Wherever you are sitting right now, look out the window. Most likely you will see buildings and streets, generally things you take for granted. What you will not see are the thousands of miles of water pipelines, sewer lines, fiber optic lines, gas lines, and other underground infrastructure systems that are located under these structures and that are needed for our civilization to exist. Another thing that you will not see is the condition of these systems.
When you turn on a water faucet you find a flow of clean water-what you don't see is that for every gallon of water you get, a full 1/2 gallon of clean, expensive water is lost underground due to leaks and breaks. You also won't see the leakage of raw sewage into our soils, ground water tables and waterways. For every gallon of sewage that is generated, 1/3 of a gallon is leaked into the environment.
These leaks are unacceptable from environmental, economic, and social aspects. Governments backed by hundreds of billions of taxpayer dollars are moving to address these matters. So why aren't the leaks fixed? Instead, they are increasing in number and severity!
The answer lies in the location and age of many of these pipelines. When many of these underground systems were installed, which in the U.S. was mostly in the 1950s and 60s, they were installed in green field conditions. After a time, roads and buildings were constructed on top of these systems with little or no thought given to how these systems were to be maintained. They are now reaching the end of their service lives and need to be repaired or replaced.
Long-term disruption of roadways will not be tolerated by the traveling public, and excavating through and under buildings is simply not an option. Just digging them up and replacing them is often not possible in most urban settings.
Trenchless Technologies
The solution lies with the development of a set of construction tools known collectively as trenchless technologies, which consists of tools for locating, assessing, repairing, and replacing underground infrastructure with minimal surface disruption. Minimal, not zero-there will always be some surface disruption. The trick is making the disruption as small as possible.
Trenchless technologies such as directional drilling, microtunneling, cured-in-place lining, ground penetrating radar, and robotics have largely replaced the more conventional equipment when urban-based construction is needed. Now engineers can rehabilitate pipes running below a street using only access holes. Pipes can be replaced and even upsized from small excavations using pipe-bursting, microtunneling and directional drilling techniques. The location and condition of pipes can be determined using robotics mounted with closed circuit televisions, ultrasonic sensors, and radar.
Functions for Trenchless Technology Trenchless
Technologies can generally be broken into the following three groupings, each of which is based on a specific function:
- Assessment technologies
- Rehabilitation technologies
- Installation technologies.1
Assessment Technologies allow the determination of the location of the pipe and its condition. Surprisingly, pipes are often not where plans show them to be because either they were not constructed as designed, or they have moved over the decades. Tools such as ground penetrating radar, electronic sondes (transmitters), and gyroscopes can help accurately map pipes into global positioning systems (GPSs). Technologies such as closed circuit television, digital scanners, lasers, and ultrasonics allow an assessment of the structural and operational condition of the pipe and surrounding soils.
Rehabilitation Technologies are used to restore degrading pipe to a working condition. Often underground pipes operate at reduced capacity with their hydraulic flows having been limited by one or more of the following causes:
Figure 1: Pipe installed using microtunneling.
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- Full or partial structural collapse
- The infiltration of groundwater that displaces design flows,
- Exfiltration of product to the soil before it reaches its destination
- Changes in friction or cross-section.
Rehabilitation tools often use lining technologies that resurface the inside of the pipe from an access hole without the need for digging. A number of effective lining products are presently available-some that spray on the surface, some that slip through the pipe, and some that start as a polymer impregnated felt tube and cure into a high strength liner supporting the host pipe all through a manhole
Installation technologies allow construction of new pipe systems without the need for open cutting. Construction methods such as microtunneling (Figure 1) directional drilling, and pipe-bursting can be used to accurately install pipes from 25 mm to 2.5 m (1-inch to 100-inches) in diameter with minimum surface disruption.
PB's Role
PB is one of the leaders of the consulting world with the use and development of trenchless technologies. Using microtunneling PB was the engineer/consultant on Portland's West Side Combined Sewer Overflow Pipelines Project, which was named the 2005 Trenchless Technology Project of the Year by the North American Society of Trenchless Technology (NASTT).
PB staff includes two past presidents of the NASTT; the past director of two national trenchless technology research centers; and the directors of the Buried Asset Management Institute International.
Trenchless technology can solve many problems that were project stoppers just a decade ago. Readers are invited to contact me about the application of trenchless technologies to any PB project.
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