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Using Acoustics to Find Sewer Blockages
sltratIn 2005, Charlotte-Mecklenburg Utility Department (CMUD) began a partnership with UNC Charlotte in the hopes of developing new technologies for pipe inspection. After two years of research, the acoustical inspection device was created and patented by UNC Charlotte.  In 2007 the company Info-Sense was formed to commercialize the technology. Info-Sense and CMUD conducted a five year partnership wherein the device was tested and adapted to ensure field readiness. Today CMUD is using the devices to specifically target sanitary sewer line segments that need cleaning, reducing the amount of unnecessary cleaning. 


                                                    How it works

slThe acoustic unit consists of two pieces, the sending unit and the receiving unit. The sending unit transmits various frequencies of sounds, the receiving unit knows expected frequencies, and calculates degradation of signal. The units are placed in adjacent manholes and specific information such as, User ID, Distance of the pipe segment are input by the user. As soon as the test is finished the display on the receiving unit shows the user a condition scale of 1-10 of that pipes condition. Along with capturing pipe condition the units also capture the GPS location of both manholes. With the tests completed the units are now taken to a workstation where the data is downloaded through the Info-Sense interface. With the use of python code the acoustic data is manipulated and given spatial reference from the sewer line segments in CMUD’s database. 
SL-RAT Diagram

What we’re doing with it

After the acoustic data is downloaded and imported into the system, it is then packaged and sent to the appropriate planner. The planner takes the information collected and makes decision based on a threshold developed by CMUD and Info-Sense. The units not only reduced the amount of cleaning required for an area, but show structural flaws that could cause problems in pipe segments. For instance, if a pre cleaning test is performed and the segment comes up as a 0, no signal was able to pass through the pipe meaning that there is either a full pipe sag, or a blockage. Cleaning crews would then be called out to jet the line. After waiting an hour or so in order to let a possible sag refill, a post cleaning inspection is performed with the units. If this measurement comes up as a 0, a full pipe sag or structure defect is assumed, and CCTV crews are called in. If the segment shows some change the pipe can be re-cleaned until the acoustic test confirms clean. If the first post clean test reveals a score within the acceptable threshold, it is assumed a blockage was In the pipe, and the cleaning truck resume normal duties elsewhere. 


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