Selected methods of ground improvement for Australian transport infrastructure

In coastal regions of Australia, high population densities and increased traffic have led to a substantial expansion of transportation infrastructure. These developments have necessitated the use of ground improvement techniques in response to environmental legislation and the need for sustained performance. In this paper, a brief overview of innovative ground improvement techniques in major areas such as railway embankments, port reclamation, and landfill operations is provided. Ballasted rail tracks are often placed on freshly quarried aggregate because it is resilient enough for cyclic and impact loads. However, ballasted layers often need periodic maintenance due to deformation and degradation, and while recycled ballast is a cheaper and environmentally viable option, its strength must be investigated beforehand, and different types of geosynthetics to improve the stability and drainage of railway tracks under high cyclic loading also need assessing. Field tests to measure the in-situ stresses and deformations of ballast have been carried out on sections of instrumented heavy haul track at Bulli and Singleton. Stabilization of soft subgrade soils using prefabricated vertical drains (PVDs) and stone columns is also needed to improve the overall stability of track and reduce differential settlement during operation. The effectiveness PVDs can be seen via field measurements and finite element analyses. Due to an increase in trade activities at the Port of Brisbane, Queensland (Qld), new facilities on Fisherman Islands at the mouth of the Brisbane River were constructed (reclamation) on the new outer area (235ha) adjacent to the existing port facilities. A vacuum assisted surcharge load and conventional surcharge scheme in conjunction with PVDs helped to reduce the required consolidation time through the deeper subsoil layers. The design of this combined vacuum and surcharge fill system and construction of the embankment are described in this paper. A 45 ha reclamation at the Outer Harbour extension of Port Kembla in Wollongong, NSW, gave us the opportunity to examine the potential use of coal wash (CW) and steel furnace slag (SFS) as predominant reclamation fill, while laboratory investigations indicated that an optimum CW-SFS mixture would meet most of the geotechnical specifications needed for an effective structural fill. A field application at Penrith Lakes, NSW, of a new methodology using the shear wave velocity (V_s) (i.e. Multichannel Analysis of Surface Waves MASW) and matric suction (u_a-u_w) or moisture content was investigated. The laboratory results and the results from preliminary field testing indicate that Vs and (u_a-u_w) trends could predict the compaction characteristics of the soil. The use of sustainable approaches for ground improvement such as bio-engineering, and recycled tyres with waste granular material, is also presented and discussed in this paper.