研究目的:在二维有限元极限平衡法基础上建立基于强度储备概念和主滑方向的三维有限元极限平衡法，明确其空间任意形状滑动体安全系数定义及其物理意义、安全系数与主滑方向的关系和可行性等关键问题。利用积分中值定理给出其空间任意形状滑动面的安全系数定义，表征空间滑面内局部安全系数和整体抗滑稳定安全系数的内在联系。
研究结论:( 1) 有限元极限平衡法得到的稳定分析结果与刚体极限平衡法和有限元强度折减法保持一致，将该法应用于空间边坡稳定安全评价是可行的; ( 2) 当计算坡体轴向长度较短时，滑坡体三维效应明显，三维稳定安全系数明显高于二维稳定安全系数; 当坡体轴向长度较长时，三维稳定分析结果与二维稳定分析结果趋于一致。
Research purposes: As an extension of two － dimensional FEM limit equilibrium method，the three －dimensional FEM limit equilibrium method based on the concept of strength reduction and the unique sliding direction，is presented． The definition and physical meaning of factor of safety ( FOS) ，the relationship between FOS and unique sliding direction are clarified as well as the application in earth and rock slope． On the basis of mean value theorem of integrals，the FOS corresponding to sliding body of arbitrary shape is defined． The relationship between partial FOS and overall FOS can be demonstrated by the definition of factor of safety in this approach．
Research conclusions: ( 1) the factor of safety and critical sliding surface for soil and rock slopes calculated from the proposed approach are in good agreement with those from 3D rigid limit equilibrium method and 3D shear strength reduction method． ( 2) 3D problem shouldn＇t be modeled as a 2D one owing to obvious spatial effect when the axial length of slope is short，the factor of safety obtained by 2D method is conservative． However，the stability analysis for 3D problem can be approximated by a corresponding 2D problem when the axial length of slope reaches a certain value．
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