Table of Content

15 November 2015, Volume 32 Issue 6

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Roof deformation characteristics with full-mechanized caving face based on beam structure in extremely inclined coal seam

LAI Xingping，LI Yunpeng，WANG Ningbo，LIU Yonghong，YAN Pengjia

2015, 32(6):  871-876. 

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In this paper, to investigate the roof deformation characteristics with full-mechanized caving face in extremely inclined and thick coal seam, taking the extremely coal seam with the dip angle of 45o in the north panel of Wudong coal mine, Urumchi coal field as research object, the roof mechanical model of extremely inclined caving face has been established by beam theory, and the deflection equation in specific settings has also been summarized. Meanwhile, FLAC3D numerical simulation was further applied for roof deformation mechanism. Analytical results indicate that the inclined length of roof beam has enormous impact on roof deformation. The roof deformation gradually increases with the increasing of roof dangling area, especially in its above middle area. Deformation region expands from the central part of roof to the outward part, and its value obtains the minimum neighboring the supporting point of the beam structure. Plastic zones characteristics of roof structure in the inclined direction was monitored by geological penetrating radar, and the roof deformation characteristics were assumed. Generally, the in-situ monitoring results are basically identical with the theoretical and simulated analysis.

Ground pressure rules and roof control technology for the longwall mining of shallow seam beneath the gully topography

WANG Fangtian，TU Shihao，ZHANG Yanwei，SONG Qi，YAN Ruilong，DUAN Chaohua

2015, 32(6):  877-882. 

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Gaotouyao Mine Area, located in the Shendong Coal Field, has typical topography features of developmental gully and large change for the slopes, thence many accidents, such as roof slice type caving and hydraulic support being iron-bound, are inclined to happen during the longwall mining of the shallow coal seams beneath the gully topography. According to the field conditions of the first longwall panel, Selian No. 1 Coal Mine, a “support-surrounding rock” relationship model has been established, and the reasonable support working resistance has been determined to be 11 000 kN in the back-gully mining period. The coal wall plastic zone development, roof pressure and roof deflection have been analyzed while the mining height are 4.0 m and 3.2 m respectively. And the strata pressure behavior degree presents a characteristic of “back-gully mining period > toward-gully mining period > bottom-gully mining period > normal mining period”. The real-time monitoring results indicate that the max support working resistance and the roof weighting dynamic factor of the gully period are larger than these of the normal mining period. Many roof control measures, including enhancement mine pressure monitoring and forecasting, regional lower mining height and rapid advance speed, are implemented in the field, hence safe and efficient mining of shallow seam beneath the gully topography has been guaranteed.

SOM-based optimization of stope structural parameters of deep & large-sized orebody

XU Shuai，AN Long，LI Yuanhui，WU Jin

2015, 32(6):  883-888. 

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Taking the deep & large-sized orebody of Sishanling iron mine as an example, the after- mining block caving filling method has been employed to obtain the optimal structural parameters. With the help of orthogonal experiment, 16 simulation schemes have been designed. Using the FLAC3D to conduct calculation, the interrelated correspondence has been achieved between 5 factors in stope structural parameters and 8 indexes for stop stability. Adopting the unsupervised and competitive study, 16 groups of scheme data have been applied to SOM model for data inputting. Therefore, based on SOM model, the analysis of the prediction for expansion schemes, reversal analysis for structural parameters and the stability-related factors have been done. The results have shown that the length of stope serves as the most influential factor to stability, then the height of stope less influential, while the other factors may not arouse much consideration. The optimal stope parameters for the deep and large-sized orebody in Sishanling iron ore are as follows：100 m level height, 50 m stope length, 15 m room and pillar width and using tailings for backfilling.

Numerical modeling of mining-induced fracturing and flow evolution in coal seam floor based on micro-crack growth

LU Yinlong，WANG Lianguo

2015, 32(6):  889-897. 

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Based on the mechanisms of micro-crack growth, a micro-crack damage tensor has been introduced to the classical Biot’s poroelasticity theory to deduce the relation between the microscopic damage evolution of rock and the macroscopic mechanical and hydraulic properties and to establish the hydro-mechanical coupling model and governing equation based on the fracturing evolution. Then the proposed model has been programmed with MATLAB and COMSOL to simulate the failure process and flow evolution of rock under hydro-mechanical couplings. On this basis, numerical simulations of coal mining above a confined aquifer have been performed and the mining-induced fracturing, failure patterns and flow evolution in coal seam floor have been analyzed systematically. The numerical results clearly show how the groundwater inrush channel is formed.

Safety area delimiting of coal mining under thick loosened aquifer with thin bedrock based on unascertained measure theory

ZENG Jialong，LIU Qiong，HUANG Rui，GUAN Yanhe，LIU Bo，TANG Zongchao，KUANG Chengbin，ZHANG Shaojun

2015, 32(6):  898-904. 

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The specific yield of aquifer at the bottom of thick unconsolidated layers, thickness of clay layer at the bottom of thick unconsolidated layers, thickness of strata, water flowing fracture height and mining height are five key factors for safety mining under thick unconsolidated aquifer with thin bedrock. By analyzing and processing the key factors, four junction points influenced the mining safety were found out, namely, the unit water inflow in bottom aquifer, the ratio of overburden thickness and mining height’s square root, the ratio of the thickness of bottom clay layer and mining height, and the ratio of water flowing fracture height and mining height’s square root. Evaluation factors were divided into five grades, to quantify the mining safety. The information entropy and unascertained measure theory were introduced to establish comprehensive evaluation model. 105 drilling data in one mine were used to evaluate mining safety, divide and predict the safety mining area according to the evaluation results. The evaluation and prediction results are quite consistent with the engineering practice and existing research results. The results show that the unascertained measurement model is feasible and effective under the studied coal seam condition.

Forecast of the height of water flowing fractured zone based on BP neural networks

LI Zhenhua，XU Yanchun，LI Longfei，ZHAI Changzhi

2015, 32(6):  905-910. 

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In order to predict exactly the forming height of water flowing fractured zone, based on summing up methods and theories to forecast the height of water flowing fractured zone, combined with a lot of practical information analysis, the main eight factors influencing the height of water flowing fractured zone have been found out, which are mining depth, coal seam inclination angle, coal seam thickness, coal seam hardness, rock structure, the uniaxial compressive strength of rock, mining thickness and goaf plagioclase. According to the typical cases in China, the forecasting model of the height of water flowing fractured zone based on BP neural networks has been built, and the input samples and testing samples needed by BP neural networks have been determined. The optimization of network model has been got after Matlab software is used in the training of network. The height of water flowing fractured zone of 11011 workface in Zhaogu No.1 Mine, Jiaozuo cola field has been forecasted according to the established network model. Compared with measured results, it has shown that the calculation results obtained by the BP neural network model are closer to the reality than those obtained according to the empirical formula.

An analysis of parameters sensitivity for vulnerability assessment of groundwater inrush during mining from underlying aquifers based on variable weight model

LI Bo，WU Qiang

2015, 32(6):  911-917. 

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To better understand the characteristics of vulnerability assessment model of water inrush from seam floor based on the variable weight theory, evaluation rendering, typical evaluation cell and comprehensive evaluation value range have been compared to analyze the advancement of variable weights evaluation model. Meanwhile, in order to assess the influence of scope and extent of the parameters on the evaluation results in the vulnerability assessment model of water inrush from seam floor based on the variable weight theory, local sensitivity analysis method has been used to carry out sensitivity analysis respectively for the adjustment weight parameters and main controlling parameters in the evaluation model. The result shows that: the relationship between vulnerability index change with adjustment weight parameters a2 and a3, aquifer pressure, water abundance of aquifer, fault-scale index, the distribution of faults and folds as well as the change of fault cross-endpoint is a positive correlation, and is negative correlation between vulnerability index change with adjustment weight parameters c, equivalent thickness of effective aquifer, the thickness of the brittle rock under the mine pressure damaged zone. There is a significant change in the sensitivity coefficient on the inflexion point of adjustment parameters amplitude plus or minus 5%. There is a major influence of adjustment weight parameters a1 and a2, equivalent thickness of effective aquifer of the main controlling factor index, aquifer pressure on the change of vulnerability index.

InSAR-based monitoring and analysis of ground subsidence in old goaf

DENG Kazhong，WANG Liuyu，FAN Hongdong

2015, 32(6):  918-922. 

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The foundation stability of old mine goaf is the key to reusing abandoned subsided land, and it needs quantities of measured data to analyze and evaluate. The traditional monitoring methods, highly precise as they are, cannot obtain historical and large-area data of subsidence. Aiming at this problem, this paper has taken the subsidence monitoring of a mine in Shaanxi province as a research subject, and the subsidence data of the mine has been obtained by processing and analyzing 19 TerraSAR images by using InSAR technology. The deformation rules of old goaf have been analyzed. Empirical formulas of subsidence velocity circulating peak and mining thickness, subsidence velocity cycle and ratio of mining depth to mining thickness and mining velocity, mining face cumulative subsidence and mining stopping halt have been established. These rules and empirical formulas can provide reference for prediction and evaluation of old goaf residual deformation.

Damage evolution law based on acoustic emission of sandy mudstone under different uniaxial loading rate

CAO Anye，JING Guangcheng，DOU Linming，WANG Guifeng，LIU Sai，WANG Changbin，YAO Xiaoxiao

2015, 32(6):  923-928. 

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To study the acoustic emission (AE) and damage evolution characteristics of sandy mudstone rock samples, MTS-C64.106 and PCI-2 AE System were utilized for uniaxial compression and acoustic emission monitoring tests during the compression. The loading rate was applied between 1.0×10-5s-1 and 1.7×10-3s-1. The results show that the peak strength of rock sample increases with the increase of loading rate. The releasing form of AE energy changes from solitary earthquake type to swarm type along with the increasing of loading rate, and the peak AE energy increases greatly under higher loading rate. In contrast, the number of accumulated ringing counts decreases significantly. In addition, the damage variable conducted by accumulated ringing counts was derived to describe the rock damage evolution, then the rock constitutive equation was deduced. Compared with the observed stress-strain curves and the conducted curves based on Weibull distribution, the damage evolution process under uniaxial compression can be well reflected by the conducted constitutive equations, especially under the higher loading rate. The conclusions can provide some reference to rock deformation, damage evolution, precursor information identification, etc., under different loading rates.

Analysis of energy dissipation for stagger arrangement roadway surrounding rock

ZHANG Junwen，SHI Qiang，LIU Zhijun，LI Xingwei，ZHAO Jingli

2015, 32(6):  929-935. 

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Based on the analysis of the expression of the external work in lateral coal fractured zone, plastic zone and increasing zone of elastic stress, the corresponding energy dissipation formulas have been deduced, applying the first law of thermodynamics. The damage variable which is the ratio of energy dissipation value and external forces work for surrounding rock has been determined. Consequently, conclusions have been drawn that damage variable continuously decreases from fractured zone to plastic zone, till to increasing zone of elastic stress. For energy dissipation, it is similar to damage variable. Mineral pressure observation of stagger arrangement workface in Zhenchengdi mine shows that roadway has less support pressure in fractured zone, making it easy to maintain. When loose gangue is above roadway, it will produce compression deformation and plastic deformation under the action of support pressure. Its energy dissipation is bigger, making it easier to maintain.

Surrounding rock stability control in gob-side entry retaining with solid backfilling in coal mining technology

JU Feng，CHEN Zhiwei，ZHANG Qiang，HUANG Peng，TAI Yang，LAN Lixin

2015, 32(6):  936-942. 

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In this paper，the gangue lane of 04(south)-2 workface with gob-side entry retaining in 63rd mining district，Jining No.3 coal mine，has been set as the engineering background. The concept of cooperative control system including overburden layers and gob-side entry retaining with solid backfilling has been put forward. Also the support characteristic of key components in such cooperative control system have been analyzed. Based on such indexes as the roof-allowing subsidence and mining cost，three parameters of affecting surrounding rock stability in roadway are obtained by using FLAC3D. In other words，the entry can be controlled stably under three conditions: 1) filling ratio of working face achieves up to 80%，2) strength of Gangue belt reaches 4 MPa，and 3) width/height ratio is 1∶1. Combined with the specific geological conditions of Jining No.3 coal mine，enhanced support plan for gob side entry has been proposed. The results from field test show that the roadway will be well maintained when the maximum convergence between roof and floor is approximately 300 mm and the side to side convergence amount is 240 mm.

The analysis of roadside supporting parameters and the support technology in the concrete filled steel tubular column in goaf-side entry retaining

WANG Jun，GAO Yanfa，HE Xiaosheng，HUANG Wanpeng，GAO Kunpeng，YANG Liu，FENG Shaowei

2015, 32(6):  943-949. 

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To start with, the roadside support action rules has been analyzed, and the roadside barrier support resistance and rational compressed volume formula have been given. A new technology about gob side entry retaining by using concrete filled steel tube column is put forward. And in order to verify reliability of this technology, the concrete filled steel tube column bearing capacity experiment has been done. Then, on the basis of experiment, the calculation theory and the method of ensuring related parameters have been given and instance analysis of selection of tubular column has been conducted. Finally, this technology has been applied to the engineering practice, which draws the conclusion that this new technology is suitable for gob side entry retaining due to its cheaper cost and higher bearing capacity.

Experimental and numerical simulation study on the progressive damage on the anchorage by the dynamic pressure in mining

LI Qingfeng，ZHOU Ze，ZHU Chuanqu

2015, 32(6):  950-954. 

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This research is conducted in order to analyze damage mechanism and bearing mode of resin bolt anchoring section of bolt support structure in floor railway under the dynamic pressure in mining, and to improve the reliability of resin bolting in coal mine field applications. First, the mine-induced stress of floor railway is simulated by UDEC while the overlying seam is mining, and the reaction of roof bolt and side bolt support structure is analyzed. Then, the bearing and deformation of resin bolt anchoring section are simulated by FLAC, and the dynamic response of resin bolt under certain load and confining pressure is obtained. Finally, surrounding rock with concrete block is simulated, and bolt pullout test is carried out in the prepared hole in which resin bolt have been anchored, at the same time elastic wave test instrument is used to do nondestructive test for the bolt. The test result shows that 1) the process of resin bolt anchoring damage is gradual, 2) the gradual failure and the effective anchoring length can be detected by elastic wave nondestructive test, and that 3) the real-time bearing capacity of the bolt can be deduced, so as to improve the timeliness of resin bolting in coal mine field applications.

Deformation mechanism of surrounding rock and support technology in deep soft rock roadway

ZHANG Hongjun，LI Haiyan，LI Shucai，BAI Jiwen，HAO Tingyu，LI Hongwei

2015, 32(6):  955-962. 

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The west track roadway in Pengzhuang coal mine is a typical soft rock roadway, which is buried more than 700 meters underground, and is frequently passing through the weak fractured mudstone layers. To better master the deformation and failure mechanism of the surrounding rock, based on field monitoring, borehole camera and geological radar detection, rock physical mechanics test, in-situ stress test and 25 kinds of numerical comparison experiments were carried out respectively in this paper. The results show that the deformation of the surrounding rock can be effectively reduced by the combined support scheme of high strength and pre-stressed anchor (bolt) & bolt-grouting, and the supporting structure integrity and bearing capacity can also be effectively improved. As a new supporting method of deep soft rock roadway, the supporting effect of the combined support scheme has significant advantages comparing with the traditional supporting method.

Study on the gateway rock failure mechanism and supporting practice of half-coal-rock extraction roadway in deep coal mine

JIN Gan，WANG Lianguo，LI Zhaolin，ZHANG Jihua

2015, 32(6):  963-967. 

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In view of the non-conformity of discontinuous structure of surrounding rock of deep half coal rock roadway and deformation, taking the specific engineering geological conditions of a coal mine 92105 working face in the half coal rock roadway as background, Abaqus software has been used to build the half coal rock extraction roadway model, study the stress, displacement and plastic zone distribution under the main controlling factors such as different coal and rock interface position and coal rock interface dip, and reveal the mechanism of deformation and failure of surrounding rock of deep soft rock roadway. It shows that the large deformation occurs in the tunnel in coal seam at the position of the side seam location; with the increase of the coal seam inclination, the concentration area of the principal stress difference gradually shift to the roadway's sides, which causes the decrease of the overall deformation of roadway, and the large deformation only appears in the coal seam location. In response to the asymmetric deformation and failure characteristics of half coal crag tunnel surrounding rock, the asymmetric coupling support countermeasure in key parts has been put forward, and the results show that: this support countermeasure can effectively control the non-conformity of the rock deformation failure in half coal rock roadway, guaranteeing the stability of the roadway surrounding rock.

A research on cable supporting and curtain grouting of hydraulic hose controlling the roadway floor heave in deep coal mine

CHANG Jucai，HE Lipin

2015, 32(6):  968-972. 

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According to the engineering conditions of the C15 haulage roadway at -960 m elevation in Xieyi coal mine, dynamic deformation characteristics of surrounding rock between the roof, two sides and the floor and the main reasons of floor heave have been obtained through monitoring the roadway deformation and analyzing floor heave factors. The results show that the main reasons of floor heave are the squeezing and flowing of fractured rock mass, which cause the stress and deformation of roadway release from the non-supporting floor. The comprehensive measures are put forward and put into practice accordingly, including the roof and two sides grouting, floor cable supporting and curtain grouting of hydraulic hose. In addition, a self-manufacturing floor drilling machine is adopted to overcome the difficulty in drilling the cable holes. Facts have proved that the technology can effectively control the floor heave and keep the roadway stable for a long time in deep coal mine.

The research and application on high-efficiency construction equipment of roadway’s floor bolt and cable

WANG Qizhou，XIE Wenbing，JING Shengguo

2015, 32(6):  973-977. 

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In response to the drilling difficulty and bad anchoring effect in the construction processing of roadway floor bolt-mesh-cable, field investigation has been adopted to analyze the reason. The result shows that ranging from floor surface to some depth in the drilling is mainly broken bits rock, which is entangled in interspace between drilling pipe and hole’s wall by friction of drilling pipe and waggle of drilling machine; the smaller rock block is unstable and caving after drilling pipe have been pulled out. There is some thickness pasty slurry in the surface of drill for reducing the cutting effect which is mixed by rock debris and water. The broken bits rock is hindering evenly stirring anchoring agent by bolt and cable, decreasing the effective contact area of bolt and anchoring agent. The concentration of synthetic resin and curing agent is reduced by water of slurry, and slowing reaction time. Decreasing the property of anchoring agent by rock debris which is located in the anchor solid between bolt and surrounding rock. Therefore, the device to improve the drilling’s efficiency and anchoring effect of roadway floor bolt and cable has been put forward. The results of studying its structure form and working characteristics by field experiment show that: the device where special drilling pipe is staying in the drilling can efficiently prevent drilling collapsing within the scope of roadway floor some depth. The time of drilling and installing the bolt or cable is shortened, and the success rate of drilling and one-time anchoring can reach up to 100% and over 95%. Therefore, the construction efficiency will increase obviously.

Roof collapse laws and reducing-span support technology in long-span roadway

LI Chong，CAO Yue，CHENG Zhengmin，XU Jinhai，CHEN Liang

2015, 32(6):  978-983. 

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In response to the support problem under high stress in long-span roadway, taking the 7801 open-off cut in Wuyang mine as the engineering case, the microfracture development, stress distribution and deformation, failure and collapse laws have been researched in surrounding rock of long-span roadway under different side pressure coefficient and buried depths. The reducing-span support technology consisting of “reasonable section shape of secondary tunneling, bolt-mesh-cable, steel strip and hydraulic single prop” has been put forward. In the meanwhile, the long-span support parameters of open-off cut have been improved. The research shows that the original support scheme can not effectively control the deformation of roadway surrounding rock when the buried depth of 7801 open-off cut is more than 600 m; while the new reducing-span support technology can effectively control the deformation of surrounding rock, when the maximum for the roof-to-floor convergence, rib-to-rib convergence, roof separation and working resistance of single prop all in control are 55.5 mm，25.1 mm，24.8 mm and 12.52 MPa respectively. The researches effectively solve the support problem of 7801 open-off cut in Wuyang mine and provide reference for support design of long-span roadway.

Measurement research of freezing pressure for large cross section mine inclined freezing shaft sinking in alluvium

WANG Jianzhou，ZHOU Guoqing，GAO Runfei，FAN Yaoguang，WEI Guojun，BAO Qiang，WANG Tao，ZHOU Tanjun

2015, 32(6):  984-988. 

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Taking freezing main inclined shaft on big cross section under construction in Gucheng Coalmine, Lu’an Group as the research object, the evolution of the frozen pressure and a large number of in-suit measured data have been obtained through the earth pressure cell during the construction process. And the freezing pressure evolution laws of the roof, floor and two sides during the construction process have been analyzed. Firstly, the freezing pressure changes showed obvious volatility in the course of construction，affected by freezing temperature, hydration heat and thawing time and so on. Secondly，the inclined shaft stress shows a general linear growth trend with the increase of buried depth, despite some differences of spatial distribution. Thirdly, after analyzing the measured and calculated value of earth pressure during the inclined shaft construction, the current design theory is observed to have shortcomings and needs improving. The findings have important reference and guiding value with data and and experience obtained for the inclined frozen wall and inclined shaft design and construction for the similar alluvium condition and freezing condition.

Fuzzy random identification and comprehensive selection for frozen clay creep model

YAO Yafeng，CHENG Hua，RONG Chuanxin，LI Mingjing，CAI Haibing，SONG Jian

2015, 32(6):  989-995. 

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The uniaxial compressive strength test has been conducted on the artificial frozen clay in Huainan mine under the temperature of -5, -10 and -15 ℃. The result shows effect law of temperature for the uniaxial compressive strength of artificial frozen clay. The uniaxial creep test of high, mid and low stress levels has been carried out under the conditions of -5, -10 and -15 ℃ respectively, which leads to the effect law of temperature and stress level for creep. The traditional ant colony algorithm has been optimized into fuzzy ant colony algorithm according to optimal-solution pheromone of fuzzy coefficient, with the search efficiency increased and local optimum avoided. It is used in random inversion for the creep compliance of the common model, then the dual factors objective function for comprehensive selection is built by taking precision and complexity into consideration, finally the optimized model is obtained under three different stresses with appropriate fuzzy weight calculation method.

A study of the prediction of artificial frozen soil thaw settlement test and thaw settlement coefficient

TAO Xiangling，MA Jinrong，HUANG Ling

2015, 32(6):  996-1003. 

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In order to investigate the changes of the additional force in the back of the shaft lining wall, which is caused by the thawing effect of the frozen wall in the construction of the special sinking shaft with freezing method, indoor freeze-thaw cycle tests have been carried out under different moisture contents, unidirectional temperature gradients and external loads, taking Xuzhou clay as the object of study. The results show that: when the test system was under water replenishment, the clay under 1.4 ℃ /cm unidirectional freezing gradient has 0.98 mm settlement, which is 60.6% larger than the clay with the same dry density but under 2.0 ℃/cm freezing gradient (with 0.61 mm in settlement). Under the same unidirectional freezing temperature gradient, the thawing settlement increases with the increment of load, of which the increasing trend of is similar while the increasing magnitude is not consistent. Based on the fact that the thawing character of freezing soil is effected by multiple factors, a relational database about thaw settlement coefficient with multi-sample and multi-factor has been built by utilizing the improved artificial neural network. The error analysis certifies that the improved prediction algorithm has greater accuracy.

Stress calculation for a double layer shaft in special strata

JIANG Lijun，DONG Jianjun，ZHAO Li

2015, 32(6):  1004-1009. 

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A stress calculation method has been established for a double layer shaft in special stratum. After some simplifications of the mechanical model，the problem has been broken down into three subproblems, and a Saint-Venant solution has been obtained by solving and adding up each subproblem. An example for certain double layer shaft has been presented, and the stress results have been compared with the single layer shaft of the same conditions. The fourth strength theory has been applied to study the security of the shafts, and the results show that, compared with the single layer shaft, the security for the inside lining of the double layer shaft is enhanced greatly, while the security of the outside lining is reduced. On the whole, the application of this double layer shaft is advantageous for the safety production of the mine，and the outside lining of this shaft is the weak zone that needs to be cured mainly.

Modified Hoek-Brown strength criterion for intact rocks under the condition of triaxial stress test

LI Bin，XU Mengguo，LIU Yanzhang，WANG Ping

2015, 32(6):  1010-1016. 

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As one of the most widely-used rock strength criteria, Hoek-Brown criterion mainly suffers two limitations. Firstly, the triaxial strength results predicted by Hoek-Brown criterion at high value of confining pressure do not agree well with experimental data. Secondly, the effect of intermediate principal stress to rock true triaxial strength is ignored by the criterion. In the present study, to overcome the limitations, Hoek-Brown strength criterion is modified by employing Barton’s critical confining pressure and Singh’s treatment of intermediate principal stress. The applicability of the modified criterion has been verified by its application to a large number of intact rocks experiment data. The analyzing result shows that the strength predicted by the two criteria are basically consistent when confining pressure is under critical confining pressure; otherwise the modified Hoek-Brown criterion agrees better with experimental data. Under the condition of true triaxial test, the average error between modified Hoek-Brown criterion considered intermediate principal stress and experimental data is the least. Thus,the modified Hoek-Brown criterion is more suitable to predict triaxial strength of intact rocks.

Comparative analysis on different AE parameters in biaxial loading of hole rock

WEI Jialei，LIU Shanjun，WU Lixin，HUANG Jianwei，ZHANG Yanbo，TIAN Baozhu

2015, 32(6):  1017-1025. 

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The aim of this paper is to derive and analyze several parameters of acoustic emission (AE) under the deformation and failure process of rock. These AE experiments of rock failure have been conducted in biaxial loading with the hole rock and some parameters of AE have been obtained. The variation features of the AE energy parameters (including energy rate and cumulative energy), the AE event parameters (including event count rate and cumulative event count), the b-value and the entropy value in loading process have been analyzed systematically. Meanwhile, the AE precursory characteristics of rock failure have been studied, and the variation and precursory characteristics of different AE parameters have also been comparatively analyzed. Furthermore, the suitable AE parameters for predicting rock failure have been explored. The results have shown that the various AE parameters are correspondent to different variation characteristics. The AE energy keeps a small release in the relatively low stress phase, and it increases gradually in the middle stress phase then dramatically in the high stress phase. The number of AE events is few in the low stress phase, and rises rapidly in the middle stress phase and drops greatly in the high stress phase. The b-value decreases with volatility during the most rock loading process and performs an evidently decrease just before the rock failure; while, the entropy value is in the reverse change trend. All the AE parameters have the precursors of rock failure which occur at 82% to 96% of peak stress, while the precursors of the entropy value occur relatively earlier and that of the b-value occur relatively later. Additionally, this study has shown that the precursor of rock failure would be easy to identify with the AE cumulative parameter curve. An integrated analysis of AE multi-parameters will provide an effective and quantitative way to derive the information for precursor of rock failure.

Research on splitting failure model of fractured rock mass under the coupling effect of seepage-stress

NIE Taoyi，PU Hai，LIU Guihong，XIAO Cheng，NI Hongyang

2015, 32(6):  1026-1030. 

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In response to the splitting failure of fractured rock mass under coupling effect of seepage- stress, the theory of fluid-solid coupling is firstly used to calculate the element stress. Then based on the rule of initiation, extension, coalescence of microcracks, the hyperbolic curve is applied to simulate the wing crack propagation path. In view of the effect of mode II stress intensity near microcrack tip on propagation path, a splitting failure model is established based on a curve propagation path under the coupling effect of seepage-stress. Fish language is utilized to program the new method through the secondary development of FLAC3D. Compared with Lajtai empirical formula, the results of new model are consistent with Lajtai empirical results.

The application research of overlying strata stress field and gas flow field coupling mechanism under the long vertical distance coal seam group mining conditions

TIAN Fuchao，QIN Yujin，LU Jintao，LIAN Yuntao

2015, 32(6):  1031-1036. 

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This paper has discussed the coupling theory of migration and seepage field of long vertical distance coal seam group in mining conditions and the variation characteristics of displacement field and gas pressure field and has established the overlying rock stress distribution and multi-physics coupling model of gas migration. Based on the numerical analysis software FLAC3D, the paper has done finite element solution of the mathematical model. In addition, the research has also analyzed the coal seam gas seepage distribution characteristics of Fengfeng Group No.2 and No.4 coal seam during mining, the strata displacement characteristics and the strata stress distribution rules under mining conditions. The engineering verification has shown that: The pressure relief effect is obvious of No.4 coal mine upon the upper part of No.2 coal mine; the actual relief range is larger than that defined by the reference pressure-relief angle on the basis of coal and gas outburst prevention regulations; the gas release field is large, and gas drainage of No.2 coal 172102，172104 working face has an obvious effect, whose drainage rate has reached 33.12% and 46.59% respectively, thus can help to eliminate the outburst danger．

A research of asynchronous and synchronous characteristics of coal seam gas pressure controlled by the mining-induced stress

HU Zuxiang，XIE Guangxiang

2015, 32(6):  1037-1042. 

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In order to reveal the coupling characteristics of coal seam gas pressure and mining-induced stress at coalface, the intensive study of coupling characteristics of coal seam gas pressure and the mining- induced stress in working face has been conducted according to the different stresses. The results show that coal mechanical state in working face is fundamental to the difference of coupling gas pressure and mining-induced stress of coal seam. Under the influence of mining，the peak position will assume asynchronous features between gas pressure and mining-induced stress of coal seam in working face and the peak position of gas pressure will present itself before the stress of mining when dilatancy happens；their peak positions will assume synchronous characteristics when the dilatancy doesn’t happen. The research of asynchronous and synchronous characteristics of coupling effect of gas pressure and mining-induced stress in working face provides the scientific evidence to effective prevention an control of the coal and gas dynamic disaster.

Numerical simulation and parameter determination in goaf spontaneous combustion prevention by injecting flue gas

JIA Baoshan，YIN Bin，ZHANG Weiliang，HAN Guang

2015, 32(6):  1043-1048. 

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Based on the cleaner production concept, we studied the technological feasibility of injecting the flue gas of power plant into the nearby goaf to prevent the spontaneous combustion of residual coal in this paper. The models of multi-component gas transport equation and heterogeneity porosity of porous media were presented, and No.92126 mechanized caving mining face in Xuecun coal mine was taken as the example for numerical calculation. The simulated results show that the maximum width of “spontaneous combustion zone” in goaf become smaller gradually with the increase of the flue gas injection rate, and the maximum width is 75 m before injecting the flue gas of power plant. The maximum width decreased to 25 m when the injected flow of flue gas is 15 m3/min. Meanwhile, the flow-field of goaf was further numerically calculated for different injection flue gas rate, and the linear regression was made for the simulated results. The dynamic equilibrium relation under the safe mining condition was obtained, and the reasonable parameters injecting the flue gas into the goaf were determined to prevent and extinguish the spontaneous combustion of residual coal in No.92126 coal face. The calculated result shows that the injection flow of flue gas should be no less than 420.15 m3/h in view of the present mining speed.