Lessons learned from the geotechnical design and construction of a temporary bridge on soft ground

A 45m long, single span temporary steel bridge was designed and constructed over a deep creek for an on-going bridge project on the east coast of Australia. This bridge was required to facilitate the construction of an 800m long permanent bridge in a flood plain. The subsurface condition comprises soft to firm Holocene clay and loose sand up to 20m in depth overlying a few metres of stiff Pleistocene clay overlying weathered rock. The original design of the foundation for the two abutments was a spread footing on a 500mm thick foundation rock with a layer of high strength geotextile on existing ground surface. Following the construction of the temporary bridge abutments before 4m fill was placed behind the abutments, measured abutment settlement under its self-weight were up to 55mm and 80mm at south and north abutments respectively. The measured settlement appeared to be on-going and much more was expected after the installation of the bridge deck and filling behind the abutments. Concerns were raised and the author was requested to review the geotechnical design of the abutments to address the concerns of the on-going and future large settlement. The author raised two major comments: (1) the global slope stability of the creek banks supporting the adjacent abutment and approach embankment was not checked and this was a major risk due to the deep soft compressible soil and the proximity of the abutments and approach embankment; (2) the consolidation settlement of the abutment under the temporary bridge and construction traffic load was not properly assessed. This paper will discuss the process of the redesign of the temporary bridge abutments and the subsequent construction monitoring to mitigate the risks of excessive ground/abutment displacement and slope failure.

Language

  • English

Media Info

  • Pagination: 555-8
  • Monograph Title: Proceedings of the 13th Australia New Zealand Conference on Geomechanics Perth, Western Australia, 1-3 April, 2019

Subject/Index Terms

Filing Info

  • Accession Number: 01714784
  • Record Type: Publication
  • Source Agency: ARRB Group Limited
  • ISBN: 9780994626103
  • Files: ITRD, ATRI
  • Created Date: Aug 26 2019 11:51AM