Completion time: 2004-2005

　　Project Location: Taiyuan, Shanxi

　　Completion unit: China Railway Third Bureau Group Corporation

　　Project host and participants: Zi Ligang, Liu Honggang, Zhang Junbing, Xu Jianzhong

　　Writer: Bai Ligang

　　1 Project Overview

　　The Datang Taiyuan No. 2 Thermal Power Plant was built in 1958. The No. 1 to No. 4 generating units have exceeded the service life. The owners decided to renovate the overdue service units and some equipment and buildings. The No. 1, No. 2, No. 3 cooling is required. tower. Because the cooling tower is tall and thin-walled reinforced concrete structure, it can not be manually removed, so it is decided to use directional control blasting technology for demolition construction.

　　Among them, the cooling tower No. 3 is a reinforced concrete structure, and the structure of the hyperbolic cylinder is shown in Fig. 1. The tower has a height of 70.15m, a bottom radius of 29.57m, an upper radius of 14.7m, a bottom wall thickness of δ = 400mm, and a top wall thickness of δ = 100mm. The tower body is located on 40 pairs of herringbone pillar reinforced concrete trusses, and the pillar section is a 40mm×40mm rectangular structure. The total amount of reinforced concrete in the cooling tower is 1085.2m3 and the total weight is 2658t. It is the highest height and largest diameter cooling tower currently removed by blasting methods in China.

Demolition of Cooling Tower of Datang Taiyuan Second Thermal Power Plant

　　Some buildings around the cooling tower need to be removed. However, the closest distance of Cooling Tower No. 3 to the newly-built office building of the key protection building is 24.067m, 28.962m from the brick house and 35.866m from the swimming pool (see Figure 2).

Demolition of Cooling Tower of Datang Taiyuan Second Thermal Power Plant

　　2 blasting plan selection

　　2.1 Engineering characteristics and design requirements

　　(1) The surrounding environment is complex and the direction of collapse must be strictly controlled.

　　(2) The bottom of the cooling tower has a large diameter and a small height ratio (1.18). When blasting, it should prevent the phenomenon of sitting without falling, falling without breaking and exploding too high.

　　(3) The cooling tower is a thin-walled structure with a large number of holes, it is difficult to fill the charge, and it is easy to produce flying stones. It is necessary to strengthen the protection.

　　(4) The detonation network is complex, and it is advisable to use a non-electric millisecond delay detonation technology or a multi-channel four-way relay network.

　　(5) Control the amount of single-shot drugs to ensure that the blasting vibration does not cause any harm to the office building, and attention should be paid to the impact of the floor-standing vibration of the tower body.

　　2.2 Blasting demolition plan

　　The blasting is controlled by “opening the window, breaking the steel bar, and retaining the supporting plate”, then using the hydraulic breaker to break, the excavator (or loader) to be shipped, and the car to the slag plant for mechanized construction.

　　2.3 Determination of collapse direction

　　Since the cooling tower structure is symmetrically arranged along the periphery, the structure itself has no influence on the collapse direction, and the collapse direction is mainly determined according to the surrounding environmental conditions. Since the right side of the No. 3 cooling tower is an office building, a brick house and a pool, both are protected buildings, and the cooling tower is designed to collapse in the direction of the north.

　　3 Determination of blasting parameters

　　3.1 Design of blasting gap

　　3.1.1 Notch design principles

　　The size, height and position of the blasting hole are important conditions for the cooling tower to collapse smoothly according to the design direction. Therefore, it should be designed according to the following principles:

　　(1) The size of the gap should meet the requirements of the tower body to collapse under the action of gravity after the blasting.

　　(2) The gap must ensure that the cooling tower body is fully ground after blasting, that is, collapsed rather than collapsed.

　　(3) The small amount of the gap itself can be created, and good protection conditions can be created. After the tower body is grounded, the crushing effect is good, and the tower body has a low stacking height to facilitate the cleaning of the slag.

　　3.1.2 gap size selection

　　(1) Gap form: adopt a "trapezoid" gap;

　　(2) Notch height (H): equal to the height of the herringbone pillar (h1), the height of the pillar ring (h2), and the height of the tower gap (h3), the total height is about 8m; H = h1 + h2 + h3, see the figure 3.

Demolition of Cooling Tower of Datang Taiyuan Second Thermal Power Plant

(Note: the shaded part in the figure is the pre-removed part, which is generally pre-dismantled with a breaker;

Each reserved support block is not less than 3.0m. ; the pillar ring only cuts three gaps)

　　(3) Notch length: according to the different components of the notch, take different lengths, wherein the length of the herringbone pillar is L1=1/2S, the length of the pillar ring is L2=220/360s, and the length of the tower body is L3=230/360s. Medium S is the perimeter of the tower.

　　3.2 Blasting parameters

　　The blasting parameters are shown in Table 1.

Demolition of Cooling Tower of Datang Taiyuan Second Thermal Power Plant

　　Note: The parameters in the table vary with the wall thickness of the tower.

　　4 detonating network

　　Because the cooling tower has large blasting surface and many holes, it is the key to the success of blasting. It is the key to the success or failure of the blasting. If the electric blasting network is used, the number of the blasting network is too large. The blast decision was made using a multi-channel four-way network. Each column pillar ring gap is used as a unit body, and 8 to 12 holes in each unit body are connected into independent unit bodies by 2 rounds of millisecond detonators, and each independent unit body is connected by a multi-channel four-way network, each The unit body consists of 4 to 8 channels, ensuring that all the medicine packs are reliably quasi-explosive.

　　5 Protective measures

　　5.1 Coverage protection

　　(1) Strong protection. Mainly used for the bottom of the pillar l ~ 1.5m, the pillar ring and the lower part of the tower support plate 3 ~ 4 holes. The pillars are protected by two layers of wet grass bags wrapped in two layers of sandbags. The pillar ring and the tower body support block are strongly protected by a three-layer grass bag tied to the bamboo plywood for the first layer of protection, and the outer plastic bag is two layers. Then tie it with 8 wire. The joint part must be overlapped, the overlap width is not less than 50cm, and the upper and lower ends must also be larger than the hole position 50cm. If necessary, add a wire mesh layer externally.

　　(2) General protection. It is mainly used for the upper part of the pillar and the pillar ring and the blasthole of the tower body. Because the blasting gap is broken and fried, the bottom 3~4 hole layer increases the dose, while the upper dose gradually decreases, and the upper part only causes loose damage, so Use general protection. Generally, a layer of bamboo plywood and three layers of straw bags are used for binding protection.

　　(3) The bottom layer protection. When there are conditions, use 2 to 3 layers of sandbag protection to prevent the occurrence of flying stones.

　　5.2 Protective protection

　　For the protection of cables, pipelines and other facilities that need to be protected, if there is a pipe trough, three layers of sandbags are piled up after the steel plates are covered on the pipe trough. For the near buildings and the buildings to be protected, bamboo poles can be used for protection.

　　5.3 Floor protection

　　In the direction of collapse of the cooling tower, sandbags, carbon residue or soil piles are used to build a protective belt with a width of 2.0m and a height of 1.5m to reduce the splash of the cooling tower and reduce the damage caused by the grounding vibration.

　　6 blasting effect

　　The blasting collapsed according to the design requirements, without recoil, the overall explosion height was about 4m, the fixed buildings and equipment were safe and sound, and the blasting achieved the expected effect and purpose.

　　Through the blasting of the 70.15m high cooling tower, there are the following experiences:

　　(1) The determination of the form of the gap, the height of the composite gap, and the length of the gap is the key to ensuring the collapse of the cooling tower;

　　(2) The bottom pool must be completely removed on the collapsed side, otherwise the collapse effect will be affected;

　　(3) Large hyperbolic thin-walled reinforced concrete cylinders can be collapsed as long as they are twisted during the blasting process, and the crushing effect is good.