VIVEK DHAKAL

# VIVEK DHAKAL

I'm a Civil Engineer. I usually write about engineering and some topical matters.

## Irrigation System in Nepal

The history of irrigation development in Nepal before 1992 shows that the irrigation system was developed, operated, and maintained by farmers called Farmer Managed Irrigation System (FMIS). After that, the government of Nepal started to make efforts for the development of irrigation infrastructures in Nepal. The irrigation system in Nepal can be broadly divided into the following two parts:

1. Irrigation System in Plains/Terai
2. Irrigation System in Hills/ Hill Irrigation System
The irrigation system in plains (Terai regions) is usually of canal irrigation type which consists of diversion headworks, canal networks, and canal structures (cross drainage structure, canal falls/drops, cross regulators, head regulators, outlets, escapes, etc). On other hand, the hill irrigation system is a small system that taps water from small streams & river tributaries & consists of narrow, deep, and long canals with steep slopes. Sprinklers & drip irrigation systems are usually suitable for hilly regions of Nepal.

## Specific Consideration for Hill Irrigation System

### 1. Social Arrangements

The irrigation system adopted in hills needs to be appropriate to the culture of different ethnic groups living in hilly regions. Junior and senior water rights should also be kept in mind while designing irritation systems in hills. Village boundaries may also affect the layout of the distribution network of the irrigation system.

### 2. Managerial & Institutional Constraints

If farmers in the hilly regions lack managerial & institutional capabilities & cannot be trained effectively within the available time period, then the distribution system should be simplified and control structures should be minimized. The regulating structures should be made easy to operate by local farmers.

### 3. Agricultural Considerations

The irrigation system proposed should also be compatible with the type of soil present in the hilly region. Also, the irrigation system should be suitable for the type of crops to be cultivated in hilly areas.

### 4. Financial Considerations

The choice of technology, methods of construction, type of materials to be used, etc may be restricted due to financial limitations.

### 5. Design Considerations

• Farmers' Participation in Engineering Design
Because of intimate familiarity with the local conditions, farmers may help to better estimate the design flood discharge, flood level in the river, boulders & sediments carried by the river, etc. By providing these facts, farmers can help designers to avoid costly mistakes.
• Field-Based Design
Decisions regarding where to place the structure, what type of structure to be built, etc should be taken in the field since the structures in hills are affected by various topographical factors of the hilly region.
• Design Standards
Design standards while designing structures in hill irrigation systems should be considered wisely. Adoption of higher design standards (structural & operational) may be unrealistic as the structures built in hill irrigation systems are subject to frequent flooding, landslides, rock falls, soil erosion, etc.
• Canal Design
Large canal sections should not be built on unstable hill slopes. Canal beds may be steep to increase the flow velocity & thus to reduce the seepage loss via canal beds. Canal linings may be done with locally available materials in hilly regions.

## Importance & Requirements of Highway Drainage

Water has detrimental effects on the good performance of road & should be drained off as soon as possible. The process of quick removal of water out of surface & sub-surface region of the road is called Highway Drainage. The surface & sub-surface water of the road should quickly pass into the longitudinal drains if a proper highway drainage system is present. The surface water passes into longitudinal drains via gravity flow due to the cross-slope provided on the road surface. The subsurface water first goes into the perforated cross drains & then into the longitudinal drains, both being under the road surface in the areas of heavy rainfall. The surface drainage system prevents the surface water from percolating down to the sub-surface layers. The sub-surface drainage system takes the sub-surface water out of the subsurface layers.

## What is the Importance of Highway Drainage?

The provision of a proper drainage system provides the following important functions:
1. It arrests the moisture variation in the subsurface layers thus preventing the reduction in bearing capacity of subgrade soil.
2. It prevents the erosion of side slopes.
3. It prevents the failure of formation slope caused by the poor drainage system.
4. It prevents the stripping of bitumen from aggregates in flexible pavements.
5. It prevents the mud pumping in rigid pavements.
6. It prevents the skidding of vehicles caused by a reduction in friction coefficient.
7. It prevents the frost action caused by the accumulation of water.

## What are the Requirements of a Good Highway Drainage System?

A good highway drainage system should fulfill the following requirements:
1. The surface water on the carriageway and shoulder should be drained off effectively as soon as possible.
2. The surface water from the adjoining land should be prevented from entering into the roadway.
3. The groundwater table should be maintained well below the bottom surface of the subgrade soil.
4. The capillary rise & seepage water should be controlled effectively.
5. The longitudinal drains & cross drains should have sufficient capacity to carry the collected water.
6. The longitudinal drains & cross drains should have sufficient bed slope for gravity flow.
7. The flow of water across the road surface & in the drains should not cause erosion.
8. Complex & costly cross drainage structures should be avoided as much as possible.

Roads in Nepal are classified according to different guidelines & standards developed by the government of Nepal. The major guidelines are Nepal Road Standard 2070 (NRS 2070), Nepal Rural Road Standard 2071 (NRRS 2071), Nepal Urban Road Standard 2076 (NURS 2076), etc.

According to Nepal Road Standard 2070, the roads in Nepal can be classified as follows:
• National Highways
• Technical/Functional Classification
• Class I
• Class II
• Class III
• Class IV

Administrative classification of roads is intended to assign national importance & level of government responsible for the overall management and financing methods.
1. National Highways
These are the major roads running east to west & north to south of the country.
These are the roads connecting the district headquarters, major economic centers & tourism centers to national highways or other feeder roads.
These are the roads within a district, serving areas of production & markets, and connecting with each other & with the main highways.
These are the road within an urban municipality.

In Nepal, the overall management of national highways & feeder roads comes under the responsibility of the Department of Road (DOR). And these roads are collectively called Strategic Road Network (SRN). The district roads & urban roads fall under the responsibility of the Department of Local Infrastructure Development & Agricultural Roads (DOLIDAR). And these roads are collectively called Local Road Network (LRN).

## Nepal Rural Road Standard 2071

According to Nepal Rural Road Standard 2055, 2nd revision 2071, the rural roads in Nepal are classified as below:
• District Road Core Network (DRCN)
1. District Road Core Network (DRCN)
It is an important road joining a VDC HQ's office or nearest economic center to the district headquarters, via either a neighboring district headquarters or the Strategic Road Network.

## Nepal Urban Road Standard 2076

According to Nepal Urban Road Standard 2076, the urban roads are classified as follows:
These are the roads generally meant for through traffic usually on a continuous route.
These are the roads of the somewhat lower levels of travel mobility than the arterial roads.

## What are the Special Considerations for Hill Road Alignment?

According to Nepal Rural Road Standards (2055), 2nd Revision 2071, the terrain is classified as Terai & Hills based on the topography of the country. The Terai covers the plain & rolling terrain having a cross slope of 0 to 25%. Hill covers the mountainous & steep terrain having a cross slope of 25 to 60% and more. The road passing through the hilly terrain with a cross slope of 25% or more is generally termed as Hill Road. A hill road usually consists of either a river route or a ridge route.

## What are the Factors Affecting the Alignment of Hill Roads?

There are various factors affecting road alignment. Moreover, there are some special considerations to be followed while selecting a hill road alignment. The major factors to be considered while deciding the alignment of hill roads are as follows:

### 1. Geological Stability

The road alignment should pass through a stable hill slope. The area should not be prone to erosion, landslides, rockfall, etc.

### 2. Availability of Construction Materials

Availability of construction materials near the construction site will reduce the transportation cost of materials thus making the project economical.

### 3. Cross Drainage Structures

Due to numerous watercourses present in the hilly regions, there may be the necessity of intense cross drainage works. The alignment should be so selected in such a way that the number of cross-drainage structures required becomes minimum.

### 4. Geological Structures

Excessive cutting of hard rock will be expensive. So, such areas should be avoided as much as possible from the road alignment.

### 5. Geometric Design

The alignment should be chosen to minimize the ineffective rise & fall, steep gradients, number of hairpin bends, etc. Also, the geometric design parameters should comply with the design guidelines & standards for hilly regions.

### 6. Altitude of the Road

• Rainfall (or Snowfall) ∝ Altitude
• Atmospheric Pressure ∝ $\frac{1}{Altitude}$
• As the altitude decreases, the number of cross drainage works required increases.

## Basics of Tunnel Engineering | Methods of Tunneling

Tunnels are underground passages used for transportation purposes. Tunnels are the underground routes driven without disturbing the overlying soil to bypass the obstacles safely. Tunnels can be used to carry passengers & freights, water, sewers, gases, etc. Tunnels are constructed in various shapes & sizes. The shape of the tunnel cross-section is governed by the nature & type of soil to be penetrated while the size of the tunnel depends on the usage to which it is subjected. The economy of tunnel construction depends on the relative cost of open cuts vs. tunneling. The tunnel becomes more economical than an open cut beyond a certain depth.

• It reduces the route distance & travel time
• It provides easy gradients in hilly terrain
• Surace activities are not disturbed
• It remains free from the weather actions like rainfall, snow, etc
• The tunnel becomes more economical than an open cut beyond a certain depth.

• The initial cost of construction may become higher
• Construction of tunnel requires skilled manpower & sophisticated equipment
• Strick supervision is necessary during construction
• Higher safety precautions are necessary during construction
• Construction of tunnel requires more time than open cuts
• A tunnel may collapse during an earthquake

## Terminologies related to Tunnel Engineering

• Tunnel Portal: The tunnel entrance is called a tunnel portal.
• Crown: It is the topmost point of the tunnel cross-section.
• Invert: It is the lowest point of the tunnel cross-section.
• Adit: It is a horizontal or near-horizontal passage that provides access to a tunnel. It may be used for the purpose of the auxiliary entrance, ventilation, drainage, etc.
• Shaft: It is a vertical passage from the ground surface that provides access to a tunnel. It may be used to transfer the centerline from the ground surface into the tunnel.
• Tunnel Linings: These are the supports erected during & after tunnel construction to ensure a safe working environment inside the tunnels. Stone masonry, brick masonry, timber, steel, etc are used as tunnel lining materials.
• Mucking: Mucking means the removal of blasted debris from the tunnel interior to a good distance outside the tunnel entrance.
• Faces of Operation or Attack: It is the surface from which a boring operation is carried out.
• Pilot Tunnel: It is a small tunnel driven, parallel & close to the proposed main tunnel, to explore geological conditions & assist in final excavation.

## Classification of Tunnels

### A. Based on Purpose

1. Traffic Tunnel
• Highway Tunnel
• Railway Tunnel
• Pedestrian Tunnel
2. Conveyance Tunnel
• Power Tunnel
• Water Supply Tunnel
• Sewer Tunnel

### B. Based on Shape/Cross-Section

1. Circular Tunnel
2. D Shaped Tunnel
3. Horse Shoe Tunnel
4. Square or Rectangular Tunnel
5. Elliptical Tunnel

## Methods of Tunneling

During tunnel construction, tunnels are lined with suitable materials parallelly with the boring operations. Tunnels are usually lined with timber, steel, cast iron, masonry, or concrete with suitable outlets to let out the enclosed subsoil water behind the linings. Other items of work include the provision of ventilation, drainage, lighting, etc. Tunneling may have to be done in the hard rock or soft soil based on which the method of tunneling differs. Hard rock is considered as a fully self-supporting soil that does not require much support except where a loose rock is occasionally met. On the other hand, soft soils like running grounds (eg: water-bearing sands) require instant supports all around. So, different methods of tunneling based on the nature of the soil to be penetrated are listed below:

### A. Tunneling in Soft Soils

1. Fore Poling Method
2. Needle Beam Method
3. Shield Method
4. Compressed Air Method
5. Liner Plate Method
6. Army Method
7. American Method

### B. Tunneling in Hard Rock

1. Full Face Method
4. Drift Method
5. Pilot Tunnel Method
For the detailed description of each method of tunneling listed above, the readers are kindly requested to go through ref 1.

References
1. Srinivasan, R.(1958). Harbour, dock and tunnel engineering. India: Charotall Book Stall

## What is Highway Alignment?

The process of establishing the centerline of a road is called highway alignment or Road alignment. It the direction through which the highway will pass. Highway alignment can be divided into two parts as Horizontal Alignment & Vertical Alignment. The horizontal alignment is seen in the plan of the road & it consists of the straight path, horizontal curves, etc. The vertical alignment is observed in the longitudinal profile of the road & it contains verticle curves, gradients, etc.

## What are the Requirements of Highway Alignment?

An ideal highway alignment may fulfill the following criteria:
• Short: The route between any two points should be the shortest route.
• Safety: The alignment should satisfy the safety requirements.
• Comfort: The alignment should have easy curves & gradients.
• Economy: The cost of construction should be economic.

## What are the Factors Controlling Highway Alignment?

There are various factors to be considered while selecting a road alignment. Additionally, there are some special considerations to be followed while selecting alignments in hill roads. In general, the following factors are to be considered while choosing a highway alignment.

### 1. Government Plannings

Since a road project involves heavy investments, it should comply with government requirements & planning.

### 2. Obligatory Points

Obligatory points are the governing points that control the highway alignment. These can be classified into two types viz. the points thorough which alignment should always pass (or positive obligatory points) & the points through which the alignment should never pass (or negative obligatory points). Ex: Highway alignment should always pass through the bridge site. In the case of mountains in the alignment, there may be options either to go round the hill or to construct a tunnel. Moreover, the highway alignment should never pass through the National Parks, Conservation Areas, Protected Areas, dense forest, costly agricultural lands, etc. In the case of an intermediate town, the highway alignment may get deviated slightly in order to connect the town.

### 3. Traffic Flow Pattern

The traffic flow pattern can be known from the origin & destination study (O&D Study). The lines are drawn in the data obtained from the origin & destination study & then, proper alignment is fixed.

### 4. Geometric Design

The road alignment is also affected by the geometric design. The horizontal curves, vertical curves, gradients, sight distance, etc should meet the requirements of geometric design standards.

### 5. Monotony

Due to very long straight paths in flat terrain, the driver may become monotonous & this may lead to accidents. Thus, small horizontal curves should be provided in suitable intervals to avoid monotony.

### 6. Economy

The alignment should be selected in such a way that the construction cost, maintenance cost & operation cost of the road is minimum. Excessive cuttings & fillings, the necessity of complex structures, etc should be avoided.

### 7. Railway Crossings

A highway alignment should cross the railway alignment preferably at a right angle.

## Definition of River Training

The process of controlling the flow in river & river bed configuration is called river training works. These are the structural measures adopted in rivers to avoid outflanking & shifting its thalweg due to geomorphological changes in the river. So, the river training works stabilize the river channel along a certain alignment.

## Methods of Soil Compaction | Types of Soil Compaction

Compaction of soil is necessary for various types of foundations used in civil engineering constructions. It improves the engineering properties of soil. Compaction is the process of reducing air voids in soil by means of mechanical compressions. During compaction, the air is expelled from the voids in the soil. It increases the dry density of soil, improves shear strength & hence stability and bearing capacity. The various methods of soil compaction are as follows:
• Tamper / Rammer
• Hand Operated Tamper
• Mechanical Tamper
• Roller
• Smooth Wheeled Roller
• Pneumatic Tyred Roller
• Sheep Foot Roller
• Vibrator