IBAK discusses the successful execution of a sewer rehabilitation project, where its inspection equipment played a critical role.
The City of Dortmund, Germany, with nearly 600,000 residents, operates a sewer network spanning 1996km. As part of modernisation efforts, the Dortmund Sewage Department commissioned VOGEL Ingenieure GmbH to rehabilitate combined wastewater sewers built between 1882 and 1920. This includes 24 brick-built sewer sections with ovoid cross-sections measuring 600/900, 700/1050, and 900/1350, totalling over 1230m. To ensure the success of rehabilitation, accurate cross-section measurements were necessary.
The historic construction methods presented unique challenges, such as curved layouts and inaccessible lateral inflows. Many of the affected sewers run beneath high-traffic areas, requiring careful planning and traffic-related permits. To obtain high-quality data, sections were temporarily taken out of service, cleaned with high-pressure jetting, and inspected optically. Existing TV inspection data (2006–2014), digital site plans, and manhole measurements supplemented the study. VOGEL Ingenieure GmbH managed coordination to ensure smooth execution and workflow.
Traditional manhole-based measurements and pointwise assessments in larger sewers were insufficient, as cross-section variations of a few centimetres remained undetected. These gradual changes impact liner dimensioning, which requires precise internal size data to ensure durability over a 50-year lifespan. Optical inspections alone do not reveal subtle variations, necessitating continuous cross-section measurement.
The IBAK solution
The IBAK ORPHEUS 2 pan-and-rotate camera with integrated lasers enabled comprehensive cross-section measurement during standard optical inspections. The laser scan took place as the camera returned from the target manhole to the starting point, traveling at a steady speed of 5–7cm per second. The rugged IBAK T 86 tractor ensured stability in sections with fractures and bends. The laser system seamlessly integrated into the inspection process, eliminating extra setup time.
Switching from inspection to laser scan mode automatically deactivated standard lighting and activated laser measurement. As the camera reversed and rotated, it generated a spiral of laser points, capturing the entire pipe cross-section. The density of the spiral depended on reversing speed—slower speeds yielded more precise measurements. The system calculated the pipe centre from measured values, allowing flexibility in camera alignment.
Data analysis with IKAS evolution software
Planning engineers analysed the captured laser points using IKAS evolution software. A reference curve of expected dimensions helped validate results, with software tools allowing direct video cross-referencing. Engineers could identify anomalies such as deposits, residual water, and structural defects.
To improve measurement accuracy, irrelevant data (such as water accumulation or deposits) was masked and replaced with ideal values. Expert post-processing ensured accurate liner dimensioning, as small errors could significantly impact liner fit and performance. For instance, an uncorrected circumference measurement of 2513mm was adjusted to 2609mm (a 3.8 per cent correction), preventing miscalculations that could affect rehabilitation planning.
Analysis revealed that all reviewed pipes had larger circumferences and heights than asset records indicated. In seven of 24 cases, circumference variations within sections exceeded seven per cent. One section exhibited a 12.5 per cent difference between its maximum and minimum circumferences, emphasising the need for precise measurements when selecting liners.
For instance, a section recorded as 600/900 showed a 17.02 per cent larger circumference than expected, prompting a reassessment to 700/1050. Another section’s minimum circumference exceeded its recorded value by 13.11 per cent, indicating an intermediate size. Even seemingly minor deviations required expert analysis to ensure liners could stretch adequately without exceeding material limits.
Correct liner sizing prevents issues such as incomplete adhesion, excessive annular gaps, and overstressing. Without proper adjustments, liners may not conform properly or could suffer premature failure.
IKAS evolution software presented results in clear, structured reports integrated with video data. This allowed the Dortmund Sewage Department to make informed rehabilitation decisions based on precise cross-section measurements.
What comes next?
Proper sewer cleaning before laser scanning is crucial to minimise measurement disruptions. The continuous, laser-supported measurement method with the IBAK ORPHEUS 2 provided significantly more accurate cross-section data than traditional optical inspections. This data plays a key role in selecting and sizing liners to match actual pipe dimensions, preventing installation failures and extending service life.
By incorporating continuous cross-section measurements during planning, delays and costly modifications can be avoided. The data also aids in optimising liner procurement, ensuring appropriate stretch capacity and durability.
VOGEL Ingenieure GmbH is now preparing implementation plans and tender documents, with additional studies such as ground investigations and static calculations underway. The project aims to launch tenders in summer 2020, with rehabilitation work beginning in 2021.
This project underscores the importance of precise sewer assessments for successful infrastructure rehabilitation, demonstrating the value of advanced measurement technologies in municipal planning.
For more information, visit ibak-australia.com.au
This article was featured in the April edition of Trenchless Australasia.
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