Shan-chao Hu

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

Experimental study of factors affecting fault slip rockbursts in deeply buried hard rock tunnels

As civil tunnelling and mining have progressed to ever greater depths, the magnitudes of the stresses resulting from these activities have also risen significantly, leading to increasingly frequent excavation-induced seismicity and rockbursts that pose a great threat to workers and equipment on site. Although considerable research effort has been devoted to understanding the factors that influence strain bursts, few studies have addressed the factors affecting fault slip rockbursts triggered by slip on discontinuities such as structural planes. Thus, in the present work, shear tests were performed under constant normal load (CNL) conditions on joints with rough surfaces and interlocked asperities to study their shear behaviour and acoustic emission characteristics. The effects of rock type, normal stress, surface morphology, infilling, and shear history on slip rockbursts were investigated. The test results indicated that slip bursts occur more easily in granite joints because of either sudden and violent post-peak stress drops or stress drops during stick slip. Static shear failure dominated in marble and cement mortar joints, except when the joint surface was extremely irregular, and rockbursts took place when asperities were sheared off or when tensile ruptures occurred on the joint. The value of the stress drop immediately after peak stress and the value of the average stress drop during stick slip of granite joints both increased with normal stress; thus, the probability and intensity of rockbursts rose with normal stress. The failure modes of the joints were strongly influenced by the normal stress level; fillings and previous shearings (i.e. a shear history) reduce the risk of rockbursts because they reduce the amount energy released.

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.

Numerical Investigation of Influences of Drilling Arrangements on the Mechanical Behavior and Energy Evolution of Coal Models

Destress drilling method is one of the commonly used methods for mitigating rock bursts, especially in coal mining. To better understand the influences of drilling arrangements on the destress effect is beneficial for rock burst mitigation. This study first introduced the rock burst mitigation mechanism of the destress drilling method and then numerically investigated the influences of drilling arrangements on the mechanical properties of coal models through uniaxial compression tests. Based on the test results, the energy evolution (i.e., the energy dissipation and bursting energy indexes) influenced by different drilling arrangements was analyzed. When the drilling diameter, the number of drilling holes in one row, or the number of drilling rows increases, the bearing capacity of specimens nonlinearly decreases, but the energy dissipation index increases. In addition, the drilling diameter or the number of drilling holes in one row affects the failure mode weakly, which is different from that of the number of drilling rows. Consequently, the bursting energy index decreases as increasing the drilling diameter or the number of drilling holes in one row, but as increasing the number of drilling rows, the variation law of bursting energy index is not obvious. At last, the influencing mechanism of drilling arrangement on the rock burst prevention mechanism of the destress drilling method was discussed and revealed.

Multiparameter Monitoring and Prevention of Fault-Slip Rock Burst

Fault-slip rock burst is one type of the tectonic rock burst during mining. A detailed understanding of the precursory information of fault-slip rock burst and implementation of monitoring and early warning systems, as well as pressure relief measures, are essential to safety production in deep mines. This paper first establishes a mechanical model of stick-slip instability in fault-slip rock bursts and then reveals the failure characteristics of the instability. Then, change rule of mining-induced stress and microseismic signals before the occurrence of fault-slip rock burst are proposed, and multiparameter integrated early warning methods including mining-induced stress and energy are established. Finally, pressure relief methods targeting large-diameter boreholes and coal seam infusion are presented in accordance with the occurrence mechanism of fault-slip rock burst. The research results have been successfully applied in working faces 2310 of the Suncun Coal Mine, and the safety of the mine has been enhanced. These research results improve the theory of fault-slip rock burst mechanisms and provide the basis for prediction and forecasting, as well as pressure relief, of fault-slip rock bursts.