If youve never seen one, theyre pretty big! These concrete drill shaft extension can be seen in the median at the west end of Gandy Boulevard sticking out of the ground. The Selmon Extension Construction crews installed them in July. What are they for you ask? They support the bridge abutment from underneath the roadway. Several drill shaft extensions will be used to form the Selmon Extension Bridge. Theyre excavated into the ground and then filled with steel & concrete.