Biaxial Geogrid Research Articles

Mechanical and hydraulic compatibility of RAP with geosynthetics used in MSE walls

Mechanical and hydraulic properties of recycled asphalt pavement (RAP) as backfill in mechanically stabilized earth (MSE) walls were evaluated. Woven and nonwoven geotextiles and uniaxial and biaxial geogrids were used as reinforcements. Results of interface direct shear tests showed that the interface friction angle (δ) of RAP-geogrid was higher than that of RAP-geotextile. On average, the δ for RAP-biaxial geogrid was 15% higher than δ for RAP-uniaxial geogrid. For geotextile reinforcement, the δ for RAP-woven geotextile was 20% higher than δ for RAP-nonwoven geotextile. Compaction of RAP at elevated temperatures only slightly affected δ. Pullout capacities of RAP-uniaxial geogrid and RAP-woven geotextile are comparable to those of sand-uniaxial geogrid at different overburden pressures. The compacted RAP reinforced with uniaxial geogrid, however, exhibited significant creep strains at a range of sustained pullout forces that led to failure of the RAP-uniaxial geogrid. Reducing the pullout capacity by 40% is recommended for design to reduce the potential of creep failure. Long-term filtration tests showed that in all cases RAP-geosynthetic systems were able to drain freely and this behavior could be predicted with the existing clogging criteria that have been previously developed for sands and gravels.

Research on Friction Characteristics of Reinforced-soil Interface under Various Pull-out Rate and Embedded Length

In highway engineering, the reinforced soil structure has been widely used, especially the reinforcement on the top of the roadbed, which can effectively prevent the pavement from cracking. The friction characteristic of the reinforced soil interface is a necessary part in the design of the reinforced soil structure. In order to study the friction characteristics of biaxial geogrid-soil under various pull-out rate and embedded length, based on self-developed test equipment, a series of pull-out tests were carried out by using the research method of controlled strain. The test results indicated that the pull-out rate has little impact on the shear strength of the reinforced soil. Moreover, the pull-out force increased with longer embedded length. The rest results have provided a reference to the design work using biaxial geogrid in the field of civil engineering, especially in highway engineering.

Natural Para Rubber in Road Embankment Stabilization

This is the first study on “ribbed smoked sheets (RSS)” as a geogrid reinforcement in geotechnical engineering. An RSS is a kind of natural para rubber. RSS (grade 3) was designed as a biaxial geogrid with an aperture size of 20 mm × 20 mm and a spacing of 20 mm. The RSS was found to be a significant functional layer when applied to the subbase lateritic soil layer. The lateritic soil with an RSS reinforcing layer was greatly improved regarding the California bearing ratio (CBR). Numerical simulation using two-dimensional finite element software was used to determine the optimal number and positions of the RSS reinforcing layers in road embankment stabilization. The simulation data in terms of horizontal displacement of unreinforced road embankments was validated by the collected data from the actual construction site. The RSS reinforced layer was varied from one to three layers under 61 analysis conditions. The highest safety factor was obtained with two layers of RSS at 0.1H below the top of the road embankment and 0.4H below the first RSS layer, suggesting a suitable installation of the RSS reinforcing layer. The RSS is thus strongly recommended as a reinforcing material in low CBR lateritic soil for the road embankment.

Anisotropic Shear Strength Behavior of Soil–Geogrid Interfaces

This paper presents an experimental study on the anisotropic shear strength behavior of soil–geogrid interfaces. A new type of interface shear test device was developed, and a series of soil–geogrid interface shear tests were conducted for three different biaxial geogrids and three different triaxial geogrids under the shear directions of 0°, 45° and 90°. Clean fine sand, coarse sand, and gravel were selected as the testing materials to investigate the influence of particle size. The experimental results for the interface shear strength behavior, and the influences of shear direction and particle size are presented and discussed. The results indicate that the interface shear strength under the same normal stress varies with shear direction for all the biaxial and triaxial geogrids investigated, which shows anisotropic shear strength behavior of soil–geogrid interfaces. The soil–biaxial geogrid interfaces show stronger anisotropy than that of the soil–triaxial geogrid interfaces under different shear directions. Particle size has a great influence on the anisotropy shear strength behavior of soil–geogrid interfaces.

Correction to: Structural Performance of Biaxial Geogrid Reinforced Concrete Slab

Correction to: Structural Performance of Biaxial Geogrid Reinforced Concrete Slab

DEM-FDM Coupled Numerical Study on the Reinforcement of Biaxial and Triaxial Geogrid Using Pullout Test

The key to modeling the interlocking of geogrid-reinforced ballast is considering both the continuous deformation characteristics of the geogrid and the discontinuity of the ballast particles. For this purpose, pullout tests using biaxial and triaxial geogrids were simulated using the coupled discrete element method (DEM) and finite difference method (FDM). In this coupled model, two real-shaped geogrid models with square and triangular apertures were established using the solid element in FLAC3D. Meanwhile, simplified shaped clumps were used to represent the ballast using PFC3D. The calibration test simulation showed that the accurately formed geogrid model can reproduce the deformation and strength characteristics of a geogrid. The pullout simulation results show that the DEM-FDM method can well predict the relationship between pullout force and displacement, which is more accurate than the DEM method. For ballast particles of 40 mm in size, both the experiment and simulation results showed that the triaxial geogrid of 75 mm is better than the 65-mm biaxial geogrid. In addition, the DEM-FDM method can study the interaction mechanism between the particles and the geogrid from a microscopic view, and also reveal the similar deformation behavior of the geogrid in the pullout process. Therefore, the DEM-FDM coupled method can not only investigate the interlocking mechanism between the ballast and particles but can also provide a great method for evaluating the performance of different types of geogrids.

Measurement of Axial Strain of Geogrid by Optical Sensors.

In recent years, the technology of optical fibers has rapidly gained ground in many areas of science and industry, including the construction industry. In this article, the technology of optical fibers based on a fiber Bragg grating (FBG) was used to determine tensile forces acting in a basal reinforcement of a scaled down physical model, which included piled embankment and basal reinforcement. Installing FBG sensors on the geogrid made monitoring of axial strains possible, thus allowing determination of the behavior of the basal reinforcement of the piled embankment. On the basis of three tests performed on the physical model, numerical model calibration with the physical model was carried out using the software PLAXIS 3D Tunnel 2.4. The results showed accurate predictions, especially for the low and middle part of the measured deformations where the numerical analysis proposed a solution that can be considered as safe. Installing FBG sensors on biaxial geogrids was a bold idea that was not easy to implement. However, other possibilities have been successfully tested, such as high-frequency measurements of the response of reinforced soil structure under dynamic loading.

THE BEARING CAPACITY OF A CIRCULAR FOOTING ON GYPSEOUS SOIL BEFORE AND AFTER IMPROVEMENT

Bearing capacity of soil is an important factor in designing circular footing. It is directly related to foundation dimensions and consequently its performance. The calculations for obtaining the bearing capacity of a soil needs many varying parameters, for example soil type, depth of foundation, unit weight of soil, etc. In this work, the comparison between the values of bearing capacity of circular footing on gypseous soil before and after improvement determined by two different methods, the first method using compacted cement dust (Case1). The improvement were performed by making trench under the footing filled with compacted cement dust (at its optimum moisture content) at three depths [(Depth of trench, D =Width of trench, B =2 * the radius of footing R); (D=2B=4R) ; (D=3B=6R)], the trench had the same footing Dimensions, The second method is reinforcing gypseous soil with biaxial geogrids (Case2) have been shown to be an effective method for improving the ultimate bearing capacity of granular soils.

Shear Characteristics of the Interface between Recycled Concrete Aggregates and Various Geosynthetics

To investigate the interface shear characteristics between various geosynthetics and recycled concrete aggregate (RCA), 30 large-scale monotonic direct shear tests were conducted. The main work was to analyse the effect of a biaxial polypropylene geogrid, a glass fiber geogrid, a warp-knitted polyester geogrid, a woven geotextile, and geonet on the interface shear properties of RCA. The test results show that adding a biaxial polypropylene geogrid or a geonet to RCA can improve its interface shear strength. The inclusion of glass fiber geogrids, warp-knitted polyester geogrids, and woven geotextiles decrease the interface shear strength of RCA. The reinforcing RCA with geosynthetics can effectively suppress its shear dilation, and the change in internal friction angle is consistent with the change law of the material interface enhancement coefficient. Finally, the aperture size of a geogrid has a significant effect on the mechanical properties of the geogrid-RCA interface. The interface shear strength increases first and then decreases with an increase in the ratio between aperture size and median particle diameter. It is concluded that there is an optimal range of aperture ratio between a geogrid and RCA.

Structural Performance of Biaxial Geogrid Reinforced Concrete Slab

Structural Performance of Biaxial Geogrid Reinforced Concrete Slab

Stabilization of soil nailed slope by flexible materials

The soil slopes alongside the roads, embankments etc. often lead to mishaps as they are prone to slide or collapse due to their instability. Soil nailing is remedial measure to such unstable soil slopes and thus to prevent such mishaps. In this research, a physical model of soil nailed slopes has been established and is tested for stress and strain with different flexible facing materials under the application of load using a hydraulic jack. Then the settlement and displacement of the soil nailed slopes with different facing materials is also calculated and compared. The several flexible facing materials used were HDPE Geomembrane Sheet, Geocomposite and Biaxial Geogrid and were compared with the soil slope without facing. This research shows that different flexible facing materials have different behaviour in terms of strain and displacement under the similar magnitude of load. And it is obtained that flexible facing materials can be a good replacement to rigid facing materials for non-critical structures and an economical and effective way to strengthen existing soil slopes and stabilize them with as they are less costly than the rigid materials. Among all flexible materials that used in this research Geocomposite has high strength of 1.23 N/mm2 and less vertical and horizontal displacement.

Polymer Geogrids: A Review of Material, Design and Structure Relationships.

Geogrids are a class of geosynthetic materials made of polymer materials with widespread transportation, infrastructure, and structural applications. Geogrids are now routinely used in soil stabilization applications ranging from reinforcing walls to soil reinforcement below grade or embankments with increased potential for remote-sensing applications. Developments in manufacturing procedures have allowed new geogrid designs to be fabricated in various forms of uniaxial, biaxial, and triaxial configurations. The design flexibility allows deployments based on the load-carrying capacity desired, where biaxial geogrids may be incorporated when loads are applied in both the principal directions. On the other hand, uniaxial geogrids provide higher strength in one direction and are used for mechanically stabilized earth walls. More recently, triaxial geogrids that offer a more quasi-isotropic load capacity in multiple directions have been proposed for base course reinforcement. The variety of structures, polymers, and the geometry of the geogrid materials provide engineers and designers many options for new applications. Still, they also create complexity in terms of selection, characterization, and long-term durability. In this review, advances and current understanding of geogrid materials and their applications to date are presented. A critical analysis of the various geogrid systems, their physical and chemical characteristics are presented with an eye on how these properties impact the short- and long-term properties. The review investigates the approaches to mechanical behavior characterization and how computational methods have been more recently applied to advance our understanding of how these materials perform in the field. Finally, recent applications are presented for remote sensing sub-grade conditions and incorporation of geogrids in composite materials.

A comparative study of bearing capacity of shallow footing under different loading conditions

ABSTRACT In the present study, the behaviour of a shallow rectangular foundation placed over the multiple layers of the geogrid reinforced sand under eccentric and oblique loads in both dimensions was studied. Various parameters were investigated in this study including the number of reinforced layers (N), eccentricity (e/B, e/L) and inclination of applied load (α). Bi-axial geogrid (Bx20/20)-reinforced sand and laboratory results were compared with PLAXIS 3D software keeping N, eccentricity ratios and angle of inclination as input parameters. The results present that the value of Ultimate Bearing Capacity (UBC) of model foundation found reduced as the axial eccentricity and inclination of applied loads increased. It also found that multiple geogrid-reinforced layers increased the UBC of about 75%. Finally, the model test results were analysed using PLAXIS 3D. A good agreement was originated between the laboratory results and numerical analysis.

Behaviour of eccentrically inclined loaded rectangular foundation on reinforced sand

Abstract This study presents the behaviour of model footing resting over unreinforced and reinforced sand bed under different loading conditions carried out experimentally. The parameters investigated in this study includes the number of reinforced layers (N = 0, 1, 2, 3, 4), embedment ratio (Df /B = 0, 0.5, 1.0), eccentric and inclined ratio (e/L, e/B = 0, 0.05, 0.10, 0.15) and (a = 0°, 7°, 14°). The test sand was reinforced with bi-axial geogrid (Bx20/20). The test results show that the ultimate bearing capacities decrease with axial eccentricity and inclination of applied loads. The test results also show that the depth of model footing increase zero to B (B = width of model footing), an increase of ultimate bearing capacity (UBC) approximated at 93%. Similarly, the multi-layered geogrid reinforced sand (N = 0 to 4) increases the UBC by about 75%. The bearing capacity ratio (BCR) of the model footing increases with an increasing load eccentricity to the core boundary of footing; if the load eccentricities increase continuity, the BCR decreases. The tilt of the model footing is increased by increasing the eccentricity and decreases with increasing the number of reinforcing layers.

Calculation Formula for the Pullout Force of Uniaxial Geogrid-Reinforced Expansive Soil

To obtain the action force between the reinforcing material and filler in reinforced soil, many scholars at home and abroad have conducted pullout tests, which are limited by the testing apparatus. Most of them have studied the pullout force between a biaxial geogrid and sand. The pullout force formula is generally believed to be composed of the surface friction and lateral resistance of transverse ribs, and uniaxial geogrids have rarely been researched experimentally on the basis of the pullout force between them and the expansive soil filler due to the large distance among transverse ribs. This study draws on existing methods to determine the pullout force, conducts a preliminary analysis, proposes a formula for calculating the maximum pullout force, uses a self-developed large-scale CNC pullout test system, and utilizes its large size, bidirectional airbag loading, and ability to eliminate side wall friction. The design of the test scheme is optimized to obtain two important calculation parameters in the formula: one is to cut grids of different lengths to provide lateral resistance and then implement them to obtain the coefficient of sliding friction between grid and fill; the other is to develop different numbers of horizontal ribs in the pullout test of a grille, and the lateral resistance of the end bearing of a single transverse rib is measured. The results of the lateral resistance of the end bearing based on the analysis of the three mechanisms of shear, punching, and Prandtl failures are compared. The lateral resistance of the lateral rib end bearing measured from the test is proven reasonable. Two types of expansive soils reinforced by different types and sizes of grids are analyzed with the calculation formula of the maximum pullout force, and the coefficient of pullout friction is determined to be rational. The research results can be used to guide the design and construction of uniaxial geogrid-reinforced expansive soil and the modification and upgrading of products by grid manufacturers.

Research on mechanical performance of industrial polypropylene biaxial geogrid

Biaxial plastic geogrid is a polymer mesh formed by biaxial stretching. When making biaxial plastic geogrids, generally, the polymer sheet made by extrusion is pre-punched first, and then the biaxial stretching is carried out at an appropriate temperature. Different sizes of pre-punched holes will affect the subsequent stretching process, thereby changing the mechanical properties of the grid. In this study, geogrids made of different pre-punched diamond-shaped hole plates were subjected to room temperature tensile test. Influence of diameter-to-distance ratio and the percentage difference of longitudinal and transverse spacing on the mechanical properties of biaxial geogrids were studied experimentally and numerically. The results show that when the holes are appropriately small and the longitudinal spacing between the holes is slightly larger than the transverse spacing, the mechanical properties of the grid can be the best, and transverse stretching process will affect the longitudinal ribs in different aspects.

Effect of Silica Fume on the Shear Strength of Cohesionless Soil

Utilization of waste materials in geotechnical applications reduces the environmental problems of factories wastes. Silica fume is a by-product of the extraction of silicon or ferrosilicon manufacturing. Using silica fume as an additive to the soil can significantly increase the strength and decrease the permeability of the mixture. In this study silica fume is used to improve the mechanical properties of cohesionless soil, with special attention when used as backfill material for reinforced earth retaining walls. Biaxial geogrid prototype was used as reinforcement sheets in prepared bed of sand-silica fume mixture. The effect of adding silica fume was evaluated based on the results of Pull-out tests under various overburden pressures. From this study it was concluded that, adding silica fume to the sand had reduced the pull-out displacement of the geogrid by about 30 to 91% depending on the applied overburden pressure. That interlocking between the sand and silica fume particles is the main cause of densifying the sand by minimizing the lateral movement of the particles. Reduction in geogrid elongation reflects the increase in shear resistance interaction of the geogrid-backfill, and consequently the increase in the stability of the reinforced earth retaining walls under static and earthquake actions.

Towards More Sustainable Materials for Geo-Environmental Engineering: The Case of Geogrids

Plastic materials are widely used in geotechnical engineering, especially as geosynthetics. The use of plastic-based products involves serious environmental risks caused by their degradation. Innovative research has been focusing on biodegradable polymers of natural origin, especially on poly(lactic acid) (PLA), to reduce the use of plastics. This study aims to explore the potentiality of biopolymers for the production of geogrids, measuring the chemical and mechanical characteristics of raw materials and of prototype samples, similar to those available on the market. First, chemical composition and optical purity were determined by hydrogen nuclear magnetic resonance (1H-NMR) and polarimetry. Furthermore, samples of uniaxial and biaxial geogrids were custom-molded using a professional 3D printer. Mechanical properties were measured both on the filament and on the prototype geogrids. The maximum tensile resistance was 6.76 kN/m for the neat-PLA filament and 10.14 kN/m for uniaxial prototype geogrids produced with PLA-based polymer mixed with titanium dioxide. PLA-based materials showed higher tensile properties than polypropylene (PP), the most common petroleum derivative. Conversely, such biomaterials seem to be more brittle and with scarce elongation rate respect PP. Nonetheless, these results are encouraging and can support the use of PLA-based materials for innovative biodegradable geosynthetics production, especially if used in combination with live plants.

Mechanical Behavior of Triaxial Geogrid Used for Reinforced Soil Structures

Geosynthetics-reinforced soil (GRS) structures have been widely used for the prevention of geological hazards. As a recently introduced product, the triaxial geogrid has been confirmed to provide improved performance due to the more stable grid structure. This paper presents an evaluation of the mechanical behavior based on a series of laboratory tests. The unconfined tensile strength of biaxial geogrid and triaxial geogrid in different loading directions relative to the orientation of ribs was investigated. Then, more than 8 pullout tests were conducted on the triaxial geogrid specimens embedded in the compacted sand. The internal displacements along the geogrid length were monitored. The results show that the triaxial geogrid has been shown to provide nearly uniform tensile strength in all loading directions as compared with the biaxial geogrid. The triaxial geogrid deformation is mainly characterized by rib bending and nodal distortion along with an inward squeeze perpendicular to the pullout direction. The interface friction between the soil and the geogrid develops in a progressive mode, and an elasto-plastic-softening characteristic is detected experimentally due to the extensibility of geogrid.

Construction, instrumentation and field performance of geogrid-reinforced unpaved roads

A research study involving full-scale unpaved road test sections was carried out to investigate the performance of unpaved roads reinforced with geogrids. Ten test sections were constructed with two different base course thicknesses. Three biaxial geogrids of different tensile stiffness and one geogrid with triangular aperture were evaluated. Geogrids were placed at the subgrade–base course interface. The sections were instrumented for measuring road response to traffic loading. Traffic loading was provided by a single-axle dump truck. Field measurements of rut depth and surface deformation were recorded at selected traffic intervals. An analysis of the measured performance data indicated that the geogrids effectively reduced surface rutting and improved the performance of unpaved thin base layers and the benefit became more pronounced when a stiffer geogrid was used. The results suggested reductions in the thickness of the base layer by using geogrids of up to 18%. The improvement by geogrids was shown to be less for increasing base layer thickness. In addition, the ability of the design procedure by Giroud and Han to predict rutting performance using the test section parameters as design inputs was assessed. The results indicated that the method underpredicted the required base thickness to support the applied traffic loads.