Time-dependent deformation and associated failure of roof in underground mines

In underground coal mines, roof falls are a major contributor to injuries and fatalities. Studies have related the occurrence of roof fall to weak immediate roof, high horizontal stress, entry orientation, etc. An often-neglected factor in studies on this topic has been the influence of time-dependent behavior of the roof rock on roof falls. The time-dependent roof failure activity involves both intact and failed rocks. Numerical simulation techniques are available that include time-dependent behavior; however, they lack constitutive models that consider both the intact and the failed behavior of rock. In addition, input properties for the creep models only include the intact rock properties that are determined through constant load (time-dependent) tests. For failed rock, standard creep tests cannot be performed on the rock specimens. This thesis aims to understand this behavior through the following steps: Develop a new laboratory test method Develop a new constitutive model that incorporates the pre- and post-failure behavior Implement the constitutive model into 3DEC Analyze the hypothetical mine geometry using the new constitutive model First, this study develops a new relaxation equation based on Burgers Model. Relaxation tests studied rock specimens in both intact and failed stages. The results from the tests showed significant difference in the viscous property between intact and failed rocks. The results of these relaxation tests determined the viscous parameters with the new relaxation equation. Next, this study constructed numerical models of laboratory sized specimens in 3DEC software. The models incorporated the new relaxation equation, and model runs showed that stress relaxation is significantly present in the post-failure region, rather than in the pre-failure region. Further, a single entry mine model in 3DEC analyzed the influence of strength degradation and the variation in the viscous property on the time-dependent failure process. Variation in the viscous parameter showed significant effects on the failure process in the rock mass. A series of unconfined relaxation tests was performed on sandstone specimens and coal measure rocks. For sandstone, specimens were cored from sandstone blocks; for coal measure rocks, which include shale, sandy shale, and shaly limestone, cores were obtained from mine sites. The test results show that the relaxation behaviors of intact and failed rock specimens are different. The stress relaxation curves in the pre-failure region showed a typical, smooth stress relaxation behavior, while the stress relaxation demonstrates stepped behavior in the post-failure region. For coal measure rocks, the variation in the time-dependent properties of failed rock were insignificant. A viscoelastic-strain-softening constitutive model was developed by incorporating both time-dependent and strain-softening behavior. The model was included in the 3DEC software as a user-defined model. Parametric model runs based on the time-dependent laboratory tests verified the accuracy of the proposed model. Finally, the user-defined model, using hypothetical condition, investigated the influence of various factors on the time-dependent deformation and failure of massive and bedded roof. These simulations investigated the influence of directional horizontal stress, step-wise excavation, and bedding planes on the time-dependent response of mine roof. This research achieved a comprehensive understanding of the time-dependent formation of roof fall

Spatial Non-Locality Induced Non-Markovian EIT in a Single Giant Atom

In recent experiments, electromagnetically induced transparency (EIT) were observed with giant atoms, but nothing unconventional were found from the transmission spectra. In this letter, we show that unconventional EIT does exist in giant atoms, and indicate why it has not been observed so far. Different from these existing works, this letter presents a consistent theory including a real space method and a time delayed master equation for observing unconventional EIT. We discover that this phenomenon is a quantum effect which cannot be correctly described in a semi-classical way as those in recent works. Our theory shows that it can be observed when the time delay between two neighboring coupling points is comparable to the relaxation time of the atom, which is crucial for a future experimental observation. This new phenomenon results from inherent non-locality of the giant atom, which physically forces propagating fields to be standing waves in space and the atom exhibiting retardations in time. Our theory establishes a framework for application of nonlocal systems to quantum information processing.Comment: 6 pages, 3 figures, Comments are welcom

Research on the carbon emission reduction effects of green finance in the context of environment regulations

The rise in carbon emissions has significantly aggravated issues related to climate change. In light of this background, there has been a strong focus on using financial methods to reduce carbon emissions. Based on panel data for China for the period 2003– 2019, we examine the effects of green finance on carbon emissions and the moderating effects of environmental regulations. The results indicate that green finance development alleviates carbon emissions. Meanwhile, our findings on the effects of green finance policies suggest that the implementation of such policies will strengthen the carbon-emission reduction effects of green finance. Additionally, the impacts of green finance on carbon emissions are moderated by administration and public-oriented environmental regulations rather than market-oriented environmental regulations. As the biggest emitter of carbon emissions in the world, China should prioritise the consistent and steady development of green finance and facilitate the green finance legislation. Furthermore, China should enhance the role of marketoriented environmental regulations while considering the synergy between environmental regulations and green finance

Detecting Red Flag of Workplace Crime Using Mobile Data on Abnormal Usage Activities

The purpose of this paper is to investigate how to detect the workplace crime of organizational sales representatives (e.g., sales who work with external customers) through abnormal activities that can be traced by mobile devices and applications. The guardianship capability of organizations is considered as the moderator influencing the monitoring of abnormal usage activities calculated by deep learning. In this study, we conduct event history analysis on the occurrence of workplace crime utilizing a longitudinal panel data set, which comprises 197179 weekly observations in 3 years (2017-2019). Our finding provides evidence that the abnormal activity pattern is an effective signal for identifying workplace crimes. Furthermore, we illustrate how to design monitoring modes based on guardianship capability in order to maximize the effectiveness of mobile monitoring in reducing workplace crimes

Can financial capability improve entrepreneurial performance? Evidence from rural China

The capability of individuals to manage their finances is essential to the outcomes of their entrepreneurial activities. Using panel data from the China Household Finance Survey (C.H.F.S.) in 2013, 2015 and 2017, this article examines how financial capability affects entrepreneurial performance in rural China. The results demonstrate that financial capability is positively correlated with the scale, profitability and sustainability of entrepreneurship, which is robust in consideration of endogeneity. The effects of financial capability are heterogeneous for different entrepreneurs. Furthermore, technology, labour and land act as the mediating variables through which financial capability improves entrepreneurial performance. Therefore, to facilitate entrepreneurial success, it is important to provide entrepreneurs with financial education. Meanwhile, improvements to the financial environment should also be considered. Additionally, financial institutions should combine financial services with factors, such as technology, land and labour, to improve entrepreneurial performance

Review of Current Coal Rib Control Practices

The instability of coal ribs in underground mines continues to result in the injuries and fatalities of mine workers. The proper estimation and evaluation of primary and secondary support for coal ribs is still a challenging problem in the field of ground control science and requires further research and study. Although mining operations have various support design criteria and support methodologies for strata control, most rib support designs are still based on experience and local practices. This review study is intended to summarize the currently applied practices for rib support and control in various countries and mining conditions. Firstly, critical parameters that control the amount and type of required rib support are considered and evaluated. The study revealed that among these parameters that control the stability of coal ribs, mining depth, rib height, cleat orientation/condition, and coal strength are the most significant parameters. Secondly, current rib support application methods were also summarized. Similar to rock mass classification systems, some studies proposed a rib control rating system for practical estimation of the current rib condition and to estimate primary support requirements. These studies are classified and summarized into two groups (categorical and empirical) based on the required inputs and methodologies. Empirically based coal rib rating systems were closely examined, and the usefulness and intuitive aspects of each rating system were compared. This comprehensive literature review demonstrates that the Australian rating system, Analysis and Design of Rib Support (ADRS), and the new U.S. rating system, Coal Pillar Rib Rating (CPRR), are highly applicable for their regions

Review of Current Coal Rib Control Practices

The instability of coal ribs in underground mines continues to result in the injuries and fatalities of mine workers. The proper estimation and evaluation of primary and secondary support for coal ribs is still a challenging problem in the field of ground control science and requires further research and study. Although mining operations have various support design criteria and support methodologies for strata control, most rib support designs are still based on experience and local practices. This review study is intended to summarize the currently applied practices for rib support and control in various countries and mining conditions. Firstly, critical parameters that control the amount and type of required rib support are considered and evaluated. The study revealed that among these parameters that control the stability of coal ribs, mining depth, rib height, cleat orientation/condition, and coal strength are the most significant parameters. Secondly, current rib support application methods were also summarized. Similar to rock mass classification systems, some studies proposed a rib control rating system for practical estimation of the current rib condition and to estimate primary support requirements. These studies are classified and summarized into two groups (categorical and empirical) based on the required inputs and methodologies. Empirically based coal rib rating systems were closely examined, and the usefulness and intuitive aspects of each rating system were compared. This comprehensive literature review demonstrates that the Australian rating system, Analysis and Design of Rib Support (ADRS), and the new U.S. rating system, Coal Pillar Rib Rating (CPRR), are highly applicable for their regions

Review of Current Coal Rib Control Practices

The instability of coal ribs in underground mines continues to result in the injuries and fatalities of mine workers. The proper estimation and evaluation of primary and secondary support for coal ribs is still a challenging problem in the field of ground control science and requires further research and study. Although mining operations have various support design criteria and support methodologies for strata control, most rib support designs are still based on experience and local practices. This review study is intended to summarize the currently applied practices for rib support and control in various countries and mining conditions. Firstly, critical parameters that control the amount and type of required rib support are considered and evaluated. The study revealed that among these parameters that control the stability of coal ribs, mining depth, rib height, cleat orientation/condition, and coal strength are the most significant parameters. Secondly, current rib support application methods were also summarized. Similar to rock mass classification systems, some studies proposed a rib control rating system for practical estimation of the current rib condition and to estimate primary support requirements. These studies are classified and summarized into two groups (categorical and empirical) based on the required inputs and methodologies. Empirically based coal rib rating systems were closely examined, and the usefulness and intuitive aspects of each rating system were compared. This comprehensive literature review demonstrates that the Australian rating system, Analysis and Design of Rib Support (ADRS), and the new U.S. rating system, Coal Pillar Rib Rating (CPRR), are highly applicable for their regions

Study on Vertical Dynamic Characteristics of Composite Sleeper Ballasted Track in Tunnels

In order to study the vertical dynamic characteristics of the composite sleeper ballasted track in tunnels, this paper establishes a dynamic model based on the finite element method, and compares the dynamic response of vehicle, wheel and rail systems, track systems and backfill layer with the type-III concrete sleeper. The research results show that the composite sleeper ballasted tracks’ acceleration of the car body and the wheel-rail force are smaller than that of the type-III sleeper. It can meet the safety of the train and passenger comfort. Because the composite sleeper has good elasticity, The rail displacement and acceleration, the sleeper displacement and acceleration of the composite sleeper are slightly larger than the type-III sleeper ballasted track, but the effect is not great. The composite sleeper has good elasticity and large damping, so that the acceleration of the track bed and the backfill layer is less than that of the type-III sleeper ballasted track. This shows that the composite sleeper has vibration damping characteristics for the track bed and the backfill layer