Comparative Analysis of Underground & Underwater Tunnel

With the urban population increasing, conurbation is getting more and more crowed, traffic jam happens everywhere. In this case, utilization of the underground and underwater space has become an effective way to undertake this set of problems. Tunnel construction is one of the important infrastructure projects, which is vital for enhancing the transportation networks, especially in congested cities. This review project presents a framework for selecting the appropriate tunneling method and transportation network with respect to the induced ground surface settlements. Parameters which have significant influence on the ground surface settlement will also be discussed in this project. This paper will help the contractors, engineers and designer in selecting appropriate method and estimating the required cost and time for construction of a


I. INTRODUCTION
Tunnel construction for transport routes is becoming increasingly important worldwide. Transport is accelerated and optimum protection is provided for the environment and the landscape. Many tunnels are considered technological masterpieces and governments have honored tunnel engineers as heroes. Constructing a tunnel, however, is one of the most complex challenges in the field of civil engineering. Tunnels are attractive solutions for railways, roadways, public utilities and telecommunications.
Worldwide population is increasing rapidly so the need of rapid or quick transportation to counter this approximately 3/4th of earth floor which is under water is to be used. This give rise to construction of underwater tunnel. An underwater tunnel is a passage, gallery or roadway beneath a body of water. Underwater tunnels are used for highway traffics, rail road and subways to transport sewage, oils, gas or vehicles and also for military and civil defense purpose Modern underwater tunneling begins by constructing an immersed tube within a pre-dug trench on the river or sea floor, to do this pre-fabricated sections of steel and concrete tube are floated into position and strategically sunk into the trench. Immersed tunneling is an art of guiding the great natural force, the water, to do Engineering works: "guiding" buoyancy for transportation, "guiding" water weights for immersion, and "guiding" hydrostatic pressure for connection. II. LIMITATION EXISTING SYSTEM 1) Immersed tunnels are often partly exposed (usually with some rock armour and natural siltation) on the river/sea bed, risking a sunken ship/anchor strike. 2) Direct contact with water necessitates careful waterproofing design around the joints.
3) The segmental approach requires careful design of the connections, where longitudinal effects and forces must be transferred across. 4) Environmental impact of tube and underwater embankment on existing channel/sea bed.

SCOPE:
1. Due to shortage of land and rapidly growing traffic and population, various underwater tunneling construction techniques should be implemented. 2. As underwater tunnel have shorter routes than bridges and roadways, its saves our important time. 3. Different materials such as oils, gas and drinking water can be simultaneously transported along with the traffic route. 4. By using advanced technologies transparent tube can be built which gives very aesthetic and attractive view for passengers and tourist. 5. Therefore making the overall project cost effective.

OBJECTIVE:
Tunnels are underground passages used for transportation. They could be used for carrying freights and passengers, water, sewage, etc. 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. Feasibility of these constructions in natural materials, such as rock and soil, causes the geological conditions to play a major role in their stability. Aspects of major importance and that is decisive for the feasibility of a tunnel project is geological conditions, construction time and costs. The objective of this lesson is to provide the general aspects of importance in tunnels, their types and methods of tunnelling.  2008), The "Cut-and-Cover" and "Cover and-Cut" Techniques in Highway Engineering: The use of "Cut & Cover" and "Cover and Cut" methods are studied in this paper for construction of underground tunnels or subways. In this paper, the overview of both the methods is presented which includes describing main features, advantages and field applications. 5

VI. DEVELOPMENT OF TUNNEL AND CONSTRUCTION METHODS
• UNDERGROUND TUNNEL a. Cut and Cover Method of Tunnel Construction Cut and cover method of tunnel construction is generally used to build shallow tunnels. In this method, a trench is cut in the soil and it is covered by some support which can be capable of bearing load on it.

b. Bored Tunnel Method
Bored tunnel method is modern technology. In this case, tunnel boring machines are used which automatically work and makes the entire tunneling process easier. It is also quicker process and good method to build tunnel in high traffic areas.

c. Clay Kicking Method of Tunnel Construction
This method is used for strong clayey soil conditions. This is an old method and used for small works like sewage pipes installations etc. In this method, a hole is excavated into the ground and after some depth tunnel is excavated which is done by the clay kicker which lies 0n a plank at

d. Shaft Method of Tunnel Construction
In this method tunnel is constructed at greater depth from the ground surface. The shaft is built up to the depth where tunnel is required.

e. Pipe Jacking Method of Tunnel Construction
Pipe jacking method is used to construct tunnels under existing structures like road ways, railways etc. In this method, specially made pipes are driven into underground using hydraulic jacks. Maximum size of 3.2-meter diameter is allowed for tunnels

A. Immersed tube tunnel
An immersed tube tunnel is made up of many prefabricated tubes constructed on land, which are then floated and moved to its dredged location by romorks in the sea. The tubes are lowered and connected with each other underwater.

a. SINGLE STEEL SHELL
A single steel shell element has an external steel shell fabricated typically from 10 mm steel plate. This does not have to be the traditional circular steel tunnel shape as can be seen in Figure. The steel shell provides strength and water tightness.

b. DOUBLE STEEL SHELL
The cross section of a double steel shell has two steel skins. There is an inner steel shell, which is thinner than the steel shell of a single shell tunnel and typically 8 mm thick. This outer form plate is slightly thinner than the inner shell at typically 6 mm.
The first, simplest and most straightforward of the concrete tunnel options is the monolithic element. Each tunnel element is a continuous structure that acts as a beam.
b. SEGMENTAL CONCRETE ELEMENT CONSTRUCTION The segmental form concrete tunnel element was developed from the original monolithic tunnel element to avoid the need for an external waterproofing membrane.

c. PRESTRESSED CONCRETE
A variation of the monolithic reinforced concrete element is to prestress it with permanent longitudinal prestress. This form of tunnel element can have advantages in reducing the amount of longitudinal reinforcement and also the overall compressive stress it provides tends to close any cracks in the concrete, reducing the likelihood of leakage.

d. COMPOSITE SANDWICH TUNNEL
The use of steel-concrete composite sandwich construction is a more recent development that has mostly been promoted in Japan, although a lot of research and testing has also been carried out in the United Kingdom. The concrete is placed between the steel plates, so a very fluid self-compacting mix is required. Placing this concrete and ensuring sufficient compaction and complete filling of the void between the plates is one of the main challenges of this method.

B. Submerged Floating Tunnel
A submerged floating tunnel (SFT), also known as submerged floating tube bridge (SFTB), suspended tunnel, or Archimedes bridge, is a proposed design for a tunnel that floats in water, supported by its buoyancy (specifically,

b. WELFARE AND FIRST AID
The provision of basic welfare in tunnels under construction is improving. Space for basic toilet and washing facilities is limited in small tunnels, but in larger tunnels there is enough space for toilet means of boiling water and heating food as part of the TBM equipment aids welfare and reduces the risk from improvised electrical installations. First aid provisions must be available to meet the requirements of the project in terms of shift working and remote working.et and washing facilities on the TBM or in the tunnel.

c. EDUCATION, TRAINING AND COMPETENCE
Large tunnelling projects may need to set up their own training facilities, for example Cross Rail in the UK set up its own 'Tunnelling Academy' to train the large number of workers required for this project.
All new employees in the industry should undergo comprehensive induction training. Site-specific training, even for experienced employees who are new to a site, is also necessary. Engineers and managers now undertake training in health and safety matters as part of their professional education and continuing professional development.

d. FIRE, FLOOD RESCUE AND ESCAPE
Among the most significant safety hazards of tunnelling, to which the workforce is exposed, are fire and smoke. Good housekeeping is another vital precaution in minimizing the buildup of flammable rubbish, which typically in tunnelling includes timber, plastic bottles, paper, discarded hoses and cables. All hydraulic systems should be well engineered.

e. ENVIRONMENTAL IMPACT
Environmental legislation is becoming stricter globally as awareness of potential impacts increases. At the same time, methods to manage impacts are becoming more sophisticated, and it is essential to understand the issues and how they can best be dealt with, whether as a planner, designer, constructor, or project sponsor. The production of an environmental impact assessment (EIA) is a standard requirement in most countries around the world and is used as a tool for ensuring impacts.

f. TUNNEL APPROACHES
The major impact of an immersed tunnel scheme generally occurs during construction when disturbance of the waterway and the banks is inevitable.. Often, the banks are environmentally sensitive, are recreational areas or protected wildlife areas, or are areas of outstanding landscape importance. In an estuary or tidal river location, constructing the approaches will almost certainly raise environmental issues relating to the intertidal mudflats.

g. MARINE WORKS
The main activity in the waterway itself is the excavation, and subsequent backfilling, of the trench for the tunnel. Placing of tunnel elements is relatively fast and causes no real disturbance to the environment. Dredging, by its very nature, stirs up the bed of the river, resulting in an increased amount of sediment in the river.

h. FISHERIES
Once a tunnel has been completed, there is no long-term effect on the movement of fish up and down the river. The one caveat to this is that if an impressed current cathodic protection system is installed, there is the potential for electric currents to disturb the fish, and this effect should not be overlooked.

i. ALGAE & WATER QUALITY
At some tunnel sites there is the possibility of blooms of algae that can hinder construction. These can be a severe handicap to the construction process.
As discussed, changes to the water quality during construction can adversely affect the marine biology. Oxygen content and turbidity are factors affecting the quality of marine life and strict limits on the extent of any changes during construction must be imposed.

j. VISUAL ASPECTS & AIR QUALITY
A tunnel imposes far less visual intrusion on a waterway and the surrounding area than a bridge. Once completed it is often almost invisible, except from the air. These include service buildings, ventilation inlet and exhaust towers, the architectural appearance of the portals, and the type of approach structures. The tunnel design needs to consider air pollution. Overall pollution from the traffic is not increased but that pollution is concentrated. If longitudinal ventilation is being used, then the pollution is concentrated around the Portals, b. HORIZONTAL DISPLACEMENTS:-From the point of view of damage to structures and services it is not only important to determine vertical displacements within the ground, but also the horizontal movements Sh = Svy/H (7.9) Where Sv is the vertical ground displacement, Sh is the horizontal ground displacement and y is the transverse horizontal distance from the tunnel centerline.
c. LONG-TERM SETTLEMENTS:-Long-term settlement is a phenomenon predominantly associated with fine grained soils and is associated with component 5 in Figure above 1. The tunnel acting as a drain 2. Time dependent distortion of the tunnel lining 3. Time dependent dissipation of excess pore water pressures due to grouting behind the lining or due to mitigation measures such as compensation grouting 4. Creep and secondary consolidation processes in soils 5. Time dependent closure of the grouted annular gap due to: bleeding and curing (hardening and shrinkage) of the grout, insufficient grout or loss of grout.

d. GROUND IMPROVEMENT AND STABILIZATION
TECHNIQUES:-This section describes a number of techniques that can be used to improve the stability of the ground to aid construction of the tunnel, and in soft ground to reduce/control ground displacements and hence mitigate the effects of the tunnelling operation on adjacent structures.

c. BEHAVIOR IN SEISMIC CONDITIONS:-
Sand foundations can perform satisfactorily under seismic load, provided some thought is given to the risks at the design stage. The issue to guard against is preventing liquefaction. This can be achieved by the selection of an appropriate grading or through stabilization. In highly active zones, a gravel or grouted gravel solution is more likely to give an appropriate solution. BURIED UTENSILS In addition to buildings, it is important not to forget about structures that lie beneath the ground surface, for example existing tunnels and buried utilities.
EXISTING TUNNELS In terms of the effects of tunnelling on existing tunnels, the overall philosophy, though, was to minimize the ground movements at source, i.e. using high specification EPB tunnelling machines, and to use a risk-based engineering assessment of the effect of the tunnelling works on the existing tunnels. Figure: 4.13 flow chart for depth, some idealized modes of behaviour for short buildings and long buildings due to a tunnel construction.

• UNDERWATER TUNNEL
A. SAND FOUNDATION LAYER Immersed tunnels are frequently located in poor ground conditions. The foundation of an immersed tunnel can be considered to be made up of two parts: 1. The foundation layer placed on the dredged surface immediately beneath the tunnel structure. 2. The deep foundations in the substrata below the level of the dredged trench.
There are two fundamental approaches that may be followed to form this bedding layer: 1. Place the tunnel elements in the trench onto temporary supports, under fill the space between the tunnel elements and the surface of the trench, and release the temporary support. 2. Lay a close tolerance foundation layer at the base of the tunnel trench that the tunnel elements can be placed directly onto.
• METHODS:a. SAND JETTING METHOD With this technique, the tunnel element is temporarily supported above the bed of the trench. The sand is then injected into the space under the element. Original sand jetting equipment is shown diagrammatically. It was developed in the 1930s by Christiani and Nielsen, the Danish contractor that was instrumental in the development of concrete immersed tunnels.
b. SAND FLOW METHOD A new method was developed in which the sand/water mixture was pumped directly into the space under the tunnel through holes in the tunnel floor. This was called the sand flow method and has, subsequently, been widely adopted as the usual method of placing tunnel foundations.

B. GRAVEL FOUNDATION LAYERS
Gravel bed foundations exhibit different characteristics than sand foundations. Gravel beds offer improved performance of foundations in seismic conditions. Although it is important to guard against shakedown effects, which may cause the gravel layer to compact, the gravel will not suffer liquefaction and can be used to relieve the buildup of excess water pressures in the substrata and reduce the risk of liquefaction & types of gravel foundation is • Underwater screeding frames • Scrading X.
ESTIMATION OF TUNNEL Before planning and estimating the cost of a tunnel, it is necessary to understand the different equipment and work methods that can be used to accomplish the job. Tunnel construction equipment may be divided into three main groups: (a) Excavation equipment such as drills, jumbos, tunnelboring machines, road headers, and mucking machines; (b) Tunnel haulage equipment such as front-end loaders, trains, and conveyors; and (c) Service equipment and facilities such as ventilation and air conditioning, generators, hoists, and lights. x. Tabulate total estimated costs of project in format required by request for bid.
• UNIT COST METHOD -The unit cost method of estimating tunnel costs is a wellaccepted simple technique for making preliminary or planning estimates. It relies on historical records of similar jobs. Basically, the estimator prepares quantity takeoffs for the tunnel and determines the unit cost of each item by comparison with other similar tunnels.
• TUNNEL COST CURVE-One of the earliest reported developments to improve the reliability and reduce the time required for preliminary tunnel estimates was made by the California Department of Water Resources (1959). Preliminary estimates to aid in route selection led to the formulation of a family of "cost curves." Case histories were analyzed to determine the cost impact of all factors involved in tunneling.
They considered four major construction items affecting cost: excavation, support, dewatering, and lining. For each item, a family of cost curves was developed. Each curve represented a specified geological classification. The curves were plotted as item cost per foot of tunnel versus tunnel diameter. The cost calculations were based on cost curves for different size tunnels and various geologic conditions developed using the COSTU' program. The method described herein allows the user to develop a more comprehensive and accurate estimate. It must be remembered, however, that the accuracy of any estimating method depends on the accuracy of the required input data.

• DISCUSSION
In tunneling projects, it is essential to control and predict the ground surface settlements observed during and after the excavation process that may cause damage to the structures present on the earth surface.. Otherwise, project time and tunneling cost significantly increase due to damage to structures caused by the surface settlement that occurs above the bearable limits. Therefore, the tunnel construction methods need Tobe chosen and used very carefully. Also, deep understanding regarding the various aspects and issues related to these tunneling methods is very necessary. Improper use can lead to discrepant results and potential hazard if used in decision making. The selection of each tunnel construction method is done on the basis of their advantages, disadvantages and limitations. Against this backdrop, the variable density tunnel boring machine is not just a further advancement of the convertible shield additionally an unequivocal development step. Variable density TBM can be very useful over other tunneling methods if utilized and handled properly. The idea unmistakably builds adaptability and security inside the tunnel and the machine is generally usable in variable (mixed) ground. For short range and We also thank Prof.Manjari Bhattacharya for their guidance and continuous encouragement throughout the academic to see that this project rights to its target from its commencement to the completion. We avail this opportunity to convey our sincere thanks to those who have directly or indirectly contributed to our project work and for the teaching us to see the silver lining in every Dark cloud.