In the open pit mining, the steps of stripping and trenching are generally carried out by deep hole blasting method. According to the characteristics of working space, geological characteristics of mining rock and conditions of mining and transportation equipment, reasonable hole pattern and blasting parameters are selected. , charge structure, blasting network, detonation method and detonation sequence to achieve good blasting effect. However, in actual production, due to many factors, there are often bad blasting phenomena such as blasting, roots, large blocks, umbrellas, and unexploded shape of explosion piles, which seriously affect the efficiency of construction, loading and transportation, and construction safety. Analyze the causes of these undesirable blasting phenomena and propose solutions.

First, the blast upturn and backlash phenomenon

In the open-pit mining blasting construction, the rear hole is rushed up and down is a common phenomenon, especially in the case of multi-row blasting, the rock mass crack and the rear hole upturn generated on the unexploded step slope. The accumulation of ore rock on the top surface of the unexploded step will bring great difficulties to the next blasting work. The main reason for the rushing up and down after blasting is that the multi-row hole blasting, the front row hole chassis resistance line is too large, the blasthole packing height is too large, the number of blasting rows is too large, and the blasting parameters and the detonation method are improperly selected. The solution is:

1. Control the resistance line of the front row hole chassis not to exceed the step height, strengthen the cleaning of the root bottom before blasting, reduce the blasting resistance of the root of the front row hole, and create a good blasting free surface for the rear row hole when the front row hole is detonated.

2, according to the design of the step height, reasonable cloth holes, the spacing charge structure can be used and reduce the amount of charge in the rear row of holes. If possible, increase the step height when the conditions of the mining equipment permit, thus promoting the horizontal movement of the rear hole during detonation, rather than the funnel and backlash up.

3. When using multi-row hole differential blasting, select the optimal interval between rows for different ore. For large-area millisecond blasting, the blasting conditions of the rear row hole are obviously different from those of the front row of holes, and the clamping is made larger, and the blasting stress wave of the front row hole and the explosive gas have a great influence on the blasting of the rear row hole. If the interval between the differentials is too short, the front row of holes cannot move to the step free surface within the desired time, and the rear row of holes will be backflushed or upturned due to excessive resistance lines. The initiation interval of the front and rear holes should be reasonable at 12-16ms/m according to the resistance line, and the rear hole should be increased by time interval, generally 10%. It is ideal to explore in the blasting experiment according to the specific conditions. The blasting effect. In general, the shorter the step height, the longer the step movement time, and the increase in the interval between the rows is particularly necessary.

4. The inclined deep hole blasting method is adopted to reduce the resistance line of the rear row hole chassis.

Second, the bottom of the blast phenomenon

The generation of the blasting roots not only seriously affects the construction quality, but also increases the unit consumption and the safety risks. The main reasons for the root cause are: the chassis resistance line is too large, the over-drilling depth is insufficient, the step slope angle is too small, and the working line is propelled along the rock layer. In order to overcome the blasting phenomenon, the following measures can be taken.

1. Ensure sufficient depth of drilling. After drilling, take effective measures to protect the hole. Before charging, carefully measure whether the hole depth meets the design requirements, and ensure that the charge is added to the bottom to improve the power of the bottom of the hole. The depth of the ultra-drilling is generally determined by the empirical value. The stronger the ore rock or the larger the diameter of the borehole and the parameters of the hole network, the larger the value; otherwise, the softness of the ore, the development of the joint or the smaller the pore size and the pore network parameters, or the small value. Deep, even super deep negative.

Third, the blasting block

The appearance of large blocks after open-pit blasting is the most common type of blasting failure. The increase in bulk rate has seriously affected the shovel, loading efficiency and construction safety of the mine. The generation of large blocks is caused by a variety of reasons, mainly in the following areas: 1 side row hole and step slope surface; 2 blast hole filling part; 3 soft and hard rock interface part; 4 hard ore rock. In the blasting, technical measures should be taken to control the large block rate according to the selection of the shovel, loading and transportation equipment and the characteristics of the rock.

1, the large block of the slope

The large block of the slope of the step is mainly a certain range adjacent to the slope of the step. The rock mass is destroyed by the previous blasting action, and a large number of rock mass cracks are generated, and even cut into larger blocks, causing the reflection of the explosion stress wave. Weak, causing the subsequent blasting side hole blasting effect to be limited to the range close to the grain column, it is difficult to reach the inside of the block slope surface, the blasting effect only causes the block to collapse from the original rock mass and produce limited crushing and crushing. In addition, the explosive gas may also be generated by the leakage of the crack formed by the previous blasting, and the super-explosion phenomenon of the rear row hole should be minimized.

Another reason for the large slope of the step slope is that the resistance line is not uniform. Due to the irregular top line of the step slope, the resistance of the front row of the chassis is large, and the bottom of the local step may have an excessive resistance line, or due to the step slope. If the face angle is too small, a small resistance line is generated in the upper part of the step, and it is easy to cause the explosion gas to generate a large block by leaking against the upper part of the weak step. In the construction, it is necessary to strictly control the resistance line of the front row of holes to be basically uniform, or pay attention to adjust the amount of charge. In addition, the slope angle of the step should be no less than 75°, and the roots should be thoroughly excavated before detonation.

2, the big piece at the top of the step

When the blasting at the bottom of the blasthole is used, the blasting action of the orifice filling part is relatively weak, and the uneven distribution of the charging structure causes more large blocks at the top of the step. Another reason for the large block at the top of the step is that the top of the step is affected and destroyed by the step blasting in a certain depth, forming a crack-cutting top rock mass, especially when the ultra-deep inconsistency is more harmful, which can cause explosive gas. Leakage or blast stress waves weaken at the top of the step and produce more bulk. To reduce such large chunks, the following measures can be taken:

1 Small aperture blasting, small aperture corresponding to small resistance line, hole spacing and filling height, this method limits the size of the large block, while the explosive energy distribution is relatively more uniform, the bulk yield is low, but will Significantly increase the cost of drilling and blasting, which can be reasonably applied according to the selection of mining and transportation equipment.

2 Using the segmented charging method, an auxiliary short-paste column is placed in the blasthole packing part. The function of the drug column is to assist the main drug column to break a large number of orifice rocks, but the dosage should not be too large, so as not to cause excessive Air shock waves, blasting flying stones or cutting off blasting networks. The essence of the charge structure is to redistribute the explosive energy in the bore. In addition, it should be noted that the short column and the main column of the charging structure need to be simultaneously detonated. If the main column is detonated before the short column, the short column may be flushed out of the hole with the filling, if the main drug The column lags behind the short column, and the short column causes cracks in the orifice, so that the main column is ineffective to release the blasting energy. When detonating, the detonating cord in the hole should be simultaneously detonated at the same time, so that the rock mass at the top of the step, that is, the top of the step, is broken at the same time.

If there are still large blocks in the above measures, it is necessary to set the auxiliary holes in the normal cloth holes in order to evenly distribute the explosive energy in the rock at the top of the steps. The above method can effectively control the bulk yield of the top of the step and the filling area of ​​the orifice.

3. Large blocks of soft and hard rock interface

In the boundary between hard rock and soft rock in the same explosion area, large strips can be clearly seen on the surface of the explosive pile, and more large blocks are easily generated in the part where the blasting medium changes significantly. This is because the hard and soft rock interface is equivalent to the free surface, which unloads the stress wave, and the change of the softness and hardness of the rock makes the impact of the collision and breakage weakened, thus producing more large blocks. In these areas, the drilling depth can be adjusted reasonably according to the position of the soft and hard rock layers or the auxiliary holes can be added to improve the blasting effect.

4, large blocks of difficult torn ore

The refractory ore rock refers to the dense and hard rock mass. In the blasting process, the explosive gas is difficult to invade and easily form a large block. Secondly, the detonation gas leaks from the cracks of the refractory ore rock. The bulky rock is not able to form a large block due to the effective breaking rate. It is often possible to see the yellow-brown native surface in the pop pile, rather than the ore. The fresh section produced after the rock blasting, the large block caused by the latter is difficult to overcome from the blasting technique. Moreover, the slope of the step, the top surface, the blasting phenomenon, the soft and hard rock interface, the improper blasting parameters, the detonation of the detonating equipment, the jump, and other large-scale unfavorable phenomena are particularly prominent in the difficult-explosive ore area, making the large The block rate has increased sharply, which seriously affects the shovel loading efficiency of mines. It is the biggest problem encountered in open pit blasting.

In the open-pit mine step blasting, when two adjacent blastholes are packaged, the stress along the direction of the medicine package is strengthened, and the stress reduction zone appears on both sides of the midpoint of the heart line. The detonation gas is prematurely Released at the heart line, resulting in an increase in the bulk rate. The long-term blasting practice of open pit mines shows that the resistance line can be reduced by adjusting the detonation sequence without changing the blasting area of ​​the hole. At the same time, increasing the hole spacing is to improve the blasting effect by increasing the blasthole intensive parameters.

The principle of large-hole blasting of small resistance line is: 1 large-pitch blasting makes the crack between the blastholes not penetrate early, the residence time of the explosive gas products is prolonged between adjacent blastholes, and the radial cracks and circumferential cracks are fully expanded; 2 small resistance line can enhance the effect of incident wave and reflected wave, increase the development of crack; 3 can increase the fracture angle, form a curved free surface for the next row of holes, approximately form the free surface of the resistance line, so that the direction along the resistance line The stress spreads evenly, which reduces the bulk. Small resistance line large hole distance blasting is realized by changing the initiation sequence on the basis of certain cloth hole parameters, and the triangle cloth hole can provide the optimal energy distribution in the rock body, and the degree of detonation sequence is adjusted to a higher degree. From the domestic blasting technical data, the best intensive parameters for open pit blasting are generally between 3.5 and 5.0, and foreign selection is between 3.5 and 4.5. In short, for the refractory ore, the principle of large hole spacing blasting and the principle of uniformity of explosive energy can be used to optimize the pore size and detonation parameters, and to increase the unit consumption of explosives to reduce the bulk rate.

In addition to the above reasons, the blasting parameters are not properly selected, and the blasting equipment quality is not related to the blasting and jumping phenomenon, which is also caused by large blocks, which can be solved by optimizing the blasting parameters and improving the quality of the blasting equipment.

references:

1. Wang Xuefeng. Experimental study on the differential interval between open-air blasting and detonation.

2, coal mine blast Practical Handbook, open deep hole blasting, Beijing Coal Industry Press, 2007

3. Changsha Mine Research Institute, domestic open pit mine large area blasting technology investigation report 1987; foreign open blasting technology introduction, 1987

4. China Coal Industry Press, open pit mining manual. Perforated blasting.

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