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Ya K.,Anhui University of Science and Technology | Feng C.,Anhui University of Science and Technology | Feng C.,Key Laboratory of Integrated Coal Exploitation and Gas Extraction of Anhui Province | Zegong L.,Anhui University of Science and Technology
Electronic Journal of Geotechnical Engineering | Year: 2014

Due to the conventional modified Cam-clay model can not describe the cohesion properties and the difference between yield strengths of tension and compression for geomaterials, a modified Cam-clay model with non-associated flow rule is proposed, and this model can take cohesion on meridian plane and the difference between yield strengths of tension and compression on deviatoric plane into account. Backward implicit Euler constitutive integration algorithm for proposed modified Cam-clay model and its numerical implementation method is systematically discussed. Using the built-in user-defined material interface of ABAQUS software, subroutine UMAT is redeveloped for proposed modified Cam-clay model. And using this subroutine UMAT, a series of numerical simulations are conducted, and comparisons between calculated results of proposed modified Cam-clay model and the calculated results of ABAQUS software as well as previous test data of Belgian Boom clay are conducted. The study results show that the proposed modified cam-clay model is fully consistent with the characteristics of Cam-clay model, the calculated results of subroutine UMAT and proposed modified cam-clay model in this paper are correct and reliable, and the proposed modified cam-clay model has a higher calculation accuracy and good stability.


Cai F.,Anhui University of Science and Technology | Cai F.,Key Laboratory of Integrated Coal Exploitation and Gas Extraction of Anhui Province | Liu Z.-G.,Anhui University of Science and Technology
Meitan Xuebao/Journal of the China Coal Society | Year: 2016

Long-time and high-efficiency CBM drainage is a problem for current CBM disasters control and CBM resource utilization. Numerical simulation and engineering experiments were conducted to systematically study the underground hydraulic fracturing technique for greatly increasing the permeability of coal seam. The research results show that there are five stages in the process of hydraulic fracturing, including energy and stress accumulating, micro cracks growing, local damage, local cracks growing and connecting, and fail to resistance of coal and rapid expansion of cracks. A large number of cracks created by hydraulic fracturing, and swelling effect of roof and floor make coal seam pressure relieved, thus, the permeability of coal seam is greatly increased. The engineering experiments validate the migration path of water, and it is in agreement with numerical simulation results. A large-range permeability increase and long-time CBM drainage are achieved. This study provides a technical way for intensified permeability increase and high-efficiency CBM drainage in deep and low-permeability coal seams. © 2016, China Coal Society. All right reserved.


Cai F.,Anhui University of Science and Technology | Cai F.,Key Laboratory of Integrated Coal Exploitation and Gas Extraction of Anhui Province | Cai F.,Key Laboratory Of Mining Coal Safely And Efficiently Mining Constructed By Anhui Prov And Min Of Educ | Cai F.,West Virginia University | And 3 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2014

Deep-hole pre-splitting explosion is an important way to intensified improve permeability of high-gas and low permeability coal-beds. Based on continuum mechanics, explosion dynamic damage constitutive model of coal under the impact of explosion was established and embedded into nonlinear finite element program LS-DYNA, and propagation and attenuation characteristics of stress waves generated by explosion in coal of different modulus was numerical simulated. Through the monitor of on-site blasting vibration of specialty explosive, propagation and attenuation characteristics of stress waves generated by explosion in high-gas coal-beds was acquired. Simulation results is basically coordinate with results of explosion experiments, and the reasonableness and correctness is verified. The researching results show that: when propagating distance is less than 4.8 m, the explosion stress waves have high peak values and sharply attenuate; when propagating distance is larger than 4.8 m, the explosion stress waves have low peak values and attenuation rate gradually going flatten.


Feng C.,Anhui University of Science and Technology | Feng C.,Key Laboratory of Integrated Coal Exploitation and Gas Extraction of Anhui Province | Feng C.,Key Laboratory of Mining Coal Safely and Efficiently Mining Constructed by Anhui Province | Feng C.,West Virginia University | And 2 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2013

In order to reveal the rules of cracks growth, stress fields evolution and high-pressure water seepage in coal-bed in the process of high-pressure water injection into coal-bed, taking consideration of the non-uniformity characteristics of coal material and non-linear changes of permeability of coal medium during deforming and cracking, RFPA2D- FLOW software is used to simulate the process of high-pressure injection into coal-bed aimed at 721 longwall panel of Qinan Coal Mine of Huaibei Mine Group, and on-site experiments are carried out. The simulation results show that, under the impact of high-pressure water, coal surrounding the injecting borehole is gradually deformed and damaged, and the cracks are generated. The maximum value of coal-bed's seepage coefficient is significantly increased from 0.5m/d to 1580.0m/d, and average 14 times more than initial value. The results of on-site practices show that, after using high-pressure water injection technology, the width of stress-relieved zone in the coal ahead of working face increases from 2.5m to 3.5m, and stress concentration zone moves 1.0m to the inner coal-bed, and this shows that high-pressure water injection has remarkable effect on diminishing the risk of coal-gas outburst. © 2013, EJGE.


Cai F.,Anhui University of Science and Technology | Cai F.,Key Laboratory of Integrated Coal Exploitation and Gas Extraction of Anhui Province | Cai F.,Key Laboratory of Mining Coal Safely and Efficiently Mining Constructed | Cai F.,West Virginia University | And 4 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2013

Deep-hole blasting is an ideal technique to increase permeability of coal-beds and is applied in more and more high-gas coal mines in recent years, but there are few theoretic studies on blasting in coal-beds. Based on the parameters of special explosive for deep-hole blast and arrangement of blast borehole and control boreholes, the mechanism of deep-hole blast in coal-bed is simulated and studied using numerical simulation method. The numerical model for simulating cylindrical explosive blast is built, and the damage range in coal-bed and blasting stress wave's impact on coal-bed is studied. The researching results show that the maximum damage radius is 40cm, and effective gas drainage radius increases to almost 10m, and gas drainage increasing results in coal-bed within 4m around blast borehole are significant. The displacement field of control boreholes are simulated and studied, and the simulated results is consistent with gas drainage data after blast. The researching results provide theoretic support for increasing permeability of soft and loose coal-beds by deep-hole blast technique. © 2013, EJGE.

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