Characteristics and modification mechanism of recycled waste silty clay slurry as the shield slag conditioner

Abstract

The construction process of earth pressure balance shield (EPBS) generates a large amount of shield slag. In China, the conventional methods for treating shield slag involve crude landfill and stockpiling, resulting in increased cost and significant environmental issues. To expand the recycling of shield slag, this study proposes to use waste silty clay to completely replace bentonite as a conditioner in coarse-grained strata. Firstly, the physical properties of silty clay slurries are investigated with four additives. There are six modified silty clay slurries with good improved performance. Then, analyzing the rheological properties of six modified silty clay slurries, and verifying the feasibility of replacing bentonite slurry with modified silty clay slurry. Next, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Zeta potential were used to analyse the micromechanisms, molecular structures and molecular forces of 14 % bentonite slurry, silty clay slurry with a soil-water ratio of 1:1, sodium carbonate 3 % and sodium silicate 0.1 % in a silty clay slurry with a soil-water ratio of 1:1. Finally, the slump test was carried out to verify the improvement effect of the modified silty clay slurry on the shield slag. The results show that sodium carbonate modified silty clay slurry has a higher interlayer water content and greater ion exchange capacity. When the soil-water ratio is 1:1 and the concentration of sodium carbonate is 3 %, the apparent viscosity and shear force of the modified silty clay slurries are between those of bentonite slurries with a concentration of 10 % and 14 %. Additionally, the modified silty clay slurry showed a stable microstructure and good residue amendment effect, making it suitable as a soil conditioner during EPBS construction in coarse-grained strata. This study offers a viable approach for recycling EPBS slurry.