小浪底工程排沙洞环形预应力混凝土施工

小浪底水利枢纽工程的３条排沙洞，洞身７０％以上采用后张法无粘结预应力混凝土衬砌。其张拉系统的施工主要包括钢绞线的就位，固定，锚具槽，锚具及张拉设备的安装，张拉等步骤，施工工艺严谨。三维有限元分析结果表明，张拉时锚具槽附近将出现明显的应力集中，为此，采取了分步张拉，加箍筋等措施，达到了对预应力的控制，也避免了产生贯穿性裂缝。

Construction of ring pre-stressed concrete of desilting tunnel of Xiaolangdi Multipurpose Project

In three desilting tunnels of Xiaolangdi Multipurpose Project, over 70% tunnel wall were lined with non cohesive pre stressed concrete by the post tensioning method. The main construction processes of the tensioning system include the location and fixation of steel spiral rope, and the installation of anchorage groove, anchorage device and tensioning equipment. Its construction techniques are strict. According to the three dimension finite element analysis results, it showed that the obvious stress concentration occurs around the anchorage groove during the tensioning. For this reason, the measures of tensioning by stage and adding hoop reinforcement have been adopted to reach the control of pre stresses and avoid the occurrence of through cracks. In order to guarantee the performances of anti corrosion and abrasion resistance of anchorage cable and devices, the measures of casing pipe, closed element and other methods have been adopted. The experience of such lining structure adopted in the desilting tunnels of Xiaolangdi Multipurpose Project can be used in the other projects for reference.