TRENCHLESS | PROJECT REPORT
COST-RISK TRADE-OFF PICKS TRENCHLESS
A microtunnelling option proved more cost-effective over an open-cut construction alternative for the overall project to install pipelines in a dense urban environment in Eugene, Oregon. The alternatives weighed and choice made, and the works execution, are discussed by Brendan O’Sullivan, Consor, and Glen Wheeler, J.W. Fowler Tunneling. Their paper to No-Dig Show 2026 is published here in an edited version, with permission of the North American Society for Trenchless Technology (NASTT).
Right: Geological section at College Hill pipelines project in Eugene, Oregon.
1. INTRODUCTION As part of a broader resilience upgrade, the Eugene Water & Electric Board (EWEB) is constructing two 17,000 m3 (3.75 million-gallon) prestressed concrete reservoirs at its College Hill site in Eugene, Oregon. A critical element of the project involves installing two mains lines - for water and storm flows, respectively - below a road intersection in a densely populated corridor that also holds utilities, and has other constraints. Ground surface disturbance had to be minimised from the selected construction method, which also had to be most cost-effective. Analyses of geotechnical conditions, community
Below: Tunnel cross-section.
impacts and cost-risk trade-offs led to selection of trenchless construction over open-cut method, which would have called for trench depths up to 9.2m (30ft), and into sandstone bedrock, to reach design grades. While microtunnelling is sometimes perceived as cost-prohibitive, in this case it proved to be the more
economical and lower-risk alternative when evaluated across total project cost, community disruption, and schedule reliability. The tunnelling works involved construction of two shafts and employing a remotely- operated Micro-tunnel Boring Machine (MTBM).
2. PROJECT SETTING The College Hill project is located within the City of Eugene in the southern portion of the Willamette Valley. The project corridor crosses beneath the intersection of Lincoln St and West 23rd Ave, a critical urban road and pedestrian intersection.
2.1 Suburban neighbourhood Community tolerance is low with regard to construction- related impacts such as noise, vibration, dust, and prolonged traffic disruption. Maintaining emergency vehicle access, pedestrian safety, and continuous traffic flow through the intersection were key considerations in evaluating the project corridor’s construction options. Public perception and stakeholder acceptance were treated as critical factors alongside cost, schedule, and technical feasibility.
2.2 Geology The project area is underlain by Willamette Valley alluvium overlying the Eugene Formation, as documented in the project geotechnical investigation. Subsurface exploration identified shallow bedrock across much of the alignment, with Eugene Formation sandstone and silty sandstone encountered at depths of approx 1.5m-3.0m (5ft-10ft) below existing grade. Unconfined compressive strength (UCS) testing indicated rock strengths ranging up to approximately 28 MPa (4,000 psi), with variable joint
20 | July 2026
All Images from authors’ original paper, courtesy of NASTT
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