Tunnel Business Magazine

FEB 2018

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TUNNELINGONLINE.COM TBM: TUNNEL BUSINESS MAGAZINE // FEBRUARY 2018 way to travel between lifts during screed rail installation and shotcrete application. It was cost effective and reduced the construction schedule and enabled efficient water curing for the shotcrete lining compared to other decking options, such as scaffolding the entire shaft. • Dry-Mix Shotcrete Application: Dry-mix shotcrete was se- lected due to its flexibility of operation, fast setting time, and suitability to deal with water leakage into the shaft. The pre- dampened dry-mix shotcrete was applied with good control over rebound and overspray. It should be noted that rebound or waste was far less than expected, approximately 10-20% of the total volume. Dry-mix shotcrete pre-bagged mate- rial worked well in providing a final liner construction with varying thickness. Rigorous QC inspection and testing con- firmed that a good quality shotcrete lining was applied. • Cold Weather Shotcrete: During cold weather, when ambi- ent temperatures fell below 5 C, additional precautions and protection measures were implemented. Hot water pres- sure washing was able to properly prepare the base course shotcrete and increase the surface temperature to be appro- priate for receiving the final finish course shotcrete with the selection of appropriate accelerator dosages. Keeping the area warm with heaters as well as keeping dry mixed bags warm prior to use was also effective. The finish course shotcrete was designed to set up quickly, while still allow- ing sufficient time for steel trowel finishing to the specified tolerances. c o n c l u s i o n s The P oject started in January 2011, and finished in February 2017. The shotcr d in Au- gust 2013 with screed rail installation followed by shotcreting in September 2013. Final patching of the shotcrete wall finished in January 2014. Upon completion, the following conclusions were reached: • Dry-mix shotcrete, when properly applied, can provide a good quality shotcrete lining, in particular, for liners with irregular shapes and varying thickness. • The floating deck construction method used is an innovative construction method for shaft lining construction. It improved the quality of shotcrete construction, reduced rebound and overspray, reduced the construction schedule, labor and mate- rials costs, and reduced the overall cost of the project. • Special measures need to be adopted to deal with the build-up of water pressure behind a layer of freshly applied shotcrete. The procedures described in this report were effective in deal- ing with this problem. Lihe (John) Zhang, Ph.D., P.Eng , Shotcrete Consultant, LZhang Consulting & Testing Ltd; D.R (Rusty) Morgan, Ph.D., P.Eng , Shotcrete Consultant; Ted Walter , President, Can Tech Shotcrete Inc; Brian McInnes, P. Eng. , Project Engineer, McNally Construction Inc.; Allen Mitchell, P. Eng. , Senior Project Engineer, Metro Vancouver, Water Services Department; Andrew Rule, P. Eng. , Project Manager, Aecon Infrastructure Inc 3 1 F E A T U R E S T O RY

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