1 Overview

North TONGCHANGHE help of a Cu ore mining area (region) 290 ~ 479m slope, complex regional structure, cracks and joints fault development, surface inclusions Longitudinal direction, exhibit different characteristics in different distribution sections. In a complex section of the Beibang (district) of the copper mining area, the rock mass of the step slope is subject to joint cutting. In different slope sections, the joint production changes greatly, and there are loose areas and slump areas. The blasting area is located in the middle of the 350m horizontal section of the section, and the northeast is adjacent to the final slope. The horizontal design has a 10m wide platform, the designed blasting area is 186.8m long, and the roof elevation is 348.2~348.6m. Below the explosion area is the transported rock road [1]. According to the operational safety requirements of the perforating equipment and the actual width of the working platform [2], in Figure 1, the blasting area I is perforated with a side rig .

2 blasting parameter design
2.1 pre-cracking
Before the main blasting blasting, the pre-splitting blasting is carried out, and the parameters of the pre-splitting blasting [3] are designed as follows:

The hole spacing of the lithology section is 1.5m, and the lithology difference is 1.3m; the hole depth is determined to be 16.0~16.5m according to the roof elevation; for the bottom of the blasthole of 1.5m pitch. 0m strengthens the charge, the line charge density is 3.0kg/m, the normal charge section is 1.0kg/m×10m, the total charge is 13kg/hole, and the bottom of the blast hole of 1.3m is 1.0m. The drug, the line charge density is 3.0kg/m, the normal charge section is 1.0kg/m×8.0m, the weakening section is 0.5kg/m×2.0m, and the total charge is 12.0kg/hole. The detonation network is segmented, and the 9 holes of the spray anchor section are a section to maximize the protection of the shotcrete concrete and the slope.
2.2 main blasting blasting
Due to the small working face in the east of the platform, the large cone rig is not operational, and the blasting area I (see Figure 2) is perforated using the CM351 slope rig. In order to speed up the construction progress, based on the principle of “pre-splitting blasting first”, it is proposed to adopt the scheme of pre-cracking and medium-deep hole blasting (the interval between the pre-split hole and the main blasthole is 100ms).

The main blasting parameters of the design are [4] as follows.
(1) Aperture D: The CM351 drill has a diameter of 140 mm.
(2) Hole depth L: The hole depth is determined by the step height H and the ultra deep h, and the front row hole depth L = H + h = 15.0 + (1.5 ~ 2.0) = 16.5 ~ 17.0 m (inclined hole), buffer hole depth L = H + h = 15.0 + 1.0 = 16.0 m (vertical hole) - 16.5 m (inclined hole), auxiliary hole depth L = 8 m (tilted hole).
(3) The safety condition of the chassis resistance line drilling operation is W1=Hctgα+Bmin, Bmin is the minimum safety platform width of the rig step edge operation, α=80°, Bmin=1.5m, and the calculation is W1≈4. 0m.
(4) Pitch a and row spacing b: a = () 0.8 to 1.4 W, taking a = 5.0 m, b = W = 4.0 m.
(5) The packing length l2 = () 20 ~ 30D, take l2 = 4.0m.
(6) Unit explosive consumption q. Refer to the Xiyuanling engineering experience [5-7] to determine the explosive consumption of q = 0.629kg / m3 (BDS on-site mixed vehicle emulsion explosives).
(7) Yanmi gun hole charge qL. BDS on-site mixed emulsion explosives 18 ~ 20kg / m.
(8) Charge amount Q per hole. The amount of charge in the front row is calculated by the following formula: Q=q·a·W1·H. The meaning of the symbol in the formula is the same as before. The charge in the front row is calculated as Q=190kg and the filling height is 7m. When the auxiliary hole is 4m deep, the charge is 20kg and the filling height is 3m. When the hole depth is 8m, the charge is divided into sections, the lower part is 40kg, the upper part is 20kg, the middle part is 1.0m, and the top is filled with 4.0m. The buffer hole charge is 185kg. Considering the fragility of the slope, the buffer hole (a row of deep holes in front of the pre-split hole) needs to be charged at intervals. The segment charge is distributed at 120kg (lower) and 65kg (upper). The intermediate backfilling 1.5m rock powder interval, filling height 8.2m. As shown in Figure 3.

In addition, for the 5~8m width position, 1 row or 2 rows of inclined holes can be arranged according to the site topography, and the inclination angle is 70°~75° (see Figure 4). The cloth hole principle is to control the chassis resistance line to approach the design value, the buffer hole bottom and the pre-crack hole bottom to reserve a protective layer thickness of 1.2 to 1.5 m. The blasting area I is shown in Figure 5. The blasting parameters of each blasthole are shown in Table 1.

2.3 detonation sequence
The free surface of the blasting area is better, and it is proposed to take a slash to detonate. The pre-split hole is detonated in two stages, one for 9ms and the other for 18ms. After the main blast hole is detonated in the pre-split hole 109ms, the hole is connected by a 25ms detonator tube, and the auxiliary hole is placed on the buffer hole with a 65ms detonator tube slant line, as shown in Fig. 6.

3 vibration reduction measures and precautions
In order to avoid the damage caused by blasting vibration to the fixed slope, the following technical and management measures are taken [8]:

(1) Control the scale of blasting, strictly implement the “Regulations on the Management of Final Slope of Mining Sites”, and control the total charge of each side of the gun to within 15t;
(2) Except for the encrypted front and auxiliary holes, all the main blast holes are in the form of a space charge;
(3) Increasing the extension time of the surface network, using the non-conducting detonator detonator (Orica detonator) detonation network, for the particularity of the geological structure of the site, the extension time of the surface network is matched with the traditionally used type II rock area with 25ms and 65ms. Instead, use 42ms with 100ms, and perform hole-by-hole detonation to reduce the impact of vibration on the slope.

Other notes:

(1) Strengthen on-site construction management, strictly in accordance with design and construction, to ensure the quality of the blasthole filling;

(2) When the gun is fired, the equipment of the 350m platform is more than 15m away from the bottom of the slope, and all personnel are evacuated to the shelter of the 320m platform (electric wheel) to avoid the gun;
(3) Before entering the explosion area after blasting, the stability of the slope above 350m should be carefully observed.
4 Conclusion
In the slope sliding zone, the design of the final slope blasting is implemented, which not only ensures the blasting effect, but also avoids the blasting vibration causing damage to the slope. We will do a good job in the quality of work in all aspects, adopt strict management and technical measures, and strive for the success of the blasting work.
On the basis of the principle of “pre-splitting blasting first”, it is feasible to adopt the scheme of pre-splitting hole and medium-deep hole blasting, but the workload is large and the process is complicated. If there is a problem in a certain link, it is likely to cause the slope. The collapse. Therefore, it is necessary to strictly design the blasting parameters and the blasting sequence, and do the corresponding vibration reduction measures.
references:
[1] Rao Yunzhang. Stability analysis of rock slope [M]. Changsha: Central South University Press, 2012.
[2] Zhou Shuliang. Advantages of perforation of open pit mine downhole drilling rig [J]. Mining Technology, 1992, 31: 7-7. Xu Jianrong, et al: A copper plant mining area is approaching the final slope blasting design 89
[3] Li Xibing. Rock drilling and blasting engineering [M]. Changsha: Central South University Press, 2011.
[4] Wang Xuguang. Blasting manual [M]. Beijing: Metallurgy Industry Press, 2010.
[5] Luo Shengping. Dexing Copper Mine. Ways to accelerate the Xiyuanling stripping project [J]. China Mine Engineering, 1997 (6): 14-16.
[6] Zhai Zigui, Luo Shengping. Accelerated Xiyuanling stripping project research [J]. Copper Engineering, 1997 (04).
[7] Zhang Fumin. Dexing Copper Mine successfully implemented special section blasting [J]. Engineering Blasting, 2014 (03): 62-62.
[8] Fu Shigen, Xu Kaili. Blasting vibration effect prediction and damping measures [J]. China Safety Production Science and Technology, 2006 (6): 45-48.