Keywords: trackbed, ballast, fouling, PUMA, strain, deformation.

It is the experience of railway authorities across the world that ballast fouling necessitates a reduced interval between tamping interventions. The work described in this paper involved a laboratory study using three different fouling materials and four different fouling degrees (in addition to zero), and it also investigated the influence of water content. The test device used was the precision unbound material analyser (PUMA), a device that delivers a repeated vertical stress and a confining stress that increases according to the lateral strain in the specimen, thus mimicking conditions in a real trackbed. Tests were carried out on a two thirds scale ballast. In general, moderate levels of fouling were found to be beneficial, typically reducing the strain accumulation rate to 75 percent that of clean ballast, and this was ascribed to the improved stability given to ballast particles by adjacent fouling material. At high degrees of fouling however strain accumulation rates 3-4 times that of clean ballast were measured. Furthermore test constraints did not permit the pumping phenomenon to occur and it is believed that the strain accumulation rates at very high levels of fouling may therefore have been under-recorded in comparison with real trackbed.

purchase the full-text of this paper (price £22)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £85 +P&P)