Development and experimental study on environmental slurry for slurry shield tunneling

Slurry shield is widely used in undersea and cross-river tunnels. The wide use of slurry shield leads to a lot of wasted excavated slurries. At present, most of the slurries are consisted of clay, bentonite, water and carboxymethyl cellulose (CMC), which makes slurries difficult to degrade and pollutes the environment. Biodegradable pregelatinized starch (PGS), harmless to the environment, was found to utilize its network structure in solutions to effectively decrease API filtration and increase Russian funnel viscosity of slurries. The effects of different PGS content on the variations in the properties of slurry were studied by experiments on mixing proportions in slurries. The filtration test of PGS slurries with a specific mixing proportion in medium-coarse sand strata was performed. By measuring the filter loss and the variation in excess static pore water pressure during the test process, whether the slurry effectively filled the strata pores and provided support pressure could be evaluated. The experimental results showed that adding 0.3% PGS by total weight to a slurry with a 0.0833 mass mixing proportion of bentonite to tap water performed good fluidity and control of water loss, and formed filter cake with a thickness of 3 mm. Based on the results from airtightness tests, the airtight pressure of the above filter cake is 0.12 MPa, and, correspondingly, the airtight time is approximately 6000 s. Thus, it is conceivable to use PGS for slurry preparation during normal tunneling. (C) 2019 Elsevier Ltd. All rights reserved.