In the past building a basement in an area where clay was compacted was impossible to build. It was not because clay would not hold a basement, but infact, it was its swelling potential. Most clays’ swelling potential can be predicted within acceptable limits. So by planning for the clay’s worst conditions a builder could build a basement, taking its potential into consideration. This would allow a basement builder to plan for the clay’s expansion during wet months and shrinkage during the summer.
What made building a basement impossible under these conditions was what happened to clay when it was compacted and under pressure. This was a game changer since no one knew a way to predict the swelling potential and pressure in compacted clay before 2010. In February of 2010, Cimen, Keskin and Yildirm published an article in the civil engineering section of a Turkey journal that changed everything.
The abstract noted that using three different samples they dried each to the same weight, point of compaction, and amount of water content. I won’t bore you with the types of equipment used, plasticity, math equations, or the type of regression analysis used in the study. In simple terms the clay was allowed to swell freely while stable and increased pressure was applied and analyzed.
Why was the study finally done to measure clay’s expansion under pressure? Due the global warming the amount of damage caused by soils being improperly predicted has risen to $2.3 billion annually in the U.S alone. The study found that expansive soil damages now exceed the combined yearly average of floods, hurricanes, earthquakes, and tornados.
It was discovered that the higher the rate of plasticity (clay content) the more swelling occurred. Under pressure the amount of swelling decreased as the pressure was increased. What we now know is that if the clay is dried and compacted under pressure, over time the clay’s swelling potential can be predicted.
In simple terms – we can now build basements on clay soils in environments where water is known to be present. Knowing that we can predict the amount of swelling possible makes it possible to literally control much the swelling over time.
September 2012, Volume 37, Issue 6, pp 1535-1546