Construction of pavements relies on obtaining the required durability and low life-cycle cost with adequate load-bearing capacity. One of the commonest and most effective ways of doing that is with the use of the biaxial geogrid which is loaded in two directions (perpendicular to one another).
Biaxial geogrid is found in practical use both in pavement for roads and at airports.
Below we discuss how, when and why this type of grid is used in pavement.
What is a biaxial geogrid?
Whereas with a uniaxial geogrid the ratio of tensile stiffness along the major to the minor access is high, with a “Biax” grid the ratio is small. The material is manufactured from either HDPE, PET or PP, having a grid structure which has the characteristic of “interlocking” with the aggregates in the pavement layer above. This increases the load transfer from the aggregates to the underlying subgrade, resulting, firstly, in less deformation, and secondly, in more favourable stress distribution. Of course, the paper “The use of stabilisation to extend pavement life” deals with stabilisation methods. However, the principle is the same and the geogrid is an important aid in extending the life of the pavement by preventing deformation in the shorter term and production of defective or cracked surfaces in the longer term. In particular it can be used to great advantage in soft soils or heavily-veined sandstone found as sub-grade. Grids can also be used for improving the performance of a pavement on light terrain.Less material to lay for that same durable structure means cheaper pavements and less time to build them.
Preventing Rutting and Cracking
Rutting and cracking occur where traffic is strongest on paved surfaces. Biaxial geogrid work to discourage both problems by stabilizing the aggregate layers. The geogrids bite into the crushed stone or gravel, holding aggregates in place, which helps maintain an even surface across the top, even under the grip of heavy trucks. Repeat 4 loading tends to ‘pump up’ the geogrid layer into place. Over time, thanks to this stabilization, the pavement should not develop the usual rutting, leading to a longer useful life and reducing maintenance and patching.
Reinforcing Soft Soil
Soft soil subgrades are a major threat to the integrity of all pavements. Deploy the geogrid broadly across soft soil, and you build an improved road. The geogrid depromotes settlement by distributing loads and keeping the pavement smooth at the surface level. This application particularly shines on and under gleaned roadways bearing clay, or silt, or that loose sand. Only light embankments are called must, so less material is required, and construction times decrease.
Stabilizing Base Course
Another widespread application of the geogrid is stabilizing the base course. Because the layer immediately adjacent to soft soils tends to seep sideways and settle in concert, when a layer (or two) of biaxial geogrid is laid on top of a subgrade, aggregate particles interlock. The process prevents lateral movement of the aggregate and yields an even compaction throughout. to be anticipated, and often significantly increase the life of a pavement. A stable base, in order to withstand deformation and shear, is of great importance on highways, and even more so on airports.
Biaxial Geogrid on Rehabilitation and Overlay Projects Biaxial geogrid is of value in rehabilitation work too. Instead of reconstructing a pavement in its entirely, the geogrid may be used in an overlay system as well. By positioning a geogrid between the old pavement and the course of new asphalt, transfer of stress to weak subgrades is limited, leading to an increased chance of reflective cracking, and enhancing the size of the whole overlay system. Biaxial geogrid overlay projects are beneficial and project for project can lengthen the life of the pavement by a number of years.
Airport Pavements Heavy, rutting loads on the high-frequency, high-cycle pavements of airports merit the greater use of the bicovalent (dual) grid for their construction. Geogrids can act to strengthen taxiways, aprons, and runways where they impinge on buildings and roads to rigidify air traffic surfaces and reduce the annual per square foot average repairs to a minimum while still maintaining safety by lessening rutted effects.
Drainage and Soil Separation In some applications of the geogrid, it may also assist in effecting drainage and soil separation in the layers of pavement. The open grid structure permits run-off water to flow while keeping fine soil particles from moving up through it into the aggregate.
Design Aspects of the Biaxial Geogrid It is important that when the correct biaxial type of geogrid is chosen, the correct earth soil, traffic flow, and usage is chosen. Site location and conditions will naturally govern as to correct decision relative to tensile strength, elongation, aperture size and chemical resistance of base material. Choice of proper quality of geogrid tailored to site location, terrain and air climate is also very vital in the survey and project undertaken. For example a HDPE geogrid would be favoured for highly corrosive soils in the earth the grid is being installed on/in. A PET geogrid appears more appropriate for heavy load purposes.
Cost Effectiveness of the Biaxial Geogrid Regardless of the depth of the covalent grid type being laid, except where such is the slight extra cost of purchase the benefit and net out of saving of thickness of base course sum sufficient to the reaping of money from that spend, is dumbfounding, perhaps in the hundreds of thousand dollar on—larger jobs such as highway pavement jobs and those worked close airfields too obviously. And against the more we demean the soil of our pond the more fit the civial ground becomes.
Summary. Biaxial Geogrids “A new and dynamic use for geogrids is made in rapid-fire pavements. They are good load bearers, using as they do the hingeing action to obstruct asphalt rakeup, lessening a rise from a ripple in so doing by virtue relieving deformation, and likening favorably to a mating rebate.”