Time Delay Rock Kaiser Effect

Accurate information about in situ stresses is required in the designs and operations of all underground and open rock excavations, including mining engineering, water conservancy and hydropower, civil engineering, railway, highway, etc. However, most of the known stress measurement methods are time and labor-consuming, and cannot provide the necessary accuracy for the scene. Therefore, a convenient, reliable and economical measurement technique is needed.The stress measurement method based on Kaiser effect of acoustic emission (AE) is a technique of simple, cost much less and can proceed much more tests. However, it is found in the previous study that this method concerns not only the axial compression to rock samples, but also quite a few other factors, such as the direction of the applied stress, and time delay been applied.As we known, since the preparation of rock samples in the laboratory needs quite lond time, Kaiser effect may disappear before tests atarts. Therefore, time delay influence of reliability of Kaiser effect, and has the vital significance to the application of the effect.In this paper, tests were carried out by making use of a servo-controle triaxial testing machine, as well as a testing apparatus of AE, SDAES. An experimental study was performed to investigate the acoustic emission characteristics and the Kaiser effect of two rock types:tuff and schist specimens which from dahongshan copper mine, Yunnan. Kaiser effect of these rock samples was investigated to loading again after the first time loading interval of2days,7days,15days,30days and45days.By analyzing the experiment results of nearly113rock samples, following main conclusions are obtained:(1) under the conditions of uniaxial compression, because of the original fissure closure in rock specimens in the early loading, acoustic emission activities are relatively strong. Along with the raise of the applied load, AE activities decreased, though it still keeps growth. On the edge of failure, activities of AE increased significantly.(2) Under the conditions of uniaxial compression, Kaiser effect exists when there is on time interval.(3) The higher level of the first loading close to rock strength, the faster Kaiser effect of rock retreat. The ability of rock previously stress memory is the best between30%and80%of rock strength.(4) Under the conditions of uniaxial compression, Kaiser effect of rock is gradually disappear with the time interval growth between the first and second loading, but remains detectable for inner30days, after more than45days resulted in hard detected the Kiaser effect of tuff and schist specimens which from dahongshan copper mine, Yunnan.