Types of Tunnels & Construction Methods

 

A tunnel is an underground passage through a mountain, beneath a city or under a 

waterway. 

It may be for pedestrians and/or cyclists, general road traffic, motor vehicles , rail traffic, 

or for a canal. Some tunnels are constructed purely for carrying water (for consumption, 

hydroelectric purposes or as sewers); others carry services such as telecommunications 

cables. 

z Mountain Tunnel 

-- Drilling and blasting (D&B) method 

NATM (New Austrian Tunneling Method) is the most common method. It originates in 

hard rock tunneling and utilizes rockbolts and shotcrete applied immediately after 

blasting. This is often followed by a cast in-situ concrete lining using formwork. 

-- Tunnel Boring Machine (TBM) method 

TMB is used as an alternative to drilling and blasting (D&B) methods. TBMs are used 

to excavate tunnels with a circular cross section through a variety of subterranean 

matter; hard rock, sand or almost anything in between. 

As the TBM moves forward, the round cutter heads cut into the tunnel face and splits 

off large chunks of rock. The cutter head carves a smooth round hole through the 

rock -- the exact shape of a tunnel. Conveyor belts carry the rock shavings through 

the TBM and out the back of the machine to a dumpster. 

Tunnel lining is the wall of the tunnel. It consists of precast concrete segments that 

form rings, cast in-situ concrete lining using formwork or shotcrete lining

. 

Why Tunnel Structures Deteriorate 

Typical Defects in the Impermeability of the Tunnel Lining




Moisture, water and chemical damage to concrete
z Even concrete of high quality is a porous material
-- Excess water evaporation during hardening will leave millions of pores and
capillaries in concrete
-- The zones between cement and aggregates are prone to cracking during
hardening due to drying shrinkage, temperature stress and outside forces
z Porosity of concrete
-- Allows moisture, water and chemicals to move freely throughout the concrete
-- Increases absorption of deleterious chemicals .

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Tunnel permanent lining construction

The basic materials for tunnel lining construction are cast-in-place concrete, cast-in-place and prefabricated reinforced concrete, cast iron and steel. These materials are chosen according to conditions of construction area and tunneling methods. The lining has permanent application as opposed to temporary lining (mine working support). The shape and size of lining are defined by size, depth and function of the tunnel and sort of take up load (rock pressure, hydrostatical pressure, traffic load, etc).

Cast-in-place lining is mainly used for construction of tunnels with most complex structure and big cross-section. Precast lining is widely used for shield and erector-arm tunneling, mainly in subway tunnels.

Technological production schemes of concreting for tunnel construction are defined according to hardness of rock, tunneling methods, depth, length and appropriation of tunnel and applied mechanic machines.

The concreting of one section of Lagar-Aul tunnel in Amur region on the basis of factors above was performed after the following works were finished: excavation form was made as designed in the project, excavation consolidation by means of shotcreting; the installation of rock bolt support, film waterproofing and reinforcement cage; placing of formwork in permanent position and release material covering.

Tunnel lining waterproofing

Various types of waterproofing materials are used in modern tunnel construction. Solid waterproofing is made of waterproof building organic or synthetic film filter materials, synthetic resinous materials, and steel sheets.

Cat-in-place tunnel lining, placed in stable rock ground, protect from water by means of external waterproof installed before lining construction. After that reinforced framework is performed.

Formwork

Tunnel formwork "Saga Сogio" (Japan) is used for mechanization of cast-in-place concrete lining construction of single track railway tunnel, excavated to the full cross-section. The total length of formwork, 20,5 m, provides heading for 20 m. The width and height of the formwork are 5.6 m and 8.2 m respectively. Weight - 100 tones. Pneumatic motion engine capacity - 10.3 kW.

Tunnel formwork "Wortington" (Italy) is appropriate for mechanization of cast-in-place concrete lining construction of double track tunnel crown. Entrance size for traffic (finished): width - 3.6 m, height - 3.7 m. Form work weight - 110 tones.

 portland cement

 

Portland cement is the basic ingredient of concrete. Concrete is formed with portland cement creates a paste with water that binds with sand and rock to harden.

Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients. 

Common materials used to manufacture cement include limestone, shells, and chalk or marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore.  These ingredients, when heated at high temperatures form a rock-like substance that is ground into the fine powder that we commonly think of as cement.

Bricklayer Joseph Aspdin of Leeds, England first made portland cement early in the 19th century by burning powdered limestone and clay in his kitchen stove. With this crude method, he laid the foundation for an industry that annually processes literally mountains of limestone, clay, cement rock, and other materials into a powder so fine it will pass through a sieve capable of holding water. 

Cement plant laboratories check each step in the manufacture of portland cement by frequent chemical and physical tests. The labs also analyze and test the finished product to ensure that it complies with all industry specifications.

The most common way to manufacture portland cement is through a dry method. The first step is to quarry the principal raw materials, mainly limestone, clay, and other materials. After quarrying  the rock is crushed. This involves several stages. The first crushing reduces the rock to a maximum size of about six inches. The rock then goes to secondary crushers or hammer mills for reduction to about three inches or smaller.

The crushed rock is combined with other ingredients such as iron ore or fly ash and ground, mixed, and fed to a cement kiln.

The cement kiln heats all the ingredients to about 2,700 degrees Fahrenheit in huge cylindrical steel rotary kilns lined with special firebrick. Kilns are frequently as much as 12 feet in diameter—large enough to accommodate an automobile and longer in many instances than the height of a 40-story building. The large kilns are mounted with the axis inclined slightly from the horizontal.

The finely ground raw material or the slurry is fed into the higher end. At the lower end is a roaring blast of flame, produced by precisely controlled burning of powdered coal, oil, alternative fuels, or gas under forced draft.

As the material moves through the kiln, certain elements are driven off in the form of gases. The remaining elements unite to form a new substance called clinker. Clinker comes out of the kiln as grey balls, about the size of marbles.

Clinker is discharged red-hot from the lower end of the kiln and generally is brought down to handling temperature in various types of coolers. The heated air from the coolers is returned to the kilns, a process that saves fuel and increases burning efficiency.

After the clinker is cooled, cement plants grind it and mix it with small amounts of gypsum and limestone. Cement is so fine that one pound of cement contains 150 billion grains.  The cement is now ready for transport to ready-mix concrete companies to be used in a variety of construction projects.

Although the dry process is the most modern and popular way to manufacture cement, some kilns in the United States use a wet process. The two processes are essentially alike except in the wet process, the raw materials are ground with water before being fed into the kiln.