超孔隙水压力对盾构隧道极限支护力影响研究

Study on Influence of Excess Pore Water Pressure on Limit Support Pressure of Shield Tunnel

为探究盾构施工时地层中超孔隙水压力的变化、空间分布特征及对盾构开挖面极限支护力的影响程度,以提出泥水压力设定建议,依托大直径过江盾构隧道工程,并基于现场测试数据,对泥水盾构在富水粉细砂地层中施工引起的孔隙水压力空间分布及变化规律进行分析,运用极限平衡法求解有约束的非线性函数,计算分析超孔隙水压力对盾构隧道极限支护力的影响,并提出修正的极限支护力计算公式。研究表明:1)盾构施工时,孔隙水压力扰动区大致为开挖面前方2倍的开挖直径及开挖面两侧1.5倍开挖直径,且越靠近开挖面,扰动程度越大;2)富水砂层中开挖面主动破坏极限支护力的设定,受盾构掘进引起的孔隙水压力变化影响较大,应适当提升泥水舱压力,或采用全泥水平衡模式保持开挖面稳定,以减小对孔隙水压力的扰动范围及扰动程度。

To study the variations and distribution characteristics of excess pore water pressure during shield tunneling in water-rich silty fine sandy stratum and explore the influence of excess pore water pressure on the limit support pressure of excavation face,the constrained nonlinear function is calculated using the limit equilibrium method,and a modified formula for calculating the limit support pressure is proposed based on field test data of a large-diameter river-crossing shield tunnel project.The study shows the following:(1)During shield tunneling,the disturbance area of pore water pressure is roughly twice the excavation diameter ahead of the excavation face and 1.5 times the excavation diameter on both sides of the excavation face;the closer to the excavation face,the greater the disturbance degree.(2)The excess pore water pressure has a great impact on active failure limit support pressure of excavation face,thus,the slurry pressure should be appropriately increased,or the whole slurry balance mode should be adopted to maintain the stability of the excavation face and reduce the disturbance range and degree of pore water pressure.