Experimental evidence on the strength of soil treated with single and double fluid jet grouting

The various technological solutions of jet grouting, normally grouped into single, double and triple fluid, aim principally at increasing the efficiency of treatments obtaining larger diameter of columns and reduce construction time and cost. Rarely attention is put on the influences of the technology on the mechanical properties of the material, considering this as a secondary issue. The present paper focuses on this aspect summarizing the observation of a comprehensive field trial where sixteen columns have been created with single and double fluid jet grouting varying the injection parameters. The large number of laboratory tests performed on samples cored from the columns show a predominant role of the technology, being the material created with single fluid systematically stronger than the one formed with double fluid. This aspect has been herein explored on samples of original soil compared with materials cored from single and double fluid jet columns: the morphology of the samples has been investigated by scanning electron microscopy (SEM), while the mineralogical composition has been inferred with X-ray diffraction (XRD), differential thermal (DTA), and thermo-gravimetric analysis (TGA). The analysis shows that, if on one side the wrapping of the jet with an annulus of compressed air enhances the cutting capacity of the double fluid jet and is this able to create larger diameters, on the other side it leads to a lower proportion of cement in the columns, that is responsible for worse mechanical properties of the material.