Inclusion Of Geogrid Research Articles

Triaxial behavior of unreinforced and geogrid-reinforced calcareous gravelly sand: Experiment and discrete element modelling

Geogrid reinforcement is a feasible technique for improving the mechanical and deformation behaviors of calcareous gravelly sand that is predominantly distributed in reclaimed foundations as construction materials. However, the shear behavior of geogrid-reinforced calcareous gravelly sand still remains unclear. In this paper, a series of large-scale drained consolidated triaxial compression tests (the specimen 300 mm in diameter by 600 mm in height) were conducted to investigate the effects of confining pressure, moisture content and geogrid inclusion on the mechanical and deformation behaviors of calcareous gravelly sand. The dilation effect, strain-softening behavior, reinforcing effect and particle breakage characteristics of unreinforced and geogrid-reinforced calcareous gravelly sand were comprehensively analyzed and discussed. Additional analysis was also performed from a microscopic perspective using the three-dimensional discrete numerical modelling. The experimental results indicate that calcareous gravelly sand exhibited a greater resistance to strain-softening tendency, and produced a higher susceptibility to crushing under the same input energy than calcareous coarse sand. Geogrid inclusion can effectively mitigate the susceptibility of calcareous gravelly sand to volumetric dilation through constraining the lateral expansion within the reinforced zone, and thus substantially increased the peak shear strength. Moreover, particle breakage appeared to be insensitive to geogrid reinforcement and water content, but increased significantly with increasing confining pressures. The numerical results further indicate that the mechanical response of geogrids was regulated by axial strain and confining pressure. As axial strain was greater than 10%, increased confining pressure resulted in a wider area of stress concentration within the geogrid meshes, and the upper geogrid sustained a greater contact force and tensile strain. The findings in this study are of practical significance for the design and construction of structures in calcareous gravelly sand reinforced with geogrids.

Use of Geogrid for Improved Performance of Ballasted Tracks: Experimental and DEM Approaches

This paper presents a study on the enhanced performance of ballasted tracks through the implementation of geogrids. A series of large-scale direct shear tests and impact tests was conducted with three distinct types of geogrids. The behavior of ballast was evaluated in terms of shear stress–strain responses and stress concentration using stress sensing sheets. Additionally, a micromechanical analysis utilizing the discrete element method was simulated on ballast assemblies with different geogrid reinforcements. The shear stress–strain responses of ballast simulated from DEM are comparable with those measured from large-scale direct shear tests, indicating that the inclusion of geogrid can enhance the performance of ballast by increasing its shear strength, as well as reducing the vertical displacement and the load distribution with depth. Micromechanical analysis was performed to investigate the influences of geogrids on contact force distribution, coordination number and orientation of contact which could not be captured in a laboratory environment. The use of geogrids in ballasted tracks certainly shows promise for sustainable and efficient railway infrastructure, as evidenced by the experimental and DEM-based findings, offering valuable insights into optimizing track stability and longevity.

Laboratory characterization of clay fouled rubber-coated ballast with and without geogrid

The utilization of rubber-coated ballast (RCB) aims to enhance the energy dissipation capacity and decrease the rate of deterioration of ballasted tracks, leading to reduced maintenance costs. Ballast fouling can affect the ballast's drainage properties, shear strength, deformation, and resilience that may ultimately lead to track misalignment. In this context, in the present study, the drainage and shear characteristics of RCB and RCB-conventional ballast mix are evaluated for various levels of clay fouling. The results of permeability tests indicated that the hydraulic conductivity (k) of RCB is more than that of conventional ballast. For example, the k of RCB is 71% higher than that of conventional ballast (fouling content = 50%). However, the k of ballast decreased significantly with the increase in the content of clay fouling. The results from the direct shear tests revealed that both RCB and RCB50% perform poorly in terms of peak friction angle (φ) when compared to conventional ballast. With the addition of clay fines, a further reduction in the shear strength is observed. For instance, the φ of unreinforced RCB, RCB50%, and conventional ballast decreases by 18.5%, 14.2%, and 10.4%, respectively, with the increase in fouling content from 0% to 50%. However, in case of geogrid-reinforced RCB50%, the peak friction and dilation angles are found to be relatively higher as compared to unreinforced conventional ballast in both clean and fouled conditions. The results of cyclic tests demonstrated that the deformation of both unreinforced and geogrid-reinforced RCB-conventional ballast samples increased while the resilience modulus (Mr), damping ratio (Dr), and ballast breakage index (BBI) decreased with the increase in fouling content. Moreover, the inclusion of geogrid significantly reduced the extent of deformation and particle breakage but enhanced the Mr and Dr when compared to unreinforced ballast. The various test results suggest that the geogrid-reinforced RCB50% performs better than unreinforced conventional ballast under both clean and clay fouling conditions. For geogrid-reinforced RCB50%, the volumetric strain (εv) and BBI are reduced by 9.7% and 69.5%, while Mr and Dr are improved by 5.75% and 176.5% as compared to unreinforced conventional ballast (fouling content = 20%). Additionally, empirical relations are developed to predict the vertical strain (ε1), lateral strain (ε3), Mr, Dr, and BBI of RCB-conventional ballast mix under clean and clay-fouled conditions.

Behaviours of geogrid-reinforced asphalt pavement over a localized void under cyclic loading

A set of large-scale physical model tests were performed to investigate the performance of unreinforced and glass fibre geogrid-reinforced asphalt pavement under the development of a void in the subgrade. Traffic loadings were simulated with repeated sinusoidal loadings of different amplitudes. The formation of the void was simulated using a novel displacement control device between loading cycles. The accumulative permanent deformation of the asphalt pavement, the composite resilient modulus and dissipated energy were presented and analysed. It was found that the inclusion of geogrid greatly improved the fatigue life of asphalt pavement, and the stronger the geogrid, the greater the improvement if a void was formed below the asphalt layer. After forming the void, the composite moduli of the pavements increased compared with that during the first cyclic loading stage (without the void) and seemed to be not much affected by the geogrid type. The effect of cyclic loading level on the composite modulus was not significant. The inclusion of geogrid in asphalt had a limited effect on the dissipated energy in the pavements with and without voids. The dissipated energy increased with the cyclic loading amplitude.

Finite Element Modelling of Geogrids Reinforced Ballasted Tracks

This paper presents results obtained from three-dimension finite element modelling (FEM) to study the effects of geogrids on the deformation responses of ballasted tracks. In this study, a series of numerical simulations are carried out on track sections with and without the inclusion of geogrids. Sensitivity analysis was carried on parameters affecting the performance of geogrid, including the axial stiffness, interface property and the location of geogrid placement in the track substructure. The tracks are subjected to moving train loading under 150 kN wheel load travelling at a given speed of 72 km/h. Based on simulation results, it is found that geogrid provides a reinforcing function to rail track primarily in the form of confinement which resulted in reduced lateral displacement in a reinforced track compared to a traditional track. A significant reduction in vertical and lateral displacement is found from the inclusion of a geogrid layer at the ballast and capping interface while the effect of geogrid reinforcement is more pronounced with increased loading cycles. The effects of geogrid stiffness, interface conditions and geogrid placement are studied and it is found that the axial stiffness of geogrid is found to impact overall track deformation while the optimum placement of geogrid is found to directly at the ballast and capping interface.

Analysis of Shear Characteristics of Recycled Concrete Aggregate–Geogrid Interface

Recycled concrete aggregate (RCA) has been widely used as a resource in reinforced soil structures, especially as a substitute for natural aggregate. Direct shear tests were conducted using a dynamic direct shear apparatus to study the effects of particle-size gradation (0.06–37.5 mm) on the shear properties of RCA-geogrid interface, in which geogrid was used to enhance the shear strength of RCA. The results exhibited that the geogrid significantly improved the interface peak strength of the RCA-geogrid interface. The inclusion of geogrid reduced the vertical displacement of RCA. The shear strength of the RCA-geogrid interface with different gradations increased with an increase in the relative density (RD) in the monotonic direct shear test. In the cyclic direct shear tests, the shear stiffness of the well-graded RCA(R2)-geogrid interface was the largest and the damping ratio of the discontinuous-graded RCA(R3)-geogrid interface was the smallest. In post-cyclic monotonic direct shear, the RCA-geogrid interface shear strength increased significantly, from 26.5% to 48.3%. After the cyclic shearing, the interface apparent adhesion and friction angle increased and the R2-geogrid interface demonstrated superior shear properties.

Experimental investigation on cyclic behavior of geogrid-reinforced coral sand from the South China Sea

The present study provides insight into the cyclic behavior of unreinforced and geogrid-reinforced coral sand. To achieve these goals, stress-controlled undrained cyclic triaxial tests were conducted on medium-dense coral sand with and without geogrid reinforcements. The influence of geogrid reinforcement, cyclic stress ratios, and confining pressure on the deformation, pore pressure, liquefaction resistance, stiffness degradation, and particle breakage characteristics of saturated coral sand was investigated. The results indicated that coral sand reinforced with geogrid increased the liquefaction resistance and decreased the rate of pore pressure accumulation. The effectiveness of the geogrid inclusion on coral sand’s liquefaction resistance was found to be more pronounced under large effective confining pressure and a smaller cyclic stress ratio. Increasing the effective confining pressure increases the liquefaction resistance for both unreinforced and geogrid-reinforced coral sand, whereas increasing the cyclic stress ratios decreases the liquefaction resistance of the unreinforced and reinforced coral sand. The particle breakage was observed to be increased with increasing the effective confining pressure and cyclic stress ratio, and the breakage was more in the reinforced coral sand than the unreinforced coral sand.

Evaluating the Shear Strength of Subbase-subgrade Interface Using Large Scale Direct Shear Test

The inclusion of geogrid in road pavements can improve pavement performance through increasing the lateral confinement, bearing capacity, and overall rigidity of the pavement, as well as reducing the vertical and lateral pavement deformations. The materials used in the present study are: subbase granular materials Type B, two types of subgrade soil; clay and sandy soil, and two nonwoven biaxial geogrids (G1 and G2) used as reinforcing materials. Direct shear testing was adopted by manufacturing a large-scale direct shear apparatus consisted of an upper, square box of size 20 cm × 20 cm × 10 cm, and a lower, rectangular box of size 200 mm × 250 mm × 100 mm is used in the present study. The results show that, for the four normal stresses equal to 25, 50, 75 and 100 kPa, the interface shear stress curves increased and followed similar trend. For clay-subbase interface, installation of geogrid decreases the apparent cohesion of the material from 16.5 kPa (without reinforcement) to be 8 kPa and 13.5 kPa for G1 and G2, respectively. At sand-subbase interface, using geogrid leads to increase the cohesion of the material from 3.5 kPa to be 15.5 and 16 kPa for G1 and G2, respectively. The friction angle increases slightly from 30o (without reinforcement) to be 35o for G1 and G2 when the interface is subbase over clay. While, it decreased from 35.8o to be 32.1o for G1 and G2 at sand-subbase interface. The interaction coefficient for G1 and G2 increased when the normal strength increased at the clay-subbase interface. Otherwise, the behavior of interaction coefficient of the sand-subbase interface appears deferent trend, where increasing normal stress leads to decrease the interaction.

Using Bender Elements to Investigate the Effect of a Multi-axial Geogrid on Aggregate Layer Stiffness

Geogrid inclusion in low-volume road applications has been shown to improve rutting performance. Although rutting performance and traditional instrumentation response data provide meaningful insights into pavement behavior, they do not provide a direct measurement of material behavior near the geogrid. Recently, the University of Illinois at Urbana-Champaign has developed field-deployable shear-wave transducers, that is, bender elements to measure the localized stiffness enhancement attributed to geogrid inclusion in unbound aggregate layers, which have been verified in laboratory and limited field applications. Bender element sensors were installed in a full-scale accelerated pavement test experiment at the U.S. Army Engineer Research and Development Center that included a recently developed multi-axial hexagonal geogrid. The sensors were installed directly on the geogrid and 10 cm above the geogrid in the unbound aggregate layer to measure the geogrid zone of influence. The test item was trafficked with a dual-wheel truck gear, and bender element measurements were made at select intervals throughout traffic application. To estimate the unbound aggregate moduli, the data were analyzed using two techniques: first arrival time and peak-to-peak arrival time. The bender element sensors were found to be sufficiently robust to survive installation, construction, and trafficking. Calculated modulus values 10 cm above the geogrid were found to be higher than those directly on the geogrid, which was an unexpected finding. However, a forensic investigation revealed moisture and fines migration into the bottom of the unbound aggregate layer, which could have dampened the shear-wave signal, resulting in lower calculated modulus values.

Load-settlement response of strip footing overlaid fine sand strengthened with different arrangements of geogrid inclusions

ABSTRACT This study reports the results of experiments conducted on strip foundations with and without reinforced geogrids over fine sand and with a wraparound geogrid arrangement. A load up to 25 kN was applied to the strip foundations to determine the loading-settlement response. These tests examined the number of planar and folded geogrid sheets, the placement of folded geogrids in the soil bed, the thickness of folded geogrid sheets, the length of wraps and overlaps, and the spacing between folded and planar geogrid sheets. The results indicate that the performance of the foundations due to static loading is better for folded geogrid-reinforced sand than for planar geogrid-reinforced sand. Overall, the results demonstrate that reinforced soil foundations with sufficiently folded geogrid layers behave much stiffer and thus can support higher loads with a lower settlement than planar reinforced soils. Moreover, the results indicate that the values of the embedment depth of the overlap element (d), the lower part (D), and the thickness (x) of the folded geogrid are 0.2, 0.4, and 0.2 of the foundation widths (B), respectively. As a result, by increasing the number of geogrid layers, the settlement rate is reduced significantly, and it is recommended that these layers be placed vertically without vertical spacing (h/B = 0).

Geosynthetic encased column-supported embankment: behavior with and without basal geogrid

Centrifuge model tests were performed to investigate the beneficial effect of the basal geogrid in improving the performance of geosynthetic encased column (GEC)-supported embankments. The digital image correlation (DIC) technique was adopted to understand the deformation behavior of GEC-supported embankment models. The mobilized tensile strain at various locations on the model basal geogrid was quantified using strain gauge-based instrumentation. The results from the centrifuge test indicate that vertical and lateral displacement of the GECs and surrounding soil has been significantly reduced with the inclusion of basal geogrid in the embankment. Moreover, the differential settlement between the GECs and surrounding soil due to embankment loading were significantly reduced with the inclusion of basal geogrid, thereby the distress in the embankment resting on soft foundation can be avoided. The basal geogrid in the embankment has enhanced the stability of the embankment and improved the load transfer between the GECs and surrounding soil. The maximum mobilized tensile strain in the basal geogrid occurred near the shoulder of the embankment, which indicates the resistance offered by the basal geogrid in preventing the differential settlement between the GECs and surrounding soil.

Large-scale triaxial tests of reinforced coral sand with different grain size distributions

The strength, deformation and particle breakage behaviors of reinforced coral sand were analyzed by performing a series of large-scale consolidated drained triaxial tests on unreinforced and two-layer geogrid reinforced samples. Two grain size distributions, namely, the natural coral sand in the South China Sea (ISG) and the uniformly graded coral sand (UG), were used to investigate the effect of gradation on unreinforced and geogrid-reinforced specimens under dry and saturated conditions. The results indicated that the inclusion of geogrid offered a great improvement to the coral sand with respect to increasing its shear strength and reducing the shear dilation. The reinforcement effect of geogrid on dry sample was better than that on saturated one. Moreover, the UG sample exhibits high compressibility and distinct strain hardening behavior due to the significant particle breakage resulting from the lack of fine content compared with the ISG sample, which induced the better reinforcement effect of geogrid on ISG sample. The increase of particle breakage further led to the decrease of peak-state friction angle.

Rocking Shallow Foundations on Geogrid-reinforced Ganga Sand Bed: An Experimental Study

ABSTRACT The efficiency of polyester and bamboo geogrids in reducing the seismic settlement of low-rise buildings has been investigated in this paper. A series of shake table experiments was carried out for this purpose. It was observed that the beneficial attributes of a rocking foundations in reducing the flexural deformation and column moment remained unchanged after inclusion of geogrids. However, the settlement, a primary adverse consequence of a rocking foundation, reduced significantly (as much as 70–75%). In a developing country like India, natural material-like bamboo threads combined with geo-polymers may be utilized for safe and sustainable seismic design.

Impact of reinforcement granular soils on the behaviour of strip footing nearby an excavation

ABSTRACT Ground improvement of the granular soils by the inclusion of geogrid makes it possible to increase the final bearing capacity of these soils. The lack of urban land, usually the construction of new buildings adjacent to the old buildings is used. In the present work, a series of numerical studies using an analysis of finite elements in reinforced and unreinforced granular soils adjacent to excavations loaded with a strip footing were carried out using two granular type soils. The work aimed to define the impact of the geogrid on bearing capacity suggests an optimal number of reinforcements, and investigates the behaviour of two closed footings adjacent to the pit. It was obtained that for granular soils using three layers of reinforcement, the ultimate capacity will be considerably increased. Moreover, final bearing capacity will increment in a non-linear manner by incrementing the distance from the edge of the excavation. As a result, a lot of care should be done to determine the footing location. Finally, the placement of foundations adjacent to each other increases their bearing capacity and efficiency factor. In the ratio of the distances between the surface foundations beyond 5 times foundation width, the effect of interference is negligible.

Laboratory evaluation of geogrid-reinforced flexible pavements

This study assessed the effectiveness of flexible pavements reinforced with two types of punched and drawn geogrids to reduce roadway base course thickness. Six laboratory tests were conducted using a steel cylindrical mold. Instrumentation included pressure cells placed at various locations of the test sections and a linear variable differential transformer which was placed on top of the loading system. A hydraulic actuator provided 40 kN (9 kips) cyclic load through a 305 mm (12 in) circular steel plate at a frequency of 0.77 Hz. Test results revealed that inclusion of both geogrid types in flexible pavement showed reductions in surface rutting and vertical stresses at the subgrade-base interface. Using the results for rutting depth, the use of geogrids increased the number of load applications by a factor of 1.5 to 7.5, depending on the test section properties and geogrid type, as well as the rutting depth experienced at various loading applications. Using the base course reduction values based on vertical stress results, the inclusion of geogrid in strong soil resulted in the reduction of base course thickness by nearly 7 percent.

Analysis of Load Carrying Capacity of Strip Footing Resting on Geogrid Reinforced Fly-Ash Over an Earthen Slope Using Plaxis2D

The current study deals with the use of material waste such as fly ash as a fill material or replaced layer placed over an earthen slope and strip footing is placed over the slope in order to explore the benefits of using geogrid sheets to strengthen the fly ash layer and to investigate its effects on the load carrying capacity. Using Program PLAXIS-2D v8.2, the fly-ash sheet is positioned over an earthen slope with slope inclination of 3H:2V, and multiple type of models were investigated, to study the integration impact of geogrid-reinforcement layers on load carrying ability. For optimal improvement in load carrying ability, models have been tested to evaluate the best location, length and configuration of geogrid layers and top fly-ash layer depth. In order to evaluate the effect of one parameter in each sequence the other factors were kept constant. The sequence of findings was illustrated using PLAXIS-2D on the strip base in both strengthened and un-reinforced cases. Test findings demonstrate that inclusion of geogrid significantly enhances efficiency of slope and footing.

Effect of geogrid on deformation response and resilient modulus of railroad ballast under cyclic loading

Laboratory investigations were carried out using process simulation test (PST) apparatus to assess the role of geogrid on the deformation response and resilient modulus of railroad ballast at different loading frequencies (f) varying from 10 to 40 Hz. The materials used for testing involved fresh granite ballast and subballast having mean particle sizes (D50) of 42 mm and 3.5 mm, and geogrids with different aperture shapes and sizes. The results from the laboratory investigations reveal that the degradation and deformation behavior of ballast is influenced by the loading frequency (f). The use of geogrids is shown to reduce the extent of deformations in ballast (both lateral and vertical) and its degradation (Bg: ballast breakage), but the effect of geogrid diminishes with the increase in frequency (f). The assessment of the lateral strain profiles along the ballast depth indicates that the geogrid influence zone (GIZ) is dependent on both the type of geogrid used and the loading frequency (f). The GIZ is found to vary from 38 mm (0.90 D50) to 237 mm (5.64 D50), with it being the lowest at f = 40 Hz and for geogrid having relatively larger apertures. Further, the geogrids are found to significantly enhance the resilient modulus (Mr) of ballast. In addition, the Mr is established to increase with f and Bg. The inclusion of geogrids also reduced the extent of vertical stress (σv) including the dynamic amplification factor (DAF).

Flexural Behavior of Compacted-Cement Sand Reinforced with Geogrid

An improvement of flexural strength of cement stabilized soils using geogrid designated as compacted cement-geogrid-sand (CCGS) is investigated in this research. The studied material performance of the CCGS includes postpeak behavior, toughness, and equivalent flexural strength ratio. The geogrid inclusion significantly improves the postpeak flexural behavior, which is a requirement for bound pavement materials. The first peak flexural strength f1 and stiffness of both compacted-cement-sand (CCS) and CCGS are essentially the same for the same cement content. The tested soils were obtained from Ayutthaya province, Thailand, and is commonly used as a construction material for backfill and pavement applications. The backfill soils were used sand. In this study, Type I Portland cement was used as a cementing agent and geogrid two type were used as a reinforcement material. Properties of the cement and the geogrid, which were obtained from the manufacturers. The specimens were subjected to a flexural performance test according to ASTM C1609/C1609M-10 (2010). The results showed that in the flexural performance of the CCGS includeing postpeak behavior, toughness, and equivalent flexural strength ratio depends on the type and shape of apertures of the geogrid. It was found that the triaxial geogrid with shape of triangular apertures was more effective in reinforcing and provided the high equivalent flexural strength over uniaxial geogrid.

Investigation of deformation and degradation response of geogrid-reinforced ballast based on model track tests

A series of large-scale cyclic tests was conducted using process simulation test ( PST) apparatus to capture the influence of loading frequency ( f) on the deformation and degradation behavior of ballast with and without geogrids. Fresh granite ballast and subballast having mean particle diameter ( D50) of 42 mm and 3.5 mm, respectively and five geogrids of different aperture shapes and sizes were used in this study. The tests were conducted at f ranging from 10 to 40 Hz and up to 250,000 load cycles. The test results from the laboratory investigations confirmed that the deformation and degradation behavior of ballast is highly influenced by loading frequency ( f). Moreover, the results showed that geogrid reinforcement stabilizes ballast by reducing the extent of lateral spreading ( ld) and vertical settlement ( Sv) and by minimizing particle breakage ( BBI). The inclusion of geogrids also reduces the extent of vertical settlement in subballast layer ( Svsb). In addition, the extent of volumetric ( εv) and shear strains ( εs) including void ratio ( ef) and density ( γbf) were found to be highly influenced by f. It is further seen that lateral spread and vertical settlement reduction index ( LSRI and VSRI) of all the geogrids decreases with the increase in f. Moreover, it is revealed that with the decrease in LSRI, the extent of Sv and BBI increases. A correlation is developed between the deformations ( ld and Sv) and interface efficiency factor ( α). The effectiveness of geogrid in keeping the ballast in place is evaluated in terms of a new parameter ‘geogrid efficiency factor ( Gef)’. The value of Gef for geogrids used is found to vary from 0.02 to 0.27. It is further shown that Gef under cyclic loading conditions is a function of the interface efficiency factor ( α) evaluated under direct shear conditions.

Laboratory examination of ballast deformation and degradation under impact loads with synthetic inclusions

This paper presents a laboratory study on alleviating the deformation and degradation (breakage) of ballast subjected to impact loads using geogrids and rubber mats. A series of drop hammer impact tests are carried out to determine how well the geogrid, under-ballast mat (UBM) or under-sleeper pad (USP) can attenuate impact loads and mitigate ballast degradation. Geogrids to be placed at different locations in a ballast assembly, in combination either with a UBM or a USP are tested. Laboratory test results prove that the inclusion of rubber mats and geogrids decrease the dynamic impact loads transferred to the ballast aggregates and subsequently decrease the degradation (breakage) and deformation of ballast. The tensile strength of geogrids and subgrade stiffness are found to considerably influence the performance of geogrid-reinforced ballast under impact loading conditions. The measured impact forces and accelerations of ballast with and without an artificial inclusion show that rubber mats definitely reduce track vibration (acceleration) and the subsequent deformation and breakage of ballast. These inclusions will not only increase safety and passenger comfort they will also lead to more economical and efficient track designs.