Student Learning Outcomes
After reading this chapter, you should be able to:
- Understand the basic practices of water main installation
- Evaluate the processes of backfilling and main testing
- List the steps of installing a water main and placing into service
- Analyze the use of maps and various types of drawings
In a previous chapter, we discussed the importance and purpose of selecting specific water mains. In some instances, plastic pipe might be a better selection and other times ductile iron pipe might be useful. There are different uses for different types of pipe too. Regardless of the type of pipe selected, all pipe needs to be installed appropriately. The installation process will be discussed in this chapter.
Water utilities need to order pipe from various manufacturers and sometimes the pipe needs to be shipped larger distances. The cost of shipping pipe is typically dependent on the distance the pipe is being transported, the size of the pipe, the weight of the pipe, and the quantity of the pipe being purchased. These variables will also dictate the method the pipe will be transported and will also contribute to the shipping costs. Ultimately, pipes are usually delivered to the water utility by truck. However, depending on the origin of the manufacturing of the pipe it may be transported by train or barge.
Once the pipe is delivered to a water utility, it should be properly inspected before it is unloaded from the truck. Even though manufacturers typically have a final inspection process prior to leaving their plant, damage can occur during transport. In addition, the wrong material or size may have been delivered by mistake. Therefore, it is important to inspect the following things prior to the pipe being unloaded:
- Size of pipe and fittings
- Class of pipe and fittings
- Quantity of pipe and fittings
- Condition of pipe and fittings
Any problems observed during unloading should be noted in writing. The driver, shipping company, and manufacturer should all be notified. The unloading process is usually accomplished using some type of equipment. Often times with smaller shipments, the pipe will be strapped to wooden pallets and they can be unloaded from the truck using a forklift. However, with larger shipments or larger size pipe, heavy equipment might be needed. It is important that the pipe not dropped or placed down roughly, Pipes should not be allowed to strike other pipes, the ground or other items. Some pipes are shipped with special coatings and it is important these coatings are in good condition and not damaged. Padded forks on forklifts, rubber hooks, or slings are ways to prevent such damage.
Once the pipe has been unloaded from the delivery truck, it must be properly stored to prevent damage and contamination. If pipe is stored at job sites or remote locations, protection from vandalism should also be considered. Stockpiles of pipe should be built on a flat base to prevent rolling. If possible, the pipe should be stored off the ground and grouped by size and class. If all different sizes and classes are stored together, it will make it more difficult to transport the pipe to the job site when it is time for construction. It is helpful to lay the pipe by alternating the bell and spigot ends. This allows the pipe to be stored evenly.
Polyvinyl chloride pipe should be stored out of direct sunlight as ultraviolet radiation can damage it. Any pipe that can crack or become damaged by hitting the ground, the height of the stacks of pipe should be limited to no more than three high. It is also prudent to cover the ends of the pipe during storage to prevent rodents or other animals from entering the pipe. Covering the ends also protects against contamination from dirt or other foreign objects. Sometimes covering the ends is not feasible and not critical since part of the installation process includes proper flushing and disinfecting of the pipe before being placed in service.
Preparing the Pipe for Installation
Pipeline projects can be small jobs requiring only a few sticks of pipe. Or, they can be extensive jobs covering several miles or more. Regardless of the size of the job, it is important to properly plan. Preparing the pipe at the job site is an important aspect of job preparation.
The pipe should be placed as close to the trench as possible. This makes it easier for the pipe to be accessed and placed into the trench. String the pipe on the opposite side of the trench as the dirt (spoils) that is being excavated and should be located away from traffic and heavy equipment. The bells should be located in the direction of installation and only enough pipe should be laid out for a days work. It is also important that the pipe is protected from rolling into the trench or away from the job site.
Trench excavation is the most expensive process of pipeline installation. It is important to know the location, depth, and width required for pipeline installation. A nonprofit organization called “Underground Service Alert” provides a means for anyone digging underground the opportunity to identify any other utilities or conflicts, which may exist. A toll-free number (811) should be called at least forty-eight (48) hours before any digging occurs. By calling this number, any utility in the area receives a notification that trenching will be occurring and they are then responsible to mark their utilities on the ground with an appropriately colored paint. Each different utility has a specific color as standardized by the American Public Works Association (APWA).
Electric Power Lines
Temporary Survey Marking
Gas, Oil, Steam, Chemical
Sewer, Storm Drain
The local soil conditions should also be considered before trenching begins. Is there local groundwater, which can fill the trench? Is there frost or freeze issues? Is the native soil in good condition or will “fill” material need to be brought in for backfilling? Sometimes in cold climates where adequate depths are not possible, special insulation might be needed to prevent the water in the pipes from freezing. In some areas (especially in warmer climates), minimum ground cover depths are required. Some common depths are thirty-six (36) inches for water mains and eighteen (18) inches for service laterals.
Whenever a pipe needs to be installed in an existing street, special consideration needs to be addressed to minimize inconveniences to the public. For example, some local cities may limit the times of construction activities. If the road is a main thoroughfare, construction may not be allowed during commute times in the mornings and evenings. Special permits for excavation may also be required. It is also very important to understand the existing and future road conditions, because these will dictate the road surface restoration requirements.
Once these and other considerations are reviewed, it is important to set an excavation plan. The construction crew should review the work zone. What heavy equipment will be needed, where will the spoils and materials be placed, where will traffic control be required, and where might there be public exposure to the work zone are just a few areas crews will need to understand prior to beginning work.
Since the excavation process is the most expensive part of pipeline installation, it is important to understand how much dirt is required to be removed. This is important because you don’t want to remove more dirt than is needed. Typically, the trench width should be one (1) to (2) feet greater than the outside diameter of the pipe.
Trenches can be very dangerous for workers from the potential of cave-ins. There are four (4) common danger signs workers should look for to help prevent trench wall failure. These are:
- Tension cracks in the ground surface parallel to the trench
- Material crumbling off the walls of the trench
- Settling or slumping of the ground surrounding the trench
- Sudden changes in soil color, which indicates previous excavations
In addition to these warning signs, certain precautions need to be in place to protect crews working in trenches. There are four (4) basic methods of preventing trench wall cave-ins.
- Sloping—If there is enough room in the construction work zone, sloping the trench walls is an adequate means of preventing cave-ins. This process involves excavating the walls at an angle. The angle of repose prevents the downward forces of the soil from exceeding the soils cohesive strength. Sloping a trench is dependent on the type of soil being excavated, the amount of moisture in the soil, the surrounding conditions, and the potential of soil vibration from heavy equipment. Various angles of repose are used depending on the type of soil. Below are some common examples.
- Compacted crushed rock—for every foot of depth, the trench is cut one half of a foot wide
- Average soils—for every foot of depth, the trench is cut one foot wide
- Compacted sharp sand—for every foot of depth, the trench is cut one and one half foot wide
- Well-rounded loose sand—for every foot of depth, the trench is cut two feet wide
- Shielding—This form of trench wall protection involves the use of a steel box, which is placed into the trench. It is open at the top, bottom, and on the ends, so workers can work inside of it. The protective box is pushed or towed along the trench to provide constant shield against cave-ins. It is important that the shield extends above the ground level in order to provide complete protection. These shielding boxes are also referred to as trench shields.
- Shoring—Shoring is a general term used when referring to trench wall projection. It is a framework system of wood, metal, or a combination of both. This support system maintains pressure against both trench walls preventing cave-ins. It is important to install shoring from the top of the trench to the bottom of the trench. Removal of the shoring should be done in the opposite manner. This will minimize worker’s exposure of unprotected trench walls. There are three (3) main components of a shoring system.
- Uprights—These are the vertical boards placed in direct contact with the face of the trench wall. The spacing of the uprights is dependent upon the soil stability. If the soil is sandy, then the uprights would be placed tightly together.
- Stringers—These are the horizontal members of the shoring system to which the braces are attached. The stringers are commonly referred to as whalers.
- Braces—The braces are the horizontal members, which run across the excavation to keep the uprights separated
The trench bottom should be level so the pipe has support along the entire length. Sometimes a leveling board is needed to ensure the bedding is level. After the pipe is placed in the trench, the backfill material should be compacted beneath the pipe curvature. This process is known as “haunching.” It is important to make sure the pipe has proper support on all sides underground. The pipe should be set on flat firm ground. This proper bedding provides support and strength under the pipe. Bedding up to fifty (50) percent of the pipe diameter increases supporting strength by thirty-six (36) percent and proper bedding up to sixty (60) percent of the pipe diameter increases supporting strength by seventy-three (73) percent. By providing bedding over one hundred (100) percent of the pipe diameter and good compaction along the sides of the pipe increases the supporting strength by one hundred fifty (150) percent.
It is also important to protect potable water mains from non-potable pipes such as sewer and storm drain. Ideally, water mains should be installed above any non-potable pipes and a one (1) foot vertical distance is commonly required. In addition, a ten (10) foot horizontal separation from sewer pipes and four (4) foot from storm drains is common. Instances where these minimum offsets cannot be achieved, special provisions and health department regulatory approval might be required. Placing water mains in a larger diameter “sleeve” and concrete encasement are some alternative solutions.
Push-On Joint Installation Procedure
- Prepare the pipe:
- Thoroughly clean the bell socket and plain end
- Inspect the gasket for any damage
- Follow the manufacturer’s recommendation on whether the socket should be lubricated
- Insert the gasket into the socket
- In cold weather, it may be necessary to warm the gasket to facilitate insertion
- Apply lubricant to the gasket and plain end
- Protect the lubricant from contamination
- Connect the pipe:
- Be sure the plain end is properly beveled. Sharp edges can damage the gasket.
- Keep pipes in line when making up the joint. Deflection should take place only after the joint is assembled.
- Push the plain end into the socket
- When pushing pipe with a backhoe or jack, use a timber header across the end of the pipe to protect it
Mechanical Joint Installation Procedure
- Prepare the pipe:
- Clean the socket and plain the end
- Lubricate the gasket and plain end with soapy water of an approved lubricant
- Install the gland and rubber gasket
- Connect the pipe:
- Keep the pipes in line during joint assembly
- Insert the plain end into the socket
- Press the gasket evenly into the bell
- Prepare the mechanical connection:
- Push the gland toward the socket
- Insert the bolts and hand tighten the nuts
- Tighten the bolts:
- Alternately tighten the nuts on opposite sides to maintain the same distance between the gland and the flange
- Tighten the nuts to the correct torque
- What is the most common cause of joint failure?
- Having the joint too clean
- Using unapproved soap or lubricant
- Not having the joint completely clean
- None of the above
- What types of things in the recesses of the bells of pipe can cause joints to leak?
- All of the above
- What is the piece of pipe that is cut out during tapping called?
- Only 1 and 2
- All of the above
- Large-diameter pipe should be unloaded ___________.
- By hand
- With heavy equipment
- By rolling it off the truck
- Any of the above
- What is the most expensive part of pipeline installation?
- The material
- The planning
- The excavation
- All of the above
- What is a “story pole”?
- A pole which is used to track the progress of the days work
- A pole designed to improve efficiency during pipe installation
- A pole that marks how many feet of pipe are installed each day
- A pole with a string used to check the depth and grade of a trench