Large Scale Tests on Jointed and Bedded Rocks Under Multi-Stage Triaxial Compression and Direct Shear     

Maximiliano R. Vergara  Peter Kudella  Theodoros Triantafyllidis 《Rock Mechanics and Rock Engineering》2015,48(1):75-92

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Subcontinental lithospheric mantle beneath Central Europe     

Jacek Puziewicz  Magdalena Matusiak-Małek  Theodoros Ntaflos  Michel Grégoire  Anna Kukuła 《International Journal of Earth Sciences》2015,104(8):1913-1924

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Modelling of earth and water pressure development during diaphragm wall construction in soft clay     

R. Schfer  Th. Triantafyllidis 《国际地质力学数值与分析法杂志》2004,28(13):1305-1326

The influence of a diaphragm wall construction on the stress field in a soft clayey soil is investigated by the use of a three‐dimensional FE‐model of seven adjacent wall panels. The installation procedure comprises the excavation and the subsequent pouring of each panel taking into account the increasing stiffness of the placed fresh concrete. The soft clay deposit is described by a visco‐hypoplastic constitutive model considering the rheological properties and the small‐strain stiffness of the soil. The construction process considerably affects the effective earth and pore water pressures adjacent to the wall. Due to concreting, a high excess pore water pressure arises, which dissipates during the following construction steps. The earth pressure finally shows an oscillating, distinct three‐dimensional distribution along the retaining wall which depends on the installation sequence of the panels and the difference between the fresh concrete pressure and the total horizontal earth pressure at rest. In comparison to FE‐calculations adopting the earth pressure at rest as initial condition, greater wall deflections and surface ground settlements during the subsequent pit excavation can be expected, as the average stress level especially in the upper half of the wall is increased by the construction procedure of the retaining structure. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

An ISA-plasticity-based model for viscous and non-viscous clays     

W. Fuentes  M. Tafili  Th. Triantafyllidis 《Acta Geotechnica》2018,13(2):367-386

The ISA-plasticity is a mathematical platform which allows to propose constitutive models for soils under a wide range of strain amplitudes. This formulation is based on a state variable, called the intergranular strain, which is related to the strain recent history. The location of the intergranular strain can be related to the strain amplitude, information which is used to improve the model for the simulation of cyclic loading. The present work proposes an ISA-plasticity-based model for the simulation of saturated clays and features the incorporation of a viscous strain rate to enable the simulation of the strain rate dependency. The work explains some aspects of the ISA-plasticity and adapts its formulation for clays. At the beginning, the formulation of the model is explained. Subsequently, some comments about its numerical implementation and parameters determination are given. Finally, some simulations are performed to evaluate the model performance with two different clays, namely a Kaolin clay and the Lower Rhine clay. The simulations include monotonic and cyclic tests under oedometric and triaxial conditions. Some of these experiments include the variation of the strain rate to evaluate the viscous component of the proposed model.  相似文献   

Monotonic and cyclic tests on kaolin: a database for the development,calibration and verification of constitutive models for cohesive soils with focus to cyclic loading     

Torsten Wichtmann  Theodoros Triantafyllidis 《Acta Geotechnica》2018,13(5):1103-1128

A database with about 60 undrained monotonic and cyclic triaxial tests on kaolin is presented. In the monotonic tests, the influences of consolidation pressure, overconsolidation ratio, displacement rate and sample cutting direction have been studied. In the cyclic tests, the stress amplitude, the initial stress ratio and the control (stress vs. strain cycles) have been additionally varied. Isotropic consolidation leads to a failure due to large strain amplitudes with eight-shaped effective stress paths in the final phase of the cyclic tests, while a failure due to an excessive accumulation of axial strain and lens-shaped effective stress paths was observed in the case of anisotropic consolidation with \(q^{\text{ ampl }}< |q^{\text{ av }}|\). The rate of pore pressure accumulation grew with increasing amplitude and void ratio (i.e. decreasing consolidation pressure and overconsolidation ratio). The “cyclic flow rule” well known for sand has been confirmed also for kaolin: With increasing value of the average stress ratio \(|\eta ^{\text{ av }}| = |q^{\text{ av }}|/p^{\text{ av }}, \) the accumulation of deviatoric strain becomes predominant over the accumulation of pore water pressure. The tests on the samples cut out either horizontally or vertically revealed a significant effect of anisotropy. In the cyclic tests, the two kinds of samples exhibited an opposite inclination of the effective stress path. Furthermore, the horizontal samples showed a higher stiffness and could sustain a much larger number of cycles to failure. All data of the present study are available from the homepage of the first author. They may serve for the examination, calibration or improvement in constitutive models dedicated to cohesive soils under cyclic loading, or for the development of new models.  相似文献   

Comparison of damage data from questionnaires and field survey: the case of the June 20, 1978 Thessaloniki (northern Greece) M6.5 earthquake     

A. A. Panou  P. M. Hatzidimitriou  N. Theodoulidis  K. C. Stylianidis  P. Triantafyllidis  S. Zacharopoulos 《Bulletin of Earthquake Engineering》2014,12(6):2821-2841

The earthquake of June 20, 1978 (M6.5) near Thessaloniki, Greece, and the abundant information on damage distribution provided researchers with an opportunity for a more detailed study of earthquake effects. The damage on buildings caused by that earthquake was recorded in several ways. In this paper two of them will be presented and discussed: First, the use of questionnaires filled in by citizens and second, the in situ inspection of the buildings by a team of expert engineers, enriched by data of retrofitting costs, where available. In the current study, the damage data derived from the questionnaires are compared against the ones given by the engineers after they have been both converted to the European Macroseismic Scale 1998 (EMS-98) Damage Grades. It is observed that for EMS-98 damage grades equal and larger than 2 the questionnaire method overestimates damage while for lower grades both approaches provide comparable results.  相似文献   

The influence of the construction process on the deformation behaviour of diaphragm walls in soft clayey ground     

R. Schfer  Th. Triantafyllidis 《国际地质力学数值与分析法杂志》2006,30(7):563-576

Conventional numerical predictions of deep excavations normally neglect the construction process of the retaining structure and choose the earth pressure at rest as initial condition at the beginning of the simulation. The presented results of simulation and measurements during the construction process of the Taipei National Enterprise Center show, that such an assumption leads to an underestimation of the horizontal wall deflection, the surface ground settlements as well as the loading of the struts in case of normally to slightly over‐consolidated clayey soil deposits. The stepwise installation process of the individual diaphragm wall panels results in a substantial modification of the lateral effective stresses in the adjacent ground. Especially the pouring process of the panel and the fresh concrete pressure causes a partial mobilization of the passive earth pressure and a distinct stress level increase in the upper half of the wall. As a consequence of the increased stresses prior to the pit excavation, up to 15% greater ground and wall movements are predicted. Moreover, the increased stress level due to the installation process of the diaphragm wall leads to substantial higher strut loadings during the excavation of the pit. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Pinios (Peneus) River (Central Greece): Hydrological — Geomorphological elements and changes during the quaternary   总被引：1，自引：0，他引：1  

George Migiros  George D. Bathrellos  Hariklia D. Skilodimou  Theodoros Karamousalis 《Central European Journal of Geosciences》2011,3(2):215-228

The Pinios River is the third longest river of Greece. It drains the entire drainage basin of Thessaly (eastern part of Central Greece), part of which is the largest plain of the country. In this research the hydrological, geomorphological and geological characteristics of the riverine area of Pinios were studied. Classification and grouping of these characteristics were then carried out, which led to the segmentation of the Pinios River into seven sections, each one with its own set of thematic data. These sets assign separate functions and evolutions of the river system during the Quaternary. Specifically, the basin of the present Pinios River, before its evolution into a river basin, comprised three separate and independent systems. The present Pinios River emerged as a river system from the merging of the lacustrine paleoenvironments along with the major tributaries that drained large parts of the present hydrological basin and as soon as the karstic openings of the central hill valley and the Tempi valley took place during the Quaternary. The followed methodology for the segmentation of the river can be used for the study of heterogeneous river systems.  相似文献   

Climate change effects on the marine characteristics of the Aegean and Ionian Seas     

Christos Makris  Panagiota Galiatsatou  Konstantia Tolika  Christina Anagnostopoulou  Katerina Kombiadou  Panayotis Prinos  Kondylia Velikou  Zacharias Kapelonis  Elina Tragou  Yannis Androulidakis  Gerasimos Athanassoulis  Christos Vagenas  Ioannis Tegoulias  Vassilis Baltikas  Yannis Krestenitis  Theodoros Gerostathis  Kostantinos Belibassakis  Eugen Rusu 《Ocean Dynamics》2016,66(12):1603-1635

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1-D Theoretical Modeling for Site Effect Estimations in Thessaloniki: Comparison with Observations     

P. Triantafyllidis  P. M. Hatzidimitriou  P. Suhadolc 《Pure and Applied Geophysics》2001,158(12):2333-2347

—?We apply an algorithm based on the modal summation method to theoretically estimate the site effect at selected locations underlain by different geological formations within the city of Thessaloniki (Greece). Complete strong motion synthetics are constructed for all components of motion at each site, for a maximum frequency of 10?Hz. The anelastic, local 1-D velocity models are based on cross-hole data. Four point sources with different azimuths and distances from the city are used to compute the input signals. The theoretical amplification is estimated through spectral ratios of accelerograms obtained by the local 1-D over those obtained by the regional 1-D velocity model. The results from the numerical modeling are compared with those derived from experimental techniques, such as of Standard Spectral Ratio and Horizontal-to-Vertical Spectral Ratio, which had been applied to acceleration data recorded at the same sites. The comparison demonstrates that the theoretical amplifications based on known and simple subsurface geology can be used as a first-order estimate, while for cases of more complex geometries the use of at least 2-D modeling in site effects estimation is mandatory.  相似文献