Channel: Tunnel Engineering http://zgglxb.chd.edu.cn EN-US http://zgglxb.chd.edu.cn/EN/current.shtml http://zgglxb.chd.edu.cn 5 -4 m·s^-1 in a short time. This does not meet the anti-permeability requirement that a permeability coefficient of less than 10^-5 m·s^-1 should be stable for more than 90 min during shield tunneling. Increasing polymer content could lengthen the initial stable period of the permeability coefficient, and significantly reduce it when permeation tended to be stable. The permeability coefficient was stable below 10^-5 m·s^-1 for a long time, and the higher the polymer content, the more obvious the effect of permeability coefficient reduction. The conditioned soil with suitable flow plasticity might not have suitable permeability. It was suggested that the flow plasticity and permeability of soil should be evaluated synthetically considering shield tunneling in the coarse-grained soil stratum with rich water. Finally, the foam-slurry-polymer composite conditioning mechanism was achieved, confirmed via optical microscopy observation. Foam alone or foam and bentonite slurry cannot effectively condition the test soil, the viscosity of bentonite slurry can be improved by the polymer, effectively dispersing the condition agents in the pores of soil, and the foam stability can be enhanced through slowing down of foam drainage besides coarsening and coalescing by the polymer, so the flow plasticity and the permeability of soil can be conditioned appropriately.]]>