Development of shield waste slurry-based tail grouting material for slurry pressure balance (SPB) tunneling: A geopolymer consolidation method

Owing to the substantial production of waste slurry in slurry pressure balance (SPB) shield tunneling, there is an urgent need to recycle SPB shield waste slurry (SWS). In this study, the proposed recycling method involves employing the geopolymer consolidation approach to develop an innovative SWS-based shield tail grouting material comprising SWS, geopolymers, and accelerators. Via the application of the Taguchi method, the optimal dosage ratio for the new grouting material was designed. An investigation was conducted to examine the influence of each component on the working and strength properties of the grouting material, and the results revealed that the most significant factor is the waste slurry specific gravity (WSSG). Moreover, the optimal grout formulation parameters included a WSSG of 1.10 g·cm⁻³, a geopolymer content (GC) of 95 %, and an accelerator content (AC) of 7 %, with the verification error of the results not exceeding 6 %. The microscopic hydration mechanisms of typical mixtures were qualitatively and quantitatively characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR), and the main gelatinous hydration structure identified is C-S-H gel. The optimal sample exhibited the highest Ca and Si concentrations of 43.21 %, and its Si-O stretching vibration band demonstrated the lowest wavenumber at 966.30 cm⁻¹. On-site industrial tests were performed against the backdrop of the Hengqin Mangzhou slurry shield tunnel (φ = 15.01 m), and the findings suggested that approximately 20.6 tons of SPB waste slurry is utilized for grouting per ring of segments. Compared with traditional mortar, the onsite production of the new grout is cost-effective, efficient, and environmentally friendly. Moreover, on the basis of real-time monitoring, ground-penetrating radar (GPR), and opening detection approaches, the new grouting material exhibited excellent deformation control (surface and segment) and high backfill density and effectiveness. In this study, effective in site resource reutilization of SPB SWS was achieved, which conforms with dual carbon goals.