The collapse of buildings and structures by explosion is carried out on their foundation or in a given direction (directional destruction). As a rule, high-rise buildings and structures (chimneys, towers, etc.) collapse in a given direction.

The collapse of buildings and structures on its foundation consists in the formation of an explosion through the lining along the perimeter of the building or structure. As a result of the explosion, the object, falling on its base, is destroyed. The height of the collapse usually does not exceed 1/3 of the height of the building, and the width of the collapse to the sides beyond the perimeter of the building is 1/2 the height of the walls. Before the explosion, all internal partitions and ceilings, rafters, roof, door and window boxes are usually disassembled and removed.

The collapse of buildings and structures is carried out by exploding charges in holes or sleeves. When buildings collapse on the base, the holes are placed on the inside of the building. The diameter of the holes is 40-60 mm, and their depth is 2/3 of the wall thickness. The holes are usually placed in two rows in a staggered order. The distance between the holes in the row is 0.8—1.4 and between the rows is 0.75—1.0 of the depth of the hole.

In the case of a change in the shape of the cross-section when the charge bends around the barrier surface, its focal length changes, and the cutting depth decreases [2]. For this reason, charges in the corners of the walls are laid in holes drilled one above the other and directed along the angle bisector (Fig. 1, a).

The directional collapse of a building or structure is carried out to preserve nearby other buildings and workshops. This direction (the axis of the roll) is usually the bisector of the permissible sector of the roll. Buildings and structures whose height is 4 times or more greater than the size of the horizontal section (at the level of the log house), measured in the direction of the axis of the roll, are susceptible to directional destruction (Fig. 1, c).

For a given direction of incidence, horizontal holes are arranged in the form of a wedge, the upper row at an angle of 10 °, and the lower one at an angle of 20 ° to its top. The narrow side of the wedge determines the direction of the fall. The depth of the holes is taken 3/4 of the wall thickness, the distance between the holes is about 30 cm.

Fig. 1. The layout of the holes:
a – in the wall during the collapse of buildings and structures on the base;
b – to the corner of the niche; c – with the directional collapse of the walls of the building; d – the same, pipes

For the collapse of a tower or pipe in a certain direction, a continuous undercut is made from the direction of the roll by 2/3—3/4 of the perimeter and a pin along the rest of the perimeter of the wall above the level of the lining by 0.7—1.5 m. The frame is created by two or more rows of charges (Fig. 1, d). The lower 2-3 rows take the same length, the rest are shorter in accordance with the accepted angle of the frame. The place of the pipe (tower) is selected at the level where there are no openings (flues, doors). If it is impossible to choose such a place, then the openings are carefully sealed to create an equally strong trunk.

With increased requirements for compliance with the specified direction of the roll (the roll sector is less than 50 °, the trunk is weakened, etc.), instead of the extreme holes of the log house located near the rear, special openings are punched in the wall. The height of these openings is usually 1-1.2 m, and the width is 0.6—0.8 m.

When felling buildings, structures and factory pipes, blasting with a detonating cord or an electric method is used. If the collapsed building is located near structures that need to be preserved from destruction or shaking, then special measures are taken to protect them (shelter with wooden shields, laying a shock-absorbing layer at the fall site, etc.).

The destruction of foundations by explosion is carried out both on open construction and factory sites, and inside the reconstructed premises. The blasting of foundations inside buildings is carried out only “for loosening”.

Charges for the destruction of foundations are placed in holes (Fig. 2) or sleeves. When the foundation is destroyed by the hole method immediately to the full height, the depth of the holes is assumed to be equal to 0.9 of the foundation height, and when the foundation is destroyed by separate layers — equal to the thickness of each layer, except for the last layer of the foundation. In it, to protect against damage to the foundations of the foundations, the holes must have a depth equal to 0.9 of the thickness of the layer being removed.

When the foundation is destroyed by horizontal holes, a protective layer 0.2—0.4 m thick is left between them and the foundation base. The diameter of the holes during the destruction of the foundations is 35-60 mm, the calculated resistance line is 0.5—0.7 of the depth of the hole. It should also be taken into account that when blasting reinforced concrete structures, the reinforcement in the body of the structure is also cut to a depth of 25 mm [3].

Fig. 2. The layout of the hole charges during the destruction of foundations
1 — foundation; 2 — explosive charge; 3 — electric detonator; 4 — face; 5 — wires

When placing charges in the sleeves, their cross sections are taken from 0.1X0.1 to 0.2X0.2 m. The sleeves are positioned so that the center of the charge is in the middle of the width of the foundation. Their length should not exceed 1.5 m. The distance between the rows of sleeves and from the edge of the foundation is assumed to be equal to their length, and the distance between the centers of charges is 1.0—1.5 sleeve lengths. Before the explosion, the foundation is dug to the depth of the drilled holes.

When blasting foundations and other horizontally located structures indoors and near buildings, structures and equipment, protective devices (shelters) are used to protect against the scattering of fragments and the action of an air shock wave.

To prevent the scattering of fragments during an explosion, the foundation is also covered with sandbags, metal mesh or protected by special shields located at a distance of about 60 cm from the foundation. As practice shows, to localize the spread of metal fragments during the explosion of factory-made shaped charges, it is enough to use the simplest shelter made of wooden shields with a thickness of 50 mm [2]. The surrounding units and other parts of the building located near the exploding foundation are covered with shields.

1. https://injzashita.com/razrushenie-konstrukciie-i-massivov-vzrivom-i-ustanovkami-elektrogidravlicheskogo-effekta.html date of application 05.07.2022
2. Nenakhov I.A., Fomenkova V.E., Kirillov S.S., Ganapolsky M.I. Experience of using cord shaped charges in explosive works on the collapse of structures // Eurasian Union of Scientists. 2015. No. 8-2 (17). pp. 86-89.
3. Galaeva N.L. The use of the explosion method for the demolition of buildings and structures in urban development // Prospects of science. 2019. No. 5 (116). pp. 54-56.

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