Previous Archaeological Research Conducted: In 1985, it was discovered that the eastern portal stone was cracked. In an attempt to fix this, excavation and restoration works were undertaken in 1986. The first excavation of Poulnabrone Dolmen was in 1986 and then again in 1988 by Ann Lynch. During this excavation, one portal stone was replaced, and the team excavated the chamber, portico, and cairn. In addition to the cracked eastern portal stone, it was found that an extra orthostat was needed to spread out the weight of the capstone. When excavating around the western part of the cairn, they inserted a new orthostat to allow the southwestern chamber orthostat to be straightened. They then left this new orthostat in its place on the western side of the tomb because the original orthostats’ bases were significantly decayed.

From http://www.nd.edu/~ikuijt/Ireland/Sites/cquinn/poulnabronedetail.htm