Condition Assessment and Repair of the Stanley Canyon Tunnel

The 3.1-mile-long Stanley Canyon Tunnel is a key component of Colorado Springs Utilities’ Northfield Water System. The 9-foot diameter tunnel is lined with cast-in-place concrete and steel, and has an operating pressure of up to 765 psi. Shannon & Wilson, Inc. performed a condition assessment of the tunnel in October 2015 using the National Association of Sewer Service Companies (NASSCO) Pipe Assessment Condition Program (PACP). A three-person team recorded more than 500 defects over a three-day period, and oversaw a non-destructive evaluation using spectral analysis of surface waves (SASW) and impact echo (IE) methods. Based on the condition assessment, repair locations were identified and prioritized; repairs consisting of steel plates and chemical grouting were constructed over a three-week period in November 2015. This paper details the execution of the condition assessment and construction of the repairs.