管幕预筑法中大直径顶管施工地表沉降研究

管幕预筑法顶管工程相比于传统管幕法顶管工程具有顶管间距小、顶管直径大等特点。目前对于密排大直径顶管的应用较少，对管幕密排顶管施工顺序和顶管施工地表沉降规律理论研究不足，密排顶管施工土体的变形趋势与单一顶管相差较大，传统的Peck公式预测地表沉降难以适用。为了解决密排顶管的施工顺序以及顶管施工地表变形规律，采用大型模型试验对三种典型的顶管施工方案进行试验，研究大直径密排顶管之间的相互影响作用和顶管施工过程中的地表变形特征。通过试验发现密排顶管之间不仅存在相互支挡现象，而且顶管与周围土体共同作用形成的管土拱效应对施工下排顶管形成“保护”，从三组模型试验方案来看，考虑管土拱效应的顶管施工方案管幕中轴线位置处地表沉降最大值仅为6.09 mm，小于其他两组方案，根据这一实验结果提出管土拱效应对于封闭管幕下排顶管的“保护”作用，确定管幕预筑法密排顶管施工最佳的顺序是先施工管幕上排顶管再施工管幕两侧以及下排顶管；同时改进Peck公式来预测密排顶管施工产生的横向地表沉降，改进的peck公式考虑了相邻顶管支挡与管土拱效应的支挡效应，修改Peck公式参数取值的具体办法，改进的peck公式预测结果与模型试验横向地表沉降曲线吻合良好。

Ground Surface Settlement Induced by Large Diameter Jacking-pipe Construction in Pipe-roof Pre-construction Method

Compared with the traditional pipe curtain method, the pipe-roof pre-construction method has the characteristics of small jacking pipe spacing and large jacking pipe diameter. At present, there are few applications for close-packed large-diameter pipe jacking. The theoretical studies on the construction sequence of close-packed pipe jacking and the surface settlement law of pipe jacking construction are insufficient. The deformation trend of soil in close-packed pipe jacking construction is quite different from that of single pipe jacking. The traditional Peck formula used to predict the surface settlement is difficult to apply. In order to figure out the construction sequence and deformation law of close-packed pipe jacking construction, a large-scale model test was conducted to study the three typical pipe jacking construction schemes. The interactions between close-packed large-diameter jacking pipes and the characteristics of ground deformation during pipe jacking construction were studied. Based on the test results, in the test scheme considering the pipe soil arching effect, the maximum surface settlement at the central axis of the pipe-roof was only 6.09 mm, which was smaller than the other two sets of schemes. There was not only mutual supports between the densely packed pipes, but also the pipe soil arching effects formed by the pipe joint and the surrounding soil providing a protection for the construction of the lower pipe. The best order of construction was first to construct the upper pipe and then to construct the pipe-roof on both sides and the lower row pipes. The ground surface settlement caused by close-packed pipe jacking construction was predicted by the improved Peck formula, which considered the supporting effect of soil arching between the adjacent pipes, and modified the specific methods of parameter selections. The prediction results of the improved Peck formula were in good agreements with the lateral surface settlement curves obtained by the model tests.