Seismic response analysis of a geogrid reinforced wall constructed with recycled Construction and Demolition Waste

Over the last years the environmental sustainability has been demanding a progressive increase in the waste valorisation in construction. The valorisation of Construction and Demolition Wastes (C&DW) reduces the use of natural resources (non-renewable) and, simultaneously, avoids congesting landfills with inert wastes coming from buildings and other infrastructures. Although some studies have been carried out on the use of recycled C&DW in construction industry, their valorisation as fill material in geosynthetic reinforced structures is almost an unexplored field. A research project aiming to contribute to the sustainable application of recycled C&DW as backfill material in geosynthetic reinforced structures, is being developed at University of Porto, Portugal. Preliminary results of this research are presented in this paper. In this work the two-dimensional finite difference program Fast Lagrangian Analysis of Continua (FLAC) was used to model the behaviour of a geogrid reinforced wall, constructed in Brazil, with recycled C&DW. The wall is 3.6m high and was constructed at an inclination of 1:4.3 (wall batter of 13° from vertical). The backfill was reinforced with six layers of geogrid placed at 0.6 m of vertical spacing and 2.52 m long. The seismic response of a similar wall, hypothetically constructed with recycled C&DW coming from a Portuguese recycling plant, is also evaluated. An earthquake ground motions artificially generated for the greatest seismicity area of Portugal was considered as seismic input. Two constitutive models were used to model the backfill C&DW material: the Mohr-Coulomb model and a Strain-Softening model. Permanent displacements of the wall face, settlements and reinforcement tensile forces are analysed and discussed. The numerical simulations have shown that the possible decrease of the backfill shear strength during cyclic loading is an important issue to be studied more closely. Notwithstanding it was concluded that a well compacted and drained recycled C&DW can be used as fill material in geosynthetic reinforced structures

Damage Induced by Recycled Aggregates on the Short-Term Tensile Behaviour of a High-Strength Geotextile

This paper presents the mechanical, chemical and environmental degradation induced by recycled Construction and Demolition Wastes (C&DW) on the short-term tensile behaviour of a nonwoven polypropylene (PP) geotextile reinforced with polyester (PET) yarns. In order to study the chemical and environmental degradation a damage trial embankment (2m x 3m in plant) was constructed using recycled C&DW as filling material. The damage caused by the mechanical actions during installation was also simulated by installation damage laboratory tests. Wide width tensile tests were performed on geotextile samples exhumed from the trial embankment after 12 months, on laboratory damaged samples and on intact (as-received) samples. Their short-term tensile behaviour is compared. Scanning electron microscope (SEM) images of intact and exhumed specimens are also presented. (c) 2016 The Authors. Published by Elsevier B.V

Geomechanical Behaviour of Recycled Construction and Demolition Waste Submitted to Accelerated Wear

The construction industry is one of the most important sectors for economic and social development. However, it is responsible for more than 50% of the depletion of natural resources, for 40% of the energy consumption and construction and demolition waste (CDW) accounting for 30-60% of the total municipal solid waste generated worldwide. In this sense, the recycling of CDW is considered a safe alternative to the current trend, which can produce environmental and economic benefits, namely the reduction of the depletion of natural resources and the volume of waste sent to landfills. Some studies have shown promising results in the use of recycled CDW as geotechnical materials. However, the degradation performance induced by the construction procedures and weather conditions on the geotechnical behaviour of recycled CDW is still a research gap, creating an obstacle for its regular use in general engineering practice. This work evaluated the mechanical performance of recycled CDW over time when subjected to wetting-drying degradation cycles under different temperature and pH conditions. The effects of such degradation were then evaluated qualitatively (changes in particle size distribution and Proctor parameters) and quantitatively (stress-strain response and permeability). The results showed that 10 wetting-drying cycles and different compaction energies have no change in the particle size distribution of CDW compared to the original CDW. The shear strength parameters were very similar for the different degradation conditions except when different pH values were used, which may have weakened the grains and decrease the friction angle of the material. Regarding the permeability, all tested samples were classified in the same hydraulic conductivity range (very low) without significant changes induced by the degradation mechanisms

Pullout Behavior of Different Geosynthetics-Influence of Soil Density and Moisture Content

Geosynthetics have increasingly been used as reinforcement in permanent earth structures, such as road and railway embankments, steep slopes, retaining walls, and bridge abutments. The understanding of soil-geosynthetic interaction is of primary importance for the safe design of geosynthetic-reinforced soil structures, such as those included in transportation infrastructure projects. In this study, the pullout behavior of three different geosynthetics (geogrid, geocomposite reinforcement, and geotextile) embedded in a locally available granite residual soil is assessed through a series of large-scale pullout tests involving different soil moisture and density conditions. Test results show that soil density is a key factor affecting the reinforcement pullout resistance and the failure mode at the interface, regardless of geosynthetic type or soil moisture content. The soil moisture condition may considerably influence the pullout response of the geosynthetics, particularly when the soil is in medium dense state. The geogrid exhibited higher peak pullout resistance than the remaining geosynthetics, which is associated with the significant contribution of the passive resistance mobilized against the geogrid transverse members to the overall pullout capacity of the reinforcement

Resíduos de Construção e Demolição. Um estado de arte visando a sua valorização em Trabalhos Geotécnicos

Relatório de Investigação no âmbito do projeto "Aplicação sustentável de Resíduos de Construção e Demolição (RCD) em estruturas reforçadas com geossintéticos - RCD-VALOR" (PTDC/ECM-GEO/0622/2012

Cyclic and Post-cyclic Shear Behaviour of a Granite Residual Soil - Geogrid Interface

The dynamic frictional properties of the soil-geosynthetic interface play an important role in the design and stability analysis of geosynthetic-reinforced soil structures under repeated loadings, such as those induced by compaction, traffic and earthquakes. This paper describes a laboratory study carried out using a large-scale direct shear test device, aiming to investigate the cyclic and post-cyclic behaviour of an interface between a granite residual soil and a biaxial woven geogrid. In the cyclic direct shear tests, the interface was subjected to 40 cycles of sinusoidal displacement, with semiamplitude and frequency ranging from 1-10 mm and 0.05-0.5 Hz, respectively. To evaluate the effect of the cyclic loading on the interface shear strength, monotonic direct shear tests were performed immediately following the cyclic tests. The results indicated that the loading frequency has little impact on the interface shear stiffness during the loading cycles. In contrast, the influence of the displacement semi-amplitude on the interface stiffness was found to be significant. The cyclic loading did not lead to the degradation of the post-cyclic interface shear strength. The post-cyclic peak shear strength tended to increase with the semi-amplitude of the shear displacement, which may be associated with an increase in soil density

Effect of wetting-drying cycles on physical and mechanical properties of a recycled construction and demolition material

Recycled Construction and Demolition (C&D) materials are progressively being used in civil engineering applications, such as base and sub-base layers of transport infrastructures. However, the knowledge related to the long-term behaviour of recycled aggregates in geotechnical and pavement applications is very scarce. The breakage of the particles, particularly when the recycled aggregate has clay masonries, is commonly pointed out as an issue for the usage of these recycled materials. A laboratory study was undertaken to investigate the effect of wetting-drying (W-D) cycles on geometrical, physical and mechanical properties of a mixed recycled aggregate coming from C&D waste. The effects of the number of cycles (10 and 20 W-D cycles) on particle size distribution, shape and flakiness indexes, particles density, water absorption, sand equivalent, methylene blue, water-soluble sulphate content, Los Angeles abrasion and aggregate crushing value were assessed. This study shows that W-D cycles have caused a slight degradation of the recycled aggregate, even if the effect of the number of cycles (above 10) is not quite relevant. LA abrasion loss of this mixed recycled aggregate is high, making its application as unbound material in pavement layers impracticable without additional measures

Pullout Behaviour of Geogrids Embedded in a Recycled Construction and Demolition Material. Effects of Specimen Size and Displacement Rate

In recent years, environmental concerns related to the overexploitation of natural resources and the need to manage large amounts of wastes arising from construction activities have intensified the pressure on the civil engineering industry to adopt sustainable waste recycling and valorisation measures. The use of recycled construction and demolition (C&D) wastes as alternative backfill for geosynthetic-reinforced structures may significantly contribute towards sustainable civil infrastructure development. This paper presents a laboratory study carried out to characterise the interaction between a fine-grained C&D material and two different geogrids (a polyester (PET) geogrid and an extruded uniaxial high-density polyethylene (HDPE) geogrid) through a series of large-scale pullout tests. The effects of the geogrid specimen size, displacement rate and vertical confining pressure on the pullout resistance of the geogrids are evaluated and discussed, aiming to assess whether they are in line with the current knowledge about the pullout resistance of geogrids embedded in soils. Test results have shown that the measured peak pullout resistance of the geogrid increases with the specimen size, imposed displacement rate and confining pressure. However, the pullout interaction coefficient has exhibited the opposite trend with the specimen size and confining pressure. The pullout interaction coefficients ranged from 0.79 and 1.57 and were generally greater than or equal to the values reported in the literature for soil-geogrid and recycled material-geogrid interfaces

Degradation assessment of recycled aggregates from Construction and Demolition Waste through wet-dry cycles

In recent years, several studies and applications of recycled aggregates coming from Construction and Demolition Waste (CDW) have been carried out, but the knowledge related to the long-term behaviour of these alternative materials is still fairly limited. The breakage of CDW particles is commonly pointed out as an issue for the use of these recycled materials. This paper studies the change of the particle size distribution of a recycled aggregate coming from CDW due to degradation agents simulated trough 10 wet-dry cycles under controlled conditions. The effects on particle density, water absorption, shape index, flakiness index, sand equivalent value, Los Angeles abrasion, aggregate crushing value, water-soluble sulphate content are assessed. Wet-Dry cycles have degraded the mixed recycled aggregate, increasing the amount of particles with small dimensions, however the changes in its mechanical and physical behaviour are not very significant. LA abrasion loss of this recycled aggregate is high making its use on unbound pavement layers difficult