稳态渗流条件下盾构隧道松动土压力计算模型研究
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摘要
越江海或地下水丰富的盾构隧道在长期使用过程中渗水情况时有发生,由此引起的渗流场对隧道顶部荷载的影响是不容忽视的,但现有的松动土压力计算理论很少考虑渗流效应,对此提出了稳态渗流条件下的盾构隧道松动土压力计算模型.考虑盾构隧道处于稳态渗流状态,基于复变函数的映射变换,推导了隧道覆土内的孔隙水压力与渗流力表达式;引入小主应力轴旋转理论,得出了相应的侧压力系数计算公式;基于太沙基土拱效应分析模型,在渗流作用与主应力轴旋转效应分析的基础上,采用极限平衡法建立了竖向应力的微分方程,给出了盾构隧道顶部的有效松动土压力解析解答,分析了关键参数对计算结果的影响,并与有限差分软件FLAC的模拟结果进行了对比验证.研究结果表明:渗透系数相对值越大,隧道拱顶的有效松动土压力越大,但渗透系数相对值增大到一定程度后,该值的变化对于土拱效应影响很小;管片内侧水头恒定时,隧道拱顶的有效松动土压力随着渗流量的增加而减少;地表水头高度越大,隧道顶部的有效松动土压力越小;地表水头高度一定时,管片内侧水头高度的增加会削弱隧道顶部土拱效应;拱顶土体的位移越大,土拱效应越强;本文模型计算结果与FLAC模拟结果吻合良好,验证了本文模型的有效性.
Water seepage occurs occasionally in the undersea shield tunnels or high groundwater level shield tunnels after long-term use. The influence of the seepage field on the tunnel top load cannot be ignored under any circumstanc.Seepage effects are rarely considered in the existing theory of loosening earth pressure.Therefore,this study proposes an analytical model to evaluate the loosening earth pressure,considering the seepage effects.The shield tunnel is in a steady seepage state;therefore,the pore pressure and seepage force around the tunnel are determined based on the conformal mapping of complex variable methods.According to the effects of the principal stress axes rotation,the lateral pressure coefficient of calculation model is obtained.Based on Terzaghi's assumption,an analytical solution of effective vertical stress is deduced using the limit equilibrium method.Seepage and principal stress axes rotation are analyzed to obtain the analytical solution.The analytical model is verified via a parametric analysis and using a FLAC numerical model.The result show that when the relative permeability between the soil and lining is high,the effective stress acting on the tunnel is high;permeability coefficient variations have negligible influence on the effective loosening earth pressure when it goes beyond a certain value.The effective loosening earth pressure decreases with the increasing tunnel seepage rate;a higher surface water head leads to lower effective loosening earth pressure at the top of the tunnel.The effect of arching will be weakened with increase in the head height inside the segment;further,larger displacement of soil mass strengthens the arching effect.The theoretical results are consistent with the numerical results.
Water seepage occurs occasionally in the undersea shield tunnels or high groundwater level shield tunnels after long-term use. The influence of the seepage field on the tunnel top load cannot be ignored under any circumstanc.Seepage effects are rarely considered in the existing theory of loosening earth pressure.Therefore,this study proposes an analytical model to evaluate the loosening earth pressure,considering the seepage effects.The shield tunnel is in a steady seepage state;therefore,the pore pressure and seepage force around the tunnel are determined based on the conformal mapping of complex variable methods.According to the effects of the principal stress axes rotation,the lateral pressure coefficient of calculation model is obtained.Based on Terzaghi's assumption,an analytical solution of effective vertical stress is deduced using the limit equilibrium method.Seepage and principal stress axes rotation are analyzed to obtain the analytical solution.The analytical model is verified via a parametric analysis and using a FLAC numerical model.The result show that when the relative permeability between the soil and lining is high,the effective stress acting on the tunnel is high;permeability coefficient variations have negligible influence on the effective loosening earth pressure when it goes beyond a certain value.The effective loosening earth pressure decreases with the increasing tunnel seepage rate;a higher surface water head leads to lower effective loosening earth pressure at the top of the tunnel.The effect of arching will be weakened with increase in the head height inside the segment;further,larger displacement of soil mass strengthens the arching effect.The theoretical results are consistent with the numerical results.
引文
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[5]张琪昌,鹿兴,李栋.考虑土拱效应平移挡土墙地震主动土压力分布[J].天津大学学报:自然科学与工程技术版,2015,48(12):1063-1070.Zhang Qichang,Lu Xing,Li Dong.Distribution of seismic active earth pressure of retaining wallin translation mode considering soil arching[J].Journal of Tianjin University:Science and Technology,2015,48(12):1063-1070(in Chinese).
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[10]项彦勇.地下水力学概论[M].北京:科学出版社,2011.Xiang Yanyong.Fundamental Theory of Groundwater Mechanics[M].Beijing:Science Press,2011(in Chinese).
[11]童磊.软土浅埋隧道变形、渗流及固结性状研究[D].杭州:浙江大学建筑工程学院,2010.Tong Lei.Studies on Land Subsidence,Seepage Field and Consolidation Behavior of Soft Soil Around a Shallow Circular Tunnel[D].Hangzhou:College of Civil Engineering and Architecture,Zhejiang university,2010(in Chinese).
[12]吴祖松,刘新荣,梁波,等.水下隧道渗流特征及计算流域界限研究[J].岩石力学与工程学报,2014,33(12):2402-2408.Wu Zusong,Liu Xinrong,Liang Bo,et al.Study of seepage property and calculated watershed around underwater tunnels[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(12):2402-2408(in Chinese).
[13]吕伟华,缪林昌,王非.基于不完全土拱效应的土工格栅加固机制与设计方法[J].岩石力学与工程学报,2012,31(3):632-639.LüWeihua,Miao Linchang,Wang Fei.Mechanism of geogrid reinforcement based on partially developed soil arch effect and design method[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(3):632-639(in Chinese).
[2]Terzaghi K.Theoretical Soil Mechanics[M].New York:John Wiley&Sons,1943.
[3]Handy R L.The arch in soil arching[J].Journal of Geotechnical Engineering,1985,111(3):302-318.
[4]陈若曦,朱斌,陈云敏,等.基于主应力轴旋转理论的修正Terzaghi松动土压力[J].岩土力学,2010,31(5):1402-1406.Chen Ruoxi,Zhu Bin,Chen Yunmin,et al.Modified Terzaghi loozening earth pressure based on theory of main stress axes rotation[J].Rock and Soil Mechanics,2010,31(5):1402-1406(in Chinese).
[5]张琪昌,鹿兴,李栋.考虑土拱效应平移挡土墙地震主动土压力分布[J].天津大学学报:自然科学与工程技术版,2015,48(12):1063-1070.Zhang Qichang,Lu Xing,Li Dong.Distribution of seismic active earth pressure of retaining wallin translation mode considering soil arching[J].Journal of Tianjin University:Science and Technology,2015,48(12):1063-1070(in Chinese).
[6]Costa Y D,Zornberg J G,Asce M,et al.Failure mechanisms in sand over a deep active trapdoor[J].Journal of Geotechnical and Geoenvironmental Engineering,2009,135(11):1741-1753.
[7]Iglesia G R,Einstein H H,Whitman R V.Investigation of soil arching with centrifuge tests[J].Journal of Geotechnical and Geoenvironmental Engineering,2014,140(2):1-13.
[8]Atkinson J H,Mair R J.Loads on leaking and watertight tunnel linings,sewers and buried pipes due to groundwater[J].Géotechnique,1983,33(3):341-344.
[9]张冬梅,刘印,黄宏伟.软土盾构隧道渗流引起的地层和隧道沉降[J].同济大学学报:自然科学版,2013,41(8):1185-1190.Zhang Dongmei,Liu Ying,Huang Hongwei.Leakageinduced settlement of ground and shield tunnel in soft clay[J].Journal of Tongji University:Nature Science,2013,41(8):1185-1190(in Chinese).
[10]项彦勇.地下水力学概论[M].北京:科学出版社,2011.Xiang Yanyong.Fundamental Theory of Groundwater Mechanics[M].Beijing:Science Press,2011(in Chinese).
[11]童磊.软土浅埋隧道变形、渗流及固结性状研究[D].杭州:浙江大学建筑工程学院,2010.Tong Lei.Studies on Land Subsidence,Seepage Field and Consolidation Behavior of Soft Soil Around a Shallow Circular Tunnel[D].Hangzhou:College of Civil Engineering and Architecture,Zhejiang university,2010(in Chinese).
[12]吴祖松,刘新荣,梁波,等.水下隧道渗流特征及计算流域界限研究[J].岩石力学与工程学报,2014,33(12):2402-2408.Wu Zusong,Liu Xinrong,Liang Bo,et al.Study of seepage property and calculated watershed around underwater tunnels[J].Chinese Journal of Rock Mechanics and Engineering,2014,33(12):2402-2408(in Chinese).
[13]吕伟华,缪林昌,王非.基于不完全土拱效应的土工格栅加固机制与设计方法[J].岩石力学与工程学报,2012,31(3):632-639.LüWeihua,Miao Linchang,Wang Fei.Mechanism of geogrid reinforcement based on partially developed soil arch effect and design method[J].Chinese Journal of Rock Mechanics and Engineering,2012,31(3):632-639(in Chinese).
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