城市浅埋软岩隧道施工沉降分析及对策

SETTLEMENT CHARACTERISTICS OF TUNNEL EXCAVATION AT SHALLOW DEPTH IN SOFT ROCK AND COUNTERMEASURES

浅埋软岩隧道施工沉降变形控制是浅埋地下工程面临的关键难题,其中最基础的内容是对开挖引起的沉降变形规律的掌握。通过对新建龙岩至厦门铁路石桥头隧道地表沉降变形观测分析,将地表沉降变形划分为三个主要阶段:初始沉降阶段、加速沉降阶段和减速沉降阶段;结合隧道拱顶沉降监测结果,得出浅埋软岩隧道地表沉降与拱顶沉降正相关的结论。隧道开挖对掌子面前后纵向地表沉降的主要影响范围分别为1.5D和3D(D为开挖跨度);横向地表沉降影响范围包括隧道中线两侧各4D的范围,地表建(构)筑物受到较大影响包括隧道中线两侧各2D的范围。针对地表和拱顶沉降过大,采取全断面超前预注浆方案进行处理,监测结果显示全断面超前预注浆能有效控制拱顶下沉和地表沉降量,收敛值减小则不显著,说明该方案达到了控制沉降变形的目的。

The control of settlement-deformation of shallow tunnel in soft rock during operation is a difficult task.The most basic content is to master the law of settlement-deformation induced by excavation.This paper presents the observation and analysis of the surface subsidence deformation at Longyan railway tunnel.The deformation of surface subsidence versus time is divided into three main phases： the initial settlement stage,the accelerated settlement stage and the decelerated settlement stage.Combining the results of sedimentation monitoring of the tunnel vault,the positive correlation of surface subsidence and sedimentation of the tunnel vault is concluded.The influenced ranges of the tunnel excavation in front of and behind of the work face are 1.5D and 3D respectively,where D is the tunnel span.The influenced ranges of traverse are 4D in both sides of the center line.The influenced ranges of the structures are 2D in both sides of the center line.Due to large ground and vault settlements were predicted,a whole section pre-grouting was adopted to prevent the large settlements.Monitoring results indicate that the whole section pre-grouting can reduce the ground and vault settlements effectively.Convergence reduction is not markable.The scheme achieved the aim of settlement reduction.