Optimization study for cement-based grout mixture ratio of shield tunnel considering spatiotemporal evolution of grout buoyancy

Abstract

The grout buoyancy for segments during shield tunnel construction can cause significant floating displacement or even cracking of the segments, and the grout buoyancy is directly related to the grout buoyancy volumetric weight (GBVW). This study proposes an optimization process for the mixture ratio of cement-based grout based on the actual engineering environment. Based on a self-designed GBVW test instrument considering the interaction between grout and strata, this study reveals the evolution law of GBVW and the 3D spatial distribution law of grout buoyancy under different mixture ratios in different strata. Then, this study calculates the segment displacement under slurry buoyancy by the multi-factor coupled numerical calculation model. Research shows that the GBVW in different strata exhibits an evolutionary characteristic of sharp fluctuation-rapid decrease-slow decrease-complete disappearance. The upward precipitation of aqueous solutions in grout in different strata occurs during the stage of GBVW sharp fluctuations, and the decrease in GBVW is mainly accompanied by the seepage of aqueous solutions into the lower strata. The average GBVW and the duration of GBVW in muddy soil are larger than those in silty soil and coarse sand, respectively. An increase in the water binder ratio will reduce the GBVW and accelerate the dissipation of GBVW, while an increase in the bentonite water ratio will promote the growth of GBVW. The lower the strata permeability, the more easily the average GBVW is affected by the water cement ratio. The peak GBVW is more easily affected by the water binder ratio, and the duration of GBVW is more easily affected by the water cement ratio.