南水北调中线穿黄工程二次衬砌预应力环形张拉施工技术

南水北调中线穿黄工程地下隧道埋深大，达到50 m，从南向北分别穿过邙山和黄河漫滩，属于有压力承水隧洞。为了达到隧洞结构的安全要求，采用预应力混凝土保证通水过程的结构安全。隧道先由盾构法施工、管片拼装成型，再进行二次衬砌混凝土浇筑，在混凝土内部预埋波纹管，穿钢绞线对已浇筑的混凝土结构进行环形张拉预应力施工。介绍环形张拉的施工工艺、技术要求、重难点及处理技术，并通过模型计算及数据建立得出钢绞线伸长值和摩阻因数的关系。实践证明： 南水北调中线穿黄工程运用二次衬砌预应力环形张拉技术能够满足正常输水对结构的要求，确保输水工程的安全。

Technology for Circular Pre stress Tensioning of Secondary Lining of Tunnels: Case Study on Yellow River crossing Tunnel on Central Route of South to north Water Transfer Project

The Yellow river crossing tunnel on the central route of south to north water transfer project is a pressured water transfer tunnel. The tunnel is excavated by shield machines, with the segment lining as the primary reinforcement. Pre stressed cast in situ concrete lining is installed for the tunnel as the final lining so as to ensure the safety of the tunnel structure. Pre stressing ducts are embedded in the cast in situ lining concrete, steel stands are installed and circular tensioning is made to achieve the pre stressing of the lining concrete. In this paper, the process, technical requirements, key points and countermeasures for the tensioning are presented. The relationship between the extended length of the steel strands and the friction coefficient is obtained by means of model calculation and data setting. The practice shows that the circular tensioning technology used in Yellow river crossing tunnel can meet the requirements of safety of the water transfer structure. 