Completion time: December 2003

　　Project Location: Xinwen Power Plant, Tai'an City, Shandong Province

　　Completed by: Guangdong Hongda Blasting Engineering Co., Ltd.

　　Project host and participants: Zheng Bingxu, Lin Zaijian, Fu Jianqiu, Luo Weitao, Wang Tie

　　Writers: Lin Zaijian, Xing Guangwu, Lu Yi

　　1 Project Overview

　　In order to expand and renovate, the thermal power plant of Shandong Electric Power Pipeline Co., Ltd. needs to dismantle the main buildings in the original plant area. The hyperbolic cooling tower is one of them. The building is a reinforced concrete structure with a total height of 51.30m, a total square of 614m3, about 1470t, the diameter of the cooling tower, the bottom is 36.5m, the top is 21.8m, the smallest part is 20.9m; the maximum wall thickness is 25cm, the minimum wall thickness 10cm; the reservoir is 1.8m deep; the water tower is 47.4m high, and its elevation is shown in Figure 1. There are 58 40cm×40cm reinforced concrete columns on the periphery of the reservoir. The cool water tower has a 10m high cooling platform. The platform is prefabricated reinforced concrete members. There is no structural connection with the cool water tower wall. There are 68 under the platform. 30cm × 30cm reinforced concrete column support, the surrounding environment is open, the general layout is shown in Figure 2.

　　2 Selection of blasting plan

　　The cool water tower is a hyperbolic façade with a light and thin wall structure, which is narrower and wider than the bottom, and is difficult to dump. The blasting scheme of the water tower draws on the blasting design mode of the tubular structure, but a large explosion height should be adopted to obtain a large impact energy, so that the thin-walled cylinder with long-term corrosion and severe weathering is easily broken and disintegrated when it touches the ground. Good blasting effect. The support column of the 10m platform is also blasted.

　　3 Selection of blasting parameters

　　3.1 Notch high

　　The trapezoidal notch is used, and the notch is 12m high.

　　3.2 Notch length and notch center angle

　　When the cylinder is blown up by directional blasting, the center angle of the blasting notch is usually between 210° and 225°. After many comparisons, it is considered appropriate to take 215°. The cold water tower has a 10m high notch perimeter of 101.2m, a notch arc length of LP=101.2×(215/360)=60.90m, and a retention arc length L1=101.2-60.90=40.30m.

　　3.3 Pretreatment and formation of blasting gap

　　Since the area of ​​the notch is large, if the concrete wall columns in the thin-walled notch are all blasted, the number of blastholes is too large, and the blasting workload is large. Therefore, for the characteristics of this project, the four "edges" of the trapezoidal notch are blasted or pretreated, that is, a trapezoidal notch is formed, and the tower wall in the "edge line" does not need to be blasted, and the cool water tower can collapse. Its specific approach is:

　　(1) The notch "beveled edge" is 2m wide and is formed by removing the concrete from the tower wall with wind.

　　(2) Using a 10m high-temperature cold water platform as a drilling-eye construction platform, the tower wall is raised up to 2m. At the same time, pretreatment is carried out in the blasting area, the 1.2 m wide tower wall is preliminarily removed, the 1.5 m wide tower wall blasting is retained, and so on. This can reduce the amount of blasting work.

　　(3) The bottom of the tower body is 1.5m high.

　　(4) Cut 3 slits with a height of 6m and a width of 1.2m in the forward direction of +12.Om to weaken the rigidity of the tower body and make the tower body easy to break when it collapses.

　　3.4 Hole arrangement and single hole charge

　　3.4.1 Tower wall blasthole parameters

　　Since the wall thickness of the 10m high notch is only 20cm, the diameter of the selected blasthole is 32mm, the hole spacing is a=20cm, the row spacing is b=20cm, the hole depth is l=12cm, the unit consumption is K=2000g/m3, and the single hole dose q= 16g.

　　3.4.2 bottom oblique support column blasthole parameters

　　The bottom support column also blasts 215° center angle, a total of 38 slanting struts, each column of single row of holes, hole spacing a=20cm, hole depth l=25cm, unit consumption K=1500g/m3, single hole dose q =50g.

　　3.4.3 Cool water platform support column blasthole parameters

　　The hole distance a=15 cm, the hole depth l=20 cm, the unit consumption K=1.5 kg/m3, and the single hole dose q=20 g.

　　3.5 Blasting network time difference

　　In this blasting network, the detonator uses a millisecond delay non-electric detonator. The specific time difference is: the cooling platform support is 25ms, the platform of the 10m high platform is 300ms, the bottom slope support is 600ms, the connection is made of four-way and plastic detonating tube, the tower wall notch, the bottom support, the cool water platform support first form two The ring is closed and then the rings are overlapped multiple times to form a closed duplex crossover network.

　　4 Safety measures

　　(1) Because the wall of the cool water tower is thin, the blasting area is large, the blasthole is dense, and the single consumption of explosives is also large. Therefore, the drilling position and depth must be strictly controlled, and the balance of the medicine package should be kept as close as possible. This can control the flying distance of the flying stone and ensure that the explosion is completely broken.

　　(2) Double-layered Jingjing and safety net attached to the outside of the blasting part of the tower wall. This kind of near-body protection can block the flying stone and shorten the flying distance of the flying stone.

　　5 Vibration safety check

　　The safety vibration of this project is mainly composed of two parts, that is, the seismic wave generated by the explosive explosion and the vibration caused by the impact of the ground when the building collapses.

　　5.1 Calculation of blasting vibration

　　V1 = K·K'(Q1/3/R)α The maximum dose of this single blasting is 40kg. The nearest building distance is 45m, K is 150, K' is 0.3, and α is 1.5. The surrogate can be obtained: V1 = O.94cm/s.

　　5.2 Earthquake vibration calculation

　　In the formula, G takes 1.470000 kg, and the height of the center of gravity h takes 20 m, and v2 = 1.5 cm/s is calculated.

　　The construction environment of this project is relatively wide, the total charge is not large, and there are three layers of near-body protective cover around the blasting body to block the shock wave. According to the relevant measured data, the above measures can reduce the peak value of the shock wave by 40%. Therefore, the shock wave and noise generated by engineering blasting will not cause harm.

　　6 blasting effect

　　After 4s of detonation, the tower body collapsed completely, the tower wall was completely broken, and the height of the explosion pile was 4-6m. The blasting was successful.

　　Excerpted from "China's Typical Blasting Engineering and Technology"