Geocell Layer Research Articles

Dynamic analysis of high-rise residential structures through the cone method

In this article, to analyze the behavior of surface foundations based on reinforced soil, a simple physical method based on material resistance called (cone method) has been used. Which is used as an alternative to the exact solution methods that are based on the three-dimensional elastodynamic theory. The purpose of this research is to introduce a simple physical method and analytical tool to analyze the surface foundation based on geocell-reinforced soil. With the cone method, it is possible to examine the effects of layered soil. Obtaining the dynamic stiffness of the foundation based on reinforced soil using the cone method for the vertical degree of freedom and also investigating the effect of various parameters related to geocell reinforcement on the dynamic stiffness of the surface foundation are the goals of this research. In general, the longer the geocell cushion has, the smaller the holes, and the higher the modulus of elasticity, the better the results. By increasing the number of geocell layers, the amount of spring stiffness coefficient and damping coefficient and as a result the dynamic stiffness coefficient increases. On the other hand, the closer the geocell is placed to the soil surface, the higher the stiffness of the spring and the lower the damping coefficient. In general, among these two parameters related to dynamic stiffness, the role of the damping coefficient has been more prominent and decisive in the investigation of foundations based on reinforced soil. One of the most obvious characteristics of geosynthetic materials in the soil, regardless of the greater hardness it gives to the soil, is the damping percentage of its constituent materials.

Parameters affecting performance of fully instrumented model testing of strip footings on geocell-reinforced soils

A thorough study was conducted to assess the performance of the strip footing reinforced with geocells in sand, focusing on understanding the enhancement effects and geocell reinforcement mechanisms. Critical factors such as geocell modulus, height, soil relative density and load eccentricity were examined through fully instrumented model tests. Measurements included surface displacement profiles, strains on the geocell layer, subsurface pressure distribution and other relevant parameters. Results revealed that the strip footing on geocell-reinforced sand beds exhibited better performance compared to those on unreinforced soil, characterized by increased load-carrying capacity and reduced settlements. Notably, stiffer geocells improved performance significantly, with a 40% higher modulus enhancing the bearing pressure by up to 25%, due to better confinement and anchorage effects. Conversely, geocells with a lower modulus demonstrated more effective vertical stress distribution. Furthermore, increased geocell height moderately enhanced footing performance by improving confinement, although wall buckling under eccentric loading limited major gains. Dense soils under centric loading exhibited up to a 20% better improvement in bearing pressure than loose soils due to higher strain mobilization within the geocell layer. These findings highlight the crucial role of geocell and soil properties, as well as loading conditions, in optimizing reinforcement effects for strip footings.

Evaluation of arched EPS block and geocell inclusions in trench backfill for protection of buried flexible pipes

This paper presents an experimental investigation examining the novel idea of employing curved expanded-Polystyrene (EPS) blocks that arch around the upper section of buried flexible pipes to reduce the pressures acting on them and hence resulting deformation/deflections. Large-scale testing was performed to examine key performance indicators for reinstated trenches with buried 250-mm diameter plastic pipe (0.75-m invert depth) when subjected to cyclic surface loading simulating vehicular traffic. The real-scale model tests investigated unreinforced and geocell-reinforced trenches with conventional rectangular and differently shaped EPS block inclusions placed above the crown or fitting snugly around the upper section of the buried pipes. Compared to conventional rectangular EPS block, the curved-arched EPS block produced greater reductions in the pressures acting on the buried pipes, resulting in substantially smaller pipe deformation/deflections. The geocell layer overlying the EPS block significantly reduced the pressures bearing on the highly compressible EPS material, thereby reducing its compression and the trench surface settlement. Optimum trench reinstatements incorporated both the geocell layer and a 75-mm thick curved-arched EPS block fitted around the top section of the pipe. Doubling the EPS block thickness produced only modest reductions in the pipe deflections, but significantly increased the trench surface settlement.

Geocell-reinforced bed anchored with additional vertical elements under repeated loading

This paper investigates the behavior of geocell-reinforced beds combined with extra vertical elements embedded into the geocell pockets at their joints. During repeated loading, the soil mass inside geocell pockets can loosen, leading to decrease in geocell layer extension. Vertical elements can help to reduce the soil loosening, alleviate deformation and distortion of the geocell wall directly under loading zone and provide anchorage at the geocell outer boundaries. Results show that, with the use of vertical elements, geocell performance is significantly enhanced due to better load distribution and extra anchorage. An average 40% reduction in cyclic settlement was observed using combined geocell and vertical elements compared with a bed reinforced with geocell alone. Also, with an optimum height of the vertical elements, a 42% reduction in geocell consumption even at higher performance can be achieved using a less extensive geocell mattress. Provision of vertical elements caused the geocell length on each side of the footing to be decreased from 1.1D to 0.5D for the same performance in some cases (D: footing diameter). Prototype experiments showed that the geocell reinforcement anchored with vertical elements experiences less deformation, distributing load over a wider area. Thus, geocell and vertical elements combine to act like a geocell with greater thickness and larger width, helping project economy by lower use of geocell material even if the additional cost of vertical elements may counteract. Calibrated numerical modelling compared favorably with experimental observations, providing insight into stress and strain distribution in the soil and geocell.

Vibration response of machine foundations protected by use of adjacent multi-layer geocells

The response of soil beds reinforced with multi-layer geocell systems that support machine foundations is investigated by laboratory testing that incorporates vertical machine vibrations of a square concrete foundation (400 × 400 mm) resting on soil that is unreinforced or reinforced with single-, double- or triple geocell layers. The tests are performed under three different vibration moment levels and three static force levels using a mechanical oscillator and concrete blocks, respectively. The vibration responses are studied in terms of resonant amplitude, resonant frequency, shear modules and damping coefficient. The results reveal that the resonant amplitude significantly reduced in the presence of geocell reinforcement whereas the resonant frequency, shear modulus and damping coefficient increased. In the range of applied vibration load and frequency, and hence the induced amplitude, maximum improvement (i.e., the greatest reduction in vibration amplitude) was observed in the presence of the triple-layer geocell reinforcement. Since the rate of improvement decreases steadily with an increase in the number of geocell layers, thus, further geocell layers would deliver little further benefit. The optimum placement depth of the first geocell layer and vertical spacing of the geocell layers were found to be 0.1 and 0.05 of the foundation's width respectively.

Sustainable pavement with geocell reinforced reclaimed-asphalt-pavement (RAP) base layer

According to the Federal Highway Administration Policy, recycled material should be the highest priority in selecting pavement materials. However, the quality of the reclaimed/recycled material should meet the minimum standard to ensure long-term benefits. This study uses geocell to enhance the performance of reclaimed asphalt pavement (RAP) material. Three pavement test sections were constructed with 0.15, 0.20, and 0.30m thick geocell reinforced RAP bases (GRRBs) by replacing the existing base layer of a farm-to-market road located in the southern part of Fort Worth, Texas, USA. These test sections were monitored for a period of three years to evaluate the pavement performance in terms of rutting, cracking, and riding quality. In addition to the regular monitoring falling weight deflectometer (FWD) tests were also conducted to determine the base layer modulus. Results showed that the geocell layer reduced the permanent deformation by at least 36% compared to the unreinforced section. The application of geocell also helped control the test sections' bottom-up longitudinal cracking by providing uniform support. The FWD test revealed that the geocell enhanced the GRRB layer stiffness by 20%. The construction cost of the GRRB layer was 22.9% less than the traditional flex base layer. Replacement of flex base material with GRRB material could reduce the emission of CO2 by 37 tons for each lane-km.

Geocell-reinforced bed under static and cyclic loads: Soil density and grain size effects

This paper reports on a series of static and cyclic plate loading tests performed on a weak unreinforced sand bed in a test pit. The weak sand was covered by a 160 mm thick layer comprised of one of three compacted soil types which was either unreinforced or geocell-reinforced. The purpose was to investigate the effects of soil density and grain size as filler materials for the covering layer. The three covering soils were granular with average particle sizes of 2.2 (Soil 1), 6.14 (Soil 2), and 8.47 (Soil 3) mm. Under static loading, the bearing pressure increased on average 23% when the average grain size of the upper, unreinforced, soil layer changed from 2.20 mm to 8.47 mm. The improvement in bearing pressure was about 37% due to the use of a soil-filled geocell but, unlike the unreinforced situation, employing larger soil grains to fill the geocell pockets didn't show significant further improvement. For cyclic loading tests, the maximum settlement reduction by employing a geocell layer was about 50% for Soil 1. Whether loaded statically or cyclically, increasing soil density likely would be more efficient for improving geocell performance than employing a soil having larger particle sizes.

Mechanical Behavior of Soil Foundations Reinforced with Geosynthetics Exposed to Normal and Reverse Fault Ruptures

Surface fault ruptures damage structures which are located at the intersecting zones of active faults. It is essential to consider the undesirable effects of surface fault ruptures when designing structures. Geotechnical measures such as reinforced soil foundations effectively mitigate the hazards related to surface faults. The present work conducted a series of tests on foundations reinforced with geosynthetics, including geogrids, geocells and geogrid-geocell layers. These tests simulated the behavior of 1.5 m-wide strip footings located in 6-m thick alluvium that had been displaced 60 cm. A total of 12 disparate tests in terms of the number and type of reinforcement were conducted at a scale factor of 10. Image analysis of the results indicated desirable behavior for reinforced soil foundations in terms of reduced angular distortion, uniform settlement and deviation of the fault path. For normal fault rupture, the angular distortion of foundations reinforced by one geogrid layer, one geocell layer, one geogrid-geocell layer or two or three geo-grid layers decreased by 60%, 30%, 70%, 80% and 80%, respectively. These results also revealed that an increase in the number of geogrid layers to more than two layers caused an insignificant decrease in angular distortion. The decrease in angular distortions observed for soil foundations reinforced by one geogrid layer, one geocell layer and one geogrid-geocell layer were 7%, 16% and 40%, respectively, for reverse faulting. The performance of a reinforced soil foundation subjected to normal faulting was more acceptable than that for reverse faulting.

Three dimensional analyses of geocell reinforced encased stone column supported embankments on lithomargic clay

ABSTRACT Geocells are a superior form of reinforcement due to their cost-effectiveness and three-dimensional confining properties. However, numerical modeling of geocell is always challenging due to its three-dimensional honeycomb structure. The limitations of the equivalent composite approach (ECA) led to the recent development of full 3D numerical models, which consider geocell-infill material interaction. This paper discusses the time-dependent performance of geocell-reinforced encased stone column-supported embankment considering the actual 3D nature of geocells using the finite element program ABAQUS. Parametric studies were carried out to study the stress transfer mechanism, vertical deformation of the foundation soil, and stress-strain variation inside the geocell pockets. It is found from the analyses that with the provision of a geocell layer on top of Geosynthetic Encased Stone Columns (GESC), the stress concentration ratio improved by 47% at the end of consolidation compared to GESC alone. Also, an 80% reduction in foundation surface settlement is observed with geocell-sand mattresses. The geocell-sand mattress decreased the bulging of the stone columns, and almost 80% of the stone column bulging occurred by the end of the embankment construction. The proposed model’s numerical results show that the equivalent composite approach overestimated the stress concentration ratio and bearing capacity. The tensile stresses are non-uniformly distributed in the geocell pockets, and the maximum tensile force was mobilised at the geocell mid-height. Among the various geocell infill materials analysed, the aggregates were best suited considering the stress concentration ratio and vertical settlement. The numerical results supported the idea that encased stone columns with geocells at the embankment base can perform similarly to a geosynthetic reinforced piled embankment system, which is costlier but very efficient. When the modular ratio is more than 40, geocell-reinforced encased stone column-supported embankment is similar to GRPES.

Model studies of square footings on geocell-reinforced slopes

This study examines the behaviour of square footings located on unreinforced, single-, and double-layer geocell-reinforced sand slopes through a series of reduced-scale model tests. Contributing factors such as the distance between the footing and the edge of the slope, depth of burial of the first geocell layer, vertical span between successive layers of the geocell, length and width of the geocell mattresses, and the number of geocell layers were considered, and their effects are discussed in detail. The results indicate that geocell reinforcement plays a more effective role as the distance between the footing and the edge of the slope decreases. The optimum depth of placement of the first geocell layer for both single- and double-layer reinforced slopes was determined, and was found to be independent of the length of the geocell. In addition, the performance of the footing continued to decrease with greater vertical distance between the top and lower geocell layers. Only a marginal improvement in the behavior of the tested models was observed for a range of widths of the geocell.

Internal stability analysis of geocell-reinforced slopes subjected to seismic loading based on pseudo-static approach

Seismic stability analysis of geocell-reinforced slopes (GRSs), considering shear and moment strength in addition to tensile resistance for geocells, is a novel topic for which scarce studies are found in the literature. Despite few available studies, an analytical approach is presented in this study to investigate the seismic internal stability of GRSs, employing the pseudo-static method based on a limit state approach. Results are given in terms of conventional design charts representing the required total strength and critical length of geocells. The results show that with increasing the horizontal seismic acceleration (kh), the internal stability degenerates since the required strength and critical length of geocells increase. For GRSs subjected to greater kh, the effect of increasing the vertical seismic component (kv) on increasing the required strength and length of geocells is more considerable than those subjected to lower kh values. Parametric analyses are conducted, under various seismic conditions, to investigate the effect of increasing the geocell height and raising the number of geocell layers, leading to the reduction in the required strength and length of geocells. Such effects are found to be dependent on the parameters such as the intensity of seismic excitation, material properties and geometry of slope.

Assessment of load distribution mechanism in geocell reinforced foundation beds using Digital Imaging Correlation Techniques

The pressure distribution below geocell reinforced foundation beds depends on several factors like height of geocell, weld distance (pocket size), infill material, etc. This paper describes a method to determine the load dispersion mechanism through a geocell layer using a non-contact Digital Image Correlation technique. Series of plate load tests were performed in a test tank having plan dimensions of 0.6 m × 0.6 m and height of 0.65 m. The loading was applied through a strip footing of width 120 mm. Two miniature geocells having heights of 60 mm and 75 mm were used for reinforcing the base layer of the foundation section. The studies were performed with two types of geocells having smooth and rough surfaces. The relative density (RD) of the base and subgrade layers were maintained as 80% and 40%, respectively during the tests. The movement of soil particles was recorded by capturing images at different stages of the test. The images were processed using a Digital Image Correlation (DIC) software to obtain displacement contours and vectors. The results show that the geocells distribute the load over a wide area of the foundation soil. The dispersion angle was found to depend on the height of geocell and the roughness of the geocell surface. The load dispersion angles obtained from Digital Image Correlation analyses of unreinforced and reinforced sections have been compared with similar published results.

Experimental Model Studies on Strip Footings Resting on Geocell-Reinforced Sand Slopes

In this study, the influence of the three significant contributing factors affecting the behavior of the footings resting on the unreinforced and geocell-reinforced sand slopes are investigated using a series of small-scale model tests. These factors consist of the back length of the geocell layer, the footing setback and the slope inclination angle. Results indicate that the geocell inclusion, even with no back length, significantly improves the behavior of the foundations overlying the slopes. In addition, the optimum geocell back length ratio was found to be 0 and 2 at settlement ratios of lower than 20% and higher than 20% respectively. Moreover, the increase in the footing setback led to considerable growth in the bearing capacity of both unreinforced and reinforced model slopes. However, the most efficient footing setback ratio was found to be 1, in particular at mean and large settlement ratio values. Furthermore, the results suggest that both unreinforced and reinforced models gain bearing capacity as the slope angle declines. However, among the different slope angles considered in this study (0°, 25°, 30°, 35°), the most efficient geocell-reinforced slope was found to be the one with an inclination angle of 30°.

Geocell Reinforced Slope Behavior under Seismic Loading Using Calibrated Hypoplastic Soil Constitutive Model

This study evaluates geocell reinforced slope behavior under seismic loading using calibrated hypoplastic soil constitutive model. The constitutive soil model used in this simulation was calibrated for poorly graded dense sand by conducting a series of triaxial and odometer tests. A three dimensional analysis is carried out to simulate geocells and this soil model using the finite element software PLAXIS3D. To investigate the geocell seismic behavior, the lateral displacement, induced tensile force in geocell, slope stability and frequency content effect have been assessed. Furthermore, a comparison has been made among hypoplastic, Hardening soil with small strain and Mohr-Coulomb model. The obtained results indicated that the volumetric plastic strain and intergranular strain consideration by hypoplastic model had a significant effect on the lateral displacement of the reinforced and unreinforced slope. Using the geocell layers leaded to decrease the plastic points. This behavior caused to decrease the estimated results difference when performing three constitutive models as soil failure criterion. Also, the tensile force showed hypoplastic model was not sensitive to the earthquake reversible force. In addition, it was found that the geocells lost their effect when the PGA increased and the slope was apt to fail.

Behaviour of geocell-reinforced strip footings on slopes

ABSTRACT This study presents the results of a series of reduced scale model tests carried out to investigate the bearing capacity and displacement behaviour of strip footings resting near both unreinforced and geocell-reinforced sand slopes. Impacts of some contributing factors such as slope angle, depth of geocell embedment, geocell pocket size and the arrangement of double layer reinforcement are presented and discussed thoroughly. Results indicate that placing a single geocell layer at a depth to footing width ratio of 0.1 (d/B = 0.1) leads to the highest bearing capacity and the lowest settlement ratio. It was observed that steepening the reinforced slope always reduces the bearing capacity and this reduction is remarkable if the slope angle approaches the soil internal friction angle. The optimum depth of the first geocell layer (µ) in a double-layer reinforced slope was found to be approximately 0.5B. At large settlements (s/B > 25%) double geocell reinforcement is always superior to single-layer reinforcement. However, at smaller settlements (s/B < 15%), double geocell reinforcement is effective provided that the spacing of the geocell layers is smaller than 0.5B.

Modeling Riverbank Slope Reinforcement Using Anti-Slide Piles with Geocells

Geocells are increasingly used in engineering applications, but the design of riverbank slope reinforcements that use only geocells limits reinforcement performance. Moreover, the design and use of anti-slide piles with geocells are mainly based on experiences that are unsupported by theoretical models. In this paper, by combining the confinement effect and vertical action mechanism of geocells, the horizontal friction mechanism of the geocell layer and the vertical support mechanism of piles, a theoretical model of riverbank slope reinforced by anti-slide piles with geocells was constructed. In addition, to describe the mechanical behavior of a riverbank slope reinforced by anti-slide piles with geocells, the slip-resisting mechanism of the anti-slide pile with interaction between geocells and their internal filler is considered in the model. Furthermore, to investigate the influence of changes in water level on riverbank slope stability, the developed model takes into account settlement, lateral displacement, pile bending moment and pile axial force. The model predications were validated by the field measurement data. The results from a series of parametric studies show that the use of anti-slide pile and geocells can effectively reduce the settlement and the lateral displacement of a riverbank slope. The developed model could contribute to an optimal design of anti-slide pile with geocells for enhancing the stability of a riverbank slope.

Design of geocell reinforced roads through fragility modeling

Several studies have confirmed the geocell reinforcement system as potential road material. However, there is a wide gap between the number of research studies evaluating the geocell in the laboratory and those dealing with road design methods using the geocell. Due to this gap, the geocell system has not reached its full potential in highways. The present study proposes fragility modeling to design low volume roads by considering the geocell reinforced layer's modulus. A predictive model was developed to estimate the geocell layer's modulus using laboratory and finite element analysis results. The results indicate that geocell reinforcement reduces the stresses on the underlying road layers. The developed fragility approach is then used to examine three road designs for Texas's low volume road involving different geocell reinforced layers. The obtained fragility curves indicate the reliability of each of the three road designs against the traffic load and can thereby assist decision-makers in selecting the optimum design. By designing geocell reinforced roads via fragility modeling, highway officials will be able to integrate any uncertainties in the design inputs and check designs against road performance criteria such as rutting and fatigue cracking, and against decision criteria such as cost, emissions, etc.

Analysis of Geocell-Reinforced Stone Column-Supported Embankment Considering Soil-Structure Interaction

Geocells are a superior form of reinforcement due to their cost-effectiveness and three-dimensional confining properties. The effect of the basal geocell layer on the performance of the stone column-supported embankment was evaluated in this paper by carrying out time-dependent coupled analyses considering the geocell-infill soil interactions. The various parameters, such as arching, stress concentration ratio, surface settlement, column bulging characteristics, and the influence of various types of infill materials and drainage blanket thickness on column-supported embankment behavior, were analyzed. The load transfer mechanism was quantified using the term stress concentration ratio, and with the use of geocell mattress above stone columns, the stress concentration ratio increased by 1.5 times that of ordinary stone columns. Also, it was observed that compared to ordinary stone column-supported embankment, the combination of stone columns with geocell-sand mattress resulted in a further reduction of the foundation settlement by 15%. Analysis results showed that the arching behavior is not predominant in geocell-reinforced columnar structures. The various analytical methods like Guido et al. (1987), Low et al. (1994), and Abusharar et al. (2009), which were developed for geosynthetic reinforced columnar embankments, were found to significantly under-predict the stress reduction ratio values with geocells.

Laboratory and Numerical Studies on the Performance of Geocell Reinforced Base Layer Overlying Soft Subgrade

The use of geocells for support of foundations on weak subgrades has been gaining popularity in recent years. Detailed studies were performed in this work through laboratory tests and numerical simulations to investigate the influence of different parameters on the geocell supported foundations on soft subgrades. A series of large-scale laboratory plate load tests were performed on the geocell-reinforced base layer overlying soft subgrade. The soft foundation soil was simulated using blocks of Expanded Polystyrene (EPS) in the laboratory tests for obtaining consistent subgrade conditions between the tests. The numerical analyses were performed in three-dimensional finite difference numerical program Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D). The numerical models were calibrated against the data obtained from laboratory tests. This paper deals with investigating the influence of different parameters such as pocket opening size, height and size of the footing on the performance of geocell-reinforced base layer overlying soft subgrade. The provision of three-dimensional cellular reinforcement (geocells) in the base layer has substantially increased the bearing capacity of the pavement section and the optimum aspect ratio of geocell pocket was found to be close to unity. From the parametric study, it is observed that the potential benefits of geocell reinforcement increases with reduction in weld spacing and height of geocell while the influence decreases with increasing loading area for constant height of geocell layer.

Static stability analysis of geocell-reinforced slopes

This paper presents an analytical approach to investigate the stability of geocell-reinforced slopes using the limit equilibrium method (LEM). The so-called Horizontal Slice Method (HSM) is employed to simulate horizontal geocell layers. Each geocell layer acts as a beam providing bending and shear resistance in addition to axial strength. A formula is devised by picking relevant governing equilibrium equations, fitted to the new concept employed exclusively for analysis of geocell-reinforced slopes. Parametric studies are conducted to evaluate the effects of increasing the geocell height and replacing geogrids by geocells with various heights for slopes with different characteristics. The results showed that such actions would reasonably reduce the required tension and length of the reinforcement layers, meaning that the stability condition is improved and the less lengthy reinforcement system is formed. Output values also showed dependency on the slope angle and its material properties.