Abstract:

The plastic flowability of soil in chamber during earth pressure balance (EPB) shield tunneling in sandy strata is bad, which would lead to collapse of excavation face, unsmooth mucking and large ground surface settlement. As a result, the soil should be improved so as to guarantee smooth advancing of the shield. The ground conditioning is carried out for sandy strata so as to find the applicable ground conditioning agent and conditioning parameters. The foaming agent and bentonite are used to improve the sandy strata. And then, the relationship between foam halflife period and foam concentration, that between foaming multiplying power and foam concentration, that between viscosity of bentonite slurry and slurry concentration, and that between specific gravity of bentonite slurry and slurry concentration are analyzed, so as to determine the best foam concentration and bentonite concentration. Meanwhile, the injection ratio of conditioning agent is determined by slump test. Finally, the soil conditioning effect is testified by field shield advancing, and a rational ground conditioning scheme for sandy strata is proposed.

Key words: Nanchang Metro, sandy strata, ground conditioning, earth pressure balance (EPB) shield