- Coventry, UK
Panagiotis (Panos) Sitarenios
Coventry University, Energy, Construction and Environment, Department Member
- 2016 - PhD in Geotechnical Engineering, NTUA, Athens, Greece 2005 - MSc. in Tunnelling - Geotechnical Engineering, N... more2016 - PhD in Geotechnical Engineering, NTUA, Athens, Greece
2005 - MSc. in Tunnelling - Geotechnical Engineering, NTUA, Athens, Greece
2003 - Diploma in Civil Engineering, University of Patras, Greeceedit
Research Interests:
The paper presents a regression analysis to fit the Burdine, Brutsaert and Mualem SWCC equations with the experimental data from seven fine- grained soils from Greece. A series of logarithmic correlations are proposed, pro-viding fair... more
The paper presents a regression analysis to fit the Burdine, Brutsaert and Mualem SWCC equations with the experimental data from seven fine- grained soils from Greece. A series of logarithmic correlations are proposed, pro-viding fair estimates of the curve-fitting parameters with classification soil proper-ties (grain size distribution and atterberg limits), expressed using the weighted PI, as proposed by Zapata et al. (2000).
Research Interests:
The paper presents a regression analysis to fit the Burdine, Brutsaert and Mualem SWCC equations with the experimental data from seven fine- grained soils from Greece. A series of logarithmic correlations are proposed, pro-viding fair... more
The paper presents a regression analysis to fit the Burdine, Brutsaert and Mualem SWCC equations with the experimental data from seven fine- grained soils from Greece. A series of logarithmic correlations are proposed, pro-viding fair estimates of the curve-fitting parameters with classification soil proper-ties (grain size distribution and atterberg limits), expressed using the weighted PI, as proposed by Zapata et al. (2000).
Research Interests:
The paper describes and evaluates an incremental plasticity constitutive model for unsaturated, anisotropic, nonexpansive soils (CMUA). It is based on the modified Cam‐Clay (MCC) model for saturated soils and enhances it by introducing... more
The paper describes and evaluates an incremental plasticity constitutive model for unsaturated, anisotropic, nonexpansive soils (CMUA). It is based on the modified Cam‐Clay (MCC) model for saturated soils and enhances it by introducing anisotropy (via rotation of the MCC yield surface) and an unsaturated compressibility framework describing a double dependence of compressibility on suction and on the degree of saturation of macroporosity. As the anisotropic and unsaturated features can be activated independently, the model is downwards compatible with the MCC model. The CMUA model can simulate effectively: the dependence of compressibility on the level of developed anisotropy, uniqueness of critical state independent of the initial anisotropy, an evolving compressibility during constant suction compression, and a maximum of collapse. The model uses Bishop's average skeleton stress as its first constitutive variable, favouring its numerical implementation in commercial numerical analysis codes (eg, finite element codes) and a unified treatment of saturated and unsaturated material states.
Research Interests:
This paper interprets the hydromechanical behaviour of a steep forested instrumented slope during an artificial rainfall event, which triggered a shallow slope failure fifteen hours after rainfall initiation. The soil’s mechanical... more
This paper interprets the hydromechanical behaviour of a steep forested instrumented slope during an artificial rainfall event, which triggered a shallow slope failure fifteen hours after rainfall initiation. The soil’s mechanical response has been simulated by coupled hydro-mechanical finite element analyses, using a critical state constitutive model that has been extended to unsaturated conditions. Failure occurs within a colluvium shallow soil cover, characterised as a silty sand of low plasticity. The hydraulic and mechanical parameters are calibrated, based on an extended set of experimental results, ranging from water retention curve measurements to triaxial stress path tests under both saturated and unsaturated conditions. Rainfall is simulated as a water flux at the soil surface and suitable boundary conditions account for the hydromechanical interaction between the soil cover and the underlying bedrock. The results are compared with field data of the mechanistic and the hydraulic responses up to failure and are found to provide a very satisfactory prediction. The study identifies water exfiltration from bedrock fissures as the main triggering agent, resulting in increased pore pressures along the soil - bedrock interface, reduced available shear strength and cause extensive plastic straining, leading to the formation and propagation of a failure surface.
Research Interests:
The present study utilizes a series of anisotropic consolidation tests followed by a decrease of the mean stress under constant axial load to define the yield locus of anisotropically consolidated soil samples and to evaluate the ability... more
The present study utilizes a series of anisotropic consolidation tests followed by a decrease of the mean stress under constant axial load to define the yield locus of anisotropically consolidated soil samples and to evaluate the ability of different yield surface shapes in accommodating the observed behaviour. Nine different axial load tests are used, including three different water contents and three different consolidation stress obliquities. For each test, the “end of compression” and the “failure initiation” stress states are assumed to define the yield locus. Two isotropic and two anisotropic ellipsoids are used to describe the experimentally determined yield points. It proves that a distorted ellipsoid is superior in capturing the behaviour, provided that its aspect ratio is handled as an independent variable.
Research Interests:
The paper discusses the effect of using several ground constitutive models on the numerical predictions of tunnelling induced ground movements. The numerical study utilizes an advanced 3D finite element model for EPB tunnelling, proposed... more
The paper discusses the effect of using several ground constitutive models on the numerical predictions of tunnelling induced ground movements. The numerical study utilizes an advanced 3D finite element model for EPB tunnelling, proposed by the authors, which allows realistic modelling of geometrical and operational complexities of EPB machines. Two constitutive models are used to describe ground behaviour, an elastic – plastic with Mohr – Coulomb failure surface and the Modified Cam-Clay (MCC) critical state plasticity model. For a fair comparison, the two models are calibrated to have similar compressibility and shear strength at stress levels corresponding to the tunnel axis. The results indicate that the MCC model leads to significantly higher crown displacements compared to the Mohr – Coulomb analyses, while ground surface settlement predictions are comparable. The observed behaviour is explained by the stress-dependent compressibility and more realistic non-linear stress-strain response of the MCC.
Research Interests:
This paper studies the influence of the tunnel face support on tunnelling-induced ground movements via numerical methods. An advanced 3D FEM numerical model is used which realistically simulates the main characteristics of an EPB tunnel... more
This paper studies the influence of the tunnel face support on tunnelling-induced ground movements via numerical methods. An advanced 3D FEM numerical model is used which realistically simulates the main characteristics of an EPB tunnel excavation procedure (i.e., the steering gap between the shield and the surrounding soil, the segmental lining, grout pressure and its consolidation characteristics, the rate of excavation advance). The Simulia Abaqus FEM code is used to perform coupled hydro-mechanical analyses which can account for the effect of the groundwater. The results suggest a strong interplay between the applied face pressure, ground strength and the anticipated surface settlement. In general, an increased ground strength (favorable geotechnical conditions) limits the anticipated surface settlements even under relatively low face pressures (i.e., 50% of the horizontal total geostatic stress), while examining excavation through poor geotechnical conditions reveals an increased sensitivity of the ground settlement on the magnitude of the applied face pressure. Overall, the results reveal a strong relation between face stability conditions and surface settlement, with face stability being a necessary but not a sufficient condition for surface settlement minimization.
Research Interests:
This paper studies numerically the influence of different: a) steering gap openings; b) tail grouting pressures and; c) steering gap pressure gradients, on surface settlements induced during EPB tunnelling. The numerical study is... more
This paper studies numerically the influence of different: a) steering gap openings; b) tail grouting pressures and; c) steering gap pressure gradients, on surface settlements induced during EPB tunnelling. The numerical study is performed with an advanced 3D finite element model in the Simulia Abaqus program, which provides detailed and realistic simulation of EPB tunnelling. The results reveal a significant effect of the size of the steering gap and its filling conditions (empty, full, partially filled with process liquids), while subsequent tail grouting proves to be incapable to reverse the adverse effects in ground surface settlement caused by various volume loss sources.
Research Interests:
The paper discusses the results of 3D finite element analyses to investigate the effect of face support pressure and soil permeability on face stability conditions in EPB tunnelling. Two main types of face behavior are identified:... more
The paper discusses the results of 3D finite element analyses to investigate the effect of face support pressure and soil permeability on face stability conditions in EPB tunnelling. Two main types of face behavior are identified: Undrained conditions ahead of the tunnel face, typically occurring in soils with permeability less than about k=5 • 10-7 m/s, are shown to be favourable for face stability; analyses show that an applied face pressure comparable with the initial hydrostatic pore pressure is sufficient for adequate face stability, even for soils of relatively low strength. Drained or partially drained conditions, typically occurring in soils with permeability higher than about k=5 • 10-6 m/s, show that face stability is strongly dependent on the horizontal effective stress of the muck in the excavation chamber; the presence of even a small effective stress in the muck is very beneficial for face stability conditions and can be a possible explanation of successful EPB tunnelling through relatively permeable soils.
Research Interests:
This paper investigates numerically face stability and deformation of EPB tunnels excavated below the groundwater table. Emphasis is given in the proper simulation of the pressure exerted by the excavated material filling the front... more
This paper investigates numerically face stability and deformation of EPB tunnels excavated below the groundwater table. Emphasis is given in the proper simulation of the pressure exerted by the excavated material filling the front chamber of the EBP machine. The paper presents the results of 3D coupled hydromechanical analyses for tunnel face stability, using the computer code ABAQUS with the Mohr–Coulomb and Modified Cam-Clay constitutive models, for various geotechnical and hydraulic conditions. The undrained shear strength of the ground is shown to be an effective control parameter for interpreting and normalising the results under different geotechnical conditions, irrespective of the adopted constitutive model.
Research Interests:
The behaviour of the excavation face is one of the most critical aspects in urban tunnels excavated with conventional methods (i.e., not with TBMs), as the majority of such failures are due to excessive face extrusion, often leading to... more
The behaviour of the excavation face is one of the most critical aspects in urban tunnels excavated with conventional methods (i.e., not with TBMs), as the majority of such failures are due to excessive face extrusion, often leading to face collapse. This paper investigates the stability conditions and deformational behaviour of an unsupported tunnel face through an extensive set of three dimensional finite element analyses. The Modified Cam-Clay constitutive model is used in modelling the behaviour of the ground. The obtained results are used in understanding how various geometrical (tunnel diameter, depth of overburden), as well as geotechnical conditions (ground strength and compressibility) affect the behaviour of the tunnel face. Using these results, face stability is quantified in terms of the magnitude of face extrusion by correlating an average normalized face extrusion with a face stability factor similar to that proposed by Prountzopoulos (2012). Finally, an attempt is made to calculate the factor of safety (FS) of an unsupported tunnel face.
Research Interests:
In this paper an Intrinsic Compressibility Framework for anisotropic clayey soils (Belokas and Kavvadas 2011), is extended, to account for the effect of partial saturation, leading to a complete volumetric compression framework for... more
In this paper an Intrinsic Compressibility Framework for anisotropic clayey soils (Belokas and Kavvadas 2011), is extended, to account for the effect of partial saturation, leading to a complete volumetric compression framework for anisotropic, unsaturated clayey soils. The proposed framework incorporates compression curves that depend on both suction and degree of saturation to capture the bonding effect of interparticle forces formed when degree of saturation drops below unity. It can reproduce: a) compression lines that depend on the level of stress induced anisotropy, b) unique compression lines for saturated materials irrespectively of the level of the applied suction, c) a continuously increasing post yield compressibility for soils compressed under constant suction, and lastly d) a maximum of collapse.
Research Interests:
The paper presents a new constitutive model to describe the mechanical behaviour of uncemented anisotropically consolidated clayey soils, by extending and improving previous models developed by the authors (Kavvadas 1982; Belokas &... more
The paper presents a new constitutive model to describe the mechanical behaviour of uncemented anisotropically consolidated clayey soils, by extending and improving previous models developed by the authors (Kavvadas 1982; Belokas & Kavvadas 2010) with respect to the anisotropic compression and the uniqueness of critical state. The model incorporates
a rotated distorted ellipsoidal yield surface, a non-associated flow rule to reproduce zero total horizontal strains under K0 conditions and a new mixed hardening rule consisting of an isotropic part to control the evolution of the size of the yield surface and a rotational - distortional part to describe the evolution of anisotropy. The model is capable of reproducing a) Intrinsic Compression Curves that depend on the degree of developed anisotropy and b) unique critical state conditions. The model capabilities are demonstrated through a series of numerical analyses.
a rotated distorted ellipsoidal yield surface, a non-associated flow rule to reproduce zero total horizontal strains under K0 conditions and a new mixed hardening rule consisting of an isotropic part to control the evolution of the size of the yield surface and a rotational - distortional part to describe the evolution of anisotropy. The model is capable of reproducing a) Intrinsic Compression Curves that depend on the degree of developed anisotropy and b) unique critical state conditions. The model capabilities are demonstrated through a series of numerical analyses.
Research Interests:
Research Interests:
The soil-water characteristic curve plays the major role in describing both the hydraulic and mechanical behaviour of unsaturated soils. In the present study the Fredlund and Xing and van Genuchten equations have been used to model the... more
The soil-water characteristic curve plays the major role in describing both the hydraulic and mechanical behaviour of unsaturated
soils. In the present study the Fredlund and Xing and van Genuchten equations have been used to model the soil-water characteristic
curves of typical Greek soils including three hard soils - weak rocks. It is attempted to correlate the optimum curve fitting
parameters with physical characteristics of the soils and compare parameters of soil-water characteristic curves of undisturbed
and recomposed soils.
soils. In the present study the Fredlund and Xing and van Genuchten equations have been used to model the soil-water characteristic
curves of typical Greek soils including three hard soils - weak rocks. It is attempted to correlate the optimum curve fitting
parameters with physical characteristics of the soils and compare parameters of soil-water characteristic curves of undisturbed
and recomposed soils.
Research Interests:
Observations from past earthquakes indicate that low to medium high earth embankments or levees, resting on soft clayey soils rarely experience catastrophic damage, unless liquefaction either of the embankment material or of sandy lenses... more
Observations from past earthquakes indicate that low to medium high earth embankments or levees, resting on soft clayey soils rarely experience catastrophic damage, unless liquefaction either of the embankment material or of sandy lenses in the subsoil is involved. However, under severe earthquake events significant permanent displacements are anticipated and should be evaluated in conjunction with serviceability and pavement reparability criteria. In this context, traditional limit equilibrium analyses and the factor of safety approach have little to offer in evaluating the embankment performance. Simplified procedures for the evaluation of earthquake induced permanent displacements in slopes provide index values of co seismic displacements which are used to assess embankment performance in many cases in an arbitrary manner. Elaborate dynamic analyses of two and three dimensional finite element/differences models provide a more complete deformation pattern of the embankment and the foundation soil and allow a more justifiable evaluation of the embankment performance. At the same time it is possible to consider explicitly the actual ground properties and stratigraphy, as well as to evaluate ground improvement effects.
In this context, a motorway embankment build on soft peaty soil, which has been improved by vibroreplacement (stone columns) and subsequent preloading, is examined with respect to its seismic performance. It is shown that two dimensional dynamic analyses of such embankments, even in cases where only conventional site investigation data is available, provide a valuable insight on their seismic response and performance. Spatial variability of the soil properties should be considered in the modeling in order to simulate a realistic pattern of embankment co-seismic deformation. Performance criteria to evaluate the results of those analyses should go beyond permanent displacements and should consider pavement crack width opening and step development. It is recognized that the complexity of such analyses and the large number of assumptions required may shadow in some cases the actual performance. The use of simplified procedures to estimate slope displacements provide an anchoring point when experimental or other empirical evidence is not available.
In this context, a motorway embankment build on soft peaty soil, which has been improved by vibroreplacement (stone columns) and subsequent preloading, is examined with respect to its seismic performance. It is shown that two dimensional dynamic analyses of such embankments, even in cases where only conventional site investigation data is available, provide a valuable insight on their seismic response and performance. Spatial variability of the soil properties should be considered in the modeling in order to simulate a realistic pattern of embankment co-seismic deformation. Performance criteria to evaluate the results of those analyses should go beyond permanent displacements and should consider pavement crack width opening and step development. It is recognized that the complexity of such analyses and the large number of assumptions required may shadow in some cases the actual performance. The use of simplified procedures to estimate slope displacements provide an anchoring point when experimental or other empirical evidence is not available.
Research Interests:
The new highway constructed in south Greece includes many civil engineer constructions, such as tunnels and cut & covers, bridges, embankments, deep excavations, improvement of existing road pavings, widening e.t.c. The paper focuses on... more
The new highway constructed in south Greece includes many civil engineer constructions, such as tunnels and cut & covers, bridges, embankments, deep excavations, improvement of existing road pavings, widening e.t.c. The paper focuses on the underground structures and especially on the design and the special conditions of “Artemissio” (Left Branch), “Neochori”, “Sterna” and “Kalogeriko” tunnel. The geotechnical conditions where they are excavated, as well as the design approach of temporary support system and final lining are described, while a mention in special geotechnical and other issues for each tunnel and their management is included.
Research Interests:
The present presentation summarizes the results of an ongoing research effort on the numerical simulation of EPB tunnelling conducted in the National Technical University of Athens within the framework of the European Research Program... more
The present presentation summarizes the results of an ongoing research effort on the numerical simulation of EPB tunnelling conducted in the National Technical University of Athens within the framework of the European Research Program (FP7) NeTTUN: "New Technologies for Tunnelling and UNderground Structures".
The presented results focus on the effect of different ground strength, permeability and face pressure on face stability of EPB excavated tunnels. Face stability is assessed through plots of face extrusion (horizontal face displacement) vs. ground strength. Face extrusion is calculated through 3D coupled hydro-mechanical analyses, using advanced critical state plasticity constitutive models (mainly the Modified Cam Clay).
The presented results focus on the effect of different ground strength, permeability and face pressure on face stability of EPB excavated tunnels. Face stability is assessed through plots of face extrusion (horizontal face displacement) vs. ground strength. Face extrusion is calculated through 3D coupled hydro-mechanical analyses, using advanced critical state plasticity constitutive models (mainly the Modified Cam Clay).