Pipe Selection Criteria for Trenchless Projects: Microtunneling to Large Tunnels

In the evaluation, planning, and design of pipes to serve as final liners for tunnels, the greatest emphasis during the design phase of the project is typically placed on the geological conditions to be encountered in the construction of shafts and the installation of the tunnel. The design of the shaft supports, selection of tunneling methods, initial tunnel supports, and control of the groundwater during tunneling become the most investigated elements in the design process. Often overlooked in the literature or in design guidelines are detailed descriptions of the processes necessary for proper pipe selection and pipe strength. If the wrong type of pipe is selected, damage during construction is possible and the system may have a less than planned service life. Using five projects as examples, this paper attempts to identify key criteria in the selection of pipe for tunnels constructed by tunnel boring machine (TBM) and microtunnel boring machine (MTBM) methods. In selecting the pipe for a given project, the following parameters must be considered: 1) Service fluid type (i.e. potable water, sanitary, or storm sewer), 2) Internal operating fluid pressure, 3) External ground and live loads, 4) External water load (groundwater), 5) Method of installation, 6) Material handling loads, 7) Owner history with pipe material, 8) Construction costs, and 9) Lifetime Expectancy.