Theoretical Modelling of Jet Grouting

Theoretical modelling of the mechanical phenomena induced by jet grouting is presented. The analysis is developed for the single-fluid method. The jet propagation across the space included between the injection nozzles and the intact soil is first modelled on the basis of the theory of submerged flows. Different possible interaction modes between jet and soil are then assumed for gravels, sands and clays, according to the results of previous experimental investigations. In the case of gravels, grout seepage is considered to be the most relevant mechanism. For sandy soils, the injected fluid is assumed to penetrate, for a limited extent, into the soil skeleton, producing a considerable increment of the pore pressures and a corresponding reduction of the grain-to-grain contact forces. The removal of the soil particles is then triggered by the dragging action of the fluid threads, and the analysis is developed under drained conditions. For clayey soils, the jet action is considered as a load imposed on the jet-soil interface, and the erosion process is modelled as an evolving sequence of undrained failures. Theoretical results obtained for the different soil types are compared with available experimental data, and the models are thus calibrated by means of back-analysis.