A case study on the seismic performance of earth dams

The seismic non-linear behaviour of earth dams is investigated by using a well-documented case study and employing advanced static and dynamic coupled-consolidation finite-element analysis. The static part of the analysis considers the layered construction, reservoir impoundment and consolidation, whereas the dynamic part considers the response of the dam to two earthquakes of different magnitude, duration and frequency content. The results of the analysis are compared with the recorded response of the dam and exhibit a generally good agreement. The effects of the narrow canyon geometry, the reservoir impoundment and the elasto-plastic soil behaviour on the seismic dam behaviour are investigated. Finally the implications of the adopted constitutive modelling assumptions on the predicted response are discussed

Thermally induced pore water pressure of reconstituted London clay

Different forms of thermo-active structures have been proposed as a way of making use of the ground temperature to achieve renewable low-carbon heating and cooling in civil engineering construction. Such structures comprise piles, retaining walls or tunnel linings, and are used both as structural components and as conduits for utilising geothermal energy. In the scenario of the underground space in London, it is the thermo-active piles that have received most attention. However, little experimental evidence exists on the thermal behaviour of London clay to aid the design of thermo-active structures. This paper presents advanced laboratory testing on the reconstituted London clay to characterise the effect of temperature on its mechanical behaviour. Particular emphasis is given to thermally induced pore water pressures, as their evolution is not well understood. Tests are conducted in a temperature-controlled isotropic cell developed at Imperial College London. The emphasis of the current paper is on the temperature-based calibrations of different transducers. Soil specimens are isotropically consolidated and then subjected to undrained heating-cooling in the temperature range of 21 to 37 °C. Results obtained are compared with an existing laboratory study on another type of clay

Numerical and analytical investigation of compressional wave propagation in saturated soils

In geotechnical earthquake engineering, wave propagation plays a fundamental role in engineering applications related to the dynamic response of geotechnical structures and to site response analysis. However, current engineering practice is primarily concentrated on the investigation of shear wave propagation and the corresponding site response only to the horizontal components of the ground motion. Due to the repeated recent observations of strong vertical ground motions and compressional damage of engineering structures, there is an increasing need to carry out a comprehensive investigation of vertical site response and the associated compressional wave propagation, particularly when performing the seismic design for critical structures (e.g. nuclear power plants and high dams). Therefore, in this paper, the compressional wave propagation mechanism in saturated soils is investigated by employing hydro-mechanically (HM) coupled analytical and numerical methods. A HM analytical solution for compressional wave propagation is first studied based on Biot’s theory, which shows the existence of two types of compressional waves (fast and slow waves) and indicates that their characteristics (i.e. wave dispersion and attenuation) are highly dependent on some key geotechnical and seismic parameters (i.e. the permeability, soil stiffness and loading frequency). The subsequent HM Finite Element (FE) study reproduces the duality of compressional waves and identifies the dominant permeability ranges for the existence of the two waves. In particular the existence of the slow compression wave is observed for a range of permeability and loading frequency that is relevant for geotechnical earthquake engineering applications. In order to account for the effects of soil permeability on compressional dynamic soil behaviour and soil properties (i.e. P-wave velocities and damping ratios), the coupled consolidation analysis is therefore recommended as the only tool capable of accurately simulating the dynamic response of geotechnical structures to vertical ground motion at intermediate transient states between undrained and drained conditions

Impact of foundation layer characteristics on the seismic response of a tailings dam

The foundation layer thickness and stiffness impact the site response by influencing the fundamental frequencies and vibration modes in soil structure interaction (SSI) problems. From a practical perspective, the geotechnical characterisation of earthfill dams is typically focused on the borrow materials comprising the dam, while the foundation materials are often under-characterised, with the depth to the bedrock commonly only approximately estimated. In the seismic response of dams, these unknowns may also impact the deformation patterns affecting the overall stability of the dam. A back-analysis of seismic recorded data for an existing tailings sand dam is performed, to determine the thickness and stiffness of the soil foundation layer by finite element analysis. A cyclic non-linear model (CNL) is employed in the Finite Element analyses which consider different depths to bedrock and soil stiffness profiles. The results suggest satisfactory agreement with the recorded data in terms of acceleration response spectra and amplification ratios and highlight the impact of the foundation layer characteristics on the overall dam response

Impact of genotype, age of tree and environmental temperature on androgenesis induction of Aesculus hippocastanum L.

Influence of ten different genotypes, age of trees and environmental temperature on induction of androgenesis and apperance albino horse chestnut embryos were studied. Efficiency of in vitro androgenesis via anther and microspore culture had been investigated. Microspores and anthers were used from the same closed flower bud. Androgenic response of different genotypes was measured and compared. Anther induction rates were from 5 to 37.6%, depending on genotype. The number ofembryos per isolated anther varied between 0.5 to 5.0 embryos in anther culture, while in microspore culture varied between 3.0 to 27 embryos, depending on genotype. A microspore culture was 5 - 6 times efficient than anther culture for same genotype. Age of the trees had no influence on androgenesis induction. Temperature of about 4 - 5°C was optimal for androgenic embryo induction. Albino horse chestnut embryos phenomenon depended on genotype. The number of albino appearing in anther washigher than in microspore culture. The same correlation of appearing albino was observed between short and long day. Flow cytogenetic analysis of androgenic embryos originating from anther and microspore culture was done after a first generation of regenerants. All androgenic embryos, the first generation from microspore culture were haploid, while 50% of the regenerants originating from anther culture were haploid, and the other half diploid