Author Bryan Gee
Date19 12 2018
When site work contractors run into bad soils, they want a solution that’s inexpensive, quick, easy to install, and effective. Chemical stabilization using materials like lime, cement, and fly ash is one option, but when you look at all the factors, it may not be the best choice. Let’s look at how chemical methods compare to mechanical stabilization with geogrids and discuss a few considerations that will lead you to the most effective solution.
COST: Does chemical stabilization cost less than mechanical stabilization with geogrid?
The factors that determine the costs of both methods are:
- Unit costs of the materials used
- Quantities of the materials used
- Cost of the labor and equipment needed for installation
For chemical stabilization, it is critical to look not just at the material cost, but to understand the potential uncertainty in the quantities required. What will happen if the expected application rate doesn’t achieve the required results? Beyond this, who is doing the installation? If you don’t have the required equipment and expertise, are you adding to the project costs by paying a markup to a specialty contractor?
With mechanical stabilization, established design methods make quantities virtually certain, so you know up front what your total cost will be. And installation is simple – just roll out the geogrid, place granular fill, and compact.
TIME: How much is time worth on your project? Have you accounted for all the time your selected solution will take?
Chemical stabilization requires you to mobilize specialized labor and equipment, and application time increases as the depth of treatment goes up. What happens if the equipment is tied up on another job? In addition, all forms of chemical stabilization require cure time to achieve the desired strength. Is that built in to your project schedule?
These concerns go away when you use mechanical stabilization with geogrid. You’ll know up front what it will take to solve the problem, and the surface will be stable as soon as installation is complete.
EASE OF INSTALLATION: Which solution is the easiest to install?
There’s no contest when it comes to ease of installation between chemical stabilization and mechanical stabilization. Anybody can roll out geogrid, and placing the granular material on the grid and compacting it can be done with equipment you already have at the job site. Plus, there are no restrictions on the weather conditions when geogrid is used. With chemical stabilization, you can’t work if it’s below 40 degrees F, or if it’s raining.
EFFECTIVENESS: Which one works better?
Chemical stabilization can be an effective way to stabilize bad soils when conditions are right and the correct material is used. But even when it works as planned, it can deteriorate over time as precipitation and groundwater gradually leach the chemicals out of the soil. That might not matter if the fix is temporary or the area won’t be exposed to moisture long term. But in other cases, it could spell trouble.
With mechanical stabilization, once it’s fixed, it’s fixed for good.
When all relevant factors are considered, mechanical stabilization with geogrid is often the best option for addressing poor subgrade soils. Contact us the next time you run into bad soils – we’d be happy to show you how it can help save time and money on your site.
Did you know our staff is also able to offer knowledgeable site assistance to help evaluate conditions and provide design assistance - at no cost to you? We have assisted contractors and engineers on thousands of projects and have the expertise, research and engineering to help provide cost and time savings to your projects.
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