Deptt. of Irrigation and Drainage Engg. Underground pipeline irrigation distribution system Shri M. U. Kale Assistant Professor Deptt. of Irrigation and Drainage Engg.

Underground pipeline irrigation distribution system An underground pipeline irrigation distribution system consist of buried pipes for conveying water to different points on the farm and allied structures required for the efficient functioning of the system. In this system pipes are laid underground, cultivation can be done above the pipeline; no culverts or other structures are required.

Advantages Disadvantages:- The system offers many advantages over open channels in water conveyance and distribution 2-4 percent of the land area out of cultivation which is saved by adopting the underground water distribution system. Pipeline do not interfere with farming operations. When properly installed, they have long life and low maintenance costs. They are essentially leak proof. Disadvantages:- Higher initial cost. Its use is limited to areas irrigated by wells using pumps.

Pipes for underground water distribution system Types of underground pipeline Non-Reinforced concrete pipes Reinforced concrete pipes Vitrified clay pipes Asbestos cement pipe plastic or PVC pipes are sometimes used.

Non-Reinforced concrete pipes Commonly used when the pipe is not subject to high pressure. Operating pressure head – not exceed 6 m (0.6kg/cm2). It is cheaper than reinforced pipes. They are cast in lengths of about 1 m and may have bell joint or tongue and groove joints.

Reinforced concrete pipes The majority of the RCC pipes used in India are manufactured according to Indian Standard IS :458. They are usually available in sizes 15 cm, 22.5cm,30 cm, 37.5cm and 45cm. Lengths vary from 2 to 2.5 m. Concrete mixes used are 1:1 ½:3,1:2:2,1:2:2 ½, 1:2:3 and 1:2:4 (cement:sand:coarse aggregate).

Types of pipes Pressure pipe (IS:1592) Non-Pressure pipe (IS:1626) The asbestos cement pressure pipe is joint together by any one of the following three ways . With asbestos cement couplers With a cast iron detachable joint. With loose concrete collar.

Discharge Capacity of Pipelines Discharge through a pipeline can be determined by applying Darcy’s equation. Where, V:-Velocity of flow of water through the pipe , cm/sec. H:- available head causing flow, cm. d :- diameter of pipe. g :- acceleration due to gravity. l :- length of pipe. f :- Darcy’s roughness coefficient.

Assignment Example : determine the discharge capacity of an underground concrete pipeline from the following data: Diameter of pipe 15cm, Length of pipe line 150 m, Difference in elevation between water levels at pump stand and discharge point 2m .

Spacing of Pipeline Pipelines are spaced to suit the field layout and soil type. One main line is usually laid along the upper boundary of the field. When the land slopes in nearly opposite directions the pipeline may be laid in the middle so that one line can command fields on either side. When the prevailing land slope is in one direction only, the spacing between pipelines varies from 100-200 m. Closer spacing :for sand soil. Farther spacing: for heavy clay soils.

Installation of Concrete Pipe Steps: Selection of depth and grade of laying, Digging to proper depth and grade, Lowering the pipe and squeezing, Sealing the joints, Backfilling the trench. To prevent damage of pipelines:- Depth should be 45 cm from the ground surface. Width of trench should be about 70 cm. To obtained uniform depth and grade, the elevations of the trench bottom are fixed with a dumpy level.

Bell Joint Pipes Pipes with bell ends are laid with sockets facing upstream. The end of the pipe are cleaned and wetted with a brush. Jute or hemp rope dipped in a cement pest is wrapped round the plane end of each pipe. Before the pipe is inserted in the socket mortar made of one part cement and two parts sand is applied thickness of about 1 cm about 1 cm over the spigot end of the pipe and also inside the socket. The pipe is placed well into the socket and care is taken that the packing is not pressed through the pipe. Steel chisels are used to ram the hemp tight. After ramming the hemp tight with a steel tool the remaining space in the socket is filled with mortar.

Pipes with tongue and groove joints This pipes are laid with the groove ends facing upstream. The tongue or spigot end of the first section of pipe is cleaned and wetted with a brush. Sufficient mortar to form the lower section of the outside band or collar is placed in a depression at the lower side of the pipe side of the pipe joint. The groove end of the next section is wetted and filled with mortar. This section is then tipped over carefully so as not dislodge the mortar is pushed into place to make slug, tight joint.

Structure of underground pipelines Inlet structure : i. Pump stands ii. Gravity inlets Gate stands Air vents End plug Outlets Riser valves Hydrants Gated pipes

Pump stand Pump stands:- a vertical pipe extending above the ground and connected to the underground pipeline system is known as stand. Pump stand are located at the inlet of an underground pipeline system. Pump stand for underground pipeline

Gravity inlets Gravity inlets :- when water enters the pipeline from an open channel , a gravity inlet is used. A screen is fixed to the inlet to keep trash out of the pipeline. The top of the structure is usually provided with a cover to prevent accidents and to keep trash from blowing in. Sectional view of gravity inlet

Gate stands Gate stands:- are provided to control the flow into laterals when pipelines branch off in different direction. They also prevent high pressures and act as a surge chambers. Isometric view of a gate stand

Air vents Isometric view Air relief valve Sectional view Air vents:- are vertical pipe structures to release air entrapped in the pipeline and to prevent vacuum.

End plug End plug:- is provided where the line terminates. The function of an end plug is to close a line and to absorb the pressure developed at the end of the line on account of water hammer. Concrete end plug and wall

Riser valves Riser valves:- it is a screw valve installed on top of a riser pipe. There are two types; the valve for releasing water directly to fields or open channels and hydrant valves which are adapted for fixing a portable hydrant on it. Isometric view showing the installation of the riser pipe and valve In an underground pipeline

Outlets :- these structures are necessary to provide controlled delivery of water to the fields at any desired location. Hydrants:- hydrants are devices placed over riser valve outlets as a means of connecting portable gated pipes to the pipeline. Gated pipes :- gated pipes are portable lines with uniformly spaced outlets used for releasing irrigation water to furrows, border strips or check basins.

Design of underground pipeline irrigation system In designing an underground pipeline system the head loss due to friction in the pipeline and other factors must be taken in to account. Loss of head due to friction in the pipe between two points in a pipe at a distance l apart is given by: Where, f:- coefficient of friction for pipe, dimensionless, L:- length of pipe, m. V: - velocity of water in a pipe, m/sec. g :- acceleration due to gravity, m/sec2. R:- hydraulic radius,m.

Design elements of an underground pipeline irrigation system

Where, a = area of cross-section of pipe, sq. m Where, a = area of cross-section of pipe, sq.m. p = wetted perimeter, m. and ; d = diameter of pipe, m. Also, Therefore,

Entrance losses in pipelines may be calculated from the following formulae, Pipe end flush with the wall of pump stand Pipe end protruding from wall Pipe with bell entrance he= head loss at pipe entrance , m.

The velocity head due to flow in pipes is obtained from the formula, hv = velocity head, m. Assignment Example: A concrete pipeline is to carry water across a distance of 700 meters from a pump which discharges 100 lit/sec. The land has a downfield slope of 0.1 per cent along the line the pipes are laid. It is desired that the maximum pressure in pipeline should not exceed 5 m of water. What size pipe is to be used? How high should be the pump stand?

Common troubles of underground pipelines Inadequate procedures in design and installation and unforeseen situation may give rise to the following trouble Development of longitudinal cracks in pipe, usually at the top or both at top and bottom. Telescoping of sections Pushing of the pipes into the stands. Development of circumferential cracks. Surging or intermittent flow of water. the first four troubles are caused mainly by the expansion and contraction of the concrete pipes by wetting and drying .

Surges in pipelines Surging is a common trouble in pipelines when adequate vents are not provided. Because of the turbulence of the flow , the tendency for the air to separate out is minimize. Provision of adequate vents will eliminate the problem