Yun-liang Tan

Case histories of rock bursts under complicated geological conditions

During the past decade’s exploitation of coal seams in Muchengjian Mine in Jingxi Coalfield, there were nearly thirty rock burst events, which hindered the safe and efficient coal production. Two typical mining areas were selected for analysis where almost half of rock burst events occurred. The research was aimed at finding connections between the occurrence of rock bursts and geological characteristics. The temporal and spatial characteristics of rock bursts were described in detail, the geological characteristics were investigated carefully, and the possible reasons for rock bursts were analyzed. The details documented in these cases not only provide an essential reference value for understanding the development mechanism of rock bursts, but also provide a basis for selecting control measures and optimizing related technical parameters during tunneling or mining under complicated geological conditions.

Case Studies of Rock Bursts Under Complicated Geological Conditions During Multi-seam Mining at a Depth of 800 m

A serious rock burst (“4.19” event) occurred on 19 April 2016 in the No. 4 working face of the No. 10 coal seam in Da’anshan Coal Mine, Jingxi Coalfield. According to the China National Seismological Network, a 2.7 magnitude earthquake was simultaneously recorded in this area. The “4.19” event resulted in damage to the entire longwall face and two gateways that were 105xa0m in long. In addition, several precursor bursts and mine earthquakes had occurred between October 2014 and April 2016 in the two uphill roadways and the No. 4 working face. In this paper, the engineering geological characteristics and in situ stress field are provided, and then the rock burst distributions are introduced. Next, the temporal and spatial characteristics, geological and mining conditions, and other related essential information are reviewed in detail. The available evidence and possible explanations for the rock burst mechanisms are also presented and discussed. Based on the description and analysis of these bursts, a detailed classification system of rock burst mechanisms is established. According to the main causes and different disturbance stresses (i.e., high/low disturbance stresses and far-field/near-field high disturbance stresses), there are a total of nine types of rock bursts. Thus, some guidelines for controlling or mitigating different types of rock bursts are provided. These experiences and strategies not only provide an essential reference for understanding the different rock burst mechanisms, but also build a critical foundation for selecting mitigation measures and optimizing the related technical parameters during mining or tunnelling under similar conditions.

Research on the Rockburst Tendency and AE Characteristics of Inhomogeneous Coal-Rock Combination Bodies

In order to research the influence of homogeneity on the rockburst tendency and on AE characteristics of coal-rock combination body, uniaxial compressive tests of inhomogeneous coal-rock combination bodies obeyed by the Weibull distribution were simulated using particle flow code (). Macromechanical properties, energy evolution law, and AE characteristics were analyzed. The results show that (1) the elastic modulus homogeneity has an exponential relation with macroscopic modulus , and the bonding strength homogeneity has an exponential relation with uniaxial compressive strength ; (2) the rockburst tendency of the coal-rock combination body will increase with the increase of or , and is the leading factor influencing this tendency; and (3) both the change law of AE hits and lasting time in different periods of AE characteristics are influenced by , but just influences the lasting time. The more inhomogeneous the coal-rock combination body is, the shorter the lasting time in booming period of AE characteristics will be. This phenomenon can be used to predict the rockburst tendency of the coal-rock combination body.

Impact of Bedding Planes on Mechanical Properties of Sandstone

Currently, many underground structures are built in rock masses with bedded structures, such as coal mine roadways (Ning et al. 2017; Tan et al. 2015a, b, 2017), chemical and nuclear waste repositories (Yang et al. 2013) and unconventional oil drilling (Meier et al. 2015). The bedding planes have a considerable influence on the behavior of the rock mass, and it is considered to be critical for slope stability (Ghazvinian et al. 2010). Hence, engineering design and stability analysis of underground structure need to consider the anisotropic properties of bedded rock masses. The mechanical parameters of bedded rock masses are related to not only the intact rock but also the distribution and properties of the bedding planes. Existing studies have focused on the mechanical properties of bedded rock and carried out conventional compression tests with various loading angles (Niandou et al. 1997; Al-Harthi 1998; Ghazvinian and Hadei 2012; Martı́nez and Schmitt 2013; Gao et al. 2015; You et al. 2015) to study the deformation, compressive strength and other anisotropic features. In addition, some investigators considered the anisotropic features of the tensile strength of bedded rock and conducted tension tests with various loading angles (e.g., Butenuth et al. 1994; Chen and Hsu 2001; Tavallali and Vervoort 2010a, b; Dan et al. 2013; Ghazvinian et al. 2013). Based on these research findings, various anisotropic failure criteria and constitutive models have been proposed. A typical one was the single plane of weakness theory proposed by Jaeger (1960). In addition, Duveau and Shao (1998) summarized the previous anisotropic failure criterions in three aspects: mathematical continuous criterion, empirical continuous models and discontinuous weakness plane theories, and he also put forward a modified singleplane-weakness theory (Duveau and Shao 1998). Thereafter, scholars made some extension and development based on the existing failure criteria and constitutive models (e.g., Tien and Kuo 2001; Hu et al. 2013; Asadi and Bagheripour 2015; Mohammad et al. 2015). Even though the data from compression and tensile tests of rock with different bedding directions are substantial, the failure mechanisms of the rock with different bedding directions subjected to compression and tension remain unclear. To address these problems, laboratory tests were carried out on interbedded sandstone under various loading angles and stress levels, and by means of scanning electron & Yun-liang Tan yunliangtan@163.com

Effect of Saturation Time on the Coal Burst Liability Indexes and Its Application for Rock Burst Mitigation

Coal seam water infusion is one of the widely used techniques for rock burst mitigation, and the saturation time of coal is one of the essential factors influencing the effectiveness of water infusion. To analyze the effect of saturation time on coal burst liability indexes, bursting liability indexes of coal specimens taken from No. 2 mining face in Changgouyu Mine in Beijing were tested under natural state and different saturation time. Compared with coal specimens under natural state, the uniaxial compressive strength, elastic strain energy index, and bursting energy index all decrease in different degrees as the saturation time increases. The dynamic failure duration, however, shows an opposite tendency. When the saturation time is 0–6xa0days, the bursting liability indexes vary significantly, but when the saturation time is longer than 6xa0days, this phenomenon is not very obvious. When the saturation time increases from 0 to 6xa0days, the uniaxial compressive strength, elastic strain energy index, and bursting energy index decreases from 18.31 to 7.15xa0MPa, 2.59 to 1.25, 3.04 to 1.20, respectively, but when the saturation time increases from 6 to 8xa0days, their corresponding increments are only 0.02–0.05. Moreover, the time of coal seam water infusion in No. 2 mining face was designed 6–8xa0days based on the test results. Practical experiences show that excellent destress effect was achieved by water infusion. After coal seam water infusion, the average moisture content of coal seam increases from 0.85 to 1.26%, and the width of destress zone increases from 0–4 to 0–6xa0m.

Bolt pull-out tests of anchorage body under different loading rates

Based on the force analysis and mechanical transmission mechanism of grouting bolts, the self-developed test apparatus for interfacial mechanics is used to study the distribution rule of axial force and interfacial stress of bolts in anchorage body. At the same time, pull-out tests of anchorage body are simulated with the particle flow code software , and stress distribution and failure patters are researched under different loading rates. The results show that the distribution of axial force and interfacial shear stress is nonuniform along the anchorage section: axial force decreases, shear force increases first and then decreases, and the maximum value of both of them is closed to the pull-out side; with the increase of loading rates, both of axial force and interfacial shear stress show a trend of increase in the upper anchorage section but changes are not obvious in the lower anchorage section, which causes serious stress concentration; failure strength of pull-out and loading rates show a linear correlation; according to loading rates’ impact on the anchoring effect, the loading rates’ scope can be divided into soft scope ( u2009mm/s), moderate scope (10u2009mm/s u2009mm/s).

Failure mechanism of layer-crack rock models with different vertical fissure geometric configurations under uniaxial compression:

Many case studies have revealed that rock bursts generally occur in high stress concentration areas where layer-crack structures often exist, especially for brittle coal or rock masses. Understanding the mechanical behavior of layer-crack rocks is beneficial for rational design and stability analysis of rock engineering project and rock burst prevention. This study numerically investigated the influence of vertical fissure geometric configurations on the mechanical behavior of layer-crack rock models through uniaxial compression tests. Results reveal that the deformation and strength behaviors of layer-crack specimens depend on the vertical fissure geometric configurations, which also influence the crack evolution process. In aspect of failure mode, it is splitting failure or shear failure of the whole layer-crack specimen when the fissure length is smaller than 40u2009mm, but it is splitting failure or shear failure of supporting bodies in other conditions. Among the three factors, the influencing degree in order from strong to weak is fissure number, fissure length, and fissure width. Meanwhile, the influence of fissure geometric configurations on the failure mechanism of layer-crack structure and the occurrence mechanism of rock burst were revealed. In addition, some advices for keeping the stability of layer-crack structure and mitigating rock bursts were given.

Compression Creep Characteristics and Creep Model Establishment of Gangue

How to describe the compression creep behavior of gangue is very essential for the design of gangue backfilling mining. In this paper, compression tests of two kinds of gangue are studied, finding that logarithmic function is suitable for describing its equal-time stress–strain relationship. Stress–strain–time relationship is proposed through modifying the Singh–Mitchell creep model based on the analysis of the test result, and this model can provide a design basis for gangue backfilling technology. Back analysis indicates that this model can basically describe the creep behavior of gangue with a few parameters that are easy to be determined. This research can provide a reference on the design of gangue backfilling mining, and on the subsidence value estimation.

Pattern Recognition of Signals for the Fault-Slip Type of Rock Burst in Coal Mines

The fault-slip type of rock burst is a major threat to the safety of coal mining, and effectively recognizing its signals patterns is the foundation for the early warning and prevention. At first, a mechanical model of the fault-slip was established and the mechanism of the rock burst induced by the fault-slip was revealed. Then, the patterns of the electromagnetic radiation, acoustic emission (AE), and microseismic signals in the fault-slip type of rock burst were proposed, in that before the rock burst occurs, the electromagnetic radiation intensity near the sliding surface increases rapidly, the AE energy rises exponentially, and the energy released by microseismic events experiences at least one peak and is close to the next peak. At last, in situ investigations were performed at number 1412 coal face in the Huafeng Mine, China. Results showed that the signals patterns proposed are in good agreement with the process of the fault-slip type of rock burst. The pattern recognition can provide a basis for the early warning and the implementation of relief measures of the fault-slip type of rock burst.

Load transfer mechanism and reinforcement effect of segmentally yieldable anchorage in weakly consolidated soft rock

Mine disasters, such as large deformation, floor heave, and roof fall, occur extremely easily in weakly consolidated soft rock strata in western China, posing enormous challenges to traditional anchorage support design. To avoid tensile failure of bolts as a result of the superposition effect of stress accumulation, a segmentally yieldable anchorage support, taking into consideration the different failure zones in surrounding rock, is presented in this paper. First, load transfer mechanisms and the process of anchorage failure are analyzed for end anchorage, full-length anchorage, and segmentally yieldable anchorage based on numerical pull-out tests. Results show that the load transfer follows a multipeak chain-like trend in the case of multipoint segmental anchorage, and that the peaks of stress attenuate slowly. Therefore, the proposed anchorage type can leverage the shear strength effectively. Furthermore, numerical models for the applications of the aforementioned three different anchoring modes to weakly consolidated soft strata are established. Results indicate that segmentally yieldable anchorage can withstand larger tensile deformation and surrounding rock deformation. Moreover, the bolt shows higher strength reservation. A combination of these characteristics is conducive to controlling deformation and damage during roadway excavation.