The Kuba coalfield in Xinjiang province is a new block for the exploration and development of coalbed methane in China, and in order to explore the coalbed methane recovery potential the coal reservoir pore-fracture system characteristics need to be researched, and favourable reservoir selection needs to be carried out. The pores, microfissures, and macro-fissures are studied as an organic whole. To characterize the physical properties and microscopic pores of coal reservoirs 4 sets of experiments are performed. A scanning electron microscope is used to study the development characteristics of micro-fissure systems; surface tectonic fissure mapping techniques and fine comparison of coal reservoirs in mines are conducted to study the endogenous and exogenous fissures. The characteristics of porosity and fissure are also studied, including the A coal seam group in the Tariqik formation, the Yangxia formation B coal seam and the Kizinur formation C coal seam. The results obtained in this study demonstrated that two coal seams in the Kuba coalfield, namely A5 and A7, are more favourable reservoirs compared to the other seams based on the perspective of pore-fissures, and these results provide a theoretical basis for coalbed methane exploration and development.
Keywords: Coalbed methane; coal reservoir; porefracture system; reservoir selection; Kuba coalfield
Stabilization of highwall slope by implementing presplit blasting and productivity enhancement by improving the powder factor using controlled blasting at Sharda project of South Eastern Coalfields Ltd. (SECL) was the endeavour of the research team of CSIR-CIMFR in the first trench highwall mining of India. Good fragmentation was achieved through improved rock-explosive interactions and redefined design parameters in the trench which had restricted width and lesser initial powder factor (in m3/kg) due to varying rock-geologic and rock-explosive characteristics. Through systemic analysis of blast-results and implementation of scientific theories combined with the usage of rock parameters and its physico-mechanical properties, it could possible to achieve around 2.0 m3/kg powder factor instead of 1.3-1.4 m3/kg maintaining stable highwall benches with 700or more slope angle. The work led to huge cost benefits in explosive consumption for the company i.e. M/s Cuprum Bagrodia Ltd. and also markedly reduced the environmental implications from production blastsduring day-to-day operations.
Keywords: presplit blasting;trench highwall mining;slope angle; controlled blasting
Longwall mining is one of the most acclaimed and widely used in underground method for coal extraction characterized with high production, productivity and safety potentials. The interaction of powered roof supports with the roof is the key issue in strata mechanics of longwall mining. Longwall coal extraction method though showed the potential of high outputs, never rose to the expectation in India due to factors pertaining to strata mechanics problems, poor spares management, adaptation of technology without suitability analysis and unyielding exertion ethnicity. The paper attempts to discuss the role of different strata monitoring instruments installation, working principle and data monitoring procedures’ in powered support longwall system in India and effective scientific tool to predict various aspects related to strata mechanics of such workings. Load density, height of caving block, distance of fractured zone ahead of the face, overhang of goaf and mechanical strength of the debris above and below the support base have been found to influence the magnitude of load on supports.
Keywords: International longwall trends, cavability of roof, instrumentations
The strength criterion is an extremely important basis for evaluating the stability of surrounding rock and optimizing the support pressure design. In this paper, nine different strength criterions are summarized and simplified based on the reasonable assumption. And then, a new unified criterion equation is established which includes all of the strength theories proposed by this paper. Meanwhile, a new unified closed-form solution for circular opening based on the newly proposed unified criterion equation is deduced with the non-associative flow rule under plane strain conditions. In the plastic zone, four different elastic strain assumptions are applied to solve the plastic zone deformation. The validity of the solution is also verified by comparing with the traditional solution. Finally, the influences of strength criterions, dilation coefficient, elastic strain form of plastic zone and rock mass damage on the mechanical response of surrounding rock are discussed in detail. The research result shows that Tresca(TR) and Von Mises (VM) criterions give a largest plastic zone radius, followed by Inscribe Drucker-Prager (IDP), Mohr-Coulomb (MC) and Middle Circumscribe Drucker-Prager (MDP) criterions and seem to underestimate the self-strength of rock mass. Circumscribe Drucker-Prager (CDP) criterion gives a smallest plastic zone radius and may be overestimated the self-strength of rock mass; Unified Strength Theory (UST0.5), Generalized SMP criterion (GSMP), Mogi- Coulomb (GMC) and Generalized Lade-Duncan (GLD) criterions which reasonably consider the effect of internal principal stresses give an intermediate range and can be strongly recommended for evaluating the mechanics and deformation behaviour of surrounding rock. As the dilation coefficient gradually increases, the dimensionless surface displacement presents the nonlinear increase characteristics; The deformation of plastic zone which are closely related to the strength criterions, are also greatly influenced by the elastic strain assumption in the plastic zone and rock mass damage degree. The assumption that the elastic strain satisfies Hook’s law (Case 3) may be more reasonable compared to the continuous elastic strain (Case 1) and thick-walled cylinders (Case 2) assumptions. In addition, the Young’s modulus power function damage model seems to give more reasonable solution for the deformation of plastic zone and is suggested to be a preferred method for solving plastic displacement. The research results can provide very important theoretical basis for evaluating the tunnel stability and support design reliability for different lithology rock mass in underground engineering.
Keywords: Unified criterion equation; circular tunnel; post-peak elastic strain; Young’s modulus attenuation
The drilling hole is an effective measure used to forecast and prevent rock bursts and is widely used during mining operations. To study the effect of a hole drilled under different stress conditions on the behaviour of a coal specimen, a drilling and reloading experiment is carried out. With increasing vertical load, the failure mode of the specimens is transformed from slow deformation to one entailing an undesirable brittle failure when a hole is drilled. The vertical load at the cut-off point between slow deformation and undesirable brittle failure is equal to, or slightly less than, 65MPa. The vertical stress-strain curve of a coal specimen with a hole could be divided into three stages, and its turning point between the first stage and the second stage is related to the stress on the coal specimen after drilling; acoustic emission events seldom occurred in the first stage, rapidly increased in the second stage, and remained at a higher level throughout the third stage. However, the vertical stress-strain curve of that coal specimen without a hole tended to be linear, and AE event counts gradually increased to a maximum. Due to the differences in the various coal specimens, there are two main failure modes seen in samples with a hole upon reloading. The failure mode is determined by the relationship between the reloading initial crack load and the stress after drilling. When the reloading initial micro-crack load is less than the stress after drilling, the coal specimen cracked slowly, otherwise, the specimens ruptured suddenly. We also found that a hole drilled can reduce the difference between the vertical stress and the confining pressure, and increase AE event counts when the coal specimen is reloaded.
Keywords: Coal specimen; failure characteristics; drilling hole; tri-axial compression; AE events
Based on Vail’s classical sequence stratigraphy theory, the sequence stratigraphy framework of Jurassic Sangonghe formation in Moxizhuang area is studied by using outcrop, logging and logging data. The first flooding surface (FFS) and the maximum flooding surface (MFS) at both sequence boundary and sequence interior are identified.The Sangonghe formation is divided into 2 third-order sequences to identify the low stand systems tract (LST), transgressive system tract (TST) and high stand systems tract (HST). Due to the mutual cutting and superimposition of multi-stage channel sand bodies, the connectivity of subaqueous distributary channel sand bodies in SQ2 sequence of Sangonghe Formation is good, especially in the sedimentary period of fan delta front in the LST of SQ2 sequence. JSQ1 sequence is mainly the development of meandering river point bar sand bodies; The sand bodies in the LST of JSQ2 sequence are mainly developed in the subaqueous distributary channel of the fan delta front. The HST of JSQ2 sequence is mainly the development of sand bodies in shallow lakes and bars. According to the development and evolution of sand bodies in the two sequences of the Sangonghe formation, places atwells Z101 – Z105, Z3 – Z5 and Z102 – Z103 are areas where sand bodies are developed intensively.
Keywords: Junggar basin; Moxizhuang area; Sangonghe formation; sequence stratigraphic framework; system tract; sandstone bodies distribution
In India, various mega infrastructure projects are upcoming for development and growth of the country. Most of these projects are in metros’ or midsize cities. With huge population in the country, mega infrastructure civil engineering are in close proximity to community. Mining is also required to be carried out close to populated villages. Although blasting is most economical, adverse environmental impacts such as fly rock, ground vibration, air blast cannot be completely ignored and eliminated. This paper illustrates existing established technologies and various upcoming technologies which are blastfree and are environment friendly. At initial stage planning excavation, determining compressive strength, tensile strength, geological strength index are essential to decide type of excavation method. Surface miner for coal and limestone mines, ripper dozer, hydraulic rock breaker for secondary breaking are successful for more than two decades in India. Foam injection, plasma technology, chemical methods are emerging technologies. Impact hammer for primary breaking can be deployed in many mines in the country in the vicinity of local community. Excavation without blasting is the present need of technological requirement which is also well accepted as environment friendly.Read more
Vibration is a common phenomenon for all rotating machines but when it reaches beyond the limit then becomes vulnerable and poses as matter of concern. This paper focuses on importance of condition monitoring in-terms of vibration analysis for a dragline machine working in an opencast coal mine of one of the major coal producing companies in India. Vibscanner of Pruftechnik is used for gathering vibration related data and plotting its frequency spectrum.
The data are analysed to prepare suitable sample size and also for finding the root cause of machine vibration. From the analysis a number of contributing factors e.g. misalignment, unbalance and looseness are observed as the main factors behind extensive machine vibration. The in-depth analysis on the machine shows that, though the highest amplitudes recorded does not depict a concern but fluctuations in frequency observed through the spectrums and variations of temperature in bearing housings poses a serious concern. Here, in this paper an attempt has been made to investigate on the generic causes of vibration behind the potent vibration of components and suitable recommendations are provided to overcome the faults as a preventive measure.
Keywords: Dragline, vibration, frequency spectrum, amplitude, misalignment, looseness