ABSTRACT
Historic structures, like all structures, can undergo settlements over their life that are generally produced from two primary sources. Settlement can occur as a result of the slow long-term consolidation process that occurs if a structure has been built on soft soils such as clays or organic soils. Alternatively, settlements can occur if subsurface changes have occurred at a site for example by lowering the water table or removing support from under or adjacent to a structure by recent excavations. No matter the cause, the result of settlements is generally structural distress that must be addressed before additional problems arise or for that matter a partial or complete failure occurs. Structural intervention to provide an engineering solution in these cases generally involves some form of underpinning although other methods, such as soil extraction which was successfully used to stabilize the bell tower at Pisa (Burland et al. 2003).
