Influence of granulometry, time and temperature on soil conditioning for EPBS applications

Earth Pressure Balanced full face tunnelling machines have got experience thanks to a remarkable increase in the number of applications throughout the world due to both mechanical developments and a more effective use of additives to condition the ground. Soil conditioning modifies the mechanical and hydraulic properties of a soil by making it suitable for the pressure control in the bulk chamber and extraction with the screw conveyor. The results of a laboratory test campaign using slump test on granular soils, turned to understand the influence of the amount of conditioning agents, of time and temperature are presented and discussed. The obtained results put in evidence that exist a conditioning optimum range, taking into account the soil water content and the amount of injected foam (FIR) and that the properties of the conditioned mix decay after one or two hours of the production. Finally the preliminary research on temperature influence, highlights the great importance of this factor.