近距离下穿车站富水圆砾地层盾构隧道开挖面稳定性研究

Research on stability of excavation face of shield tunnel undercrossing station in water-rich gravel stratum

依托南宁市轨道交通5号线新—广区间下穿1号线广西大学站工程,利用FLAC3D软件对近距离下穿车站底板富水圆砾地层盾构隧道开挖面稳定性展开研究,探究支护应力比、地下水位对开挖面稳定性的影响,并给出下穿时合适的开挖面支护压力控制值,作为现场施工的技术指导,研究表明:随着支护应力比的减小,开挖面土体水平位移不断增加,其变形符合土体塑性区的发展趋势;富水圆砾地层开挖面失稳后破坏模式表现为开挖面前方为楔形状,破坏区域向前方和上方逐渐发展至既有车站结构底板处;开挖面失稳破坏后车站结构底板与底板下方土体形成临空面;随着地下水位的升高,开挖面发生失稳破坏的支护应力比增加,开挖面稳定性显著降低;下穿时应将土仓压力控制在111 k Pa以上。

Based on the project of Nanning Metro Line 5 undercrossing Guangxi University Station of Line 1 in Xinguang Section,FLAC3D software was used to study the stability of the excavation face of the shield tunnel undercrossing the waterrich gravel stratum of the station bottom plate at ultra-close distance. The influence of support stress ratio and groundwater level on the stability of excavation face was explored,and the appropriate supporting pressure control value of excavation face was given as the technical guidance for field construction. The research showed that with the decrease of the support stress ratio,the horizontal displacement of the soil on the excavation face increased continuously,and its deformation conformed to the development trend of the soil plastic zone. The failure mode of the excavation face in the water-rich gravel stratum was wedge-shaped ahead of the excavation,and the failure area gradually developed to the bottom plate of the existing station structure. After the instability and failure of the excavation face,the bottom plate of the station structure and the soil belowed the bottom plate form the free surface;with the increase of groundwater level,the supporting stress ratio of instability failure of excavation face increased,and the stability of excavation face decreased significantly. The earth pressure should be controlled above 111 k Pa when crossing station.