Construction HydroPower

Tunnels and factor affecting the tunnelings

Tunnels are artificial underground passages constructed for various purposes like transportation, navigation, water supply, sewer, hydro-power, public utility, canals, etc.

In this article, we mainly discuss the point should consider while selecting the alignment of the tunnel. And also the necessary things such as Tunnel Drainage, Lighting Of Tunnels, Tunnel Ventilation and Lining In Tunnel respectively.

While selecting the alignment of the tunnel following points should be considered :

  • The route should as short as possible
  • The straight path is preferred
  • Easily accessible
  • Careful selection of entry and exit location

Factors affecting the tunneling

  • Land topography
  • Geological selection of the alignment
  • Hard rocks
  • Groundwater
  • Creep or tectonic movements

Factor need to consider while doing work of alignment of the tunnel

1. Tunnel Drainage

PRE DRAINAGE: A drainage arrangement before the construction of the tunnel is known as pre-drainage.

DE-WATERING: It is the drainage arrangement that is carried out during the construction time of the tunnel.

PERMANENT DRAINAGE: The methods of permanent drainages are:

  1. Provision of longitudinal pipelines
  2. Concrete lining
  3. Grouting with cement or chemicals

2. Lighting Of Tunnels

The lighting of the tunnel is a very important environmental factor to utilize the full efficiency of manpower or machine involved in work with proper safety.

The minimum requirements for lighting in tunnel are as follows:

  • Adequate lighting should be provided at each and every point
  • Lighting at the working face should be provided
  • Lamps should be fixed at both sides and center
  • Hauling equipment should have their own lighting system
  • Excavating equipment and other heavy equipment should have their own lighting system

3. Tunnel Ventilation

Ventilation is the process of replacing used air with fresh air. It is done by both artificial and natural methods.

Objectives of ventilation:

  • To replace the used air by fresh air
  • To remove harmful gases
  • Supply adequate amount of oxygen to workers
  • Remove the excessive amount of moisture present inside the tunnel.

4. Lining In Tunnel

Tunnel lining is a part of the support design provides inside the construction area of tunnels. Lining can be done by brick, timber, concrete, stone, rock reinforcement, steel, etc.

Objectives of lining in tunnel:

  • It withstand the soil pressure
  • It gives support to loose soil
  • Provides proper shape to the tunnel
  • It strengthen the weak portion
  • It makes the tunnel free from water penetration
  • To ensure streamline flow for water tunnels.

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Selection of the bridge site

A structure constructed over an obstacle to provide safe passage is known as a bridge.

A passage for the movement of traffic is known as a rad bridge. If the level of the bridge is much higher than the level of the road, then it is over a bridge. Similarly, if the level of the bridge is below the ground level it is called the subway.

Characteristics Of Bridge

  1. Line of the bridge should not have a serious deviation from the line of the road.
  2. Bridge should be properly levelled.
  3. Width of a bridge should be sufficient for the traffic.
  4. Foundation should be kept on strong ground and at sufficient depth
  5. It should be as economical as possible in terms of construction and maintenance
  6. It should provide the passage for services like water pipes telephone wires etc.

Selection of the bridge site

In field we take account of different things, while selecting the bridge site. One basic thing we consider is “SESE’ where S= small, E= economical, S= safe and E= earlier.

  1. A straight section of bridge should be choosen
  2. Steady river flow without any serious whirls and cross current
  3. The channel should be as narrow as possible with firm banks
  4. Suitable high river banks on each side above the high flood level
  5. Absence of expensive river training works
  6. Absence of expensive under water construction works
  7. Long detours should be avoided
  8. The bridge axis should be free from geological folds and faults

Classification Of Bridge

According to the span (NRS 2045)

  • Culvert (length up to 6m)
  • Minor bridge (span less than 20 m but total length may be up to 20 m)
  • Medium bridge (span less than 20 m but total length more than 20 m)
  • Major bridge (span and whole length of bridge more than 20m)

According to the structures

  • RCC bridge
  • Cantilever bridge
  • Arch bridge
  • Truss bridge
  • Stayed cable bridge
  • Beam bridge
  • Suspension bridge
  • Movable bridge

According to materials used

  • Timber bridge
  • RCC bridge
  • Masonry bridge
  • Steel bridge

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Road Transportation

Bitumen – Properties and Uses

Bitumen is known as petroleum in the fluid state, mineral tar in the semifluid state and asphalt in the solid-state. It is a solid or semi-solid black, sticky, ductile substance, obtained as a crucial byproduct from the distillation of crude fossil oil.

It may even be outlined as that portion of fossil oil asphalt and tar product, which is able to dissolve in carbon disulphide. Bitumen implies a bunch of hydrocarbons typically mixed with some organic matter.

Properties of bitumen

  1. It’s characteristically solid or semi-solid, black and sticky.
  2. It melts or softens on the application of warmth.
  3. Its specific gravity is 1.09.
  4. It is completely soluble in carbon disulphide.
  5. it’s a binder all told kinds of asphalt.
  6. It possesses nice chemical stability but is affected by oil.
  7. it’s low permittivity and high insulation resistance

Uses of bitumen

It is used as a damp proof course in walls and under-basements and inlining tanks, swimming pools, urinals, etc. Since it forms a smart growth joint so, it’s used for filling up the joints in leaky roofs.

Construction Road Transportation

Road Maintenance and its types.

The process of preserving and keeping the conditions of the highway serviceable and as best as practicable normally as far as possible is known as highway maintenance or road maintenance. The cost of road maintenance depends upon the road location, design of the road, the quality of construction and the quality of maintenance.

A) Roadside Maintenance

The maintenance activity on the structures and surface above as well as below the road having a direct or indirect influence on the road falls under roadside maintenance. It includes protection walls, retaining walls, cut slopes, fill slopes, unstable natural slopes, river protection activities and bio-engineering works.

B) Road Maintenance

All the maintenance activities are related to roadway and all the structures within and immediately adjacent to the roadway such as ditches, culverts, causeways, bridges, etc. 

Road maintenance is divided into the following subcategories:

A) ROUTINE MAINTENANCE: The maintenance activities that are done regularly or daily is called routine maintenance. The activities carried out under the routine maintenance are:-

  • Grass and bushes cutting
  • Grading and reshaping of unpaved shoulders
  • Road sign maintenance
  • Clearing and cleaning of ditches culverts etc.

B) RECURRENT MAINTENANCE: The maintenance activities that are done more and more or less regular intervals of six months to two years frequency is called recurrent maintenance. Maintenance’s under recurrent maintenances are

  • Sealing off cracks in highway and roads
  • Patching of potholes
  • Repairing depressions, holes and ruts
  • Repairing road edges

C) PERIODIC MAINTENANCE: The maintenance activities that are carried out at an interval of 5 to 7 years are periodic maintenance. The main activities under periodic maintenance are resealing and resurfacing.

D) EMERGENCY MAINTENANCE: It is divided into two subcategories:

i) Urgent emergency maintenance: It refers to the reopening of roads under any cost. The following activities fall under urgent emergency maintenance.

  1. Removal of debris.
  2. Obstacles removing
  3. Diversion works

ii) Reinstatement of roads: This activity is done generally when the rainy season is over by reconstruction or repair of pavement, structures, and the drainage as per the requirement of highway geometry.         

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Construction Road Transportation

Water bound macadam road construction procedure

The water-bound macadam construction named after john macadam. In the macadam road construction, the crushed or broken aggregates are bound together by using the rolling procedure.

Binding can be achieved by the use of stone dust as a filler in the presence of water.

The WBM roads are divided into the following types according to the materials used for construction:

  1. WBM roads with gravel including crushed gravel
  2. WBM roads with hard broken stones
  3. WBM roads with soft broken stone and brick residue

Procedure for macadam road construction

a) The thickness of WBM should be from 8cm to 30 cm with each layer of compaction from 7.5cm to 15 cm.

b) The camber provided should be a minimum of 1 in 36 to a maximum of 1 in 48.

c) Materials:

  1. Coarse aggregates:
    1. the crushed and broken stones should be hard,
    2. durable,
    3. strong,
    4. and free from excess of flaky and elongation.

The requirements of coarse aggregates are:

  • Aggregate impact value (AIV) = 30%
  • Los angles abrasion value (LAA) = 40%
  • Flakiness index (FI) = 15%

2. Screening materials of grade A with passing through screening size of 12.5 mm and grade B with a size of screening 10 mm

3. Filler materials of plasticity index (PI) up to 9 shall be used

d) Equipment used

  1. Aggregate spreader
  2. Water tankers
  3. Grader
  4. Compaction equipment (road roller)

e) Construction procedure

  1. 20% of extra broken stones should be provided than estimated.
  2. The subgrade surface is prepared
  3. Pavement construction is carried out by lateral confinement and spreading of coarse aggregates
  4. Dry rolling is done by roller with a load of 6 to 10 tons
  5. Application of screening materials
  6. Wet rolling is carried out to fil about 50% of remaining voids
  7. Filer materials with plasticity index up to 9 are applied in two successive thin layers
  8. Finishing off is done by 6 mm thick sand or earth spreading, sprinkled with water and rolled.
  9. Shoulders are prepared
  10. The WBM is opened for traffic after a few days of construction.

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