- Email: [email protected]
Stability assessment and feature analysis of slope in Nanfen Open Pit Iron Mine
International Journal of Mining Science and Technology 22 (2012) 329–333
Contents lists available at SciVerse ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Stability assessment and feature analysis of slope in Nanfen Open Pit Iron Mine Yang Jun ⇑, Tao Zhigang, Li Baoliang, Gui Yang, Li Haifeng School of Mechanics and Civil Engineering, China University of Mining & Technology, Beijing 100083, China State Key Laboratory of Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Beijing 100083, China
a r t i c l e
i n f o
Article history: Received 15 October 2011 Received in revised form 4 November 2011 Accepted 19 December 2011 Available online 17 May 2012 Keywords: Landslide disaster MSARMA method Stability assessment Sensitivity analysis Safety mining Analysis system
a b s t r a c t Under the combined influences of special topography and the long term mining in Nanfen Open Pit Iron Mine, many large scale landslide masses appeared in heading side of stope, and tens of millions of iron mine is buried underside, making great economic losses. In order to guide the safety mining and increase the supply quantity, this paper through the use of MSARMA-method and the ‘‘MSARMA evaluation and analytical system for slope stability analysis’’ based on this method, which aimed at the quantitative evaluating of the slope stability before and after the actual mining below the slip mass, and the sensitivity analysis for the main influencing factor, providing scientific proof for the parameter optimization of open mine surface slope, the security and sustainable exploitation. Ó 2012 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction As the mining method is turning from open pit mining to sag by mining, vertical height of open-pit mine slope continues to increase, the slope deformation and failure mode has close relationship with regional geological structure characteristics and the rock mass structure feature, the stability is influenced largely by rock mass, joints and fissures, and blasting vibration [1]. Particularly, openpit mine’s productive blasting vibration and rainfall has an important effect on the mine slope stability. Productive blasting vibration has an indirect dangerous damage on the high and steep slope. It is mainly caused by blasting seismic wave after the blasting, especially for the joint fissures development. The high and steep rock slope containing fault or fracture zone is more likely as this [2]. Nanfen Open Pit Iron Mine is located in Taizi rivers subsidence formation which is in the north edge of Yingkou-kuandian anticline of Liaodong platform of north China platform. It is the largest open pit iron mine in the Asia, and the current production capacity of iron ore is around 10 million ton per year [3–7]. In 2008, in order to increase the supply of ore, prolong service life in coal mining, and give full play to the mining capacity of super-huge mining, under the premise of guaranteeing economic and reasonable conditions of mining technology in stope, open pit iron ore launched the project three phase for expanding and four phase for mining. At present, the bottom elevation of the stope is above 238 m, the
highest elevation of the head side near slope side is about 694 m, forming a high steep stope and the elevation of which is about 456 m, the angle of the section slope surface is of 46–54°. Due to the complex of engineering geological conditions in the mining area, landslide development, rolling stone accumulation, and blasting mining disturbances, all those make the platforms below 370 platform of head side slope in stope complete, but do not meet with the design requirements, almost ten million tons of highgrade iron ore have been buried below the earth, causing great economic loss of the mine. Based on deep understanding of previous research achievements, the author has done lots of detailed investigations of the characteristics of slope for landslide and distribution law and got a lot of firsthand information. In order to ensure the safe implementation of the third period expansion stage and the fourth mining project of Nanfen Open Pit Iron Mine, the author uses slope stability analysis and evaluation of engineering MSARMA system to complete the landslide quantitative evaluation aiming at the landslide’s stability of pressure below before and after ore mining, and do the sensitivity analysis of main influence factors, offering scientific basis for the geometric parameter optimization and open-pit mine slope safety mining [8–13]. 2. Characteristics of landslide body 2.1. General introduction to the project
⇑ Corresponding author. Tel.: +86 10 62339819. E-mail address: [email protected] (J. Yang).
Nanfen Open Pit Mine is located in the south of Benxi, Liaoning province, 7.5 km from Nanfen town, Nanfen district of Benxi,
2095-2686/$ - see front matter Ó 2012 Published by Elsevier B.V. on behalf of China University of Mining & Technology. http://dx.doi.org/10.1016/j.ijmst.2012.04.008
330
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
6.5 km from Nanfen concentrator, which has s railway special line connected with mine area. Geography coordinate: 123.50° east longitude and 41.07° north latitude, illustrated as Fig. 1. 2.2. Structure characteristics of rock mass (1) Topography and geomorphology The mine area is a uniclinal structure composed of metamorphic rock series layer, it’s a erosion middle-high mountain, extending from east to west, crisscrossed by canals and ditches, little vegetation on the surface, the common attitude of the mountain is range from 500 to 600 m and relative height is about 350 m. The attitude of Huangbaiyu river bed in the south of mine area is around 327 m, and Miaoergou river bed in the north has the attitude of 296 m. (2) Formation lithology According to the investigation data, Nafen Open Pit Mine is located in Taizihe subsidence formation which is in the north edge of Yingkou-kuandian anticline of Liaodong platform of north China platform. The stratum is mainly composed of the Archean Anshan group, Algonkian Liaohe group, Sinian system and Quaternary system. 2.3. Characteristics of geologic structure The main fault of the mine area is F1, which is the SW extending of the NE compressive-twisting fault in the district, striking NNE or approaching SN in the mine area, the fault plane dips to west with the angle of 45°, 10 km in length and 5–20 m in width. Although the fault has contacted with the third layer of iron ore, the ore body is not damaged, just cutting roof rock. 2.4. Characteristics of environment and physics field (1) Climate and surface flow The mine area located in the north temperate monsoon climate zone, the lowest temp is 32.3 °C in winter, the highest temp is 37.3 °C in summer, the annul average temperature is 8.2 °C, the mean annual precipitation is 880 mm, the maximum daily precipitation is 274 mm, concentrating in July, August, and September. The mean annual evaporation capacity is 1729 mm which belong to humidity deficit zone. There are Miaoergou and Huangbaiyu two perennial rivers in the area.
(2) Characteristic of ground water seepage field Ground water of the stope can be divided into pore water and fracture water according to hosting feature. Pore water is mainly alluvium pore water, and has contact with fracture water in bed rock. Fracture water in bed rock can be divided into weathered zone fissure water and tectonic crack water according to hosting location. Fracture water which is located 298 m and higher in bed rock is supplied by meteoric water, and the water below has contact with surface water. Therefore, ground water is closely related with the distribution of annual precipitation. 2.5. Distribution of landslide There are four large-scale landslides in the heading side. According to succession of formation and the scale of the landslide, landslides can be divided into four areas, A, B (Fig. 2), C and D. Among them, C landslide is the typical along-bedding rock landslide located in slope expansion working area, it has the relatively small scale and small influence on the safe of the slope. Landslide disaster in D area happened in July 31, 2011, it’s the newly developing landslide, but because of its small scale, it’s now in its natural stability, not in our study interest. (1) Characters of A landslide A landslide is a medium-size along-bedding rock landslide, developing from 8, 2008, near the No.12 exploration line on heading side. The landslide body run from 370 bench to 526 bench, 132 m in height, 200 m in width, strike direction is 270°, average grade of sliding face is 37°, and shearing opening is in 370 bench. Crown of the landslide is clear, altitude difference is 5 m. Fractures on top of the sliding body are developed and fractured, seriously threaten the safety of the mining below. Obvious altitude difference appeared in No.12 exploration line on 478 bench, 25 m in length, and 1.3 m in altitude difference (Fig. 3). Shearing cracks are 5–20 mm, convenient for rainfall infiltrating, then decrease the shear strength of sliding face, inducing landslide disaster getting worse. A 12 m scarp emerge in crown of landslide in 526 bench, with the development of mining and the influence of rainfall, slope sliding and settlement would increase constantly. (2) Characters of B landslide B landslide is in the north of landslide A under dealing, just below the reinforced area. Sliding mass run from the 430 bench to the 526 bench, witch is 170 m in length. The slope sliding 0.5–1.0 m from 526 bench, and the crown of 80 m in length formed in 526 bench. The crown is composed of powdery or thin layer green mudstone, the composing of slip
Tieling
Fuxin
Shenyang
Chaoyang
Fushun
Liaoyang
Huludao
Benxi Jinzhou Panjin An shan Nanfen Yingkou
Dandong
Bohai sea Bohai sea Lalian Fig. 1. Location of landslide in Nanfen Open Pit Mine.
Fig. 2. Characteristic of landslide mass.
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
331
3. Slope stability analysis before and after mining Due to the existence of the landslide, Nanfen Open Pit Iron ore slope has not mined in normal way according to the original design. In order to increase the resisting sliding force and the slope stability, the 394 bench and its below bench were retained in the southern slope, which lead to a convex appeared near the No. 12 exploration line, and formed the convex slope (Fig. 4). MSARMA method is used to analysis the stability of slope before and after the mining. The MSARMA slope analysis method is an improved method of Sarma form, which stands for Modified Sarma method. The method is based on Sarma method and makes improvements from the following aspects such as the mechanical model, calculation method, and boundary conditions and has been written into the compounding computer program and become a wider scope calculation method and the practical evaluation for the slope engineering design [14].
Fig. 3. Slab staggering in 478 bench.
3.1. Stability analysis before mining tongue is not clear. The side boundary of the landslide is clear, especially the north boundary which is cut by a large crack, the width of the crack is 0.4–2.0 m, the depth is not known. Rock surface of the landslide body is fractured, rolling stones can be seen anywhere, especially on 526 bench, and holes caused by rolling stones can be seen anywhere too. Reinforced engineering from 574 to 526 has local-deformation of obvious fracture which is also caused by rolling stones.
2.6. Landslide mechanism analysis Major joint: average attitude is 295°/48°, the joints in the slope are through, and they form the main sliding surface of the landslide of heading side. Rock mass of heading side is mainly green mudstone, which is susceptible to weathering, has low strength, its strength declined sharply after water, then change to be weak intercalated layer. Rock of heading side strike parallel with slope, they have the same dip direction, and the similar dip angle, all these are convenient for along-bedding landslide or local landslide happening. Rock mass of slope is fractured, which applying good seepage channel. Rainfall triggered landslide, physical and mechanical parameters are changed because of the softening of rainfall, and rock and soil are in saturated conditions, gravitational density increases, shearing strength and modulus of deformation declined. Blast and rolling stone impact accelerate the sliding process.
N
No water doesn’t slide is what people summarize the role of water in the landslide [15]. In order to truly reflect the slope stability state in Nanfen Open Pit Iron Mine in the natural environment, we use MSARMA slope stability assessment design system to do the safety assessment of the stope slope stability under natural state. The data of numerical calculation profile is selected from area B landslide I-I’ computing profile, and profile throughout 346–526 bench. For a specific slope engineering, the first task to do is to generalize its geometry state model, then do the slope stability analysis. Get the data based on the in-site measured terrain and the simplified engineering geology section and the real status of the slope, and then do some generalization according to it, finally we establish the stability calculation model before mining landslide (Fig. 5). According to the field test and the indoor soil test, we got the slope rock mass and the weak physical and mechanical parameters statistics (Table 1). Among them the testing of c and u use indoor directly shearing tests. However, the testing of rock mass C and U adopt laboratory tri-axial compression testing. According to the calculation, the stability coefficients in all situations are shown in Table 2. Data in Table 2 shows that: (1) Under dry conditions, with the increase of earthquake intensity, slope safety parameters are reduced. Among them, with non-drainage condition (0% drainage), slope safety parameters is reduced from 1.1356 to 0.9942; With the condition of complete drainage (100% drainage), slope safety coefficient fell to 1.3547 from 1.1429, showing that the slope drainage has positive effect on improving the stability of slope;
Convex slope
294°
Bottom of stone 12 line
Fig. 4. Slope with convex shape.
S
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
16 15 12 14 11 13
Mining area 358 346
5 3 4 1 2
6
910 78
526
180
502
160 140
478 454 430
Sliding surface
406 382
Guess water level
358 334 310
Elevation (m)
17
Elevation (m)
332
120 100 80 60
Guess water level
40 20 0
20
40 60 80 100 120 140 160 180 200 220 Distance (m)
Fig. 5. Computational model of landslide before mining.
Table 1 Strong index value between rock mass and weak plane [3]. Name
Unit weight (g/ cm3)
Quartz Luni schist Luni angle flash rock Two mica schist quartz Fault gouge
2.91 2.93 2.71
Strength of joint surface
Shear strength
C (kPa)
U
C (kPa)
U
(°)
56.0 69.0 77.4
23.0 27.0 27.6
317 414 825
37.0 38.0 36.0
12
24.7
1.825
(°)
(2) In the same basic earthquake intensity, with increase of slope drainage rate, the slope safety coefficient increases, the slope develops toward the stable direction. Among them, 0° seismic intensity conditions, namely non-earthquake zones, slope safety coefficient improved from 1.1356 to 1.3547, the slope becomes more stable; (3) Nanfen Open Pit Iron Mine belongs to VI degrees belt, in the non-drainage condition (0% drainage), slope stability coefficient is 1.1068, which is in limit equilibrium state. With the increase of the drainage rate, when slope is in a fully drainage condition (100% drainage), slope safety coefficient is 1.2231, increasing 0.1163. 3.2. Stability analysis after mining
Table 2 Coefficient of stability under the current situation. Intensity
Natural drainage rate of slope (%)
0 VI VII VIII
0%
25%
50%
75%
100%
1.1356 1.1068 1.0203 0.9942
1.1728 1.1429 1.0921 1.0636
1.2642 1.1839 1.1202 1.0932
1.3043 1.2012 1.1460 1.1057
1.3547 1.2231 1.1922 1.1429
526 bench
Elevation (m)
180 160 140 120 100 80
The simulation calculation of the mining project mainly aimed at 346 bench and 358 bench for mining simulation, its mining quantity is about 100 104 m3. In dry conditions, after 358 bench and 346 bench mining, the slope numerical calculation mechanics model is shown in Fig. 6. Model 358 bench and 346 bench supportive parts have been removed. Table 3 shows that after 346 platform and 358 platform mining, due to the excavation at the foot of the slope under the stope, sliding resistance were reduced and slope safety coefficient were reduced. The slope safety coefficient, which was in limit equilibrium state before mining, quickly decrease to 1 (Table 3), slope becomes very unstable, particularly with effects of vibration, rainfall, the slope safety coefficient reduced to 0.6739 at minimum, an extremely unstable situation. These data indicates that, slope of Nanfen Open Pit Iron Mine mining is in limit equilibrium state
430 bench Sliding surface
60 40 370 bench 20
1.24 1.22
Guess water level
1.20
0
40
80
120
160
200
240
280
1.18
Distance (m)
1.16
Fs
Fig. 6. Computational model of landslide after mining.
1.14 1.12
Table 3 Coefficient of stability after the mining. Intensity
0 VI VII VIII
1.10
Natural drainage rate of slope (%)
1.08
0%
25%
50%
75%
100%
0.8553 0.8018 0.7551 0.6739
0.8553 0.8018 0.7551 0.6739
0.8556 0.8021 0.7554 0.6742
0.8998 0.8438 0.7947 0.7094
0.9321 0.8613 0.8124 0.7389
1.06
0
20
40
80
100
Dr (%) Fig. 7. Sensitivity analysis curve between stability and Dr.
120
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
sensitive to vibration intensity and drainage rate; According to the evaluation results, the author suggest open pit mine should strengthen monitoring on the slope stability, such as: the slippery ability monitoring, displacement monitoring, rainfall monitoring, etc.; Especially should perfect, and capture landslide characteristics and tendency of evolution in advance. Based on this, form a systematic of remote monitoring and warning network of slippery power in Nanfen Open Pit Iron Mine, involving data of slippery power monitoring, the displacement monitoring and rainfall monitoring to complete the comprehensive landslide warning.
1.36 1.18
Fs
1.00 0.82
Dr=0% Dr=75% Dr=25% Dr=100% Dr=50%
0.61 0.46
333
Acknowledgments
0.28 0
0.2
VII
VIII
0.4
IX
0.8
0.6
1.0
X
Fig. 8. Sensitivity analysis curve between stability and earthquake intensity.
Financial support for this work, provided by the National Natural Science Foundation of China (No. 40972196) and the Scientific Research Foundation of China University of Mining & Technology (Beijing) (No. 2010QL03) are gratefully acknowledged. References
under the natural condition. However, with the influence of rainfall, vibration, the slope is very unstable, and even destructive. 4. Sensitivity analysis of slope stability to the impact factor Use the sensitivity analysis function of slope stability assessment design software to do the sensitivity analysis of new landslide severe RR, bottom sliding surface CB and UB value, lateral spreads the CS and US value, the earthquake coefficient kc and slope reinforcement angle GM in the Nanfen Open Pit Iron Mine. Among that, sensitivity analysis curve of the stable degree to the intensity of earthquake and drainage rate in area B is shown in Figs. 7 and 8. Not hard to see that the drainage rate and the vibration intensity slope are still very active environmental factors influencing slope steady state, are the important factors of slope deformation. Fig. 7 shows that the stability coefficient of the dry slope significantly increased of 15% than the full water slope. Fig. 8 shows that the stability coefficient under the VII effects of earthquake significantly increased of 0.1045 than the ones under the VIII effects of earthquake, and with the increase of the coefficient, the stability coefficient diminished quickly. 5. Conclusions The MSARMA analysis method is used to do the quantitative evaluation of the stability of landslide by analyzing the steadystate before and after ore mining under the landslide pressure, and do the sensitivity analysis of main impact factors. The results show that under the landslide slop of open pit mine stope is very
[1] Qiao Lan, Li Yuan. Engineering geological model of high-steep slope damagein opencut mines. J Univ Sci Technol Beijing 2004;26(5):461–4. [2] Li Wenxiu, Wang Jing, Dal Lanfang. Safety criterion of blasting shock for the high deep slope of open pit in mountain area. IM&P 2006;1:20–2. [3] Gong Yongjun, Dai Yongxin. Research on landslide treatment in Nanfen Open Pit Iron Mine. Express Inf Min Ind 2007;7:42–3. [4] Gao Lie, Ge Yongli, Liu Junjie. A preliminary discussion on the slope sliding mass in the bottom wall in Nanfen Iron Surface Mine and its control measures. Min Res Dev 2001;21(6):4–6. [5] Anders Ansell. Laboratory testing of a new type of energy absorbing rock bolt. Tunn Undergr Space Technol 2005;20(4):291–330. [6] Li Guofeng, Tao Zhigang, Guo Hongyun. Stability control of a deep shaft insert. Min Sci Technol 2010;20(6):491–8. [7] Liu Shuangwei, Liu Ketong. Study on the causes of the local landslide in Nanfen Open Pit Iron Mine. Benxi Steel Technol 2001;1:2–7. [8] Wu Xiong, Yao Aijun, Heng Zhaoyang, He Manchao. Study on the MSARMA Method for evaluating the slope stability and the optimum reinforcement force. Chin J Geol Hazard Control 2004;15(2):104–7. [9] Yao Aijun, Xue Tinghe. Stability evaluation methods and engineering practice of complex slope. Beijing: Science Press; 2008. [10] Yao Aijun, He Manchao. Application of MSARMA in the probability analysis of slope stability. Chin J Rock Mech Eng 2002;21(12):1839–42. [11] Yang Jun, Li Guofeng, Zhang Guofeng, Yu Shibo, Ma Chong, Su Fengbin. Effect of a single weak lithological structure on the height of a collapsing roof in a deep soft rock roadway. Min Sci Technol 2010;20(6):820–4. [12] He Manchao, Tao Zhigang, Zhang Bin. Application of remote monitoring technology in landslides in the Luoshan mining area. Min Sci Technol 2009;19(5):610–4. [13] Tao Zhigang, Zhang Bin, He Manchao. Research on mechanism and monitoring and eearly-warning technology of landslide in luoshan mining area. Chin J Rock Mech Eng 2011;30(Suppl. 1):2931–7. [14] Yao Aijun. Study of coupling analysis theory and method for slope engineering stability. Beijing: China University of Mining & Technology Press; 1999. [15] Zhang Zhuoyuan, Wang Shitian, Wang Lansheng. Engineering geological analysis principal. Beijing: Geological Publishing House; 1981.
Contents lists available at SciVerse ScienceDirect
International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Stability assessment and feature analysis of slope in Nanfen Open Pit Iron Mine Yang Jun ⇑, Tao Zhigang, Li Baoliang, Gui Yang, Li Haifeng School of Mechanics and Civil Engineering, China University of Mining & Technology, Beijing 100083, China State Key Laboratory of Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Beijing 100083, China
a r t i c l e
i n f o
Article history: Received 15 October 2011 Received in revised form 4 November 2011 Accepted 19 December 2011 Available online 17 May 2012 Keywords: Landslide disaster MSARMA method Stability assessment Sensitivity analysis Safety mining Analysis system
a b s t r a c t Under the combined influences of special topography and the long term mining in Nanfen Open Pit Iron Mine, many large scale landslide masses appeared in heading side of stope, and tens of millions of iron mine is buried underside, making great economic losses. In order to guide the safety mining and increase the supply quantity, this paper through the use of MSARMA-method and the ‘‘MSARMA evaluation and analytical system for slope stability analysis’’ based on this method, which aimed at the quantitative evaluating of the slope stability before and after the actual mining below the slip mass, and the sensitivity analysis for the main influencing factor, providing scientific proof for the parameter optimization of open mine surface slope, the security and sustainable exploitation. Ó 2012 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction As the mining method is turning from open pit mining to sag by mining, vertical height of open-pit mine slope continues to increase, the slope deformation and failure mode has close relationship with regional geological structure characteristics and the rock mass structure feature, the stability is influenced largely by rock mass, joints and fissures, and blasting vibration [1]. Particularly, openpit mine’s productive blasting vibration and rainfall has an important effect on the mine slope stability. Productive blasting vibration has an indirect dangerous damage on the high and steep slope. It is mainly caused by blasting seismic wave after the blasting, especially for the joint fissures development. The high and steep rock slope containing fault or fracture zone is more likely as this [2]. Nanfen Open Pit Iron Mine is located in Taizi rivers subsidence formation which is in the north edge of Yingkou-kuandian anticline of Liaodong platform of north China platform. It is the largest open pit iron mine in the Asia, and the current production capacity of iron ore is around 10 million ton per year [3–7]. In 2008, in order to increase the supply of ore, prolong service life in coal mining, and give full play to the mining capacity of super-huge mining, under the premise of guaranteeing economic and reasonable conditions of mining technology in stope, open pit iron ore launched the project three phase for expanding and four phase for mining. At present, the bottom elevation of the stope is above 238 m, the
highest elevation of the head side near slope side is about 694 m, forming a high steep stope and the elevation of which is about 456 m, the angle of the section slope surface is of 46–54°. Due to the complex of engineering geological conditions in the mining area, landslide development, rolling stone accumulation, and blasting mining disturbances, all those make the platforms below 370 platform of head side slope in stope complete, but do not meet with the design requirements, almost ten million tons of highgrade iron ore have been buried below the earth, causing great economic loss of the mine. Based on deep understanding of previous research achievements, the author has done lots of detailed investigations of the characteristics of slope for landslide and distribution law and got a lot of firsthand information. In order to ensure the safe implementation of the third period expansion stage and the fourth mining project of Nanfen Open Pit Iron Mine, the author uses slope stability analysis and evaluation of engineering MSARMA system to complete the landslide quantitative evaluation aiming at the landslide’s stability of pressure below before and after ore mining, and do the sensitivity analysis of main influence factors, offering scientific basis for the geometric parameter optimization and open-pit mine slope safety mining [8–13]. 2. Characteristics of landslide body 2.1. General introduction to the project
⇑ Corresponding author. Tel.: +86 10 62339819. E-mail address: [email protected] (J. Yang).
Nanfen Open Pit Mine is located in the south of Benxi, Liaoning province, 7.5 km from Nanfen town, Nanfen district of Benxi,
2095-2686/$ - see front matter Ó 2012 Published by Elsevier B.V. on behalf of China University of Mining & Technology. http://dx.doi.org/10.1016/j.ijmst.2012.04.008
330
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
6.5 km from Nanfen concentrator, which has s railway special line connected with mine area. Geography coordinate: 123.50° east longitude and 41.07° north latitude, illustrated as Fig. 1. 2.2. Structure characteristics of rock mass (1) Topography and geomorphology The mine area is a uniclinal structure composed of metamorphic rock series layer, it’s a erosion middle-high mountain, extending from east to west, crisscrossed by canals and ditches, little vegetation on the surface, the common attitude of the mountain is range from 500 to 600 m and relative height is about 350 m. The attitude of Huangbaiyu river bed in the south of mine area is around 327 m, and Miaoergou river bed in the north has the attitude of 296 m. (2) Formation lithology According to the investigation data, Nafen Open Pit Mine is located in Taizihe subsidence formation which is in the north edge of Yingkou-kuandian anticline of Liaodong platform of north China platform. The stratum is mainly composed of the Archean Anshan group, Algonkian Liaohe group, Sinian system and Quaternary system. 2.3. Characteristics of geologic structure The main fault of the mine area is F1, which is the SW extending of the NE compressive-twisting fault in the district, striking NNE or approaching SN in the mine area, the fault plane dips to west with the angle of 45°, 10 km in length and 5–20 m in width. Although the fault has contacted with the third layer of iron ore, the ore body is not damaged, just cutting roof rock. 2.4. Characteristics of environment and physics field (1) Climate and surface flow The mine area located in the north temperate monsoon climate zone, the lowest temp is 32.3 °C in winter, the highest temp is 37.3 °C in summer, the annul average temperature is 8.2 °C, the mean annual precipitation is 880 mm, the maximum daily precipitation is 274 mm, concentrating in July, August, and September. The mean annual evaporation capacity is 1729 mm which belong to humidity deficit zone. There are Miaoergou and Huangbaiyu two perennial rivers in the area.
(2) Characteristic of ground water seepage field Ground water of the stope can be divided into pore water and fracture water according to hosting feature. Pore water is mainly alluvium pore water, and has contact with fracture water in bed rock. Fracture water in bed rock can be divided into weathered zone fissure water and tectonic crack water according to hosting location. Fracture water which is located 298 m and higher in bed rock is supplied by meteoric water, and the water below has contact with surface water. Therefore, ground water is closely related with the distribution of annual precipitation. 2.5. Distribution of landslide There are four large-scale landslides in the heading side. According to succession of formation and the scale of the landslide, landslides can be divided into four areas, A, B (Fig. 2), C and D. Among them, C landslide is the typical along-bedding rock landslide located in slope expansion working area, it has the relatively small scale and small influence on the safe of the slope. Landslide disaster in D area happened in July 31, 2011, it’s the newly developing landslide, but because of its small scale, it’s now in its natural stability, not in our study interest. (1) Characters of A landslide A landslide is a medium-size along-bedding rock landslide, developing from 8, 2008, near the No.12 exploration line on heading side. The landslide body run from 370 bench to 526 bench, 132 m in height, 200 m in width, strike direction is 270°, average grade of sliding face is 37°, and shearing opening is in 370 bench. Crown of the landslide is clear, altitude difference is 5 m. Fractures on top of the sliding body are developed and fractured, seriously threaten the safety of the mining below. Obvious altitude difference appeared in No.12 exploration line on 478 bench, 25 m in length, and 1.3 m in altitude difference (Fig. 3). Shearing cracks are 5–20 mm, convenient for rainfall infiltrating, then decrease the shear strength of sliding face, inducing landslide disaster getting worse. A 12 m scarp emerge in crown of landslide in 526 bench, with the development of mining and the influence of rainfall, slope sliding and settlement would increase constantly. (2) Characters of B landslide B landslide is in the north of landslide A under dealing, just below the reinforced area. Sliding mass run from the 430 bench to the 526 bench, witch is 170 m in length. The slope sliding 0.5–1.0 m from 526 bench, and the crown of 80 m in length formed in 526 bench. The crown is composed of powdery or thin layer green mudstone, the composing of slip
Tieling
Fuxin
Shenyang
Chaoyang
Fushun
Liaoyang
Huludao
Benxi Jinzhou Panjin An shan Nanfen Yingkou
Dandong
Bohai sea Bohai sea Lalian Fig. 1. Location of landslide in Nanfen Open Pit Mine.
Fig. 2. Characteristic of landslide mass.
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
331
3. Slope stability analysis before and after mining Due to the existence of the landslide, Nanfen Open Pit Iron ore slope has not mined in normal way according to the original design. In order to increase the resisting sliding force and the slope stability, the 394 bench and its below bench were retained in the southern slope, which lead to a convex appeared near the No. 12 exploration line, and formed the convex slope (Fig. 4). MSARMA method is used to analysis the stability of slope before and after the mining. The MSARMA slope analysis method is an improved method of Sarma form, which stands for Modified Sarma method. The method is based on Sarma method and makes improvements from the following aspects such as the mechanical model, calculation method, and boundary conditions and has been written into the compounding computer program and become a wider scope calculation method and the practical evaluation for the slope engineering design [14].
Fig. 3. Slab staggering in 478 bench.
3.1. Stability analysis before mining tongue is not clear. The side boundary of the landslide is clear, especially the north boundary which is cut by a large crack, the width of the crack is 0.4–2.0 m, the depth is not known. Rock surface of the landslide body is fractured, rolling stones can be seen anywhere, especially on 526 bench, and holes caused by rolling stones can be seen anywhere too. Reinforced engineering from 574 to 526 has local-deformation of obvious fracture which is also caused by rolling stones.
2.6. Landslide mechanism analysis Major joint: average attitude is 295°/48°, the joints in the slope are through, and they form the main sliding surface of the landslide of heading side. Rock mass of heading side is mainly green mudstone, which is susceptible to weathering, has low strength, its strength declined sharply after water, then change to be weak intercalated layer. Rock of heading side strike parallel with slope, they have the same dip direction, and the similar dip angle, all these are convenient for along-bedding landslide or local landslide happening. Rock mass of slope is fractured, which applying good seepage channel. Rainfall triggered landslide, physical and mechanical parameters are changed because of the softening of rainfall, and rock and soil are in saturated conditions, gravitational density increases, shearing strength and modulus of deformation declined. Blast and rolling stone impact accelerate the sliding process.
N
No water doesn’t slide is what people summarize the role of water in the landslide [15]. In order to truly reflect the slope stability state in Nanfen Open Pit Iron Mine in the natural environment, we use MSARMA slope stability assessment design system to do the safety assessment of the stope slope stability under natural state. The data of numerical calculation profile is selected from area B landslide I-I’ computing profile, and profile throughout 346–526 bench. For a specific slope engineering, the first task to do is to generalize its geometry state model, then do the slope stability analysis. Get the data based on the in-site measured terrain and the simplified engineering geology section and the real status of the slope, and then do some generalization according to it, finally we establish the stability calculation model before mining landslide (Fig. 5). According to the field test and the indoor soil test, we got the slope rock mass and the weak physical and mechanical parameters statistics (Table 1). Among them the testing of c and u use indoor directly shearing tests. However, the testing of rock mass C and U adopt laboratory tri-axial compression testing. According to the calculation, the stability coefficients in all situations are shown in Table 2. Data in Table 2 shows that: (1) Under dry conditions, with the increase of earthquake intensity, slope safety parameters are reduced. Among them, with non-drainage condition (0% drainage), slope safety parameters is reduced from 1.1356 to 0.9942; With the condition of complete drainage (100% drainage), slope safety coefficient fell to 1.3547 from 1.1429, showing that the slope drainage has positive effect on improving the stability of slope;
Convex slope
294°
Bottom of stone 12 line
Fig. 4. Slope with convex shape.
S
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
16 15 12 14 11 13
Mining area 358 346
5 3 4 1 2
6
910 78
526
180
502
160 140
478 454 430
Sliding surface
406 382
Guess water level
358 334 310
Elevation (m)
17
Elevation (m)
332
120 100 80 60
Guess water level
40 20 0
20
40 60 80 100 120 140 160 180 200 220 Distance (m)
Fig. 5. Computational model of landslide before mining.
Table 1 Strong index value between rock mass and weak plane [3]. Name
Unit weight (g/ cm3)
Quartz Luni schist Luni angle flash rock Two mica schist quartz Fault gouge
2.91 2.93 2.71
Strength of joint surface
Shear strength
C (kPa)
U
C (kPa)
U
(°)
56.0 69.0 77.4
23.0 27.0 27.6
317 414 825
37.0 38.0 36.0
12
24.7
1.825
(°)
(2) In the same basic earthquake intensity, with increase of slope drainage rate, the slope safety coefficient increases, the slope develops toward the stable direction. Among them, 0° seismic intensity conditions, namely non-earthquake zones, slope safety coefficient improved from 1.1356 to 1.3547, the slope becomes more stable; (3) Nanfen Open Pit Iron Mine belongs to VI degrees belt, in the non-drainage condition (0% drainage), slope stability coefficient is 1.1068, which is in limit equilibrium state. With the increase of the drainage rate, when slope is in a fully drainage condition (100% drainage), slope safety coefficient is 1.2231, increasing 0.1163. 3.2. Stability analysis after mining
Table 2 Coefficient of stability under the current situation. Intensity
Natural drainage rate of slope (%)
0 VI VII VIII
0%
25%
50%
75%
100%
1.1356 1.1068 1.0203 0.9942
1.1728 1.1429 1.0921 1.0636
1.2642 1.1839 1.1202 1.0932
1.3043 1.2012 1.1460 1.1057
1.3547 1.2231 1.1922 1.1429
526 bench
Elevation (m)
180 160 140 120 100 80
The simulation calculation of the mining project mainly aimed at 346 bench and 358 bench for mining simulation, its mining quantity is about 100 104 m3. In dry conditions, after 358 bench and 346 bench mining, the slope numerical calculation mechanics model is shown in Fig. 6. Model 358 bench and 346 bench supportive parts have been removed. Table 3 shows that after 346 platform and 358 platform mining, due to the excavation at the foot of the slope under the stope, sliding resistance were reduced and slope safety coefficient were reduced. The slope safety coefficient, which was in limit equilibrium state before mining, quickly decrease to 1 (Table 3), slope becomes very unstable, particularly with effects of vibration, rainfall, the slope safety coefficient reduced to 0.6739 at minimum, an extremely unstable situation. These data indicates that, slope of Nanfen Open Pit Iron Mine mining is in limit equilibrium state
430 bench Sliding surface
60 40 370 bench 20
1.24 1.22
Guess water level
1.20
0
40
80
120
160
200
240
280
1.18
Distance (m)
1.16
Fs
Fig. 6. Computational model of landslide after mining.
1.14 1.12
Table 3 Coefficient of stability after the mining. Intensity
0 VI VII VIII
1.10
Natural drainage rate of slope (%)
1.08
0%
25%
50%
75%
100%
0.8553 0.8018 0.7551 0.6739
0.8553 0.8018 0.7551 0.6739
0.8556 0.8021 0.7554 0.6742
0.8998 0.8438 0.7947 0.7094
0.9321 0.8613 0.8124 0.7389
1.06
0
20
40
80
100
Dr (%) Fig. 7. Sensitivity analysis curve between stability and Dr.
120
J. Yang et al. / International Journal of Mining Science and Technology 22 (2012) 329–333
sensitive to vibration intensity and drainage rate; According to the evaluation results, the author suggest open pit mine should strengthen monitoring on the slope stability, such as: the slippery ability monitoring, displacement monitoring, rainfall monitoring, etc.; Especially should perfect, and capture landslide characteristics and tendency of evolution in advance. Based on this, form a systematic of remote monitoring and warning network of slippery power in Nanfen Open Pit Iron Mine, involving data of slippery power monitoring, the displacement monitoring and rainfall monitoring to complete the comprehensive landslide warning.
1.36 1.18
Fs
1.00 0.82
Dr=0% Dr=75% Dr=25% Dr=100% Dr=50%
0.61 0.46
333
Acknowledgments
0.28 0
0.2
VII
VIII
0.4
IX
0.8
0.6
1.0
X
Fig. 8. Sensitivity analysis curve between stability and earthquake intensity.
Financial support for this work, provided by the National Natural Science Foundation of China (No. 40972196) and the Scientific Research Foundation of China University of Mining & Technology (Beijing) (No. 2010QL03) are gratefully acknowledged. References
under the natural condition. However, with the influence of rainfall, vibration, the slope is very unstable, and even destructive. 4. Sensitivity analysis of slope stability to the impact factor Use the sensitivity analysis function of slope stability assessment design software to do the sensitivity analysis of new landslide severe RR, bottom sliding surface CB and UB value, lateral spreads the CS and US value, the earthquake coefficient kc and slope reinforcement angle GM in the Nanfen Open Pit Iron Mine. Among that, sensitivity analysis curve of the stable degree to the intensity of earthquake and drainage rate in area B is shown in Figs. 7 and 8. Not hard to see that the drainage rate and the vibration intensity slope are still very active environmental factors influencing slope steady state, are the important factors of slope deformation. Fig. 7 shows that the stability coefficient of the dry slope significantly increased of 15% than the full water slope. Fig. 8 shows that the stability coefficient under the VII effects of earthquake significantly increased of 0.1045 than the ones under the VIII effects of earthquake, and with the increase of the coefficient, the stability coefficient diminished quickly. 5. Conclusions The MSARMA analysis method is used to do the quantitative evaluation of the stability of landslide by analyzing the steadystate before and after ore mining under the landslide pressure, and do the sensitivity analysis of main impact factors. The results show that under the landslide slop of open pit mine stope is very
[1] Qiao Lan, Li Yuan. Engineering geological model of high-steep slope damagein opencut mines. J Univ Sci Technol Beijing 2004;26(5):461–4. [2] Li Wenxiu, Wang Jing, Dal Lanfang. Safety criterion of blasting shock for the high deep slope of open pit in mountain area. IM&P 2006;1:20–2. [3] Gong Yongjun, Dai Yongxin. Research on landslide treatment in Nanfen Open Pit Iron Mine. Express Inf Min Ind 2007;7:42–3. [4] Gao Lie, Ge Yongli, Liu Junjie. A preliminary discussion on the slope sliding mass in the bottom wall in Nanfen Iron Surface Mine and its control measures. Min Res Dev 2001;21(6):4–6. [5] Anders Ansell. Laboratory testing of a new type of energy absorbing rock bolt. Tunn Undergr Space Technol 2005;20(4):291–330. [6] Li Guofeng, Tao Zhigang, Guo Hongyun. Stability control of a deep shaft insert. Min Sci Technol 2010;20(6):491–8. [7] Liu Shuangwei, Liu Ketong. Study on the causes of the local landslide in Nanfen Open Pit Iron Mine. Benxi Steel Technol 2001;1:2–7. [8] Wu Xiong, Yao Aijun, Heng Zhaoyang, He Manchao. Study on the MSARMA Method for evaluating the slope stability and the optimum reinforcement force. Chin J Geol Hazard Control 2004;15(2):104–7. [9] Yao Aijun, Xue Tinghe. Stability evaluation methods and engineering practice of complex slope. Beijing: Science Press; 2008. [10] Yao Aijun, He Manchao. Application of MSARMA in the probability analysis of slope stability. Chin J Rock Mech Eng 2002;21(12):1839–42. [11] Yang Jun, Li Guofeng, Zhang Guofeng, Yu Shibo, Ma Chong, Su Fengbin. Effect of a single weak lithological structure on the height of a collapsing roof in a deep soft rock roadway. Min Sci Technol 2010;20(6):820–4. [12] He Manchao, Tao Zhigang, Zhang Bin. Application of remote monitoring technology in landslides in the Luoshan mining area. Min Sci Technol 2009;19(5):610–4. [13] Tao Zhigang, Zhang Bin, He Manchao. Research on mechanism and monitoring and eearly-warning technology of landslide in luoshan mining area. Chin J Rock Mech Eng 2011;30(Suppl. 1):2931–7. [14] Yao Aijun. Study of coupling analysis theory and method for slope engineering stability. Beijing: China University of Mining & Technology Press; 1999. [15] Zhang Zhuoyuan, Wang Shitian, Wang Lansheng. Engineering geological analysis principal. Beijing: Geological Publishing House; 1981.