中文摘要：

为了分析盾构进出洞时隧道端部土体的失稳破坏模式,为端部土体合理加固范围的确定提供理论依据,基于颗粒流分析程序（PFC）,对砂层盾构隧道端部土体的失稳破坏过程和机理进行了数值分析,并采用FLAC3D程序进行对比验证。根据土体滑动规律,给出一种对数螺旋线与直线组合的滑动破坏模式,运用颗粒流计算数据对滑动面进行曲线拟合,并进行相关性分析和显著性检验,得到颗粒摩擦因数取不同数值时的土体滑移面曲线方程。研究结果表明：隧道端部连续墙破除后,土体先在洞门附近发生局部破坏,随后土体颗粒松动破坏向内部发展,颗粒逐步发生位移重定向,最终在土体内部形成了一条显著的滑动破坏面,若隧道埋深较浅,滑动面将延伸贯通至地表;随着土体强度的增高,土体滑移直线倾角变大,对数螺旋线初始半径变小,土体破坏范围相应变小,端部土体越稳定,反之,端部土体滑移范围就会变大,稳定性变差;端部土体经过局部加固后,土体变形较小,内部不能形成滑动面,端部土体稳定性得以提高。

英文摘要：

In order to analyze the failure mode of tunnel end soil during shield launching and arriving,and provide theoretical evidence for the determination of reinforcing range of end soil,the process of instability and failure and its mechanism of end soil were numerically analyzed in sand shallow shield tunnel,based on particle flow code（PFC）.As the verification,comparative analysis was conducted by the FLAC3D model.A combined sliding failure mode of logarithmic spiral and straight line was developed by dint of sliding law of soil.Through the curve-fitting of sliding face,correlation analysis and significance test,on the basis of PFC data,curvilinear equations of sliding face at different friction coefficients were obtained.The results show that soil near the tunnel door might be subjected to severe local failure after punching the diaphragm wall at the end of the tunnel,and internal failure of soil particles occurs subsequently.Displacement of soil particles is redirected with the form of a clear shear sliding face inside soil.If the tunnel isembedded shallowly,the sliding face will extend to the ground surface.With the increase of soil strength,tilt angle of sliding line becomes large,the initial radius of the logarithmic spiral diminishes and the damage range of soil narrows.It is indicated that end soil tends to be stable.Conversely,with the increase of soil strength,the damage range widens and end soil tends to be instable.After local reinforcement of end soil,the deformation of soil becomes smaller and the sliding face is difficult to form.The stability of end soil is improved.