Delma de Mattos Vidal
@ita.br
Geotechnical Engineering Professor
Technological Institute of Aeronautics
Scopus Publications
Scholar Citations
Scholar h-index
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Scopus Publications
Keli Bohrer and Delma Vidal
EDP Sciences
Mechanically stabilized earth (MSE) systems are a well-known and applicable solution for retaining walls, that presents a composite structure consisting of layers of backfill soil with rigid or flexible reinforcement inclusions. The stability of the wall system is derived from the interaction between the backfill and soil reinforcements involving friction and tension. The wall facing has as its main function to prevent erosion of the structural backfill. The design of MSE walls is usually divided in two phases: external and internal stability. Although there are many methods to design MSE walls, the Coherent Gravity Method is the most common used for MSE walls reinforced with inextensible (steel) reinforcements, the Simplified Method for both steel and geosynthetics reinforced wall systems and the new one included in 2020, Stiffness Method, to calculate the maximum reinforcement loads, Tmax, for extensible (geosynthetics) reinforced MSE walls (all these methods are outlined in Section 11 of the AASHTO LRFD Bridge Design Specifications 2020) . The main objective of this paper is to carry out the analysis of the 3 methods available at AASHTO and compare the results from full-scale MSE walls and the predicted Tmax values.
J. L. E. Dias Filho, J. L. Silva, C. A. Valentin, M. P. Fleury, M. A. Aparicio-Ardila, D. M. Vidal, and C. M. L. Costa
Emerald
Humidity, air temperature, rainfall and solar radiation all contribute to the weathering of geosynthetics. Over time, their useful life can be affected and changes in properties can be observed, which affects the performance of these materials. As geosynthetics durability analyses must encompass each work condition, assessing the climate effects is essential for design purposes. This study exposed a nonwoven needle-punched poly(ethylene) terephthalate geotextile to natural weathering in three Brazilian cities (different exogenous environments) for 18 months. Mechanical tests were conducted to evaluate the geotextile changes due to weathering. This was demonstrated by the results: exposure to weather leads to the deterioration of the geotextile mechanical properties and increased stiffness. After four months, the tensile strength fell by half, while the deformation needed more than 12 months to have this same reduction; ultraviolet radiation intensity was the most effective weathering condition in the field; humidity and rainfall can affect the stiffness of geotextiles; the impact of accumulated climate factors gradually showed a convergence in the response of geotextile to weathering. Thus, this work highlights the need to evaluate the climate conditions in each location to understand the material's behavior on the exposure time.
Rodrigo A. e Silva and Delma Vidal
Elsevier BV
Livia Luiza de Souza Avancini, Matheus Muller, and Delma de Mattos Vidal
Instituto de Pesquisas Ambientais em Bacias Hidrograficas (IPABHi)
The sludge generated at drinking water treatment plants (WTPs) is a high-moisture content residue, and therefore difficult to handle, transport, dispose of or recover. During the last decades, geotextile tubes have been successfully applied to reduce the residue volume, facilitate its handling and subsequent reuse. This study aimed to understand the factors that interfere in the filtration and dewatering efficiencies and to experimentally analyze the dewatering process of WTPs sludge, evaluating different test procedures and investigating the influence of the type and dosage of polymeric additives on dewatering performance. Geotextile cone dewatering tests and geotextile bag dewatering tests were performed, using four different woven geotextile samples and an aluminum sulfate WTP sludge sample. The results showed that the use of geotextile cone dewatering tests for geotextile selection and for additive selection and dosage was representative for the dewatering process intended, reflecting the results verified in the geotextile bag dewatering tests. Sludge chemical conditioning increased dewatering rate and solids retention during the tests’ early stages, but it did not result in a higher final solids content sludge cake.
 Keywords: dewatering systems, geosynthetics, waste management.
Gabriel Luis Anibal de Oliveira and Delma De Mattos Vidal
Instituto de Pesquisas Ambientais em Bacias Hidrograficas (IPABHi)
The need to investigate viable methods to facilitate correct disposal of high-water content waste is immediate in the scenario of water source degradation. In this context, Closed Geotextile Systems (CGS) have shown promise for dewatering a variety of high water-content sediments, aiming to reduce the waste final volume, encapsulating particles, and at the same time allowing fluid drainage. Especially in Water Treatment Plants, the geotextiles generally employed in these systems have good tensile strength and rigidity to support mechanical solicitations and hydraulic properties that warrant good drainage conditions. In these applications, the geotextile element should assure the waste confinement and retention of some particles that will form a filter cake which will control internal flow conditions. The present work investigated how small portions of sand influence fine-particle retention. The sludge used consisted of a mixture of filtered water with two well-defined fractions of ground quartz: FG, a silt and CG, a fine sand. The results show that small amounts of sand are capable of leading to the formation of a pre-filter, even if the maximum diameter of the fine particles is much less than the geotextile filtration opening size. The test results indicate that the retention efficiency gradually increases as CG increases in the solution, up to a fraction of CG close to 14%, which represents only 0.7% of the total solution mass. The increase in particle retention was directly proportional to the increase in the GC fraction until reaching the filtration efficiency of approximately 72% where it stabilizes.
Marcus Guadagnin Moravia, Pascal Villard, and Delma De Mattos Vidal
EDP Sciences
With the advancement of the use of synthetic reinforcements in geotechnics, a greater understanding of the mechanisms involved in soil-reinforcement interaction is the focus of major research centres on the subject. The topic of this study is the shearing behaviour at interfaces between granular materials and geogrids. The main objective is to provide a more fundamental understanding of some micromechanisms present in this type of interface, which in turn are important to optimize the design of such reinforcement. The numerical modelling of these reinforced structures must deal with the complexity of the material-reinforcement interaction problem; therefore, it requires specific numerical models whose formulations admit localized behaviours in the contacts as well as the granular nature of the material (e.g., soil, gravel, ballast). A robust and flexible way of modelling this problem is through the Discrete Element Method (DEM). The DEM proposes to model this granular nature by representing the soil as interacting constituent particles, whose behaviour is ruled by physical laws defined at the contact points. The numerical approach is desirable since it allows, in an articulated and relatively fast way, studying closely different regions of the interface, in order to identify factors and variables that are important for the problem. The purpose involves the DEM for a 3D modelling of a geogrid pull-out test to calculate the magnitude of forces in different elements of the geogrid (i.e., nodes, longitudinal and transverse members). Preparation of numerical samples has a particular importance in the final results of simulations. Thus, the numerical techniques used to obtain better geometry for the geogrid and a granular assembly with a representative grain rolling effect are also presented in this paper.
R. A. e Silva, R. G. Negri, and D. de Mattos Vidal
Thomas Telford Ltd.
The use of digital images to evaluate geotextile characteristics has appeared in the scientific literature, particularly for estimating the pore size distribution (PSD) of nonwoven geotextiles used...
Luiz Gustavo Paulo Oran, Delma Mattos Vidal, José Souza Romero, Kledermon Garcia, and Elizeu Nascimento Filho
Coimbra University Press
Os lastros constituintes da superestrutura de vias permanentes, quando submetidos a cargas cíclicas de alta intensidade e frequência, sofrem desgaste rápido em sua estrutura portante. Os desguarnecimentos e nivelamentos dos lastros demandam grandes volumes por quilômetro devido à sua degradação. Seus ombros e altura mínimos de construção definem contornos de seções com largas bases de brita. Devido a isso, o desgaste do particulado e seus custos de manutenção inflam o orçamento das ferrovias. Com esse mote, escolheu-se aqui caminhar por um itinerário investigativo cujo paradigma tem seu cerne no conceito de confinamento e seus efeitos sobre o Módulo de Resiliência do lastro. A pesquisa se manteve nos efeitos práticos de reforços por geogrelhas aplicado dentro do corpo do lastro e não na interface com a camada subjacente. Nesse trabalho atingiu-se o objetivo proposto de levantar parâmetros diretivos para orientar ensaios de desempenho de reforços e possibilitar a melhor compreensão das causalidades decorrentes das propriedades específicas das geogrelhas como abertura da malha e rigidez dos elementos, bem como correlacionar o efeito da cota de posicionamento do reforço e os efeitos sobre o grau de confinamento gerado.
M. G. A. Guimarães, D. de Mattos Vidal, D. de Carvalho Urashima, and C. A. C. Castro
Thomas Telford Ltd.
Maintaining satisfactory properties in geosynthetics exposed to factors that could lead to their degradation needs to be considered in projects employing these materials. Geosynthetics subjected to tensile creep and weathering can undergo premature degradation over time. It is essential to study the influence of these factors, since they could act simultaneously in some applications. To assess the synergetic effects, frames were developed and four groups of a woven geotextile polypropylene sample were tested. The first and second groups were subjected to tensile creep at 5% and 10% of the tensile strength in conjunction with weathering for 2160 h. The third group was exposed to the same weathering conditions without tensile load. The fourth group was subjected to tensile creep at 10% of the tensile strength in laboratory conditions. Frames were built with a slope similar to the location of exposure to guarantee greater effects of weathering on the material surface. A meteorological station at the site mon...