Biaxial geogrids are called biaxial geogrids because they contain similar strength in both the machine and cross machine direction. It does not necessarily mean they have the same strength in both directions just that the geogrids are designed to provide support in both directions. Biaxial geogrids can be knitted, woven or extruded but the majority are extruded. Extruded biaxial geogrids are generally extruded using polypropylene with a small amount of carbon black added to give the geogrid the ability to resist UV degradation. Biaxial geogrid's primary application is for use in base stabilization. By placing the geogrid in the gravel base so that it can interlock with gravel above and below you can extend the service life or reduce the total amount of aggregate needed for a road or parking lot application.
Testing Properties of Biaxial Geogrids
When dealing with biaxial geogrids, there are two orthogonal sets of polymeric tension-resistant components that are generally referred to as ribs. Junctions are formed at the crossover points of those ribs while the apertures between them allow for particles of the surrounding soil to penetrate between the ribs. Additionally, other testing properties include the ability of the soil surrounding the area to transfer stresses and strains on the surface of the ribs and the junctions, ultimate tensile strength and the ability of the ribs to meet minimum rib thickness.
How Does Biaxial Geogrid Stabilize the Subgrade?
In order to better stabilize the subgrade, biaxial geogrids confine the compacted aggregate soil into its apertures. Since the geogrid provides strength in both directions, the weight of the load across the surface of the geogrid is supported horizontally and vertically. When more weight is added to the load, the aggregate layers are compacted even more, further increasing the stability of the subgrade.
Combining Geogrids and Geotextiles
Geotextiles are used to separate dissimilar materials which prevents the mixture of granular subgrade materials into softer subsoils. Not only does this ensure that the ground is more stable for rigid pavement sections, but it also controls erosion and reinforces the strength of steep slopes in paved areas. When combined with an area where geogrids are in use, the stability of the subsoil is improved even more, creating a safer, more secure area.
How Do Biaxial Geogrids Save Time and Money?
Biaxial geogrids save time and money by simplifying the construction process, reducing the need for sub-excavation and reducing aggregate fill thickness. Once the process is complete, it also cuts down on the need for pavement replacement, which saves time and money in regard to future labor costs and the price of equipment use.
Common Extruded Biaxial Geogrid Questions with an Industry Expert
Q: What are the main conditions on a site that might lead someone wanting to utilize either biaxial extruded or another extruded grid for a project?
A: When we look at the use of Geo grid there's usually two main camps that you're in. The first one being soft soil, you get out there and you have an immediate problem. The contractor must either get equipment across or he's looking for a way to build some sort of working platform, the soils are too soft and so we use the geogrid in conjunction with stone and we build it up high enough thick enough that we can bridge over the soft soils that's the easy the simple hey we have a problem here's the solution. More of an immediate fix.
The second way we use it, or the other most common way is through pavement design where we're taking a complete pavement section usually asphalt on top of aggregate and then we're including a geogrid at the bottom. For one of two purposes, one being to extend the life of the pavement. Maybe your design is for 10 years, and you wanted it to last for 15 or 20, so you'd add the geogrid at the bottom to increase the life. The second way to look at it is we need it to last for 10 years but we can't afford this much asphalt thickness wise or this much aggregate and so we're adding a geogrid at the bottom and reducing either the asphalt thickness and or the aggregate thickness. That is all done through engineering, it's not black box it's all through AASHTO, the way that we do that. Those are the two main reasons or the two main uses of the Geogrid.
Q: Other than the design life are there other things that would help you determine what type of geogrid? What type of information would you need from a customer to point them in the right direction as far as on the design?
A: There's a lot of different ideas that go into this design. The main one being the softness of the soil, you know how soft, and we use a term called CBR, which is California bearing ratio and in layman's terms what that means is can I drive a truck across it without losing the truck or how much is it rutting when I drive the truck across or can I wear my good shoes out there without losing them, you know am I going to sink in. We use that softness of the soil as probably the main one. Then the type of aggregate that we're going to use. You know some places use concrete others use a regular Stone base, others even use a Sandy mix and so depending on the size of the aggregate and the thickness helps determine what strength geogrid we would like to use. Lastly, we're using what are we driving over, is it something like a Dairy Queen which would be 95 percent you know just regular folks like you and me driving over and
then a trash truck once a week so we will not need something as strong or says if we were doing a a railroad or a port or an interstate highway or even some of these major collector roads but you're going to have more truck traffic on it, once we get into construction equipment then we're at a whole different level and we're bumping up the strength of the Geogrid. So, we need to look at the soil, we need to look at the aggregate that's being used on top of it and then what is the actual application of this section.
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Whip and pause with 6013s? - Page 1CanDo Sitting Wedge Active Seat Wobble Cushion for ...Q: Do you often see non-woven filter Fabrics or some other type? I know there are some grids out there that have a non-woven fabric bonded to the grid and then some people use them in conjunction. What would be the purpose of that?
A: Well 95 of the time we do not use a fabric. A fabric is great to use as a factor of safety you know if you don't have all the field conditions, or they change throughout your area and it's great for separation. If for nothing else adding that in adds a degree of separation.
Now with geogrid based on the sizing of the aggregate and the type of soil will naturally separate the two materials. For example, the Corps of Engineers though always recommends I shouldn't say always but most time recommends a non-woven fabric under the grid, that can never hurt. Most of the time if you're including it there's a reason for it such as separation or maybe a little bit of added strength and like you said before we can connect the two. We can either stitch it or bond it or weld it where you're not having to roll out two different products but just one product with both applications on it.
Q: Where would the extruded geogrid be placed? Is it at the bottom of the aggregate or do you put it kind of in the middle of the aggregate? How do you decide where to place the grid?
A: Good question, we have done, when I say we, the industry, has done lots of tests on where we should put that geogrid in the aggregate to give you the greatest benefit. It has come back that the greatest benefit is when you put the geogrid right on top of the soil, the existing or the prepared soil, and the aggregate right on top of that so it would be right at the interface of the soil and the rock. That being said, sometimes the thickness of the stone is 20 inches, obviously that would be at a port or an airport or something else that's receiving some ungodly amount of heavy-duty traffic. If you have, usually the rule of thumb is 12 to 14 inches, if you have more than 12 to 14 inches of stone you should either move the geogrid up about halfway or just add a second layer of grid which is what we do. The problem is when the grid gets too far away from the surface whether that be the surface of the asphalt if you're doing a paved application or the top of the aggregate section the benefit that it's showing goes down considerably if that grid is too far away from the surface because it's naturally spreading out right the load and by the time it gets down to the grid it's not doing as much as if you had moved it up halfway. Nine out of ten times you're putting it right on top of the soil and putting the grid right on top of that.
Q: On the site visits and everything that you've done are there common installation mistakes or best practices that you see as far as actually putting the geogrid in the ground?
A: I like to tell people when I'm out there I should be able to teach your 15-year-old how to put Grid in in about 30 minutes. It is a very simple product it comes in rolls you can kick it out and what they say is kick it and then you stack it, so you'll roll the grid out and then you put an aggregate on top of it. That's the key to installation, I mean it's not hard but, that being said there are some it's amazing what people will do to try and mess up a project. So, when you're putting rock on top of it you'd like to back dump onto the edge of the grid and kind of fan it out, if that makes sense, with your equipment. It is a very stiff product and so you'll get waves in it, and you want those waves to be able to escape to the edges and the back of the roll. If you're just doing it on one side and working your way down, you could have a little bit of ripple which could pop through the aggregate depending on how thick it is.
Other common-sense things we always recommend are for people to use gloves because it&#;s a stiff plastic and without gloves it'll rip your hands wide open. There's just no getting around that, it can cut you up something fierce. So be sure to have gloves and long sleeves. When you're cutting a roll, you can easily use a chop saw that'll cut a roll right in half, unlike a fabric for instance where the fabric is so thick and everything tends to melt, the grid has those openings and so you can cut right through it. Again, that edge is going to be very dangerous, I guess is the right word. With other people there's instances where you're on site and the weather is not helpful and it's windy, well this product will blow all over the place so some people will zip tie two rolls together. Your overlap is usually one to three feet. The wider the overlap the softer the soil. On the competent ground you just overlap it one foot so that it doesn't separate during installation, but some people will zip tie those together. You do have to worry about the waves not being able to get out, some people when they're starting will put big rocks on the edge of the grid and then take those off as that roll of geogrid has been covered up. It's all very simple but some common sense is required and the first time you put it down it's not bad to have someone out there just to make sure or answer any questions like that.
Q: Is there anything else you wish more people knew about the extruded geogrid and its use and just the industry in general? What are some places it's not being utilized as well as it should?
A: Well, that's the big thing, the rule of thumb or what people in the industry say is it's only being used on about 20% of the projects where it could be used. If you have some sort of construction need or interest most of the time, we can include some type of geosynthetic, specifically Geogrids for this one, to extend the life of your pavement, to get over some of those issues you have with soft soils, and or to save you money where we're taking the thickness and pushing it down. For instance, if you went through the engineering and your engineer says &#;hey you need 20 inches of stone to mitigate these soft soils&#; we can, this is rule of thumb, cut that in half with the use of the right geogrid where you're saving 10 inches of stone. If it's super expensive or you're having to haul it a long way another option where you can look at grid is chemical stabilization. Which works fine, chemical stabilization is a viable option, but you have issues with weather and availability which you don't have with extruded biaxial Geogrid. The opportunity to use grid, Extruded geogrid is out there, and definitely not used as much as it could be so I would encourage you if you're watching this video to at least put a call in the worst thing that we can say is in this instance you know the grid isn't going to do anything for your project but we'd be willing to bet that we can do something to at least give you an option where you can cost it out.
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