A biomass-enhanced bentonite slurry for shield tunnelling in the highly permeable soil

Abstract

Laboratory tests were conducted to investigate the properties of a bentonite slurry enhanced by the biomass derived from wheat straw. The bentonite concentration of the basic slurry varied from 40 kg/m3 to 60 kg/m3. The biomass contents of the enhanced slurry were between 37.5 kg/m3 and 87.5 kg/m3. Compared to the pure bentonite slurry, the viscosity of the biomass-enhanced bentonite slurry did not show significant increase. Moreover, the density of the biomass-enhanced bentonite slurry did not significantly increase. It appeared that the stability of suspended particles was slightly weakened by the added biomass. The minimal content of biomass needed for filter cake formation in the coarse sand decreases with the bentonite concentration. With a proper biomass content, the slurry pressure could be fully transferred to the effective support pressure within 120 s. Generally, the hydraulic conductivity value of the filter cake was less than 10-7 m/s, meeting the requirement for safe construction. Furthermore, as the biomass was gained from wheat straw, the enhanced slurry showed a high possible application in slurry-shield tunnelling.