(3) Because the construction period is only 20 days, plus the construction is catching up with the students' college entrance examination and the middle school entrance examination period, it is impossible to work overtime at night, which brings great difficulty to the construction progress.

　　3 Selection of blasting demolition plan

　　According to the on-site environmental conditions and the structural characteristics of the building, a blasting demolition scheme with multiple gaps to the south is used.

　　3.1 Blasting gap

　　The maximum notch height of the lower notch, the formula: H=Btanф

　　In the formula B - the width of the building, B = 16.2m; ф - the notch elevation angle, take ф = 41 °, tanф = 0.87.

　　The surrogate value is calculated as H=14.1m.

　　The height of the top panel of the fourth floor of the building is just 14.1m, which means that the front row can be fried up to the fourth floor. In order to make the building collapse smoothly, the height of the elevator shaft and the stairwell is increased by one layer higher than the height of the front row of columns.

　　Two auxiliary gaps are opened in the 9th to 10th floors and 14th to 15th floors of the building. The internal I-shaped shear wall is also pre-treated and drilled and blasted. The blasting gap and the hole are shown in Figure 3.

　　3.2 Pretreatment of shear wall

　　The main building is divided into front and rear two-span I-shaped shear walls, that is, the north and south spans. In order to reduce the drilling and blasting workload, the intermediate pre-treatment can form four rows of load-bearing columns with T-shaped ends, which become the main bearing of the main building. The component is then drilled and blasted. The three principles of shear wall pre-cutting are: 1) the principle of ensuring the safety and stability of the building before explosion; 2) the principle of retaining the shear wall node; 3) the principle of normalizing the post-body shear wall column.

　　3.3 drilling and blasting parameters

　　The building to be exploded is mainly carried by the I-shaped shear wall. The blastholes on the shear wall are arranged in two ways, namely vertical shallow holes. In order to ensure the blasting effect, the flying stone is controlled, and the longitudinal drilling parallel to the shear wall is decided. .

　　Calculation of blasting parameters: the aperture ф=38～40mm, the minimum resistance line is l/2 of the thickness of the shear wall, ie W=O.125m, the hole spacing δ=(1.5～2.0)W(m), take δ=20 ~25cm, the hole depth L is the width of the shear wall wall minus 25cm, if the wall width exceeds 1.5m, you can enter the hole from both sides of the shear wall section. At the elevator shaft, the maximum hole depth on the shear wall is 2.6m, and the center line of the blasthole is not more than 2cm parallel to the shear wall. A total of 1,720 longitudinal holes are arranged on the shear wall column, which is about 2095 meters.

　　The thin-wall structure of the shear wall is 1000-1200g/m3 for the bottom explosive. The single-explosion consumption of the two-layer explosive is 800g/m3, and the explosive consumption of the upper two blasting shear walls is controlled at 600g/m3.

　　4 Construction process

　　4.1 Deferred segmentation and detonation network

　　The non-electric detonators of MS2, HS2, HS3 and HS4 are detonated in the hole of the 1~4 row of shear holes in the building, the detonation of the non-electrical detonators of the MS2, HS2, HS3 and HS4 sections is used. The detonation of the detonators of HS5 is adopted for the gaps of 9 to 10 layers, and the detonation of the detonators of HS6 is adopted for the 14 to 15 layers of notches. The internal transmission blast network consists of two-way non-electric detonators and detonating cords; the external blasting network route blasting detonator and the compound closed four-way detonating tube blasting network. The network between the upper and lower floors has 8 paths on the 1st to 3rd floors, 4 channels on the 4th floor and above, and finally merges into two detonation buses.

　　4.2 Detonation kit processing

　　The in-hole initiation kit consists of a plurality of drug packs, detonating cords, and detonating detonators. In order to facilitate the charging, the medicine package and the detonating cord are tied together on the thin bamboo strips, and the medicine is wrapped around the detonating cord every 40cm and fixed; 15cm away from the tip of the detonating cord, the two detonators are activated. Tied up. The processed drug pack is slowly pushed into the blasthole, and the orifice is blocked by about 20cm, and the number of times is blocked, ensuring the quality of the blockage. The entire building was blasted with 4,200 non-electric detonators, including 3,440 holes in the hole, 760 rounds of external holes, 115 kg of emulsion explosives, and 1930 m of detonating cords.

　　5 Vibration check and test

　　5.1 Evaluation of blasting vibration

　　The maximum single-shot dose of this blasting is 48kg; when the nearest distance is 25m, it is calculated that v=1.06cm/s. Therefore, the blasting vibration will not cause any damage to buildings around 25m.

　　5.2 Assessment of collapse vibration

　　The vibrations generated by the building (which weighs thousands of tons) when it hits the ground are threatening to the surrounding environment. We adopt multi-notch directional blasting, and the technical measures of segmentation and cross-span collapse make the building block the ground in turn. Effectively reduces the impact of landing vibration on surrounding buildings.

　　5.3 Live real-time testing

　　The site uses real-time blasting vibrometer for real-time testing. A total of 9 measuring points are placed on the protected buildings for real-time monitoring. The test results show that the maximum vibration is O.37cm/s. The reason why the measured value is less than the theoretical value is that the building is disintegrated in the air, and the buffer belt and the anti-vibration groove play a great role in damping.

　　6 Other safety technical measures

　　In order to ensure that the building is completely dumped and collapsed in the correct direction, the following measures have been taken:

　　(1) Demolition of the podium machinery before the explosion; the pre-explosion pretreatment and the opening of the blasting gap are symmetrical to ensure that the building is backwards accurately.

　　(2) For the protection of blasted flying stones, cover protection and detachment protection are adopted. The cover protection is covered by three layers of bamboo rafts and three layers of grass bags directly on the blasting body, and is fixed by wire tying; the detachment protection is to erect a fully enclosed protective truss with a bamboo raft at a distance of 1.5 m from the main building, the height of which is greater than the height of the blasting gap. Om.

　　(3) Excavate the anti-vibration ditch on the east and west sides of the building. The width of the ditch is 1.5m and the depth is 2.Om. At the same time, three buffer belts and buffer belts are piled up with muck at 20m, 30m and 45m away from the building. The bottom width is 1.5m, the top width is 1.Om, and the height is 1.5m, and sandbags are laid on the surface of the buffer belt to prevent secondary splashes.

　　7 blasting effect

　　At 6 o'clock on June 22, blasting on time, the building collapsed to the south according to the design requirements, without deflection and recoil, the forward tilting distance is about 35m; the building is fully dismantled, the explosion height is less than 9m; there is no damage to the surrounding underground pipelines and communication cables. The southwest side residential building and the north side national land building were repeatedly tested and contrasted by the house quality inspection department and the notary department before and after the explosion, and the structure was not damaged. The blast was a complete success.

　　8 Conclusion

　　The success of this blasting operation mainly includes the following points:

　　(1) Buildings with full shear wall structure, shear wall is the load-bearing component. Safety analysis and evaluation should be carried out on the pre-demolition plan before explosion to ensure safe blasting.

　　(2) After the pre-treatment of the shear wall, it is necessary to keep the standardization of the wall column to facilitate the drilling and blasting operation and the extension of the section.

　　(3) The drilling method of shear wall blasting is suitable for longitudinal drilling, and the blasting effect is better, and the flying stone is easy to protect, but

　　The drilling quality is required to be high; the method of introducing the medicine package by the thin bamboo strip is very effective and simple for the positioning of multiple medicine bags in the deep hole; the detonation of the detonating cord in the blasthole doubles the detonator and the explosive The amount of use increases the synchronism of the detonation, thus ensuring the blasting effect.