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Measurement and interpretation of the small strain stifness of Boštanj silty sand
Gregor Vilhar, Vojkan Jovičić, 2009, original scientific article

Abstract: This paper presents measurements, and an interpretation of these measurements, based on the use of bender-element probes for Boštanj silty sand. The samples were prepared at different initial void ratios and isotropically compressed up to 5 MPa. The bender-element technique was used to determine the dynamic shear modulus ($G_0$) of the soils at very small strains. The multiple bender-element probes were shot at different excitation frequencies in order to increase the reliability of the measurements. The $G_0$ stiffness was determined by using three different techniques: a) the first-time arrival, b) the phase-change method and c) the cross-correlation method. The systematic differences observed between the $G_0$ values, calculated using the three techniques, are discussed. The variation of $G_0$ in the log$G_0$ - log$p'$ plane was evaluated for the Boštanj silty sand and compared with other sands.
Keywords: silty sand, triaxial testing, small strain stiffness, bender elements, time-domain and frequency-domain, measurements
Published: 06.06.2018; Views: 458; Downloads: 36
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Advances and uncertainties in the design of anchored retaining walls using numerical modelling
Antun Szavits-Nossan, 2008, original scientific article

Abstract: This paper describes research on the prediction of horizontal displacements and internal forces in an anchored wall for the protection of an excavation, using standard field and laboratory tests and a finite-element programme with a soil model that can simulate the key aspects of soil behaviour at a construction site. It is important to be acquainted with the constitutive model incorporated in the programme, and the selection of the appropriate soil parameters for the numerical analysis is a crucial part of the modelling. As a result, it is useful to carry out numerical simulations of standard laboratory tests with well-known soil behaviour in order to select the relevant parameters for the simulation of the actual construction process. It is shown in this paper that the measurements of the shear-wave velocities, which can provide the soil’s stiffness at very small strains, can also be useful for determining the static stiffness at a magnitude of the strains relevant for the geotechnical structure under consideration, for both cohesive and noncohesive soils. The research was carried out by a detailed analysis of a case history involving an anchored, reinforced concrete wall supporting the walls of an excavation in a relatively stiff soil. The wall displacements were monitored using an installed inclinometer. The major part of the paper is devoted to an analysis of the selection of parameters, especially the stiffness parameters. The simulation of the triaxial, consolidated, undrained tests was used in order to assess the reduction of the secant stiffness modulus with an increase of the relative mobilized shear strength for the hard clay layer according to the published empirical evidence. It is shown that by selecting the appropriate stiffness parameters for the soil model used in the numerical analysis, it is possible to get an acceptable prediction of the anchored-wall displacements. This is just one example of a successful analysis, but it is encouraging in the way that it shows how it is possible to make reliable predictions based on standard field and laboratory tests and with the use of an available computer programme with a realistic soil model.
Keywords: anchored wall, soil model, shear stiffness, numerical modelling, measured displacements
Published: 01.06.2018; Views: 379; Downloads: 45
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On the application of a simple computational model for slender transversely cracked beams in buckling problems
Matjaž Skrinar, 2007, original scientific article

Abstract: This paper discusses the implementation of a simplified computational model that is widely used for the computation of transverse displacements in transversely cracked slender beams into the Euler's elastic flexural buckling theory. Two alternatives are studied instead of solving the corresponding differential equations to obtain exact analytical expressions for the buckling load ▫$P_{cr}$▫ due to the complexity of this approach. The first approach implements wisely selected polynomials to describe the behavior of the structure, which allows the derivation of approximate expressions for the critical buckling load. Although the relevance of the results strongly depends on the proper prime selection of the polynomial, it is shown that the later upgrading of the polynomials can lead to even more reliable results. The second approach is a purely numerical approach and presents the geometrical stiffness matrix for a beam finite element with a transverse crack. To support the discussed approaches, numerical examples covering several structures with different boundary conditions are briefly presented. The results obtained with the presented approaches are further compared with the values from enormous 2D finite elements models, where a detailed description of the crack was achieved with the discrete approach. It is evident that the drastic difference in the computational effort is not reflected in the significant differences in the results between the models.
Keywords: columns, transverse cracks, stability problems, buckling load, computational model, polynomial solutions, finite element method, geometrical stiffness matrix
Published: 01.06.2012; Views: 1528; Downloads: 78
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