Mountain Tunnel

It shoud be noted that tunnels through mountains or underwater are usually worked from the two opposite ends, or faces. In long tunnels, vertical shafts may be dug at intervals to excavate from more than two points.

Drilling and blasting (D&B) method

The advancement of long tunnels through hard rock before tunnel boring machines (TBMs) were invented relied on the drill-and-blast method. Today, the drill-and-blast method is still widely practiced and used in building shorter tunnels through hard rock where the use of tunnel boring machines is not justified (oправдано) and too expensive. The drill-and-blast method is also used in combination with full face drilling with tunnel boring machines.

In the drill-and-blast method, a drilling jumbo is used to drill a predetermined (заранее установленный) pattern of holes to a selected depth in the rock face of the proposed tunnel’s path (прохождение). The drilled holes are then filled with explosives such as dynamite. The charges are then detonated, causing the rock to crack and break apart. The loosened debris or muck is then dislodged and hauled away. Other tools such as a pneumatic drill or hand tool are then used in smoothing out (сглаживать) the surface of the blasted rock. Aside from manually digging tunnels, blasting and removing rock debris manually was undertaken by the drill-and-blast method in its most rudimentary (зачаточный) form, which was the process by which most tunnels were advanced until the advent of tunnel boring machines. The first blasting agent was gunpowder, used to carve out a long canal tunnel measuring 515 feet (157 m) in length in France in 1681. Gunpowder was replaced with nitrogylcerine in tunnel blasting by 1850. Steam and compressed air were also used to power drills that bored holes in rock.

Rock Drilling Jumbo

By 1931, the first drilling jumbos comprised of 24 to 30 pneumatic drills rigged on a frame and welded to a truck bed were developed to advance tunnels that would reroute the Colorado River around the Hoover Dam (платины) construction site in the U.S.

Drill-and-blast tunnels may vary in length from 16.4 to 197 feet (5 to 60 m) and are used for underground utility, highway, railroad, mass transit tunnels, and underground mining.

The most important principle associated with the drill-and-blast method is that the energy generated from the explosives must be allowed to be directed in the correct alignment (расположение). To carry this out properly, the geological condition of the rock bed, the angle, size, and spacing of the drill holes, and the energy factor have to be taken into consideration and precisely calculated.

One of the drawbacks of the drill-and-blast method is that it poses some obvious safety risks for workers. The fumes and gases generated from detonating explosives are toxic. This is why the air always has to be circulated through some type of ventilation duct in the blast section following detonation. The charging of explosives also produces a high volume of dust. Other risks are undetonated explosives and the noise pollution generated from blasting. Blasting can also weaken or fracture the rock around the tunnel, thereby increasing the likelihood of uncontrolled rockslides or falling debris. Additional temporary ground support in the form of rock bolting and shotcrete is often utilized once the tunnel is excavated.

Дата добавления: 2015-10-31