A surface instability detection apparatus for investigating axial spli
tting and spalling phenomena in rocks and rock-like materials is descr
ibed. The apparatus simulates the conditions under which these phenome
na occur and allows one to accurately measure them. Experimental resul
ts from tests on Berea sandstone are presented where the successive fo
rmation of spalling fractures was monitored with an acoustic emission
system and the location of the seismic events was mapped. The test res
ults show the potential for benchmark tests in determining the spallin
g tendency and characteristics of different rocks.