We have developed a test method for acoustic emission assessment of large rocks such as used in construction of breakwaters. The test allows detection of embedded cracks and other discontinuities that may affect structural integrity of rocks under stress. This fast and reliable procedure is used to sort rocks by their overall strength and integrity.
During the test, stress is applied artificially by excavator clamps while the rock is continuously monitored for possible crack development. There are other alternatives for rock loading such as weight or press. In all cases stress level and direction should be applied as close as possible to real service conditions.
Almost every rock will demonstrate some level of acoustic emission activity due to micro- and even macro-cracking processes. However, rocks with considerable defects are exhibit continuous acoustic emission activity long after they subjected to load. A special propriety signal analysis procedure assist to identify defective rocks with low load bearing capabilities.
Acoustic emission technology can be also used for prediction of failure load without bringing rocks to high stresses. For this purpose, laboratory load tests to failure of rock cores and full size rocks are conducted to study typical stages of damage accumulation and development vs. stress. This information is later used in routine examination of rocks and assessment of their strength.