Stabilizing Foam-Bearing Tunnel Boring Machine Muck by Using Calcium Oxide-Ground Granulated Blast Furnace Slag

Abstract

Muck generated by tunnel boring machines (TBMs) poses significant environmental challenges, primarily due to the use of shield foaming agents (SFA) that contain sodium dodecyl benzene sulfonate (SDBS). This study investigates the mechanical performance and environmental safety of calcium oxide-activated ground granulated blast furnace slag (CaO–GGBS) as an eco-friendly stabilizer for treating SFA-contaminated TBM muck. Two types of muck—silty clay and silt—were stabilized with CaO–GGBS at various mixing ratios under three SFA concentrations (0%, 2%, and 4%). The pollutant retention, engineering feasibility, and underlying micro-mechanisms were systematically evaluated through unconfined compressive strength (UCS), freeze–thaw (F–T) cycling, leaching, x-ray diffractometer, and scanning electron microscope tests. A key finding is that the optimal CaO–GGBS mixing ratios (3:7 for silty clay and 1:9 for silt) yield maximum UCS values exceeding 3 MPa even at 4% SFA after 10 F–T cycles, meeting the requirements for roadbed filler. Importantly, SDBS was undetectable in leachates, indicating effective contaminant immobilization and elimination of associated ecological risks. Overall, the CaO–GGBS stabilizer offers a low-carbon, waste-synergistic solution for repurposing SFA-containing TBM muck into safe engineering materials, with significant environmental and practical implications.