Delft University of Technology
Section Sanitary Engineering
Department Water Management
Faculty of Civil Engineering and Geosciences
Quality of visual sewer inspection data: the
need for a new coding system?!
Jojanneke Dirksen, Arjan van der Steen, Jeroen Langeveld, François Clemens
In order to improve the quality of visual
sewer inspection data the complexity of the
(European) coding system should be
drastically reduced.
CONTACT: Jojanneke.Dirksen@waeternet.nl/+31 641112779
MAIN CONCLUSION
TEST YOUR OWN SKILLS!
Introduction
Previous research learned that the reproducibility of visual sewer inspection data is poor (Dirksen et al.). Further research by Arjan et al. showed that the applied coding system has a major influence on the reproducibility. The aim of this study was to give relevant suggestions to improve the quality by defining defects that are in the current standard defined ambiguously (i.e. can be understood in more than one way). For this, the database of sewer examination data of graduated sewer inspectors in the Netherlands was studied.
Results
Evaluation of the way how clearly visible features shown on the photographs are reported by the candidates showed that the results are very much depended on the inspector (not reproducible). It is shown that the difference between the following defects is not clear:
• Fissure (BAB) and break collapse (BAC)
• Attached deposits (BBB), settled deposits (BBC) and ingress of soil (BBD) • Other obstacles (BBE) and settled deposits (BBC)
For the following defects there is a high possibility of being overlooked: • Intruding sealing material (BAI)
• Mechanical damage (BAF-A)
Furthermore the differentiation between fine and coarse deposits proved impossible.
As only ten photographs were used for the examination, this list of ambiguities is probably only the tip of the iceberg.
Below you find three photographs used for the examination. Look carefully at the photographs and decide which defects are present (you find a list of defects below the poster). If you flip the image, you find the answers given by the candidates.
photograph 1 0 10 20 30 40 50 60 70 80 90 100 d e fo rm fi s s u re c o lla p s e d e f. b ri c k . m is s .m o r s u rf .d a m in tr .c o n n d e f. c o n n in tr .s e a lm . d is p l. j. d e f. lin in g d e f. re p a ir d e f. w e ld p o ro u s ro o ts a tt .d e p . s e tt .d e p . in g re s s o b s t. in fi lt r c o n n . lo c .r e p a ir c u rv . w a te rl e v . % o f c a n d id a te s class 5 class 4 class 3 class 2 class 1 photograph 2 0 10 20 30 40 50 60 70 80 90 100 d e fo rm fi s s u re c o lla p s e d e f. b ri c k . m is s .m o r s u rf .d a m in tr .c o n n d e f. c o n n in tr .s e a lm . d is p l. j. d e f. lin in g d e f. re p a ir d e f. w e ld p o ro u s ro o ts a tt .d e p . s e tt .d e p . in g re s s o b s t. in fi lt r c o n n . lo c .r e p a ir c u rv . w a te rl e v . % o f c a n d id a te s class 5 class 4 class 3 class 2 class 1 photograph 4 0 10 20 30 40 50 60 70 80 90 100 d e fo rm fi s s u re c o ll a p s e d e f. b ri c k . m is s .m o r s u rf .d a m in tr .c o n n d e f. c o n n in tr .s e a lm . d is p l. j. d e f. lin in g d e f. re p a ir d e f. w e ld p o ro u s ro o ts a tt .d e p . s e tt .d e p . in g re s s o b s t. in fi lt r c o n n . lo c .r e p a ir c u rv . w a te rl e v . % o f c a n d id a te s class 5 class 4 class 3 class 2 class 1
From the graph it is clear that the defects of the sewer shown in
this photograph were easy to
recognize: surface damage and a displaced joint (it is not obligatory to denote water level class 1:
h< 10% of the diameter).
The responses of the candidates do not make clear what kind of defects were present in the
photographed sewer. For this
sewer the candidates did not agree on the presence of the defects
fissure, defective connection, displaced joint and infiltration.
Photograph 4 shows a sewer with a crack on the soffit and bottom of the pipe. Two thirds of the
candidates recognized this crack and described it as a fissure
(36%), collapse (26%) or both (18%).
References
Steen, van der, A.J. Dirksen, J. Clemens, F.H.L.R.
Accepted. Visual sewer inspection: detail of coding system versus data quality? Structure and Infrastructure
Engineering.
Dirksen, J., Clemens, F.H.L.R., Korving, H., Cherqui, F., Le Gauffre, P., Ertl T., Plihal, H., Müller, K., Snaterse, C.T.M. 2013. The consistency of visual sewer inspection data.
