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采用土体卸载条件下的塑性有限元模型,以苏州某地铁换乘站坑中坑为基本模型,系统研究了坑趾系数α对粉土坑中坑基坑支护结构内力的影响。结果表明,α变化对内外坑支护结构深层部位内力影响较为显著。外墙最大正负弯矩、最大正负剪力随α增大而减小,最大正负弯矩作用位置上升,外坑第三道支撑轴力随α增大急剧减小约30%左右;内墙最大负弯矩随α增大而减小,最大正弯矩却随α增大而增大,但最大正弯矩不到最大负弯矩的1/3,最大正负弯矩位置随α增大而上升,最大正负剪力均随α增大而减小,内坑第二道支撑轴力则随α增大显著减小。坑趾系数α变化对坑中坑深层土体应力场产生影响,当α超过0.75时影响趋于减缓。
The plastic finite element model under soil unloading condition was used to study the influence of pit-toe coefficient α on the internal force of pit-supporting structure in silt pit with a model of pit-in-pit in a subway transfer station in Suzhou. The results show that the variation of α has a significant effect on the internal forces in the deep part of the pit support structure. The maximum positive and negative bending moment of the external wall, the maximum positive and negative shear force decreases with the increase of α, and the maximum positive and negative moment position increases. The third support axial force of external pit decreases sharply by about 30% The maximum negative moment of internal wall decreases with the increase of α, while the maximum positive moment increases with α, but the maximum positive moment is less than 1/3 of the maximum negative moment. The maximum positive and negative moment positions follow α increases and increases, the maximum positive and negative shear force decreases with the increase of α, and the second support axial force of inner pit decreases with the increase of α significantly. The variation of pitting coefficient α has an impact on the stress field in deep soil pits. When α exceeds 0.75, the influence tends to slow down.