Completion time: October 1958

　　Project Location: Shenyang City

　　Completed by: Northeast Institute of Technology (now Northeastern University)

　　Project host and participants: Liu Qingrong, Ma Yuhang

　　Contributed by Liu Qingrong

　　1 Project Overview

　　The chimney to be demolished is located in a factory in Shenyang. The height of the chimney is 50.5m, and the barrel body is a reinforced concrete structure. The outer diameter of the root of the chimney cylinder is 5.Om and the wall thickness is 0.3m.

　　There are buildings around the chimney. The nearest building to the chimney is the 10.8m building on the south side, and the buildings in other directions are 20~30m away from the chimney. Only a zone with an open angle of 30° in the northeast can collapse. The project decided to use the blasting method to remove it. The explosion zone environment is shown in Figure 1.

　　2 blasting design

　　2.1 Blasting gap design

　　The blasting notch is expanded in a rectangular shape (Fig. 2).

　　The length of the gap is 2/3 of the circumference of the chimney. The outer circumference of the chimney at the notch is 15.7 m, that is, the length of the notch is 10.5 m. The height of the notch is calculated as 2 to 3 times the wall thickness of the chimney, and 0.5 m is taken. The bottom line of the notch is located at 0.5 m below the ground plane.

　　2.2 Hole network parameter design

　　In order to facilitate the construction, the hole is drilled inward from the outside of the chimney. The diameter of the blasthole is 38-40 mm, and the hole depth is 2/3 of the wall thickness of the chimney at the notch, that is, 0.2 m. The hole spacing is 0.3m, the row spacing is 0.25m, and the rows are staggered. A total of three rows of holes are arranged, each row of 34-35 holes, a total of 104 holes (Figure 2).

　　2.3 Dosage and Network

　　The No. 2 rock ammonium nitrate explosive was used for blasting. The test unit determined that the explosive consumption was 2kg/m3, the charge per hole was 45g, and the total charge was 4.68kg.

　　In order to reduce the impact of blasting on the vibration of surrounding buildings, a second delay electric detonator is used to detonate. The blasthole is divided into 6 sections, the number of blasting holes in each section is 17-18, and the explosive quantity in a single section is 810g. The series-parallel electric blast network connection is used, the alternating current is detonated, the detonation voltage is 380V, and the current obtained by each detonator is greater than 4A.

　　3 Security

　　(1) The mouth part is covered and blocked with a wet straw bag to form the first flying stone barrier.

　　(2) 2 m from the periphery of the chimney, a fence is formed by wooden boards to form a second barrier to prevent the fragments from scattering.

　　(3) The doors and windows of the buildings near the chimney are all open and fixed to prevent the damage of the shock wave.

　　(4) All personnel are evacuated to 100m.

　　4 blasting construction

　　(1) Drilling. During the drilling construction, the ground is dug 1 m deep along the bottom of the chimney, and the first row of blastholes is arranged 0.5 m below the ground.

　　(2) Charge. According to the designed single-hole charge, the explosive is weighed and placed in a paper bag prepared in advance. Insert the detonator into the bag before loading and put it into the blasthole, then use the clay to block the blasthole.

　　(3) Test explosion. The chimney has a long service life, and there is no drawing to check the internal structure of the chimney. In order to verify the size of the single hole charge and the distribution of the proven steel bar, the test explosion occurred at the center of the blasting notch and burst 0.5mx0.6m. The gap determines the single-hole charge; to weaken the support of the vertical reinforcement to the chimney, the main rib exposed by the notch is cut off (the calculation of whether the main rib is unstable when the notch is formed).

　　5 blasting effect

　　After the explosives detonated, a gap was formed at the bottom of the chimney, and the chimney lost its balance and slowly fell to the northeast. The actual dump centerline coincides with the design dump centerline. After the chimney touches the ground, most of the simplified body is broken and the debris is easy to remove. The buildings and pipes near the chimney are safe and the glass windows are not damaged. This is the first blasting demolition of a chimney by a blasting method in China.