Research on highly-weathered swelling granite roadway support technology

Aug 2017 / by Fan Shen, Jun Du and Guojian Feng

Granite can be easily weathered and often gets disintegrated and argillated when wet. In this paper, we take the granite roadway support work as the research object. Through analysis by X-ray diffraction and scanning electron microscope (SEM), we find that granite contains a great amount of montmorillonite, which is a hydrophilic mineral, and that the rock mass will be rapidly disintegrated when absorbing water. We use the 3D non-linear finite element method to build an elasto-plastic numerical calculation model for the granite roadway, analyze the shotcretingbolting support schemes with different support parameters, optimize the technical parameters of shotcreting-bolting support from the stress state of the surrounding rock, roadway safety factor and distribution of rock plastic zones, and recommend reinforcing the roadway with 1.8m anchor bolts with spacing of 1.0m × 1.0m and shotcrete with a thickness of 5cm. At the same time, the support monitoring data show that the deformation of the roadway can be clearly divided into three stages – roadway excavation impact, deformation control and stable deformation stages. For a weathered roadway that can be easily disintegrated, it will take the support structure about 3 months to be stabilized. By that time, the anchor bolts and concrete will coordinate well with the deformation of the surrounding rock and have good supporting effects.
Keywords: Granite; disintegration; argillization; shotcreting-bolting support; monitoring

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A step toward achieving a zero accident potential in Indian mining industry

Aug 2017 / by Aveek Mangal, Falguni Sarkar and P. S. Paul

Mining has been and continues to be an industry where the concern for miners’ safety is of great importance. Even though the mining industry has experienced a considerable improvement in the reduction of accident rates in underground and surface mines, further reduction of accident rates is necessary. In general safety problems in the Indian mining industry in terms of the reduction of accidents and injuries are mainly being addressed through reactive measures of hazard control rather than proactive measures. Though, mining employs one per cent of the global workforce, but it is disproportionately responsible for eight per cent of fatal workplace accidents due to the nature of the work, injuries and deaths which have historically been accepted as an inevitable consequence of mining. With this track record, focus on safety improvement, and all the improvements that have been made over the years, we believe that our industry are in a position to drive for the ultimate goal – that NO ONE is hurt in mines. The tool for achievement is for each manpower company to develop a zero accident potential with their measure of achievement being zero first aids, injuries or illnesses.
Keywords: International safety status, statistical analysis, safety compliance and outcomes, zero accident potential

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Instability analysis of anchorage supporting in soft rock roadways based on strain softening

Aug 2017 / by Lei Wang Yao Wei and Yongyi Ren

In view of the problems such as spray layer peeling-off, reduced anchoring force and serious floor heave in the weakly cemented soft rock roadway in the west region, we took samples from the sandy mudstone formation in the main haulage roadway of Luxin Coal Mine in Inner Mongolia and performed triaxial compression tests at different confining pressure in the lab. The test data show that the post-peak strain behaviour of the mudstone is obviously softened and there exists residual deformation, thus the trilinear strain-softening model is more suitable for analysis. We made fish corrections to the bi-linear strain-softening model in FLAC to achieve the numerical application of the model. The verification model shows that the tri-linear strain-softening model better describes the deformation features of mudstone. We analyzed the construction stability of the mudstone roadway and conducted evaluation based on the softening index. The results show that due to the increasing softening degree and softening depth of the mudstone roadway, the shotcreting support system has no obvious effect in controlling the deformation of the surrounding rock, and that the bolt axial force first increases and later decreases, losing its retaining effect.
Keywords: Weakly cemented mudstone, triaxial compression, strain softening, degree of softening, numerical simulation

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Effect of uniaxial compressive strength of rock on penetration rate and bit wear rate of drill

Aug 2017 / by Sandeep Kumar Sahoo and B. S. Choudhary

Drillability plays a crucial role in increasing the capability of blasthole drills in drilling and thereby contributing valuable input for the mining industry. The productivity of the mines and the life of the machines are directly dependent on the wear rate of the drill bit. In this light, an investigation was conducted to illustrate the relationship between the uniaxial compressive strength (UCS) of the rock, the penetration rate of the drilling machine and the bit wear-out rate at overburden benches of a surface coal mine. The wear-out rate of drilling bit estimated from digital imaging of the diametrical distribution of button bits obtained from imaging software, that was taken ‘Before’ and ‘After’ drilling. The UCS of rock mass was measured using Schmidt Hammer while wear-out rate of the drill bit was measured through computer software. The results obtained from the experimental observations and graphical plot shows that as the UCS (in N/mm2) increasing from 27.5 to 42.46 the penetration rate (in mm/s) decreases from the 30 to 14 and wear-out rate (in mm2/meter of the hole drilled) are increasing from 0.339 to 1.05.
Keywords: Rotary-percussive drilling, uniaxial compressive strength, wear-out rate, penetration rate, drill bits

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Experimental study on reservoir acidification and application effect of interstratified illite/smectite clay

Aug 2017 / by Qu Xiyu, Dong Xiaofang, Liu Zhen, Zhang Shoupeng, Wang Weiqing and Fang Zhengwei

This paper investigates and studies the advantages and disadvantages of existing acidification plans at home and abroad. In view of the high content of clay matrix in the glutenite reservoir, and in accordance with the mix proportion plan of “HF/HBF4+HCl+oxidants/additives”, the author selects different types of chemical reagents and concentrations, and conducts hydrothermal experiments on smectite and illite by different acidification plans. In the light of mass loss and variation in ion concentration, it is determined through preliminary selection and optimal selection that the best acidification plan is “15%HCl +8%HBF4 + 30%H2O2 + 9%NH4F”. The proposed acidification plan is applied to clay mineral samples purified from the cores and real core samples, and its effect is analyzed in the light of mass loss, permeability changes, variation in ion concentration, and with the aid of Scanning Electron Microscope (SEM). The experiment reveals that over 40% of the mixed clay minerals are corroded in the reaction, the core samples feature significant increase in the number of corrosion holes and fissures and exponential growth in permeability, and the corroded minerals are mainly interstratified illite/smectite (I/S) and illite. The findings demonstrate that the proposed acidification plan has a good effect on interstratified I/S clay.
Keywords: Clay minerals, acidification experiment, application effect, oilfield development

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On the deformability and mobility of clay-cement grout

Aug 2017 / by Jingtai Ran, Kepeng Hou, Niyan Dai and Kegang Li

As a low-cost grouting material, clay-cement grout has been increasingly applied to grouting construction and other aspects. The current research on its properties is, however, limited to physical mechanical properties such as the compressive strength of its hardened body, permeation coefficient, setting time and stability. As a comparison, there are few studies of the deformability and mobility of grouting materials. To enrich this research area, we used NXS-11A rotational viscometer to gauge the relationship between the change of intermolecular shear force and the change of intermolecular shear rate as our test method. The corresponding results show that the clay-cement grout can be regarded as a type of viscoplastic fluid because its’ deformability and mobility curves resemble the viscoplastic fluid counterparts to a large extent.
Keywords: Grouting material, property, deformability and mobility curve

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Research on the application of chaos dynamics in coal mine risk prediction

Aug 2017 / by Kun Liu

As an extremely complex dynamic phenomenon in coal mine, gas outburst is an urgent problem to be resolved in international mining engineering and engineering mechanics. This paper puts forward the dynamic inversion theory based on the comprehensive hypothesis of coal and gas outburst, which takes the process of coal and gas outburst as a dynamic evolution process. With the aid of chaos dynamics theory, a new prediction method for chaotic time series prediction is creatively proposed and a good fitting effect is obtained.
Keywords: Coal and gas outburst; dynamic inversion; chaotic time series; prediction

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