Surveys of the future

Exjet, which has been providing drainage services for over 27 years, describes how it has been improving survey data for sewerage, using a range of high-technology offerings including laser beam-based light line surveys

While for many years Paignton-based Exjet’s core market has been drain cleaning and unblocking services, including 24/7 blockage removal, the range of services now oered has been expanded to include CCTV surveying to WTIstandards and includeslight line proling; drain repair, including in-situ pipe lining and pitch bre pipe rehabilitation; open cut excavations and high volume water jetting using jet vac units. As part of this service expansion, over the past few years Exjet has, as part of its CCTV survey operations, increasingly employed the use of laserbased light line surveys to improve the range of information that can be made available to clients during pipeline surveys. Most recently the company has invested in a triple laser light unit for even greater accuracy of data in larger diameter pipes from such surveys than has been previously available using a single laser system. The company utilises a Clearline laser proling system with its associated analysissoftware. An example of light line prole surveying was completed recently for Wessex Water, requiring the examination of the interior of an existing concrete pipeline before a rehabilitation operation commenced. The project involved surveying a 68 m long, 1,050 mm diameter pipeline with an invert 300 mm diameter low-ow channel built in which runs under the M5 motorway near Banwell. The survey wasrequired after the pipe had been deep cleaned to established residual wall thickness and therefore residualpipestrengtharoundwhicha rehabilitation and redesign of the pipe use took place. The plan wasto install a full circular CIPP liner in the low-ow channel using a glass-bre, UV cured liner, and part ll the pipe with 200 mm of grout onto which were laid two SDR11 PE100 HDPE over-pumping pipelines. Main contractor was Onsite, but the light line prole survey wassubcontracted to Exjet given its previous experience with light line proling. The physicalsurvey ofthe pipewas completed in just one day utilising a standardtechniquewhereby a visual/laser prole is completed on the outward run through the pipe from the start shaft. This allows a full visual check to be made for defects, protrusions and other faults at the same time as undertaking a light line survey. A second light line prole only survey is completed on the reverse run asthe tractor isretrieved through the pipe to verify the data, which isthen fed into analysissoftware. According to Exjet general manager, Rob Dowell: “The real work begins once the practical survey is done. The highly sophisticated software brings out the true depth available from the results of the survey data and that is usually done back at the oce.” The level of data can be varied to give the client the information it is seeking over a wide range of options. The Quick Analysis shows variance of diameter using colour dierence along the pipe length showing increase or decrease of diameter in relation to the nominal pipe. The software can also produce an ovality check, minimum and maximum diameter measurements, an XY crosssection at any point in the pipe length surveyed, the potential capacity loss or gain, and residual pipe wall thickness. The software can also then generate a 3D image of the pipe over the survey length with colour dierence showing variations from those expected. In the case of the Banwell survey it was also possible to split the data stream to analyse just the smaller diameter low-ow prole in the invert. In the event the data showed that the pipe had sucient residual strength to be rehabilitated successfully and redesigned. At the end of the processing run the client receives the full analysis results or the set of results requested prior to the survey. The type of data produced using a light line prole survey can oer signicant increases in the base understanding of any pipeline length. This enables site operations to run more smoothly because there is a greater understanding of what to expect, and the survey can provide a solid foundation on which liner design and liner type can based. Rob Dowell concludes: “There is often a need for more detailed information in relation to future repair/ maintenance and rehabilitation optionsthat can be impossible to gain using visual survey techniques alone.”

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