ABSTRACT
This chapter introduces two non-destructive techniques, the ground-penetrating radar and multichannel analysis of surface wave (MASW) to evaluate the ballast layer conditions with the aid of a model track built at the University of Wollongong. GPR has increasingly been employed for monitoring track conditions because it is non-destructive and can monitor the track at high speed. In radar survey, two kinds of velocity measurements can be carried out depending on whether the antenna offset is fixed or can be raised. If the antenna offset can be changed, the common mid-point or wide angle reflection measurements can be used to calculate the propagation velocity. A number of geophysical methods have been employed for near-surface characterisation and measurement of shear wave velocity using a wide variety of testing configurations, processing techniques, and inversion algorithms. The most widely used approaches are spectral analysis of surface waves and MASW. Shear modulus obtained from seismic survey is adopted for site response and seismic microzonation studies.
