Conference Agenda

<p>The growing concern regarding waste and water management activities is pushing the worldwide geomembrane market, thanks to its excellent technical, environmentally friendly, and cost-effective solutions. They have been employed to perform a variety of activities that greatly contribute to the successful completion of numerous projects, such as storing water in reservoirs, and preventing leaks from landfills that retain municipal or hazardous wastes and their harmful leachates. Geomembranes are not designed to provide structural resistance but they frequently undergo mechanical solicitations that may mishandle their impermeable property. For instance, the contact between a geomembrane and a drainage layer (i.e. granular material) increases the risk of puncture. In this study, we adopt an original multiscale view of a geomembrane to relate microstructural features to its macroscopic mechanical properties. A micromechanical model has been developed based on the discrete element method (DEM) to derive the mechanical response of a Polyvinyl chloride (PVC) geomembrane from the modelling of its microstructure which consists of a set of crystallites that are tied together through an amorphous network of polymers. Such an approach offers the potential to highlight the elementary mechanisms responsible for the mechanical response of PVC geomembranes and to improve the understanding of the puncture failure mode.</p>

<p>An embankment underlain by permafrost foundation was reinforced with woven geotextiles at its side slopes to reduce slope displacements when the compacted frozen fill used to construct the embankment thaws. The fully-instrumented embankment along the Inuvik-Tuktoyaktuk Highway in the Northwest Territories, Canada has thermistor strings to monitor soil temperatures as well as ShapeAccelArrays installed at the midslope of the embankment to measure displacements. Four years of monitored data shows reduction in slope movements compared to an unreinforced embankment. A numerical model was developed in a commercially-available finite element software to simulate the thermal and mechanical behaviour of this embankment and further understand the benefit of using geotextiles in cold regions environment. Multi-layer woven geotextiles with varying reinforcement length and vertical spacing were also investigated. The monitored performance and the model results presented will help optimize embankment design in cold regions environment using geotextiles.</p>

<p>Internal stability analysis of segmental geosynthetic reinforced soil walls includes the verification of connection strength at the geosynthetic-block interface. The calculation of the connection load (To) has been a hard task as mechanisms are still not completely understood. This fact makes current guidelines to suggest assumptions of connection loads equal to, or a percentage of, the maximum tensile load at the potential failure surface. This paper presents a laboratory model test of a reinforced soil wall developed to understand mechanisms of geosynthetic-modular blocks connection forces. The test simulates a soil mass with sand backfill and concrete block face using one reinforcement layer of geogrid under working conditions. During the process, lateral earth pressure, horizontal displacements of the block face wall, the pull-out force and the strains of the reinforced layer were monitored. Digital image analysis was used to examine the backfill behavior on the connections between the elements during the test. The results shows differential settlements of the backfill and the facing wall leading to a downdrag effect on the reinforcement. This effect associated to face wall displacements led to a significant impact on connection loads at geosynthetic-blocks conecetion.</p>

Geosynthetics are widely adopted within the asphalt layers to enhance the pavement performance through various functions such as reinforcement, stiffening, and moisture barrier. Specifically, these functions help retard the reflective cracking, formation of rut and permanent deformation, and fatigue cracking in the asphalt layers. However, a major concern of adopting geosynthetic reinforcements is the reduction in interlayer shear resistance between the asphalt layers. In this study, the impact of various geosynthetic-asphalt inter-face characteristics on the interface shear resistance was evaluated by testing cores obtained from an in-service highway. Specifically, the Leutner shear device was used to test seven interfaces including an unreinforced (control) interface and six geosynthetic-asphalt interfaces that were formed by different types of geosynthetic reinforcements including both polymeric and fiberglass products. Although the Leutner shear test results indicated reduced interface shear resistance in all geosynthetic-reinforced specimens, the percentage reduction was found to be particularly affected by the composition of the reinforcements. Specifically, the reinforcement materials (glass or polymer) and form (grid or textile or composite) were found to significantly affect the asphalt-reinforcement bond strength. Additional factors affecting the geosynthetic-asphalt interface characteristics included tack coat application rates, characteristics of the apertures, and the thickness of the geosynthetic reinforcements.

The objective of this study was to analyse the short-term tensile response of a geocomposite (a geotextile and a geogrid overlapped) and apply hyperbolic models to describe its load-strain tensile curves. Data from specimens submitted to mechanical damage, abrasion, and mechanical damaged followed by abrasion were analysed. Reduction factors were proposed by comparing data from damaged specimens with those from undamaged specimens. The experimental results were compared with those fitted by the constitutive models to evaluate the goodness of the fits. The constitutive models demonstrated good fitting capacity. For any mechanical condition, the model parameters could be estimated by relating the experimental tensile properties of the geocomposite with adjustment coefficients, which allowed for describing the tensile load-strain curves with good accuracy. The reduction factors for the specimens subjected to mechanical damage followed by abrasion were lower than those which would be obtained if those damages were considered individually.

<p>The current design methods for Geosynthetic-Reinforced and Pile-Supported embank-ments disregard on one side the effect of the embankment construction and on the other one the stiffness of embankment, foundation soil, column and geosynthetics. What is missing nowadays is a simplified design method capable of taking all these aspects into account. To this aim, in this paper the authors present the results of a series of numerical analyses simulating the embankment construction. In particular, the evolution during con-struction of embankment displacements is discussed and the maximum tensile force in the geosynthetic reinforcements is compared with the one suggested by the most popular standards. To clearly highlight the mechanical processes taking place in the embankment, an ideal problem is considered: the pile shaft is assumed to be smooth, the piles to be founded on a rigid bedrock and the embankment construction to take place under drained conditions.</p>

The finite element method is a powerful tool that can be used to analyse problems including complex geometries and material properties. In this study, the general-purpose finite element software ABAQUS was used to investigate the load-strain response of a biaxial geogrid under in-isolation tensile loading. A 3D model was developed, accounting for different thickness of geogrid elements and their nonlinear response. Then, TOSCA module was used to investigate an alternative design of a junction profile. The geogrid was submitted to uniaxial and biaxial tensile loading, simulating a wide-width tensile test and a biaxial wide-width tensile test. Validation was performed by comparing the numerical model with experimental data. Optimization results showed that it was possible to reduce the junction volume profile by 53% with a compromise of 3% in maximum bearing capacity.

<p>Selection of geosynthetics, for stabilization of unbound aggregate layers in pavements, in-volves the unconfined properties of geosynthetics and/or the large displacement confined properties. However, geogrids within a pavement system are neither unconfined nor undergo large displacements. This study proposes using the confined Soil-Geosynthetic composite stiffness (K_SGC), obtained from Soil-Geosynthetic interaction (SGI) tests, to predict pavement performance when using geogrid-stabilized road bases. A series of identical one-third scale accelerated pavement tests (APTs) were performed on pavement test sections stabilized with various geogrids, diverse in terms of geometry and materials. The rutting from these sections was compared to that in the non-stabilized (control) section to evaluate the Traffic Benefit Ratio (TBR) at failure rut depth for each geogrid. The TBR obtained showed a strong linear correlation to the soil-geosynthetic composite stiffness (K_SGC) of the corresponding geogrid obtained from the SGI tests. It is concluded that K_SGC is a particularly good indicator of the performance of pavements with geosynthetic-stabilized road bases.</p>

<p>Recent work has shown that GCL hydration by subgrade is complex and influenced by a series of variables related to GCL characteristics, as well as subgrade initial moisture content, particle size and mineralogy. Another major variable is the effect of GCL exposure to daily thermal cycles during landfill construction phase. Additionally, tropical climate conditions, such as in Brazil, favor the occurrence of lateritic fine soils, which present high moisture content and a particular mineralogy. The present study aims to evaluate GCL hydration by lateritic subgrades under isothermal conditions and simulated daily thermal cycles. Two lateritic soils (clay and clayey sand) were examined with different foundation moisture contents. Isothermal conditions were evaluated through hydration columns. Daily thermal cycles were simulated in a physical model with application of heating and cooling periods. Isothermal analysis confirmed the influence of subgrade initial moisture content on GCL hydration, since both soils with highest moisture content showed 50% higher values of GCL hydration. GCL samples exposed to thermal cycles revealed great interference of the climatic conditions on hydration, showing that the increase in subgrade moisture content was not able to significantly hydrate the samples, even dehydrating the GCL in the case of clayey sand. This study evidenced the importance of soil properties on hydration process, since the clayey soil with a small portion of active minerals and finer particles avoided GCL dehydration. Thermal cycle’s analysis under tropical climate conditions revealed difficulties in hydrating GCL in exposed field conditions, possibly not guaranteeing liner correct performance. Overall, lateritic soils showed higher GCL hydration speed than soils formed in temperate climates. </p>

Different variables shows to affect shear bond performance of geosynthetic paving interlayers. The correct evaluation of the interface shear bond is fundamental to estimate design parame-ters and the service life of the pavement. The present study evaluated five types of geosyn-thetics, including four different geogrids and a paving fabric, using Leutner shear tests. In ad-dition, the influence of geosynthetics characteristics on interface shear bond parameters was analyzed. Double-layered asphalt specimens were prepared in the laboratory considering the same binder impregnation rate of 600 g/m2. Geogrids showed overall superior interface shear strength behavior compared to geocomposite, although inferior to control samples. Further-more, the geogrid aperture size played an important role in shear bond results, corroborated by the through hole bonding mechanism. The presence of bituminous coating contributed to in-terface shear bond results. Interface shear stiffness and accumulated energy analyzes showed that large geogrids aperture sizes presented similar behavior to control samples.