Lightweight Backfill Material Research Articles

Strength characteristics of lightweight soil with waste modified expanded polystyrene particles

With the increase in population and urbanization around the world, waste materials have a significant negative impact on the environment; therefore, it is essential to reduce the adverse effects of waste materials on nature through innovative and sustainable solutions. This study aims to reveal the threefold benefits of utilizing waste modified expanded polystyrene (WMEPS) as a soil improvement agent, including the reuse of a waste material by recycling it from nature, obtaining lightweight backfill material, and the enhancement of the compressive behavior of the soil. For this purpose, two different sizes of WMEPS were added to the soil to varying proportions by dry weight of the soil (i.e., 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5%, and 6%) and their unconfined compressive strength (UCS) behavior was experimentally investigated on both 1 and 28 day cured specimens. The results were evaluated in terms of stress-strain behavior, UCS value, UCS increase ratio, normalized energy absorption index, deformability index, and elastic modulus. In addition, the optimum WMEPS participation ratio was determined by linear weighted sum optimization method. As a result, by adding the optimum rate of 5% WMEPS to the soil, the dry density decreased by 15% and UCS increased by 45.22% for the specimen cured for 28 day.

Dynamic leaching assessment of recycled polyurethane-coated tire rubber for sustainable engineering applications

Assessing the material ramifications of waste tire rubber stands as a pivotal endeavor for its practical utility. Dynamic leaching analysis emerges as indispensable in delineating its potentialities within sustainable engineering domains. Waste materials stemming from tire recycling industries, notably polyurethane-coated rubber (PUcR), may exhibit promising viability owing to attenuated leaching, thus fostering the circular economy paradigm. Towards this end, upflow column percolation leaching tests were conducted on recycled rubber-soil mixture (RSM) alongside PU-coated rubber-soil mixture (PUcRSM). Analysis through Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) unveiled the leaching dynamics of assorted metals in RSM and PUcRSM, notably showcasing markedly diminished cumulative zinc content (by 99.4%) in PUcRSM, coupled with mitigated electrical conductivity, redox potential, and eluate pH. Leveraging HYDRUS-1D for analytical modeling predicated on the advection-dispersion equation further underscored these insights. These findings suggest that waste PUcR presents itself as a viable option, distinguished by its diminished leachability, suitable for a wide array of applications. These applications include vibration damping in infrastructure, tunnel linings, asphalt roads, rubberized concrete, and lightweight backfill materials for bridges and retaining walls, among others. This initiative will contribute to recycling a substantial quantity of over 1 billion used tires produced annually, ultimately supporting the circular economy ethos through assured and adaptable repurposing of waste from tire rubber recycling industries.

Numerical Simulation Study on the Applicability of Lightweight Foamed Soil Backfill of Railway Bridge Structure under Train and Seismic Impacts

The sudden bump at the transition area from the bridge usually cultivates to vigorous railway deterioration because of the variation in the railway's supporting foundation. Therefore, this study focuses on the development of an advanced lightweight backfill material that can resolve the serious settlement in the transition zone. Besides, due to the strict soil properties requirements for construction, some excavated local soils are not preferred. This issue leads to the expansion in the construction budgets and the consumption of natural resources. In this research, the usage of excavated locally silty soil can mitigate this issue. To improve the self-leveling of fresh material and further broaden the range of applications, the air-foam technique is integrated into this material with a ratio of 10% by volume. The resilient modulus test was conducted to investigate the engineering characteristic of the backfill mixture. The reinforcing effect of the lightweight backfill was then evaluated through the numerical simulation method under repeated trainloads and earthquakes. Overall, the laboratory and the simulation results suggest a potential application of lightweight soil as a sustainable material since this material can substantially enhance the durability of the railway structure and provide smoothness for train operation.

Utilization of tunnel spoils as a lightweight filling material for the voids behind tunnel excavation contour

Tunnel spoils has put great pressure on the environment protection, geological risk control and construction cost because of the increasing tunnel construction in China. This paper aims to investigate the possibility of reusing the spoils from tunnel as a lightweight filling material for the voids behind tunnel excavation contour. Laboratory tests were carried out with an orthogonal table L16 (44) by varying the water-cement ratio from 0.8 to 1.8, the tunnel spoils content from 40% to 100%, the sodium dodecyl benzene sulfonate content from 1% to 7%, and the sodium meta-aluminate content from 0.5% to 1.5%. The tests results show that optimum formulation of lightweight filling material for the voids behind tunnel excavation contour is suggested to be water-cement ratio of 1.2 and corresponding weight percentages of tunnel spoil content (80%), sodium dodecyl benzene sulfonate (5%), and sodium meta-aluminate (1%). The optimum formulation exhibited the good performance in pumping, short gel time, high stability (2 h bleeding rate was 0%), minimal shrinkage (bulk shrinkage was 0.7%) and light weight of hardened material (the dry density was 1.19 g/cm3). Furthermore, a detailed microanalysis illustrated the micro-characteristics of the lightweight backfill materials. Finally, a guiding framework was proposed for recycling the discharged tunnel spoils as the lightweight backfill material. These findings suggested that discharged tunnel spoils can be suitably used as a lightweight backfill material for filling the voids behind excavation contour in tunnel construction, and such light filling material not only can fulfill the engineering requirements but also turns out cost effective and eco-friendly.

Effects of Crumb Rubber on the Shear Strength of Sand: An Experimental Study

The application of waste rubber tires for ground improvement helps to improve the environment by recycling and reusing it as admixtures. This research aims to investigate the shear strength parameters of rubber-sand mixtures. By using crumb rubber with a constant size (425μm), the sand is replaced by different percentages (0, 2.5, 5.0, 7.5, and 10%) of crumb rubber by weight. A direct shear box test is used to determine the shear strength parameters of rubber-sand mixtures with two different controlled densities. The samples were loaded with normal stresses of 20, 40 and 80kPa and were sheared at a rate of 1mm/min. Although, this experiment discovered that crumb rubbers improve the shear strength parameters in loose sand, however, a reduction in shear strength parameters was found in dense sand. Moreover, it was observed that the inclusion of crumb rubbers into sand greatly improve the strain energy of both loose and dense sand. Likewise, rubber has a low unit weight which makes it suitable for lightweight backfill materials. The surface properties of rubber should be further studied to understand the contribution of shear strength in the rubber-sand mixture.

Geofoam: A potential for Indonesia’s soil problem III – stabilizing retaining wall

Increasing elevation of ground level is a common necessity in the construction world. For steep inclination, a retaining system is necessary to retain the soil embankment. When the embankment height is high, the required dimensions for the retaining wall can become humongous. This will result in excessive use of concrete, hence higher carbon footprint for the construction. To enable high retaining wall to be built without the support of huge retaining wall, light-weight backfill materials, such as geofoam can be used. In this paper, the use of geofoam to stabilize an eleven metre high retaining wall is presented. The eleven metre high retaining wall was filled with soil up to seven metre high, when cracks started to form in the retaining wall. Analysis show that failure would occur if the embankment continue to be filled. By replacing three metres out of the leftover four metres embankment with geofoam, the displacement of the retaining wall can be reduced from 2.1 m to 0.1 m.

Morphological and physico-mechanical properties of mycelium biocomposites with natural reinforcement particles

Mycelium biocomposites represent a potential sustainable lightweight alternative materials due to their low energy consumption and lack of pollution to the environment. However, the low compression strength of mycelium biocomposites limits its application. In this study, three fungal strains (Pleurotus ostreatus, Oudemansiella radicata, and Acremonium sp.) were incubated in substrates (cotton stalk, wheat bran, and natural reinforcement particles (NRPs)) to obtain mycelium biocomposites. The physico-mechanical properties, morphological properties, and thermogravimetric analysis were examined. The colonization periods of the mycelium biocomposites varied with the different fungi, and adding NRPs to the substrates obviously improved the physico-mechanical properties of the mycelium biocomposites. The Pleurotus ostreatus biocomposites with 37.5% NRP had the highest UCS strength of 508 kPa and Young’s modulus of 38.5 MPa, which satisfies the requirements of backfill materials in geotechnical engineering, and its cohesion and internal friction angle were 178 kPa and 21.8°, respectively, based on triaxial tests. Moreover, although the addition of NRP will increase the density of the material, the density of mycelium biocomposites with NRP (0%–37.5%) only ranged from 0.310 g/cm3 to 0.413 g/cm3. The water absorption characteristics of the mycelium biocomposites with NRP were similar to those without NRP. The permeability coefficient decreased slightly with increasing NRP content, and the decreased percentage was related to the mycelium growth. All mycelium biocomposites showed lower thermal stability but a higher residue mass than EPS (expanded polystyrene). The results illustrate that the mycelium biocomposites proposed in this study could be used as lightweight backfill materials that are widely needed in geotechnical engineering.

Use of Granulated Rubber Tyre Waste as Lightweight Backfill Material for Retaining Walls

The use of industrial waste in civil engineering applications constitutes a potential innovative effort to reduce environmental degradation and enable a sustainable use of natural resources. This paper reports a comprehensive laboratory study that was performed to evaluate the rubber granulates from End-of-Life Tyres (ELTs) as a lightweight backfill material in retaining walls. Various tests have been performed to provide specific information on the mechanical and physical properties of a detailed range of particle sizes smaller than 12 mm, with six different particle size distributions (S1: 0.0–0.8 mm/S2: 0.6–2.0 mm/S3: 2.0–4.0 mm/S4: 2.0–7.0 mm/S5: 90% 2.0–7.0 mm + 10% 0.6–2.0 mm/S6: 50% 2.0–7.0 mm + 50% 0.6–2.0 mm). The density and unit weight, compaction energy, compressibility, shear strength, and deformability have been evaluated to determine their performance. As a main conclusion, the research confirms that rubber granulates from ELTs possess great potential as backfill material behind retaining walls. The characteristic values of the geotechnical parameters have been estimated according to Eurocode 7. The friction angle results range from 18.27 to 23.21 degrees, and the cohesion results are wide-ranging, with values from 9.35 to 17.83 kPa. For this reason, two cantilever L-shaped retaining walls, selected as representative case studies, have been tested with these sample properties. The results of the geotechnical verifications are presented together with a comparison of the safety factors in accordance with the Spanish standard design (CTE-DB-SE-C) and the European (EC7-1) regulations. The calculations indicate that the overdesign factors (ODF) achieved in the verifications using the material properties of the S4, S5, and S6 combination improve the calculation results obtained if a conventional filler material such as sand is considered.

Shallow foundations on lightweight TDA backfill: Field tests and 3D numerical modelling

Recent advances in tire recycling technologies coupled with increasing global environmental awareness have resulted in several new products derived from scrap tires, including tire-derived aggregate (TDA). TDA is an inexpensive engineered lightweight backfill material with excellent geotechnical properties, produced by shredding scrap tires into sizes ranging from 12 mm to 305 mm. This paper examines the performance of rigid footings resting on a surface of conventional backfill materials overlying a TDA layer. The study includes three full-scale field tests with TDA layers of different thicknesses. Based on the field tests, rigorous 3D finite element analyses (FEA) were developed to study the failure mechanism of shallow foundations over TDA. In addition, the effect on the footing performance of changing critical parameters including the TDA layer thickness, the strength of the top granular backfill, the foundation depth, the footing width, the footing shape, and subsurface soil conditions was studied. It was found that in comparison to using only conventional granular backfill, using an underlying TDA layer for shallow foundations results in a significant improvement in transferring the stresses and reducing the stress influence zone underneath the footings. For instance, before the punching shear failure in the top layer occurred, TDA was able to reduce the transferred stresses by almost one half of that by the natural backfill. Furthermore, the results of the parametric study illustrated the dependency of the bearing capacity of the spread footing on the relative thicknesses of the TDA and the top granular layers, in addition to the foundation width.

Behavior of box culvert with geofoam as a backfill material in Highway

Box culverts are generally required to provide a passage for drainage and small vehicle and act as a stable base for a road embankment. Box culverts are subjected to traffic load and overburden pressure due to the cushion. Mostly box culverts are subjected to the lateral earth pressure and overburden pressure. The quantities of reinforced concrete in box culvert depends upon the anticipated lateral earth pressure which may be larger than overburden pressure. The magnitude of earth pressure due to a large quantity of backfill generates stresses and deformations on the face of box culvert. For counteracting this large pressure, either more thickness of reinforced concrete in box culvert is provided or light weight material is used as a backfill. EPS geofoam is a light weight backfill material which reduces the dead and lateral load on box culvert. The objective of this paper is to optimize the thickness of box culvert with the use of EPS geofoam as backfill material. For achieving this objective, finite element analysis has been done using PLAXIS 3D. The results of finite element analysis shows that the inclusion of geofoam as backfill material helps in reducing lateral deformation at the face of box culvert as compared to conventional backfill material. The use of geofoam makes it possible to reduce the thickness of box culvert which is beneficial in minimizing concrete requirement therefore reducing total cost of project.

Utilization of Quarry Waste and Granulated Rubber Mix as Lightweight Backfill Material

In the present investigation, an attempt has been made to propose a lightweight backfill material using industrial wastes, namely quarry waste and granulated rubber. Granulated rubber was added in varying percentages (5%, 10%, 15%, 20%, 25%, and 30%) to quarry waste for obtaining lightweight material. Laboratory investigation has been performed in the present study to examine the physical, chemical, and geotechnical properties of quarry waste and the geotechnical behavior of quarry waste–granulated rubber (QWGR) mixes. Using granulated rubber as additive, the unit weight of quarry waste material was found to reduce from 21.8 to 14.1 kN/m3 for QWGR30 mix. The friction angle of quarry waste was obtained to be 51.2°, which increased by about 14° with rubber addition for the QWGR30 mix. The permeability of quarry waste was found to improve from fine sand to coarse sand range with the granulated rubber inclusion, making it an efficient backfill material. QWGR30 mix was found to be an efficient lightweight backfill material with reduced lateral pressure by about 73% and 85% compared to quarry waste and conventional sand, respectively. The economic savings of the project on backfill material by using QWGR30 over conventional sand would be around 8.35%.

2D numerical analysis of a cantilever retaining wall backfilled with sand–tire chips mixtures

Previous research has shown that the backfill behind a retaining wall can be constructed with sand–tire chips (STC) mixture; this can lead to reduced horizontal displacements and earth pressures on the structure and allows lower design requirements, which implies lesser dimensions of the retaining wall. In this paper, the performance and stability of a cantilever retaining wall (CRW) with different STC mixtures, as lightweight backfill materials, were evaluated and analyzed numerically using the finite element software, RS2. The elastic parameters of the STC mixtures were computed using homogenization techniques, and the other engineering properties were obtained based on published literature. The results show that total displacement, vertical displacement, lateral pressures, lateral displacements, maximum shear forces and maximum bending moments are reduced considerably, and global stability of the retaining wall is enhanced when STC mixtures are used instead of sand alone. The mixture with the best overall mechanical behaviour was the one with a tire chips/sand ratio of 66.54/33.46 by weight or 81/19 by volume is used compared to the other mixing ratios.

Influences of particle characteristic and compaction degree on the shear response of clinker ash

Clinker ash is regarded as a granular waste of coal combustion but potentially employed as a recycled and light-weight backfill material for retaining wall and embankment in recent years. The physical, particle, compaction and mechanical properties of six selected types of clinker ash were thoroughly examined in this experimental investigation. Clinker ash owns very complex and angular shapes and it gives rise to the larger difference between the maximum and minimum void ratios. The single particle crushing strength of clinker ash is around 1/5–1/10 lower than natural sands and it indicates high crushability in nature. With similarity to natural sands, the mean crushing strength of clinker ash displays a decreasing tendency with the increase in grain diameter. A series of triaxial compression tests were performed on different types of clinker ash to examine the influences of particle characteristics, degree of compaction and effective confining pressure on their shear behaviour and deformation characteristics. Test results demonstrate that clinker ash possesses a higher peak friction angle at low effective confining pressures and gradually loses its shear strength with the rise in effective confining pressure. The great shear strength dependence on the stress level for clinker ash is confirmed. The stress-dilatancy behaviour of a given type of clinker ash is minimally affected by the degree of compaction and level of effective confining pressure. The stress ratios at the critical state of clinker ash are well correlated with the mean crushing strengths. A larger N value for clinker ash determined using Nova's rule indicates its higher crushability. The downward shift of critical state line of clinker ash due to grain crushing is identified on the void ratio and logarithm of effective mean stress plane. Additionally, grain crushing was confirmed by the comparison of the variation in grain size distribution curves and the observation of colored particles previously seeded in the tested samples before and after shearing.

Recycled Tire Chips Mixed with Sand as Lightweight Backfill Material in Retaining Wall Applications: An Experimental Investigation

This paper presents studies on use of recycled tire shreds in sand–tire chips (STC) mixture for retaining wall applications. Small-scale physical model tests were performed on rigid retaining wall with different STC mixtures. Rigid retaining wall model of 600 mm height was constructed in a Perspex container. The wall was made with hollow rectangular steel sections. STC mixtures with different tire chips proportions, such as 10, 20, 30, 40, and 50 % along with pure sand were considered as backfill materials. Static surcharge load, up to 10 kPa, was applied using concrete blocks. Model wall behaviour in terms of displacements and earth pressures has been discussed for sand alone (control case) and STC mixtures as backfill materials. The experimental results indicate that the horizontal displacements and lateral earth pressures are reduced to about 50–60 % of that of control case by using STC mixtures which functioned as light weight backfill materials.

Lightweight backfill materials in integral bridge construction

Analysis of integral bridge structures shows that lateral earth pressures on the end abutments have a dominant influence on the sizing of bridge components. Thermal cyclic movements induced by deck expansion cause densification of backfill material, leading to the build-up of high pressures behind the abutments. Measures to reduce these pressures by the use of alternative backfill materials can be highly beneficial to the structure as a whole, with extra expenditure on the backfill material being offset, and in some cases exceeded, by savings in material quantities in the rest of the structure and build time. This paper examines three contrasting backfill options that were considered during the design of Cottington Road overbridge in Kent: 6N granular backfill; lightweight expanded clay; and expanded polystyrene blocks. Although more expensive as a material than the other options investigated, the expanded polystyrene block option was selected as the most economical solution for this particular structure owing to large material savings in the foundations, abutment walls and wing walls as a direct result of reduced lateral pressures. Although it did not form part of the decision-making process, this paper also shows a significant saving in embodied and transport-related carbon dioxide emissions through preferring expanded polystyrene blocks to expanded clay.

On the Important Mechanical Properties of Rubber-Sand

More than a billion rubber tires are discarded annually around the world. Growing piles of discarded tires create fire and environmental hazards. Current disposal methods are mostly wasteful and costly. Tires possess high tensile strength, are chemically very stable, practically non-destructible and light in weight. All of these properties make tires a potentially useful geo-material. This paper presents the results of an extensive laboratory testing study investigating the potential of using shredded tires mixed with sandy soils (rubber-sand) as lightweight fill and backfill material in road construction. The results show that rubber-sand has significant promise for use as an earthwork fill material. In addition to its engineering benefits, such use of scrap tires would significantly contribute to solving the ever-growing tire disposal problem.

낙동강 하류 및 부산연안지역의 준설토와 퇴적토 활용을 위한 특성 평가

Although the quantity of dredged soils has increased owing to recent new harbor construction, sea course management, polluted sediment dredging, and four-river project, the reuse or recycling of those dredged soils has not done properly in Korea. To develop measures to utilize them in various ways for reuse or recycling, the biophysicochemical properties of dredged soils and sediment were assessed in this study. Samples were classified according to their sources-river and sea-by location, and as dredged soil and sediment depending on storage time. The results showed that dredged materials from the sea have high clay content and can be used for making bricks, tiles, and lightweight backfill materials, while dredged materials from the river have high sand content and can be used in sand aggregates. Separation procedures, depending on the intended application, should be carried out because all dredged materials are poorly sorted. All dredged soils and sediments have high salinity, and hence, salts should be removed before use for cultivation. Since dredged materials from the sea have adequate concentrations of nutrients, except phosphate, they can be used for creating and restoring coastal habitats without carrying out any additional removal processes. The high overall microbial activities in dredged materials from the river suggested that active degradation of organic matter, circulation of nutrients, and provision of nutrients may occur if these dredged materials are used for cultivation purpose.

Numerical analysis of reinforced wall using rubber tire chips–sand mixtures as backfill material

Scrap tires are undesired urban waste and the volume is increasing every year. One of the possible utilization of this waste is to use it as shredded tires alone or mix it with soil as lightweight backfill materials. This paper presents the state-dependent constitutive model for rubber tire chips and rubber tire chip–sand mixtures and its successful implementation into a numerical analysis (FLAC) program. The implemented model was verified by simulation of the stress–strain characteristics of rubber tire chip–sand mixtures in triaxial testing. Furthermore, the numerical simulations as well as the parametric studies of the effects of the reinforcement stiffness and interface shear stiffness on the behavior of the reinforced wall have been performed. With increasing reinforcement stiffness, the lateral deformation decreased, while the tensile force in the reinforcement increased. Moreover, with increasing shear stiffness at the interface, the tensile force in the reinforcement increased, while the lateral deformation of the reinforced wall decreased.

Use of Shredded Tires as Lightweight Backfill Material for Retaining Structures

Each year in the United States, approximately 242 million automobile, truck and specialty tires are discarded. Almost 78% of these scrap tires wind up in overcrowded landfills, and thousands more are strewn across the country's empty lots, highways and illegal tire dumps. Used tires pose both a serious public health and an environmental threat. Therefore, economically feasible alternatives for scrap tire disposal must be found. Some of the current uses of scrap tires are tire-derived fuel, barrier reefs, and crumb rubber as an asphalt additive. However, all of the recycling, re-use and recovery practices combined only consume about 22% of the discarded tires. Thus, a need still exists for the development of additional uses for scrap tires. This paper addresses one potential use of scrap tires within the civil engineering field. Specifically, the feasibility of using shredded tires as a lightweight backfill material for retaining walls has been investigated. In this study, laboratory tests were first performed to determine the engineering properties of shredded tires. Based on sieve analyses, the shredded tires used for this study can be classified as uniformly graded material. The unit weight of shredded tires was found to range from 35 to 38 lbs ft-3 (pcf), and the hydraulic conductivity was determined to be 0.03 cm s-1. The values of shear strength parameters, cohesion and angle of internal friction, were determined to be 147 lbs ft-2 (psf) and 27 degrees, respectively. Using these properties, retaining walls of various heights were then designed using shredded tires as the backfill material. Retaining walls were also designed using conventional sand as the backfill material for comparison purposes. When comparing the overall cost for the retaining wall using shredded tires with the retaining wall using sand, a substantial cost saving was realised by the use of shredded tires. An increase in the factor of safety was also a result of using shredded tires instead of sand as backfill. The results of this study indicate that shredded tires have a definite potential to be used as a backfill material for retaining structures.

Dynamics Characteristics of a Light Weight Backfill Material

A granular air-mortar is a light weight backfill material and it's unit weight and strength can be control. Therefor it is estimated to reduce earth pressure acting on the revetment and the retaining wall. In the case of using this light weight material at a revetment, liquefaction and seismic earth pressure of backfill are difficult planning problems. And so static and cyclic triaxial tests and shaking table tests were performed on a granular air-mortal. This report deals with the shear characteristics and the seismic earth pressure acting on the retaining wall.