|The Last Mile
Developing Standards for the Deployment of Optical-Fiber Cable in Underground Utility Systems
by Jey K. Jeyapalan
Your city office building may be only one kilometre or a mere 10 metres from the nearest end of laid optical-fiber cable, but it might as well be one thousand kilometres. The prospect of upheaval caused by the street excavations required to complete the optical-fiber circuit is too great for most city officials to tolerate. So in many municipalities, whats known in the industry as the last mile remains unbridged.
The innovative process of either robotically laying optical-fiber cable in existing underground utility pipes or including it as part of the relining of these pipes offers a way to complete the circuit without destroying city streets. But standards are essential to assure telecom and utility companies that public safety will be preserved, and thats where a new ASTM technical committee comes inas a place where telecom companies and others will pull together their expertise to serve the optical fiber in underground utilities industry.
More than 110 million North Americans are expected to telecommute to work by 2010. This will increase productivity and quality of life significantly, saving energy, reducing pollution, and re-distributing wealth and real estate values. To meet the current and anticipated demand, the telecommunications industry has kept pace, creating technology that allows up to 10 trillion bits per second to travel through a single strand of fiber measuring a mere seven microns (this is equivalent to carrying 150 million phone calls simultaneously).
Some economists predict that without true broadband, our technology industry and economy could remain stalled, and currently the installation of an optical fiber network to your office building or home is itself stalled. The primary obstacle is the last milethe section of a network that connects from the basement of an end-user building in a metropolitan area to the metro-area network surrounding the city. This connection requires extensive construction, usually involving the excavation of city streets.
These excavations cause pollution, traffic hold-ups, economic loss, and unsafe conditions for city inhabitants. Even worse, the repair of streets after excavation rarely leaves the streets in acceptable condition. Consequently, most cities discourage the new open-cut excavations that would bridge the gap between laid cable and end user.
North America already has invested many trillions of dollars in the past century in building over 2,000,000 kilometres of sewers in the ground. Over 1,000,000 kilometres of natural gas pipes come into our homes and businesses. So it makes sense for either telecommunications companies, utilities, or city-owned telecom carriers to lease space in existing sewers and natural gas pipes for the laying of optical-fiber cables. Owners of these underground utilities can generate a new revenue stream and telecommunication companies could install their optical fiber cables at an attractive cost. But all parties must be aware of the need to follow proper standards of care to build networks in publicly owned sewer systems and gas pipes.
The numerous stakeholders involved in this effort have joined together to form new ASTM Committee F36 on Technology and Under- ground Utilities. The group will create standards for the deployment of optical-fiber cables in underground utilities. Participants in the new committee include municipal authorities; building owners; robot, pipe, and optical-fiber cable manufacturers; telecom corporations; and construction, architectural, and engineering consultants, to name just a few.
How This Works
There are at least five robot companies, namely: CableRunner, DTI-CableCat, Ka-te, Nippon Hume, and RCC. CableRunner uses a drill-and-dowel system in sewers of 250 to 700 mm in size. DTI-CableCat uses either a back-reamed anchor or an adhesive bed system in sewers of sizes 200 to 1200 mm, while Nippon-Hume and RCC use drill-and-dowel systems for the same sized sewers. Nippon-Hume uses a plunger pin stem for the anchor along with a two-part resin system while RCC uses a frictional stem anchor. Ka-te uses a stainless steel clamp and conduit system for sewers of sizes 200 to 700 mm.
In the drill-and-dowel system, a drill hole is made into the upper part of the sewer pipe wall and the cable is attached using either an anchor or a cable tray. In the adhesive bed system, the sewer pipe surface is coated with a glue and either the cable is directly attached or fitted into either trays or clips attached to the glue bed. In the clamp-and-conduit system, stainless steel rings are fitted inside the pipe where the stainless steel conduits to house the optical fiber cables are clipped.
Each method has its advantages and disadvantages and is likely to find its own market niche where the user will take some responsibility for using suitable engineering criteria to pick the best product to fit their budget and project needs.
In addition, there are liner systems vying to do some of this as part of routine sewer maintenance programs. There is a good chance that these liner companies will succeed if they are able to offer value-added relining systems for an attractive incremental fee to the city sewer agencies over the standard lining systems without cutting too much into the current functions of the sewers.
The standards that deal with materials and installation practices may require additional work within ASTM Committee F17 on Plastic Piping Systems rather than Committee F36, whenever these involve those liners already covered within F17.
As one example of the numerous questions and concerns raised by the possibility of placing optical-fiber cable in existing underground utility conduits, well look at the issues raised by sewer agency engineers. These concerns about allowing anything other than sewage in their sewers are based on sound engineering principles.
The operation and maintenance of sewage conveyance systems need active preventive maintenance and sound pipeline engineering input. If proper standard of care is not practiced, it is only a matter of time until major problems will manifest. At that point the sewer lease fee paid by a fiber installer to city hall will amount to nothing compared to the cost the public will have to bear to return the sewers back to normal. Historical lessons learned more than 100 years ago in the Paris sewer tunnels when engineers attempted to place more than one utility in the same space must be studied thoroughly so as not to repeat the same mistakes.
A new committee formed within the Collection Systems Committee (CSC) of the Water Environment Federation has conveyed most of these concerns among the sewer agencies in a letter to Committee F36 and have requested that these be addressed in the standards under development. Here is a sampling of their concerns:
The extent to which hydraulic characteristics of the sewer would be altered when optical cables and the fasteners are introduced needs to be assessed by physical tests.
These cables also would restrict many of the tools used for routine sewer monitoring, operation and maintenance.
The corrosive effects of the sewage on the cables and fasteners and their longevity need to be addressed through extensive research.
Debris, rags, and grease are likely to accumulate at a faster rate, causing blockage.
Consensus standards need to address how to select suitable sewers, design, installation, operation, and maintenance considering the technology used for fiber installation, pipe wall material, size, applications, and how laterals are connected to the mainline sewers.
Debris accumulates at the interior protrusions of the manholes when surcharged. How would this be handled if valuable telecom gear and customer connection gear were housed in these manholes?
And most importantly, how would it affect the current functions of the sewer if additional fiber companies want to install their cables in the same sewers at a later time?
Technology-Specific ASTM Standards
For the development of standards that will address these concerns, Committee F36 is looking to an existing standardization model. Over the past two decades, ASTM standards have served the trenchless technology industry well. Committee F17 on Plastic Piping Systems specified many trenchless pipeline technologies within separate standards. This approach never gave any advantage to one technology over another, since each technologys engineering merits were captured in their own ASTM standards. Consequently, this approach of technology-specific standards development within ASTM never excluded any meritorious technology from the marketplace either.
This is precisely the reason that the creation thus far of 78 ASTM standards, rather than one generic standard, helped the trenchless technology industry reach over 35 percent of all rehabilitation work in the sewer market. The technology-specific standards also encouraged many new innovations in the marketplace when the new kids on the block were assured that they too would receive due process within the ASTM standard-writing system.
ASTM Committee F36 has drafted a useful generic standard on how to select sewers suitable for this work that is likely to find wide usage among municipalities. But a strong case may emerge in the future for the committee to develop a whole matrix of technology-specific standards, the very set the city sewer owners have asked for. This is understandable in that the sewer agency engineers have a paramount duty and a legal responsibility under the federal Clean Water Act to protect the health, safety, and welfare of the public they serve. While there is ample merit in ASTM providing generic standards in the early stages of a new committee such as F36, it is this authors opinion and not the consensus of Committee F36, that the following points could support the sewer agencies needs for technology-specific standards:
1. There are five robot manufacturers named on page 20. With the exception of some similarities on the surface among the robots offered by CableRunner, Nippon Hume, and RCC (because of the same drill and dowel approach), the other robots operate differently and install optical fiber cables using varying methods. DTI-CableCat offers an adhesive bed system while Ka-te offers a conduit and clamp system.
2. The following attributes make one technology much different from another:
a. The size range of sewers in which each robot can work;
b. The sewer wall materials in which these robots can be employed;
c. The composition and engineering properties of the deployment components;
d. The cost of the materials of deployment;
e. The cost of labor for each method;
f. The set up time for each technology;
g. The rate of production for each technology;
h. The ability of the optical cable owner to replace an installed cable either due to damage or rapid progress in optical-fiber cable technology;
i. The ability to use existing technology to clean the sewers;
j. The ability of the sewer owner to inspect the sewers using current technology;
k. The ability of the sewer owner or its contractor to maintain the sewers; and
l. Most importantly: How an engineer licensed to practice goes about choosing the suitable sewers in which these robots could be used, and how these vary dramatically from one robot system to another.
3. Working in the sewer will affect the health, safety, and welfare of the people we serve and any shortsighted approach to selecting the sewers for installing and operating optical-fiber cable would expose all those in this new industry to an enormous liability. Developing sound engineering standards falls well within this obligation.
4. If one were to include all five different robot systems in the same pipe selection standard, this would create more confusion than clarity among the users of this technology.
5. With techniques involving liners that embed the optical fiber cable in them, we would create even more confusion in the minds of the users of our standards.
6. No two technologies operate the same way; no two technologies cost the same; and no two technologies provide the same end results. Given the newness of this technology, we have an obligation to communicate to the users of our standards the drastically different attributes of various techniques that we have at our disposal. A single generic standard encompassing all technologies may not provide all the guidance the owners of pipes have asked for from ASTM in the past.
7. If something were to go wrong with any one of the many technologies, in this authors view, even the ones that have the potential to serve intended functions would be eliminated from the market place en masse. And this will make the public wonder why its trained civil engineers, licensed to protect their health and welfare, failed to follow appropriate standard of care.
Sewer Selection Criteria
As an example, let us address one of the most pressing issues in every sewer owners heart at the present time. If we were to consider allowing optical fiber cables in existing sewers, what criteria should a fiber cable installer use to select the sewers that are suitable for optical fiber deployment?
Operating an optical fiber network in the sewers poses its own challenges. Proper civil engineering input is essential for the selection of the suitable sewer system for deployment. The factors to consider in selecting the right sewer path are:
1. Access to the Sewer
The primary access to the sewer for fiber cable installation using either a robot or other means is through the manholes at both ends of the reach. It is desirable that the length of the reach is shorter than what is reachable by the umbilical cable needed for the supply of air, electricity, and communications circuits. If man-accessible pipes were chosen, then this limitation would not apply.
2. Hydraulics of the Sewer
Given the ubiquity of infiltration and inflow problems, sewer designers have been able to count on only 85 percent of the actual flow area to convey the flow. The impact of optical fiber cables, their fasteners, and other deployment parts on flow characteristics need to be evaluated by running physical hydraulic studies with and without such components. Hydraulic studies of the flow conditions under the worst possible scenario based on past flow records in that sewer also needs to be done before the sewer is considered for optical fiber cable installation.
3. Structural Capacity of the Sewer
An evaluation of the structural capacity of the sewer to carry the soil load, groundwater load, and live load needs to be conducted. This is to ensure that the current condition of the sewer is adequate to house the optical fiber network.
4. Sewer Cleaning After Installation of Optical Fiber Cable
Sewers need to be cleaned periodically as part of their maintenance. Once optical fiber cables are installed in the sewer, special precautions must be taken in choosing and applying suitable cleaning methods that would not cause damage either to the sewer wall or the optical fiber cables.
5. Sewer Inspection After Installation of Optical Fiber Cable
Periodic maintenance of the sewer will also involve inspection of the internal condition of the sewer system once the optical fiber cables are installed. Special precautions need to be taken in choosing and applying suitable technology for sewer system inspection in order not to cause damage to either the sewer walls or the optical fiber cables.
6. Sewer Maintenance After Installation of Optical Fiber Cable
Sewers require periodic maintenance involving anything from point repairs, grouting and relining, to total replacement. The current condition of the sewer system and its need for repair or rehabilitation during the design life of the optical fiber network must be carefully evaluated.
7. Compatibility of the Sewer Wall
It is not possible to work with certain sewer wall materials depending on the fiber installation technology used, and so the materials will need to be evaluated.
8. Excessive Grease in the Sewer
Sections of pipe that have grease accumulations of more than a suitable thickness within one year of cleaning should not be considered candidates for optical-fiber system installation until proper remedial action is taken.
9. Excessive Chemical Reagents in the Sewage
Sewage carries many chemical reagents and the compatibility of fiber deployment materials and components with all such chemicals needs to be tested.
10. Calcium Deposits on the Sewer Walls
Optical-fiber systems should not be deployed in sewers with excessive calcium deposition.
11. Joint Separations/Offsets
Joint separations/offsets can lead to both infiltration and exfiltration. Structural damage to the sewer may result from pipe bedding material being transported into the pipe. Enough care should be exercised when such sewers are encountered before these are chosen for optical fiber deployment.
12. Excessive Root Intrusion
Sewers should be free of excessive root intrusion to be eligible for installation of a optical-fiber system.
13. Condition of the Manholes
Manholes should be in an acceptable physical condition for that sewer system to be used for optical-fiber cable installation.
14. Condition and Frequency of Lateral Connections
The condition of the lateral connections to the mainline sewer is important both to the hydraulic functioning of the sewer and to the installation and operation of the optical-fiber network.
It Takes a Village to Grow
Consensus standards developed within ASTM International and engineering guidelines developed in the American Society of Civil Engineers are needed to address technical issues such as these for every technology in this marketplace. The standards we write need to be based solely on engineering merits.
For more information, contact the author Jey K. Jeyapalan, P.E. (phone: 860/354-7299). //
Copyright 2002, ASTM