MODELLING HIGH-SPEED RAILWAY-INDUCED VIBRATIONS AROUND TUNNELS (GROUND-SUPPORT)

SCIENTIFIC BACKGROUND
The demand for fast commuting between densely populated cities has increased over the last 30 years. This is evident with the existence of high-speed railway lines mainly in central Europe where within in 2 hours you can travel 500 - 600 km. The need of such infrastructures has risen along with the technological advancement and the environmental advantage to cars and social benefits that encounters. The latter implies that the number of railway tunnels connecting (remote) areas faster due to topographical limitations has also risen. One of the key considerations on railways tunnels especially high speed lines is the propagation of vibrations generated as the train(s) passes through. Although significant scientific progress has been made on investigating and analyzing on the ground vibrations from high speed rail lines (Connolly et al. 2013; 2015; 2016), it focuses commonly on embankments and soils. There is a gap of scientific knowledge in the tunneling environment where the vibrations propagate from the tunnel support to the surrounding rock or ground. The proposed project aims to develop a better understanding of the tunnel behaviour due to the initiation and propagation of vibrations induced in high speed railways. More specifically the main focus of this project is to investigate how the vibrations propagate from the support system to the ground and this system's interface as different rocks (rock masses) and different types of ground behave in different ways when subjected to dynamic loading, especially over time. One of the main factors controlling their mechanical behaviour is geology and more specifically the mineralogical content and its structural characteristics (Paraskevopoulou, 2016, et al. 2017, 2018). During tunnel construction there is re-distribution of stresses around the tunnel vicinity that creates the Excavation Damaged Zone (EDZ) in which new cracks and fractures are formed and or existing cracks and fractures propagate and dilate which can lead to progressive damage and failure over time. The wave propagation path (of vibrations) is directly influenced by the latter, as it depends on the discontinuities (joints, faults etc), elements of weaknesses (shear zones, geological contacts etc) on the geological setting and fracture stiffness (Hildyard, 2007). The EDZ can be deteriorated further and further damaged by fracture initiation due to the high-speed railway induced vibrations. Being able to predict the tunnel system's reaction during high-speed railway operations can be paramount of importance especially for the system's lifetime and therefore its resilience. The project will involve field work for sample collection to specific tunnel HS2 sites, experimental testing on 3-D physical models to simulate in a smaller scale the real problem and monitor the system's response using sensors and as well numerical analyses using finite-element, finite-difference, distinct-element methods. The results of the experimental testing will be used to numerical analyses in order to develop a constitutive model that can describe the response of the interface between the tunnel structural support elements and the ground. The ultimate goal of this project is to develop practical tools and models that can find use not only in the field of research but also in industry is of utmost importance.
AIMS AND OBJECTIVES
The main aim is to develop a better understanding of the tunnel behaviour due to the initiation and propagation of vibrations induced in high speed railways. objectives include:-
- Developing constitutive relationships to describe the mechanical behaviour of the tunnel (ground-support) system during high-speed railway induced vibrations
- Gaining understanding of how the vibration-induced mechanisms can affect the mechanical behaviour on a range of time-scales.
- Assessing the implications of these results for issues such as closure (or non-closure) of fractures, long-term