How to Use Geogrid in a Retaining Wall Project
Geogrid is a polymeric material that has ribs in two directions. Using it in a project can save time, money and labor by avoiding deep excavation and minimizing the amount of backfill needed.
It can also reduce the risk of rutting or eroding, and improve load-bearing capacity in soils and earth embankments. This article will review advances in geogrid materials and their environmental behavior, with emphasis on tensile characteristics and long-term durability.
Reinforcement
When soils need reinforcement, geogrids provide an efficient and cost-effective option. Their high tensile strength allows them to distribute loads over a larger area, preventing the formation of rutting and eroding areas in the ground. In addition, they can handle lateral loading. This is especially beneficial in the case of retaining walls.
In this case, the geogrid acts as a structural support to the retained backfill material. Its ability to withstand lateral loads means that you can use thinner backfill materials, geogrid for retaining walls which will reduce construction costs. Furthermore, the geogrid will last for a long time as it is resistant to degradation from exposure to the elements.
It can also improve the overall quality of a pavement structure by increasing its stiffness. This will prevent road vibrations and improve ride quality for drivers. In addition, it can help to overcome poor pre-existing subgrade conditions that would otherwise impede the constructability of the pavement section.
Moreover, studies have shown that the optimum design tensile strength of a geogrid can be obtained by utilizing stress safety factors and incorporating the effect of shear stresses on the interface between the soil and the geogrid. However, there is a need for further research to study the effects of confining pressure and specimen size on the shear interaction coefficients between soil-geogrid and C&D waste-geogrid interfaces.
Drainage
The simple fact is, when you compress soil it loses its shape and can crumble or spread out. When you place a soil clump into a square plastic mould, however, the pressure of your hand compacts the soil inside the confines of the mould and stops it from moving or spreading beyond its boundaries, making the soil a much more stable base material. This is exactly what a geogrid does on a large scale.
There are different types of polymer geogrids available on the market, all designed to better suit specific projects and applications. These options include extruded, woven, and bonded. Choosing the right one will depend on your project’s goals and budget, as well as how much flexibility you are looking for in your structure.
In addition to being a key component in retaining walls, geogrids can be used to stabilize slopes and soft earth embankments, reduce the amount of aggregate layer thickness needed in unpaved roads, and make railway work platforms safer by increasing soil strength. They can also reduce costs by allowing for the use of cheaper fill materials.
When installing a uniaxial geogrid in a retaining wall, it must be rolled out perpendicular to the wall and in lengths that are dictated by a certified engineer’s recommendations based on the height of the wall and the conditions of the soil and subgrade. It must then be hand-tensioned to ensure it is taught and has the unified strength necessary to keep your retaining wall safe.
Stabilization
The ability to transfer load is critical to many applications of geogrid. This is accomplished by the ribs and junction points interlocking with soil particles to create a mechanically stabilized layer. This helps minimize differential settlement, reduce granular layer thicknesses, increase trafficking performance, and improve bearing capacity.
To understand how a geogrid transfers loads, consider holding compacted sand in your hand. When you press down on it, the sand gives way for a short distance until all the friction between the sand particles equals the force that you are applying. This is the same principle as soil giving way under a road, footing or foundation, and it is what engineers refer to as settlement.
When designing a geogrid for a specific application, there are several considerations, including its geometry, material type and coating, and loading direction. The grid should also have sufficient tensile modulus and shear strength to resist deformation. In addition, it is important to understand the physical characteristics of the junction point — the area between the ribs where the grid is manufactured — since this may be an area of potential failure.
A geogrid’s mechanical properties are influenced by the aperture size, percent open area and thickness. The aperture size should be large enough for sand and aggregate to penetrate, but not too large so that the soil can’t interlock with the geogrid. It is also critical that the junction point is thicker than the ribs to prevent stress concentrations.
Protection
When installing a geogrid, it is important to keep in mind that the grid can be damaged during shipment, storage or installation. To minimize damage, the geogrid should be stored in dry conditions, protected from sunlight and ultraviolet rays, temperatures greater than 160 Uniaxial Plastic Geogrid degF (71 degC), flames including welding sparks, mud, dirt, dust and debris. Also, before installation it is a good idea to smooth the rutted subgrade and compact the soil with a vibratory roller in order to minimize any drops that could damage or displace the grids.
Geogrids are ideally suited for wall and slope applications that require reinforcement against forces pointing towards the wall or down the slope. The ribs in the geogrids can be oriented to resist these forces and increase the tensile strength of the wall or slope. This provides superior protection of the soil behind the geogrid, reducing erosion and protecting against the collapse of steep slopes and landfill liner systems.
Mechanical testing of geogrids is an area that needs improvement. Testing standards need to be more consolidated in order to reduce the number and types of tests needed to characterize these materials. It is also critical to understand the impact of the geogrid structure and aperture size on its performance. For instance, a woven geogrid with smaller aperture size exhibits less interlocking between the soil and grid, resulting in a lower pullout resistance.
