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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.

Pile foundation heat exchangers (PFHX) are increasing in popularity as an alterna- tive to conventional air conditioning systems in large, commercial buildings. PFHX provide a sustainable means of building cooling and are compatible with the struc- ture of pile foundations given the constant ground temperatures. However, increased understanding of the behaviour of clay subject to seasonal temperature cycles is re- quired to ensure that PFHX can safely operate for the building's design life. This study has developed a conceptual model for the microstructural behaviour of clay subjected to heating and cooling cycles. This conceptual model accounts for the effect of temperature on the clay particles, adsorbed double layer and pore water within the clay; identifying how this microstructural behaviour influences the bulk behaviour of the clay and therefore the observed response in the pile foundation. The conceptual model has been supported through thermal triaxial experiments on kaolin and Durham clays. Testing considered the change in sample volume, critical state friction angle and stiffness of two varying plasticity clays. The model has been further strengthened in its application to existing pieces of similar literature for both experimental and field study findings. This study concludes by providing an understanding of how this conceptual model applies to the real world response of PFHX installed in low and high plasticity clays, detailing the impact of the initial heating and cooling cycle on the longer term pile head displacement. These results support the use of PFHXs and recommend extending their temperature ranges to increase their efficiency without detrimental impact on the load bearing performance of the clay.

The frequent appearance of sinkholes has become a hazard due to their instantaneous development and the damage they can cause to infrastructure. The term sinkhole indicates a location in which the ground is sinking into cavities. The process is caused by water penetration into the ground. Water causes dissolution of soluble rocks in the bedrock resulting in the creation of a void and consequent collapse of the overlying soil. Water also affects the stability of voids from former old mine works. Despite the increasing interest in this phenomenon, rarely the geotechnical aspects of the event are studied. In particular, the characteristics of the soil standing over the cavity are usually neglected. This research aimed to study clay behaviour in tensile conditions, investigating the effects of moisture content and plasticity index. The results will aid future research on the determination of a predictive model for sinkhole appearance. The project was divided into two parts: the first was based on the collection of data of previous events, the second was related to laboratory tests performed on small clay models. The creation of the historical database showed the importance of studying cohesive soils behaviour and common features of past sinkholes. The laboratory tests allowed the effect of moisture content and plasticity index on the fracture failure modes of clay to be determined. Two types of experiments were performed to study the instantaneous failure caused by cracks propagation: direct tensile and bending tests. The results found showed that fracture in clay is affected by both moisture content and plasticity index. High moisture contents determined gradual collapses in which clays underwent large deformations before reaching failure. This explained why sinkholes usually form after some time from the rain event. Instead, dry clays represent a more dangerous situation for their unexpected collapse without any deformation.