Use of Shotcrete From the Standpoint of the Designer

The view is expressed that where the designer feels that shotcrete is the applicable method of support based on reasonable geologic evaluation of the proposed tunnel alignment, it should be included in the design. The designer should also urge the owner to establish incentive for the contractor to use shotcrete and to do a good job. The designers work would be greatly aided if he could be provided with good case history data. The type of acceleration, concrete mix and compressive strength test results could provide excellent data if new studies were made of the existing conditions including careful examination of the surface, compressive tests of cored samples, petrographic analyses and perhaps non-destructive tests. Interest is expressed in information on the effect of time on the various high early strength shotcretes using different accelerators. The experiences are briefly summarized of various shotcrete projects. These include the construction in Canada of a large diameter shaft and a shot tunnel section in which efficient support was achieved in the first attempt with limited technical guidance. A case of failure is described which involved a large diameter tunnel in fairly good metamorphic rock. The view is expressed that shotcrete has a true place in tunnel construction when applied very soon after the excavation cycle and when applied with reasonable care.