We have discussed many aspects of foundation problems associated with black cotton soils in previous several posts. Our most successful post, about black cotton soil, “Foundation on black cotton soil” has become very popular and we are receiving thousands of viewers for this post. In this post we will discuss about French drains that can be used to drainage control within the foundation soils and thus restricting many harmful impact from black cotton soil.
At first we will learn about French drains in brief. French drains are trenches that are filled with gravel. This granular fill captures moisture that are intending to pass through fill. The fills of gravels the removes unwanted moisture through a pipe or system of pipes. Generally a set of perforated pipes are placed at the bottom portion of trench. These perforated pipes collects moisture that accumulated below the fills through the gravel fills and then discharge to a suitable point situated at the end of these pipes.
Thus a well planned and distributed perforated pipe system in between French drain provides a barrier to groundwater flow towards foundation. This renders a inert properties to black cotton soil as black cotton soils shows its destruction capacity when it receives moisture from ambient environment.
The French drains are suitable where water table is high and subgrade soils are receiving a huge volume of water. A small modification to this makes it to perform as cut-off wall. The modification is providing a heavy and thick plastic liner between foundation of building structures and French drain.