Bing-Rui Chen

Rock Burst Intensity Classification Based on the Radiated Energy with Damage Intensity at Jinping II Hydropower Station, China

Based on the radiated energy of 133 rock bursts monitored by a microseismic technique at the Jinping II hydropower station, in Sichuan province, China, we analyzed the advantages and disadvantages of qualitative classification methods for the rock burst intensity. Then, we investigated the characteristics, magnitude, and laws of the radiated energy, as well as the relationship between the rock burst radiated energy and intensity. Then, we selected the energy as an evaluation index for the rock burst intensity classification, and proposed a new rock burst intensity quantitative classification method, which utilized the hierarchical clustering analysis technique with the complete-linkage method. Next, we created a new set of criteria for the quantitative classification of the rock burst intensity based on radiated energy and surrounding rock damage severity. The new criteria classified the rock burst intensity into five levels: extremely intense, intense, moderate, weak, and none, and the common logarithms of the radiated energy of each level were >7 lg(E/J), >4 lg(E/J) and <7 lg(E/J), >2 lg(E/J) and <4 lg(E/J), >1 lg(E/J) and <2 lg(E/J), and <1 lg(E/J), respectively. Finally, we investigated the factors influencing the classification, and verified its feasibility and applicability via several practical rock burst examples.

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.

Time-dependent damage constitutive model for the marble in the Jinping II hydropower station in China

To accurately describe the damage creep properties of marble, especially during the acceleration creep phase, creep testing was performed on the marble in the Jinping II hydropower station in China. Based on the experimental results, a time-dependent damage constitutive model was proposed in terms of fractional calculus theory and damage variables to describe these time-dependent damage characteristics. The time-dependent constitutive equations were derived for constant loading levels below and above the marble’s long-term strength. The robustness and parameter sensitivity of the proposed model were analysed by utilizing data of creep testing. The results of the analysis showed that the proposed model could describe not only the attenuation and steady-state creep of marble but also the acceleration creep characteristics and negative exponential attenuation law of the yield strength over time when the constant loading was above the long-term strength. These are crucial to failure prevention during rock engineering construction and operating periods.

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.

CSV-PSO and Its Application in Geotechnical Engineering

Since the particle swarm optimization (PSO), being a stochastic global optimization technique,was proposed by Kennedy and Eberhart in 1995(Kennedy & Eberhart, 1995; Eberhart & Kennedy, 1995), it has attracted interests of many researchers worldwide and has found many applications in various fields such as autocontrol, machinofacture, geotechnical engineering et al. (Mark & Feng, 2002; Dong et al, 2003; Su & Feng, 2005). There are two main reasons: one is the preferable performance of PSO, the other is its simplicity in operation. In order to avoid the premature and divergence phenomena often occurring in optimization process by using the PSO, especially for multi-dimension and multi-extremum complex problems, as well as to improve the convergence velocity and precision of the PSO to a maximum extent, many kinds of schemes were introduced to enhance the PSO. The following are some representative schemes: inertia weight (Shi & Eberhart, 1998), constriction factor (Eberhart & Shi, 2000), crossover operation (Lovbjerg et al, 2001) and selfadaptation (Lu & Hou, 2004). The PSO modified by introducing the inertia weight or crossover operation or self-adaptation technique has an excellent convergence capability with a decreased velocity of convergence. The PSO with a constriction factor can reach the global goal quickly, but the divergence phenomenon sporadically occurs in the optimized solutions. So we proposed an improved PSO, named CSV-PSO, in which flight velocity limit and flight space of particles are constricted dynamically with flying of particles (Chen & Feng, 2005). A great deal of numerical calculation indicates CSV-PSO has a faster convergence velocity, greater convergence probability and is a more stable. But this algorithm with a random number generator having time as its random seed may obtain different goal values at different running time. It is difficult to determine uniqueness of solution, especially for complicated engineering problem. So a random number generator with mixed congruential method is introduced to solve uncertainty of solution, and its random seed can be set artificially. To indicate advantage of the proposed algorithm, it is compared with other modified vertions and sensitivity analysis is carried out for its several important parameters, which the five benchmark functions are as examples. The results show CSV-PSO with a new random number generator is excellent. Back analysis which is based on monitoring information with numerical method is a very time-consuming job in geotechnical

Laboratory creep tests for time-dependent properties of a marble in Jinping II hydropower station

Abstract In order to investigate the time-dependent behaviors of deep hard rocks in the diversion tunnel of Jinping II hydropower station, uniaxial creep tests were carried out by using the triaxial testing machine RC-2000. The axial compressive load was applied step by step and each creep stage was kept for over several days. Test results show that: (1) The lateral deformation of rock specimens is 2–3 times the axial compressive deformation and accelerates drastically before damage, which may be employed as an indicator to predict the excavation-induced instability of rocks. (2) The resultant deformation changes from compression to expansion when the Poisson’s ratio is larger than 0.5, indicating the starting point of damage. (3) In the step-loading stages, the Poisson’s ratio approximately remains constant; under constantly imposed load, the Poisson’s ratio changes with elapsed time, growing continuously before the specimen is damaged. (4) When the applied load reaches a certain threshold value, the rock deteriorates with time, and the strength of rocks approximately has a negative exponent relation with time. (5) The failure modes of the deep marble are different in long- and short-term loading conditions. Under the condition of short-term loading, the specimen presents a mode of tensile failure; while under the condition of long-term loading, the specimen presents a mode of shear failure, followed by tensile failure.

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.

A Self-adapting Algorithm for Identifying Rheology Model and Its Parameters of Rock Mass

As it is difficult to previously determine rockmass rheology constitutive model using phenomena methods of mechanics, so a new self-adapting system identification method, a hybrid genetic programming (GP) with the chaos-genetic algorithm(CGA) based on self-rheological characteristic of rock mass, is proposed. Genetic programming is used for exploring the model’s structure and the chaos-genetic algorithm is produced to identify parameters (coefficients) in the tentative model. The optimal rheological model is determined by mechanical and rheological characteristic, important expertise ect and can describe rheological behavior of identified rock mass perfectly. The assistant tunnel B of Jinping-2 hydropower station is used as an example for verifying the proposed method. The results show that the algorithm is feasible and has great potential in finding new rheological models.

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.