Citation

Conlon RJ, Tanner RG, Coldwell KL. Can. Geotech. J. 1971; 8(2): 299-314.

Copyright

(Copyright © 1971, National Research Council of Canada)

DOI

10.1139/t71-025

PMID

unavailable

Abstract

The Townline road-rail tunnel is being constructed beneath the relocation of the Welland canal to the east of the city of Welland. Construction is by opencut and cut-and-cover through up to 80 ft (24 m) of lacustrine clays and clay tills. The lower stratified zone in the lacustrine clays has a minimum shear strength parallel to the bedding in some critical layers. Slope stability studies involved detailed sampling and testing, including block samples and 5-in.(13-cm) tube samples, and correlations with previous landslides in the area. These studies demonstrate that the mechanism of landslides in this stratigraphy involves a long flat portion of failure surface in the lower stratified zone, and that the shear strength available along this portion of the failure surface is consistent with the minimum shear strengths measured parallel to the bedding. Slopes as flat as 8.5:1 are required in areas which combine the deepest cuts and deepest overburden deposits.The concrete tunnel structure is being founded on bedrock consisting of a gypsiferous dolomite containing thick layers and lenses of essentially pure gypsum. Within the upper broken zone of the bedrock and some thin pervious lenses of sand and gravel immediately overlying the bedrock is an aquifer zone which is a major source of groundwater. Prior to construction, the piezometric level in this aquifer was approximately at the ground surface. The groundwater level in the aquifer zone had to be drawn down during construction and must be controlled throughout the life of the structure to provide for the stability of the overburden slopes. At the same time, the gypsum beneath the tunnel structure will be maintained intact by a drainage scheme which essentially isolates the rock beneath the structure from future groundwater flow, thereby precluding any significant solutioning of the gypsum.


Le tunnel rail-route est construit en dessous du réalignement du canal de Welland à l'est de la ville de Welland. L'excavation se fait à ciel ouvert à travers des couches d'argiles lacustres et de till argileux atteignant une épaisseur de quelques 80 pieds (24 m). Les niveaux inférieurs de l'argile lacustre présentent une résistance au cisaillement minimale dans le plan du litage. Les études de stabilité des talus ont compris des essais sur un grand nombre d'échantillons, y compris sur des blocs et sur des cylindres de 5 po. (13 cm), ainsi qu'une analyse comparative des glissements de terrain de la région. Ces études ont montré que ce type de terrain entraîne des surfaces de glissement présentant un long segment pratiquement horizontal dans les couches inférieures. Ce segment suit l'orientation de moindre résistance au cisaillement. Des pentes de talus de 1:85 sont nécessaires dans les zones où l'excavation la plus profonde correspond avec les dépôts argileux les plus épais.Le tunnel, en béton précontrain...

Language: en