Wei-yao Guo

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.

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

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 (  mm/s), moderate scope (10 mm/s  mm/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 40 mm, 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.

Experimental Investigation of the Influence of Drilling Arrangements on the Mechanical Behavior of Rock Models

Destress drilling method is one of the commonly used methods for mitigating rock bursts. To better understand the influence of drilling arrangements on the destress effect is beneficial for rock burst mitigation. This study experimentally investigated the influence of drilling arrangements (i.e. drilling diameter, number of drilling holes and number of drilling rows) on the mechanical properties of rock models through uniaxial compression tests. The acoustic emission (AE) technique was applied to record and analyze the information of failure processes. Test results show that both the stress–strain curves and the AE characteristics of rock models are controlled by drilling arrangements. Moreover, the uniaxial compressive strength and elastic modulus decrease as increasing the drilling diameter, number of drilling holes or number of drilling rows. The splitting failure accompanied with local shear failure is the main failure mode for specimens with different drilling arrangements, but the drilling arrangements influence the crack propagation and the damage degree. The test results can provide basic experimental data for further study on the destress drilling method.

Influence of Fissure Number on the Mechanical Properties of Layer-Crack Rock Models under Uniaxial Compression

Many case studies have revealed that rock bursts generally occur in the high stress concentration area where layer-crack structures often exist, especially for brittle coal or rock masses. Understanding the mechanical properties of layer-crack rock models is beneficial for rational design and stability analysis of rock engineering project and rock burst prevention. This study experimentally investigated the influence of fissure number on the mechanical properties of layer-crack rock models through uniaxial compression tests. The digital speckle correlation method (DSCM) and acoustic emission (AE) techniques were applied to record and analyze the information of deformation and failure processes. Test results show the following: the bearing capacity of layer-crack specimen decreases compared with intact specimen, but their failure modes are similar, which are the splitting failure accompanied with local shear failure; the nonuniform deformation phenomenon begins to appear at the elastic deformation stage for layer-crack specimens; the AE behavior of intact specimens consists of three stages, that is, active stage, quiet stage, and major active stage, but for layer-crack specimens, it is characteristic by three peaks without quiet stage. In addition, as the fissure number of layer-crack specimens increases, the bearing capacity of specimens decreases, the appearing time of nonuniform deformation phenomenon in the specimen surface decreases, the AE events are denser and denser in each peak stage, and the risk of dynamic instability of layer-crack structure increases. At last, the failure mechanism of layer-crack structure and the related mitigation advices were discussed based on the test results. In general, the novelty is that this paper focuses on the failure mechanism of layer-crack structure directly.

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.