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Gold Science and Technology ›› 2019, Vol. 27 ›› Issue (2): 189-198.doi: 10.11872/j.issn.1005-2518.2019.02.189

• Mining Technology and Mine Management • Previous Articles    

Numerical Simulation Research of Natural Caving Method Based on PFC2D-DFN

Chuanfeng FANG1,2,3(),Jinmiao WANG1,4,Shanbing LI5,Mingtao JIA1,4   

  1. 1. School of Resources and Safety Engineering，Central South University，Changsha 410083，Hunan，China
    2. Changsha Institute of Mining Research Co. ，Ltd. ，Changsha 410012，Hunan，China
    3. State Key Laboratory of Safety Technology of Metal Mines，Changsha 410012，Hunan，China
    4. Center of Digital Mine Research，Central South University，Changsha 410083，Hunan，China
    5. Yunnan Diqing Nonferrous Metal Co. ，Ltd. ，Shangri-La 674400，Yunnan，China
  • Received:2018-02-01 Revised:2018-05-30 Online:2019-04-30 Published:2019-04-30

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Abstract:

Surface subsidence and rock burst may occur during mining in mines using natural caving method，which affect the safety of mine production and the life safety of underground workers.Therefore，it is necessary to research the evolution law of caving area with the advance of undercutting.The research process of this paper is as follows.Firstly:using two-dimensional discrete element software PFC2D to construct a geometric model consistent with the actual topography of a mine.Secondly，according to the complete rock parameters obtained from laboratory mechanical experiments，by means of simulating physical experiments，the meso-parameters are continuously adjusted to approximate the actual physical parameters，the meso-mechanical parameters used in PFC2D are calibrated.In addition，according to the statistic law of joint sets distribution obtained on the spot，choose an appropriate joint generation method，make use of discrete fracture network DFN to reconstructe a joint model consistent with the statistical law.Then，based on the caving height of a certain period obtained by mine drilling television，the simulation results are approximated to the monitoring values by dichotomy method，and the corresponding joint strength parameters are back analyzed.Finally，the whole mine model is coupled with the joint model，and the particles and joints are assign property.After stress balance，the excavation is simulated.Statistic simulation results，the conclusions are as follows:Cracks first develop at the intersection of the undercutting advance working face and the roof，then extend，develop and penetrate in the arch region，resulting in crushing and collapse of the original rock.The main failure types of ore and rock are joint tensile failure，while shear failure often occurs in caved ore and rock.In the early stage，the caving area develops arch upward，which causes the adjacent steep slope to slide to the valley after penetrating the surface.In some undercutting steps，the caving area only occurs in the local area above the newly excavated undercutting region，which is consistent with the change trend of caving quality and roof height.

Key words: natural caving method, numerical simulation, PFC2D software, DFN, undercutting, rock failure, stress analysis, caving evolution

CLC Number: 

  • TD853.36

Fig.1

Mine topography and terrain contour"

Fig.2

PFC2D mine model"

Table 1

Statistical results of dominant joint set occurrence"

组号占比/%倾向/（°）倾角/（°）
最大值最小值均值方差分布规律最大值最小值均值方差分布规律
136.36166120143.17126.89正态分布417971.7821.75正态分布
232.74196239216.2195.13正态分布447971.8619.83正态分布
35.41329306317.0735.58正态分布517569.2221.58正态分布
43.99314839.9923.69正态分布567770.5128.00正态分布

Table 2

Statistical results of joint spacing and continuity(m)"

项目最小值最大值均值标准差分布规律
节理间距0.001.380.0930.15对数正态分布
节理连续度0.0510.612.3500.37正态分布

Table 3

Parameters of DFN generated"

节理分组节理与坑道单位长度交点数/个DFN节理倾角/（°）
最小值最小值均值标准差
10.36407071.784.67
20.33100136108.144.45
30.05104130110.784.64
40.04567770.525.29

Fig.3

Local enlarged diagram of discrete joints generated with DFN"

Fig.4

Statistical chart of DFN spacing"

Fig.5

Plots of uniaxial compression test"

Fig.6

Plots of triaxial servo compression test"

Table 4

Comparison of actual physical mechanics parameters of rock with physical and mechanical parameters of rock simulation"

对比参数试验结果模拟值误差/%
弹性模量/GPa54.5854.290.53
泊松比0.270.263.70
抗压强度/MPa127.96125.931.60
黏聚力/MPa22.0624.8312.50
摩擦角/（°）47.849.002.50

Table 5

Microscopic parameters used in the sumulation"

参数类型参数名数值
密度/（kg·m-3）2 700
线性参数弹性模量/GPa48.0
刚度比1.0
摩擦系数1.0
平行粘结参数弹性模量/GPa9.0
刚度比2.5
抗拉强度/MPa75.0
黏聚力/MPa25.0
摩擦角/（°）75.0
半径系数1.5

Fig.7

Flow chart of joint parameters calibration"

Table 6

Parameters of joint"

参数名称数值参数名称数值
法向刚度/GPa6.0摩擦角/（°）25
切向刚度/GPa3.0抗拉强度/MPa0.7
黏聚力/MPa7.0

Fig.8

Crack propagation in the first step"

Fig.9

Crack propagation and statistics of fracture types"

Fig.10

Evolution characteristics of caving area shape"

Fig.11

Statistics of caving area"

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