Slope Redesign and Slope Remediation during Design/Build Construction at Kicking Horse Canyon– Phase 2

This paper describes the adjustments to the design and stabilization of the excavated highway slopes during construction of the Phase 2 Upgrades to the Trans Canada Highway in Kicking Horse Canyon between Golden and Yoho National Park. After the start of the construction of the design/build project, the detailed snow avalanche analysis indicated that the bid design for slopes on the western end of the project that were proposed to be cut at an angle of 1:1 for geological reasons would generate an unacceptable avalanche risk. Consequently, it was necessary to steepen the rock and overburden cuts from 1:1 to 0.5:1 and install slope support. In some areas the rock structure varied significantly over short distances and caused unexpected, local failures which required “on-the-fly” designs of additional rock and overburden support in the form of steel mesh, shotcrete and rock bolts. The Kicking Horse Phase 2 Project consisted of 6 kilometres of new 4 lane highway which included the 400m long, 100m high New Park Bridge over the Kicking Horse River. The project is in the heart of the Rocky Mountains in an area that is subject to rockfalls, snow avalanches and debris flows. The natural slopes in the area of the project are very high and steep and many of the soil and rock units are relatively weak – a combination that provided significant geotechnical challenges and resulted in slope instability in places that required remediation to constructed works. This paper describes the initial and revised designs and construction of the up to 75m high rock slopes and the support for the till and colluvium slopes above the rock cuts. The paper also describes the revisions to the design of rock support for one of the large bridge piers as a result of discovering adversely dipping rock jointing after overburden removal. Construction of the Phase 2 Project was carried out under a design-build contract which was a part of the Design-Build-Finance-Operate Concession. This contract delivery method enables projects to be brought into service in compressed schedules and has been praised by the politicians, but it involves significant challenges and additional risks for design engineers. These aspects of the Kicking Horse Phase 2 Project are also addressed in the paper.