Engineering Understanding

I N October 1997 four cows on a farm situated on the Halland Ridge in southern Sweden died after drinking water from a nearby stream. The water was contaminated with acrylamid which, it emerged, came from a nearby 10 kilometre railway tunnel construction site. The railway project had been plagued by trouble from the beginning. The Halland Ridge is a `horst', a heap of earthcrust formed by tectonic forces, with the highest ground water yield of all pre-Cambrian rocks. An attempt to use a huge full-face drill to open up the tunnel failed because the brittle rock of the horst just collapsed. This should have been no surprise. Past experience from similar constructions in the neighbourhood suggests that drilling makes the groundwater level sink, often well below the limit approved by the Water Board. Gunnar Jacks, Professor of Ground Water Chemistry at the Royal Institute of Technology, Stockholm, says that working in this sort of environment is notoriously difficult. In an attempt to salvage the project another contractor took over and started to line the inner walls of the tunnel with a two-component material imported from France. The alternative of building a concrete inner ceiling was considered too expensive. The flow of water was, however, such that the individual components were washed away before the composite was formed. One of the components, acrylamid, is known to be carcinogenic. When the water was pumped from the building site it found its way to the stream where the cows had been drinking. It was later shown that the workmen had also been exposed to acrylamid.