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Damages of manholes made of concrete, reinforced concrete and masonry according to DIN EN 13508 - crack formation
- break/collapse
- defective brickwork or masonry
- missing mortar
- surface damage
- displaced joint
- intruding connection
- defective connection
- intruding sealing material
- obstruction caused by lining defect
- defective repair
- porous pipe wall
- soil visible through defect
- void visible through defect
- defective step or ladder
- defective cover or frame
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| (Image: Damages of manholes made of concrete, reinforced concrete and brickwork)
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(Image: Infiltrating groundwater)
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(Image: Manhole top below the street level as a result of settling of the manhole or failure of the mortar gaps between the manhole top and the manhole taper)
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(Image: Defective (1) or missing (2) step irons)
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(Image: Manhole - Displacement)
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(Image: Defective step in a masonry manhole)
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(Image: Biogenic sulphuric acid corrosion … |
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Sewer systems are constantly or temporarily subject to different physical, chemical, bio-chemical and biological stresses. In genaral, damage is caused, on the one hand, by exceeding the normative utility period and, on the other hand, by the different external or internal influencing stresses during operation. The aim of this lecture is to provide an overview of the main damage groups, its causes and its consequences. |
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Damage: In the sense of rehabilitation, damage is the condition that is inherent or to be expected in view of the impermissible impairment of functionality. |
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The damage can either be limited to a small area or can be spread over a wider region of a section of a sewer or network region. The knowledge of the damage, its manifestation, causes and consequences is one of the most important conditions for successful planning and structuring of maintenance and rehabilitation measures and here especially for the selection of suitable processes for damage elimination or rehabilitation. |
(Image: Damage limited to … |
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(Image: Leaking branch connection [FI-IfK])
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(Image: Root ingress)
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(Image: Positional deviation in the longitudinal direction [FI-Jtele])
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(Image: Internal corrosion of a concrete pipe [FI-Jtele])
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(Image: Deformation of an angular-flexible pipe)
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(Image: Fragmentation of a vitrified clay pipe)
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In the following, the main damage groups that occur in sewer systems and which are mentioned in [ATVM143-1:1989] are: - Leaks ;
- Flow obstacles ;
- Positional …
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The position of the individual points of damage in a section of the sewer must be defined by the position with reference to the beginning of the section of the sewer. The centre of the manhole is usually regarded as the beginning of a section. In special constructions (e.g. basins, traps, etc.) the section begins at the inner side of the wall (pipe end); this is where the pipeline runs through the wall.. |
(Image: Position of single damages in a section … |
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| (Image: Positioning of connections in the manhole to ATV-M 143E Part 2 [ATVM143-2])
The start and end of any section damage must be described in a suitable manner. In the inspection of manholes or structures, the position of the individual points of damage must be positioned at least approximately with a characteristic number . The main flow sewer receives the number 12, the other connections (side connections, property connections, street drains) … |
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Leaks are present when water obviously enters or leaves or when a test for leaks is not successful. |
(Image: Leaking pipe joint [FI-IfK])
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(Image: Leaking branch connection [FI-IfK])
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There are numerous causes for the occurrence of leaks and they can be arranged in the following groups [ATVM143-1:1989] : - Non-adherence with EN 1610 [DINEN1610:1997], DIN 19550 [DIN19550], prEN 12889 [DINEN12889:1997], material standards or regulations and guidelines for
- Planning,
- Material and component selection,
- Workmanship,
- Operation;
- Material ageing;
- As a result of other damage.
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(Image: Street collapse caused by leakiness) The primary consequences of damage caused by leaks in sewers as well as to structures of drain and sewer systems are: - The exiting of sewage (exfiltration); and
- The ingress of groundwater (infiltration) and soil.
In both cases they always form the starting point for possible consequential damage [Horne85] [Young84]. |
(Image: Infiltration)
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(Image: Exfiltration)
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Flow obstacles are objects or materials lying in the cross section of the pipe, which project into it or cross through it in such a manner that the cross section required for a proper flow of the sewage is no longer completely available. | (Image: Incrustrations in a vitrified clay sewer [FI-IfK])
| | (Image: Buidling connection projecting into a sewer [FI-KMG])
| (Image: Root ingress in the region of a pipe joint [FI-KMG])
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According to [ATVM143-1:1989], the following are the causes of damage from flow obstacles: - Non-adherence to the standards and regulations such as EN 1610 [DINEN1610:1997], prEN 12889 [DINEN12889:1997], ATV-A 115E [ATVA115b] ;
- Incorrect planning (e.g. pipe gradients);
- Incorrect construction work;
- Insufficient cleaning;
- Introduction of depositing and/or materials capable of binding;
- Pipe gaskets or pipe joints that are not root resistant;
- Influences …
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Possible consequences of damage caused by flow obstacles in sewer systems according to [ATVM143-1:1989] are: - Reduction of hydraulic capabilities;
- Blockage ;
- Increase of the maintenance effort.
Because of the increase in backing up, flow obstacles generally increase the danger potential of exfiltrating groundwater. |
(Image: Sewer blockage caused by deposits [FI-KMG])
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(Image: Blockage of a sewer due to dropped in items [FI-KMG](KMG Deutschland))
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Positional deviation is understood to be the unplanned deviation of sewers and structures from a nominal position determined by planning and/or by the situation during construction. | (Image: Positional deviation in the vertical direction [FI-KMG])
| | (Image: Positional deviation in the horizontal direction [FI-IfK])
| (Image: Positional deviation in the longitudinal direction [FI-IfK])
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Possible causes of positional deviations can be [ATVM143-1:1989] - Incorrect planning and construction work;
- Hydro-geological changes;
- Load changes;
- Settling;
- Subsidence [Hollm85] [Meißn76] [Schil81] and earthquakes;
- As a result of leaks .
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The consequences of positional deviations on the sewers depends on the type of pipe - pressure pipe or gravity flow pipe - and on the pipe-soil-system - inflexible or flexible - or on the type of pipe joint - rigid, tensile stiff or flexible. (Image: Longitudinal crack in the region of the pipe joint resulting positional deviation with reference to [Young84] [Image: S&P GmbH])
The most common causes of damage resulting from movement associated with … |
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| (Image: Tilting channel experiment to DIN 19565 - Surface of a concrete pipe after 100000 changes of load)
According to [DIN50320], wear is the continuing loss of material from the surface of a solid body due to mechanical action, i.e. contact and relative movement of a solid, fluid or gaseous counter body. In the case of sewers, the wear process takes place in the region of the wetted pipe inner surface and here mainly in the region of the invert. … |
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(Table: Overview of tribological stresses in sewers during operation in accordance to with [DIN50323-2] [DAfStB468]) |
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As already mentioned, mechanical wear causes the removal of the piping material from the inner wall surface. The consequences of the damage [ATVM143-1:1989] are: - Increase of the roughness of the walls with, for example, reduction in the hydraulic effectiveness;
- Reduction of the wall thickness (reduction of the bearing strength and watertightness ).
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(Image: Reduction of the pipe wall thickness due to wear (determined in the mechanical rocking abrasion … |
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