Consider an 800-mm water transfer tunnel with mean loading equal to 2 m³/s and coefficient of variation equal to 0. 20. Calculate the risk of failure of a pipe using safety margin approach when MS is normally distributed. The energy slope of tunnel is 0. 0002 with a coefficient of variation of 0. 11. The Darcy–Weisbach friction factor is 0. 0002 and has a coefficient of variation of 0. 15.