• Building
• How To Guide
• Concrete Technology
• Construction
• Geotechnical

Surveying for Construction of Irrigation Projects

First step in construction of an irrigation project like dams, barrage or weir requires surveying of whole area. Surveying for an irrigation project is done to understand if the dams or other irrigation construction is required or not.

The area should benefit to its larger extent when the completion of irrigation structure is done. So, survey is needed to conclude this.

Surveying for Construction of Irrigation Projects

The steps involved in surveying to build an irrigation structure are

1. Examine the water availability
2. Examine the topography
3. Selection of site
4. River gauging
5. Marking of CCM
6. Marking of tentative alignment
7. Reconnaissance survey
8. Preliminary survey
9. Final location survey
10. Final Survey Report

Examine Availability of Water

To construct an irrigation project whether it is a dam or weir or barrage, first and foremost observation should be the presence of water and its availability.

The availability may be of different types, but proper examination is required before construction.

Some important observations are:

• If there is any river flowing in that area, we should know the type of river whether it is perennial or inundation type. If it is perennial, then the water is available throughout the year. If it is Inundation River, then study its previous yearly discharges.
• The river should meet the requirement of water in that area.
• Suitable site be available to construct an irrigation project.

Examine Topography

After investigating the water availability, topography map of the area is studied. This study is more useful when marking the tentative alignment for irrigation project. The behavior of agricultural lands are examined in this stage.

Selection of Construction Site

When plenty of water or major source of water is available then the location to construct an irrigation project is selected. The project may be dam or barrage or weir.

The selection of site is done by considering the following points.

• The soil survey is conducted by boring and pile testing to know about the foundation depth required.
• Sufficient basin area should be available and the capacity must fulfill the required demand.
• The site should be easily accessible. Materials and labor should be readily available.
• The allowable bed slope should be maintained as far as possible in the canal.
• The structure should not submerge valuable lands and areas.

River Gauging

River gauging is measuring of water discharge at point. The point in this case where river gauging is conducted is the site selected for project.

After river gauging following details are obtained:

• The discharge of river is calculated on daily basis and the yearly discharge records are studied.
• The HFL (high flood level) and LWL (lowest water level) are recorded based on the old observations.
• To find out the possible silting of river bed, silt analysis is conducted, and manorial value of fine silt is recorded.

Marking of CCM

CCM is the cultivable command area which is mainly fit for cultivation of crops. The area under this category should be marked on the topographic map. So, the construction should not disturb or damage this area and required demand discharge can also be known.

Marking of Tentative Alignment

After the selection of site for irrigation structure, it is time to select the tentative alignments for canals or branch canals. These alignments should be marked in topographical and contour maps.

Marking should be done by following considerations.

• The alignment marked should cover the whole area when it is cut into canal.
• The alignment should minimize the earth filling and cutting costs.
• It should not pass through valuable agricultural lands, religious places etc.
• It should cross rivers, roads, rails etc. perpendicularly.

Reconnaissance Survey of Irrigation Projects

After marking the tentative alignments, then reconnaissance survey is conducted for all the alignments. This survey provides the following details:

• Nature of ground slope along the alignment.
• Magnetic bearings of lines of the traverse along the alignment are recorded.
• Alignments passing through religious places, valuable lands are eliminated. If they are unavoidable, they are marked as special areas and suitable compensation is provided.
• Nature of ground up to a distance of 100m on both sides of alignment are noted.
• Alignments cutting the crossings perpendicularly are noted.
• Distances are measured by pacing.
• Past records of floods in that area are noted.
• Suitable cross drainage works should be noted.
• If there is any river across the alignment, the alignment should cut the river across its shortest width.

Preliminary Survey of Irrigation Projects

After completion of reconnaissance survey, a good alignment is selected, and they are allowed to conduct preliminary survey.

Following steps are involved in this survey.

• Pillars are constructed on both banks of river and they represent the center line of irrigation project.
• Similarly pillars are constructed to mark the center lines of head works for both bank canals.
• Boring is done along the center line of irrigation structure to determine the depth of foundation.
• A permanent benchmark is created and its value is noted by connecting it to the nearby GTS benchmark by fly leveling.
• Plane table survey or prismatic survey is conducted on the both sides of alignments up to 100m and route survey map is prepared.
• Longitudinal leveling is conducted with an interval of 20 m.
• Cross leveling is conducted with an interval of 100 m.
• Permanent bench marks are arranged with some interval gap along the alignment.
• Water table level is studied on both sides of alignment covering up to 200 m.
• Soil along the alignment is surveyed.
• The details of road and railway crossings are noted to design cross drainage works.
• At river crossings, the cross section details of river are noted. The cross sections of river are taken on both upstream and downstream sides with covering of 500 m distance.
• Drawings are prepared for all the maps and cross sections.
• Estimate sheets are prepared for earth works, compensations for lands etc.

Final Location Survey

After preliminary survey, most economical alignment among all is selected and final location survey is conducted. In this final stage following steps are involved:

• Center line of final alignment is marked with pillars and pegs.
• The width of alignment is also marked by the pillars.
• Similarly for the branch canal also, pillars are marked.
• Final Eligible properties for compensation are recorded.

Final Survey Report of Irrigation Project

It is the last stage of the whole process and in this stage a report should be prepared with the details of final alignment.

This report is submitted to higher authorities to get an approval for an irrigation project.

• Introduction
• Justification and necessity of project
• Justification for the selection of final alignment
• Detailed estimate sheets for earth works, compensation, head work, etc.
• Detailed specification for project
• Benefit of project
• Recommendation of the project

And following maps are to be submitted along with the above.

• General map of area through which canal passes
• Route survey map
• Longitudinal section of alignment
• Cross section of alignment
• Contour map of alignment
• Drawings of dam, head works, cross drainage works etc.

  

• Building
• How To Guide
• Concrete
• Construction
• Geotechnical

Types of Railway Sleepers, Their Functions, Benefits and Drawbacks

What is a Railway Sleeper?

Railway sleepers are the components on which the rails are arranged with proper gauge. These sleepers generally rests on ballast and is also called as ties in some regions. The load from rails when train passes, is taken by these sleepers and is distributed it to the ballast.

Functions of Railway Sleepers

The basic functions of Railway sleepers are to:

• hold the rails strongly and to maintain uniform gauge.
• transfer the load from rails to the ballast or ground.
• reduce the vibrations coming from rails.
• offer longitudinal and lateral stability.

Classification of Railway Sleepers

Based on the materials used, railway sleepers are classified into following types.

1. Wooden sleepers
2. Concrete sleepers
3. Steel sleepers
4. Cast iron sleepers
5. Composite sleepers

Wooden Sleepers

These are sleepers made of wood. Wooden sleepers are used since olden days. These are still widely using in some western countries. Either hardwood or softwood can be used to make wooden sleepers. However, hardwood sleepers made of oak, jarrah, teakwood are more famous.

Benefits of Wooden Sleepers

• Wood sleepers are cheaper than others and easy to manufacture.
• They are light in weight so, they can be easily transported and handled while installing.
• Fasteners can be easily installed to wooden sleepers.
  They are good insulators so, rails are well protected.
• Any type of gauge can be maintained by wooden sleepers.
• They are suitable for all types of rail section.
• They are well suitable for tracks in coastal areas.

Drawbacks of Wooden Sleepers

• Life of wooden sleepers is very less compared to others.
• Weak against fire.
• Easily affected by humidity which will cause dry rot, wet rot etc.
• Vermin attack can be possible if it is not properly treated.
• Poor creep resistance.
• Good Attention is required even after laying.

Concrete Sleepers

Concrete sleepers are manufactured by concrete with internal reinforcement. Concrete sleepers used in many countries due to its high stability and small maintenance. These are more suitable for high speed rails.

Most of the concrete sleepers are made from pre-stressed concrete in which internal tension is induced into the sleeper before casting. Hence, the sleeper withstand well against high external pressure.

Benefits of Concrete Sleepers

• Concrete sleepers are heavier than all other types hence, gives good stability to the rails.
• They have long life span so, economically preferable.
• They have good Fire resistance.
• Corrosion is not occurred in concrete sleepers.
• Vermin attack, decay etc. are not occurred. Hence, they are suitable for all types of soil and moisture conditions.
• Bucking strength is more.
• Concrete is good insulator so, this type of sleepers are more suitable for circuited tracks.
• Concrete sleepers holds the track strongly and maintains gauge.

Drawbacks of Concrete Sleepers

• Because of heavy weight, handling is difficult.
• For tracks on bridges and at crossings, concrete sleepers are not suitable.
• Damage may occur while transporting.

Steel Sleepers

Steel sleepers are more often used because of stronger than wood and economical than concrete. They also have good life span. They are molded in trough shape and placed on ballast in inversed trough shape.

Benefits

• They are light in weight so, easy to transport, to place and to install.
• They are recyclable hence possess good scrap value.
• Life span of steel sleepers is more and is about 30 years.
• They are good resistant against fire.
• They have good resistance against creep
• They cannot be attacked by vermin etc.
• They are well suitable for tracks of high speeds and larger loads.
• They holds the rail strongly and connecting rail to the sleeper is also simple.

Drawbacks

• Steel can be effected by chemicals easily.
• Steel sleepers requires high maintenance.
• They are not suitable for all types of ballast which is provided as bed for sleepers.
• If derailment is happened, they damaged very badly and not suitable for re using.
• These are not suitable for all types of rail sections and gauges.

Cast Iron Sleepers

Cast iron sleepers are widely used in the world especially in Indian railways. They are available in 2 types, pot type sleepers and plate type sleepers. Pot type sleepers are not suitable for curves sharper than 4 degrees. CST 9 type sleepers more famous in Indian railways.

Benefits

• Cast iron sleepers can be used for long period up to 60 years.
• Their manufacturing is also easy and it can be done locally so, there is no need for longer transportation.
• Vermin attack is impossible in case of cast iron sleepers.
• They provide strong seat to the rail.
• Damaged cast iron sleepers can be remolded into new sleepers hence, scrap value of cast iron is good.
• Creep of rail can be prevented by cast iron sleepers.

Drawbacks

• Cast iron is brittle in nature and it can be damaged easily while handling. So, transportation, placing is difficult to deal.
• Cast iron sleepers can be easily damaged and corroded by salt water so, they are not suitable for coastal regions.
• They may damage badly when derailment happened.
• Cast iron is expensive in market when compared to some other sleeper materials. Hence it is uneconomical.
• So many fastening materials are required to fix the rail to the sleeper.
• Proper Maintenance is required.

Composite Sleepers

Composite sleepers are modern type sleepers which are made from waste plastic and rubber. Hence, it is also called as plastic sleepers. They have many combined properties of all other types.

Benefits

• Composite sleepers are serviceable for longer spans about 50 years.
• Composite sleepers are eco-friendly sleepers.
• They are light in weight but possess great strength.
• Their scrap value is good because of recyclable property of composite sleepers.
• They can be resized easily like wooden sleepers. So, they can be used for any type of rail section.
• Vibrations received from rails are reduced well by these composite sleepers.

Drawbacks

• Composite sleepers are not that much good against fire.
• The cost of sleepers may increase for large scale production.

  

• Building
• How To Guide
• Concrete
• Construction
• Geotechnical

Antifreeze Admixtures for Concrete during Cold Weather Concreting

Freezing reduces strength of concrete by 20 to 40 % when fresh concrete is subjected to freezing. Antifreeze admixtures of concrete, its properties and uses in cold weather concreting are discussed.

The resistance of the fresh concrete against the freeze and thaw cycle is given by the durability factor which is also lowered by 40 to 60%. There is 70% decrease in the bond between the reinforcement and the concrete that is normally cured.

Hence it is very essential during the concreting in cold weather conditions to ensure that the concrete will not undergo freezing in its plastic state.

There are two methods for carrying out cold weather concreting:

1. Provision of normal ambient temperatures for the concrete. This can be done through the heating of the concrete ingredients or by providing heating enclosures.
2. The addition of chemical admixtures.

Conventional Chemical Admixtures in Cold Weather Concrete

Conventional concrete used calcium chloride as accelerating admixtures to offset the retarding effects of slow hydration of concrete in low temperatures. This admixture is not effective below the freezing temperatures.

This is found to be a drawback in the conventional form of admixtures. Hence, for arctic weather conditions, special admixtures are necessary. One such is antifreeze admixtures.

Antifreeze Admixtures for Concrete

The antifreeze admixtures affect the physical condition of the mix water used in the concreting. These can depress the freezing point of the water to a large extent and can be used in temperatures lesser than -30 degrees Celsius. This can enable the extension of the period of the construction activity.

Chemical Composition and Action of Antifreeze Admixtures

There are two groups of antifreeze admixtures that provide the characteristics of antifreeze and the accelerated setting and hardening properties.

They are:

1. First Group:

This includes chemicals, weak electrolytes, sodium nitrite, sodium chloride and non-electrolytic organic compounds which lower the freezing point of the water used in the concrete. But these group acts as weak accelerators to promote the setting and hardening.

2. Second Group

These include binary as well as ternary admixtures which contains potash and additives based on calcium chloride, sodium nitrite, calcium chloride with sodium nitrite, calcium nitrite -nitrate-urea and other chemicals.

These have effective antifreeze properties and accelerating property to promote the setting and hardening. These are used in larger dosages compared to that of conventional admixtures.

One such example is the use of 8% of sodium nitrite to keep the liquid at a temperature of -15-degree Celsius.

These admixtures function by lowering the liquid phase freezing point and by accelerating the cement hydration at the freezing temperatures.

Based on the dosage in the mixture, the non-chloride admixture enables the mix (concrete or the mortar) to be placed at sub-freezing temperatures. This hence reduces the need of protective measures required during the cold weathering works.

The method improves the quality of the concrete and as it facilitates early setting, early stripping of formworks can also be carried out. This helps in the reuse of the form within a small duration and hence speed up the construction.

The table-1 shows the significant difference is strength gain at 3, 7 and 28 days for plain concrete and antifreeze admixture used concrete.

Table.1: Concrete Compressive strength with and without antifreeze admixture

(As per Ratinov and Rosenburg)

Property	Plain Concrete	Freeze-protection Admixture
Set time (-4 degree Celsius)	–	–
Compressive strength (MPa)
-4 degree Celsius (3 days)	3.4	9.24
-10 degree Celsius (7 days)	8.3	39.3
-10 degree Celsius (28 days)	18.1	49.9

It is possible for the incorporation of other admixtures that contains superplasticizers to be incorporated with the antifreeze admixtures. The main advantage of such combination is that in totality there will be a reduction of water.

The water reduction will reduce the freezable free water content in the mix. This freezable water content is the one that serves as the heat sink for the heat liberated by the initial hydration reactions. This will hence reduce the number of antifreeze admixtures.

Selection of Antifreeze admixtures

The factors based on which the selection of antifreeze admixtures is carried out are:

1. The type of structure
2. The operating Conditions
3. Protecting methods employed in winter concreting
4. Cement brand and aggregate types

A laboratory test must be carried out with the operating materials and the dosage of antifreeze admixtures that are intended to be used in the field.

The incorporation of other admixtures like retarders, superplasticizers with antifreeze admixtures is not restricted in cold weather concreting. The dosage of all the admixture that are used must be established experimentally.

Application and Advantages of Antifreeze admixtures

The antifreeze admixtures are technologically simple and beneficial for cold weather concreting. The admixture helps in improving the cohesiveness, cold joint minimizations, sand streaking, and plasticity. These are estimated to provide large cost saving than other methods of steam curing or concrete enclosures.

The combination of antifreeze agents with water reducing agents or air-entraining agents will help in increasing the resistance of concrete towards the frost action and corrosion.