Márcio Muniz de Farias

Safety analysis using finite elements

Abstract A finite element based method for determining safety factors which has certain advantages over conventional limit equilibrium methods is described. The stress field produced by a finite element analysis is used in conjunction with a conventional limit method to determine the safety factor. It is shown how the stress values at the finite element integrating points may be interpolated to points on a potential slip surface selected by trial as in the conventional method. This involves three basic problems: (a) identification of the element which contains a chosen point on the slip surface; (b) determination of the local co-ordinates of this point; and (c) determination of the element nodal stress values. Procedures to solve these problems are described. The problem of a vertical cut in clay is analysed and the results are compared with analytical solutions.

Influence of crumb rubber and digestion time on the asphalt rubber binders

ABSTRACT The behavior of asphalt binders modified with recycled crumb rubber depends on several factors, such as: rubber content and type, temperature and time employed during the digestion process. Some of these aspects are investigated in this paper by means of a series of tests performed on asphalt-rubber produced via the wet process. Crumb rubber manufactured by ambient grinding and cryogenic processes were used in this work. Reduction of penetration and sharp increase of viscosity, softening point and resilience were observed for increasing rubber contents. The results show that the Brookfield viscosity limits the crumb rubber content incorporated into straight binder, once it tends to become too high above a certain critical amount of incorporated rubber. The effect of digestion time on the viscosity of the modified binders depended in this research on the rubber content. For high rubber contents, there seems to exist a critical time after which viscosity tends to decrease for continuing digestion process. A rubber-binder interaction model, which could explain such results, is proposed. The influence of rubber type occurred especially in terms of Brookfield viscosity and softening point. It was observed a decrease in these properties for the asphalt-rubber binders produced with crumb rubber obtained by cryogenic process in relation to those produced by the grinding process.

Correlations and Analyses of Longitudinal Roughness Indices

ABSTRACT This paper analyses some of the most widely used indices for the characterization of longitudinal roughness. Measured longitudinal profiles available in the Long-Term Pavement Performance (LTPP) program database were used. A total of 207 pavement sections, in 42 States of the USA, were used in these analyses. Using a suitable software, the International Roughness Index (IRI), the Standard Deviation of longitudinal roughness (σ) and the Root Mean Square of Vertical Acceleration (RMSVA) with different base lengths were computed for every measured longitudinal pavement profile. Linear regression analyses between the IRI and σ statistics produced a very high correlation (R2=0.93). Multivariate regression between IRI and the RMSVA also showed a high correlation (R2=0.96) for base lengths of 1.0 m and 3.5 m. On the other hand, when the RMSVA and σ statistics were analyzed, it was observed that all regressions including a RMSVA with the base length of 1.5m presented a nearly perfect correlation (R2≅1.00...ABSTRACT This paper analyses some of the most widely used indices for the characterization of longitudinal roughness. Measured longitudinal profiles available in the Long-Term Pavement Performance (LTPP) program database were used. A total of 207 pavement sections, in 42 States of the USA, were used in these analyses. Using a suitable software, the International Roughness Index (IRI), the Standard Deviation of longitudinal roughness (σ) and the Root Mean Square of Vertical Acceleration (RMSVA) with different base lengths were computed for every measured longitudinal pavement profile. Linear regression analyses between the IRI and σ statistics produced a very high correlation (R2=0.93). Multivariate regression between IRI and the RMSVA also showed a high correlation (R2=0.96) for base lengths of 1.0 m and 3.5 m. On the other hand, when the RMSVA and σ statistics were analyzed, it was observed that all regressions including a RMSVA with the base length of 1.5m presented a nearly perfect correlation (R2≅1.00). Probabilistic analyses were also carried out using the First Order Second Moment (FOSM) method applied to the regression models obtained between the IRI × RMSVA and σ × RMSVA. Thus, it was possible to determine the relative contribution of different base lengths used in the RMSVA statistic on each roughness index. It was concluded that the base length of 1.5 m contributed in average with 96% of roughness values computed for σ statistic, whereas the base length of 1.0 m was responsible for 74.5% of computed IRI values.

Damage Theory Applied to Flexural Fatigue Tests on Conventional and Asphalt Rubber Hot Mixes

ABSTRACT Application of the Continuum Damage Theory (CDT) to evaluate the evolution of internal damage in Hot Mix Asphalt (HMA) is investigated in this paper. The CDT leads to the formulation of a characteristic curve relating normalized pseudo-stiffness and the internal damage variable, and this curve is supposed to be unique for each material. The uniqueness of the characteristic curve was investigated in this paper by performing fatigue tests in which prismatic samples of HMA were subjected to cyclic bending loads under strain controlled tests. Asphalt mixtures with dense, open and gap gradation using conventional and rubber modified binders were tested. The results of all the tests showed the existence of unique curves independent of loading mode, amplitude or frequency within the studied range. This property may be implemented in numerical codes to simulate the behavior of flexible pavements under a variety of field conditions, using a well formulated mechanistic approach.

Dense Graded Hot Mixes using Asphalt-Rubber Binders with High Rubber Contents

ABSTRACT This paper shows the results of a study about the mechanical behavior of dense graded asphalt-rubber hot mixes prepared with two different types of asphalt-rubber binders. These asphalt-rubber binders were obtained with penetration grade asphalt (AC 50/70) mixed with 21% and 25% of crumb rubber in weight. The rubber was recycled from unserviceable tires using the ambient grinding process. Hot mixes made with the conventional binder AC 50/70 were also studied for comparison. The mechanical behavior of hot mixes was evaluated through laboratory tests for fatigue life, permanent deformation and indirect tensile strength. The results showed that asphalt-rubber hot mixes presented better mechanical behavior for fatigue life and permanent deformation than those obtained with the straight binder.

Dense packing of general-shaped particles using a minimization technique

The discrete element method (DEM) is a numerical method that has achieved general acceptance as an alternative tool to model discontinuous media, with a wide range of practical applications. Given that spheres are not always a suitable shape for DEM simulations, other particle shapes need to be used. However, for shapes different from spheres, there are not many advancing front packing algorithms, which are, in many cases, the best algorithms that allow obtaining an appropriate initial set of particles for a DEM simulation. This lack of advancing front packing algorithms for shapes different from spheres is mostly due to the difficulty of solving the problem of placing a mobile particle in contact with other two (in 2D) or three (in 3D) particles. In this paper, a new method for solving the problem of the particle in contact is proposed, and it is compared with the well-established wrappers method. It is shown that the new proposed method is a promising alternative for spherocylinders. For other shapes the formulation of the new method is shown to be correct, but it was clearly outperformed by the wrappers method and the efficiency of the proposed formulation needs to be improved by optimizing the solution procedure.

Simple Methodology to Obtain Critical State Parameters of Remolded Clays Under Normally Consolidated Conditions Using the Fall-Cone Test

The falling cone is widely used as a laboratory test to determine the liquid limit for the characterization of clay soils. However, remolded undrained shear strength and deformability and strength parameters of critical state models can also be estimated. The objective of this paper is to show a simple methodology to determine these important parameters for engineering simulations. Controlled laboratory tests were carried out on kaolin clay samples using a cone with 30° of tip angle and 30 g of mass. Mini-vane tests were also performed to determine the remolded undrained shear strength of the samples. The experimental results were used to calibrate the Hansbo cone factor, K, from which it is possible to relate the undrained shear strength and the cone penetration for different water contents. The study shows that a calibrated cone and the proposed methodology may be used to estimate strength and deformability parameters for preliminary stages of design involving remolded clays under normal consolidation conditions in a quick way and at very low cost.

Simulations of Fall Cone Test in Soil Mechanics Using the Material Point Method

The material point method is a particle-based method that uses a double Lagrangian-Eulerian discretisation. This approach has proved its functionality for the simulation of large deformation problems. Such problems are frequent in geotechnical engineering, more specifically those related to penetration during pile driving and conventional in situ tests such as the Cone Penetration Test. The shallow laboratory fall cone test is considered in this paper. This test is widely used for the determination of the liquid limit of clays, but it is also used to study the relationship between penetration (h) and the undrained shear strength of clays (su). Simulations are verified against laboratory vane shear tests and fall cone tests performed on samples of kaolin clay at different moisture contents. Calibrations using a simple penetration-strength (h-su) model are made based on a single coefficient named the cone factor (K). The numerical results closely match both the experimental data and analytical solutions available in the literature.

Validación de modelos constitutivos avanzados de comportamiento mecánico para la arcilla estructurada de Brasilia

La mayoria de los modelos constitutivos inicialmente no tomaron en cuenta el efecto de la estructura y la cementacion del suelo. Sin embargo, en las ultimas decadas estas variables han sido incorporadas en varios modelos constitutivos para describir el comportamiento mecanico del suelo en estado natural. Para incluir estas variables es necesario desarrollar leyes de estructura que reproduzcan adecuadamente el comportamiento del material. En este articulo se analiza el comportamiento de la arcilla estructurada y cementada de la ciudad de Brasilia por medio de ensayos triaxiales y simulaciones numericas. Para realizar las simulaciones se escogieron los modelos Cam Clay con estructura, Subloading Cam Clay e Hipoplasticidad con estructura combinados con dos leyes de estructura. Los dos primeros estan basados en elastoplasticidad y el ultimo en hypoplasticidad. De las simulaciones, se obtuvieron varias virtudes y defectos en comparacion con los ensayos realizados. Finalmente, se discute ampliamente cual es el modelo mas conveniente para simular el comportamiento mecanico de la arcilla de la ciudad de Brasilia. Palabras claves: ensayo triaxial, modelo elastoplastico, modelo hipoplastico, arcilla estructurada de Brasilia.The majority of the classical constitutive models for soils does

Alternative Solution for Advective-Dispersive Flow of Reagent Solutes in Clay Liners

AbstractAn analytical solution for the advection-dispersion equation, including sorption effects, was first proposed by Akio Ogata and Robert Banks in 1961. This solution allows the computation of the percentage of dissipation of the contamination plume at a given point in space and time. However, environmental engineers generally wish to determine the time period necessary for this dissipation to take place to reach a minimum acceptable level established in environmental laws. This paper presents a simplified solution that closely matches the exact solution but has the advantage of allowing a numerical-analytical computation of the flow time and/or thickness of the clay liner, using a scheme also developed in this paper. The proposed solution is compared with the simplified solution known as first-order approximation. The comparison shows that, contrary to the method proposed here, the first-order approximation does not satisfy the limit case of purely diffusive flow and gives unsafe estimates of the sol...