and treatment efficiency has accordingly improved, there is still a great level of uncertainty on the results of treatments, in terms of both column diameter and mechanical properties of cemented material. This paper focuses on the estimate of diameter, which is by far the most important geometrical parameter of jet grouted columns at the design stage: it is fundamental for overlapping of adjacent columns in linear barriers and massive treatments, but plays a still important role in reinforcements made with isolated columns. In principle, the diameter of a column is strongly dependent on the characteristics of the injected fluids and on the physical and mechanical properties of soils, being the result of a very complex interaction between these two elements. Comprehensive analyses of these mechanisms have been rarely attempted, but several studies can be found in the literature trying to establish relations, on empirical or sound theoretical basis, between diameters and injection parameters or soil properties. A critical review of these relations is initially presented in the paper together with their classification on the basis of the governing factors described by each of them. In the attempt to establish more rational and complete design correlations, a large number of experimental data have been then collected by the authors and analysed to sort out the most relevant factors for jet grouting effectiveness. A dependency has been in particular inferred for single and double fluid jet grouting systems between efficiency of treatments and soil type. A possible interpretation of these observations is finally provided by a theoretical model describing the role of the injection parameters and soil properties for single fluid jet grouting. The performed analyses represent a preliminary step toward the production of reliable charts for the design of jet grouting treatments.