The PiP model and progress in ground vibration from railways

Abstract

Vibration in the ground causes problems. At large amplitude vibration causes damage, the most obvious example being earthquake damage. But the ground motion in a damaging earthquake is typically low-frequency (below 1Hz) and large-amplitude (above 10mm). At higher frequencies and lower amplitudes (above 10Hz, below 0.01mm) vibration is simply bothersome. Rarely do perceptible vibrations cause damage - the cracks in the plaster of a house near a busy road are most probably due to subsidence, or perhaps due to the kids jumping down the stairs two-at-a-time and slamming doors. Vibrations from man-made sources are arguably preventable and if we are disturbed by them, generally there is someone we can sue. Railway companies are an easy target for litigation so there is clear motivation for keeping vibration levels low. This paper addresses the general topic of ground vibration from railways and some of the common techniques used to control railway vibration and also the predictive tools available to engineers. It is often believed that the environmental concerns of residents near a proposed railway development will be met by putting the trains underground - in tunnels. Even though modern tunnelling methods are now quicker and cheaper than ever before, vibration concerns turn the average "nimby" into a NUMBY (Not Under My Back Yard). The underground-railway problem encapsulates all that is difficult about controlling a distributed source of ground-borne vibration. The paper also illustrates the features of the PiP model (Pipe in Pipe) developed in Cambridge and used to predict vibration levels in the ground near railway tunnels. It will also cover progress with other computational tools including MEFISSTO from CSTB in France, the Elasto-Dynamic Toolbox (EDT) from KU Leuven, FINDWAVE and the MOTIV project in the UK.