The swelling capacity is one of the most characteristic properties of bentonites. This property, along with others, made bentonite a candidate material for the safe disposal of high-level radioactive ...waste (HLRW). For HLRW-barrier systems the swelling pressure is of particular interest because it basically controls sealing properties (a large swelling pressure generally results in low permeability). Commonly, the swelling pressure is investigated as a function of compaction and hence plotted against the density, usually the dry density. Different dry density/swelling pressure relations of bentonites were published. Therefore, the aim of the present study was to identify reasons for these differences. To be able to compare a significant set of different bentonites, a small scale swelling pressure device was developed which is based on measuring a swelling pressure related value of 500mg bentonite powder. This device allowed recording about 200 single values (in duplicate) and hence dry density/swelling pressure relations of thirty six different bentonites. The differences of the dry density/swelling pressure plots of different bentonites could be explained by i) different ways to obtain a range of dry densities (either constant load or constant water content), ii) different portions of uncompactable porosity of the different bentonites, and iii) different smectite contents.
•A small scale device for fast estimation of bentonite swelling pressure is shown.•For the first time a significant set of well characterised bentonites was investigated.•Reasons for the existence of different dry density-swelling pressure plots were identified.•The dry density–swelling pressure relation depends on initial water content and uncompactable porosity.
In this paper a probabilistic-based analysis is presented for evaluating the influences of subsoil parameter uncertainties on tunnel-induced ground movements in mechanized tunneling. The procedures ...of the tunneling process using Slurry Shield Tunnel Boring Machine are numerically modeled and simulated by utilizing a finite element code. To keep the computational cost of the presented simulation model low, an efficient and reliable surrogate modeling technique is used to substitute the original simulation model. The input parameter uncertainties are mathematically represented by adequately chosen probability density functions within their extreme lower and upper bounds. Subsequently, a variance-based global sensitivity analysis is conducted for quantifying the impact of each uncertain parameter on different system responses that are considered in this study. Afterwards, the propagation of parameter uncertainties are evaluated by performing a Monte Carlo-based simulation using the computationally inexpensive surrogate model. At this stage, the variations of system responses, which result from input parameters propagating uncertainties, are compared with predetermined threshold values and, based on that, failure criteria of the tunneling system are defined as well as probabilistically quantified. In a last step, a Bayesian updating procedure is employed for reducing subsoil parameter uncertainties by utilizing recorded synthetic measurements.
The present paper validates two alternative global sensitivity analysis methods, namely variance-based and elementary effect, for the purpose of detecting key subsoil parameters that influence the ...output of mechanized tunnel finite element simulation. In the elementary effect method, a strategy for considering the dependencies, that result from a set of constraints between different parameters, is proposed. Moreover, because the numerical implementation of variance-based sensitivity estimates, in particular, has been proven to require intensive evaluations of the system under investigation, a practical surrogate modeling technique is utilized. This technique is based on quadratic polynomial regression and represents a reliable approximation of the computationally expensive mechanized tunnel simulation. Furthermore, a convergence analysis based on Central Limit Theorem for the numerical implementation of the methods is introduced. The adopted analysis highlights model evaluations needed for the sensitivity measures to converge, as well as the uncertainty involved in these measures.
The tendency to shift from fossil and nuclear energy sources to renewable energy carriers has increased during the past couple of decades. Subsequently, development of effective energy storage ...systems has become more attractive. Nowadays, caverns excavated in rock salt formations are recognized as the appropriate places for underground storage of energy in the form of compressed air or hydrogen. Accurate design of these underground cavities requires suitable numerical simulations employing appropriate constitutive models to describe the material behavior of rock salt under various geological conditions. It is obvious that to have a realistic numerical simulation, it is essential to have a comprehensive knowledge concerning the unknown material parameters and their influence on the calculation results. In this paper, a time dependent model is selected to describe the mechanical response of the rock salt around the cavern. This model is implemented in a finite element code and its application in numerical modeling of salt caverns is illustrated. In addition, global sensitivity analysis is used to investigate the influence of material parameters on the mechanical behavior of the salt cavern. Finally, inverse analysis of the synthetic data is performed to identify the material parameters of the selected model. The applied global sensitivity and inverse analysis algorithms employ metamodeling technique in order to reduce the time which is needed for these computationally expensive calculations.
The liquefaction susceptibility of saturated medium sand-silt mixture samples is evaluated by monotonic and cyclic undrained triaxial laboratory tests that were carried out on reconstituted specimens ...at various relative densities (D
r
= 20, 53 and 91%) and a constant confining pressure (
kPa). The test results were used to conclude on the effect of grading characteristics and other parameters on the liquefaction resistance of the sand-silt mixtures. The monotonic test results indicate that the undrained shear strength at the peak and the undrained residual strength can be correlated to the coefficient of uniformity (C
u
) and the average diameter (D
50
). Indeed, they decrease linearly with the increase of the uniformity coefficient and decrease of the average diameter. It is found that a relationship between the liquefaction resistance and any of the diameters (D
10
or D
50
) and the coefficient of uniformity (C
u
) would be more realistic than to build a relation between the coefficient of gradation (C
c
) and the liquefaction resistance. Undrained cyclic triaxial tests indicate that the cyclic liquefaction resistance of the sand-silt mixtures decreases linearly with the decrease of the effective diameter (D
10
) and mean size (D
50
) and increase of the fines content for the fines content range tested (Fc = 0–40%).
The main objective of this paper is to construct a robust and reliable metamodel for the mechanized tunnel simulation in computationally expensive applications. To accomplish this, four metamodeling ...approaches have been implemented and their performance has been systematically evaluated through a comparative study utilizing pure mathematical test functions. These metamodels are quadratic polynomial regression, moving least squares, proper orthogonal decomposition with radial basis functions, and an extended version of the latest approach. This extended version has been proposed by the authors and named proper orthogonal decomposition with extended radial basis functions. After that, a system identification study for mechanized tunneling has been conducted through the back analysis of synthetic measurements. In this study, the best performing metamodel, that is the one suggested by the authors, has been employed to surrogate a complex and computationally expensive 3D finite element simulation of the mechanized tunnel. The obtained results demonstrate that the proposed metamodel can reliably replace the finite element simulation model and drastically reduce the expensive computation time of the back analysis subroutine.
The paper at hand investigates a strategy to calibrate different constitutive models for soils via back analysis. The efficiency and reliability of the parameter identification for soil models is ...worked out. In order to demonstrate of how to utilise identification procedures, results from optimisation against conventional oedometer and drained triaxial compression tests on natural Pappadai clay are presented and discussed. The aim of geotechnical optimisation problems is to obtain a set of model parameter values that provide the best match between soil model simulations and appropriate measurements. For the parameter identification process, a constrained population-based algorithm is chosen, namely the Particle Swarm Optimiser. The identification is carried out in an initial step separately on each test and then simultaneously on oedometer and triaxial tests. The evaluation is performed employing three different constitutive models of varying complexity and number of constitutive parameters.
A subsequent residual analysis and the computation of confidence intervals for the parameters provide valuable results to assess the quality of the identified parameters in correlation with the evaluated data. Therefore, criteria of the utility and reliability of the mathematical models for further prognosis computations can be estimated.
AbstractThe load deformation and failure behavior of shallow footings can be described in a macroelement formulation. This paper deals with the study of the failure surface and the definition and ...validation of plastic load deformation by single surface hardening models. The straightforward application of the plasticity theory to the soil-foundation system makes it possible to extend the given expression for the case of unsaturated soils. This paper studies a small-scale footing test on unsaturated sand for the formulation of the elastoplastic macroelement of shallow footings under a centrally applied vertical load. The influence of soil suction on different parameters associated with the macroelement is studied and calibrated against experimental results. The presented model shows good agreement with the experimental results. Finally, the limitations and still open questions of the approach are discussed in detail.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Gypsiferous soils are usually stiff when dry, mainly because of the cementation of soil particles by gypsum. However, significant loss in strength and sudden increase in compressibility can occur ...when these soils are fully or partially saturated, and the dissolution of the cementing gypsum causes a high degree of softening of such soils. The problem becomes more complex when water flows through gypsiferous soil, causing leaching and movement of gypsum. This study examines the improvement of gypsiferous soil properties by using silicone oil to minimize the effects of moisture and gypsum loss. The work was conducted on artificial gypsiferous soil (30% Silber sand and 70% pure gypsum) treated with silicone oil in different percentages. Silicone oil was selected as an additive because of leakages of oil-related products from an oil refinery north of Iraq built on gypsiferous soil. Thus, this oil product provides a suitable analogue for that which has infiltrated the foundation soil of the refinery buildings. The results show that the silicone oil is a suitable material for modifying the basic properties of the gypsiferous soil, such as collapsibility and shear strength.
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