Mechanical characteristics of concrete pipes under the coupled effects of the pressure, seepage, and flow fields

Concrete drainage pipelines are typical underground concealed structures in urban, which are subjected to the synergistic effects of covering soil, live traffic, groundwater, and flow within the pipelines during their service life. The complex mechanical mechanisms involved in these interactions have not been fully understood. In this paper, stress-seepage coupled structure models for the pipe-soil and fluid models inside the pipes were separately established. With the help of the MpCCI (Mesh-based parallel Code Coupling Interface) multi-physics coupling software, the synergistic simulations of pressure, seepage, and flow fields of the concrete drainage pipes in time and space scales were innovatively realized, and the simulations were compared with the full-scale tests. Firstly, the mechanical characteristics of the concrete pipes under single filed and multiple fields were investigated. Subsequently, parametric analyses were conducted for factors including pipe diameter, burial depth, bedding strength, backfill strength, traffic load size, vehicle speed, groundwater level, fluid height, and flow velocity. The influences of these factors were ranked through an orthogonal experiment consisting of 27 working conditions. The results indicated that the order of influence of different fields on pipe stress from large to small under different fields was pressure field, multi-field, flow field, and seepage field, while the order of influence on pipe vertical displacement was pressure field, flow field, multi-field, and seepage field. When the nine factors varied from minimum design values to maximum design values, the maximum pipe stress increased by 83.6%, 97.5%, 60.8%, and 20.0% due to changes in pipe diameter, burial depth, traffic load, and bedding strength, respectively, while decreased by 17.0% and 21.4% with the increase of backfill strength and groundwater level. Vehicle speed, fluid height, and flow velocity had an impact of less than 2% on the maximum pipe stress. When the groundwater is upward from 0.8 m below the invert to 0.8 m above the crown, the maximum vertical displacement of the pipe is upward by 80.5%.