ANALYSIS OF THE DIFFUSION OF SUBMERGED JETS FOR THE PREDICTION OF THE DIAMETER OF SINGLE FLUID JET GROUTING COLUMNS

The jet grouting is one of the most popular ground improvement techniques and is largely used to increase the bearing capacity of foundations below new or pre-existing buildings. Most frequently the adopted systems consist of arrays of isolated columns, behaving in principle similarly to piled foundations, but massive blocks of cemented soil formed by overlapped columns can be also created. In both cases, the performance of the reinforced foundation is strongly dictated by the achievement of adequate dimensions and mechanical properties of the columns. Therefore, an accurate prediction of the real dimensions of columns is very important at the design stage. Different approaches can be found in the literature with the purpose of providing formulas able to predict the dimensions of jet grouting columns starting from characteristics of the jet and/or properties of the original soil. In principle, the diameter of jet grouting columns results from an interaction between the erosive capacity of jets and the resistance of soil to cutting. Therefore a detailed analysis has been performed in this paper to study the evolution of high speed submerged jets. Different simulations have been performed with a finite element code to calculate the longitudinal and transverse profile of velocity of jets diffusing within homogeneous fluid masses. The model is initially calibrated with the results of experimental data found in the literature. Finally, different scenarios have been reproduced by parametric calculations in order to compare the obtained numerical results with theoretical relations available in the literature. The analysis has been herein confined to single fluid jet grouting, considering a systematic variation of the injection parameters (namely diameter of nozzle, injection flow rate or velocity and composition of grout).