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Machine learning-based constitutive models for cement-grouted coal specimens under shearing

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International Journal of Mining Science and Technology 2021年第5期31卷 813-823页

作者： guichen li Yuantian Sun Chongchong Qi School of Mines China University of Mining and TechnologyXuzhou 221116China State Key Laboratory of Coal Resources and Safe Mining China University of Mining and TechnologyXuzhou 221116China School of Resources and Safety Engineering Central South UniversityChangsha 410083China

Cement-based grouting has been widely used in mining engineering;its constitutive law has not been comprehensively *** this study,a novel constitutive law of cement-grouted coal specimens(CGCS)was developed using hybrid machine learning(ML)*** tests were performed on CGCS for the analysis of stress-strain curves and the preparation of the *** maintain the interpretation of the trained ML models,regression tree(RT)was used as the main *** effect of maximum RT depth(Maxdepth)on its performance was studied,and the hyperparameters of RT were tuned using the genetic algorithm(GA).The RT performance was also compared with ensemble learning *** optimum correlation coefficient on the training set was determined as 0.835,0.946,0.981,and 0.985 for RT models with Maxdepth=3,5,7,and 9,*** overall correlation coefficient was over 0.9 when the Maxdepth≥5,indicating that the constitutive law of CGCS can be well ***,the failure type of CGCS could not be captured using the trained RT *** forest was found to be the optimum algorithm for the constitutive modeling of CGCS,while RT with the Maxdepth=3 performed the worst.

关键词： Constitutive law Cement-grouted coal specimens Machine learning Regression tree Ensemble learning

Creep characteristics of coal and rock investigated by nanoindentation

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International Journal of Mining Science and Technology 2020年第6期30卷 769-776页

作者： Changlun Sun guichen li Mohamed Elgharib Gomah Jiahui Xu Yuantian Sun School of Mines Key Laboratory of Deep Coal Resource MiningMinistry of Education of ChinaChina University of Mining and TechnologyXuzhou 221116China Mining and Petroleum Engineering Department Faculty of EngineeringAl-Azhar UniversityCairo 11435Egypt

In coal mining industry,with the depth growing of coal mines,the creep behaviours of coal and rock can extensively affect the mining safety,coalbed methane recovery and *** acquire a better insight into their creep characteristics,an efficient and robust researching technique,nanoindentation,was applied to investigate the creep performances of coal and rock samples obtained from two coal mines in the east of *** characteristics were reflected by evaluating the curves of creep depth versus creep time of nanoindentation tests during the load-holding period at the peak load of 30 *** curves can be divided into two stages:transient stage and steady stage;and the time of load-holding period of 5 s,which is the dividing point between two stages,can efficiently avoid the influence of creep displacement on the unloading *** exponential function can perfectly fit creep curves and Kelvin model can be used to calculate the rheological parameters of coal and rock *** results yield values for the creep modulus and viscosity terms of coal and *** study also settled a particular emphasis on the selection of the positions of indentations to obtain the rheological properties of mineralogical constituents in heterogonous coal and rock samples and their elastic aftereffect.

关键词： Coal and rock Nanoindentation Creep Heterogeneous properties Elastic aftereffect

Numerical study on the heat transfer performance of coaxial shallow borehole heat exchanger

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Energy and Built Environment 2021年第4期2卷 445-455页

作者： guichen li Jianzhi Yang Xiaowei Zhu Zhihe Shen Department of Built Environment Hefei University of TechnologyHefeiAnhui 230009China State Key Laboratory of Aerodynamics China Aerodynamics Research and Development CenterMianyangSichuan 621000China Department of Mechanical Engineering Johns Hopkins UniversityBaltimoreMD 21218USA Anhui’s International Joint Research Center on Hydrogen Safety HefeiAnhui 230009China

In the present work,a numerical investigation on the coaxial shallow borehole heat exchanger based on Com-putational Fluid Dynamics(CFD)technique in Hefei city of China has been *** effects of design parameters,including inlet flow rate,inlet fluid temperature,inner pipe material and outer pipe diameter,on the heat transfer performance were systematically ***,the thermal behavior along the pipe has been carefully examined with focus on the thermal short-circuiting *** the fluid inlet velocity is less than the critical value,the turbulence intensity increases and the Nusselt number increases with the inlet flow rate ***,there is sufficient time for heat transfer between the fluid in inner pipe and outer pipe because of low flow rates,leading to large heat loss,i.e.,thermal short-circuiting *** is found that with the inlet flow rate increasing,the heat transfer increases first and then decreases,and the rate of reduction slows down *** the inlet flow rate increases,the pumping power undergoes exponential *** the inlet temperature increasing,the heat transfer decreases almost ***,when the soil temperature at the top of the casing is lower than that of the fluid in the casing,heat is transferred from the fluid in the casing to the soil,and the heat loss increases with the increase of the inlet fluid *** material of inner pipe with high heat conductivity would result in large heat loss under the influence of thermal *** heat load increases while the pumping power required decreases with the increasing of outer pipe *** study is very beneficial for the coaxial shallow borehole exchanger designs and energy conservation of buildings.

关键词： Coaxial borehole heat exchanger Geothermal Heat transfer performance CFD

Development of ensemble learning models to evaluate the strength of coal-grout materials

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International Journal of Mining Science and Technology 2021年第2期31卷 153-162页

作者： Yuantian Sun guichen li Nong Zhang Qingliang Chang Jiahui Xu Junfei Zhang School of Mines Key Laboratory of Deep Coal Resource MiningMinistry of Education of ChinaChina University of Mining and TechnologyXuzhou 221116ChinaDepartment of CivilEnvironmental and Mining EngineeringThe University of Western AustraliaPerthWA 6009Australia

In the loose and fractured coal seam with particularly low uniaxial compressive strength(UCS),driving a roadway is extremely difficult as roof falling and wall spalling occur *** address this issue,the jet grouting(JG)technique(high-pressure grout mixed with coal particles)was first introduced in this study to improve the self-supporting ability of coal *** evaluate the strength of the jet-grouted coal-grout composite(JG composite),the UCS evolution patterns were analyzed by preparing 405 specimens combining the influential variables of grout types,curing time,and coal to grout(C/G)***,the relationships between UCS and these influencing variables were modeled using ensemble learning methods *** boosted regression tree(GBRT)and random forest(RF)with their hyperparameters tuned by the particle swarm optimization(PSO).The results showed that the chemical grout composite has higher short-term strength,while the cement grout composite can achieve more stable strength in the long *** PSO-GBRT and PSO-RF models can both achieve high prediction ***,the variable importance analysis demonstrated that the grout type and curing time should be considered *** study provides a robust intelligent model for predicting UCS of JG composites,which boosts JG design in the field.

关键词： Jet grouting JG composite Roadway support Gradient boosted regression tree Random forest Particle swarm optimization

Instability mechanism and control technology of soft rock roadway affected by mining and high confined water

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International Journal of Mining Science and Technology 2015年第4期25卷 573-580页

作者： li guichen Jiang Zuohan Lv Chuangxin Huang Chao Chen Gui li Mingyuan School of Mines Key Laboratory of Deep Coal Resource Mining Ministry of Education China University of Mining & Technology Huaibei Coal Mining limited Company Huaibei Pingyuan Soft Rock Engineering Company

Based on deformation and failure characteristics of the second belt conveyor roadway at level II of Zhuxianzhuang coal mine, laboratory experiments, numerical calculation and field test were adopted to analyze the composition and microstructure of mudstone, the law of mudstone hydration and its strength weakening induced by water, the characteristics of surrounding rock deformation and failure under the action of confined water. Results showed that montmorillonite clay minerals accounted for as much as 76% of mudstone, with a large number of pores existing in the microstructure. Besides, as the molecular structure of montmorillonite changed, mudstone microstructure damage occurred with the macroscopic manifestation of its theological instability. Weakening degree of confined water on residual strength of mudstone was almost 50%. The instability mechanism of soft rock roadway caused by high confined water is that surrounding rock circulates the process of ＂fracture-seepage-mud ding-closed＂ twice, which weakens its strength and leads to roadway instability. A combined support technology, namely the, ＂high-toughness sealing layer ＋ hollow grouting cables ＋ full-length anchoring bolts with deep borehole＂ was proposed. Based on field observation, the soft rock roadway was controlled effectively, which also verified the effectiveness of new control technology for surrounding rock.

关键词： High confined water Soft rock roadway Instability mechanism Control technology

De-stressed mining of multi-seams:Surrounding rock control during the mining of a roadway in the overlying protected seam

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Mining Science and Technology 2011年第2期21卷 159-164页

作者： Wang Cheng Zhang Nong li guichen Zhang Nianchao School of Mines State Key Laboratory of Coal Resources and Safe Mining China University of Mining ＆ Technology Xuzhou 221008 China

Surrounding rock control in the overlying protective coal seam is a challenging topic for de-stressed mining of multi-seamed *** research findings on roadway control were used in the design of a physical model of a complex textured roof having a varying *** model was used to study roadway instability and collapse caused by dynamic *** results show that when the thickness of the roof exceeds the bolted depth the roadway security is least and the roof has the greatest possibility for *** simulations were also carried out to study stress redistribution before and after roadway excavation during underlying protective seam *** evolution of roadway displacement and fracture,as affected by support methods,has been well studied.A series of support principles and technologies for mining affected roadways has been proposed after demonstration of successful practical application in the Huainan *** principles and technologies are of extended value to deep coal mining support in China.

关键词： Multi-seams De-stressed mining Mining influenced roadway Control technology

Experimental investigation on the nanoindentation viscoelastic constitutive model of quartz and kaolinite in mudstone

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International Journal of Coal Science & Technology 2021年第5期8卷 925-937页

作者： Changlun Sun guichen li Mohamed Elgharib Gomah Jiahui Xu Haoyu Rong School of Mines Key Laboratory of Deep Coal Resource MiningMinistry of Education of ChinaChina University of Mining and TechnologyXuzhou 221116JiangsuChina Mining and Petroleum Engineering Department Faculty of EngineeringAl-Azhar UniversityCairo 11435Egypt

The creep behaviors in deep underground engineering structures,especially in soft rocks,have a remarkable impact on the long-term stability of the excavations,which finally leads to the high risk and failure of ***,it is essential to recognize the time-dependent deformation through the investigation of this *** this study,the creep behaviors of soft rocks were examined to help understand the underlying mechanism of the extended time-dependent *** to the limited results about the time-dependent properties of the constituents of the rock that reveal their heterogeneity,the targeting nanoindentation technique(TNIT),was adopted to investigate the viscoelastic characteristics of kaolinite and quartz in a two-constituent mudstone *** TNIT consists of identifications of mineralogical ingredients in mudstone and nanoindentation experiments on each identified *** conducting experiments,the unloading stages of the typical indentation curves were analyzed to calculate the hardness and elastic modulus of both elements in ***,the 180 s load-holding stages with the peak load of 50 mN were transformed into the typical creep strain-time curves for fitting analysis by using the Kelvin model,the standard viscoelastic model,and the extended viscoelastic *** results show that the standard viscoelastic model not only can perfectly express the nanoindentation creep behaviors of both kaolinite and quartz but also can produce suitable constants used to measure their creep *** creep parameters of kaolinite are much smaller than that of quartz,which causes the considerable time-dependent deformation of the soft ***,the standard viscoelastic model was also verified on the quartz in a sandstone sample.

关键词： Mudstone Constituents Viscoelastic properties TNIT Creep constitutive model

Numerical modeling on strain energy evolution in rock system interaction with energy-absorbing prop and rock bolt

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International Journal of Mining Science and Technology 2023年第10期33卷 1273-1288页

作者： Yang Hao Chunhui liu Yu Wu Hai Pu Yanlong Chen lingling Shen guichen li State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering China University of Mining and TechnologyXuzhou 221116China School of Mechanics and Civil Engineering China University of Mining and TechnologyXuzhou 221116China School of Mines China University of Mining and TechnologyXuzhou 221116China

The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to high geo-stress and strong disturbed effects. This paper is to investigate the strain energy evolution in the interaction between coal and rock masses with self-designed energy-absorbing props and rock bolts by numerical modeling with the finite difference method. The interaction between rock and rock bolt/prop is accomplished by the cables element and the interface between the inner and outer props. Roadway excavation and coal extraction conditions in deep mining are numerically employed to investigate deformation, plastic zone ranges, strain energy input, accumulation, dissipation,and release. The effect on strain energy input, accumulation, dissipation, and release with rock deformation, and the plastic zone is addressed. A ratio of strain energy accumulation, dissipation, and release with energy input a, β, γ is to assess the dynamic hazards. The effects on roadway excavation and coal extraction steps of a, β, γ are discussed. The results show that:(1) In deep high geo-stress roadways, the energyabsorbing support system plays a dual role in resisting deformation and reducing the scope of plastic zones in surrounding rock, as well as absorbing energy release in the surrounding rock, especially in the coal extraction state to mitigate disturbed effects.(2) The strain energy input, accumulation is dependent on roadway deformation, the strain energy dissipation is relied on plastic zone area and disturbed effects, and strain energy release density is the difference among the three. The function of energyabsorbing rock bolts and props play a key role to mitigate strain energy release density and amount, especially in coal extraction condition, with a peak density value from 4×10^(4) to 1×10^(4)J/m^(3), and amount value from 3.57×10^(8) to 1.90×10^(6)J.(3) W

关键词： Strain energy Coal and rock mass Energy-absorbing prop and rock bolt Strain energy evolution

Analysis on mechanism and key factors of surrounding rock instability in deeply inclined roadway affected by argillation and water seepage

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International Journal of Mining Science and Technology 2015年第3期25卷 465-471页

作者： Ma Rui li guichen Zhang Nong liu Cong Wei Yinghao Zhang Ming School of Mines China University of Mining & Technology Key Laboratory of Deep Coal Resource Mining Ministry of EducationChina University of Mining & Technology School of Mines Kunming Metallurgy College JCHX Mining Management Co. Ltd

Based on the characteristics of surrounding rocks for deeply inclined roadway affected by argillation and water seepage, a structure model of layer crack plate was established to analyze the shear sliding instability mechanism. Through solid mechanics analysis of anchored surrounding rock with defect from water seepage, combined with numerical analysis for instability mechanism under water seepage in deeply inclined roadway, key factors were proposed. Results show that with increasing height of layer crack plate, lateral buckling critical load value for high wall of the roadway decreases; there is a multistage distribution for tensile stress along the anchor bolt with defect under pulling state condition;groundwater seepage seriously affects the strength of surrounding rock of the roadway, to some extent the plastic zone of the high side rises up to 8 m. Finally some support strategies were proposed for the inclined roadway and successfully applied to Haoyuan coal mine in Tiela mining area,western China.

关键词： Deeply inclined Argillation and water seepage Shear sliding instability Anchoring defect