2. Maintenance & Repair

3. Renovation

4. Replacement & New Installation

2. Maintenance and Repair

Maintenance refers to surveying, inspecting, and cleaning of a watermain or sewer. This includes minor repairs but does not involve the reconstruction of the structural fabric or altering the dimensions. Repair includes the reconstruction of short lengths of pipe but not the entire pipeline.

Maintenance and repair are both necessary for any product. The difficulty with
underground utilities is determining the location and extent of existing problems and the
potential for future problems, as well as finding a proper and efficient way to correct
them. Before a maintenance and repair schedule can be determined, the location and
condition of the buried utility must be known. The condition of the pipe is determined by
a visual inspection, pipe integrity inspection, or a combination of both. Pipe cleaning is
usually performed to provide a more accurate profile of the problem, as well as to provide a clean surface for repair techniques. Depending on the problem and its size, spot repair may be used or a more comprehensive renovation plan may be required.

2.1 Pipe Location
There are two main ways of determining the location of buried utilities.

1) Electromagnetic induction

2) Ground probing radar


The method used depends upon the resolution required as well as the results required. A combination of the two can ensure more accurate results and a wider range of utilities located.

2.1.1 Electromagnetic induction

Electromagnetic induction works on a simple principle. Anything metallic present in the
ground can be persuaded to create a magnetic field, which can be detected by some form of aerial. The magnetic field is caused by a signal emitted by a small generator. Recentdevelopments have led to the use of two aerials. Location of objects is clearer,
especially when services are crowded together. With two aerials it is also possible to
determine the depth of the buried pipe. This method is effective in locating metal pipes
and cables.

2.1.2 Ground probing radar

Ground probing radar is used in conjunction with electromagnetic induction, and is
similar in that it uses electromagnetic fields. It sends an electromagnetic pulse into the
ground which rebounds off objects and is received by an antenna. This enables the user to determine locations of utilities as well as voids. It is useful in surveys where high
resolution is required and is able to locate underground utilities like plastic and cement
pipes. It cannot locate metallic objects and the signal is disturbed by the presence of
metal pipes and cables. It is also restricted by the conductivity of the soil and the
depth of the utility.

2.2 Visual Inspection Systems

Visual inspection of sewers and pipelines is performed to determined the condition of
the system and location of defects. For man-entry systems, the visual inspection can be
done manually by entering the system. For non-man-entry systems, the following techniques are used:

1) Closed circuit television

2) Sonar systems

2.2.1 Closed circuit television

Closed circuit television (CCTV) is used for a variety of reasons. One of the major
uses is the inspection of sewer lines and watermains. The camera is placed in the pipeline and is either winched through, as seen in Figure 1, or it is self propelled. The picture, which is available in both colour and black and white, is displayed on a monitor. The user is visually able to determine whether cleaning is needed, where repairs are needed, and location of services for reconnection following repairs. CCTV is also used to monitor work being done by remotely controlled robots. If too much water is present in the pipeline, it may have to be drained, in the case of watermains, or an alternative method used.


Recent developments have led to lateral inspection systems. They are able to enter the
service connection from the main using remote control.

2.2.2 Sonar systems

Sonar is a practical alternative to CCTV. It is used for overloaded sewers or undrained
watermains. Usually the excess water hampers visual techniques, but with sonar it is a
positive factor. In fact, it is a vital medium for the acoustic method. The results from
the sonar are displayed on a graphic screen on the surface. Different objects are shown as different colours and can be easily identified.

2.3 Pipe Integrity Inspection

2.3.1 Pipe wall thickness - Ultrasonic

The ability to determine the wall thickness of pipelines without excavation is
extremely valuable. The information received is important in evaluating the deterioration
due to corrosion or the buildup of deposits.


Ultrasonic thickness measurement has proven to be an acceptable method of determining pipe wall thickness. It uses a bullet-shaped tool which is placed inside the pipeline. The ultrasonic waves from the tool travel through the liquid couplant to the inner wall, and return, as seen in Figure 2. Some of the waves proceed to the exterior wall before returning. The time between the two waves is converted into thickness, using an on-board computer. As the tool proceeds through the pipe, the data are recorded in the data acquisition section of the tool. The technique is a relatively simple one, but requires rather sophisticated equipment.

2.3.2 Leak detection

Leak detection is a very important part of the inspection of a pipeline. Infiltration,
water entering the system from the ground through defects in the pipe, and exfiltration,
water leaving the system through defects in the pipe, are major causes of erosion of the
surrounding soil. This can cause collapsing of pipes and the soil above, as well as
collapsing of the ground surface. Infiltration also increases demands on sewage treatment plants, increasing operating costs. The ability to locate and repair leaks without excavating saves valuable time and money. The methods used are:

1) Flow monitoring weirs

2) Smoke/gas testing

3) Sonic leak detectors

2.3.2.1 Flow monitoring weirs

Weirs have been used to monitor flow rates for quite some time. Conventional methods of collecting and analyzing data are expensive and time consuming. However, the development of new techniques has led to more efficient and inexpensive methods of flow monitoring.


This system can be used to monitor entire systems or sections of a system, depending on the requirements. It can be used to measure flows over a period of hours, days, or even months. The main part of the system is the weir. It is designed and calibrated to enable flows to be measured using the upstream water level, as seen in Figure 3. Depending on the system, a micro-computer can be placed in the manhole to record the water level at predetermined intervals. The information from the microcomputer can then be used to determine the flow rates. The location of leaks can then be determined by discrepancies in the flow rates between two points.


Weirs can be used in pipes from 200 to 1500 mm and at virtually any water levels.

2.3.2.2 Smoke/gas testing

Smoke testing is used to determine the presence of broken pipes, improperly sealed
laterals, illegal lateral drains, and cross connections between different systems. Smoke
canisters are released in the sewer system. The smoke filters out through the ground via defects in the pipe, as seen in Figure 4. These non-toxic and non-staining smoke devices quickly determine deficiencies.


A tracer gas procedure using helium has also shown a high level of success for
determining leaks. The system is dewatered and pressurized with helium. Because helium is lighter than air, it rises easily through the soil to the surface. An instrument that is extremely sensitive to helium is then used to locate the seepage.

2.3.2.3 Sonic leak detectors

Sonic leak detectors provide accurate locations of leaks. The instruments consist of a
highly sensitive microphone and electronic frequency filters to enable the user to hear
leaks in a pipeline. The sound produced by a leak is different than the sound produced by normal flow, which enables the user to determine the location of the leak. The differences are displayed visually and audibly. A variety of different instruments available on the market operate on this principle. The limitations of each will determine the one which is best suited.

2.4 Pipe Cleaning

Pipe cleaning is a fundamental preparatory step in most rehabilitation projects. It can
be effective for the short-term resolution of hydraulic and water quality problems but
should not be considered as a stand-alone technology.

2.4.1 Hydro-cleaning

Sewers and drains can be effectively cleaned using hydro-pressure. The work is
accomplished using high pressure water jets and regulated flows. As the pressure is
applied, the nozzle is forced through the pipe, passing by the various debris. The hose is then hydraulically pulled back, cleaning all the debris from the interior walls as it
moves (see Figure 5). The waste travels downstream to a selected manhole for removal. The process is compatible with all types of pipe and, if necessary, can be repeated any number of times.

2.4.2 Swabbing

Pipeline and sewer lines can also be cleaned by hydraulically pushing flexible
projectiles of different densities and abrasive surfaces through the pipeline. These
projectiles can be inserted and removed from a fire hydrant or manhole and are flexible
and elastic enough to pass through a right angle bend. With a properly selected
"swab," it can be a very effective method of cleaning pipelines (see Figure 6
for details).

2.5 Spot Repairs

2.5.1 Reaming and chemical sealing

Reaming is the process of scraping the internal walls of the pipe to remove the debris
and create a rough surface for application of a chemical sealant. A rough surface may or may not be required for the application of the chemical sealant, depending on the
individual manufacturer. The sealant is applied at locations of infiltration or
exfiltration to prevent the surrounding soil from being eroded away, and prolonging the
life of the pipeline. The sealant can be applied manually for man-entry pipes or by remote control for non man-entry pipes, as illustrated in Figure 7.

2.5.2 Resin injection

Epoxy resin is a relining technique which can be used for spot repair. It is a
structural repair that also acts as a waterproofing agent. A tube is lowered into the pipe
and moved by either pulling or pushing to the location of the damaged area. The tube is
then inflated to the pipe diameter to fit tightly against the walls as illustrated in
Figure 8. The resin is released all around the tube as well as around the damaged areas. The excess resin is forced out through the pipe into the soil, which creates a seal on the outside of the pipe. The repair head remains in place for approximately 90 to 120 minutes to allow the resin to harden enough to remove the head cleanly. The entire process is performed by remote control with the aid of CCTV. The curing process takes about 24 to 36 hours and is not affected by the lack of applied pressure or by the presence of water or air.

2.5.2 Keyhole technology

Pipeline maintenance using keyhole technology is becoming more common. It is the act of excavating a small hole, about 300 mm in diameter, from the surface, using either a vacuum excavator, an air knife, or an air badger. The repair is then performed from the ground surface using long handled tools.


The vacuum excavator consists of a large vacuum, run by a compressor, a hopper for
spoil, and a separate compressor for additional air tools. The equipment is carried by a
small truck. The vacuum sucks up the soil and stores it in the hopper until the repair is
complete. The soil is then placed back in the hole.


The air knife utilizes compressed air and concentrates the flow through a small orifice
on the head to give a high velocity air stream. When the soil is cut it is removed, either
manually or by a vacuum excavator. It has several extensions so it can be used at a
variety of depths.


The air badger consists of a rotating auger and a vacuum. The auger, at the end of the
badger, cuts through the soil and the vacuum sucks up the spoil. It is not very fast and
requires frequent cleaning, especially in wet soils. These tools can be used independently or in conjunction with one another.


When the hole is excavated, a variety of spot repairs are possible. They range from the
sealing of joints, to service line cut-offs, to placement of anodes for cathodic
protection. The repairs are carried out from the surface and the methods vary depending on the user and the situation.

2.5.3 Internal sleeves

Spot repairs can be done using internal sleeves on pipe diameters ranging from 150 to
2800 mm. For diameters between 150 and 600 mm, a stainless steel sleeve is used. The sleeve, which is wrapped in polyethylene foam, and an inflatable sewer plug are placed over the damaged area. With the aid of a CCTV, the plug is inflated until the sleeve locks in place. The plug is then deflated and a visual inspection takes place (see Figure 9 fordetails).


For pipe diameters between 600 and 2800 mm, a polyvinyl chloride (PVC) sleeve is used. It consists of six longitudinal segments. The edges are grooved to lock each segment together. The sleeve is wrapped in a polyethylene foam gasket. This provides the radial force to secure the sleeve in place. If grouting is required, small port holes are drilled in the sleeve and filled with grout upon completion of installation. If laterals are blocked because of the sleeves, they are reconnected by drilling through the liner upon completion (see Figure 10 for details).


This system can be used to repair any length. The sleeves come in lengths of 300, 600,
and 900 mm and any number of them can be used to repair a pipeline.


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