1,720,974 research outputs found
Coupled thermo–hydro–mechanical processes for the Dutch radioactive waste repository
No full textDisposal of spent nuclear fuel and long lived radioactive waste in deep clay geological formations is one of the promising options worldwide. In this concept of the geological disposal system, the Boom Clay is considered as a potential host rock when designing a generic waste repository in the Netherlands. For design and evaluation of a repository for geologic disposal of nuclear wastes one of its principal concern is the thermal loading. High-level radioactive waste and spent fuel generate considerable amounts of heat. When those waste types are disposed in a geological repository the elevated thermal effect on the behaviour of soils surrounding nuclear waste disposal give rise to change in hydraulic and mechanical properties is a significant factor for repository design. Understanding these time-dependent phenomena processes in relation to both the effects of pore water dissipation and of the thermal expansion is essential for reliably assessing repository performance and evaluating the safety case. This paper presents some of the investigation on the thermal processes with emphasis on the coupled Thermo-Hydro- Mechanical (THM) processes for the disposal concept of a radioactive waste disposal facility, in Boom Clay at a depth of about 500m.Geo-engineerin
Probabilistic performance assessment of a deep tunnel for a radioactive waste repository in French COx claystone
No full textA preliminary probabilistic study of the stability of a circular drift excavated for a radioactive waste repository in the French Callovo-Oxfordian claystone is presented and discussed. An analytical mechanical model assuming isotropic elastic behaviour and linear plastic softening was used. Particular emphasis here is placed on the uncertainty of mechanical property values. The test results from several laboratories showed considerably variable property values and they have been interpreted statistically in this investigation. The obtained statistical results were used in a Monte Carlo framework. The performance of the drift was evaluated in terms of the probability of threshold exceedance in the extent of the plastic zone.Geo-engineerin
Contact modelling in the Material Point Method
No full textIn recent years, the Material Point Method has emerged as a promising alternative to the Finite Element Method for solving problems involving localised deformations, large displacements or rotations, fracture, contact/impact problems and others. FEMhas been a staple of engineering disciplines both in academia and industry for decades, however its shortcomings make it less suitable for certain applications in geotechnical engineering. MPM, bridges the gap between Finite Elements and meshless methods by using a reference background grid and moving material points to represent the discretised material. This gives it the capacity to faithfully reproduce behaviours which would be difficult to capture without involved procedures with other presently availablemethods. In this work, methods of modelling contact between deformable continua were explored in the context of theMaterial PointMethod with the goal of producing usable code applicable to geotechnical engineering scenarios, thus supplementing the work of the Geo-Engineering section at TU Delft. A dynamic, explicit computational framework was developed in the FORTRAN programming language allowing efficient modelling of multi-body interactions using different contact conditions. The influence of decisions regarding the contact logic, definition of surface normals and variable update procedures were compared. Coupling between FEM and MPM was explored for solving problems involving regions with small and large deformations. The work presented here aims to extend the applicability of theMaterial PointMethod to soil-structure interaction problems. In addition to the contact algorithms explored, an alternative method for material point generation using Centroidal Voronoi Tessellations was explored. This allowed for improved distribution of material points over domains of generic shape, while achieving results similar to a FEM-based approach, which uses Gauss Points. Placing material points at the integration points brings the inherent disadvantage that complex domain shapes cannot be easily discretised using a structured grid. The ability of the two methods to reproduce a uniform density field was compared and the novel approach was implemented for a contact problem - an elastic collision between two disks. Results showed a the potential of the CVT-based scheme for use in further analyses.Civil Engineering and GeosciencesGeoscience & EngineeringGeo-Engineerin
Numerical Investigation of Inverse Analyses Using Hydraulic Measurements of Embankments
No full textFor decades, researchers try to model the subsoil as accurate as possible in order to make cost-efficient and safe geotechnical decisions. A troublesome aspect in modelling of the soil is to determine the heterogeneity within the soil, as this is usually associated with a great deal of uncertainty. Delft University of Technology used a recursive filter, the Ensemble Kalman Filter (EnKF), to reduce the spatial uncertainty of a numerically modelled hydraulic conductivity field, using pore water pressure measurements at limited locations. The EnKF does however require prior knowledge of the involved probability distributions concerning the hydraulic conductivity field. In addition, Gaussian assumptions of the involved probability distributions are ought to be valid. Many more methods are available to back calculate a hydraulic conductivity field from pore water pressure measurements, i.e. to perform an inverse analysis. A proper overview of these methods and their respective usability is however not available. The aims of this thesis are to provide a clear overview of the available methods to perform inverse analyses and to describe the similarities and the differences between them. In this thesis, a complete inverse analysis is divided into the formulation of the inverse problem and the optimisation method used to solve the inverse problem. An inverse analysis can be formulated as an objective function to be minimised in order to find the optimal approximation of the hydraulic conductivity. Such formulations include, the Least Square objective function, the Maximum Likelihood based objective function and several Bayes' theorem based objective functions. Objective functions are minimised using optimisation methods. The optimisation methods are subdivided in finite difference based optimisation methods and metaheuristics. Finite difference optimisation methods include the Gauss-Newton method, Steepest-Descent method and the Levenberg-Marquardt method. Metaheuristics include the Genetic Algorithm (GA), Particle Swarm Optimisation (PSO), Ant Colony Optimisation (ACO), Greedy Randomised Adaptive Search Procedure (GRASP), Guided Local Search, Iterated Local Search and Tabu Search. Alternately, an inverse analysis can be formulated as a probability distribution to be approximated, such methods are regarded as sequential Monte Carlo based inverse analyses. Sequential Monte Carlo based inverse analyses include Particle Filters (PF) and the Ensemble Kalman Filter, which are derived from Bayes' theorem. Based on the usability following a literature study, several complete inverse analyses are numerically implemented and applied to multiple cases which vary in geometry and available information. The numerical analysis concerns an analysis of the numerical stability, accuracy, uniqueness, computational effort and reliability of the results. The main conclusion is that the Ensemble Kalman Filter is the most appropriate method to use when reliable information concerning the correlation structure and the mean and variance of the involved Gaussian distributions is available. When the statistical information is unreliable, the Levenberg-Marquardt optimisation method combined with the Sequential Bayesian objective function is more appropriate. In one dimensional linear problems, the Gauss-Newton Least Square method and the Levenberg-Marquardt Least Square method can be used, given that the expected soil variability is limited and the measurement errors are negligible.Civil Engineering and GeosciencesGeoscience & EngineeringGeo-Engineerin
The impact of overburden pressure on unsaturated shrinkage behavior of fine-grained soils
No full textThe impact of overburden pressure on shrinkage behavior of fine-grained soil is investigated by means of a shrinkage curve based on experimental data. It was found that to speak of shrinkage means that one must define the initial soil volume and occurring changes. Three definitions of soil volume were determined, based on settlement, horizontal & vertical shrinkage and soil matrix only. For the first two definitions, a decrease in minimal void ratio was found, indicating impact of applied pressure. The impact was quantified using a mathematical formulation based on incremental stress and a compression constant. For the last definition, no impact was detected, indicating that shrinkage is a characteristic material relationship on soil matrix level.Geo-engineeringGeoscience & EngineeringCivil Engineering and Geoscience
Editorial: Soil–atmosphere interaction
No full textThis themed issue has its origin in the 14th IACMAG conference in Kyoto, Japan where a conference session on this topic was convened. The success of the session and debate caused by the session led to the idea of a special issue published in Environmental Geotechnics. After which, a call was made to the research community for papers. The wide range of topics and enthusiastic response illustrates that this topic is an important one for geotechnical engineering and the wider society.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Geo-engineerin
Probability distribution functions for geomechanical properties from well log data
No full textReliability based calculations and the identification of uncertainties in geomechanical calculations are receiving an increasing amount of attention to evaluate risk. This poses multiple challenges, of which one is the variability of input parameters such as geomechanical properties, geological structures and distribution of material properties. In this thesis, the use of reliability geomechanical analysis in oil and gas reservoirs is investigated. The focus lies on obtaining PDF from well log data, to investigate the effect of stochastic material properties on geomechanical analysis and to identify important uncertainties other than material properties in geomechanical analyses e.g. geometry and depletion pressure distribution. A method of deriving stochastic material properties from well log data is presented and stochastic material properties are described using PDF. A test is introduced to select the most appropriate PDF in terms of best fit. The most appropriate PDF can be obtained by comparing a PDF to the histogram of a set of well log data. In addition to this, it was observed that removing linear depth trends reduce the uncertainty in most observed material properties. Stochastic material properties have been used as input for a series of probabilistic geomechanical analyses. The main geomechanical reliability response studied in this thesis is large scale subsidence caused by pressure changes in a reservoir. Large scale subsidence has also been compared to a small scale SCU response. The effects of stochastic material properties on subsidence are compared to SCU in geomechanical reliability response. For subsidence it was found that, increasing the resolution of uncertainty, i.e. increasing the amount of layers, reduces the variation of results. For SCU geomechanical reliability, increasing the resolution of uncertainty The results increases the variation of results. For the geomechanical analyses, example real reservoir data are used to study uncertainties in geomechanical reliability analyses. Data from a real case were used to illustrate the effects of reservoir geometry and depletion pressure distribution on the calculated subsidence above a depleting reservoir. The different geomechanical analyses demonstrate the need to include spatial variation of the reservoir, i.e. the variation of the pressure distribution and both vertical and lateral variation in material properties.Geo-engineeringGeoscience & EngineeringCivil Engineering and Geoscience
Assessing the performance of ground source heat pumps in neighboring medium-size households
No full textThe Master's programme Industrial Ecology is jointly organised by Leiden University and Delft University of Technology. This research project was done during an internship of 8 months completed with Royal Dutch Shell within the department of Future Energy Technologies of The Netherlands. It is focused on a case study of a medium size house (2202) situated in The Hague, NL and the neighboring households with the same characteristics along the same street. Homes in the Netherlands are likely to have their heat requirements fulfilled by conventional natural gas systems due to the relatively cheap cost compared to other systems (installation and investment wise) that could have a lower carbon footprint. However, innovative installations could make other more environmentally friendly systems as accessible as conventional systems. The Netherlands as one of the European member states have the goal of reducing CO2 emissions to accomplish their Kyoto targets; however, The Netherlands was not able to meet this target by 3.24% (target of 200.4 megaton CO2-eq). Besides, there is a general lack of financial incentives, making it in many cases an obvious decision to keep and use standard fossil fuel energy systems (both large- and small-scale) regardless of the environmental impact they may have. The building energy consumption sector provides a great opportunity and focus area for trying to reduce even more those emissions, and efforts have been made to introduce into the market more environmentally friendly systems. Until now, exploitation of geothermal shallow energy using a Ground Source Heat Pump (GSHP) has generally been limited to large commercial / industrial units. One reason for this is that the technology used for obtaining the geothermal energy and raising it to an appropriate temperature for the heat requirements of a typical house requires a big space for its installation which in turn proves to be a disruptive and complex process that requires the use of heavy and bulky machinery which immediately translates in a restriction for small homes. Innovations for installations of Ground Source heat pumps are starting to appear in the market, giving the possibility and the opportunity to install those systems in smaller areas, with less disruption and lower investment costs, although some concerns may arise when considering the thermal interference between the boreholes. This project examined the geological characteristics of the case study as determined by a Thermal Response Test (TRT) where parameters such as the thermal conductivity, the thermal resistance and the thermal diffusivity of the ground were obtained. Furthermore, the heat requirements of the test house were calculated with real data obtained during a year between 2012 and 2013 in order to determine the size of the system that would be required for each one of the houses assuming they all have the same demand throughout the year, having a peak demand for a winter day of 16 KW and an average demand of 10 KW in the winter months. Calculations of the length required of every Borehole Heat Exchanger (BHE) and the distance between them were made for the area of each house assuming no thermal interference. The first set of results indicated that a BHE length of 268 m would be needed, and with borehole thermal interference introducing a temperature penalty calculated with an analytical model, the length required increased to 332 m, 68 m more. After this a proposed design of borehole arrangement is suggested for the test house considering the space constraints. Calculations on the Economic and Environmental advantage from Ground Source Heat Pump (GSHP) compared to a Gas Boiler is done, taking into consideration two scenarios for the GSHP, 1) with a Seasonal Performance Factor (SPF) of 3.5 and 2) with a SPF of 3.0. Domestic gas and electricity price fluctuations over the past years were included, extrapolating this behavior for the years 2015 and 2020. Gas prices are considered to have changed 9% per year given the data from 1996 – 2013. Having extrapolated the prices, calculations are done on running costs and investment cost, to give the payback times when considering current power and gas prices for 2015 and 2020. The current situation (2013) seems the more expensive moment for having the system with a payback time of 24 years however a GSHP system in 2020 with electricity and gas prices following a 9% increase for gas prices would take just 8 years to have the investment back. For the environmental performance the Dutch footprint of power generation is calculated for the average predicted trends of different scenarios in the future for European power generation where GSHP with a SPF of 3.5 in 2020 seems to have the best Carbon Footprint advantage of all with 59% advantage of the compared systems. Recommendations are made in order to come up with connected scenarios of Dutch power and natural gas to have a coherent and timely understanding of GSHP and other renewable systems in the Dutch heating market for the coming years. Further recommendations are made in order to have a clear understanding on all the interrelated factors that have an impact on the efficiency, feasibility and performance of GSHP systems and how this research project could be broadened.Industrial EcologyChemical EngineeringTechnical University of Technolog
An improved semi-analytical method for 3D slope reliability assessments
No full textAn improved semi-analytical method for calculating the reliability of 3D slopes with spatially varying shear strength parameters is proposed. The response of an existing semi-analytical method has been compared with that of the computationally more intensive, but more general, random finite element method (RFEM), demonstrating that the simpler method underestimates the failure probability. An alternative relationship for the expected failure length and two correction factors are proposed, which modify the original formulation of the simpler method. The proposed approach gives substantially improved results that compare favourably with those obtained by RFEM, and therefore provides a more accurate simplified solution.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Geo-engineerin
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