Fernando Henrique Martins Portelinha

This study aims to enhance the understanding of the mechanisms that govern the deformation and stress behaviors of geotextile-encased column-supported embankments constructed over soft foundation soils, particularly with the inclusion of a geosynthetic-reinforced granular base. The study details the construction process and challenges involved in creating a transparent, layered, 2D physical model, allowing full observation and quantification of the problem. For the level of column stiffness used in this investigation, arching and membrane effects developed after a certain compression of the geosynthetic encased column, causing initial settlements that transferred stresses to the soft foundation soil. The study demonstrates that using geosynthetic reinforced granular base with multiple geogrid layers improves performance by creating a stiffer layer, which helps to distribute vertical stresses more uniformly with mechanisms that resemble the catenary effect.

Geobags have been applied in many coastal protection solutions giving them effective performance against cyclic hydrodynamic loading. However, polymer materials, such as the geotextiles used for geobags production, are susceptible to environmental degradation which is critical for engineering applications. This study aims to investigate the durability of woven polypropylene geotextiles under coastal environmental conditions, considering different exposure surface characteristics, such as varied slope surfaces, type of application surface, and surface color. Exposure panels were constructed, and geotextiles samples were exposed to the coast environment of Natal (Brazil) for period reached 492 days, during which specimens were collected, and geotextile tensile properties have been obtained as a reference of material degradation. Results indicated a strength depletion of 35% by the end of the exposure period. No significant influence of surface inclination on degradation was observed, while surface color emerged as a potentially influential factor. The findings of this study are essential for informing the design and implementation of mitigation strategies in coastal engineering works involving geosynthetics.

Laboratory-scale physical modeling has established itself as an effective technique for investigating mechanisms underlying geotechnical problems. Recently, the use of transparent materials, combined with advances in digital imaging technologies, has emerged as an innovative and non-invasive approach for analyzing soil behavior. Transparent soils are biphasic systems composed of translucent solid particles and saturating fluids with closely matched refractive indices, enabling clear observation of internal processes. Digital Image Correlation (DIC) has proven particularly effective when integrated with transparent soil models. As a non-contact optical method, DIC minimizes interference and measurement inaccuracies associated with traditional instrumentation, allowing more reliable interpretation of displacement and strain fields. Recent studies have increasingly focused on transparent soils for modeling geosynthetic-reinforced soil structures. In this work, the behavior of embankments constructed over soft soils improved with geosynthetic-encased granular columns (GECs) was investigated using stratified transparent soil models. The study evaluated the mechanisms of load transfer from the embankment to the columns, as well as resulting deformations and differential settlements. Transparent soil modeling allowed observation of key load transfer mechanisms, such as soil arching within the PTC, and enabled evaluation of the soil arching ratio. Overall, transparent soil modeling proved to be a suitable and effective technique for simulating this type of geotechnical system, providing valuable insights into its behavior.

This study compares how geosynthetics behave under load, under strain, and over time when subjected to confined tensile tests in soil, employing two commonly used mechanisms in research. One test type simulates a reinforced layer, where tensile loads are indirectly applied to the geosynthetic via stresses transferred from the soil. In contrast, the other test applies tensile loads directly to the geosynthetic material using clamps while under soil confinement. The objective is to elucidate how these testing mechanisms might yield differing in-soil tensile characteristics for different geosynthetics. The study involved conducting load-strain-time tests on samples of nonwoven and woven geotextiles, as well as a geogrid, under varying sustained loads over a 120-h period within a sand clay soil providing soil confinement to geosynthetics at different surcharge levels. The results suggest that soil confinement plays a significant role in shaping the load-strain-time behavior of geosynthetics. Furthermore, it was noted that the impact of testing mechanisms on this behavior is contingent upon the type and stiffness of the geosynthetics, as well as their interaction with the confining soil. In general, in-soil tests in which tensile loads are mobilized by geosynthetics and transferred from the soil provide more confident results for better simulating operation conditions. Tests that directly apply tensile loads to the geosynthetic while maintaining stationary soil confinement may yield misleading results, especially for geosynthetics that have poor interaction with the soil.

Geosynthetic reinforced piled supported embankments have been widely used in recent years as a solution to embankments over soft soils. Geosynthetic-reinforced load transfer platforms (LTPs) have been used at the bottom of embankments to improve the distribution of stresses over piles. However, mechanisms governing this technique still demand to be fully understood. This paper employs a transparent soils technique to investigate the mechanisms governing geosynthetic-reinforced LTPs. Transparent small-scale 1-g laboratory models were constructed using two different transparent materials composing a layered transparent system. Fused quartz grains were used to simulate the granular fill material of the LTP, while Laponite RD® was employed to replicate the soft clay. A seeding particles plane was installed inside the model generating a stochastic pattern for images capturing. Distribution of displacements and strains were then interpreted using the Digital Image Correlation (DIC) technology. Based on the displacements and strains responses of the small-scale model, this paper discusses the mechanisms acting in unreinforced and geosynthetic-reinforced LTP (single layer). The presence of geosynthetic reinforcement reduced, in general, the displacements and deformations of the models.

Environmental conditions have become a concern when involving the use of Geosynthetics clay liners (GCLs) as leachate barriers, particularly because they can be subjected to daily thermal cycles during construction and operation of landfills, which can affect their properties. This paper investigates the hydration behavior of a nonwoven geotextile carrier-GCL in contact with lateritic subsoils under isothermal and simulated thermal conditions as commonly found in tropical regions. A thermal insulate testing box was used to shelter an instrumented liner landfill allowing the investigation of thermal and hydraulic responses during hydration. Lateritic subsoils were observed not to provide high levels of GCLs hydration under isothermal conditions, whereas thermal daily cycles led to capillary break that restricted the moisture uptake at the interface between subsoil and the nonwoven geotextile carrier. Higher values of subsoil initial moisture contents were found to be significant to reduce capillary effects and to allow some GCL hydration. The poor hydration demonstrated to be critical in terms of GCL hydraulic behavior.