PHYSICAL AND CHEMICAL GROUND IMPROVEMENT FOR SUSTAINABLE TRANSPORTATION INFRASTRUCTURE UNDER CYCLIC LOADS

Railways form one of the major worldwide transportation networks and they continue to provide quick and safe public and freight transportation. In order to compete with other modes of transportation and to meet the ever growing demand of public and freight transport, railway industries face challenges to improve their efficiency and decrease the costs of maintenance and infrastructure. 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. Hundreds of millions of dollars are spent each year for the construction and maintenance of rail tracks in large countries like the USA, Canada and Australia. A proper understanding of load transfer mechanisms and their effects on track deformations are essential prerequisites for designing the new track and rehabilitating the existing one. The reinforcement of the track by means of geosynthetics leads to significant reduction in the downward propagation of stresses and assures more resilient long-term performance. The geocomposite (combination of biaxial geogrid and non-woven polypropylene geotextile) serves the functions of reinforcement, filtration and separation, thereby reducing the vertical and lateral deformations. To stabilise subgrade soil under rail tacks and road embankments, two advanced ground improvement schemes have been introduced. Stabilization of soft subgrade soils using prefabricated vertical drains (PVDs) is essential for improving overall stability of track and reducing the differential settlement during the train operation. The effectiveness of using geocomposite geosynthetic and PVDs has been observed through field measurements and elasto-plastic 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. Moreover, the improvement of an unstable formation soil with pH neutral chemical admixture and the sub-surface drainage is described. Internal erosional behaviour of lignosulfonate treated erodible soils has been studied using the Process Simulation Apparatus for Internal Crack Erosion (PSAICE) designed and built at the University of Wollongong (UOW). Effectiveness of lignosulfonate treated erodible soils on the erosion resistance has been investigated and its advantages over conventional methods are presented and discussed.