Abstract:

Migrating pingos formed along fault zone in permafrost north Tibetan Plateau, destructing bridge, culvert and oil pipeline. Here displacement and stress fields caused by migrating pingos and stresses of bended bridge pier were calculated by three dimensional finite element modeling based on field observation and laboratory tests, and breaking mechanism of bridge pier was analyzed after the numerical modeling. It is proved that expansion of migrating pingo can produce axis stress of 11 to -21 MPa, formed concentration of stresses and caused evident displacement and deviation of bridge pier. The bending and deviation further result in extensional stress of 61.9 to 64.6 MPa and compressional stress of -45.0 to -49.0 MPa within the bridge pier, exceeding strength limit of the bridge pier. And stress concentration forms in size change area of upper bridge pier with maximum extensional stress of 26 to 30 MPa and maximum compressional stress of -25 to -28.8 MPa. The maximum extensional stress concentrated in size change area also exceeds strength limit of the bridge pier, formed shear-extensional fractures of the Chumaerhe Bridge. Three dimensional numerical modeling on migrating pingo destructing bridge pier can provide important factors for designing bridge and protecting geological hazard in permafrost.

Key words: migrating pingo, heterogeneous freezing expansion, bridge pier, numerical modelling, north Tibetan Plateau