Three failures of hydroelectric power tunnels–one in Canada and two in Australia–are discussed. All three were similar in that pumping action of water, resulting from variations in operating pressures, removed soft material from rock joints, thereby permitting masses of rock to fall into the tunnel and create an obstruction. All three were quickly repaired by tunneling through the rock debris, using concrete, grout and steel support members as required. Such failures teach the need for more careful inspection of tunnel arches before putting them into service, and the use of more shotcrete, rock bolts and concrete in doubtful zones. A serious collapse occurred during construction of a highway tunnel in Hawaii. It showed that the excavation of tunnels through soft ground demands much greater safety precautions than when the same sized tunnels are being driven in solid rock. Natural gas caused an explosion in a water tunnel under construction in California. It was learned that the best way to protect against an explosive mixture of air and gas is to use abundant ventilation, together with constant monitoring, A railway tunnel was shortened seven feet as a result of an earthquake and was put out of service until it could be replaced by open cut.