Behaviour of a Slope Excavation in Clean Sand with High Groundwater at Tretheway Creek Hydroelectric Project

C Harrison

Dans les comptes rendus d’articles de la conférence: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: CASE HISTORIES - IV Miscellaneous

ABSTRACT: Section 1 of the penstock at the Tretheway Hydro Project required excavation of a 45 m high slope in uniform clean sand. No sub-surface investigations had been done in this area of the project so the uniform sand and high water flows were not anticipated. The sand was found to be highly susceptible to seepage-induced instability (piping) so sloughing of the slope face occurred immediately following excavation of each excavation lift unless the face was protected. The short-term mitigation included placement of coarse aggregate to armour the face of the slope. In most places this worked well but, in zones of heavy seepage higher on the slope, piping still occurred, and caused large piping cavities in the face of the slope. The long-term stability was provided by constructing a drained stability berm and weighting blanket on the lower half of the slope and repairing the piping cavities. This paper presents a case history of the excavation, performance and stabilization measures for the slope at the Tretheway Hydro Project to allow for installation of the penstock and the long-term performance of the slope and adjacent access road.

RÉSUMÉ: roduit systématiquement à chaque -ci ne soit renforcée. Les mesures de mitigation appliquées à court-terme ente excavée. Dans importantes dans le haut de la pente, le lessivage des matériaux en place se produisait tout de même, causant la formation réstabilité prises sur la pente excavée afin de permettre la mise en place de la conduite forcée au projet hydroélectrique Tretheway ainsi que adjacent.

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