Loss of a 30″ directional crossing due to pipeline collapse during pullback

This article concerns the loss of a Horizontal Directional Drilling crossing due to a failure that took place during pullback of the pipeline. The more than 500 m long drilling was meant to lodge a 30″ pipeline that crossed a large river. The failure caused the total loss of the crossing, and the necessity to repeat the entire process in another, less favorable location. Root causes involved a difficult soil composition, and constraints at a populated bank that led to engineering solutions not proved before on a pipe of such diameter. Discontinuities on the tunnel and the use of a sacrifice pipe at the front end of the pipe column, which was related to the need for more pipes than originally calculated because of a series of problems at the beginning of the perforation, were also defined as root causes. Lessons learned are highlighted.