泥水盾构圆砾地层开挖面泥膜闭气过程试验研究

Experimental Study on the Airproof Process of Filter Cake on Excavation Face in Round Gravel Stratum by Slurry Shield

针对武汉越江地铁泥水盾构在江中高渗透性圆砾地层带压开舱时泥膜闭气问题,开展不同配比泥浆渗透-成膜-闭气试验,测试泥浆成膜及闭气过程中泥膜性质及内部孔压变化.结果表明,泥浆密度的增大会使闭气前后泥膜压缩量及闭气值逐渐增大,而泥膜含水率、孔隙比及渗透系数逐渐减小;小密度泥浆(≤1.1g/cm^3)形成的泥膜在小于0.2MPa气压下被击穿,表现为圆孔透气,且内部孔压降低明显;大密度泥浆(1.15~1.2g/cm^3)形成的泥膜均能在0.4MPa气压下保持稳定.对本工程而言,可采用密度为1.15~1.20g/cm^3的膨润土-黏土混合泥浆并渗透成膜8h的方案,以满足带压开舱时开挖面稳定性要求.

Focusing on the problem of retaining gas pressure of filter cake when opening chamber under pressure by slurry shield in composite strata of round gravel with high permeability in Wuhan cross-river subway,a series of permeability-filter cake forming-airproof experiments with different ratio were carried out to test the properties of filter cake and the changes of inner pore pressure during the process of filter cake formation and airproof. The results showed that,with the increase of slurry’s density,the amount of compression as well as the airproof value of filter cake were increased gradually,while the water content,pore ratio and permeability coefficient were decreasd gradually before and after the process of airproof. The filter cake formed by less dense slurry(no more than 1.1 g/cm^3) was broken down under the pressure in less than 0.2 MPa of showing the hole was breathable and the pore pressure inside the filter cake was decreased significantly. While the filter cake formed by the slurry with high density(1.15- 1.2 g/cm^3)was confirmed to be stable under the pressure of 0.4 MPa. In view of this project,the plan of mixing slurry of bentonite and clay with a density of 1.15-1.20 g/cm^3 and infiltrating into filter cake for 8 hours was adopted in order to meet the requirement of excavation face’s stability when opening chamber under pressure.