ABSTRACT
The strength, deformation and degradation behaviour of fresh and recycled ballast has been studied in a series of monotonic triaxial shearing tests using a large-scale triaxial apparatus (Fig. 4.1, Chapter 4). The effects of confining pressure on friction angle, dilatancy, stress-ratio and particle breakage were particularly examined. The stressstrain behaviour (both fresh and recycled ballast) under cyclic loading has also been investigated in a large prismoidal triaxial chamber (Fig. 4.6) simulating a small track section. The stabilisation aspects of recycled ballast using various types of geosynthetics were also studied in these model tests. To quantify ballast degradation, each specimen was sieved before and after testing. The crushing strengths of ballast grains were determined by conducting a series of single particle crushing tests. The behaviour of fresh ballast has been studied in a series of impact loading tests using large-scale drop-weight impact equipment (Fig. 4.13, Chapter 4). This Chapter describes the strength, deformation and degradation behaviour of fresh and recycled ballast under monotonic, cyclic and impact loadings. The effectiveness of various geosynthetics in stabilising recycled ballast is presented and discussed through laboratory model test results. The benefits of shock mats in the effective mitigation of ballast degradation under impact loads are also discussed.
