The effect of stress level on the resilient modulus of non-engineered mudrock backfill materials

In the UK, High Speed Rail 2, (London to the ‘North’) is surrounded by a number of questions regarding construction technologies which can minimise the impact of the route. The rail industry in the UK has vast experience based with ballasted track, but this is not necessarily the most appropriate choice for new high speed rail construction when crossing problematic soils. This paper aims to investigate the use of different track types (ballasted and ballastless) and the influence they will have on the underlying soil in areas predominated by non-engineered mudrock backfills, relics of the UK’s mining heritage. Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. Structural performance of the railway track strongly depends on the level of stress that is transmitted to the ground and this must be reduced to an acceptable level to minimise deterioration in the mudrock if they are to be utilised effectively. The main objective for this paper is to investigate the impact of the initial stress conditions and dynamic stress on the permanent deformation of mudrock under different physical conditions. Triaxial testing is used to estimate the stiffness characteristics of the mudrock. The results show that the resilient modulus increases with a decrease in the stress amplitude. In addition, ballasted track shows a higher suitability for use in design in terms of the stiffness generated within the mudrock.