Use of geosynthetics in railways including geocomposites and vertical drains

Australia relies heavily on rail for the transportation of bulk commodities and passenger services, and has introduced faster and heavier trains in recent years due to a growing demand. Large cyclic loading from heavy haul and passenger trains often leads to progressive deterioration of the track. The excessive deformations and degradations of the ballast layer and unacceptable differential settlement or pumping of underlying soft and compressible subgrade soils necessitate frequent costly track maintenance works. A proper understanding of load transfer mechanisms and their effects on track deformations are essential prerequisites for minimising maintenance costs. The reinforcement of the track by means of geosynthetics leads to significant reduction in the downward propagation of stresses and assures more resilient longterm performance. The geocomposite serves the functions of reinforcement, drainage and separation, thereby reducing the vertical and lateral deformations. Stabilization of soft subgrade soils by using prefabricated vertical drains (PVDs) is also essential for improving the overall stability of track and to reduce the differential settlement during the operation of trains. The effectiveness of using geocomposite geosynthetic and PVDs has been observed through field measurements and finite element analyses. These have been the first fully instrumented, comprehensive field trials carried out in Australian Railways, and it was very encouraging to see the field observations matching the numerical predictions.