In order to study the acoustic emission of rock when subjected to compressive loads, some uniaxial compression tests on a kind of limestone of Guangxi Province were carried out by means of the Rock Acoustic Parameter Dynamic Testing System (RAPDTS). It was concluded that the formations of new micro clefts generated in the rock and the enlargements of existing clefts are the principal factors that cause the acoustic emission.
Acoustic Emission Technique has been widely used in Geotechnical Engineering. It plays an important role in Rock Mechanics research. Acoustic Emission Technique is a testing method to inspect inner status and to grip the mechanical behaviors of rock by means of rock acoustic emission. When rock is under compressive stress, stress concentrates around the pre-existing or new-produced micro clefs, and the strain energy also increases. When outside force increases to a certain value, microcosmic yielding and distortion occur in the region with flaws in rock. Clefts expand and the Stress relaxes. Some strain energy releases as an elastic wave (Sound wave). That calls rock's Acoustic Emission (AE). The inner status of rock can be found out by observation and analysis of rock acoustic emission. It is an inverse problem to probe the changes of rock property and status with Acoustic Emission Technique. so study on acoustic emission of rock in laboratory is essential for inverse analysis of rock's properties in nature.
As a kind of elastic wave, the signal of Acoustic Emission not only can reveal rock's properties, but also reflect properties of spreading and receiving easily. So monitoring system with AE has the advantages of high -speed, large-scale of monitoring, long-term and dynamic monitoring. Early in the end of 20 century, engineers of bureau of mines of USA, Obert and Duvall(1) detected the AE activity in rock when to load on rock structure. And a series of indoor tests and field tests indicate that AE is a measurement of rock and it's stability of mechanical structure. At the present time, AE technique has been widely adopted for stability monitoring in underground stope, goaf, slope in the open air and foundation of the dam, and also used in petroleum engineering, seismological engineering, underground engineering and etc.
The rock AE is a signal of transient random wave whose rise time is just scores of or several hundreds of millimicroseconds and whose repetition frequency is also high. The transient vertical displacement is about 10 −7 ~ 10 −14 m. The frequency distributes in the range from infrasound to ultrasonic, i.e. from several HZ to scores of HZ. It demands that the AE monitoring system has properties of high speed of response, high sensitivity, high gain, wide dynamic scope, resumption from high block and choosing the frequency in the monitoring windows.