Lightweight Backfill 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.

Integral bridge abutments in response to seasonal temperature changes: State of knowledge and recent advances

Expansion and contraction of integral abutment bridges due to temperature changes force integral bridge abutments (IBAs) to move toward and away from the backfill, thus increasing horizontal earth pressures behind the abutments and inducing bending moments on pile foundations. This paper presents the state of knowledge and recent advances in understanding the behavior of IBAs in response to temperature changes including abutment movement, pile response, and horizontal earth pressure behind the abutment, examines the effect of bridge skew on the behavior, and discusses possible measures to mitigate temperature change-induced problems for IBAs. Field data show that both bending moments of piles near the bottom of abutments and axial loads of piles fluctuated with temperature. Redistribution of dead loads among bridge components due to planar temperature gradients and earth pressure changes behind the abutment contributed to axial load fluctuations in piles. Magnitude and distribution of horizontal earth pressures behind the abutment depend on factors such as abutment movement and abutment movement mode. Most of the current design methods overestimated the horizontal earth pressures at the bottom of the abutment during bridge expansion. Compressible inclusions placed behind the abutment, geosynthetic-reinforced backfill, and lightweight backfill in place of typical aggregate backfill are helpful to reduce horizontal earth pressures behind the abutment at high temperatures and temperature change-induced backfill settlements.

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.

Strength, Durability, and Microstructures characterization of sustainable geopolymer improved clayey soil

Geopolymer has been emerged as an innovative and eco-friendly alternative to traditional soil improvement products such as Ordinary Portland Cement (OPC) and lime, which have negative environmental consequences. Geopolymer has been employed in various geotechnical applications as alternative lightweight backfill in highway barriers and/or behind retaining walls, providing technical, environmental, and economic benefits. The present study aims to evaluate the mechanical, durability, and Microstructure properties of clayey soil (with different percentages of sand) stabilized using coal-fired fly and a sodium hydroxide/sodium silicate solution alkali activator. Stabilized soils exhibited high strength of 1–8 MPa compared with less than 0.3 MPa for untreated soils. Moreover, adding sand to clay soil reduced the optimum ratio of alkaline activator from 0.8 for clayey soil with 5% sand to 0.6 for clayey soil with 10, 20, 30% sand. The geopolymer treated samples also showed high resistance to the acidic environments and chlorides. Finally, SEM results revealed a clay fabric modification caused by inter-particle contacts and the resulting bonding caused by gel formation and hardening. According to the outcomes of this study, it can be concluded that using a fly ash geopolymer binder for soil stabilization is a viable alternative to cement in geotechnical applications.

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.

Sustainable Implementation of Recycled Tire-Derived Aggregate as a Lightweight Backfill for Retaining Walls

The study examined the use of recycled tire-derived aggregate (TDA) mixed with kaolin for retaining wall applications. The effects of the TDA content on the geotechnical properties of TDA-kaolin specimens such as the internal friction angle, maximum dry density (MDD), optimum moisture content (OMC) and saturated density (SD) were investigated. A total of 13 physical model tests were performed on a polymer concrete retaining wall using kaolin and TDA-kaolin mixtures as backfill material. Powdery, shredded, small-sized granular (1–4 mm) and large-sized granular (5–8 mm) TDA were mixed with kaolin at contents of 0%, 20%, 40%, and 60% by weight. The lateral wall displacement was measured on a fabricated steel strip footing close to the wall during loading. Lateral wall displacement also was simulated using finite element (FE) software (Optum G2). The results indicated that the addition of 60% TDA decreased the internal friction angle of the samples up to 8% compared to pure kaolin. In addition, the TDA particles caused the MDD of the TDA-kaolin samples to decrease up to 45%. The physical modeling results indicated that the kaolin samples mixed with 60% shredded TDA showed the highest elasticity in all tests at the failure moment of the footing.

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.

Earth Pressures on Retaining Walls backfilled with Red Soil admixed with Building Derived Materials under Rotational Failure mode

ABSTRACT Proper estimation of earth pressures plays a major role in assessing the stability of retaining structures. The present study proposes a sustainable and eco-friendly usage of building-derived materials (BDMs) mixed with red soil as a backfill for retaining walls under rotational failure mode. Small-scale laboratory model tests are conducted on a cantilever rigid retaining wall with different red soil–BDM blends as backfill. The width of the backfill is varied to assess its effect on the variation of earth pressures. The experimental results indicate that the earth pressures are not increased significantly by the inclusion of BDM to red soil, which suggests that BDM can be used as an effective lightweight backfill. The optimum pressure is obtained on mixing 20% BDM with red soil. It is observed that since the wall is rotated about its bottom end with the help of a hydraulic jack, the variation in magnitude of earth pressure is maximum near the top and decreased non-linearly with depth which is in contrast with the classical earth pressure theories. The experimental results also demonstrate that the failure planes are limited by the width of the backfill.

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.

Investigation of thermal conductivity and prediction model of recycled tire rubber-sand mixtures as lightweight backfill

Thermal conductivity is an important parameter in investigating the thermal properties of geotechnical materials. In this paper, a series of thermal needle tests were carried out on recycled rubber-sand mixtures. The effects of sand fraction, moisture content, dry density, and particle size on thermal conductivity were investigated in detail. The results showed that the thermal conductivity of rubber-sand mixtures was observed to be a parabolic increment at a low sand fraction and a linear increment at a high sand fraction with an increasing dry density. A value of 6% can be regarded as critical moisture content. The larger the sand particle size, the higher the thermal conductivity exhibited by the mixtures was. Additionally, based on a scanning electron microscopy (SEM), the heat transfer mechanism was investigated. Importantly, a simplified multiple linear regression (MLR) model for recycled tire rubber-sand mixtures was proposed, and significant test (correlation coefficient R2, F-test, and t-test) results presented a good regression effect for this model. This research will provide a more reasonable thermal parameter for recycled tire rubber-sand mixtures as a lightweight backfill in geothermally-related structures. Moreover, the effective utilization of scrap tires can reduce environmental pollution and promote sustainable infrastructure.

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.

Using TDA underneath shallow foundations: simplified design procedure

ABSTRACTTire recycling and reuse in North America and worldwide have increased considerably, with the aim of reducing the harmful effects of scrap tires on the environment. Accordingly, the use of tire derived aggregates (TDA) in civil engineering applications is on the rise at an unprecedented rate. In comparison to conventional backfill aggregates, TDA is an inexpensive, lightweight material that costs about 25% of the cost of conventional backfill. Thus, there is an increasing trend of using TDA under shallow foundations as a lightweight backfill alternative. However, limited information exists for the design of shallow foundations built on TDA. Hence, the main objective of this paper is to develop a simplified design procedure for shallow foundations built over a TDA layer. Rigorous finite element models were developed and validated using field tests results. Subsequently regression analyses were used to develop the proposed ultimate bearing capacity equation, taking into account the granular layer thickness, TDA layer thickness, footing width, footing shape, footing depth, and the allowable settlement.

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%.

Strength and Deformation of Sand-Tire Rubber Mixtures (STRM): An Experimental Study

Abstract Waste material such as used tires is increasing every year, which poses environmental problems. However, such material has been used in several geotechnical applications as alternative lightweight backfill in highway embankments and/or behind retaining walls, providing environmental, economic and technical benefits. These applications require knowledge of engineering properties of soil-tire rubber mixtures. The present study aims to show the possibility of tire rubber usage in sand by evaluating the shear strength and deformability of sand mixed with granulated rubber, in weight percentages between 0 and 50%. The tire rubber content was found to influence the stress-strain and deformation behavior of the mixtures. The shear strength of sand mixed with 10% or 20% tire rubber was higher than that measured for sand only. However, the trend for TRC = 30–50% was different. Samples with a rubber content of 30-50% exhibited a rapid decrease in the stress ratio compared with that of sand. The major principal strain at maximum stress ratio was found to increase with increasing tire rubber content. However, it was observed that the lateral strains (minor and intermediate principal strains) of samples reduced significantly with the addition of tire rubber to the sand.

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.

Sand\u2013rubber mixtures undergoing isotropic loading: derivation and experimental probing of a physical model

The volume of scrap tyres, an undesired urban waste, is increasing rapidly in every country. Mixing sand and rubber particles as a lightweight backfill is one of the possible alternatives to avoid stockpiling them in the environment. This paper presents a minimal model aiming to shed light on the relevant physical parameters governing the evolution of the void ratio of sand–rubber mixtures undergoing an isotropic compression loading, where the mixtures consist of various volume ratios of rubber. It is based on the idea that, when pressure is applied, the rubber particles deform and partially fill the porous space of the system, leading to a decrease of the void ratio with increasing pressure. We show that our simple approach is capable of reproducing experimental data obtained with sand and rubber of similar particle size distributions up to mixtures composed of 50% of rubber. The effect of the particle shape and size on the model parameters is discussed.