Guang-Liang Feng

Studies on the evolution process of rockbursts in deep tunnels

Abstract This paper focuses on the evolution processes of different types of rockbursts occurring in deep tunnels. A series of laboratory tests and in-situ monitoring in deep tunnels excavated by tunnel boring machine (TBM) and drill-and-blast (D&B) method have been conducted to understand the mechanisms and processes of the evolution of different types of rockbursts, including strain rockburst, strain-structure slip rockburst, immediate rockburst and time-delayed rockburst. Three different risk assessment methods are proposed to evaluate the intensity and potential failure depth of rockbursts. These methods can be applied before excavation and the results can be updated according to the real-time information during excavation. Two micro-seismicity based real-time warning systems have been established for predicting various intensities of rockbursts, such as slight, moderate, intensive and extremely intensive rockbursts. Meanwhile, the probability and intensity of the rockburst are also given. The strategy for excavation and support design has been suggested for various intensities of rockbursts before excavation. The strategy for dynamic control of the rockburst evolution process is also proposed according to the monitoring results. The methodology has been successfully applied to rockburst risk reduction for deep tunnels at Jinping II hydropower project. The results have illustrated the applicability of the proposed methodology and techniques concerning rockbursts.

ISRM Suggested Method for In Situ Microseismic Monitoring of the Fracturing Process in Rock Masses

The purpose of this ISRM Suggested Method is to describe a methodology for in situ microseismic monitoring of the rock mass fracturing processes occurring as a result of excavations for rock slopes, tunnels, or large caverns in the fields of civil, hydraulic, or mining engineering. In this Suggested Method, the equipment that is required for a microseismic monitoring system is described; the procedures are outlined and illustrated, together with the methods for data acquisition and processing for improving the monitoring results. There is an explanation of the methods for presenting and interpreting the results, and recommendations are supported by several examples.

Microseismic monitoring of columnar jointed basalt fracture activity: a trial at the Baihetan Hydropower Station, China

Severe stress release has occurred to the surrounding rocks of the typically columnar jointed basalt after excavation at the Baihetan Hydropower Station, Jinsha River, China, where cracking, collapse, and other types of failure may take place occasionally due to relaxation fracture. In order to understand the relaxation fracture characteristics of the columnar jointed basalt in the entire excavation process at the diversion tunnel of the Baihetan Hydropower Station, real-time microseismic monitoring tests were performed. First, the applicability of a geophone and accelerometer was analyzed in the columnar jointed basalt tunnel, and the results show that the accelerometer was more applicable to the cracking monitoring of the columnar jointed basalt. Next, the waveform characteristics of the microseismic signals were analyzed, and the microseismic signals were identified as follows: rock fracture signal, drilling signal, electrical signal, heavy vehicle passing signal, and blast signal. Then, the attenuation characteristics of the microseismic signals in the columnar jointed basalt tunnel were studied, as well as the types and characteristics of the columnar jointed basalt fracture. Finally, location analysis was conducted on the strong rock fracture events, in which four or more sensors were triggered, to obtain the temporal and spatial evolution characteristics and laws of the columnar jointed basalt relaxation fracture after excavation. The test results are not only of important reference value to the excavation and support of diversion tunnel at the Baihetan Hydropower Station, but also of great referential significance and value to the conduction of similar tests.

Monitoring, Warning, and Control of Rockburst in Deep Metal Mines

Abstract This paper reviews the recent achievements made by our team in the mitigation of rockburst risk. It includes the development of neural network modeling on rockburst risk assessment for deep gold mines in South Africa, an intelligent microseismicity monitoring system and sensors, an understanding of the rockburst evolution process using laboratory and in situ tests and monitoring, the establishment of a quantitative warning method for the location and intensities of different types of rockburst, and the development of measures for the dynamic control of rockburst. The mitigation of rockburst at the Hongtoushan copper mine is presented as an illustrative example.

Chapter 9 – Microseismic Monitoring Method of the Rockburst Evolution Process

Abstract This chapter describes the microseismic monitoring method of the rockburst evolution process in tunnels or large caverns in the fields of civil, hydraulic, or mining engineering. Several key points (e.g., equipment selection, measures for improving monitoring quality, data analysis, and results presentation) are illustrated in detail by a typical intense rockburst case in the Jinping II tunnels.

Characteristic Stress Levels and Brittle Fracturing of Hard Rocks Subjected to True Triaxial Compression with Low Minimum Principal Stress

In this study, true triaxial compression tests were carried out on three types of hard rocks (i.e., granite, marble and sandstone) using rectangular prismatic specimens (50 × 50 × 100 mm3) with low minimum principal stress σ3, and various intermediate principal stresses σ2. The main purposes were to establish the relationship between the characteristic stress levels (i.e., crack initiation stress, crack damage stress and peak stress) and the corresponding principal stresses and to investigate the brittle fracturing process of hard rocks near excavation boundaries. The test results indicated that the stress–strain curves were primarily characterized by the linear-elastic–brittle behavior. The failure planes of the specimens in the tests were found to be adjacent to the σ3 loading surface, and almost parallel to the σ1–σ2 plane, which were analogous to the spalling of the surrounding rock. With the aid of scanning electron microscopy, it was shown that cleavage fractures accounted for the majority of the fracture morphology in the sandstone specimens. Two revised methods were developed to determine the crack initiation stress of hard rocks under true triaxial compression, and these characteristic stress levels could be appropriately fitted by utilizing both the parabolic and power functions. Although the power function achieved better fitting results, the parameters in the parabolic function could be associated with the tensile cracks induced during the loading process. The influence of intermediate principal stress on the strength, deformation and failure was significant. In addition, the brittle fracturing process could be illustrated by the crack-induced strains in three principal stress directions.