深基坑隔离桩对坑外既有隧道保护效果分析

Protection effect analysis of isolated piles for deep foundation pit on existing tunnel outside the pit

依托南昌市某深基坑开挖时采用隔离桩保护临近既有地铁隧道工程,采用ABAQUS有限元数值建模并结合实测数据,研究隔离桩在基坑开挖时对坑外既有地铁隧道的保护效果。通过建立多组有限元模型,研究基坑开挖时隔离桩在不同水平位置和不同桩顶埋深条件下既有隧道衬砌内力、直径变形情况。研究结果表明:隔离桩水平位置对隧道衬砌的内力影响较为明显,隔离桩离隧道越近,隔离桩对既有隧道的保护效果越好;设置隔离桩能明显减小既有隧道衬砌的变形,且隔离桩对其竖向变形影响小于对其水平变形的影响;埋入式隔离桩隔离效果在一定程度上优于非埋入式隔离桩,在实际工程中可以采用埋入式隔离桩,适当减小桩身长度,降低工程造价。

The isolated pile technique was adopted in a practical foundation project in Nanchang.Based on this project,numerical modeling simulations built with ABAQUS were combined with the observed data to study the protection effect of isolated piles on adjacent subway tunnel when the foundation pit was proceeded.The influences of horizontal location as well as buried depth of the isolated piles on internal stress and diameter variation of lining in existing tunnel during excavation were studied,based on the analysis on several sets of numerical models.A significant influence of the horizontal location on internal stress of the lining has been observed,a shorten gap of the isolated piles to the tunnel implied an improved protection effect.In addition,the deformation of the lining could be greatly suppressed by setting the isolated piles and more prominent effect on horizontal deformation compared with that on vertical direction.A further analysis indicated that the buried isolated piles performed better than the exposed ones.In general,the buried isolated piles with shortened pile length could be used in practical engineering to reduce the project cost.