Application ranges of EPB shields in coarse ground based on laboratory research

Earth Pressure Balance (EPB-) Shields were originally used in fine-grained soils as well as in mixed-grained soils with a content of fines (d < 0.06 mm) of at least 30 M%. In these soils, if an adequate consistency is given, an EPB-Shield can be used without additional ground conditioning. Further, the application ranges of EPB-Shields have successfully been extended to mixed-grained and coarse-grained soils by ground conditioning, see Herrenknecht et al. (2011). In these soils, foams, if required also foams with polymers, polymer suspensions or high density slurries, are applied to change the properties of the soil in the excavation chamber. So far, the application ranges of EPB-Shields in mixed-grained and coarse-grained soils were based on experience with former tunnelling projects with different hydro-geological boundaries and different conditioning agents. First investigations on the properties of soil-foam-mixtures were done in different laboratories (Mair et al., 2003; Borio et al., 2011; Bezuijen, 2011). In these investigations, the focus was on the determination of special properties of the conditioning agents and conditioned soils. These laboratory investigations were the basis for further examination. Laboratory research was carried out at the Institute for Tunnelling and Construction Management at the Ruhr-University Bochum, Germany, using selected methods for the reproducible determination of essential properties of foams, foams with polymer additives, polymer suspensions and high density slurries. The results are summarised in a doctoral thesis (Budach, 2012). These methods were tested systematically regarding their workability. Furthermore, coarse-grained soils were mixed with the selected conditioning agents and methods to determine the essential properties of the conditioned soils were developed and tested on their suitability as well. Based on the results of this research, application ranges for EPB-Shields were developed based on extensive laboratory research considering varying hydro-geological ground conditions and conditioning agents.