Sewers - nothing very sexy about them.  My 16-year old daughter is proud when she tells her friends that her dad is an engineer with PB and that he works on projects all over the world, but she always seems to omit the fact that my main function is working with sewers.  The reaction of most people when they think of sewers:  Yes they are there, someone needs to build them, someone needs to repair them - but not me!

With about 1 million miles of sewers in the U.S. valued at over $1 trillion, and with most of them reaching the end of their service lives, at least I have job security!  To look at my workplace you would not guess that I spend most of my professional time contemplating sewers.  My office is neat and clean, not smelly, and I wear a suit and tie to work, not a rubber suit.  Further, we generally refer to sewers as "underground infrastructure."-names do make a difference.  One of the reasons why I am able to perform my functioned as an underground infrastructure engineer is that I am able to obtain the information about the sewers that I need to rehabilitate without leaving my office. 

Early Technology:  Robot-Mounted Camera 

One of the first tasks performed when managing any system is to gather information about its structural, functional, and operational condition.  Sewers are no exception.  Luckily information about sewer pipes can be obtained by several technologies that do not require engineers, or anyone else for that matter, to actually enter the sewer. 

One of the main data gathering tools available is a robot-mounted camera that can travel along the sewer pipe guided remotely by an operator on the surface (Figure 1).  This technology was developed in the 1970s and 80s when analogue closed circuit televisions (CCTV) had evolved to the point where they could survive and function in the hostile environment of underground sewers.  These systems rely on the optics of the CCTV to view the interior of the pipe wall looking for signs of distress (cracking, holes, infiltrating water, etc.).  CCTV mounted robots have become very reliable and sophisticated, with modern systems utilizing:      

• Detachable cameras that can travel up laterals
• Pan and tilt capabilities to get different perspectives of pipe features      
• Cool and long-lasting light emitting diodes that provide light
• Sophisticated data retrieval systems that can map images into a GIS system.

These cameras can provide excellent high resolution pictures that can be used to assess the condition of the pipe and tell the engineer if the system needs repair (Figure 2).

Gathering sewer pipe data from a CCTV based system does create some problems, however.  The images need to be reviewed by someone who then assigns a condition rating to the pipe, and humans are prone to making mistakes.  CCTV videos of sewer interiors are, to say the least, not exciting and the operator needs to view hours of tapes to get a complete data set.

The Latest Technology:  Digital Sewer Scanners

The digital sewer scanner was developed in Japan in the early 1990s as a down-hole oil drilling assessment system to determine the condition of production wells.  It was brought to the U.S. in the mid-1990s by Dr. Tom Iseley, who worked with researchers in the U.S. and Finland to modify and perfect the scanner for sewer assessment.  The digitized scanner (Figure 3) uses a multi-dimensional imaging system, a gyroscope, and a data management system to gather, analyze, and display optical and positional information about sewers in a way that greatly enhances the entire process. 

The robot-mounted system gathers a forward view, an axial view and positional information from an internal gyroscope; and generates an ergonomically effective display of the sewer condition.  The entire process is digital, which allows sophisticated computer manipulation of the data for easy interpretation and analysis. The robot travels at a constant speed along the axis of the sewer pipe gathering an oblique image (fisheye) and a right angle image (radial scanner) of the pipe wall, and recording the inclination of the pipe (Figure 4).  These data are stored digitally and analyzed after the scan is completed in the comfort of an office.  Because the rate of travel is constant, exact measurements of interior sewer features are possible-something a normal CCTV system can't do.

The digital nature of the data capture allows the entire sewer segment (generally about 90 m (300 feet) from access hole to access hole) to be viewed at once; or specific sections to be studied in depth.  The differential viewing angles supplied by both the fisheye camera and the radial scanner provide the engineer with a stereoscopic 3-dimensional view of the pipe's interior, allowing something close to a virtual walk though of the sewer.  Presenting the images and positional information of the sewer pipe in this format greatly increases the speed and accuracy of the assessment process.

PB Uses Latest Technology

We first used this technology in our Tower Grove Project in St. Louis, where the digital scanner was used to survey and assess a total of 7300 m (24,000 feet) of sewers in record time and with outstanding accuracy.  It is now our standard tool for sewer assessment projects.  When combined with our proprietary predictive modeling software, and computer vision software, PB is able to provide more accurate assessments of the interior conditions of sewer pipes in a fraction of the time.