盾尾密封对盾构周边渗流场及正面稳定的影响

基于地下渗流基本方程,采用有限差分法对江底隧道盾构施工中产生的周边渗透力进行了分析,并推导了渗流条件下盾构正面稳定的判别公式.分析表明:隧道开挖后,隧道周边土层的孔隙水压力将重新分布,开挖面附近孔隙水压力等值线呈楔形体,隧道开挖面上孔隙水压力变化达到最大;而开挖面附近的总水头等值线围绕开挖面呈环形分布,渗透力的最大值出现在开挖面上及盾尾透水处.土中渗透力使隧道开挖面稳定性系数减小,但盾构压力舱内的泥水压力有利于隧道正面的稳定.分析还表明,如果盾构掘进过程中盾尾有透水现象,则整个盾构机将处于水头产生较大变化的范围之内,会导致极其严重的后果.

Effect of Shield Sealing on Stability of Workface and Seepage Field Around Shield

An analysis is made of seepage forces around shield under river by finite differential method and the stability factor of workface with regard to seepage effects is deduced. The computation results show that the pore water pressure will redistribute in sandy soils around the shield tunnel after excavation and the contour lines of the pore water pressure exhibit sphenoid shape. The pore water pressure changes severely at the excavation face. The contour lines of the total water head display circularly around the excavation face of the tunnel and the maximum value of the .seepage forces exists on the excavation face and shield tail. The stability factor of tunnel face decreases due to the existence ofseepage forces, but the slurry pressure in the shield cabinet benefits the face stability. The results also show that the whole shield head will be trapped in the sharply changing zone of pore water pressure and severe consequences will arise if leakage occurs at the shield tail.