Geotechnical modelling of CPR Grouting

The CPR Grouting has been investigated by means of a literature review and comparison with all similar grouting technique (especially compensation and compaction grouting) and a theoretical approach has been used in order to establish a design method for future applications. Several new concepts has been introduced in this work. First of all, the concept of unit cell has been reviewed and improved by introducing a new definition of Substitution Ratio. An expression for the prediction of the void ratio change due to the grouting process has been derived and it was showed that the zero grout efficiency assumption is valid in the case of normally consolidated soils and non-simultaneous injections. Finally, by means of the modified Cam Clay model, the gain in undrained strength due to the grouting has been calculated knowing the compression ratio of the clay and the variation of the void ratio. The cavity expansion theory outlined the stress field and excess pore pressure induced during the formation of the bulbs. The results show that generally three zones – the external elastic zone, the intermediate plastic zone, and the internal critical state failure zone – may coexist around the cavity. It is found that within the critical state region the effective stresses are practically constant and no excess pore pressure is generated in the elastic zone. A model has been developed to provide the stress state after the dissipation of the pore pressure due to the expansions. The results show significant alteration of the stress state and the soil stiffness after the bulb expansion. As a consequence, embankment settlement are reduced due to two major effects: the ground movements and the stiffness of the composite soil. Indeed, the displacement of the ground due to the expansions leads to a radial consolidation that increases the horizontal effective stress in the ground, improving the compressibility characteristics of the soil. Furthermore, being many thousands times stiffer, the grout can the treated as a rigid inclusion within the soil mass. In this study it is seen that the Paul model is a composite model that can be employed to estimate the composite stiffness. It is favored due to its simplicity and its approach, which considers a non-continuous dispersed reinforcement. Finally, a simplified method for predicting embankment settlement has been proposed. The simplification allows to carry out a Terzaghi's one dimensional consolidation analysis, since the equivalent parameters are estimated correctly. To calibrate the model parameters, two test embankments have been studied. The field settlement curves fitted reasonably the prediction, showing that a simplified consolidation analysis can be easily carried out for practically purposes.