电力盾构隧道近接侧穿施工时立交桥桩基的变形特征分析

Analysis of the Deformation Characteristics of the Pile Foundation of the Overpass in the Approaching Construction of the Power Shield Tunnel

城市隧道近接施工对既有建筑物安全的影响是工程中必须关注的问题。以河北某市电力隧道盾构施工侧穿既有城市立交桥桩基为工程依托,隧道距最近的两桩基的水平距离为1.68 m和1.73 m,为确保在隧道施工过程中邻近既有立交桥桩基的安全,采用三维有限差分数值分析的方法,研究盾构开挖对临近桩基及地层沉降稳定性的影响。研究结果表明:同一承台下靠近隧道一侧的桩基桩顶沉降大于远离隧道一侧的桩基,桩顶沉降随着盾构接近逐渐增大,当隧道开挖经过桩基4m左右时,竖向变形达到最大,随后趋于稳定。水平方向桩身向隧道中轴线变形,且距离盾构隧道越近桩基的水平位移越大,最大变形位于隧道拱顶上方1/2D处。隧道开挖通过桩基的过程中,桩身变形从开始增加到趋于稳定,影响范围为桩前后各8地表沉降从隧道中轴线处向两侧逐渐减小,沉降曲线呈凹槽型,沉降槽宽度在60~80m之间。

The impact of the approaching construction of urban tunnels on the safety of existing buildings is an issue that must be addressed in the project.As for the shield-driven power tunnel construction adjacent to the pile foundation of existing urban overpass in a city of Hebei,the horizontal distance between the tunnel and the nearest two pile foundations is 1.68 m and 1.73 m respectively.In order to ensure the safety of adjacent pile foundation in the construction process of power tunnel,three-dimensional finite difference numerical analysis method is used to study the influence of shield excavation on the stability of adjacent pile foundation and stratum settlement.The results show that:for the same pile cap the settlement of pile top near the tunnel side is larger than that of pile top far away from the tunnel side.The settlement of pile top increases gradually with shield approaching.When the tunnel excavation passes through the pile foundation about 4 m,the vertical deformation reaches the maximum,and then tends to be stable.The pile body in the horizontal direction is deformed towards the central axis of the tunnel,and the closer the shield tunnel is to the pile foundation,the larger the horizontal displacement value is,and the maximum deformation occurs at 1/2 D above the tunnel vault.In the process of tunnel excavation passing through the pile foundation,the deformation of pile body increases at the beginning and then tends to be stable,the influence range is about 8 m before and after the pile.The surface settlement is gradually reduced from the central axis of the tunnel to both sides,and the settlement curve is in the form of a trough with a width of 60-80 m.