Numerical Analysis of the Ground Vibration Isolation of Shock Wave Propagation under Blasting in NuiBeo mine, Quang Ninh

021 area is important information. It directly affects the choice of solution and Accepted 16th Aug 2021 blast parameter. Applying techniques and numerical analysis methods Available online 29th Nov 2021 using a database of shock waves after each explosion can help describe somewhat the image of the geological structure of the explosion area. Keywords: Numerical Analysis, Shock This paper introduces a technique of numerical analyzing shock wave data obtained from delay-time blasting to determine wave propagation Wave, Ground Vibration, velocity. This is one of the parameters that indirectly describe the rock Shock Wave Propagation. physical - mechanical property. The results of experimental application in Nui Beo coal mine area have confirmed the feasibility of the solution. Copyright © 20201Hanoi University of Mining and Geology. All rights reserved. 1. Introduction enable the blaster to make enlightened judments, when adjusting his blasting pattern Mining blasting breaks rock’s structures, to to compensate for rock structure, he must have facilitate the process of mining. When an a through understanding of exactly how the explosive detonates, the sudden change explosive funtions during blasting. generates waves in the surrounding area In reality, each type of rock in one area has causes the ground to be vibrated. As the unique characteristics and irregular changes, vibration passes through the surface making the understanding of exactly of geologic structures, it induces vibration in those structures of one area become an impossible structures. These shock waves can cause mission. So, the execution of blasting always several damages to the nearby structures or contain experience factors and approximate surrounding rock mass. Rock strengths change calculation methods. over both small and large scale. Geological The size of an blast is not the decisive factor structures such as joints, bedding planes, faults affecting the maximum particle velocity, but the and mud seams cause serious problems. simultaneous explosives weight. To reduce the (Charles H. Dowding 1984; Langefors U et al seismic wave, the explosion is divided into 1958). Therefore, the rock’s physical- several smaller explosions using the delay time mechanical features are significant parameters with a difference of 1/1000 s. Another method in designing blast and have a directly influence for this issue is to arrange the explosion so that on explosions effectiveness. The drilling of the blast wave collides with each other to self- blastholes provides information about the type destruct the vibration. An electronic of intersectional structures at those holes. To differential detonator with a capability of 105 HỘI NGHỊ KHOA HỌC TOÀN QUỐC VỀ CƠ KHÍ – ĐIỆN – TỰ ĐỘNG HÓA (MEAE2021) regulating the delay time provides flexibility - Point number 2: CA > CB; two peaks when controlling the explosion direction, appear at the same time, almost, as described in leading to the reduction of vibrations and the case (2). In that, the propagation velocity is increase of breaking capacity. However, the determined by the formular: implementation process can not be relied on (CA – CB)/ T. the theoretical calculation. - Point number 2 or 3: CA  CB; two peaks The released energy from the blast point is of wave are independent; the time from one represented by the level of ground vibration peak to the other is t, as described in case (3) and the peak particle velocity of vibration wave or (4). The propagation velocity is determined which spreads in all surrounding directions. If by the formular: the ground is homogeneous and the energy |CA – CB| / |T - t|. transmitted in all directions is the same, the - Point number 2: CA – CB = AB = a (m); two vibrations in all directions would be equal. peaks of wave are independent; the time from However, in fact, the propagation of vibrations one peak to the other is t, as described in case is not ideal due to changes in the earth's (3) or (4). The propagation velocity is structure and changes in the vibrations in determined by the formular: different directions. a / (T - t) The seismic wave propagating from the blasting point is composed of three C 3 1 C 2 C  T components: a P wave (pressure wave or (1) longitudinal wave), an S wave (shear wave) and (2) a Rayleigh wave. Its speed varies in the range of t between 1000 and 20000 feet/s depending on (3) t the working area. The P wave gives the highest (4) breaking effect and the propagation velocity of B C the P wave (Vp) is also the greatest. In some A 4 cases, Vp=2Vs and it is almost the same for all T(s), a(m) areas (Vs is the propagation velocity of the shear wave). That is the basis to reduce the impact of blasting vibration by using delay time Figure 24. Theoretical basis for calculating the (Calvin J. Konya et al, 1991). propagation velocity of shock waves 2. Analytical basis In reality, the rock of explosion area is not uniform. That changes the propagation velocity Assuming that, there are two explosives at of the shock wave. However, because of some two points in a homogeneous environment: A following reasons: The propagation velocity is and B (Figure 1). The distance between these so large with the distance explosion-mesuring points is a (metre). The explosive at point B point; The calculation is performed at the same explodes after point A with a delay time of T blast; The directions of propagation of waves miliseconds. At the measuring point C, the can be considered to be the same. Then, the measuring device receives two peaks of shock propagation velocity of two corresponding wave at two explosion times, corresponding. shock waves will have the same error, so, the There are a few cases: time from one peak to the other is remained as - Point number 1: CA = CB; two peaks of the theoretical condition. Therefore, this wave are independent; the time from one peak calculation method can be applied to determine to the other is approximate T, as described in the actual propagation velocity of shock wave case (1). In this case, it is not possible to in a certain area. That result will be an determine the wave propagation velocity. 106 HỘI NGHỊ KHOA HỌC TOÀN QUỐC VỀ CƠ KHÍ – ĐIỆN – TỰ ĐỘNG HÓA (MEAE2021) important information for design the highly each measurement: 1 – 90 seconds. Sampling effective blasting. rate: 1024, 2048, 4096 samples/sec. It can 3. Experimental application in Nui Beo coal store data for 1000 measurements with a mine area, Quang Ninh sampling rate of 2048 samples/second and a recording time of 1 second. Vibration range 3.1. Measure and record data of shock waves that can be recorded: 0.2÷30.0 mm/s. Results caused by blasting can be printed in the field as a graph. Although actual blasts have a lot of delay Experimental data are measured and times. But, the explosion speed is so high and recorded in the area of reservoir 10, Nui Beo vibration duration of the paticiples is very coal mine, Quang Ninh (circled area on the map short, only one data can be recorded after each in Figure 3). The measurement location is at the blast. To ensure recorded data is the best, the mine boundary, belonging to Mr. Pham Dinh measurement and recording systems need to Thu family, address: group 9, zone 7, Ha Tu meet some principles that: ward, Ha Long city, Quang Ninh (is the x - The measurement equipment must be marked on the map in Figure 3). The work was standard; done by blasting seismic expert Nguyen Duc - The recorded data must be completed and Chinh, Cam Pha Mining Chemical Company continuous over time to avoid the fluctuations (Figure 3). Some measurement results are of participles by the effects of blasting; shown in Figure 4. - Information that cannot be recorded from the measuring, such as: total of holes; the number of rows and columns; row and column spacing; diagram of delay time; delay time, explosion location; measuring point; the distance from explosion point to measuring point. Mine-blasting area The measuring equipment used is Blastmate III (Figure 2). This is a vibration Measuring meter from Instantel, Canada. It is used in more point than 110 countries and is one of the most Map of Nui Beo coal mine reliable vibration meters in the world, today. Figure 2. Vibration meter Blastmate III Blastmate consists of two basic Measuring and recording data components, a meter and two sensors. The Figure 3. Recording data at Nui Beo coal mine sensor system including: a triaxial vibration sensor (Geophone) a sound sensor (Microphone) connected to the meter by wires. The measured data is sent to the meter in the electrical signal form. Recording interval for 107 HỘI NGHỊ KHOA HỌC TOÀN QUỐC VỀ CƠ KHÍ – ĐIỆN – TỰ ĐỘNG HÓA (MEAE2021) 2 Amount of explosives 61 61 in a borehole (Kg/hole) 3 Total number of holes 12 18 4 Row, column spacing 5 - 6 5 – 6 (m) 5 Rock hardness f 10,03 10,03 6 Type of delay-time 42 42 detornator and and (miliseconds) 100 100 7 Measuring distance 196 233 (a) (m) 8 Recording time 2 2 (seconds) 200 ms 242 ms 284 ms 326 ms 368 ms 410 ms 100 ms 142 ms 184 ms 226 ms 268 ms 310 ms 0 ms 42 ms 84 ms 126 ms 168 ms 210 ms Figure 5. The used delay-time diagram (ms - (b) miliseconds) Figure 4. Some data recorded Figure 4 shows the graphs of two blasts. 3.2. Analysis and comments The MicL axis describes the sound intensity of With the delay-time diagram described in the explosion; The vibrational velocities of Figure 5, it is easy to determine that the particles are described on 3 axes that are Long, periods between the explosive charges Vert and Tran. In which, the Long axis is the including: 100ms, 42 ms, 26 ms, 16 ms and 10 straight axis from the measuring point to the ms. Due to each charge, a peak of shock wave explosion point, so the waveform in this axis will be generated, these periods will be used for describes the effect of the compression wave the analysis. In three components P, S and R of component P in the 3 components of the shock the shock wave, P is the fastest component and wave (Press, Shear and Rayleigh). is the main cause of structural breakage and Explosions with measured results are vibration, so the analysis will focus on the data described in Figure 4. The detailed parameters on the Long axis (which describes the action of are shown in Table 1. The delay-time diagram the P wave). In addition, synthetic vibrations ( for blasts in this mine uses a unique type shown 2 2 2 in Figure 5. PPV= L + V + T ) are also analyzed for Table 1. Some parameters of blasting data reference data. The analysis process is recorded at Nui Beo coal mine (Lê Văn Công et al performed in 2 steps. In the first step, the data 2012; Souknavong Maniphet 2016) is performed in the frequency domain to No. Parameter (unit) (a) (b) determine the frequency range containing the 1 Total amount of 732 1098 highest peaks. In the second step, the data is explosives (Kg) described in the time domain to identify the times at which the peaks appear, the analytical method in Section 2 is applied to determine the 108 HỘI NGHỊ KHOA HỌC TOÀN QUỐC VỀ CƠ KHÍ – ĐIỆN – TỰ ĐỘNG HÓA (MEAE2021) propagation velocity of the shock wave. The results of calculating propagation velocity are wave peaks found are shown in Figure 6 for the described in Table 2. two data cases respectively in Figure 4. The Figure 6. Results of determining wave peaks Table 2. Calculation results of the propagation velocity of the shock wave Range of calculated propagation velocity in case 1 1250 - 1800 Average velocity when analyzing data of the L1 axis (longitudinal wave velocity) 1477 Average velocity when analyzing synthetic vibration PPV1 1238 Range of calculated propagation velocity in case 2 1250 - 2100 Average velocity when analyzing data of the L2 axis (longitudinal wave velocity) 1655 Average velocity when analyzing synthetic vibration PPV2 1573 109 HỘI NGHỊ KHOA HỌC TOÀN QUỐC VỀ CƠ KHÍ – ĐIỆN – TỰ ĐỘNG HÓA (MEAE2021) The results in Table 2 show that the range of the analysis results in any region can only be calculated results is quite large. It means that the applied in that region. When the amount of data analysis process still contains many errors analysis results is large enough, it will become coming from objective reasons, including: the database for the modeling of rock structure - The type of delay detonator used in the in the monitoring area. The larger the database, explosions is a non-electric delay time, they have the more convergent and accurate the model, low accuracy (allowed time delay error is ± 5ms especially, when the explosions ensure a number according to QCVN01:2019). That leads to errors of constant conditions such as measurement in the calculation expressions defined in Section position, measurement direction, measurement 2; terrain, explosion direction and delay time are - The explosion has many consecutive performed accurately. explosion points creating the mutual influence of the waves; Reference - The physical - mechanical properties of the rock and the change in the direction of explosion Paper published in journal compared with the measurement direction, make the results of different explosions Iau Teh Wang, (2019). Field Experiments and different. numerical analysis of the ground vibration However, the average velocity is determined isolation of shock wave propagation under by applying the expectation maximization (EM) explosion shock loading. MDPI Journal, algorithm to eliminate a certain amount of errors 11/2019, doi:10.3390. (Simon Haykin 2001). The average results found Langefors U, Kihlstrom B, Westerberg H, (1958). in Table 2 for the two cases are not much Ground Vibrations in Blasting. Water Power, different. The found value is consistent with the September, pages 335-38. October, pages common type, structure and hardness of soil and 390-95, 424. rock in Quang Ninh mine area (Lê Văn Công et al Lê Văn Công, Đặng Hồng Thắng, Lưu Công Nam, 2012; Nghiêm Hữu Hạnh 2001; Souknavong Nguyễn Trí Thắng, Phí Văn Long. (2012). Maniphet 2016) Công nghệ thi công và những yêu cầu cần 4. Conclusion and Discussion thiết khi thi công giếng đứng trong điều kiện các mỏ hầm lò Việt Nam . Viện Khoa học công The blasting shock wave propagates in the nghệ Mỏ - Vinacomin. rock, so it is directly affected by the properties of this environment. And therefore, the shock wave Sjoberg, J., Schill, M. Hilding, D., Yi, C., Nyberg, U., is the best information reflecting the structure, and Johansson, D. (2012). Computer mechanical and mechanical parameters of the Simulations of Blasting with Precise soil and rock in the blasting area. Numerical Initiation. Eurock, Stockholm, Sweden, 2012. Analysis is an analysis technique based on the Presentation at conferences digitization of data, so the analysis is detailed and accurate. Analysis results from experimental I Pinnock, DS Collins, Y Toya, Z Hosseini, 2015. data recorded at Nui Fat coal mine confirm that The use of microseismic acquition for Numerical Analysis of shock wave data can help vibration monitoring applications. 2015 determine the propagation velocity of blasting Australian centre for geomechanics, Sydney, shock waves. Australia. The velocity of shock wave propagation is Vedala Rama Sastry, Garimella Raghu Chandra, one of the important parameter to choose the (2016). Signal processing computation right differential time for blasting. Because the based Seismic energy estimation of blast geological structure of each region is different, induced ground vibration waves. IEEE 110 HỘI NGHỊ KHOA HỌC TOÀN QUỐC VỀ CƠ KHÍ – ĐIỆN – TỰ ĐỘNG HÓA (MEAE2021) International Conference On Recent Trends Công ty Hóa chất mỏ Cẩm Phả, Các hộ chiếu nổ In Electronics Information Communication mìn đã được thiết kế và sử dụng tại mỏ Núi Technology, May 20-21, 2016, India. Pages Béo. 216-220. Nghiêm Hữu Hạnh, (2001). Cơ học đá. Nhà xuất V V S Avinash Teja, S Venkata Chaitanya, Uday bản Giáo dục. Akula, Pathipati Srihari, V R Sastry, (2016). Quy chuẩn kỹ thuật Quốc gia về an toàn trong bảo Blast vibration signal analysis using S- quản, vận chuyển, sử dụng và tiêu hủy vật transform. IEEE International Conference on liệu nổ công nghiệp, QCVN01:2019/BCT, Hà Electrical, Electronics, and Optimization Nội 2019. Techniques (ICEEOT) – 2016. Pages 4182- Simon Haykin. (2001). Kalman filtering & neural 4186. networks. John Wiley & Sons, Inc. ISBNs: 0- 471-36998-5 (Hardback); 0-471-22154-6 Book (Electronic) Calvin J. Konya, Edward J. Walter, (12-1991). Simon Haykin. (2001). Kalman filtering & neural Rock blasting and overbreak control. networks. John Wiley & Sons, Inc. ISBNs: 0- National Highway Institude, Publication No. 471-36998-5 (Hardback); 0-471-22154-6 FHWA-HI-92-001. (Electronic). C. E. Needham, (2010). Blast Waves, Shock Wave and High Pressure Phenomena, ISBN 978-3- Master and Doctoral Thesis and Dissertation 642-05287-3, DOI 10.1007/978-3-642- Souknavong Maniphet (2016), Đánh giá hiện 05288-0, Springer Heidelberg Dordrecht trạng và đề xuất giải pháp quản lý môi trường London New York. một số mỏ than vùng Đông Bắc ở Việt Nam. Charles H. Dowding, (1984). Blast vibration Luận văn thạc sỹ, Đại học khoa học tự nhiên, monitoring and control. Evanston, Illinois, Đại học Quốc Gia Hà Nội. USA. 280 pages. 111