In this paper, an attempt has been made to investigate the influence of confining pressure on deformation and degradation behaviour of railway ballast using the Discrete Element Method (DEM). A novel approach has been employed to model the two dimensional projection of field size ballast particles as cluster of bonded particles. Bonded particles are held together by a bond, and debonding is considered as particle breakage. A series of cyclic loading simulations using DEM were carried out on an assembly of angular ballast particles at different confining pressures (10 kPa to 240 kPa). The results highlight that the development of axial strain during cyclic loading as a function of initial confining pressure and number of cycles. Very high axial strain and breakage of particles have been observed at low confining pressure (< 30 kPa) owing to dilative volumetric strain behaviour. In terms of particle breakage, there exists an optimum range of confining pressures where breakage is minimal. In addition, the evolution of particle displacement vectors explains the breakage mechanism and associated deformations during cyclic loading.