Geofoam Density Research Articles

Numerical Modeling of Cantilever Retaining Wall Using EPS Geofoam

Earth retaining wall structures are common civil engineering structures. Estimation of magnitude and distribution of earth pressure on retaining structures under different surcharge loading conditions is essential as they influence the design and overall economy of retaining structures. Numerical modeling using finite element code PLAXIS is used static analysis. 7 m height of non-yielding cantilever retaining wall with and without EPS geofoam structure is studied and 20 m backfill width was considered. In the present study backfill was modeled as Mohr-Coulomb yield criteria and EPS geofoam and wall were modeled as Linear-elastic. EPS geofoam densities namely 12 kg/m3 and 15 kg/m3 and two different geofoam thicknesses 0.107H and 0.143H were used for static analysis. Three different surcharge loading namely 10 kPa,30kPa and 50kPa which were kept at a distance of 2.0 m away from the wall face. In the static analysis earth pressure distribution for wall with and without geofoam were analyzed. Approximately 50% isolation efficiency was reported. At lower surcharge loads the effectiveness of EPS is more as compare to higher surcharge load and with increase in surcharge load, isolation efficiency gradually decreases and isolation efficiency decreases with increase in buffer modulus. Apart from these serviceability criteria was also checked. Serviceability criteria comprise of lateral deformation of EPS geofoam at sand-geofoam interface and backfill surface settlement were studied. Lower EPS geofoam density and higher EPS geofoam thickness reduces higher magnitude of earth pressure but in this combination the backfill surface settlement was coming very high.

Role of geofoam inclusions on the liquefaction resilience of transportation geostructures

Though the effectiveness of geofoam buffers for improving the dynamic load response and seismic performance of road embankments and retaining walls is well-established, their role on soil liquefaction is not investigated by many. This study explores the potential of Expanded Polystyrene (EPS) geofoam inclusions for liquefaction mitigation in sands through a series of stress-controlled constant volume cyclic simple shear tests. The study quantifies the increase in liquefaction resistance of sand with geofoam inclusions and reduction in modulus degradation and shear deformations and increase in energy dissipation with loading cycles. Effects of geofoam density and thickness of the layer on the liquefaction response were also investigated through systematic series of experiments with geofoam of three different densities and two different thicknesses. Findings from this experimental study suggest that providing a thick low-density geofoam layer provided the maximum benefit among all the inclusions. Fundamental mechanisms governing this improved response are explored through a series of bender element tests. Results from this study confirm the effectiveness of geofoam buffers in mitigating liquefaction in granular soils and recommend their use in road embankments and retaining walls being constructed in zones of high seismicity to avoid liquefaction and associated lateral spreading failures in these structures.

Construction of geofoam block embankments atop existing transportation infrastructure

Expanded polystyrene (EPS) block (geofoam block) is a mature geotechnology for constructing highway embankments. In addition to preventing bearing capacity and settlement related stability problems for the embankments constructed on soft soil sites, geofoam blocks are also used to construct embankments atop existing infrastructure. Selecting geofoam technology for these applications not only prevents possible structural problems due to the lightweight nature of geofoam blocks but also eliminates costly remediation alternatives. The details of three well-documented and monitored different geofoam embankments constructed atop different existing infrastructures (buried pipeline, buried culvert and pile cap of drilled shafts for a deep excavation) are presented. The backgrounds of these projects, design considerations, construction and instrumentation details are discussed. The monitoring results were presented, and long-term performance predictions were evaluated. Numerical modeling effort was utilized to model the both short- and long-term behavior of geofoam embankments. Time-dependent behavior of the embankments under service loads was compared with numerical simulations. Constitutive modeling and related mechanical properties of geofoam blocks, which mimicked the long-term field behavior, as a function of geofoam density were proposed for future numerical modeling efforts.

Short- and long-term behavior of EPS geofoam in reduction of lateral earth pressure on rigid retaining wall subjected to surcharge loading

Retaining walls are subjected to dead loads from backfill and adjacent structures, live loads and other loads from the vicinity of the structure. Retaining walls need to withstand earth pressure generated from above mentioned loads satisfactorily throughout their service life. Lateral earth thrust on retaining walls can be minimized by placing a compressible inclusion, such as, EPS geofoam, between the backfill and retaining wall. The present study is aimed at understanding both short- and long-term influence of EPS geofoam on surcharge induced lateral earth pressures on retaining walls through 1-g model studies. Four densities of geofoam in the range of 10–25 kg/m3 and three thicknesses of geofoam in the range of 25–75 mm were used in the present study. Lateral earth pressure at several locations along the height of the wall were monitored using earth pressure cells. Geofoam compression and backfill settlements under the surcharge load were also quantified using image analysis. From the series of model tests, it was observed that with the use of geofoam, lateral earth pressure on retaining wall was reduced under both short- and long-term loading conditions. However, higher reduction was observed under long-term loading.

Evaluating the Role of Geofoam Properties in Reducing Lateral Loads on Retaining Walls: A Numerical Study

Expanded polystyrene (EPS) geofoam is a lightweight compressible material that has been widely used in various civil engineering projects. One interesting application of EPS in geotechnical engineering is to reduce the lateral earth pressure on rigid non-yielding retaining walls. The compressible nature of the EPS geofoam allows for the shear strength of the backfill soil to be mobilized, which leads to a reduction in lateral earth pressure acting on the wall. In this study, a finite element model is developed and used to investigate the role of geofoam inclusion between a rigid retaining wall and the backfill material on the earth pressure transferred to the wall structure. The developed model was first calibrated using experimental data. Then, a parametric study was conducted to investigate the effect of EPS geofoam density, relative thickness with respect to the wall height, and the frictional angle of backfill soil on the effectiveness of this technique in reducing lateral earth pressure. Results showed that low-density EPS geofoam inclusion provides the best performance, particularly when coupled with backfill of low friction angle. The proposed modeling approach has shown to be efficient in solving this class of problems and can be used to model similar soil-geofoam-structure interaction problems.

Monotonic, cyclic and post-cyclic shearing behavior of sand-EPS geofoam interface

Sand-EPS geofoam is commonly used as a seismic buffer in a variety of geotechnical applications to alleviate damages imposed by seismic vibrations. Evaluation of the properties of the sand-EPS geofoam interface is an essential part of the design and installation of EPS geofoam in direct contact with the parent sand. In this study, a series of laboratory tests are carried out using a large-scale direct shear apparatus to evaluate the monotonic, cyclic and post-cyclic behavior of the sand-EPS geofoam interface. Adopting the relative density of the parent sand, the density of EPS geofoam, the applied normal stress, the cyclic shear strain semi-amplitude and the number of cycles as the variable parameters, their influence on the response of the sand-EPS geofoam interface is investigated. According to the experimental results, with the increase in the number of cycles, sand relative density, EPS geofoam density and the applied normal stress, the equivalent or secant stiffness of the sand-EPS geofoam interface increases while its damping ratio declines. The results of the monotonic (MDS) and post-cyclic monotonic (CMDS) shearing experiments also show that with an increase in the EPS density and normal stress, which offers greater resistance against sliding, the mobilized shear stresses generally increase.

EPS Geofoam as a Wave Barrier for Attenuating High-Speed Train-Induced Ground Vibrations: A Single-Wheel Analysis

Vibrations induced by high-speed trains in the ground are a common cause of concern in the urban railway lines due to construction of buildings and inhabitation of residents close to railway lines. The present study aims to evaluate the potential use of geofoam as an in-fill material for passive trenches to reduce the vibrations generated by railways. Considering the higher frequencies of railway vibrations in comparison with earthquake excitations, characterization of vibration attenuation efficiencies of geofoam in-filled trenches is done in the scale of peak particle velocities (PPV). A comprehensive study is conducted on the effects of buffer stiffness, geofoam density, and dimensions and location of the in-filled trench away from the railway track. Results indicate that having low buffer stiffness for the geofoam in-filled trenches are efficient in reduction of railway-induced ground vibrations. Grades of geofoam with smaller densities are observed to have better vibration attenuation characteristics as well. It is also characterized that the location of the trench close to the railway embankment results in an overall reduction in the vibration levels in the ground. A higher depth of in-filled trench is requisite, if the trench is located at higher distance from the track. It is ascertained that geofoam in-filled trenches are highly suitable for attenuating the train-induced vibrations in the native sub-soil.

The experimental investigation of behaviour of expanded polystyrene (EPS)

Low-strength substrates and anthropogenic soils are always an issue in civil engineering. Based on the soil layer types, several methods could be used to improve the basic/foundation layer however it would be difficult to make sure if the specified requirements are achieved. Nowadays, Expandable Polystyrene (EPS) as a lightweight material found as a substitution for traditional methods like soil replacement, soil mixing, using piles driving and other treatment techniques. This paper will demonstrate the static properties of EPS foams in a view point of construction material which will be a key for the future study of these materials. A series of compression tests were carried out on different types of EPS foam to study the effect of EPS geofoam density on the mechanical behaviour of these materials.

An alternate arrangement of geofoam blocks and air pocket to mitigate confined blast induced vibration

ABSTRACT The present study focuses on the performance of intermittent geofoam in-filled (IF) trench as a passive vibration screening when a reinforced concrete (RC) lining tunnel is subjected to internal blast load. The blast analysis of lined tunnel is performed using a three dimensional non-linear finite element (FE) method. The coupled Eulerian-Lagrangian (CEL) analysis tool has been employed in the FE software ABAQUS/Explicit for the purpose of this study. The explosive trinitrotoluene (TNT) has been modelled using Eulerian elements as the blast source in the tunnel. The IF has been installed at the far field from the source to protect the vibration sensitive buildings and equipment in that region. The parameter, which controls the design of intermittent geofoam trench, is its geometric parameters (width, depth, location). EPS geofoam density and soil Poisson’s ratio have been considered to investigate the performance. In addition to IF, another newly proposed technique named staggered intermittent geofoam (SIF) has also been investigated in the present study. The results of simulation show that both IF and SIF can be a very good passive vibration screening technique subjected to blast sources.

Short-Term and Long-Term Behavior of EPS Geofoam

Abstract Expanded Polystyrene Styrofoam (EPS) geofoam is widely used in various civil engineering applications. To predict the responses of structures to external loading, when in the presence of geofoam, understanding physical and mechanical behavior of geofoam, both short and long term, is very essential. A series of laboratory experiments was conducted on EPS15, EPS20, and EPS25 geofoam specimens under different loading conditions. To understand the short-term behavior, static uniaxial compression and cyclic uniaxial compression (CUC) tests were performed; however, for long-term behavior, accelerated creep and pseudo long-term tests were conducted on geofoam samples. CUC tests were performed at different static and cyclic stress amplitudes and loading frequencies for 5,000 load cycles, and the results reveal that, irrespective of geofoam density, secant modulus (Edyn) decreases and the damping ratio of geofoam increases with the increase in cyclic axial strain. Also, it was observed that an increase in cyclic axial strain and the number of loading cycles reduced the Poisson’s ratio of geofoam from positive to negative values. From the time-temperature-stress superposition accelerated creep testing method, creep strains developed in EPS15, EPS20, and EPS25 geofoam samples at the end of 100 years were 2.12, 2.4, and 2.11 %, respectively. From pseudo long-term tests, the estimated Young’s modulus (E) of geofoam decreases with the increase in compressive creep strain for all three densities of geofoam.

Experimental-numerical assessment of geogrid-EPS systems for protecting buried utilities

Expanded polystyrene (EPS) is a lightweight material commonly used in sensitive geotechnical applications, particularly in transportation applications that often see a confluence of buried utilities and traffic loading. This study investigates the behavior and efficacy of EPS geofoam post-beam (PB) systems as a means of protecting underground utilities. The PB system consists of two EPS geofoam ‘post’ blocks that both protect buried utilities and support a capping EPS beam and soil overburden. Two series of laboratory large-scale model tests of the EPS PB system under both unreinforced and geogrid-reinforced soil cover were conducted to explore the effect of beam thickness, soil cover thickness and density of geofoam blocks on system deformations and stress distributions. Experimental results showed that the EPS PB system was effective in bearing the applied load without transferring it to the utilities below. The improvement in system performance was most pronounced when higher geofoam density, thicker EPS beams, geogrid reinforcement and increased soil cover were used. Three-dimensional finite element (FE) numerical models were developed and validated based on test results, and leveraged to provide insight into internal system behavior and design parameter selection.

On the role of geofoam density on the interface shear behavior of composite geosystems

Expanded polystyrene (EPS) geofoam has been increasingly used in geotechnical engineering applications to replace conventional backfill material or to reduce earth pressure on retaining and buried structures. In most of these applications, geofoam blocks are installed in direct contact with different construction material (soil, concrete, steel, wood, etc.). This results in a composite system that is subjected to loading in both the normal and shear directions. Therefore, successful analysis and design of these composite structures require a detailed knowledge of interface strength characteristics of geofoam under a combination of normal and shear stresses. In the current research, an attempt has been made to study the interface shear characteristics of geofoam with selected materials, including concrete, wood and steel. Three different geofoam densities namely, 15, 22 and 39 kg/m3 were used in this study. A series of direct shear tests (DST) was conducted with a shear box of dimension 100 mm × 100 mm × 50 mm under three different normal stresses 18, 36 and 54 kPa. Test results revealed that geofoam density and applied normal stress have significant effects on the vertical compression and interface strength properties (i.e. adhesion and friction angle) of the investigated geosystem. Surface roughness was found to play a significant role in the shear resistance at the contact. Geofoam–concrete interface showed maximum strength as compared to wood and steel materials. Care should be exercised when placing geofoam against steel or wood surfaces as the mobilized friction angle is generally small and sliding may develop depending on the applied normal stress level.

Influence of Contacting Material on Calibration Response of Diaphragm Earth Pressure Cells

Earth pressure cells (EPCs) are widely being used for the measurement of pressure acting on structures or within the soil. Output from an EPC varies with properties of contacting media (fluid or soil), density of media, etc. As geofoam is used in many geotechnical applications, especially to control earth pressures, it is prudent to calibrate earth pressure sensors, with geofoam as a contacting material with EPCs (geofoam calibration of EPC). In the present study, two diaphragm-based EPCs of different make are used to perform in-soil and geofoam calibration studies. A deadweight calibration set-up is developed to perform both soil and geofoam calibration tests. Effect of soil thickness, geofoam thickness, combined geofoam and sand thickness, geofoam density and displacement/loading rate on the EPC output under external loading is studied. From soil calibration results, it is observed that optimum sand thickness is 4.17d for both types of EPC. The response of EPC in geofoam calibration resembles the stress–strain response of geofoam, and it varies with the density of geofoam. At any applied pressure, output from an EPC is much higher in the case of geofoam calibration compared to that of soil calibration.

Reduction of lateral earth pressure using Geo-foam blocks

Geo-foam is an expanded polystyrene (EPS) or extruded polystyrene manufactured into large lightweight blocks. EPS Geo-foam density is only about 1% that of soil and rock, making it a superior, ultra-lightweight fill material that significantly reduces the stress on underlying subgrades. The lighter load can reduce settlements and can improve stability against bearing and slope failures. Geo-foam offers special advantages for construction on soft ground, slope stabilization, and retaining walls. A parametric study is carried out using ADINA program, different values of Geo-foam thickness (t), and Geo-foam height (H). Loaded and unloaded retaining wall models are also studied. The study aims at achieving the lowest possible stresses in both soil and the retaining wall body. This will reduce the expected soil settlement. Results showed that the most effective and preferable value of the Geo-foam thickness (t) is equal to 1.00 m. Numerical results pointed indicated that the decrease in soil settlement was about 35% when using Geo-foam of thickness equal to 1.00 m. Also, results showed that soil settlements and lateral stresses decreased by about 20% for loaded cases for different values of the Geo-foam thickness when compared with unloaded ones.

Experimental Investigation of the Shear Behavior of EPS Geofoam

Geofoam has been used in a wide range of geotechnical engineering projects since 1960s; either as lightweight fill material (e.g. embankments and bridge approaches) or as compressible inclusion (e.g. retaining walls and culverts). In most of these projects, geofoam is installed either in direct contact with other geofoam blocks or other construction material. Successful design of these composite systems requires a good understanding of both the compression and shear behavior of the geofoam blocks as well as the shear strength of the interface. In this study, an attempt has been made to measure the shear strength parameters of expanded polystyrene (EPS) geofoam blocks of different densities as well as the interface strength parameters as these blocks interact with sand as well as polyvinyl chloride (PVC) material. A series of direct shear tests has been carried out on geofoam samples of three different densities, namely, 15, 22 and 35 kg/m3. Shear test results on geofoam monoblocks showed that the increase in density results in an increase in the material cohesion, which is associated with a decrease in the internal friction angle. Most of the interface resistance was found to develop at small displacements. For geofoam–PVC interface, both the adhesion and angle of interface friction slightly increased with the increase in geofoam density. The measured geofoam–sand interface strength revealed a consistent increase in the angle of interface friction as the density of geofoam material increased. These experimental results can be used to guide engineers in estimating the interface parameters needed for both analytical and numerical analyses involving soil–EPS–structure interaction.

Combined Use of Jute Geotextile-EPS Geofoam to Protect Flexible Buried Pipes: Experimental and Numerical Studies

This paper addresses the results of the experimental and numerical studies conducted on 4.2 mm thickness and 110 mm diameter high-density polyethylene (HDPE) pipes buried in fly ash material overlying stone dust beds. The model tests were performed using single and double layers of expanded polystyrene (EPS) geofoam as compressible inclusions. In addition to that, jute geotextile was used as a reinforcement for the infill fly ash along with EPS geofoam inclusion to obtain induced trench condition. The test beds were subjected to loading on the fly ash surface with the help of a rigid steel plate to simulate as a strip footing in different embedment depths of the pipe (1–3 times pipe diameter). The test results revealed that the pressure and strain values in the pipe reduced significantly in the presence of EPS geofoam and jute geotextile related to the location of the pipe. In the case of double layers of EPS geofoam could induce reduction of the pressure up to 87.2% and strain about 63.5% respectively depending on the density and width of EPS geofoam. Whereas, at the same burial depth, in the presence of jute geotextile together with EPS geofoam can be reduced up to 93.8 and 73.4% for pressure and strain respectively depending on EPS geofoam density and number of reinforcement. Moreover, the jute geotextile-EPS geofoam combination of model test results were validated with finite element program. A good agreement was observed on pressure-settlement response and pipe strain between experimental and numerical investigations. The numerical studies show that the jute geotextile distributes stresses in the lateral direction and then the stresses on the pipe significantly reduced.

Earth Pressure Distribution on a Rigid Box Covered with U-Shaped Geofoam Wrap

Earth loads acting on buried structures are known to be influenced by the characteristics of the soil, and the stiffness and geometry of the structure. To reduce earth pressure acting on buried structures, the induced trench installation technique has been recommended and applied in practice for several decades. It involves the installation of a soft zone immediately above the buried structure to mobilize shear strength in the backfill material. In this study an experimental investigation is conducted to measure the changes in contact pressure on the walls of a rigid structure buried in granular backfill with a U-shaped geofoam wrap. The results are compared with the conventional induced trench method as well as the positive projection installation with no geofoam. Contact pressures on the walls of the structure are measured using the tactile sensing technology. The experimental results are used to validate a finite element model that has been developed to analyze this soil–geosynthetic–structure interaction problem. The numerical model is then used to study the soil arching and the stresses developing in the backfill material for three different EPS densities. In addition, the role of geofoam density and the maximum fill height that can be carried safely without exceeding the design strain levels are examined. Conclusions are made regarding the effectiveness of this type of EPS inclusion on the earth pressure distribution around the buried structure.

Investigation of soil-geosynthetic-structure interaction associated with induced trench installation

The design of subsurface structures associated with transportation and other underground facilities, such as buried pipes and culverts, requires an understanding of soil-structure interaction. Earth loads on these structures are known to be dependent on the installation conditions. To reduce earth pressures acting on buried structures installed under high embankments, the induced trench method has been recommended and applied in practice for several decades. It involves the installation of a compressible material (e.g. EPS geofoam blocks) immediately above the buried structure to mobilize shear strength in the backfill material. A first step towards understanding this complex soil-geosynthetic-structure interaction and accurately modeling the load transfer mechanism is choosing a suitable material model for the geofoam that is capable of simulating compressive testing results. In this study, an experimental investigation is conducted to measure the changes in contact pressure on the walls of a rigid structure buried in granular backfill with an overlying geofoam layer. Validated using the experimental results, finite element analysis is then performed and used to study the role of geofoam density, thickness and location on the load transferred to the buried structure. Conclusions are made regarding the effect of modeling EPS inclusion as a non-linear material and the role of EPS configuration on the earth pressure distribution around the buried structure.

A Numerical Procedure for the Assessment of Contact Pressures on Buried Structures Overlain by EPS Geofoam Inclusion

Extruded Polystyrene (EPS) geofoam is a light weight material used in a wide range of geotechnical engineering applications including embankment construction and bridge approaches to reduce earth loads imposed on the adjacent or underlying soils and structures. EPS is also used as a compressible material above deeply buried culverts to promote positive arching and reduce the load transferred to the walls of the structure. An important step towards understanding the soil-geofoam-structure interaction and accurately model the load transfer mechanism is choosing a suitable material model for the EPS geofoam that is capable of simulating the material response to compressive loading for various ranges of strains. In this study, a material model that is able to capture the response of EPS geofoam is first established and validated using index test results for three different geofoam materials. To examine the performance of the model in analyzing complex interaction problems, a laboratory experiment that involves a rigid structure buried in granular material with EPS geofoam inclusion is simulated. The contact pressures acting on the walls of the structure are calculated and compared with measured data for three different geofoam materials. The developed numerical model is then used to study the role of geofoam density on the earth loads acting on the buried structure. Significant pressure reduction is achieved using EPS15 with a pressure ratio of 0.28 of the theoretical overburden pressure at the upper wall. The proposed FE modeling approach is found to be efficient in capturing the behavior of EPS geofoam material under complex interaction soil-structure condition.

Numerical study on intermittent geofoam in-filled trench as vibration barrier considering soil non-linearity and circular dynamic source

Open and in-filled trenches are found to be quite impressive vibration screening technique among the researchers. This paper mainly aimed to examine the efficacy of using intermittent expanded polystyrene (EPS) geofoam in-filled trench as the vibration barrier, which is practically a combination of geofoam and air pocket placed alternately throughout the depth of the trench. The vibration screening efficiency of intermittent geofoam in-filled trench is determined under a constant force amplitude-type vertical oscillation of a machine resting on a circular embedded foundation. The effect of various parameters such as depth, width, inclination, and location of trench, excitation frequency of the source, and density of geofoam on the screening efficiency of geofoam in-filled is explored using 2D finite element method. The soil is modelled as non-linear elastic under the excitation of moderately high-speed machine. In the presence of machine-induced vibration, the vertical displacement at different locations along the ground surface is captured to determine the amplitude reduction ratio (ARR), which helps in assessing the efficiency of the vibration screening technique.