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

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.     

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

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.     

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

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.     

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

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.     

Horse mackerel egg identification using DNA methodology

Egg identification in plankton samples is usually needed for purposes of stock assessment. Until recently, only morphological characters were used for identifying the eggs of different fish species. Late developmental stages are easily distinguishable due to pigmentation as well as egg and oil globule size range. However, for early stages, these characteristics are difficult to be discriminated and may overlap with other species. European horse mackerel species (Trachurus trachurus, T. mediterraneus, T. picturatus) overlap significantly in their spawning areas in some European waters. Because of the fact that their eggs are morphologically similar, genetic methodologies are needed to identify eggs and larvae to species correctly. In the present study, formalin‐ and ethanol‐preserved eggs were tested to estimate the efficacy of genetic methodologies for species identification of eggs when different preservatives are used. A 370‐bp fragment of cytochrome b was successfully amplified followed by restriction fragment analysis with two restriction enzymes aiming to identify the eggs to species. Horse mackerel egg identification was accomplished with the maximum success in ethanol‐preserved eggs. However, it seems that various preservatives had different effects on the DNA quality of eggs as genetic identification was less successful in formalin‐preserved eggs. Preserving in ethanol a part of the eggs obtained in plankton surveys is suggested for purposes of accurate genetic identification, even if their morphological features are distorted in time.     

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

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.     

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

—?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.     

Mineral formation in an acid pit lake from a high-sulfidation ore deposit: Kirki, NE Greece

Open pit mining of base-metals from the high-sulfidation epithermal type deposit of Kirki (Thrace, NE Greece) resulted in the formation of an acid pit lake by infilling of the open cast by rain and draining waters after mine closure. The high toxic metals content of the ore, the limited buffering capacity of host rocks and the direct exposure of the ore zone to weathering result in an intense release of metals into the pit lake. The acidic and oxidative pit lake waters show high concentrations of trace metals. A mineral precipitate, covering the floor of the pit lake, comprises secondary anglesite, several species of the jarosite-group, rozenite, melanterite, wroewolfeite, gypsum, bukovskyite, beaverite, scorodite and minor goethite. The mineral precipitate presents a significant heavy metal content indicating effective removal of metals from the acid waters. Compared to other pit lakes in high-sulfidation type deposits it has a higher metal load, consistent with the mineralogy and grade of ore in pit walls.