ABSTRACT
The design and execution of good soil conditioning plays a major role in the success of mechanized tunnelling with Earth Pressure Balance Tunnel Boring Machines (EPB-TBMs). During mechanized tunnelling in fine-grained soil, achieving a proper workability of the excavated soil in the working chamber is important to maintain the stability of the excavation face by balancing the pressure in the excavation chamber and in front of the cutting head. Much research has been carried out in recent years and several laboratory tests have been proposed, but a widespread and unified method for predicting the conditioning parameters required to achieve the right workability for clayey soils is still missing and there is a lack of knowledge regarding the correlation between the results of different tests.
WEBUILD and GEEG, innovative startup company of Sapienza University of Rome, conducted several research studies for major underground projects, aimed at improving Italian railways lines. These studies involved an intensive experimental activity focused on investigating the physical and mechanical properties of conditioned fine-grained soils, using the flow table test.
This paper describes the results of the flow table tests carried out on a large number of clayey soils (15) with different grain size distributions and plasticity, conditioned through the addition of water and foam. The results have been systematically analysed, identifying a correlation between the workability of the conditioned soils and their geotechnical properties. This correlation can be of much interest as it allows the use of a quick test, such as the flow table test, to check whether the conditioning process has produced the desired workability.
