Research on optimizing performance of new slurries for EPBS soil conditioning based on response surface method

Abstract

Earth pressure balance shield (EPBS) construction process produces a large amount of untreatable shield dregs. Transporting these dregs directly to the landfill not only increases the costs, but also causes severe environmental problems. In order to improve the utilization rate of fine-grained shield dregs, a method of using waste silty clay to partially replace bentonite as a conditioner is proposed. Bentonite, wasted silty clay, additives, and tap water are selected to prepare the bentonite- silty clay modified slurry (BSC) and its various properties are tested. The whole tests are completed by the phased test method. Firstly, four additives are added into silty clay slurry for modification, and sodium carbonate is determined as the optimal additive and its dosage scheme. On this basis, the quantitative function relationship between the content of materials and the performance of BSC is established according to response surface method (RSM), and the performance optimization of BSC is completed. Finally, the microstructure of slurry is studied by scanning electron microscope (SEM) to explain the modification mechanism of BSC by sodium carbonate. The results show that the slurry-making capacity of silty clay can be modified effectively when the mixing ratio of sodium carbonate is 1%–3%. The regression model established by RSM is in good agreement with the experimental results, which can effectively predict the BSC properties under different material contents. When the mass ratio of water: bentonite: silty clay: sodium carbonate is 1000:58.91:297.97:3.14, the performance of BSC is close to that of bentonite slurry with soil–water ratio of 1:10. This study provides a feasible way for the recycling discharged soil from EPBS tunnel construction.