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Performance of MSE walls with sustainable backfills subjected to differential settlements

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Abstract

The scarcity and fast depletion of granular materials necessitated to find alternative backfill materials in MSE walls. In the present study, application of construction and demolition waste (CDW) as a backfill for MSE walls was investigated. The physical, chemical, hydraulic and mechanical properties of CDW were found to meet the requirements of ideal backfills mandated by various design standards of MSE walls. At the end of construction, maximum facing deformation was at lower one-third height of the wall for MSE wall resting on a firm foundation. Influence of yielding foundation on the performance of MSE wall was also studied by varying the distortion levels to 0.2, 0.4 and 0.6. At the onset of differential settlements, the location of maximum facing deformation changed to the bottom of the wall. The maximum facing deformation and axial strain increased by 15 times and 2.5% respectively, when the wall underwent a distortion of 0.6.

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Construction and demolition waste disposal is a major challenge in developing nations due to its ever increasing quantities. In this study, the recycling potential of waste concrete as aggregates in construction activities was studied. The metal leaching from the recycled concrete aggregates (RCA) collected from the demolition site of a 50 year old building, was evaluated by performing three different leaching tests (compliance, availability and Toxic Characteristic Leaching Procedure). The metal leaching was found mostly within the permissible limit except for Hg. Several tests were performed to determine the physical and mechanical properties of the fine and coarse aggregates produced from recycled concrete. The properties of recycled aggregates were found to be satisfactory for their utilization in road construction activities. The suitability of using recycled fine and coarse aggregates with Portland pozzolanic cement to make a sustainable and environmental friendly concrete mix design was also analyzed. No significant difference was observed in the compressive strength of various concrete mixes prepared by natural and recycled aggregates. However, only the tensile strength of the mix prepared with 25% recycled fine aggregates was comparable to that of the control concrete. For other mixes, the tensile strength of the concrete was found to drop significantly. In summary, RCA should be considered seriously as a building material for road construction, mass concrete works, lightly reinforced sections, etc. The present work will be useful for the waste managers and policy makers particularly in developing nations where proper guidelines are still lacking.
Article
Construction and Demolition Wastes (C&DW) are increasingly being reused in civil engineering applications, mainly in concrete production and base layers of roadway infrastructures. However, frequently the fine grain portion of these recycled aggregates is not considered suitable for those applications being landfilled instead of recycled. Moreover, the value-added utilisation of recycled C&DW in the construction of geosynthetic reinforced structures (steep slopes and retaining walls) is almost an unexplored field. This research assesses the feasibility of using fine-grain recycled C&DW as filling material of geosynthetic reinforced structures (GRS), appraising the physical, mechanical and environmental characterization of the construction and demolition material (C&DM), as well as, the direct shear and pullout behaviour of the interfaces between this material and three distinct geosynthetics (two geogrids and one geocomposite reinforcement or high strength geotextile). Direct shear tests results have shown that fine-grain recycled C&DW, properly compacted, exhibit similar shear strength to natural soils used commonly in the construction of GRS. The potential contamination of groundwater by these recycled C&DW was evaluated through laboratory leaching tests and, excepting the values of sulphate and total dissolved solids (TDS), this recycled C&DW complies with the provisions of European Council Decision 2003/33/EC for inert materials. High values of coefficients of interaction for C&DW/geosynthetic interfaces, a parameter of utmost importance in the design and performance of GRS, were achieved. The results herein presented support the viability of using these recycled C&DW as filling material for GRS construction.
Article
Mechanically stabilized earth (MSE) walls reinforced by geogrids and geotextiles have seen a tremendous growth over the past thirty years. However, along with this growth has come numerous failures consisting of excessive deformation and, in some cases, actual collapse. Of the 82-cases in the authors data base, improper drainage control was the cause in 68% of them. As a result, this paper is focused on both internal drainage issues within the reinforced soil mass within the reinforced soil mass (46%) and external drainage issues around the soil mass (22%). After a brief introduction of the technology some elements of traditional design will be presented. The issue of proper versus improper methods of drainage control will then form the core of the paper. A summary and recommendations section aimed at preventing drainage problems in the future will conclude the paper.
Article
The use of recycled aggregates (RA) in construction constitutes a significant step towards a more sustainable society and also creates a new market opportunity to be exploited. In recent years, several case-studies have emerged in which RA were used in Geotechnical applications, such as filling materials and in unbound pavement layers. This paper presents a review of the most important physical properties of different types of RA and their comparison with natural aggregates (NA), and how these properties affect their hydraulic and mechanical behaviour when compacted. Specifically, the effects of compaction on grading size distribution curves and density are analysed, as well as the consequences of particle crushing on the resilient modulus, CBR and permeability. The paper also contains an analysis of the influence of incorporating different RA types on the performance of unbound road pavement layers as compared with those built with NA by means of the International Roughness Index and deflection values. The results collected from the literature indicate that the performance of most RA is comparable to that of NA and can be used in unbound pavement layers or in other applications requiring compaction.
Article
The proper use of natural resources is one of the fundamental pillars of sustainable development imposed on modern societies. A more effective and efficient use of natural resources, as well as the mitigation of environmental impacts induced by their extraction could be achieved if proper management and recycling policies of Construction and Demolition (C&D) wastes were implemented. The valorisation of wastes in the construction industry is needed and is a way toward sustainability. This paper provides a literature review on studies related to the valorisation of Construction and Demolition (C&D) materials in geotechnical engineering applications, with an emphasis on their use as recycled aggregates in base layers of roadway infrastructures and as filling material for geosynthetic reinforced structures. Specifications that should be followed when these materials are used in such projects are also summarised. With this review it is intended to promote the use of recycled C&D materials, showing that research carried out all over the world has demonstrated their good performance in general.
Article
Geosynthetic reinforced soil walls are now an accepted technology for the solution of earth-retaining problems due to cost savings, easy and quick construction, and ssociated environmental benefits. Additional savings and reduction in environmental impact can be realised by using recycled construction and demolition waste (RCDW) as the backfill material. This paper describes two such structures that were built to full scale and instrumented. One of the walls was reinforced with a woven polyester geogrid (wall 1) and the other (wall 2) with a relatively more extensible nonwoven polypropylene geotextile. Both walls were constructed using RCDW as backfill material and were built on a foundation soil prone to fabric collapse due to increased stress and/or increase in moisture content. During the monitoring period the walls were subjected to a rainy season followed by induced inundation of the foundation to trigger soil fabric collapse. The results showed that foundation soil collapse influenced wall behaviour more than geosynthetic type. The exception to similar performance was local face bulging which was greater for wall 2 (geotextile) with the more extensible reinforcement under unconfined conditions than for wall 1 (geogrid) which was expected in the moving formwork construction method. However, directly behind the wall face where both reinforcement material types were confined the horizontal displacements were similar. In addition, at locations beyond half of the wall base length the strain distributions were low (1% or less) for both walls. A practical conclusion from this study is that if the wrap-face appearance at end of construction is not a concern (i.e. large bulging) then wall performance is unaffected by the choice of reinforcement types used in this investigation.
Article
This paper presents the findings of a laboratory investigation of the characterization of recycled crushed brick and an assessment of its performance as a pavement subbase material. The properties of the recycled crushed brick were compared with the local state road authority specifications in Australia to assess its performance as a pavement subbase material. The experimental program was extensive and included tests such as particle size distribution, modified Proctor compaction, particle density, water absorption, California bearing ratio, Los Angeles abrasion loss, pH, organic content, static triaxial, and repeated load triaxial tests. California bearing ratio values were found to satisfy the local state road authority requirements for a lower subbase material. The Los Angeles abrasion loss value obtained was just above the maximum limits specified for pavement subbase materials. The repeat load triaxial testing established that crushed brick would perform satisfactorily at a 65% moisture ratio level. At higher moisture ratio levels, shear strength of the crushed brick was found to be reduced beyond the acceptable limits. The results of the repeat load triaxial testing indicate that only recycled crushed brick with a moisture ratio of around 65% is a viable material for usage in pavement subbase applications. The geotechnical testing results indicate that crushed brick may have to be blended with other durable recycled aggregates to improve its durability and to enhance its performance in pavement subbase applications.
Article
Following the introduction of mechanically stabilized earth walls with metallic reinforcement in 1966, polymeric reinforced structures (both geotextile and geogrid) followed shortly thereafter. A major item that accompanied this change in reinforcement type was the nature of the backfill soil. Corrosion of metallic reinforcement was no longer an issue with polymer-related geosynthetics and thus locally available fine-grained soils were generally used in place of quarried coarse-grained gravel soil. The cost savings are obvious as are the implications for concerns over inadequate performance. While failures have occurred in both types of reinforced walls, this paper focuses only on geosynthetic reinforced walls.
Article
Recycled Asphalt Pavement (RAP) is the most reused and recycled material in the United States. It has been included at percentage of 15–50% in new hot mix asphalt (HMA) concrete and used as a base course material up to 100% for pavement construction. Due to the existence of asphalt in RAP, RAP base courses may have increased or excessive permanent deformation under traffic loading. To minimize such deformation, use of geocell was proposed by authors to confine RAP. To verify the performance of geocell-reinforced RAP bases and the benefit of geocell reinforcement, an experimental study was conducted on geocell-reinforced RAP bases over a weak subgrade under cyclic plate loading. A large geotechnical test box was used for the cyclic plate loading tests. The subgrade was a mixture of sand and kaolin and compacted at the moisture content corresponding to a California Bearing Ratio (CBR) value of 2%. The fractionated RAP was compacted at the moisture content close to the optimum value. A total of four sections with three base thicknesses (0.15, 0.23, and 0.30 m) were prepared and tested, which included one 0.30 m thick unreinforced section and three geocell-reinforced sections. During the testing, surface deformations and vertical stresses at the interface of base and subgrade and strains in geocell walls were monitored. Test results show that the geocell-reinforced RAP bases had much smaller permanent deformations than the unreinforced RAP bases. The geocell-reinforced bases reduced the vertical stresses at the interface between base and subgrade as compared with the unreinforced base. The strain measurements demonstrated that the thicker geocell-reinforced RAP base behaved as a slab while the thinner base behaved as a tensioned membrane. The experimental results indicated that novel polymeric alloy (NPA) geocell reinforcement improved the life of 0.15, 0.23, and 0.30 m thick reinforced RAP base sections by factors of 6.4, 3.6, and 19.4 at a permanent deformation of 75 mm as compared with the 0.30 m thick unreinforced section at the same permanent deformation, respectively. Geocell reinforcement increased the minimum stress distribution angle by 2°, 3.5°, and 7° for the 0.15, 0.23, and 0.30 m thick reinforced RAP base sections as compared with the unreinforced section.
Article
Clay-based landfill covers often have a geomembrane (GM) layer sandwiching between the clay barrier and the cover soil. The knowledge pertaining to the deformation behaviour of a clay barrier along with geomembrane subjected to differential settlements is very limited. Hence, the main objective of this paper is to examine the influence of GM on the integrity of clay-based landfill covers subjected to differential settlements in a geotechnical centrifuge. First, scaling considerations required for modelling geomembrane in a centrifuge are presented. A series of centrifuge tests were performed at 40 gravities using a 4.5 m radius beam centrifuge having a capacity of 2500 g-kN available at IIT Bombay on model clay-based landfill covers with and without GM. By maintaining type moist-compacted conditions of the clay barrier as constant, the thickness of the clay barrier was varied as 0.6 m and 1 m. The performance of the clay barrier with and without GM was monitored by measuring water breakthrough at the onset of differential settlements. The analysis and interpretation of centrifuge test results reveal that with the provision of a GM and an overburden pressure equivalent to that of a landfill cover, the sealing efficiency of the cover system was found to be maintained even after the formation of full-depth cracks within 0.6 m and 1 m thick clay barriers subjected to a maximum distortion level of 0.125. This observed behaviour is attributed to the downward thrust exerted by the deformed geomembrane at the zone of maximum curvature which hinders the infiltration of water through cracks. This indicates the significant influence of GM in maintaining the sealing efficiency of a landfill cover system.
Article
The paper describes the novel use of recycled construction and demolition waste (RCDW) material as the backfill material in an otherwise conventional 3.6-m high wrapped-face geosynthetic reinforced soil wall. The wall was constructed over a collapsible foundation soil which is common in the area around the capital city of Brasilia. The wall was instrumented and then monitored though dry and wet rainy seasons. The influence of cumulative rainfall on foundation compressibility was detectable and seasonal wetting and drying was shown to quantitatively influence wall deformations, settlement, horizontal earth pressures and reinforcement strains. Nevertheless, wall performance was judged to be satisfactory when compared to the performance of other walls of similar size constructed with traditional select granular soils over non-collapsible foundation soils. The results of this investigation demonstrate that significant project cost savings may be possible by avoiding more expensive traditional backfill materials and larger societal economic savings accrued by diverting RCDW waste streams from landfills.
Article
At present an enormous amount of pond ash is being produced by thermal power plants throughout the world. Storage of pond ash requires vast land area and disposal of ash becomes problematic and also it creates environmental hazards. To mitigate these problems, pond ash has been used in the low-lying areas as structural fills for developing residential and industrial sites. To enhance the bearing capacity of pond ash, it may be reinforced with jute-geotextile, a textile made from jute (natural fibre) for the purpose. In the present study an attempt has been made to study the bearing capacity of square footing on pond ash reinforced with jute-geotextile. The effects of different parameters like number of layers (N) of reinforcement, the depth of the upper most layer of reinforcement from the base of the footing (u), friction ratio (f), i.e. the ratio of the pond ash jute-geotextile interface friction angle (ψ) to the direct shear friction angle of pond ash (φd) and jute-geotextile sheet length (Ls) on bearing capacity of square footing (qrs) at any settlement resting on pond ash reinforced with jute-geotextile are discussed. A non-linear power model has been developed to estimate qrs based on 1399 experimental data.
Article
Today, geosynthetic-reinforced soil structures are widely used to support bridge abutments and approach roads in place of traditional pile supports and techniques. In such situations, foundation conditions have been shown to adversely affect the stability and deformation behaviour of overlying geosynthetic-reinforced slopes and walls. This paper addresses the response of geotextile-reinforced slopes subjected to differential settlements in a geotechnical centrifuge. Centrifuge model tests were carried out on model geotextile-reinforced sand slopes with two different types of reinforcement. A wrap-around technique was used to represent a flexible facing. In order to initiate failure in the reinforcement layers, the ratio of length of reinforcement to height of the slope was maintained as 0.85. One of the objectives of this paper is to present about a special device developed for inducing differential settlements during centrifuge test at 40g for a reinforced soil structure. A digital image analysis technique was employed to arrive at displacement vectors of markers glued to the reinforcement layers. The displacements were used to compute and analyze the strain distribution along the reinforcement layers during different settlement stages. Results of the centrifuge test indicate that even after inducing a differential settlement equivalent to 1.0m in prototype dimensions, the geotextile-reinforced soil structure with a flexible facing was not found to experience a collapse failure. Analysis of geotextile strain results shows that the location of the maximum peak reinforcement strain occurs along the bottom-most reinforcement layer at the onset of differential settlements, at the point directly below the crest of the slope.
Article
A study has been made of the metastable structure of partly saturated soilt that collapse when wetted under load. This has been done using the scanning electron microscope on air-dried specimens of collapsing soil representative of various types. These include aeolian sand from South Africa, loess from Europe, clay from America and a range of compacted soils. The nature of the intergranular contacts has been studied at magnifications up to 20,000. It is shown that a common basic collapse mechanism applies to the different types of soil ranging from sand to clay.
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