We are having some soil issues regarding flexing of the pavement during expansion and contraction. We have treated the soil by stabilizing with lime to a depth of 8 inches. Would it be suitable to add a geogrid product, in addition to the lime stabilization?
The use of geogrids in pavements become problematic when it comes time to rehabilitate the road. Also, geogrids should be installed between a section and not between two sections. It sounds like you need to increase your lime treatment thickness. This would increase the thickness of the non-expansive section, while reducing the influence of seasonal moisture fluctuations of the expansive materials. The key is create a stable pavement foundation below the HMA wearing coarse.
HSI Engineering, Inc.
By the way, please remember that if you do put a geogrid into contact with the lime, you have to think of the raw material of the geogrid, as PET ones do not create their true strength due to hydrolysis. Ones made with PP or HDPE are ok.
Both suggestions will work. But here are the differences.
1) ECONOMICS – The lime stabilization will be 30 to 50 percent less cost than excavate, export, and import.
2) CONSTRUCABILITY – The project sounds like it’s experience underlying stability issues within the subgrade. If you excavate down to the problematic soils, you will have to deal with construct-ability issues and additional cost to stabilize that elevation. The chemical stabilization process will allow you to work from a higher elevation and if designed right will bridge over the underlying conditions.
3) ENVIRONMENTAL – The trucking and material ratio between importing versus chemically stabilizing is 40 to 1, plus the additional off-hauling. As an example: If this project was 50K SF @ 12″ you will eliminate 120 trucks to export unsuitable materials and 145 trucks to import granular material .. or 4 trucks loads of lime or cement.
4) ENGINEERING – Soils and aggregate instability is do water infiltration, overtime unbound sections begin to move under active loading. Bound sections will remain stable (bound) under such conditions. A stabilized section is defined as a high strength, non-plastic, and low permeable section.
If you have granular material available, then replace the whole of the lime stabilisation and use an appropriately strong geogrid with the granular material. The thickness of the granular material depends upon the strength of the subgrade and what strength you need on top of the granular layer.