Since the American Society of Civil Engineers’ (ASCE) 2005 Report Card on America’s Infrastructure, the needs of the nation’s transportation and utility systems have been on the minds of civil engineers, legislators, government officials, the public, and leaders within public agencies nationwide. The recently released 2009 Report Card indicates that conditions have not improved. This is evident visually, as roads and bridges deteriorate or become unable to meet capacity. But our "invisible" infrastructure—mainly the underground network of pipelines—also needs major rehabilitation. This out-of-sight, out-of-mind part of our world is vital for human health and welfare.
Across the country, many water, sewer, stormwater, and gas pipelines and electrical conduits need evaluation, inspection, management, rehabilitation, and repair. The typical lifespan of water and wastewater pipes ranges from 25 to 85 years or longer, but conditions inside and outside the pipes, such as corrosion, can significantly affect that lifespan, as can the materials and methods used in construction. So how can we know, short of pipeline failures, that rehabilitation is needed?
New technologies in evaluation, inspection, management, rehabilitation, and repair allow us not only to understand and see what’s going on in the underground infrastructure with increasing success, but also to rehabilitate without significant service interruptions.
Historic pipeline materials
Since civilization began, pipe has been a major factor in the conveyance of water, wastewater, and stormwater. Whether made of stone, wood, lead, clay, cast iron, ductile iron, concrete, or steel, the materials that were used at the time sometimes did not make sense 100, 50, 20, or in cases such as asbestos pipe, even 10 years later. Technology has changed the materials used to make pipes— from bored trees to steel, concrete, polyvinyl chloride, and high density polyethylene, among other materials. At each stage, newer materials theoretically provided for more efficient systems.
Hollowed and bored trees such as hemlock, elm, and redwood comprised many of the early pipes. Such applications were common in London in the 16th to 18th centuries and continued to the mid-1950s when a 10-inch wood stave pipe was installed near Telluride, Colo. Wood pipe is still being discovered and removed. In the summer of 2007, workers in Holly, Mich., discovered a thimble used to join two wooden pipe segments.
Records document much of what lies in our underground world of pipe, but not everything. Today, as in the past, field crews must either attempt to predict conditions or sometimes must enter manholes for direct interior pipe views or excavate pipe for exterior inspections. However, newer technologies provide options that further the science of pipe evaluation by exposing interior conditions. With the corrosiveness of water, wastewater, and stormwater, which varies greatly from region to region, mineral deposition, corrosion, and altered flows are inevitable. Biogrowth can cause blistering, impacting capacity and useful life. Acidic soils can literally draw steel out of pipes and into the ground, causing pipe failure.
The first phase of work in characterizing aging infrastructure is evaluation and documentation. But if a GIS system is not yet in place, getting the initial information involves carefully poring over every inch of the plans, creating a database, and developing an integrated map and database of the system in a GIS. From the plans, technicians document in the GIS system each pipe segment’s size, diameter, length, installation date, and composition. A database for leak and repair experience can also be critical to tracking trends in pipeline performance and condition.
Large-scale GIS conversion and implementation projects can last 24 months. This includes conversion of thousands of map sheets of sewer, water, and utilities, and GPS location and mapping of more than 15,000 facility locations (thousands of fire hydrants, main pipe segments, and valves) that can cover more than 50 square miles. The completed GIS provides agencies with automated mapping systems of their water and sewer facilities that allow them to track maintenance and improvements quickly and accurately.
To help map such a large number of data points, a differential GPS strategy can be used to expedite the project survey. Use of preprogrammed GPS receivers can save critical time and money at the location phase of the project and can help keep on schedule.
GIS conversion includes development of custom GIS coding forms for extracting information from as-built drawings for entry into databases such as the Oracle Relational Database Management System and graphic database entry to the Graphic Design System (GDS) GIS.
|A complete GIS provides agencies with automated mapping systems of their water and sewer facilities that allow them to track maintenance and improvements quickly and accurately.|
Assessing pipe conditions
In addition to estimating the conditions of aging infrastructure, high-technology solutions are available to compliment the GIS database. Testing for external and internal corrosion can involve drilling into the side of the pipe and taking a coupon sample to evaluate the materials and determine the pipe’s integrity and degree of deterioration.
Closed-circuit television (CCTV) techniques allow in-ground inspection and inventory of the internal pipe conditions. CCTV technology provides an enhanced ability to see inside to more accurately evaluate the need for pipe repair or replacement. CCTV technology has applications for all types of water, sewer, stormwater, and other pipes from 3-inch-diameter laterals to the largest pipelines. Digital video inspections with concise, meaningful, customized reports are designed to meet the needs of each specific agency. Video information can be coordinated geographically to a GIS database.
Challenges of CCTV work include managing large amounts of digital data and managing the risks of the advanced digital equipment being used in corrosive environments such as sewers. Careful planning and complex logistics are required to televise in easements, canyons, sensitive habitats, or other inaccessible areas. Coordinating field crews for large projects, supplying them with maps and electronic data, and training them to submit consistent inspections with standardized coding are also challenging. Crew safety must always be at the forefront.
In a study in San Diego, CCTV cameras were used at targeted points to try to determine why wastewater flows were decreasing. The results showed grease and hardened waste build-up adjacent to downtown restaurants because of food and grease entering the wastewater system. The study was displayed at the ESRI User Conference in an award-winning GIS poster session called "Heart Attack of a City." "The CCTV analysis is truly one of the most accurate and detailed methods of pipe evaluation that we can employ today," said John Harris, vice president of RBF Consulting.
The bottom line is that flow monitoring and analysis and system modeling, combined with field testing, are critical to determine both current and future conditions for capacity assurance. Considerations include the following:
Corrosion and metallurgical engineering—Forensic analysis—including analysis of coating failures for pumps, valves, tanks, and piping—can be conducted on failed metallic structures used in potable, reclaimed, and sewage systems. Keys to success are corrosion-control design, electrical continuity surveys, electro potential surveys, electrical interference studies, metallurgical evaluation, induced voltage analysis, and inspection.
Planning for the future—Through records evaluation and onsite analysis, the pipe’s remaining life can be determined and future needs superimposed on the existing system. Easy-to-use, customized project reports listing the condition of pipes, recommended maintenance and repairs, and the priority of the recommended work should be prepared. Construction cost estimates for repair and rehabilitation for development of capital improvement replacement budgets are then developed to support fiscal planning. Master plans can be updated for entire systems, or plans and strategies developed for individual pipelines.
Rehabilitation and technology—Pipe replacement has taken on new challenges in recent years and newer technologies to reduce service interruptions are being developed. Live-stream slip line of existing pipelines is occurring across the nation with insertion of segmental, rubber-gasketed bell and spigot pipeline into existing unlined, reinforced concrete pipelines. The new pipe is structurally designed to fully or partially withstand anticipated sediment and external water level loading.
For installation, openings are cut into the top of the pipe at specific intervals, and new pipe is inserted into the existing pipeline followed by additional segments. As each segment is installed, pipe is pushed downstream to make room for the next pipe segment. Openings are spaced as far as 2,500 feet apart. When the new pipe is in place, the annular space between the exiting and new pipe can be pressure-grouted. All of this can be done without service interruptions.
Another technology—Cured-in-place pipe (CIPP)—retrofits existing pipe with a felt tube liner impregnated with a vinyl ester epoxy resin. Liner thickness and resin can be designed to accommodate specific loading and surface conditions. Liner tube is inserted into each manhole or at access points and is pushed through existing pipe using water pressure. Once in place, water in the tube is heated to activate the resin to create a firm, corrosion-resistant pipeline that closely matches the internal pipe diameter.
For non-live-stream lining, a continuous spigot pipeline can be inserted into existing pipe. New fused HDPE pipe is structurally designed to withstand loading. Contractors must cut openings at intervals to install the new pipe as it is pulled into the existing pipeline as one continuous segment. Individual HDPE pipe segments are fused together ahead of installation to create a joint-free pipeline.
Pipe bursting is also used for higher-technology solutions. In addition to extending useful life, improved "C" values can increase pipeline capacity.
The need for rehabilitating our nation’s "invisible" infrastructure grows clearer as we begin to develop more advanced methods to evaluate existing conditions. The intensive work required to document, evaluate, and determine the future course of pipelines serving America’s public is well worth the effort to avert emergency situations, prevent rupture, and alleviate potential risks of severe corrosion and deterioration. These high-technology solutions are also often environmentally superior to the older technologies, less disruptive, and provide the accurate assessment necessary to ensure the future of underground systems. Competition for local, state, and federal money demands that we plan and implement the upgrade of the country’s pipeline infrastructure as cost-effectively as possible.
Barbara Eljenholm, AICP, REA, LEED AP, is a senior vice president with RBF Consulting. Information in this article was derived from collaboration with the multi-faceted RBF Water Resources Team, including Ron Craig, MA, senior vice president, Ontario office; Cindy Miller, P.E., vice president, Irvine office; Steven Bein, P.E., vice president, GIS; and John Harris, P.E., vice president, San Diego office.