Abstract

Hungarian experience about the correlation of CPT and DPH results is summarized. A historical review of CPT-DPH and CPT-SPT correlations is presented, and the reliability of the published CPT-DPH correlations is analyzed using recent data from Hungarian geotechnical practice. Based on these data the paper defines soil types where reliable correlation exists and proposes formulas describing the relationships between the CPT and DPH results, because in the case of hard state clays and soils containing gravel an acceptable relationship cannot be stated.

In case of some nuclear power plants constructed at the soft soil sites, liquefaction should be analysed as beyond design basis hazard. The aim of the analysis is to define the postevent condition of the plant, definition of plant vulnerabilities, and identification of the necessary measures for accident management. In the paper, the methodology of the analysis of liquefaction effects for nuclear power plants is outlined. The procedure includes identification of the scope of the safety analysis and the acceptable limit cases for plant structures having different role from accident management point of view. Considerations are made for identification of dominating effects of liquefaction. The possibility of the decoupling of the analysis of liquefaction effects from the analysis of vibratory ground motion is discussed. It is shown in the paper that the practicable empirical methods for definition of liquefaction susceptibility provide rather controversial results. Selection of method for assessment of soil behaviour that affects the integrity of structures requires specific considerations. The case of nuclear power plant at Paks, Hungary, is used as an example for demonstration of practical importance of the presented results and considerations.

Due to the construction of underground structures and hazardous waste storages, understanding and modelling of seepage in concrete has become an important issue in life-span analyses. The theories and calculation methods of unsaturated soil mechanics provide an opportunity to analyze water flow in other types of porous media (e.g. concrete) as well. This study deals with the determination of the permeability for unsaturated and saturated concrete and modelling the water flow in concrete. The direct measurement of the saturated permeability, the preparation of the drying water retention curve and determination of the depth of penetration of water under pressure are involved in the series of tests. For the fitting method of the experimental water retention curves were used Fredlund and Xing (1994) and van Genuchten (1980) model. The theory of lateral shift was applied to estimate the wetting water retention curve from the drying WRC. Thus, we could calculate the unsaturated permeability functions with Fredlund et al. (1994) and van Genuchten (1980) model. The finite element modelling of the standard test for watertightness were performed with Midas GTS using the measured and calculated unsaturated property functions.

The major objective of this paper is to evaluate a stand-point for integral shroud coupling, regarding the complex problem of nonlinear resonance vibrations of a shrouded blade with friction and impact effects. Following the load sequence in the start-up and further uploading to base load, a nonlinear cyclic FE static computation with friction forces at the shroud interface delivers contact stress results essential for assessment of a reliable shroud coupling. The FE refinement study at the shroud interface proves the reliability of the computed eigenfrequencies with respect to the harmonic engine excitation. Using nonlinear dynamic simulations of the shroud connection with friction forces, contact stiffness, surface roughness and impacts, the decoupling between the static and dynamic motions at the shroud interface is demonstrated. Based on the one-dimensional description of vibration characteristics for the shrouded blade, the resulting normal and tangential contact stiffness are evaluated from the computed 3D FE nodal diameter diagrams. The excitation forces acting on the blade are determined with the stimulus concept, in which an empirical factor is estimated from pulsation measured in the combustor chamber over the frequency range of the blade vibrations. The entire process is illustrated for the redesigned Z-lock interface on the shroud of a gas turbine stage whose contact surfaces had shown fretting problems. The numerical results confirm possible contact failures for the old shroud configuration. The blade calculated with the modified shroud connection shows numerically, stable dynamic behavior and will therefore prevent further fretting contact problems.

Abstract

The seismicity of Hungary can be considered moderately active, nevertheless contemporary reports from the past approx. 350 years documented surface manifestations of liquefaction occurrences. The last such earthquake was the 1956 Dunaharaszti ground motion, for which the location of two liquefied sites could be identified approx. 60 years after the event. This provided an excellent opportunity to analyze possibly the only accessible liquefied sites in Hungary. Analysis of the two sites included field and laboratory tests allowing the back-calculation of maximum horizontal ground acceleration of the earthquake. This parameter was previously unknown because the closest seismometer saturated during the event. The performed back-analysis using the principles of paleoliquefaction studies was the first of such analyses in the country. In areas with low to moderate seismicity, geotechnical engineers often neglect and overlook liquefaction hazard, however, when it is addressed, the hazard is often overestimated due to improper characterization of the seismic loading and site characterization. To explore this observation more deeply, probabilistic seismic and liquefaction hazard assessment were carried out at the two liquefied sites and it was found that this conclusion is also valid for Hungary, but the degree of conservatism of the pseudo-probabilistic procedures decreases with increasing earthquake return period (lower annual probability of occurrence).

Vulnerability assessment of structures is a vitally important topic among earthquake engineering researchers. Generally, their primary focus is on the seismic performance of buildings. Less attention is paid to geotechnical structures, even though information about the performance of these structures (e.g. road embankments, levees, cuts) during an earthquake is essential for planning remediation and rescue efforts after disasters. In this paper the seismic fragility functions of a highway embankment are defined following an analytical methodolgy. The technique is a displacement-based evaluation of seismic vulnerability. Displacements of an embankment during a seismic event are approximated by a 2-D nonlinear ground response analysis using the finite element method. The numerical model was calibrated based on the results of a 1-D nonlinear ground response analysis. The expected displacements were calculated for 3 different embankment heights and Peak Ground Acceleration (PGA) values between 0,05 and 0,35g. Based on the results of the 2-D finite element analysis, the relationship between displacements and different seismic intensity measures (PGA, Arias-intensity) was investigated. Different damage states were considered, and the probability of their exceedance was investigated. The seismic fragility functions of the embankments were developed based on probability of exceedance of these different damage states based on a log-normal fragility function. The legitimacy of using a log-normal fragility function is also examined.