Pressure grouting of microfine cements in soils: micromechanical processes

The injection of microfine cements in soils is a common stabilization technique for improving both mechanical and hydraulic ground properties, but the micromechanical processes locally occurring are not yet understood and hence rightly modelled. In this work, the microfine cement injection is micromechanically analysed, soil grains-grout local interaction is accounted for by employing a discrete element method code, where the microfine cement particles are simulated by means of tiny rigid frictionless spheres. To simulate injection, these spheres are initially put in place in a tube, then pressurised by means of a servo control procedure and, finally, allowed to dynamically flow into a granular cubic specimen. Numerical analyses, considering different sand-grout particle diameter ratios, sand initial states and injection pressures, are performed. Numerical results reveal the formation of three grout diffusion processes in the granular medium: two mechanisms associated with soil grain dislocations (cavity expansion and claquage) and seepage of microfine cement within soil pores without any change in the initial soil microstructure.