SHI Yanke1，ZHANG Dekang1 ，ZHANG Jiarui2，ZHANG Duoxin1，KE Wang1
1．College of Civil Engineering and Communications，North China University of Water Resources and Electric Power，Zhengzhou 450045，Henan，China;
2．Yunnan Institute of Water ＆Hydropower Engineering Investigation Design and Research，Kunming 650021，Yunnan，China
Objectives of the study
The determination of a reasonable length of pipe section is one of the key issues in the design，construction and operation of a large inverted siphon structure．Taking a large inverted siphon to be built as the research object，and considering the influences of pipe-soil interaction，backfill material consolidation，foundation deformation and other factors，the threedimensionalfinite element models of inverted siphon with pipe section lengths of 15 m，20 m and 25 m are established respectively，and the nonlinear mechanical analyses are carried out considering the load condition combination during the operation period．The overall settlement of the inverted siphon，the vertical deformation of the pipe body，the stress and the opening amount of the pipe section of the three kinds of pipe section lengths are compared and analyzed，and on this basis，the reasonable pipe section length is proposed．Simultaneously，the stress analysis is also carried out with the proposed length of the pipe section，and the location where it is prone to damage is pointed out and the corresponding structural measures are put forward to provide reference forthe design and construction of the inverted siphon to be built and similar engineering practices．
Conclusions
This article establishes a nonlinear three-dimensional finite element model for the interaction between pipes and soil. From the perspectives of settlement, deformation, and stress, it explores the reasonable pipe joint length and stress distribution state of a large inverted siphon structure to be built in a certain area. The main conclusions are as follows: (1) It is appropriate to choose a reasonable pipe joint length of 20m for the inverted. (2) The vertical settlement of the pipe section directly below the river is relatively large, and the opening and deformation of the water stop connections on both sides are the greatest, which is prone to damage. Therefore, it is advisable to replace the water-tight seal. (3) The concrete inside the water hole of the pipe section is subjected to significant tensile stress. Therefore, the partition, side wall, and bottom plate of the inverted siphon pipe structure should be appropriately reinforced to avoid cracking of the pipe concrete.