Assignment

ASSIGNMENT TUNNEL ENGINEERING

JAN ALI KHAN Reg # 14 M2-213016 Course: B-Tech (HON:) Civil Semester: 6th

SUBMITTED TO ENGR. BASHIR AHMAD

PRESTON UNIVERSITY ISLAMABAD.

CHAPTER NO: 1

Q.No.2

Describe the Advantages and Disadvantages of Tunnels?

Ans.

Advantages of Tunnels: Following are the advantages of Tunnels.

1. Tunnels are more economical than open cuts beyond certain depths 2. Tunnels protect the system i.e. railway track ,highway, sewer line, Oil line etc. for which it is constructed from weather effects such as snow, rain etc. thus the tunnels reduce the maintenance cost of the system. 3. Tunnels avoid disturbing or interfering with surface life and traffic during construction. 4. During war time tunnels protect the system from destruction due to bombarding. 5. In certain place tunnels have proved cheaper for crossing the mountain or river than open cut or bridges. 6. In most congested urban area under ground railways or highway is the best alternative to provide means of transportation. 7. In soft-rocked hills, construction of tunnel has proved cheaper than open cut due to large number of slips etc. 8. In circuitous route to reach the other side of the mountain, tunnel reduces the length of the railway line etc. considerably. 9. Tunnels avoid the dangerous cut very near the structure. 10. Tunnels have proved cheaper to carry public utilities services as water, gas sewer etc. 11. Tunnels if provided with easy gradients, the cost of hauling is reduced. 12. The safety of tunnel construction has considerably increased due to improved modern methods of construction.

13. Due to shortening in distance tunnels have proved economical. Disadvantages of tunnels: Following are the disadvantages of tunnels. 1. Initial cost of tunnel construction is more. 2. Tunnel construction requires skilled labor and supervision of high order. 3. The construction duration of tunnels is more than bridges or open cut. 4. The construction of tunnels requires sophisticated and specialized equipments

Q.No.4 Ans:

Discuss the favorable conditions for the construction of tunnels? Favorable conditions for the Tunnel constructions.

Tunneling operations are advisable if the depth of open cut is more than 18 meters. In addition the following conditions are considered favorable for tunnel construction. 1. Tunneling allows rapid and un obstructed transport facilities in big congested cities. 2. It avoids acquisition of valuable land for its construction. 3. It avoids long circuitous routs around a mountain or spur. 4. It connects two terminal stations separated by an obstacle with the shortest route. 5. It diverts water for power generation. 6. It is a desirable to carry public utility services like water, oil ,gas etc. across a mountain or stream. through a tunnel. 7. It permits easy gradients in mountainous terrain resulting in high speeds of vehicles 8. Tunnel being hidden in ground is safer in war time. 9. In soft soil open cuts may slide where as tunnel does not.

Q.No.5

Give the classification of tunnels?

Ans.

Classification of Tunnels. Tunnels can be classified in various ways as follows.

1. According to Alignment. Under this head tunnels are sub divided as. a. OFF-SPUR Tunnels. These are short tunnels to negotiate minor local obstacles. b. SADDLE OR BASE Tunnels. These tunnels are constructed in the valley along with the natural slope till the slope does not exceed the ruling gradient. c. SLOPE tunnels. These tunnels are constructed in steep hills for economic and safe operations of roads and route ways. d. SPIRAL tunnels. These tunnels are constructed in narrow valleys in the form of loops in the interior of the mountain. These are constructed to avoid steep slopes by increasing their lengths. 2. According to Purpose. Under this heads, tunnels are further sub divided as follows. a. Traffic tunnels : These tunnels are constructed to carry , highway, railway , navigation, sub way and pedestrian etc. and are known as highway tunnel, railway tunnel, navigation tunnels, sub- way tunnel and pedestrian tunnel etc. b. Conveyance tunnel. These tunnels are constructed to carry sewer, water, oil etc. and are known as sewer tunnels, water supply tunnels, hydro electric power tunnels etc. 3. According to type of soil met during construction: According to this classification, tunnels are sub classified as follows: a. Open cut tunnels. b. Tunnels in hard rocks. c. Tunnels in soft rocks. d. Tunnels underneath river bed. Q.No.6.

Write a note on the selection of route for a tunnel.

Ans.

Selection of route of a tunnel: The selection of route of tunnel

depends upon the following factors. 1.

Natural features of topography of the area through which tunnel passes.

2. Convenient points of its entrance and exit. The selection of site for tunnel should be made by proper study of the following two points. 1. Alignment restraints. The under ground space is a heterogeneous mass and problems like water table, position of fractured rocks etc, are encountered. Also on the ground presence of service lines, filled up grounds, are also to be tackled. Thus a detailed study of the rock formation and existing alignment restraints should be made before a final alignment is chosen. 2. Environmental considerations: The site of tunnel construction should be selected in such as way that least difficulty is experienced for disposal of exhust gas, ground water and muck etc.

CHAPTER NO. 2

Q.No.1

What is a tunnel. Discuss the advantages and disadvantages of

tunnel as a means of communication? Ans.

Tunnel: Tunnel is an under ground artificial passage which is constructed without

disturbing the ground surface. Advantages and Disadvantages of tunnel as means of communication: Advantages: As means of communication the tunnel has the following advantages: 1. It provides short route. 2. It allows all Heavy & Light vehicles 3. It provides easy grade and alignment to the vehicles 4. It links banned terminals to each others. 5. It make journey fast and safe. Disadvantages: Following are the disadvantages of the tunnel as means of

communication.

1. It is a confined and single route can jam the system at any misshape. 2. It has no alternative or diversion in case emergency. 3. It event can cause fatal. 4. It needs high standard maintenance, unawareness can cause any hazard. Q.No. 6.

Write short notes on the following.

a. Tunnel alignment and grade b. Tunnel approaches. c. History of tunnels. d. Shape and size of tunnels.

e. Selection of route of tunnel. f. Emergency services. Ans. a. Tunnel alignment and grade : Alignment of tunnel is the center line of the tunnel which is located on the ground precisely fixing monuments on the line at short distance points. Grade is the longitudinal slope of the tunnel route, provided as per design. b. Tunnel approaches : These are open cuts on both sides of the tunnel. In case of very steep hill slopes, these are very short , while for flat sloped these are longer. c. History of tunnels: Development of tunnel is very old. Generally a tunnel is needed when an obstacle in the form of a hill or rising ground is met within the alignment of railway track or highway etc. The first tunnel was of the world was constructed by Egyptians and Babylonians about 400 years ago to connect two buildings in Babylon d. Shape and size of tunnels : The shape of the cross section is the geometrical texture of a tunnel designed as requirements i.e. pressure of the ground usage purpose etc. Size of the tunnel is internal dimension of the tunnel its height and width. The size of the tunnel is determined by its utility aspect. e. Selection of route of tunnel : The selection of route of a tunnel depends upon the following factors. 1. Natural features of topography of the area through which tunnel passes. 2. Convenient points of its entrance and exit. f. Emergency services: To handle any misshape in a tunnel emergency equipments are installed in the tunnel e.g. Fire fighting equipments, standby power supply source for tunnel lighting system, fire indicators etc.

Q.No.8

Write short notes on the following.

a. Tunnel and open cut. b. Tunnel approaches and portals. c. Circular section and horse shoe section. d. Road tunnel and railway tunnel. e. Twin tunnel and single tunnels. f. Rectangular section and egg shaped section Ans. a. Tunnel and open cut Tunnel: Tunnel is an under ground artificial passage which is constructed without disturbing the ground surface. Open cut: Open cut is the underground artificial passage open to sky. b. Tunnel approaches and portals: Tunnel approaches: These are open cuts on both sides of the tunnel. In case of very steep hill slopes, these are very short while in case of flat slope hills these are longer. Portals: The actual door ways or main entrances of tunnels are known as portals c. Circular section and horse shoe section: Circular section: A tunnel in the shape of circular is known as circular section. It is suitable for heavy internal and external radial pressure. It is mostly constructed for sewer and water carrying purposes Horse shoe section: It is very popular form of tunnels. It has semicircular roof together with the arched sides and a curved invert. The cement concrete lined horse shoe cross section offers a good resistance to external ground pressure. d. Road tunnel and railway tunnel. Road tunnel: tunnel constructed for the road vehicle is called, Road tunnel Railway tunnel: Tunnel constructed for the use of rail is called railway tunnel.

e. Twin tunnel and single tunnels: Twin tunnel: Tunnels constructed in the form two small tunnels adjacent is called twin tunnel. Twin tunnels are constructed in case of railway tunnels with double lines. Single tunnels: A tunnel consists of one unit is called single tunnel. f. Rectangular section and egg shaped section: Rectangular section: A tunnel constructed in the shape of rectangular figure is called rectangular tunnel. It is suitable in hard rock. egg shaped section: This section gives self cleansing velocity , therefore, it is used for carrying sewage. Q.No.14.

What points should be kept in mind while deciding the alignment

and grade of tunnel. Ans.

The following points should be kept in mind deciding the alignment and

grade of tunnel. 1. Proper ventilation and lightening arrangements should be made if the grade is in one direction. 2. Minimum possible grade should be provided in tunnel and its approaches. A . 2% grade may be provided for proper drainage. 3. As far as possible straight alignment should be provided, as it will be shortest and economical. 4. For good drainage, the side drains should be given a minimum grade of 1in 500. In longer tunnels a grade from the center to both sides should be provided towards the ends for proper and efficient drainage.

CHAPTER NO.3 Q.No.2.

Enumerate the factors which influence the selection of drilling

equipments? Ans.

There are many factors which affect the selection of the equipment.

1. Nature of the terrain. Rough surfaces dictate the choice of jack hammers, regardless of other factors. 2. Purpose of holes, such as blasting, grouting, exploration etc. 3. Required depth of holes. 4. Hardness of the rock. 5. Extent to which the formation is to be broken or fractured. 6. Size of the project. 7. Extent to which the rock is to be broken for handling. 8. Availability of water for drilling purposes. Lack of water Q.No. 5: What do you understand by the drilling pattern? What factors govern the drilling pattern? Ans:

Selection of drilling pattern of holes to be loaded with explosives is governed

by the following factors. 1.

Kind of rock.

2. Depth of holes desired. 3. Type of drill to be used and method of mounting. 4. Maximum size of broken rock desired. 5. Size of tunnel etc. If the rock is to be blasted for producing aggregate, in that case the drilling pattern should be so planned that rock pieces obtained should be small enough, so that secondary blasting may be avoided and rock pieces may be used in crushers directly. In order to obtain a uniform breakage of rock, the small diameter holes should be drilled at close space. In this case the distribution of explosives will be better.

However a study of cost analysis is necessary. In case of large diameter holes, they need more explosives; hence to educe the cost, the spacing between holes may be increased. Thus while analyzing the drilling and blasting operations, following factors should be studied carefully. 1. The cubic meter of rock blasted per linear meter length of hole. 2. The number of kg of explosive required per linear meter length of hole. 3. The number of kg of explosive required per cubic meter of rock. Before starting an work the study of the above factors should be done and modifications can be effected after experimental drilling operations, if needed.

Q.No.8.

Explain with neat sketches the following.

a. Bottom cut. b. Buster cut. c. Pyramid cut. d. Horizontal wedge cut. e. Vertical wedge cut.

CHAPTER NO. 4. Q.No.2

Enumerate different types of explosives used for blasting of rocks.

Ans.

Types of Explosives: The different types of explosives are the following. 1. Powder explosives 2. Liquid air explosives 3. Disruptive explosives

1. Powder explosives: Under this group are the following explosives. a. Blasting powder b. Nitrate explosives c. Nitramon. 2. Liquid air explosives: This class of explosives contains oxygen at a temperature of 190C and requires special skills in their manufacturing, transportation and storing. so these explosives are not popular for rock tunneling. 3. Disruptive explosives: These explosive are available in market in various sizes, grades and strength in the form of cartridges of 2.5 to 20 cm in diameter and 20 to 70 cm in length. The strength of these explosives are specified as a percentage or the ratio of weight of nitroglycerin to the total weight of the cartridge. This group is further sub divided in the following groups. 1. Straight dynamite: It is highly sensitive and water proof explosive. primarily it consists of 15% to 60% nitroglycerin absorbed by an absorbent i.e nitroglycerin is 15%- 60%in it. The smell of gases produced by these explosives is very foul and bad. Hence they are not suitable for tunneling. However they can be used in tight spots in the tunnel and for block holding or mud capping boulders and pieces of rock too large to handle. 2. Ammonia dynamite: They are also called extra dynamite. They contain equal parts of nitroglycerin and nitrate of ammonia. The strength of this type of explosives is 155- 60%. They are not as quick or sensitive as straight dynamites. They are fairly

water resistant and their fumes are also not as bed as that of straight dynamite. so suitable for tunneling in soft rocks. 3. Gelatin dynamite. They are of two types (a) Straight Gelatin dynamite (b) Special or Extra gelatin dynamite. Both of them consist of jelly of nitroglycerin and nitro cotton. In case of special gelatin dynamite a part of nitroglycerin is replaced by nitrate of ammonia. The strength of

straight and special gelatin are 20-90% and 30-90%

respectively. Both of them are highly water resistant and their fumes are also not objectionable. In fact they're least objectionable in regard to their fumes. They are quick in action if confined. Semi gelatin : This type of explosive is of recent development Primarily. It is consists of nitrate of ammonia with some gelatinized nitroglycerin and nitro cotton It is heavier and bulkier than straight and special dynamite. They are available in two strengths of 45% and 60% only. Their fumes and water resistance qualities are better than other gelatins. They have lower density and are cheaper than other gelatins. They are useful for tunneling in soft rocks. Blasting Gelatin: They are also of recent origin .They are just like rubber and fully water proof. They are very fast and strong explosives but the smell of their gases are very bad. Their strength is 100% hence they are suitable for tunneling under water. Special high explosives: There are several special types of explosives in the market developed for special conditions but they rarely used for tunneling. Q.No.6. Explain how a bore hole is loaded with explosives? Ans.

Loading of bore holes: (a) After drilling the hole, first of all it is cleaned of

all lose cuttings etc. Any cuttings and water etc. are removed by sending air under pressure from compressor. (b)

The cartridge of explosive is place at the bottom of the hole and tamped well

with wooden stick. (c)

The primer with detonator is inserted in the hole and embedded into the

cartridge. The primer should be prepared correctly. There are basic rules which govern the making up of a primer.

(i) Placing the detonator well within cartridges and parallel to the axis so that full force of the exploder is directed against the mass of the powder and not against the stemming or walls of the hole. (ii) Protection of exploder from accidental firing and the wire from injury. (d) To prevent jarring of the detonator , the primer and second cartridge if place d and tamped slightly. During tamping detonator wires should be damaged. (e) If required more cartridges may be placed at the desired depth and tamped as above. (f) Now the electric blasting caps are inserted. (g) The remaining empty space is filled with stemming. Stemming consists of rock cutting or other suitable inert material. It confines the energy and increases the efficiency of explosion. Q.No.7

Explain briefly springing method of blasting?

Ans.

Springing method of blasting: This method of blasting was adopted

on Bhakra project and proved very useful. In normal open cut blasting operations, the holes drilled by jack hammer or wagon drills and loaded with special gelatin up to 50 to 66% of its depth. The balance depth is stemmed with rock cuttings or other inert material. The force of blasting in such cases is not concentrated at the bottom of the hole, but spread from the bottom up to height of the explosive charge. In springing method of blasting, the force of the blast is concentrated at the bottom or back of a hole by making an enlarged chamber to to hold the explosive charge. This is done by exploding a small quantity of special gelatin say 1 or 2 cartridge, in the bottom of the hole. The hole may be stemmed with dry sand or water. The explosive of the charge will make a cavity by crushing the surrounding rock and blowing it out the hole. Two or three blasts of increasing size will make the chamber large enough to hold the requisite quantity of explosive. Springing is thus accomplished by firing a series of charges of special gelatin, one after another at the bottom or back of the bore hole. The explosion of each charge fired in this manner increases the size of the cavity of the chamber. The amount of enlargement depends upon the hardness of the rock and the size of the charge