Rock squeeze at Thorold Tunnel

Abstract

The Thorold Tunnel, constructed between 1965 and 1968, provides a four-lane highway crossing under the Welland Canal at Thorold, Ontario. Horizontal cracking, initially observed in late 1967, has since become more evident in the outer walls of the tunnel at the east and west service buildings. This paper describes the instrumentation installed, and the investigations into the cause of cracking carried out between 1971 and 1974. These investigations have led to the conclusion that the cause of the cracking is an imposed deformation resulting from a time-dependent, non-elastic displacement of the adjacent rock mass, known as rock squeeze. The effect of a slot cut in the rock in 1974 to relieve the west service building from the deformations imposed by the rock squeeze is also reviewed.