Investigation of a Plate Index Test for Railroad Ballast
A need exists to determine the physical state of ballast in railroad track. The use of a small surface bearing plate was investigated for this purpose. The measurement problem is particularly difficult because ballast is a coarse, angular material with particle sizes up to 50 to 75 mm (2 to 3 in.) in diameter, for which the bulk properties to be assessed vary over distances as short as 300 mm (1 ft). Thus, the plate size can neither be very small or very large. Laboratory tests were first conducted to determine the effects of the following variables: ballast type, ballast density, ballast layer thickness, plate seating method, plate size, plate shape, and repeated load cycles. The procedures developed were also successfully field-tested. The study showed that using a 127-mm (5-in.) diameter plate with plaster of Paris as a seating material gave the most consistent results. The derived index parameters were found to be significantly affected by all of the variables considered.