软土地区钢顶管施工引起的地表变形规律

Ground deformation law of steel pipe jacking construction in soft soils

为研究软土地区钢顶管施工引起的地表变形规律,以东莞某输水工程为背景,分别采用预测公式、数值模拟和现场监测的方法对顶进过程中引起的地表变形进行了计算和监测,以期得到顶进过程中纵、横方向的地表变形规律。首先推导出了基于顶进间隙的地表变形预测公式并计算出顶管施工可能产生的最大竖向位移为14.1 mm,此变形量在规范允许路面沉降范围内(≤20.0 mm),无须进行土体加固等措施;然后采用数值模拟的方法建立有限元模型对顶进导致的地表变形进行了计算,并就减轻地表变形的方法进行了讨论;最后与现场监测的结果进行了对比分析。结果表明:3种方法得到的变形曲线形状除了顶管轴线处地表峰值位移(数值模拟数值为13.7 mm,现场监测为15.2 mm)有稍许差异外,整体基本一致;顶管顶进时,横向监测断面的沉降槽呈“V”形,最大沉降值在顶管中心轴线处,随着距离中心轴线越远,沉降值越小,最后趋于0;纵向监测断面呈倒“S”形,大致可分为顶进前土体的隆起,顶进中土体的沉降,顶进后土体轻微回隆,顶进后土体稳定4个阶段;在顶管施工前可以对地表变形进行预测和数值模拟计算,结合预测和模拟计算的结果,通过合理的设置顶推力、注浆压力以及必要的土层加固来控制土体的变形。提出的预测公式具有概念清晰、可操作性强的特点,在软土地区适应性好,后续类似工程可以采用。研究成果可为软土地区类似顶管工程施工诱发的地面沉降进行预测及变形控制提供科学参考。

In order to study the ground deformation law caused by steel pipe jacking construction in soft soil area,prediction formula,a water conveyance project in Dongguan was taken as the background,and numerical simulation and field monitoring methods were adopted to calculate and monitor the ground deformation caused by the jacking process,so as to obtain the vertical and horizontal ground deformation law during the jacking process.Firstly,the ground deformation prediction formula was deduced to consider the jacking clearance,and then the maximum vertical displacement 14.1 mm generated by pipe jacking construction was calculated.This deformation is within the allowable range of road settlement specification(≤20.0 mm),and there is no need to take measures such as soil reinforcement.Secondly,the finite element model was established by numerical simulation to calculate the ground deformation caused by the jacking,and the method to reduce the ground deformation was discussed.Lastly,the results from the above three methods were compared with those of field monitoring.The final results show that the shape of deformation curves obtained by the three methods is basically the same,except that the ground peak displacement at the pipe jacking axis(13.7 mm in numerical simulation and 15.2 mm in field monitoring)is slightly different.When the pipe jacking is carried out,the sedimentation tank of the transverse monitoring section is V-shaped,and the maximum settlement value is at the central axis of the pipe jacking.As the distance from the central axis increases,the settlement value decreases and eventually approaches 0.The longitudinal monitoring section shows an inverted“S”shape,which can be roughly divided into four stages:uplift of soil before jacking,settlement of soil in jacking,slight uplift of soil after jacking and stability of soil after jacking.Before pipe jacking construction,how to get the ground deformation is very necessary.Combined with the results of prediction and simulation,the soil deformation is controlled by setting the top thrust,grouting pressure and necessary soil reinforcement.The prediction formula presented in this paper has the characteristics of clear concept and strong operability,has good applicability in soft soil areas and can be used in similar projects in the future.The research results in this paper can provide scientific reference for ground settlement prediction and deformation control induced by similar pipe jacking projects in soft soil areas.