It is well known that water inrush during excavation is one of the greatest challenges in modern underground engineering. However, the fracture propagation and inrush characteristics induced by excavation and high-pressure water are poorly understood due to the lack of an appropriate experimental apparatus and an online and real-time monitoring approach. Accordingly, a model test system for the simulation of water inrush during excavation and water injection was developed. Acoustic emission (AE) monitoring during excavation and injection was used to investigate the fracture propagation and water-inrush channel formation in the host rock. Three distinct stages were observed in the AEs over time and were related to the fracture propagation during excavation and injection, namely fracture initiation, fracture extension, and unstable fracture growth (fracture network). The AE results exhibited an increase in AE activities and changes in the AE spatial correlation during the excavation and during the increase in injection pressure. A comparison of photographs of the water-inrush locations and the mechanical characteristics obtained from the AE test verified the proposed method. The results provide valuable insights and a suitable method for the investigation of the mechanism of water inrush in underground engineering.
Optically stimulated luminescence (OSL) dating methods have been widely applied in Quaternary glaciology. However, glacigenic deposits are considered in general as problematic for OSL dating, mainly because they are transported shorter distances prior to burial and are usually partially bleached. Thus, most researchers choose glaciofluvial and glaciolacustrine sediments (with relatively longer transportation times) for OSL dating when constraining the age of glaciation. In this study, four samples were collected from a lateral moraine series at Zhuqing Village, northern margin of Queer Shan Mountain, eastern Tibetan Plateau, in order to investigate the applicability of OSL dating for morainic deposits. Quartz grains (38–63 μm) were extracted and measured using single aliquot regenerative-dose (SAR) protocol. Internal checks and dose recovery test show that the SAR protocol is appropriate for equivalent dose (De) determination. The effect of thermal transfer is small for all samples and the recycling ratio for each individual sample is close to unity. The symmetry in the De distributions indicates that quartz grains were well-bleached prior to burial. OSL ages show good agreement with geomorphological and field investigations, and are also concordant with an independent ESR age. It is concluded that: (a) the morainic deposits in Zhuqing were well-bleached and suitable for OSL dating; (b) SAR protocol can be applied to morainic deposits for samples under study. 相似文献