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Effect of Underground Blasting on Surface Slope Stability: A Numerical Approach

Mohammed Sazid
American Journal of Mining and Metallurgy. 2017, 4(1), 32-36. DOI: 10.12691/ajmm-4-1-2
Published online: June 08, 2017

Abstract

Stability of surface slope is a big challenge when underground excavation carried out just below the slope by the conventional drilling and blasting method. Blasting generates huge intensity of dynamic loading in the surrounding rock mass. If the intensity of dynamic loading is high, then it may be one of the reason for the triggering of instability in the surface structures. So, in the present paper, underground coal blast model has been developed using finite element method to understand the ill effects of underground blasting on the surface slope stability. Slope instability results have been represented by Peak Particle Velocity (PPV) of blast waves at varying time frames. Results have been computed on predefined specific target points which are crucial in terms of stability of surface slope. It has found that lowest bench has greater impact of blast loading and it can be dangerous from the stability point of view, whereas lower particle velocity monitored at the top most bench, compared to the other target points. It is all due to the attenuation of blast vibration energy with respect to the time and distance. From this study, it can be said that numerical modelling tool can be used to understand the phenomenon of dynamic blast vibration loading and its effects on the surface slope stability.

1. Introduction

The stability of surface slope is an important issue for safety reasons. This becomes of more concern when these surface slopes are located above underground mine. These mines usually use blasting for rock fragmentation to desired size as well as to displace the fragments. Only a fraction of explosive energy is utilised in fragmentation and displacement of rock mass and rest of the energy is wasted in various blast nuisances, like, blast vibration, air blast, flyrock, noise, etc. Among these, blast vibration is a big threat for the stability of surrounding structures in the vicinity of the mining areas leading to their failure 3, 4, 9, 24. Several examples of pit slope failure due to underground rock blasting are reported in various published literature 2, 22, 23. Many authors attributed such slope failures to blast vibration 12, 20, 26. However, many researchers reported the difficulty of monitoring underground blast vibration intensity at various locations of surface slope. This was attributed to the fact that monitoring of blast vibration is carried out using seismographs. This procedure has many disadvantages among which is time consuming, and large number of needed seismographs in addition to its high cost. Therefore, numerical modelling was considered as an alternative technique for this purpose. Besides its low cost, it is easy to use and has the capability to deal with dynamic loading conditions. Where, this dynamic loading is usually expressed in peak particle velocity (PPV) which reflects slope stability with respect to the intensity of blast vibration waves 5, 24, 25. In this paper, surface slope stability at Indian coal mine will be investigated as a function of PPV resulted from underground mine blasting. In this regard, two dimensional finite element numerical modelling will be used.

2. Numerical Model

Figure 1 shows geometry of 2D model reflecting the geological column of the investigated Indian area. The deposit has three coal seams of approximately three meter impeded within shale and sandstone rocks. The first and the second coal seams are economically excavated using surface mining techniques. On the other hand, the third seam is 57 meter below surface and it is exploited using underground mining. The model also illustrates that the underground mine have galleries with 3 m (wide)*1.2 m (height) separated by 19 m pillars. However, properties of coal and the different surrounding rock masses are shown in Table 1. In this study, mine working is starting from the central gallery due to its nearness from the surface and thus considered as blast dynamic loading source. Central underground gallery has been denoted as the source of dynamic explosion.

Several numerical tools are available to investigate the slope instability due to PPV (Preece and Thorne 1996; Jia et al. 1998; Wang et al. 2009). This model will investigated using commercial software Abaqus/explicit. In the model, the peak particle velocity will be predicted in different bench crest (1 to 4) as denoted in Figure 1.

Results of finite element models are elaborated in terms of PPV with time frame. The model analyzed for a total duration of 100 millisecond to reduce computational cost. Table 2 demonstrates the explosive properties used in this model.

Detonation energy products has defined by JWL (Jones Wilkins Lee) equation of state 6, 7, 10, 11. JWL equation is most versatile and widely used to assign the explosive material properties for pressure generation as given in equation 1.

(1)

Where, A, B, R1, R2, Em0 and are constants, P is the pressure (depended variable), internal energy per unit mass, user defined density of explosive and density of the detonation product. In addition, ω is the Gr ̈uneisen coefficient and A, B, R1, R2 are parameters. The parameters A and B have dimensions of pressure, while R1, R2 and ω are dimensionless. They are subject to the constraints that R1>R2>0 and ω>0. Moreover, for explosive products A>B> 0. But, when used for reactants A>−B>0.

3. Results and Discussion

Figure 2 (a-j) shows the total different frames used to represent the PPV with time. It can be seen from this figure that PPV started to propagate around the blasting area. The maximum value of PPV is 114.5 m/s at 3 millisecond after the blast, which is very high (Figure 2a). However, this PPV has still existing in surrounding blast gallery but could not reach to the surface. At around, 25 millisecond, the PPV become affects the surface and at 35 millisecond it started to affect the first bench of mines. It took nearly 100 millisecond to reach at the upper most bench of the mine. Figure 2 (a-j) clearly demonstrates the velocity vector at different time frames and its impact on the surrounding rock mass.

It also indicates that as the time and distance passed, velocity vector scale is substantially decreased and it is all due to the attenuation of blasting energy. The peak particle velocity curve of target points with time frame are shown in Figure 3. It can observed that the first bench of mine is severely affected by blasting, whereas the top most bench of mine is less affected due to the attenuation of blasting energy. The measured peak particle velocity at target points 1 and 4 are 0.55 m/sec and 0.08 m/sec, respectively.

The purpose of blasting is to fracture the rock mass and it should be exceeded the strength of the rock or exceed the elastic limit of the rock mass. When this limit crosses, fracturing occurs. As fracturing continues, the energy is used up and eventually falls to a level less than the strength of the rock and fracturing diminishes. The remaining energy travels through the surrounding rock mass, and deform it but could not able to fracture the rock mass due to elastic limit. This will result in the generation of ground vibration and it could damage the nearby structures. If there is any rock slope situated nearby to the blasting source, it stability would be effected by ground vibration.

The PPV damage criteria has been widely used for blast-induced damage. Therefore, in the present study, slope target nodes were analyzed (Table 3) to understand the damage on each bench with respect to blast vibration. It can be observed that first target point is heavily affected due to high PPV (550 mm/sec), whereas target node of the upper most bench shown the lowest value of PPV (80 mm/sec). As per the damage criteria suggested by the Adhikari et al., 1 for medium rocks, first target slope node can be considered under induced cracking categories, second denoted the falling of loose pieces, third and fourth can be represented the no damage categories. Therefore, first target point can be considered as most vulnerable slope under the condition of underground blast loading.

4. Conclusions

The instability of slope due to underground blast loading was investigated through numerical simulation using Abaqus/explicit finite element. Slope instability was identified by peak particle velocity (PPV) at previously marked target points at various bench slope using numerical model. Different velocity vectors were studied on each bench slope to find out the influence of PPV on the slope instability. Nearest target point from blasting represented the more vulnerable slope and its effect attenuated with respect to time and distance. This numerical study provides useful information of blast energy propagation in the rock mass which can be understood and visible during blasting operation in the field. Therefore, numerical modelling can be considered as a useful tool to understand the complex processes of blast wave propagation, which is very difficult to study at the field or mine site.

References

[1]  Adhikari G.A., Rajan B., Venkatesh H.S. Thresraj A.I. (1994). Blast damage assessment for underground structure. Proc Nat symp on emerging mining and ground control technologies. Varanasi, India. 247-55.
In article      
 
[2]  Chang-jing X, Song Z, Tian L, Liu H, Wang L, Wu X (2007). Numerical analysis of effect of water on explosive wave propagation in tunnels and surrounding rock. J Univ China Min Tech 17(3): 368-371.
In article      View Article
 
[3]  Deb D, Jha AK (2010) Estimation of blast induced peak particle velocity at underground mine structures originating from neighbouring surface mine. Min Technol 119(1): 14-21.
In article      View Article
 
[4]  Deb D, Kaushik K.N.R., Choi B.H., Ryu C.H., Jung Y.B., Sunwoo C. (2011). Stability Assessment of a Pit Slope Under Blast Loading: A Case Study of Pasir Coal Mine. Geotech Geol Eng. 29: 419-429.
In article      View Article
 
[5]  Hakan Ak, Melih I, Mahmut Y, Adnan K (2009). Evaluation of ground vibration effect of blasting operations in a magnesite mine. Soil Dyn Earthquake Eng 29(4): 669-676.
In article      View Article
 
[6]  He H., Liu Z., Nakamura K., Abe T., Wakabayashi K., Okada K., Nakayama Y., Yoshida M., Fujiwara S. (2002). Determination of JWL equation of state parameters by hydro-dynamically analytical method and cylinder expansion test. J. Japan Explosives Soc. 63(4): 197-203.
In article      View Article
 
[7]  Itoh S., Hamashima H., Murata K., Kato Y. (2002). Determination of JWL parameters from underwater explosion tests. In: 12th Int. Detonation Sym. San Diego, California. 1-6.
In article      View Article
 
[8]  Jia Z, Chen G, Huang S (1998). Computer simulation of open pit bench blasting in jointed rock mass. Int J Rock Mech Min Sci 35(45): 476-483.
In article      View Article
 
[9]  Khandelwal, M., Armaghani, D.J., Faradonbeh, R.S. et al. (2017). Classification and regression tree technique in estimating peak particle velocity caused by blasting. Engineering with Computers (2017) 33: 45.
In article      View Article
 
[10]  Lee E., Finger M., Collins W. (1973). JWL Equation of state coefficients for high explosives. Technical report UCID-16189, Lawrence Livermore National Laboratory, Livermore, CA.
In article      View Article
 
[11]  Menikoff R. (2015). JWL Equation of State. LosAlamos National Laboratory, LA-UR-15-29536.
In article      View Article
 
[12]  Monjezi, M., Hasanipanah, Khandelwal M. (2013). Evaluation and prediction of blast-induced ground vibration at Shur River Dam, Iran, by artificial neural network. Neural Comput & Applic. 22: 1637.
In article      View Article
 
[13]  Preece D.S., Thorne B.J. (1996). A study of timing and fragmentation using 3-D finite element technique & damage constitute model. Proc of 5th Int symp on rock frag on blasting. Montreal, Canada. 25-29 August.
In article      View Article
 
[14]  Qu S, Zheng X, Fan L, Wang Y (2008). Numerical simulation of parallel hole cut blasting with uncharged holes. J Uni Sci Technol Beijing 15(3):209-215.
In article      View Article
 
[15]  Saharan M.R., Mitri H.S. (2009). Numerical simulation for rock fracturing by distress blasting- As applied to hard rock mining condition. VDM Verlag Dr. Muller, Germany. p. 243.
In article      
 
[16]  Sanchidria´n JA, Segarra P, Lo´pez LM (2007). Energy components in rock blasting. Int J Rock Mech Min Sci 44(1): 130-147.
In article      View Article
 
[17]  Sazid M, Wasnik A.B., Singh P.K, Kainthola A., Singh T.N. 2012. A Numerical Simulation of Influence of Rock Class on Blast Performance, International Journal of Earth Sciences and Engineering, 5 (5), 1189-1195.
In article      
 
[18]  Sazid M., Saharan M.R. and Singh T.N. (2011). Effective Explosive Energy Utilization for Engineering Blasting- Initial Results of an Inventive Stemming plug, SPARSH. Harmonising Rock Engineering and the Environment, 12th ISRM Congress, 1265-1268.
In article      View Article
 
[19]  Sazid M., Singh T.N. (2013). Two dimensional Dynamic Finite Element Simulation of Rock Blasting. Arab J Geosci. Vol 6(10), 3703-3708.
In article      View Article
 
[20]  Sazid M., Singh T.N. (2015). Numerical assessment of spacing–burden ratio to effective utilization of explosive energy. Int J Min Sci & Tech. 25 (2), 291-297.
In article      View Article
 
[21]  Singh T.N. Sazid M. and Saharan M.R. (2011). A study to simulate air deck crater blast formation-A numerical approach. ISRM Regional Symposium-7th Asian Rock Mechanics Symposium pp. 495-505.
In article      View Article
 
[22]  Wang ZL, Konietzky H, Shen RF (2009). Coupled finite element and discrete element method for underground blast in faulted rock masses. Soil Dyn Earthquake Eng 29(6):939-945.
In article      View Article
 
[23]  Wang ZL, Li YC, Shen RF (2007). Numerical simulation of tensile damage and blast crater in brittle rock due to underground explosion. Int J Rock Mech Min Sci 44(5):730-738.
In article      View Article
 
[24]  Wu YK, Hao H, Zhou YX, Chong K (1998). Propagation characteristics of blast-induced shock waves in a jointed rock mass. Soil Dyn Earthquake Eng 17(6):407-412.
In article      View Article
 
[25]  XinPing Li, JunHong H, Yi Luo, Qian D, YouHua Li, Yong Wan, and TingTing Liu (2017). Numerical Simulation of Blast Vibration and Crack Forming Effect of Rock-Anchored Beam Excavation in Deep Underground Caverns. Shock and Vibration 17: 13.
In article      View Article
 
[26]  Zhi-liang W, Yongchi L, Wang JG (2008). A method for evaluating dynamic tensile damage of rock. Eng Fract Mech 75(10): 2812-2825.
In article      View Article
 

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Cite this article:

Normal Style
Mohammed Sazid. Effect of Underground Blasting on Surface Slope Stability: A Numerical Approach. American Journal of Mining and Metallurgy. Vol. 4, No. 1, 2017, pp 32-36. http://pubs.sciepub.com/ajmm/4/1/2
MLA Style
Sazid, Mohammed. "Effect of Underground Blasting on Surface Slope Stability: A Numerical Approach." American Journal of Mining and Metallurgy 4.1 (2017): 32-36.
APA Style
Sazid, M. (2017). Effect of Underground Blasting on Surface Slope Stability: A Numerical Approach. American Journal of Mining and Metallurgy, 4(1), 32-36.
Chicago Style
Sazid, Mohammed. "Effect of Underground Blasting on Surface Slope Stability: A Numerical Approach." American Journal of Mining and Metallurgy 4, no. 1 (2017): 32-36.
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[1]  Adhikari G.A., Rajan B., Venkatesh H.S. Thresraj A.I. (1994). Blast damage assessment for underground structure. Proc Nat symp on emerging mining and ground control technologies. Varanasi, India. 247-55.
In article      
 
[2]  Chang-jing X, Song Z, Tian L, Liu H, Wang L, Wu X (2007). Numerical analysis of effect of water on explosive wave propagation in tunnels and surrounding rock. J Univ China Min Tech 17(3): 368-371.
In article      View Article
 
[3]  Deb D, Jha AK (2010) Estimation of blast induced peak particle velocity at underground mine structures originating from neighbouring surface mine. Min Technol 119(1): 14-21.
In article      View Article
 
[4]  Deb D, Kaushik K.N.R., Choi B.H., Ryu C.H., Jung Y.B., Sunwoo C. (2011). Stability Assessment of a Pit Slope Under Blast Loading: A Case Study of Pasir Coal Mine. Geotech Geol Eng. 29: 419-429.
In article      View Article
 
[5]  Hakan Ak, Melih I, Mahmut Y, Adnan K (2009). Evaluation of ground vibration effect of blasting operations in a magnesite mine. Soil Dyn Earthquake Eng 29(4): 669-676.
In article      View Article
 
[6]  He H., Liu Z., Nakamura K., Abe T., Wakabayashi K., Okada K., Nakayama Y., Yoshida M., Fujiwara S. (2002). Determination of JWL equation of state parameters by hydro-dynamically analytical method and cylinder expansion test. J. Japan Explosives Soc. 63(4): 197-203.
In article      View Article
 
[7]  Itoh S., Hamashima H., Murata K., Kato Y. (2002). Determination of JWL parameters from underwater explosion tests. In: 12th Int. Detonation Sym. San Diego, California. 1-6.
In article      View Article
 
[8]  Jia Z, Chen G, Huang S (1998). Computer simulation of open pit bench blasting in jointed rock mass. Int J Rock Mech Min Sci 35(45): 476-483.
In article      View Article
 
[9]  Khandelwal, M., Armaghani, D.J., Faradonbeh, R.S. et al. (2017). Classification and regression tree technique in estimating peak particle velocity caused by blasting. Engineering with Computers (2017) 33: 45.
In article      View Article
 
[10]  Lee E., Finger M., Collins W. (1973). JWL Equation of state coefficients for high explosives. Technical report UCID-16189, Lawrence Livermore National Laboratory, Livermore, CA.
In article      View Article
 
[11]  Menikoff R. (2015). JWL Equation of State. LosAlamos National Laboratory, LA-UR-15-29536.
In article      View Article
 
[12]  Monjezi, M., Hasanipanah, Khandelwal M. (2013). Evaluation and prediction of blast-induced ground vibration at Shur River Dam, Iran, by artificial neural network. Neural Comput & Applic. 22: 1637.
In article      View Article
 
[13]  Preece D.S., Thorne B.J. (1996). A study of timing and fragmentation using 3-D finite element technique & damage constitute model. Proc of 5th Int symp on rock frag on blasting. Montreal, Canada. 25-29 August.
In article      View Article
 
[14]  Qu S, Zheng X, Fan L, Wang Y (2008). Numerical simulation of parallel hole cut blasting with uncharged holes. J Uni Sci Technol Beijing 15(3):209-215.
In article      View Article
 
[15]  Saharan M.R., Mitri H.S. (2009). Numerical simulation for rock fracturing by distress blasting- As applied to hard rock mining condition. VDM Verlag Dr. Muller, Germany. p. 243.
In article      
 
[16]  Sanchidria´n JA, Segarra P, Lo´pez LM (2007). Energy components in rock blasting. Int J Rock Mech Min Sci 44(1): 130-147.
In article      View Article
 
[17]  Sazid M, Wasnik A.B., Singh P.K, Kainthola A., Singh T.N. 2012. A Numerical Simulation of Influence of Rock Class on Blast Performance, International Journal of Earth Sciences and Engineering, 5 (5), 1189-1195.
In article      
 
[18]  Sazid M., Saharan M.R. and Singh T.N. (2011). Effective Explosive Energy Utilization for Engineering Blasting- Initial Results of an Inventive Stemming plug, SPARSH. Harmonising Rock Engineering and the Environment, 12th ISRM Congress, 1265-1268.
In article      View Article
 
[19]  Sazid M., Singh T.N. (2013). Two dimensional Dynamic Finite Element Simulation of Rock Blasting. Arab J Geosci. Vol 6(10), 3703-3708.
In article      View Article
 
[20]  Sazid M., Singh T.N. (2015). Numerical assessment of spacing–burden ratio to effective utilization of explosive energy. Int J Min Sci & Tech. 25 (2), 291-297.
In article      View Article
 
[21]  Singh T.N. Sazid M. and Saharan M.R. (2011). A study to simulate air deck crater blast formation-A numerical approach. ISRM Regional Symposium-7th Asian Rock Mechanics Symposium pp. 495-505.
In article      View Article
 
[22]  Wang ZL, Konietzky H, Shen RF (2009). Coupled finite element and discrete element method for underground blast in faulted rock masses. Soil Dyn Earthquake Eng 29(6):939-945.
In article      View Article
 
[23]  Wang ZL, Li YC, Shen RF (2007). Numerical simulation of tensile damage and blast crater in brittle rock due to underground explosion. Int J Rock Mech Min Sci 44(5):730-738.
In article      View Article
 
[24]  Wu YK, Hao H, Zhou YX, Chong K (1998). Propagation characteristics of blast-induced shock waves in a jointed rock mass. Soil Dyn Earthquake Eng 17(6):407-412.
In article      View Article
 
[25]  XinPing Li, JunHong H, Yi Luo, Qian D, YouHua Li, Yong Wan, and TingTing Liu (2017). Numerical Simulation of Blast Vibration and Crack Forming Effect of Rock-Anchored Beam Excavation in Deep Underground Caverns. Shock and Vibration 17: 13.
In article      View Article
 
[26]  Zhi-liang W, Yongchi L, Wang JG (2008). A method for evaluating dynamic tensile damage of rock. Eng Fract Mech 75(10): 2812-2825.
In article      View Article