Water Supply Part-1

                         Let's talk about a topic in which currently I am working on which is pipeline work. I am working currently as a contractor in a water supply project. Basically, in a water supply system, there are two parts which are: -

• Structure Part
• Pipeline Part

Structure Part: -

                     The starting of the structural part consists of an intake structure. Then from there, raw water is taken to another structure called a grit chamber and sedimentation tank. From the sedimentation tank, the raw water is taken to another structure called the water treatment plant where the raw water is purified. Then the purified clear water is taken to different storage structures such as reservoirs and overhead tanks. This is a very brief introduction to the structure portion of a water supply system. Here we are going to discuss the pipeline part.

Pipeline Part: -

                    We all know what is a pipeline. It is laying of pipe for the flowing of fluids. In the water supply system pipe is layed for the moment of the water from the source to the users. Pipelines are divided into the following types which are: -

1. Transmission line
2. Main Line
3. Distribution Sub-Main Line
4. Service Line

Transmission Line:-

                    Transmission lines are of two types which are raw water transmission lines and clear water transmission lines. Raw water transmission lines are the pipeline that is laid in order to transfer raw water or unclear water from the intake to the sedimentation tank and to the water treatment plant. When the water is purified then they are transferred to the storage tanks through clear water transmission lines. Basically, transmission lines are the pipelines which connect reservoir to reservoir. Generally, ductile iron pipes are used as transmission lines depending upon the head and quantity of water. Service lines are not given from transmission lines. They are used to connect the reservoirs.

                                                                            

                                         

                                                             Fig: - Raw Water Transmission Line

Main Line:-

                    Main lines are the pipeline which carries clear water from the reservoirs to the users' areas. They are laid on the main roads and they are used to supply water to the distribution lines. Main lines are not used for connecting the service lines by the users. In main lines Ductile Iron (DI) pipes are used and are smaller in dimension then transmission lines. 

Distribution Sub-Main Lines: -

                Distribution sub-main lines carry clear water from the main lines to the user. Generally, in a water supply system distribution sub-main lines are the longest to be laid. From these sub-main lines, the public connects the service lines to their homes to use pure water. The service lines are connected to the sub-main lines using a connector called a ferrule. HDPE pipes are highly used as distribution lines but ductile iron and cast iron are also used depending upon the designer's calculation.

Service Lines: -

                Service lines are laid by the public themself coordinating with the Nepal Water Supply Corporation (NWSC). They are connected to the distribution sub-main lines to supply water to the public. GI pipe is used as service lines of varying sizes depending upon the house owners demand. Commonly, for residential purposes 0.5" to 1" diameter GI pipe is used. For industrial purposes, higher diameter GI pipes are used.

Now let's study the installation process of the pipe. What we need to keep in mind is that all the pipe installation is not done from one side. The pipeline is divided into different routes according to the type of pipeline we are installing. Here we will be discussing the installation of the HDPE pipe. Following is the process of installation of the HDPE pipe: -

1. Safety material arrangement and setting up at the site:-

                     The first and foremost thing to do in every construction is safety. It is one of the main thing to consider because during the construction the workers should feel safe to work to do efficient work. Some of the safety materials needed for the pipeline are safety cones and bars, barricades, safety jackets, safety helmets, gloves, proper shoes, etc. Before starting work, safety materials should be set up at the site and clear the working space. In traffic areas, signalmen are very important because there are conditions when we need to arrange a proper flow of traffic and simultaneously run our work. 

                

                                         Fig: - Providing safety barricade during and after day

     2. Asphalt Cutting work:-

                    

                    Asphalt cutting is the initial and very important step in pipeline installation. Asphalt cutting is done by equipment known as asphalt cutter. It is done only if the route where we are installing pipe has an asphalt layer at the top. If it has rigid concrete then concrete blade is used in the cutter. It helps in minimizing the loss of asphalt while excavation and decrease excavation width.

                                                                                

                                                       Fig: - Asphalt cutting by asphalt cutter

    3.  Trench Excavation: -

            

                  The third step is starting of the excavation of the trench.  It is better to keep the top of the pipe at depth of about 1 m for the safety of the pipe installed mainly in city areas. However, the depth is altered depending upon the design and location of the project conducted. The depth of the trench depends upon the dimension of the pipes. Trench excavation can be done by the mini excavators or backhoe loader depending upon the cost and availability or can be done manually if laid in the footpath. Generally, the distribution sub-main line is laid on the footpath because it will be easier for the users to connect the service line, and also it's effect on traffic flow is relatively low.

                    Pipeline work is technically not a difficult work to execute but in terms of management and progress, it is very challemging. Meeting the schedule in pipeline especially in city areas is a challenge so the role of engineers in pipeline is very important in the management of the available manpower and equipment. The main reason for the delay in the pipeline work is excavation work.  Many obstruction and problems appear in the excavation process and we need to overcome and solve the problems and start the work. The major problems in the excavation are existing pipelines in the excavation area, service lines, disputes with locals, presence of hard rocks and conglomerates in the excavation route.

So idea of the circulation of manpower and equipment in different working groups is very important. Before starting the excavation, the subsurface investigation is another very important part. The subsurface investigation helps to find the types of soil present in the route and existing pipeline in the route and considering this the route can be shifted to allowed and suitable place. For the subsurface investigation, trial excavation can be conducted and data about soil type and existing pipeline direction can be found. The public dispute can be solved by consulting with the client and locals. Hence, before starting the excavation a proper inspection of the route is needed to be done by all three parties which are client, consultant, and contractor, and verify the route.

                                                            

                                                    Fig: - Problems in Trench Excavation

To be continued in next blog.......

                                                                                                                Prepared By: - Er. Biplov Sapkota