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This paper presents the three-dimensional discrete element method (DEM) that was used to study the shear behaviour of fresh and coal fouled ballast in direct shear testing. The volumetric changes and stress-strain behaviour of fresh and fouled ballast were simulated and compared with the experimental results. 'Clump logic' in Particle Flow Code (PFC3D) incorporated in a MATLAB Code was used to simulate irregular shaped particles in which groups of ten to twenty spherical balls were clumped together in appropriate sizes to simulate ballast particles. Fouled ballast with various Void Contaminant Index (VCI), ranging from 20%VCI to 70%VCI, were modelled by injecting a specified number of miniature spherical particles into the voids of fresh ballast. The DEM simulation captures the behaviour of fresh and fouled ballast as observed in the laboratory showing that the peak shear stress of the ballast assembly decreases and the dilation of fouled ballast increases with an increasing of VCI. Furthermore, the DEM also provides insight to the distribution of contact force chains and particle displacement vectors, which cannot be determined experimentally. These micromechanical observations clearly justify the formation of a shear band and the evolution of volumetric changes during shearing. The reduced maximum contact force associated with increased particle contact area due to fouling explains the decreased breakage of fouled ballast. An acceptable agreement was found between the DEM model predictions and laboratory data.

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Sand-tyre chip (STCh) mixtures can be used in many geotechnical applications as alternative backfill material. The reuse of scrap tyres in STCh mixtures can effectively address growing environmental concerns and, at the same time, provide solutions to geotechnical problems associated with low soil shear strength and high dilatancy. In this paper, the shear strength and dilatancy behaviour of STCh mixtures have been investigated. A series of monotonic triaxial tests has been carried out on sand mixed with various proportions of tyre chips. It has been found that tyre chips significantly influence the shear strength and the dilatancy behaviour of STCh mixtures. The effects of confinement and relative density on the shear strength, dilatancy and initial tangent modulus of the STCh mixtures have also been investigated. Moreover, a dilatancy model for STCh mixtures has been proposed and validated with the experimental results.

This article presents the results of probabilistic seismic hazard analysis (PSHA) for Bangalore, South India. Analyses have been carried out considering the seismotectonic parameters of the region covering a radius of 350 km keeping Bangalore as the center. Seismic hazard parameter 'b' has been evaluated considering the available earthquake data using (1) Gutenberg-Richter (G-R) relationship and (2) Sellevoll (1989, 1992) method utilizing extreme and complete catalogs. The 'b' parameter was estimated to be 0.62 to 0.98 from G-R relation and 0.87 ± 0.03 from Kijko and Sellevoll method. The results obtained are a little higher than the 'b' values published earlier for southern India. Further, probabilistic seismic hazard analysis for Bangalore region has been carried out considering six seismogenic sources. From the analysis, mean annual rate of exceedance and cumulative probability hazard curve for peak ground acceleration (PGA) and spectral acceleration (Sa) have been generated. The quantified hazard values in terms of the rock level peak ground acceleration (PGA) are mapped for 10% probability of exceedance in 50 years on a grid size of 0.5 km 9 0.5 km. In addition, Uniform Hazard Response Spectrum (UHRS) at rock level is also developed for the 5% damping corresponding to 10% probability of exceedance in 50 years. The peak ground acceleration (PGA) value of 0.121 g obtained from the present investigation is slightly lower (but comparable) than the PGA values obtained from the deterministic seismic hazard analysis (DSHA) for the same area. However, the PGA value obtained in the current investigation is higher than PGA values reported in the global seismic hazard assessment program (GSHAP) maps of Bhatia et al. (1999) for the shield area.

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Internal erosional behaviour of a lignosulfonate-treated dispersive soil has been studied using apparatus designed and built at University of Wollongong. The effectiveness of lignosulfonate-treated dispersive clay on its erosion resistance has been investigated and its advantages over traditional admixtures (cement) have been presented. Lignosulfonate is a non-toxic admixture that can stabilise certain erodible and dispersive soils effectively, without causing any adverse environmental impact on the ground unlike some traditional stabilisers. Test results show that the erosional parameters such as critical shear stress and coefficient of soil erosion are improved with the increase in the amount of lignosulfonate. Knowledge about the clay particles and lignosulfonate interaction mechanisms is pertinent for long-term environmental sustainability of treated soils, a factor which is poorly understood at microscopic level. Considering this, X-ray diffraction, and Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy were carried out on representative samples to understand the stabilisation mechanism at the particle scale level. The improvement of performance exhibited by the lignosulfonate-treated soil can be mainly attributed to the reduction of the doublelayer thickness by the neutralisation of surface charges of the clay particles and the formation of more stable particle clusters by polymer bridging. Internal erosional behaviour of a lignosulfonate-treated dispersive soil has been studied using apparatus designed and built at University of Wollongong. The effectiveness of lignosulfonate-treated dispersive clay on its erosion resistance has been investigated and its advantages over traditional admixtures (cement) have been presented. Lignosulfonate is a non-toxic admixture that can stabilise certain erodible and dispersive soils effectively, without causing any adverse environmental impact on the ground unlike some traditional stabilisers. Test results show that the erosional parameters such as critical shear stress and coefficient of soil erosion are improved with the increase in the amount of lignosulfonate. Knowledge about the clay particles and lignosulfonate interaction mechanisms is pertinent for long-term environmental sustainability of treated soils, a factor which is poorly understood at microscopic level. Considering this, X-ray diffraction, and Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy were carried out on representative samples to understand the stabilisation mechanism at the particle scale level. The improvement of performance exhibited by the lignosulfonate-treated soil can be mainly attributed to the reduction of the doublelayer thickness by the neutralisation of surface charges of the clay particles and the formation of more stable particle clusters by polymer bridging.the Institution of Civil Engineers Ground Improvement 163 February 2010 Issue GI1 Pages 43