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Soil Composition

Foundation Failure

Foundation repair requires a specialist. The Leaning Tower of Pisa, most likely the most famous leaning building in the world, wasn’t constructed to lean. It is, perhaps, the most renowned example of foundation failure. There were several attempts to correct the problem. Eight hundred years after its construction, the Tower was stabilized with a massive engineering project that was performed in the 1990’s.*

Each foundation failure is unique. Your solution may not be the same as the famous Tower’s. But yours will have its singular problem that will benefit from a professional. There are a number of solutions and many address unstable soil conditions. The Leaning Tower of Pisa sits on a mixture of clay, sand, and shells. Soil conditions needed to be stabilized.

And soil is a complex structure. Support the foundation often requires getting into the load bearing strata or bedrock. And that can be far below the surface. Soil has several layers that are called horizons. Each layer has a specific name that corresponds to a letter, and the contents of each layer are different. There are six soil horizons in all.

Soil Horizons

The O Horizon is the top layer. It contains leaf litter and decomposing matter. This is what you would rake up in the spring.

Horizon A is topsoil. This is where seeds germinate and plants grow. It’s a dark-colored layer, made up of humus or decomposed organic matter mixed with mineral particles. This is what you fertilize and feed to get lush foliage. If you love to dig in the dirt and plant a garden, you’ll know that this layer is not going to support a building. If you water a lot, it probably won’t support a shepherd’s hook hanging structure if you try to hang anything relatively heavy from it.

Horizon E does not contain many minerals. And it’s lighter in color than Horizon A. This layer is made up mostly of sand and silt. It has lost most of its minerals and clay, because in the process of eluviation or leaching, the water dripping through this layer has carried the minerals down to the next layer.

Horizon B is also known as subsoil, and this layer contains clay and mineral deposits like iron, aluminum oxides, and calcium carbonate. This layer contains slightly broken-up bedrock. Plant roots do not penetrate down this far, and not very much organic matter exists in this layer.

Then we come to the sixth layer down. This is the R Horizon. This is the unweathered rock or bedrock layer that is beneath all the other layers. This is solid and strong. When it comes to foundation repair, often the professional will be looking to sustain at this layer.