When the Worst Soils Are Under the Best Sites

When the Worst Soils Are Under the Best Sites

From time to time on our Florida projects, we run across sand mixed with a high concentration of organic matter. Depending on building loadings, this can be a huge challenge when selecting a foundation system that makes economic sense.

Recently on a Florida site, we worked with Hayward Baker to determine if the load characteristics of the insitu material, which in this case contained an unusually high quantity of organics, could be improved. Our idea was to try a wet mass stabilization ground improvement method, a technique using a cementitious binder slurry mixed with the insitu soils to form a stabilized subgrade. Under the right conditions, this method will reduce building cost by increasing bearing capacity and decrease settlement for the subgrade vs. other deep foundation systems.

For several months, we collected and tested soil samples, mixing with varying ratios of cement, trying to attain improved soil strength to bear the new structures. While a good system, on this particular site adding a cement binder to the insitu soil samples did not produce the desired results, nor did adding slag along with the cement binder to improve strength. We found that regardless of the ratios of cement binder and slag mixtures, the insitu soils would not allow the cement binder to solidify enough to achieve the needed soil bearing capacity.

Now we are back to a piling foundation system. While we tried, the wet mass stabilization soils have a mind of their own.

Addendum: We first worked with Hayward Baker when Wally Baker ran it. We worked together a site that was made usable by “deep dynamic compaction” and saved several million for the customer. More to come on this one…

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