How close are the edges of a closed fracture?

Introduction In the night between the 11th and the 12th of April 1997 a fire heavily damaged the “Sacra Sindone” Chapel of the Turin cathedral. One of the restoration steps following the accident consists of the substitution of the irreparably damaged marble blocks covering the inner surfaces of the Chapel dome. We show the results of a research aimed to localize joints in the blocks of “Bigio di Frabosa” marble, quarried for the replacements of the damaged blocks. Detection of fractures in rocks is a well known investigation field (Grandjean and Gourry,1996; Myeong-Jong et al., 2004; Tsoflias et al., 2004; Porsani et al., 2006; Ferrero et al., 2007). We verified the GPR capability to localize joints that would be able to cause the breakup of the block, during the expensive cut and polishing workmanships performed by numerically controlled machines.