Analises paramétricas de colunas granulares encamisadas com tecido geossintético através de software Ringtrac

This study attempts a preliminary assessment of the behavior of a soil improvement system with the use of encased columns of granular material with geosynthetic (columns Ringtrac ® ). This evaluation was performed using the software Ringtrac ® (developed by Huesker GmbH, Germany), which required different parameters such as soil Oedometric Module, friction angle of soil, thickness of soft soil and the embankment height .In each analysis, one parameter was varied and the other different parameters considered were fixed, resulting in a total of 726 results. Were considered valid only the results where the radial deformation of the geosynthetic encased column did not exceed the value of 4%, which is the maximum radial deformation of the geosynthetic adopted by the Ringtrac ® program. The analysis results are shown graphically in this study, evaluating the tension values in the column and obtained settlements in each analysis. It’s proven in this preliminary study that the variation of the soft soil friction angle in the Ringtrac ® column, will not significantly affect the values of strain on the tension in the column and settlements on the ground. Furthermore, the variation of Oedometric Module on the soil, will significantly affect the tension values in the column and the settlements in the soil

Equipamento para realização de ensaios de tração confinada e aquecida em geossintéticos

Pós-graduação em Engenharia Civil - FEIS

Il dimensionamento delle sovrastrutture stradali non pavimentate

A comparison between main design methods for unpaved roads is presented in this paper. An unpaved road is made up of an unbound aggregate base course lying on a usually weak subgrade. A geosynthetic might be put between the two in reinforcing and separating function. The goal of a design method is to find the appropriate thickness of the base course knowing at least traffic volume, wheel load, tire pressure, undrained cohesion of the subgrade, allowable rut depth and influence of the reinforcement. Geosynthetics can reduce the thickness or the quality of aggregate required and improve the durability of an unpaved road. Geotextiles contribute to save aggregate through interaction friction and separation, while geogrids through interlocking between his apertures and lithic base elements. In the last chapter a case study is discussed and design thicknesses with two design methods for the three possible cases (i.e. unreinforced, geotextile reinforced, geogrid reinforced) are calculated.

RELIBILITY ANALYSIS OF SIMPLE SLOPES AND SOIL-STRUCTURES WITH LINEAR LIMIT STATES

The first objective of this research was to develop closed-form and numerical probabilistic methods of analysis that can be applied to otherwise conventional methods of unreinforced and geosynthetic reinforced slopes and walls. These probabilistic methods explicitly include random variability of soil and reinforcement, spatial variability of the soil, and cross-correlation between soil input parameters on probability of failure. The quantitative impact of simultaneously considering the influence of random and/or spatial variability in soil properties in combination with cross-correlation in soil properties is investigated for the first time in the research literature. Depending on the magnitude of these statistical descriptors, margins of safety based on conventional notions of safety may be very different from margins of safety expressed in terms of probability of failure (or reliability index). The thesis work also shows that intuitive notions of margin of safety using conventional factor of safety and probability of failure can be brought into alignment when cross-correlation between soil properties is considered in a rigorous manner. The second objective of this thesis work was to develop a general closed-form solution to compute the true probability of failure (or reliability index) of a simple linear limit state function with one load term and one resistance term expressed first in general probabilistic terms and then migrated to a LRFD format for the purpose of LRFD calibration. The formulation considers contributions to probability of failure due to model type, uncertainty in bias values, bias dependencies, uncertainty in estimates of nominal values for correlated and uncorrelated load and resistance terms, and average margin of safety expressed as the operational factor of safety (OFS). Bias is defined as the ratio of measured to predicted value. Parametric analyses were carried out to show that ignoring possible correlations between random variables can lead to conservative (safe) values of resistance factor in some cases and in other cases to non-conservative (unsafe) values. Example LRFD calibrations were carried out using different load and resistance models for the pullout internal stability limit state of steel strip and geosynthetic reinforced soil walls together with matching bias data reported in the literature.

Análise experimental e numérica do comportamento de estruturas de solo reforçado com geossintéticos : solo granular versus fino

As estruturas de solo reforçado com geossintéticos são normalmente constituídas por solos granulares com boas propriedades físicas e mecânicas. O uso de apenas este tipo de solos pode proporcionar o aumento, por vezes insustentável, do custo da execução das estruturas e o aumento do seu impacto ambiental. Deste modo, as estruturas de solo reforçado perdem a sua vantagem competitiva em relação a outros tipos de estruturas (muros de betão, muros de gravidade, muros de gabiões, etc.). Para resolver este problema podem ser utilizados outros tipos de solos (solos locais, finos, com propriedades físicas e mecânicas piores mas, no entanto, mais baratos) para a execução deste tipo de estruturas. De forma geral, com este estudo pretendeu-se contribuir para o incremento do conhecimento sobre a utilização de solos finos para a construção de estruturas de solo reforçado (muros e taludes). Para tal avaliaram-se as diferenças no comportamento mecânico dos materiais compósitos (solo granular reforçado versus solo fino reforçado) e das estruturas de solo reforçado constituídas com os dois tipos de solos. Assim, os objetivos deste estudo foram avaliar: a influência de vários parâmetros nas propriedades mecânicas e na capacidade de carga dos solos reforçados com geossintéticos; a influência de vários parâmetros no dimensionamento das estruturas de solo reforçado; e o comportamento das estruturas dimensionadas (incluindo a estabilidade global e a influência do processo construtivo) recorrendo a uma ferramenta numérica (PLAXIS). Para cumprir os objetivos propostos foram realizadas análises experimentais em laboratório (análise do comportamento do solo reforçado através de ensaios triaxiais e de California Bearing Ratio) e análises numéricas (dimensionamento de estruturas de solo reforçado; modelação numérica do comportamento através de uma ferramenta numérica comercial com o método dos elementos finitos). Os resultados dos ensaios experimentais mostraram que o comportamento mecânico e a capacidade de carga do solo foram incrementados com a inclusão das camadas de geossintético. Este efeito variou com os diversos parâmetros analisados mas, de forma geral, foi mais importante no solo fino (solo com propriedades mecânicas piores). As análises numéricas mostraram que as estruturas de solo fino precisaram de maior densidade de reforços para serem estáveis. Além disso, as estruturas de solo fino foram mais deformáveis e o efeito do seu processo construtivo foi mais importante (principalmente para estruturas de solo fino saturado).

Potential hydraulic barrier performance of cyclic organic carbonate modified bentonite complexes against hyper salinity

The effect of adding glycerol carbonate (GC) or propylene carbonate (PC) to sodium (Na)-bentonite on the hydraulic performance of geosynthetic clay liners (GCLs) under hypersaline conditions is examined. Fluid loss (FL), swell index (SI) and solution retention capacity (SRC) measurements were carried out to compare the potential hydraulic performance of these two cyclic organic carbonates (COCs) as bentonite modifiers. A modified FL test enabled quantitative measurement of both the water retention characteristics of untreated and COC modified bentonites as well as calculation of hydraulic conductivity values. Tests under aggressively saline conditions (ionic strength, I ≥ 1 M of NaCl and ≥3 M of CaCl2) showed that at a mass ratio of 1:1 (GC to bentonite), the FL of a GC-Na-bentonite was ≈40–104 mL in NaCl and ≈61–91 mL in CaCl2. This was about 10–20 mL and 70–200 mL, respectively, lower than that of a comparable PC-Na-bentonite (1:1 PC to bentonite) and untreated Na-bentonite. Greater swelling (SI) and greater solution retention capacity (SRC) was observed for the GC treated Na-bentonite compared to untreated Na-bentonite in all salt solutions, and for PC-Na-bentonite at high ionic strength of both NaCl and CaCl2 solutions, demonstrating the superior hydraulic barrier performance of COC-bentonites under severely saline conditions. Experiments conducted in flexible-wall permeameters with I = 3 M CaCl2 showed approximately one order of magnitude lower (∼10−11 m/s vs ∼1.9 × 10−10 m/s) hydraulic conductivity of GC treated bentonite cake compared to the k value of the untreated Na-bentonite cake. Calculated hydraulic conductivity from fluid loss tests estimated the measured values in a conservative way (overestimation).

Geosynthetics in Antarctica: performance of a composite barrier system to contain hydrocarbon-contaminated soil after three years in the field

An overview of the design and performance of geosynthetics in composite barrier systems for biopiles used to remediate hydrocarbon-contaminated soil at Casey Station, Antarctica, is presented. Seven instrumented biopiles were constructed over three field seasons. To minimize the risk of hydrocarbon migration to groundwater, composite barrier systems were used (each using different combinations of geosynthetic clay liners (GCLs), high density polyethylene (HDPE) geomembranes (GMB), and geotextiles (GTXs)). One biopile used a co-extruded geomembrane (HDPE with an ethylene vinyl alcohol (EVOH) core). The liner system was subject to a combination of coupled phenomena that could interact and affect the GMB-GCL composite barrier performance. The exposure conditions involved potential freeze-thaw cycling, hydration-desiccation cycles, cation exchange, direct and diffusive exposure to hydrocarbons. The effect of these phenomena was investigated by monitoring GCL and GMB sacrificial coupons. GCL coupons were placed between the main GCL component and the main geomembrane component of the composite liner and GMB coupons placed between the main GMB sheet and the GTX protection layer. Coupons were exhumed from the biopiles each year. The exhumed GCL field moisture content values ranged from 162% to 22%. After three (3) years in the field, GCL coupons that had undergone at least one hydration/desiccation cycle showed no significant change in swell index values or fluid loss values. The measured hydraulic conductivity of exhumed GCL coupons from Biopiles 1 and 2 (3 × 10-11 m s-1) was within the expected range and not significantly different from the values for virgin GCL. GMB coupons exhumed after three years from Biopiles 1 and 2 showed no significant change in oxidative induction time (OIT), melt flow index or tensile properties. Diffusion tests were performed as an index test for establishing the performance of the GMBs as a diffusive barrier to hydrocarbons, with permeation parameters for BTEX contaminants ranging from P g = 0.9-9.2 × 10-13 m2 s-1 for the exhumed GMB (with values depending on the contaminant and GMB). These values were similar to the parameters obtained for virgin GMBs and there was no significant change with field exposure, with GMBs appearing to be performing well.