Applications of HDPE geogrid include in road construction, slope stabilization, retaining walls and soft soil reinforcement geocomposites etc. HDPE geogrid is a clear favoured choice of a lot of engineers, especially in the tough environment layouts. Yet, the life expectancy in service is not always clear cut. Let’s have a chat about that.
One of the advantages that HDPE geogrid for civil engineering applications is it tends to last. The life expectancy in most challenging jobs can be anywhere between 30-50 years and longer. However, if it’s not treated with the right chemicals etc. in certain harsh environments, this can reduce its life expectancy.
Now, what actually is a ‘harsh environment’? Well, think of it but broadly it could be:
Exposed to high levels of UV
Being subjected to acid or alkaline soil
Installation in coastal areas (distance from sea or any other type of saltwater)
Freeze-thaw challenges
Heavy traffic or loading demands (in embankments etc.)
Continued inundation or simply ineffectively draining soil
Each of these alter the lifespan for HDPE geogrid.H2: Threats from UV Exposure and Surface Aging
Direct ultraviolet (UV) rays present another hazard for exposed geogrid. HDPE does possess good resistance, but prolonged exposure to the sun can set off a slow oxidation of the surface.
If the geogrid is laid in position, flat on the ground in the sunlight and left unattended, ageing of the surface accelerates. The surface becomes more brittle.
Fortunately, for practical situations in the real world HDPE geogrid is usually laid buried. Once covered by soil or aggregate, the effects of the sunlight are minimal. The degree of burial therefore assists in protection against this hazard.
For situations where the geogrid is left exposed, UV stabilisers and the addition of carbon black protectants are widely used and extend the effective service life considerably.
Chemical Resistance when In-Situ in Soil
Most of the time, HDPE geogrids are in soil conditions. Typically, they will be well within the range of acid, alkali and salt concentrations where the geogrid will ‘forget’ about the chemicals. Occasionally however, extreme conditions arise which must be factored in to any long term strength gain/loss figures, for example, in:
- Industrial waste zones;
- Landfill sites with aggressive leachate; and
- Coastal reclamation applications
In these situations, a comprehensive chemical analysis of the situation, concentration, degree of permanence, and temperature, must be completed, before drawing on proper design in the “real” project at hand.
The more concentrated and hotter the whole scene is, the quicker the polymer will become aged, so proper site testing is paramount.
Mechanical Load and Stress Thereon
This is again important to longevity of the applied grid. The HDPE geogrid works very well in tension, and spreads the load over a wider area – but if the load applied exceeds the design limits then creep deformation can make up part of the picture.
It is stretching of the grid – over the longer term. Creep wilts – reduces the “efficiency” of the reinforcement.Heavy traffic roads, railway foundations, or on incline slopes has a greater tendency to stress the geogrids very seriously and require stronger tensile grades such as TGSG4040, TGSG5050 or TGDG series products.
Get your product selection right and it gently impacts long-term durability.
Temperature and the Effect on Long-term Performance
The effect of temperature change plays a second part in the longevity of a product. The effect of warmth is to allow polymer chains a little greater freedom within each other resulting in a slight decrease in tensile strength – that means it will begin to deteriorate a little quicker. Conversely, a much frostier spell increases stiffness but not necessarily weakness. It is not that issue that causes problems either since it is the repeated cycling of freeze and thaw that eventually takes its toll – and indirectly puts stresses on the grid since that is being placed under soil that begins to compress. The answer lies in proper drainage design for the most part – dry soil always having a more effective service life.
Quality of Installation a Priority Over Material Selection
There are great materials out and your HDPE geogrid might be one of them, but if installation is bad – so is your ROI on that decision. Quality in the install process carries relevance too and factors involved include:
Overlaps not of the correct length
Compacting fill material unevenly
Backfilling damage of the grid
Layers wrongly orientated
Society has grown lazy to a degree, and it is very much the case that once something is damaged in install, then the reduction isn’t just expected to have occurred, but the sooner the installer accepts fact the easier it becomes. Compaction compresses and then links the two with the technology of interlock thus being pursued. Risk averted with care – or closed if that wasn’t the case.
Usual Lifespan Expectation from Real Engineering Projects
Lifespan of geogrids in actual practice of engineered design tends toward variation from project to project but some feel for useful service life converts to:
Road base geogrid: 30 to 50 years.
Retaining wall systems: 40 to 50 years, 60 for a covered system.
Soft soil stabilization: 30 years at least to 50 more so.
Landfill reinforcement: at least 50 years, and a little more provided in buried design.
Exposed slope protection: serious risk here, not less than 15 years and on a good project 25 at a stretch.
Figures denote proper install of course, and under Standard environmental effects.
Bear in mind in actual practice that in the long run, buried HDPE geogrid frequently lasts an awful lot longer than the structure itself.
Ways to Lengthen Your HDPE Geogrid Service Lifetime
Lifespan of course can yet still be lengthened from those projections I made:
Try to apply correct strength grade to conditions, chiefly using too light a product in the first place.
Avoid fooling around with the drainage of earthworks in conjunction to an installed geogrid; once moisture collects, greater stresses ensue plus negatives of weakening its stabilising the foundation soils.
Mechanical contact with the installed geogrid is a foe of success.
Never skip a covering layer. With protection from soil, UV is all but ineffective.