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Evergreen Line Rapid Transit Project: Subsurface Conditions and Geotechnical Challenges

J Pellett

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: CASE HISTORIES - IV Miscellaneous

ABSTRACT: The Evergreen Line Rapid Transit Project (ELRT) is an 11 km extension of the SkyTrain system through Burnaby, Coquitlam and Port Moody in the Lower Mainland of British Columbia, Canada. This paper discusses the subsurface conditions and geotechnical challenges encountered along the elevated and at-grade portions of the alignment, which total approximately 9 km in length. A bored tunnel comprises the remaining 2 km of the alignment but is not discussed in the paper. The surficial geology of the area and geotechnical conditions along the ELRT corridor are complex and highly variable. In the southwestern (Burnaby) part, the alignment crosses Pleistocene (ice-age) uplands comprised of dense glacial till and glaciofluvial sediments; in the central (Port Moody) part the route crosses overlapping debris fans underlain by soft marine and glaciomarine sediments; and in the eastern (Coquitlam) part the route ascends a raised marine delta which consists of coarse granular deposits underlain by interlayered sand, silt and clay. The geotechnical challenges related to subsurface conditions encountered during construction in each of these sections are described; these challenges included obstructions (boulders), artesian/confined groundwater, compressible soils, liquefiable soils, variable fill and impacts to adjacent utilities and infrastructure. Due to the highly variable and challenging soil conditions, a number of structural and ground improvement techniques were employed in areas underlain by liquefiable soils to mitigate potential post-seismic settlements and lateral spreading of the foundations.

RÉSUMÉ: Le projet Evergreen Line Rapid Transit (ELRT) est une extension de 11 km du système SkyTrain grâce à Burnaby, Coquitlam et Port Moody dans le Lower Mainland de la Colombie-Britannique, Canada. Cet article traite des conditions du sous-sol et les défis géotechniques rencontrées le long de la hauteur et à niveau des portions de l'alignement, qui totalisent environ 9 km de longueur. Un tunnel foré comprend les 2 km restants de l'alignement, mais n'a pas été discuté dans le document. La géologie de surface de la zone et les conditions géotechniques le long du corridor ELRT sont complexes et très variables. Dans le (Burnaby) partie sud-ouest, le tracé traverse Pléistocène (période glaciaire) des hautes terres composées de glaciaire dense till et les sédiments fluvioglaciaires; dans le (Port Moody) partie centrale croix de route qui se chevauchent les fans de débris reposant sur des marins doux et sédiments glaciomarins; et dans le (Coquitlam) partie orientale de la route monte un delta marine surélevée qui se compose de dépôts granulaires grossiers reposant sur des sables interstratifiée, de limon et d'argile. Les défis géotechniques liés aux conditions souterraines rencontrées lors de la construction dans chacune de ces sections sont décrites; ces défis comprenaient des obstacles (rochers), artésienne eaux souterraines / confiné, les sols argileux compressibles, sols liquéfiables, remplissage variables et les impacts sur les services publics et les infrastructures adjacentes. En raison des conditions de sol très variables et difficiles, un certain nombre de techniques structurelles et au sol amélioration ont été employées dans les zones reposant sur des sols liquéfiables pour atténuer les établissements post-sismiques potentiels et étalement latéral des fondations.

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Cite this article:
J Pellett (2016) Evergreen Line Rapid Transit Project: Subsurface Conditions and Geotechnical Challenges in GEO2016. Ottawa, Ontario: Canadian Geotechnical Society.

@article{4202_0721093652, author = J Pellett,
title = Evergreen Line Rapid Transit Project: Subsurface Conditions and Geotechnical Challenges,
year = 2016
}