Acoustic emission induced by progressive excavation of an underground powerhouse

Abstract

a b s t r a c tWe monitored acoustic emission (AE) events associated with the progressive excavation of an underground chamber for a powerhouse at a depth of 280 m below the surface in a porphyritic rock mass of the Mesozoic era. Large AE events rarely occur under such conditions; specifically, low-stress environments due to the shallow depth, careful excavation, and sufficient reinforcement. However, upon employing sensitive, high-frequency monitoring (15 to 40 kHz) in a relatively small region, some AE events were located and, by using fault-plane solutions, their fracture mechanisms were identified. Strike and dip angles of fracture planes and the directions of principal stresses, all derived from faultplane solutions, were consistent with the directions of dominant joint surfaces, the measured initial stress conditions, and the shape of nearby excavated openings. This suggests that by employing sensitive, high-frequency AE monitoring, fault-plane solutions can be effectively utilized as a tool to assess the stability of a chamber excavated at shallow depth, as well as in deep mines where fault-plane solutions have already been used in practice to assess and control rockbursts.

Early‐warning signal recognition methods in flawed sandstone subjected to uniaxial compression

“…AE technique has been widely used to study the micro‐cracking mechanism (i.e., the microcrack location) of rocks in the laboratory and project site 27,28 . In the process of seismic surveying, large‐magnitude events occur less frequently than small‐magnitude ones.…”

“…AE technique has been widely used to study the microcracking mechanism (i.e., the microcrack location) of rocks in the laboratory and project site. 27,28 In the process of seismic surveying, large-magnitude events occur less frequently than small-magnitude ones. According to the amplitude-frequency relation proposed by Gutenberg and Richter, it is found that the numbers of seismic events against the considerable magnitude follow the power law distribution.…”

Damage and fractal evolution trends of sandstones under constant-amplitude and tiered cyclic loading and unloading based on acoustic emission

“…Sandstone samples were collected from the Xieyi coal mine in Huainan, China. Sample density was 2.6 g/cm 3 and average uniaxial compressive strength was 50 MPa. The proposed methods of preparing standard rock samples for uniaxial compression testing recommended by International Society for Rock Mechanics (ISRM) were strictly obeyed.…”

“…The rupture scale of rock was reflected by the energy information received by acoustic-emission sensors. The damage variables of sandstone under constantamplitude and tiered cyclic loading and unloading were calculated using equation (3). The relationships between D and the stress-strain curves are shown in Figure 9.…”

“…He et al 2 used a self-designed test facility to analyze the relationship between AE signal amplitude and rock burst mechanisms. Ishida et al 3 monitored AE events during a progressive chamber excavation and considered the fault-plane solution superior to the moment tensor inversion for identifying the fracture mechanism. Dresen et al 4 investigated nucleation and propagation of borehole breakouts and predicted a size effect of the critical pressure required to initiate breakouts.…”