Maria de Lurdes Lopes

Influence of the confinement, soil density and displacement rate on soil-geogrid interaction

Abstract The testing equipment, specimen preparation and testing procedures are described for a series of pull-out tests on geogrids in granular soil. The interaction between a well graded very gravelly sand and a uniaxial geogrid made of high density polyethylene is studied in a pull-out box with dimensions of 1.53 m length, 1·00m width and 0·80m height. The influence of the confinement pressure, soil density and displacement rate on the pull-out resistance of the geogrid is discussed by analysing the results of the pull-out tests.

Soil–geosynthetic inclined plane shear behavior: influence of soil moisture content and geosynthetic type

Abstract This paper deals with the inclined plane shear on three different geosynthetics (a geocomposite (GC), a non-woven geotextile (GTX), and an extruded geogrid (GGR)) with a residual soil from granite. Soil and geosynthetic properties, test equipment, and procedures are described. The influence of soil moisture content and geosynthetic type on soil–geosynthetic interaction behavior is discussed by analyzing the results of the inclined plane shear tests. The main conclusions that can be outlined from the present study are the following: (1) the influence of soil moisture content was relevant for the soil–GTX and soil–GC interfaces. Indeed, the resistance of those interfaces decreased with the increase of soil moisture content. No significant differences were observed between the behavior of those geosynthetics; (2) the influence of soil moisture content on the behavior of the soil–GGR interface was less evident. A slight decrease on the interface friction angle was only observed for the highest soil moisture content; (3) the dry soil–GGR interface resistance was lower than that observed for the other two geosynthetics due to the relevance of soil–soil friction at the GGR apertures, to the high percentage of fines of the soil used in the research (D50 = 1·00 mm), and to the smoother solid lateral surface of the extruded GGR when compared with the surface of the GTX or GC.

MODELLING PERFORMANCE OF A SLOPED REINFORCED SOIL WALL USING CREEP FUNCTION

Abstract The paper describes a rheological model based on a series of Kelvin models for analysing creep behaviour. This model is implemented in a finite element analysis to predict the behaviour of an instrumented sloped reinforced soil wall. The performance of the numerical model and the actual behaviour of the structure are compared. The analysis is carried out using both constant and variable reinforcement stiffness with respect to time. The results and the findings are discussed.

Experimental investigation on the pullout behaviour of geosynthetics embedded in a granite residual soil

Geosynthetics, including geogrids and geotextiles, have been extensively used for stabilisation and soil reinforcement in several geotechnical structures, such as foundations, abutments, walls and slopes. In these applications, soil–geosynthetic interaction plays a determinant role. This paper describes an experimental study carried out using a large-scale pullout test apparatus, aiming to investigate the pullout behaviour of different geosynthetics embedded in a granite residual soil. The study involved two geogrids (one biaxial and the other uniaxial), one geocomposite reinforcement (high-strength geotextile) and one geotextile. The soil was compacted to different relative densities. Test results have revealed that soil–geosynthetic interaction under pullout loading conditions is highly influenced by the geosynthetic properties and soil density. Regardless of soil density, the biaxial geogrid exhibited higher pullout resistance than the other geosynthetics. At maximum pullout force, the deformation along the length of the geotextiles was considerably more pronounced than that along the geogrids. For the conditions adopted in this study, the soil–geosynthetic pullout interaction coefficients ranged from .25 to .52. In general, the values of the scale effect correction factor obtained for the geotextiles were slightly lower than the value recommended by the Federal Highway Administration in the absence of test data.

Accelerated weathering of polypropylene geotextiles

Abstract This paper reports research about the durability of non-woven geotextiles when exposed to artificial weathering conditions [ultraviolet (UV) radiation, rain and dew] on a laboratory weatherometer. The geotextiles were specially manufactured from polypropylene fibers stabilized with different amounts of the additive Chimassorb 944 and the pigment carbon black. The degradation suffered by the geotextiles was evaluated by tensile tests and by scanning electron microscopy.

Determination of Chimassorb 944 in Polypropylene Geotextiles by HPLC-UV

This paper reports the development of a method for the determination of Chimassorb 944 (C944), in polypropylene geotextiles, by high performance liquid chromatography with ultraviolet detection. The C944 was removed from the geotextiles by an ultrasonic extraction and then separated in a NH2 column, followed by UV detection at 244 nm. Analytical validation showed that the method is accurate and precise. The developed methodology was applied for the determination of C944 in geotextiles exposed to artificial UV radiation and to natural weathering. To the best of our knowledge, this is the first method proposed for the determination of C944 in geotextiles.

Laboratory Evaluation of Interactions in the Degradation of a Polypropylene Geotextile in Marine Environments

The long-term behaviour of geosynthetics applied in coastal engineering structures can be adversely affected by many agents. This paper studies the resistance of a nonwoven polypropylene geotextile against some degradation agents present in marine environments and evaluates the existence of interactions between them. For that purpose, the geotextile was exposed to some laboratory degradation tests: immersion tests (in seawater, deionised water, and sodium chloride 35 g·L−1), thermooxidation, and artificial weathering. The geotextile was (1) exposed separately to each degradation test and (2) exposed successively to combinations of two or three degradation tests. The damage caused by the degradation tests was evaluated by monitoring the tensile properties of the geotextile. Based on the changes occurred in tensile strength, reduction factors were determined. The reduction factors obtained directly in the multiple exposures were compared with those obtained by the traditional methodology for the combined effect of the degradation agents. The results, among other findings, showed the existence of relevant interactions between the degradation agents and showed that the reduction factors obtained by the traditional methodology were unable to represent accurately (by underestimating) the degradation occurred in the geotextile.

Resistance of Geotextiles Against the Isolated and Combined Effect of Mechanical Damage Under Repeated Loading and Abrasion

The installation procedures (which may cause mechanical damage) and abrasion may provoke unwanted changes in the properties of the geosynthetics, affecting their performance. This work evaluated the resistance of two geotextiles (with different structures) against two degradation mechanisms: mechanical damage under repeated loading and abrasion. The geotextiles were (1) exposed in isolation to each degradation mechanism and (2) exposed consecutively to both degradation mechanisms. The damage suffered by the geotextiles (in the degradation tests) was evaluated by monitoring changes in their tensile and static puncture behaviour. Based on the changes occurred in tensile and puncture strength, reduction factors were determined. The reduction factors obtained in the successive exposure to mechanical damage under repeated loading and abrasion were compared with the reduction factors determined by the traditional methodology for the combined effect of those degradation mechanisms.

Mechanical Damage of Geosynthetics Used in the Base Liner System of Landfills Caused by Different Aggregates

The installation process may cause unwanted changes in the mechanical behaviour of the geosynthetics. In this work, some geosynthetics used in the base liner system of landfills (a combination of a geotextile, a geomembrane and a geosynthetic clay liner) were submitted to mechanical damage under repeated loading tests (procedure adapted from EN ISO 10722), being monitored the changes occurred in their short-term behaviour. The mechanical damage under repeated loading tests consisted in placing the geosynthetics between a flexible base (granite residual soil with a relative density of 80%) and an aggregate and submitting them to cyclic dynamic loading. The geosynthetics were damaged with a natural aggregate (gravel 14/20), a recycled ceramic aggregate and corundum (synthetic aggregate used in EN ISO 10722). The damage suffered by the geosynthetics was evaluated by monitoring changes in their tensile, tearing (only for the geomembrane) and static puncture properties.

Geotechnical characterization of recycled C&D wastes for use as trenches backfilling

DTU Orbit (03/11/2019) Recycling of MSWI fly ash in clay bricks-effect of washing and electrodialytic treatment Fly ash generated from municipal solid waste incineration (MSWI) is a hazardous waste due to presence and leachability of heavy metals and organic pollutants (e.g. dioxins and polycyclic aromatic hydrocarbons). In 2000, approximately 25 Mt/year of fly ash was generated in USA, Japan and EU (Reijnders 2005). Electrodialytic remediation (EDR) is one technique for MSWI fly ash treatment (Ferreira et al. 2005), where an electric DC field is applied to an ash-water suspension to extract and separate heavy metal by migration towards anode or cathode through ion exchange membranes. Ferreira et al. (2008) observed that in MSWI ash treated by water washing and EDR, metals were mainly in the strongly bonded and residual phases, indicating a reduction in the ash’s environmental risk. Belmonte et al. (2016) made Greenlandic bricks (∼2 g discs) containing 20% and 40% of EDR treated MSWI fly ash, and found that bricks had a low durability and high leaching of As and Cr. In the present study, fired fly ash-clay bricks with a larger size and with lower EDR-treated ash (water-washed before EDR) contents (5%, 10% and 20%) were made and characterized. These bricks were compared with 100% clay bricks and with bricks made from original MSWI fly ash at 20% substitution rate. The feasibility of incorporation of MSWI fly ash treated by combined washing and EDR in production of sintered clay bricks was investigated.