Mankind has been successfully mastering the underground space for more than a century. This is not only about the subways that are present in all the major cities of the world, but also about the mine workings created for mining. In both cases, special equipment is used - sinking shields, which guarantee the safety of equipment and maintenance personnel during earthwork.
The tunneling shield was first used in 1825 during the construction of a tunnel under the River Thames. Since then, this type of equipment has been repeatedly used in the construction of subways in such large cities as Moscow, St. Petersburg, Yekaterinburg and other megacities.
Tunnel shield
The tunnel shield is a movable prefabricated metal structure in the form of a hollow cylinder. It is built at the place of mining or during the construction of the subway to protect the mines laid in the horizontal direction from collapse. Sometimes it is also called temporary or mobile support - a special structure that is built to protect the walls of the tunnel from collapse.
Structurally, tunnel shields are a complex set of equipment, which consists of three main parts:
- Knife. The process of drilling and rock development takes place in it.
- Supporting. Serves for the placement of auxiliary equipment, as well as hydraulic jacks, forcing the shield to move forward.
- Tail. Provide protection to personnel when erecting a permanent lining.
The tunnel shield may include a variety of equipment, which is necessary to simplify the work on developing the face, transporting earth masses, strengthening and protecting the walls from collapse.
Tunnel shield design
The main elements of the shield are the sheath and knife ring, on which the cutting elements of the tunnel shield are located. In some models, “cutters” are made in the form of carbide inserts located at a certain angle to each other on the working surface of the rotor, as well as a support ring.
Forward, into the space in front of the knives, the shield is advanced with the help of hydraulic cylinders, which are supported by the last lining ring. After that, downhole hydraulic cylinders are involved in the process, which press the prefabricated wooden panels to the rock so that it does not collapse.
The free space between the support and knife rings is divided into cells by vertical partitions and into tiers by horizontal bulkheads. Inside these "compartments" is the necessary equipment. Horizontal bulkheads can be extended by hydraulic jacks.
Classification of tunnel shields by cross-sectional shape
As a rule, tunneling boards are assembled directly at the place of work. A support ring and a knife ring are constructed from steel segments, and a shell is formed from steel sheets curved along a cylindrical surface.
Equipment for horizontal drilling differs in cross-sectional shape, dimensions, development method and field of application. The most common cross-sectional shape is the circle. Less common are cars of rectangular, arched and other shapes.
Types of shields according to the length of the diameter
Based on the diameters of the tunnel shields, the following types of structures are distinguished:
- Small (up to 3200 mm) - are used in urban services for laying collector tunnels.
- Medium (up to 5200 mm) - used for laying hydraulic communications and mining.
- Large (over 5200 mm) - are practiced when creating railway tunnels, subway lines, large mine workings.
The cross-sectional area of the working surface varies from 10 to 16 or more square meters, depending on the diameter of the working surface.
Types of equipment by the method of development of the face
When developing minerals or creating underground railways, horizontal drilling is carried out with various types of sinking shields.
They differ among themselves in the degree of mechanization of the executive bodies:
- Fully mechanized. To destroy the rock in such structures, special equipment is used - excavator, planetary, rod working bodies, as well as hydromechanical impact units.
- Partially mechanized. The lack of a special device for the development of soil layers is their exceptional feature. For the destruction of rocks, jack hammers are used here , blasting is carried out or the front pointed part of the shield is pressed into the ground.
- Special sinking shields. In such structures, the head is closed. They are used to create tunnels in particularly difficult geological conditions.
At the same time, designs are divided into types intended for work in various conditions - moistened soils, for the development of faces in loose and unstable rocks, and for penetration into the earth with a fortress of 0.5 to 5 and above.
Purpose of equipment
Tunnel shields are used to create shafts in the horizontal direction. This type of work is referred to as “horizontal drilling” and is used in various fields of human activity. Most often, it is used to create and expand existing subways and develop mineral resources.
Recently, widespread work on laying various communication lines under roads, highways and other means of communication, referred to as horizontal directional drilling, or HDD.
Horizontal directional drilling
The widespread use of this technology is due to high economic efficiency. In particular:
- the need to repair roads at the end of activities disappears;
- there is no need to block the car flow and create bypass routes;
- it is possible to lay new lines without violating the integrity of existing ones.
When applying the method of horizontal directional drilling, the operator of the tunneling shield creates a pilot well, which is then expanded with a rimmer - a reverse expander. Through the finished tunnel stretches a whip of the pipeline.
As the latter, a polymer sleeve is often used, which is then filled with concrete. After the cement mixture has hardened (about 21 days), a new communication line is ready.
Driving Shields Today
A living example of the use of the tunnel shield can be the construction of a section of the tunnel along the Frunze radius of 3,760 meters in length between the Prospekt Slavy and Yuzhnaya stations in the St. Petersburg metro.
Herrenknecht AG, a company from Germany, is involved in the project, which is committed to manufacturing a tunnel shield. Metrostroy is a member company from the Russian side, whose employees developed a project to create the first double-track tunnel in the post-Soviet space.
Previously, a domestic company has already collaborated with a German manufacturer. The Aurora shield provided by him is actively used for the construction of oblique passages at Spasskaya station.