基于强度折减法的三维边坡稳定性与破坏机制
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摘要
基于强度折减技术的三维弹塑性有限元法是当前较为有效的边坡稳定性评价方法,但很少应用于复杂地质环境及负载条件下的三维边坡稳定性与破坏机制分析。拓展这一方法,利用典型算例,探讨了单元尺寸、边界条件、土体强度、局部超载和地震荷载等因素对三维边坡稳定性及潜在滑动面的影响;在此基础上,着重研究含软弱夹层及地下水的复杂三维边坡在负载条件(坡顶局部超载及地震荷载)下的破坏模式及滑动机制。结果表明:随着黏聚力的增加,潜在滑坡体的剪出位置远离坡脚,滑坡后沿远离坡肩,滑坡深度加深;坡顶超载强度较低时,边坡表现为整体破坏模式,而高超载强度下表现为局部地基破坏;考虑地下水后边坡的稳定性显著下降,且潜在滑动面加深,滑坡体体积有所增大。含软弱夹层的三维边坡,其潜在滑动面呈折线型,当受超载作用时,其破坏模式和滑动机制与地震荷载作用下不同:前者为竖向剪切和水平错动的联合作用,而后者为软弱夹层水平错动起主导作用。
Three-dimensional elasto-plastic finite element method(EP-FEM) based on strength reduction technique is an effective numerical method to evaluate the slope stability.However,this approach is seldom employed to analyze the stability and failure mechanism for a 3-D slope under complex geological environments and local surcharge.The strength reduction numerical method is extended by combination with several typical cases.The effect of many factors,such as element size,boundary condition,soil strength,local surcharge on the slope top and the seismic loads,on the slope stability and the potential sliding surface is discussed in detail.On the basis of this,a typical 3-D slope including soft interlayer and ground water is investigated to elucidate the failure mode and sliding mechanism under the framework of strength reduction FEM,local surcharge on the slope top and seismic loads are also considered in the present analysis.The calculated results indicate the following understandings: 1)With an increase of cohesion,locations of potential slip surface and out-slip point are respectively far away from the toe and the top of slope;2)An overall slope failure is observed under a low surcharge,while a local foundation failure is found under a high surcharge on the top of slope;3)When the groundwater is considered,the slope stability reduces,the slip depth and the volume of sliding body increase;4)The potential sliding surface shows a fold-line in a 3-D slope containing a soft interlayer,the failure mode and sliding mechanism of the slope is completely different under two cases as local surcharge on the slope top and seismic loadings.For the former,a combined failure mode with vertical shear and horizontal dislocation is observed,while for the latter a horizontal dislocation along the soft interlayer is found.
Three-dimensional elasto-plastic finite element method(EP-FEM) based on strength reduction technique is an effective numerical method to evaluate the slope stability.However,this approach is seldom employed to analyze the stability and failure mechanism for a 3-D slope under complex geological environments and local surcharge.The strength reduction numerical method is extended by combination with several typical cases.The effect of many factors,such as element size,boundary condition,soil strength,local surcharge on the slope top and the seismic loads,on the slope stability and the potential sliding surface is discussed in detail.On the basis of this,a typical 3-D slope including soft interlayer and ground water is investigated to elucidate the failure mode and sliding mechanism under the framework of strength reduction FEM,local surcharge on the slope top and seismic loads are also considered in the present analysis.The calculated results indicate the following understandings: 1)With an increase of cohesion,locations of potential slip surface and out-slip point are respectively far away from the toe and the top of slope;2)An overall slope failure is observed under a low surcharge,while a local foundation failure is found under a high surcharge on the top of slope;3)When the groundwater is considered,the slope stability reduces,the slip depth and the volume of sliding body increase;4)The potential sliding surface shows a fold-line in a 3-D slope containing a soft interlayer,the failure mode and sliding mechanism of the slope is completely different under two cases as local surcharge on the slope top and seismic loadings.For the former,a combined failure mode with vertical shear and horizontal dislocation is observed,while for the latter a horizontal dislocation along the soft interlayer is found.
引文
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[2]Chugh K A.On the Boundary Conditions in Slope Sta-bility Analysis[J].International Journal for Numericaland Analytical Methods in Geomechanics,2003,27:905-926.
[3]Griffiths D V,Marquez R M.Three-Dimensional SlopeStability Analysis by Elasto-Plastic Finite Elements[J].Geotechnique,2007,57(6):537-546.
[4]方建瑞,许志雄,庄晓莹.三维边坡稳定弹塑性有限元分析与评价[J].岩土力学,2008,29(10):2667-2672.Fang Jianrui,Xu Zhixiong,Zhuang Xiaoying.Ap-praisal and Analysis of Three-Dimensional Slope Sta-bility Based on Elastoplastic FEM[J].Rock and SoilMechanics,2008,29(10):2667-2672.
[5]刘红帅,年廷凯,万少石.三维边坡稳定性分析中的边界约束效应[J].吉林大学学报:地球科学版,2010,40(3):638-644.Liu Hongshuai,Nian Tingkai,Wan Shaoshi.Effect ofBoundary Constraint Condition on the Stability Analy-sis of 3DSlope[J].Journal of Jilin University:EarthScience Edition,2010,40(3):638-644.
[6]万少石.涉水边坡稳定性的三维强度折减有限元分析[D].大连:大连理工大学,2009.Wan Shaoshi.Three-Dimensional Slope StabilityAnalysis by Shear Strength Reduction Finite ElementMethod(SSR-FEM)Under Drawdown Condition[D].Dalian:Dalian University of Technology,2009.
[7]Wei W B,Cheng Y M,Li L.Three-Dimensional SlopeFailure Analysis by the Strength Reduction and LimitEquilibrium Methods[J].Computers and Geotechnics,2009,36:70-80.
[8]Manzari M T,Nour M A.Significance of Soil Dilatan-cy in Slope Stability Analysis[J].Journal of Geotech-nical and Geoenvironmental Engineering,2000,126(1):75-80.
[9]Hibbitt,Karlsson,Sorensen,et al.ABAQUS/Stan-dard User’s Manual;ABAQUS/CAE User’s Manual;ABAQUS Keywords Manual;ABAQUS Theory Man-ual;ABAQUS Example Problems Manual;ABAQUSVerification Manual[M].[s.l.]:HSK Corporation,2005.
[10]万少石,年廷凯,蒋景彩.边坡稳定强度折减有限元分析中的若干问题[J].岩土力学,2010,31(7):2283-2288.Wan Shaoshi,Nian Tingkai,Jiang Jingcai.Discus-sion on Several Issues in Slope Stability AnalysisBased on Shear Strength Reduction Finite ElementMethods[J].Rock and Soil Mechanics,2010,31(7):2283-2288.
[11]郑宏,李春光,李焯芬,等.求解安全系数的有限元法[J].岩土工程学报,2002,24(5):626-628.Zheng Hong,Li Chunguang,Lee Chackfan,et al.Finite Element Method for Solving the Factor of Safe-ty[J].Chinese Journal of Geotechnical Engineering,2002,24(5):626-628.
[12]段庆伟,王玉杰.试论强度折减有限元法变形参数折减的必要性和相应判据[J].水利学报,2008,39(11):1251-1256.Duan Qingwei,Wang Yujie.On the Necessity of Re-ducing Deformation Parameters for Strength-Reduc-tion FEM and Corresponding Criteria[J].Journal ofHydraulic Engineering,2008,39(11):1251-1256.
[13]Chen Z,Mi H,Zhang F,et al.A Simplified Methodfor 3D Slope Stability Analysis[J].CanadianGeotechnical Journal,2003,40(3):675-683.
[14]Chen Z,Wang J,Wang Y,et al.A Three Dimen-sional Slope Stability Analysis Method Using the Up-per Bound Theorem:Ⅱ:Numerical Approaches,Ap-plications and Extensions[J].International Journal ofRock Mechanics&Mining Sciences,2001,38:379-397.
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