南水北调超大钢筒混凝土管道结构安全评估

我国从2006年开始首次把直径4 m的超大预应力钢筒混凝土管道(简称PCCP)用于南水北调中线京石段供水工程中.基于PCCP结构安全使用100年的要求,针对南水北调中线PCCP项目遇到的管芯裂缝和预应力松弛等对结构安全影响如何评估的技术难题,采用现场实体管道试验(裂缝PCCP抗裂外压承载力试验、PCCP现场断丝原型试验、预应力钢丝松弛PCCP内水压承载试验)和非线性有限元数值模拟等方法对PCCP结构的承载能力进行了系统分析研究.结果表明:管芯出现一条或少量细小裂纹,不需修补或用水泥净浆涂刷即可;较宽的裂缝,可按规定程序进行修补;出现多条纵向裂缝、或环向裂缝长度超过周长的裂缝、或出现十字交叉裂缝的管芯为废品管.预应力钢丝作为PCCP的主要承载体,应确保钢丝质量,避免断丝.有关部门基于研究结果和提出的工程处置建议,并借鉴国外先进国家PCCP制造厂商经验,对工程中已经出现裂缝的PCCP进行了全方位安全评估,对不满足管芯外表面裂缝控制要求的管道进行报废处理(该工程共计报废35根),以满足工程安全需要;对一些裂缝影响较小的PCCP可用在埋深较浅的地段,从而节省了工程成本.最后阐述了下一步需继续研究的工作.

Study on structural safety evaluating technique for pre-stressed concrete cylinder pipe (PCCP) in the South-to-North Water Diversion Project

The PCCP with 4 meter in diameter has been applied in the Beijing to Shijiazhuang reach of the South-to-North Water Diversion Project for the first time since 2006 in China. Based on the safe use of PCCP engineering structure for 100 years, aiming at the technology problems of how to evaluate safety influence on PCCP with broken wires and relaxation of prestressing in the South-to-North Water Diversion Project, the bearing capacity of PCCP has been studied with the methods of actual PCCP test (anti-crack external pressure test with cracks, anti-crack external pressure test with broken wires and anti-crack internal pressure test with relaxation of prestressing) and non-linear finite element numerical simulation funded by the National Scientific and Technological Support Plan and the Nation Natural Science Foundation Project. The results show that the PCCP with a chip or a few small cracks needn′t repair or just need brush cement paste;the PCCP with wide cracks should be repaired according to codes;and the PCCP with a number of vertical cracks or cross cracks and the PCCP with circumferential cracks longer than circumference are judged to be waste pipes. As the main bearing body, the quality of prestressed wires shoud be ensured to avoid broken wires. The impact assessment on PCCP with broken wires should be analyzed with actual test results. Based on the test results and engineer suggestions, and learning from the advanced foreign experiences, the safety assessment of PCCP with cracks has been proposed. The PCCP which does not satisfy the outer surface crack control requirements should be abandoned to meet the security needs (a total of 35 PCCP have been abandoned in this project), and the PCCP which has little cracks is used in the relatively shallow depth region to save the cost of the project. Finally, the next work which is needed to do is described in the paper.