用有限元强度折减法求边(滑)坡支挡结构的内力

CALCULATION OF INNER FORCE OF SUPPORT STRUCTURE FOR LANDSLIDE/SLOPE BY USING STRENGTH REDUCTION FEM

边(滑)坡体的破坏属于破坏力学范畴,当滑面上每点都达到极限应力和极限应变状态时,材料进入破坏,此时岩土体抗剪强度得到充分发挥,这就是破坏力学中的破坏准则。通常当有支挡结构与岩土介质共同作用时,滑面上土体一般不处于极限平衡状态,而可能处于弹性平衡或者局部塑性极限平衡状态。这种受力状态不是设计情况下的受力状态。多年来,岩土工程设计一直采用极限状态设计方法,即传统方法中计算得到的支挡结构上的岩土侧压力是在坡体整体破坏且岩土体强度充分发挥时的岩土侧压力,也就是土体处于极限平衡状态且支挡结构有充分位移时作用在支挡结构上的岩土压力,按此设计既能保证坡体安全,又能最大限度地节省经费。因此,采用有限元强度折减法来考虑岩土介质与支挡结构的共同作用时也应遵循这一原则,即要求作用在支挡结构上的岩土侧压力与传统方法计算得到的岩土侧压力大体相当,在此条件下根据岩土介质与支挡结构的共同作用来确定支挡结构的内力。按照此原则,采用有限元强度折减法,不但得到了滑坡推力的大小和分布,而且通过有限元桩-土共同作用模型计算得到了抗滑桩的弯矩和剪力,并与传统方法进行了比较。算例表明采用有限元强度折减法来计算抗滑桩的内力是可行的,该方法增大了支挡结构设计的可靠性和经济性。

The failure of landslide/slope belongs to the category of failure mechanics. When the stress and strain of failure surfaces reach the limited state and the shear strengths are fully utilized, the slope failure occurs at the same time, which is the failure criterion of slope failure mechanics. Usually, the soil does not reach the limited state completely when there is interaction between soil and support structure, instead, some soil is in the elastic state and some soil is in plastic limited state. This stress state is not the design state. The design method of limited state is adopted in geotechnical engineering for many years, which utilizes the soil shear strength fully and assume the soil to reach the plastic limited state completely, so that a safe and economic structure is made. This principle should be followed when the internal forces of support structure is calculated by FEM, and the lateral earth pressure computed by FEM should be equal to the earth pressure by traditional limited equilibrium method. Under this condition, the interaction between the soil and support structure is considered. According to this principle, the shear strength reduction FEM is adopted to analyze the interaction between soil and support pile with prestressed cable. The thrust distribution in landslide and internal forces of support pile are obtained with the c-tanφ reduction. Through a series of case studies, the applicability of proposed method is clearly exhibited.