tunnels ppt

TunnelsPrepared By:-Asim

NabeelHassad

OmerAli

• WHAT IS TUNNEL?

• It is an underground or underwater passageway, dug

through the surrounding soil/earth/rock.• They could be used for carrying freights and

passengers, water, sewage, etc.• A tunnel may be for foot or vehicular road traffic, for

rail traffic, or for a canal.• Secret tunnels are built for military purposes. • Special tunnels, such as wildlife crossings, are built to

allow wildlife to cross human- made barriers safely.• The methods involved are underground operations

known as tunnel driving and the surface is not disturbed.

• REASONS TO BUILD A TUNNEL

• When the lane encounters an obstacle such as a mountain to

avoid bypassing the obstacle.

• Built sometimes to overcome a water obstacle as a

replacement for building a bridge above it.

• Built to connect between military posts so the movement

between them will not be visible for the enemy.

• Sometimes built for infrastructure like electricity cables, water,

communication and sewerage to avoid damage and disruption

above ground.

• HISTORY • the first tunneling was done by prehistoric people

seeking to enlarge their caves.• First tunnel in Babylonia was a brick-lined pedestrian

passage some 3,000 feet (900 meters) long was built about 2180 to 2160 B.C. under the Euphrates River to connect the royal palace with the temple.

• The largest tunnel in ancient times was a 4,800-foot- long, 25-foot-wide, 30-foot-high road tunnel (the Pausilippo) between Naples and Pozzuoli, executed in 36 B.C.

• In 1681 gunpowder was first used for blasting the tunnels. First time the ventilation system for tunnel was developed in 1927 in Holland tunnel.

• In 1952 James . S. Robbins comes up with a good idea and designs the modern tunnel- boring machine.

• In 1988 Japan's 33-mile-long Seikan Tunnel, the world's longest and deepest railway tunnel (787 feet below sea level), connects the islands of Honshu and Hokkaido.

• In 1994 after 192 years of planning and six years of building, the Channel Tunnel runs under the English Channel.

TUNNELING METHODS

• depends on

• ground conditions,

• the ground water conditions,

• the length and diameter of the tunnel drive,

• the depth of the tunnel,

• the logistics of supporting the tunnel excavation,

• the final use and shape of the tunnel and appropriate

risk.

• ADVANTAGES OF TUNNELING

• Tunnels are more economical than open cuts beyond certain depths

• Tunnels avoid disturbing or interfering with surface life and traffic during construction

• Tunnels prove to be cheaper than bridges or open cuts to carry public utility services like water, sewer and gas

• if tunnels are provided with easy gradients, the cost of hauling is decreased

• In case of aerial warfare and bombing of cities, the tunnels would grant better protection as compared to bridges.

• Parts of Tunnel

TUNNEL LININGS

These are the permanent or temporary support for

keeping tunnel from collapse and provide safe.

• Tunnel linings are grouped into three main forms

some or all of which may be used in the construction

of a tunnel:

• 1. Temporary ground support

• 2. Primary lining

• 3. Secondary lining

4. WIRE MESH:-

• Wire mesh is used to support small pieces of loose

rock or as reinforcement for shot crete.

• Two types of wire mesh are commonly used in

underground excavations:

• 1. Chain-link mesh:- commonly used for fencing

• 2. Weld mesh:- commonly used for reinforcing

shotcrete.

5. IN SITU CONCRETING

• The process of placing concrete in situ was

incompatible with timber supports.

• The first uses of concrete were for tunnels in good

rock and it was only with the introduction of steel

supports that concrete became the norm for a tunnel

lining material.

• In-situ forms used for lining tunnels are, with few

exceptions, of the travelling type, constructed of steel.

• VENTILATION IN TUNNELS

• Ventilation is required because of

• 1) Dust and gas caused by drilling, blasting, loading of excavated materials and Shot creting

• 2) Exhaust gas and smoke discharged by diesel• 3) Poison gas made from explosive or organic solvent• 4) Poison gas, flammable gas or oxygen shortage gas

in ground • 5) High temperature and high humidity

VENTILATION DURING CONSTRUCTION

• During construction it is necessary to ventilate a tunnel for various reasons:

• To furnish fresh air for the workers • To remove the dust caused by drilling, blasting,

mucking, diesel engines, and other operations• To remove obnoxious gases and fumes

produced by explosives

• SHAPES OF TUNNELS

• (A) CIRCULAR :This type of section offers greater resistance to external pressure .

• If ground is highly unstable , such as soft clay or sand , it is necessary to use circular section .

• For carrying water and sewerage circulation shape tunnels are used .ex. Aqueduct

• Circular tunnel are not prefer as traffic tunnel.

• ELIPTICAL SECTION

• They are used in grounds compare than rock . • These tunnels serve as water sewage

condition.• They are difficult construct .• They cannot be used as traffic tunnels because

of their narrow base.

• EGG – SHAPED SECTION

• These section have narrow cross sections at bottom. They are best suited for carrying sewage. They maintain self-cleansing velocity of flow of sewage both in dry and rainy seasons .

• They are resist external as well as internal pressure due to their circular walls .

• These tunnels are difficult to construct

• HORSE SHOIE SECTION

• This form consists of a semi-circular roof together with arched sides and a curved invert.

• They are most popular as traffic tunnels for road and railway routes .

• These tunnels are also difficult to construct.

• TUNNELLING METHODS

• SHIELD TUNNELLING METHOD• This method involves the use of shield

machine to drive the tunnels below the ground. After completion of a work shaft, the shield machine is lowered into the shaft and assembled there before excavation and construction of the tunnels using precast concrete lining segments of about 1.2 meter width. This construction method causes minimal disruption to traffic and the environment because all the work takes place below ground and the ground level environment is unaffected.

• CUT and COVER TUNNELLING METHOD • This construction method, whereby the site is

fully excavated, the structure built and then covered over, uses diaphragm walls as temporary retaining walls within the site area. Step one :Construction of diaphram walls, pin piles, and decking. Step two :Excavation within the diaphragm walls, installing structures as work progresses. Step three :Construction of permanent floor slabs and walls. Step four : Fitting out the internal structures, backfilling, and reinstating the surface structures.

• TBM (Tunnel Boring Machine) • tunnel boring machine (TBM) is a machine

used to excavate tunnels with a circular cross section through a variety of soil and rock strata. They can bore through anything from hard rock to sand. Tunnel diameters can range from a meter to 19.25metre.

• 1. Mechanical-support TBM • 2. Compressed-air TBM • 3. Slurry shield TBM • 4. Earth pressure balance machine.

• 1- Mechanical Support TBM

• A mechanical-support TBM has a full-face cutter head which provides face support by constantly pushing the excavated material ahead of the cutter head against the surrounding ground.

• 2- Compressed-Air TBM

• A compressed-air TBM can have either a full- face cutter head or excavating arms. Confinement is achieved by pressurizing the air in the cutter chamber.

• Geological Survey For Tunneling

• A geological survey is the systematic investigation of the subsurface and surface of a given piece of ground for the purpose of creating a geological map ,model and feasibility studies.

• A geological survey employs techniques from the traditional walk-over survey, studying outcrops and landforms, to intrusive methods, such as hand auguring and machine driven boreholes, use of geophysical techniques and remote sensing methods, such as aerial photography and satellite imagery etc.

• Types Of Geological Survey

• Mainly geological surveys are classified into two types:

• Surface Geological Survey• Subsurface Geological Survey• Surface Geological Survey:• includes on land geology and geological structures,

landforms, hydrology, outcrop pattern ,engineering properties etc

• Subsurface Geological Survey:

• includes on underground geology and geological structures, Geo-hydrogeology, subsurface rock or soil pattern etc.

• Surface Geological Survey

• Geological profile is prepared along line of tunnel.

• Geological observations are done along this profile like engineering properties of rock/soil, geological structures like fold, faults, joints, spring, stream, river alignment and any seepage etc

• Trial boring plan is prepared along the tunnel line.

• Subsurface Geological Survey• Trial boring is done along the tunnel line.• Different rock and soil samples are collected from

subsurface and their physical and chemical properties are observed.

• Some samples are sent to laboratory for determination of engineering properties like shearing, strenght, permeability, porosity, compressive strenght , and other test are performed.

• GWT(Ground Water Table) is noted and water bearing strata is marked in geological profile.

• Different geophysical surveys like refraction, resistivity, GPR(Ground Penetrating Radar) and bore hole logging etc are also done.

• In situ testing like Packer-testing, hydro fracturing, load-testing etc are performed.

• A geological/feasibility report comprising all information ,photographs, profile and others necessary data are presented for final tunnel design and construction.