Pressure gradients during train entry - practical design data

Predictions of rates of change of pressure caused by trains entering tunnels with simple portals are presented in sufficient detail for use to be made of them in practical tunnel design. The analytical method is not new; it is the work of MS Howe and collaborators. However, the results are presented in a form that is more accessible to most engineers than the mathematical expressions used by Howe to present extensive work in a concise form. It is shown that the maximum rate of change of pressure for trains with short noses is almost independent of the nose length (provided that they are suitably rounded), but that rates of change reduce with increasing nose length. Detailed data are presented in graphical and tabular form for three generic nose shapes and a practical method of using the data for non-generic shapes is proposed. The overall purpose of the paper is to provide a simple means of avoiding the need for resource-intensive calculations in design studies where it is not obvious a priori whether special precautions will be needed at tunnel entrances to prevent the radiation of unacceptable MPWs from tunnel outlets.