Laboratory Investigation on Excavation Performance of Foam-conditioned Weathered Granite Soil for EPB Shield Tunnelling

As weathered granite soils are extensively distributed in the Korean Peninsula, determining the optimal foam conditioning parameters for weathered granite soils can provide a high workability, low permeability, and high compressibility of weathered granite soils for successful operation of an earth pressure balance (EPB) shield tunnel boring machine (TBM). In this study, a laboratory-scale excavation apparatus was developed to conduct various laboratory excavation simulations for measuring the excavation-induced torque and the abrasivity of cutter bits. In addition, slump values, compressibility, and permeability were measured to evaluate the workability of foam-conditioned weathered granite soils. From the experimental results, the optimal foaming conditions for the weathered granite soil was obtained at foam injection ratios (F/Rs) of 60-70%, foam expansion ratios (FERs) of 15-18, and foaming agent concentrations (Cf) of 3-4%. The experimental results presented in this study can provide the rheological, mechanical, and hydraulic behavior of foam-conditioned weathered granite soils for successful EPB TBM operation.