Browsing by Author "Rodriguez Roa, Fernando"

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    Design load of rigid footings on sand
    (CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS, 2010) Diaz, Edgar G.; Rodriguez Roa, Fernando
    Experimental evidence has shown that most current methods are not able to predict design loads of footings on cohesionless soil with an acceptable degree of accuracy. In the present study, a simple and realistic settlement-based method is proposed to estimate the design load of rigid footings on sand subjected to static vertical loading. The design criterion based on restricting the end-of-construction settlement to 16 mm because of the inherent variability of the real soil deposits is herein adopted. A series of finite-element analyses based on an advanced constitutive model were carried out to study the load-settlement response of footings supported on 14 sandy soils. Routine design charts were developed to predict the net allowable soil pressure of footings on normally consolidated and overconsolidated sands. These charts consider footing shape, embedment depth, grain diameters D(10) and D(60), particle shape, unit weight (or submerged unit weight for saturated sands), and indirect measurements of the shear strength derived from in situ tests, such as relative density, standard penetration test (SPT) or cone penetration test (CPT). As shown, the proposed charts match well with available experimental data.
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    Three-dimensional finite element model for flexible pavement analyses based on field modulus measurements
    (KING FAHD UNIV PETROLEUM MINERALS, 2008) Lacey, Geraint; Thenoux, Guillermo; Rodriguez Roa, Fernando
    In accordance with the present development of empirical-mechanistic tools, this paper presents an alternative to traditional analysis methods for flexible pavements using a three-dimensional finite element formulation based on a linear-elastic perfectly-plastic Drucker-Prager model for granular soil layers and a linear-elastic stress-strain law for the asphalt layer. From the sensitivity analysis performed, it was found that variations of +/- 4 degrees in the internal friction angle of granular soil layers did not significantly affect the analyzed pavement response. On the other hand, a null dilation angle is conservatively proposed for design purposes. The use of a Light Falling Weight Deflectometer is also proposed as an effective and practical tool for on-site elastic modulus detennination of granular soil layers. However, the stiffness value obtained from the tested layer should be corrected when the measured peak deflection and the peak force do not occur at the same time. In addition, some practical observations are given to achieve successful field measurements. The importance of using a 3D FE analysis to predict the maximum tensile strain at the bottom of the asphalt layer (related to pavement fatigue) and the maximum vertical compressive strain transmitted to the top of the granular soil layers (related to rutting) is also shown.