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East Side Combined Overflow (ESCSO)

As a highly important measure in Portland, USA, the East Side Combined Sewer Overflow (ESCSO) is devised to significantly curtail overflows resulting from sewage and floods. The “ESCSO" project extends from the Insley St. and McLoughlin Blvd. area running north along the bank of the Willamette River to the West Side CSO facility on Swan Island. Construction involves the excavation and supporting of an 8,800 m long and 26 to 50 m deep tunnel with 6.70 m internal diameter. It also relates to the setting up of 7 separate diaphragm wall shafts along the route as well as the product ion of a total of 3,100 m long micro-tunnelling and trench work sections to divert the existing sewers into the CSO Tunnel. The tunnel is being driven with the aid of a hydro-shield TBM. The tunnel is mainly lined (85 %) with steel fibre reinforced segments, which are being used for the first time in the USA. Towards this end during the planning phase extremely detailed load case analyses as well as extensive series of tests were undertaken. The expected geological and hydrological conditions for the ESCSO Tunnel are governed by the "Troutdale Formation'; which can be described as follows:

  • Sand/silt with only occasional boulders (up to 0.76 m)
  • Gravel layers comprising medium-dense, poorly graded gravel, stones and scattered boulders in a sandy to silty matrix
  • Embedded lentils of silt, fine sand and sand
  • Groundwater levels 15 to 24 m above the tunnel roof with seasonal fluctuations depending on the surface contour and distance from the Willamette River.

Once completed the CSO will accept the discharge from 14 existing flood and waste water sewers and divert it into the Willamette River.


  • Country: USA
  • Region: Portland, Oregon
  • Tunnel utilization: Utility
  • Type of utilization: Combined Sewer Tunnel
  • Client: Bureau of Environmental Services, Portland
  • Consulting Engineer: Parsons Brinckerhoff
  • Contractor: Bilfinger Berger AG
  • Main construction method:  Trenchless
  • Type of excavation: Shield machine (SM)
  • No. of tubes: 1
  • Tunnel total length: 8,913 m
  • Cross-section: 6.70 m (internal diameter), 7.74 m (shield diameter)
  • Contract Volume: approx. 286 mill. euros
  • Construction start/end: 2006 till 2011
  • Opening: 2011