盾构近距侧穿高架桥桩的施工力学行为研究

 针对合肥地铁1号线盾构近距侧穿城市高架桥桩施工存在的巨大安全隐患，基于桥桩结构耦合弹簧力学计算原理与有限差分方法，分析盾构推进过程中不同工况下桥桩结构受力、水平变形、地层沉降的变化规律，探讨桩实体结构单元弯矩、剪力计算方法的可行性，研究表明：(1) 盾构近距(最近距离0.63 m)侧穿施工对高架桥桩产生较大影响，其影响程度与盾构施工工况位置密切相关，且双隧洞盾构依次掘进对高架桥桩的力学行为影响具有叠加效应；(2) 随着盾构逐步接近桩体，桩弯矩、剪力、位移不断增大，叠加后的最大弯矩、剪力和水平位移分别为700.5 kN?m，159.6 kN，2.39 mm，位于右隧洞开挖盾构刀盘已侧穿穿越第二排桩，而盾尾刚进入第一排桩对应工况；(3) 千斤顶推动盾构机前行时，在盾尾衬砌管片外围形成建筑空隙，是引起地层损失的主要原因；(4) 桥桩实体结构单元变形挠曲方程通过桩位移离散点监控数据拟合，由此计算盾构推进各工况高架桥桩的弯矩和剪力，经典案例验证表明，桥桩实体结构的弯矩和剪力计算方法可行。

MECHANICAL BEHAVIOURS OF A SHIELD TUNNEL ADJACENT TO EXISTING VIADUCT PILE FOUNDATIONS

The metro line 1 in Hefei is in a close distance to piles of a viaduct foundation. Shield tunneling of the metro line 1 could therefore affect the safety of the piles of the viaduct. The stresses and the horizontal deformation of the piles and the ground settlements under different working conditions during the process of shield advancing were analyzed based on the mechanical principle of coupled springs for bridge-pile structures and the finite difference method. Close-distance shield tunneling with the nearest distance of only 0.63 m was found to have great effect on viaduct piles and the magnitude of the effect was closely related to the position of shield machine. The effects were superimposed upon the shield advancing of the twin tunnels in succession. As the shield was gradually close to the piles，the bending moments，the shear forces and the displacements were increased continuously. The maximum superimposed values of the bending moments，the shear forces and the horizontal displacements were 700.5 kN?m，159.6 kN and 2.39 mm respectively and were occurred when the head of the shield just passed the second row of piles and the shield tail just entered the first row of piles in the right tunnel. The space formed at the peripheral of lining segments in the rear of shield tail was found to be the main cause of the ground loss when jack pushed forward the shield machine. The flexural equation of piles was fitted by the displacements from the monitoring of piles. The bending moments and shear forces of piles in various advancing steps were thus calculated and the calculation method was verified by a case study.