Workity Workity Work. . .

Sorry for the extended absences, but work has been the mother of all mothers lately. I guess that's the penalty for taking a little vacation time and enjoying myself away from the rigors of work.

Currently, we are involved in a very large soils investigation. In a weeks time, we have performed 207 exploratory borings across an 80-plus acre site and in the laboratory have completed roughly 2/3's (about 400 individual samples) of the soil classifications using the test methodology invented by Albert Atterberg. Let me simplify that for the layman. . .we've been eating dust sandwiches all week.

Most of the work, actually all of the work, is quite repetitive and mind-numbingly boring (get it? boring?), but on occasion you run across an anomaly in the soil which raises some interest. Such as in the photo below. . .



We're not quite sure what this crystalline substance is, but our geologist seems to believe that it is either gypsum or some sort of calcite. I'm hedging on the calcite as Yazoo clay (the type of soil shown) is loaded with calcareous nodules. Interesting, isn't it?

The difficulty with heavy (Yazoo) clay is the ability of the material to retain large quantities of water, which in turn, creates tremendous changes in volume. Yazoo clay can easily take on it's own weight in water and it is this "activity" exacerbated by seasonal water changes that can tear a home or building in half, literally. That is what makes the material difficult to build upon and the reason our roads in Jackson are so terrible.

In this part of Mississippi, there are a couple of options: you can try to create a buffer of at least 7 feet of less-expansive clay in between the bottom of the foundation and the Yazoo clay or you can use a deep foundation system, such as underreamed (bell) piling. Cost is typically the issue and usually the undercut and backfill option is the most cost effective, unless it is a large or heavy construction like a multi-story office building, parking garage or a large warehouse with high walls where wind pressures and uplift are concerned.

The truth, as in most cases with Mother Nature, is that she usually wins. I posted a photo some time ago of an odd shaped concrete structure and what that thing is, is the top of a bell piling. Obviously the shaft should be straight like the ones in the background and not mushroomed out as in the photo, but I suspect that there was some sloughing or possibly it was raining that day the concrete was poured for that piling.

Anyway, that building was constructed back in the early 1970's and the Yazoo clay beneath it has swelled so much that the crawl space under the building no longer existed and the soil was pushing against the floor joists above it. The pressure became go great that it heaved the floor and broke two piling where they were connected to the building by an exterior poured-in-place concrete grade wall.

I'd say that's some badass dirt, wouldn't you?