The Cyclic Response of Mudrock

With the upcoming construction of High Speed Rail 2, (London to the ‘North’) a number of issues surrounding the construction technology and track design need to be answered. Previous experience in the UK rail industry has been based on ballasted track but this is not necessarily the most appropriate choice for new high speed rail construction. This project aims to investigate the use of different track types and the influence they will have on the underlying soil. In the case of this project that soil is mudrock, a weak prevalent rock which response under indicative loading of a high speed rail line is unknown. Ballastless track is a well established concept in Europe. This project aims to investigate the benefits of this form of construction due to its known savings in maintenance costs. In order to evaluate the behaviour of the underlying soil, physical tests will be conducted to assess the mechanical behaviour of mudrock under a range of dynamic loads which could be generated beneath different track constructions.
Some further parameters are required to frame the problem, including determining the stress change with depth and cyclic response to determine the cumulative strain which is of major concern. The shear strength of the soil highly depends on the stress-strain state during the passage of the axle load, which the study will aim to recreate in the laboratory.
Increasing water content, decreasing particle size and loading frequency were found to reduce the stiffness of the mudrock tested. Load frequency was found to have a positive effect on the performance of the soil. Inundation of the soil after a set of cyclic loading has been shown to significantly affect the performance by reducing the stiffness of the soil and increasing the settlement. Mudrock colliery spoil in the conditions simulated in this research can be classified as a medium stiffness subgrade. Settlement can be controlled with proper compaction and drainage of the material which will enable its use as a railway foundation subgrade.