
Chrysothemis ParaskevopoulouUniversity of Leeds
Chrysothemis Paraskevopoulou
MEng, MSc, PhD | MBA
About
86
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Introduction
I am currently an Associate Professor at the University of Leeds in Rock Mechanics, Tunnelling and Underground Space and Geotechnical Engineering with a main research focus on time-dependent and long-term behaviour of geomaterials, advanced numerical modelling and data analysis from laboratory and in-situ testing, risk management, geothermal and sustainability in geo-engineering related projects.
Education
April 2013 - August 2016
Publications
Publications (86)
Underground openings can experience time-dependent deformations and stress changes. Studying time-dependent rock behaviour is commonly done with static load (creep) tests in the laboratory which typically exhibit three distinct stages of behaviour. In this study relaxation tests were conducted to examine if three stages also exist under constant st...
Cumulative elastic and inelastic strain and associated internal stress changes as well as damage evolution over time in brittle rocks control the long-term evolution of the rockmass around underground openings or the land surface settlement. This long-term behaviour is associated with time-dependent deformation and is commonly investigated under st...
During the excavation of a tunnel the accumulated wall displacement and the loading of tunnel support is the
result of both the tunnel advance (round length and cycle time) and the time-dependent behaviour of the surrounding rock mass. The current approach to analyze the tunnel wall displacement increase is based on the
Convergence-Confinement Meth...
The Victorian tunnels that lie on the nation’s railway network have been vital to facilitating a reliable rail service across the country for the past 150 years. However, some of these tunnels have started to challenge the existing network. These tunnels were originally constructed using several rings of brick masonry as a lining. After many years,...
Investigating the geomechanical engineering behaviour of Chalk is challenging since it is a generally soft rock formation and presents in cases a different behaviour from other competent rocks. Additionally, Chalk is widespread throughout the United Kingdom and other parts of the world. Thus, an in-depth understanding of Chalk is paramount when con...
Masonry lined tunnel condition assessment is a predominantly manual process. It consists primarily of a visual
inspection followed by a lengthy and subjective manual defect labelling process. There is therefore much potential
for automation. Masonry spalling is a key indicator of a masonry tunnel’s condition. To obtain actionable
detail about a tun...
The Bedretto adit, in the Alps of Switzerland, was excavated in 1972–1982 as an auxiliary adit for the main Furka Base Tunnel. The adit is 5218 m long, being excavated mostly in the Rotondo Granite with drill and blast methods to create a horseshoe cross-section. Much of the tunnel has remained unlined and such long observation periods are seldom a...
In deep hard rock environments under high-stress conditions, rockmasses behave in a brittle manner resulting in spalling and strain bursting. This paper examines the occurrence of brittle failure and its impact on face stability. Generalised Hoek-Brown failure criterion modified after the Damage Initiation and Spalling Limit (DISL) approach is adop...
This paper presents a comparison between the response of an isotropic continuum and a jointed discontinuum when subject to a moving point load source. A numerical model was setup in the Universal Discrete Element Code (UDEC) and a tunnel was modelled longitudinally as nodes within the model. Discontinuum models with four different joint angles and...
There has been a wide effort to develop constitutive models to aid prudent engineers or scientists in understanding materials' behaviour in rock mechanics. Hoewever, there is still a lot of work to be done when considering time-dependent behaviour that can lead to instabilities and progressive failures which cannot be captures when considered the c...
Urban tunnelling can be highly challenging, especially in areas where limited ground settlements and environmental disturbance is required. Mechanised tunnelling is usually preferred in such ground environments, specifically Slurry or EPBM (Earth Pressure Balance Machine), depending on the ground properties. Being able to predict the anticipated tu...
Transfer Learning in Rock Strength Predicton
Strain bursting is a phenomenon associated with deep underground excavations and tunnelling in brittle hard rocks that result in a sudden and violent failure, posing high risks and damage. This work aims to assess the strain bursting and the energy response characteristics and develop a guideline that can be utilized in the preliminary investigatio...
Strain bursting is a phenomenon associated with deep underground excavations and tunnelling in brittle hard rocks that result in a sudden and violent failure, posing high risks and damage. This work aims to assess the strain bursting and the energy response characteristics and develop a guideline that can be utilized in the preliminary investigatio...
Urban tunnelling can be a highly challenging process, especially where ground settlement is not tolerated well, and limited environmental disturbance is required. Controlled mechanised tunnelling is usually preferred in such ground environments, specifically Slurry or EPBM, depending on the ground properties. Although analysis of tunnelling is a th...
Resonance effects in parallel jointed rocks subject to stress waves are investigated using transfer functions, derived from signals generated through numerical modelling. Resonance is important for a range of engineering situations as it identifies the frequency of waves which will be favourably transmitted. Two different numerical methods are used...
The excavation of tunnels in brittle rocks with high in-situ strengths under large deviatoric stresses has been shown to exhibit brittle failure at the periphery of tunnels parallel to the maximum in-situ stress. This failure can either occur instantaneously or after several hours due to the strength degradation that is implicitly and indirectly co...
As the tunnelling industry is an ever-expanding market the need to lower the cost of construction immerses. There is an understanding deficit on historical tunnel failures which is partly due to sensitive information on insurance losses and delays not being formally released to the public but also the lack of a comprehensive database. This research...
Cities are shaped and reshaped dynamically, through spatial and social interactions that occur and develop among places and people, and the way they inhabit them. Graffiti and street art are urban phenomena that illustrate and reveal these socio-spatial interactions. While they are formed by other cultural, historical, and aesthetic components of a...
This study investigates the capability of the Southeast Mesohellenic Trough (SE MHT) sandstone formations to serve as a potential reservoir for CO2 storage in response to the emerging climate change issues by promoting environmentally friendly mineral sequestration applications. Sandstone samples, for the first time, were evaluated for their petrog...
As the tunnelling industry is an ever-expanding market due to the switch to electric vehicles and expensive air space, the need for attaining a cost-efficient construction has never been greater. However, there is an under- standing deficit on historical tunnel failures. The latter is partly due to sensitive information on insurance losses, delays...
Tunnelling construction is growing worldwide as a result of increasing population requiring a wider use of confined space as well as the upkeep of the existing one resulting in rising cost (Paraskevopoulou et al. 2019). The demand for these costly projects is being financed by both public and private sector assisting national economies being greatl...
Network rail oversees and maintains the UK's railway lines, around 20,000 miles of track, carrying around 4.7 million passengers a day. It also oversees all of the major infrastructure on the lines, including bridges and tunnels. Between the years 2014 and 2019 the total amount of money spent on maintenance was approximately £11 billion (Network Ra...
It has been observed that conventional design approaches in geotechnical design neglect the long-term timed-dependent response of the ground. Time-dependent phenomena (ie.. creep, strength-degradation, swelling etc.) can take place either in series or even act simultaneously. Is is paramount thus to investigate and examine their behaviour character...
Uncertainty is prevalent in the ground due to constant modifications throughout its geological history, which results in temporal and spatial variability of its properties and stress regime (Yau et al. 2020). In tunnelling, uncertainty has the tendency to propagate through the different project' stages, e.g. from geotechnical parameters to rock mas...
Underground excavations for the development of infrastructure, mining operations, waste management etc. require support measures to ensure stability both during their construction and operational phases, which highly depends on the rock mass strength and deformability. Discontinuities within the rock mass are intrinsic features which determine said...
The long-term strength and time-to-failure of brittle rocks has become increasingly important with the increased interest in the storage of used nuclear fuel in deep geological repositories. This paper critically reviews and analyzes the currently available time-to-failure data for various brittle rock types. The current best approach on estimating...
Overbreak can be a significant challenge in tunnelling and is usually assessed on a project-by-project basis. This paper attempts to quantify tunnel overbreak in jointed rock masses by producing a predictive model that practitioners can utilize at the preliminary design stage. Discontinuum numerical analysis of a circular-shaped tunnel is performed...
Underground excavations for the development of infrastructure, mining operations, waste management etc. require support measures to ensure stability both during their construction and operational phases, which highly depends on the rock mass strength and deformability. Discontinuities within the rock mass are intrinsic features which determine said...
Overbreak can be a significant challenge in tunnelling and is usually assessed on a project-by-project basis. This paper attempts to quantify tunnel overbreak in jointed rock masses by producing a predictive model that practitioners can utilize at the preliminary design stage. Discontinuum numerical analysis of a circular-shaped tunnel is performed...
A major challenge that TBM performance is requested to deal with for a successful and effective progress is tunnelling through lithologically and geomechanically heterogeneous rock masses. Such heterogeneous environments are common and recent tunnel examples in the UK include the Hinckley Point C offshore cooling tunnels being driven through interb...
A systematic but straightforward probabilistic approach was adopted for the preliminary design using a tunnel case in Egnatia Odos Highway. This tunnel was excavated in a heterogenous molassic formation in Northern Greece, and more specifically in tectonically undisturbed but lithologically varied sedimentary series. This research aimed to identify...
Understanding the geomechanical behavior of a geological model is still an on-going challenge for engineers and scientists. More challenges arise when considering the long-term behavior of rock materials, especially when exposed to environments that enable time-dependent processes to occur and govern overall behavior. The latter is essential in und...
Site S3 of the King’s Cross Development Zone is located in Central London to the North of King’s Cross Station. The site directly overlies the 11 m deep Thameslink twin-rail tunnels. The excavation of a rotary core borehole on site led to tunnel inward movement recorded by in-tunnel prism arrays. Live monitoring data has been used to investigate an...
The Victorian tunnels that lie on the British's railway network have been vital to facilitating a reliable rail service across the UK for the past 150 years. However, some of these tunnels have started to cause some issues for the network. These tunnels were originally constructed using several rings of brick masonry as a lining. After many years,...
Tunnelling projects seldom meet the initial budget requirements. Commonly, these types of projects suffer from cost overruns, which subsequently lead to project delivery delays mainly due to unsuccessful ground investigation as specified in the literature. The presented work scrutinises the effect of ground investigation in cost overruns. More spec...
The effect of discontinuity stiffness and spacing and intact block stiffness on the transmission of stress waves through a rock mass has been assessed with the use of a large database of 1531 analysis results, generated using a 1D numerical model. This was undertaken by modelling different jointed rock masses as a discontinuum in the Universal Disc...
Time-dependency manifests as several different mechanisms, namely creep, swelling, consolidation, stress relaxation, and dilatancy. Creep is an important mechanism to consider in the design of projects with ultra-long lifespans or for projects developed in rocks that readily creep, such as rock salt. Creep models are typically calibrated at the lab...
Probabilistic methods can provide more insight and facilitate rationalized risk allocation when used in the framework of geotechnical baseline reports (GBR) by assessing the influence of a spatially variable distribution of cavities to tunnelling projects. A novel, probabilistic approach of the spatial distribution of karstic cavities is presented...
Traditional heating using non-renewable energy resources contributes up to 50% of current carbon emission level. Different sources of renewable energy are being exploited and developed to lower the carbon emission level for continuity of healthy living environment. It is found that thermal energy is stored in minewater flooding abandoned mines. The...
Building S1 is a 12-storey office development site that is situated within London, north of King’s Cross Station. The site directly overlies twin Thameslink rail. The construction activities include: ~3 m of surface excavation; insertion of piles either side of – and between – the tunnels; subsequent loading of the piles; and excavation of a 1-stor...
The use of underground space is not a recent novelty. Its use was primarily defined in regards to survival reasons; protection from natural hazards. Currently, there is a notable increase of underground space applications especially in urban environments. The field of underground space uses is vast in response to various reasons: for commuting and...
In the past, engineering geology mainly focused on soil and hard rocks, with little attention paid specifically to weak/soft rocks, defined by a UCS below 25 MPa (ISRM in Int J Rock Mech Min 18:85–110, 1981). Weak rock is an intermediate, which is difficult to analyze, and requires application of both soil and rock mechanics principles. The Sherwoo...
This study uses numerical analysis to preliminarily model the anticipated ground defor-mation and surface settlement that could occur during tunnelling though weak deposits of phosphatic chalk using the finite element program RS2. This paper focuses on the factors that lead to increased and severe surface settlement and proposes mitigation measures...
Probabilistic methods can provide more insight on risk allocation and can be used in ge-otechnical baseline reports (GBR). A novel, probabilistic approach of the spatial distribution of karstic cavities is presented to assess the risk of liner instabilities when tunnelling through karstic limestone. The presented research work is based on the follo...
Being able to predict how the rocks will behave and deform in underground environment over time using practical tools and applied methodologies can lead to design optimization preventing projects delivery delays and cost overruns. Especially in the case of underground nuclear waste repositories where their lifetime is estimated to be over one milli...
During the excavation of a tunnel the accumulated wall displacement and the loading of tunnel support is the result of both the tunnel advance and the time-dependent behaviour of the surrounding rockmass. The current approach to analyze the wall displacement increase is based on the convergence-confinement method performed with either analytical (c...
Understanding how rocks deform over time can lead to elimination of conservatisms in regards to tunnelling design, especially, in the case of nuclear waste repositories where the lifetime span of these projects exceeds one million years. Such projects are designed to be constructed in good quality rocks, most likely brittle rocks. It is commonly as...
The time-dependent behaviour of an elasto-visco-elastic medium is investigated and examined further. Numerical analysis of an advancing tunnel is performed via isotropic axisymmetric finite difference modelling (FLAC by Itasca, 2011) to examine the interaction of tunnel advance and instantaneous closure, short to medium term primary creep and long-...
The formulation of a geotechnical model and the associated prediction of the mechanical behaviour is a challenge engineers need to overcome in order to optimize tunnel design and meet project requirements. Special challenges arise in cases where rocks and rockmasses are susceptible to time-effects and time-dependent processes govern. Progressive ro...
The generally accepted time frame for underground nuclear waste repositories is in the order of one million years. It is necessary to understand the time dependent mechanisms of the host rock and the gradual development of the irreversible deformations around repository excavations, as they will have an impact on the excavation damage zones. In thi...
Over the past few decades’ significant interest from rock engineers has been given to the understanding of the long-term strength and the susceptibility to damage of different rock types. The long-term behaviour of underground openings, in general, is usually associated with time-dependent deformations. Tunnel construction can be very challenging d...
The accurate cost estimation in engineering projects and underground construction in particular, is a key parameter for the project's success. Especially in the preliminary conceptual and design stages, such cost data is crucial for the whole project development, affecting major decisions to be taken. This paper presents cost data focusing on Greek...
In underground projects time-dependent deformations can occur and terminate during the construction process or continue over a long period of time. This kind of behavior takes place under a particular combination of rock mass mechanical properties and in-situ stresses and can occur either under sustained loading and constant stresses or as a relaxa...
Time-dependent deformation processes can occur under sustained loading or as a relaxation process under conditions of fixed strain. Both boundary conditions may within the influence zone of an excavation. The mechanics of response can be visco-elastic deformation or relaxation, time-dependent plastic creep, or time-dependent strength degradation. I...