Field performance of large section concrete pipes cracking during jacking in Chongqing - A case study

摘要

Long-distance large-section pipe jacking inevitably encounters a variety of complex engineering problems in the construction process, one of which is the pipe concrete cracking during jacking. A large-area rupture and leakage occurred at pipe No. 61 during the large-section concrete pipe jacking adopted in the project studied in this paper. After a detailed field investigation and on-site pipe strain monitoring, the possible causes of pipe cracking were analysed. First, a direct compression failure of the pipes was ruled out. Additionally, a large number of pores were found inside the concrete fragments falling from pipe No. 61's site. Thus, we suspected that the pipe cracking was attributed to the conversion of the pipe's compressive stress into the concentrated tensile stress by the substantial pores inside the pipes, which resulted in a concrete tension fracture. The core sampling results of the pipes after monitoring confirmed that there were indeed plenty of small pores in multiple pipe concretes, while the strain monitoring results indicated that the compressive stress of the pipes during normal jacking had the potential to produce the tensile stress that could crack the concrete. Combining this with the jacking deviation monitoring curves, it could be deduced that the upper right side of the pipes was most prone to failing initially. This coincided with the rupture area of pipe section No. 61 but was also consistent with the prediction of pipe No. 60 cracking, thus proving the rationality of the pipe rupture cause hypothesis. Finally, no cracking occurred after improving the production quality of the pipes. This not only shows that the pipe quality is indeed the root cause of cracking but also effectively solves the engineering problems and provides an excellent reference for similar projects.