Sewer systems are constantly or intermittently subject to differing physical, chemical, bio-chemical and biological stresses.

Depending on

• Planning
• Material
• Construction
• Maintenance
• Type and duration of use
• External influences such as ground at the construction site, traffic loads, etc.,

these stresses can lead sooner or later to the depletion of the originally available wear reserve of 100 % (Bild 2.1) (Abschnitt 4.1) [ATVM143-1:1989] [ATVM143-2b].

Leaks are present when water obviously enters or leaves or when a test for leaks (Abschnitt 4.5.1) is not successful.

According to [ATVM143-1:1989], leaks can occur with or without recognisable other damage in

• Pipe joints (Bild 2.2.1) or component or structural joints;
• Pipes or pipe walling;
• Connections to pipes (Bild 2.2.1) ;
• Manholes or other structures of drain and sewer systems.

(for types of pipe joints (Abschnitt 1.7.1) ; requirements see DIN 19543) [DIN19543:1982]

• Missing or incorrectly inserted gasket ring (Bild 2.2.2.1.3.1) (Bild 2.2.2.1.3.1) (Bild 2.2.2.1.3.1) (Bild 2.2.2.1.3.1).
• Incorrect application of sealing materials, e.g. on to dirty or incorrectly prepared socket areas.
• Working of sealing material or media at too high or too low temperatures.
• Incorrectly and not centred abutment of pipes, e.g. by using unsuitable …

• Inflexibility of the connection of the sewer/ structure, for instance in the region of the manhole (Abschnitt 1.8) (Abschnitt 2.4.1).
• Joining the lateral by means of caulking the sewer. Especially in the non-man-accessible, earlier hardly controllable nominal size range, many laterals were connected to the previously caulked sewer. It is impossible to achieve a permanently watertight and flexible joint with this method. In addition, there is the …

The main cause of leaks is the result of construction work that is not carried out in accordance with the recognised rules of the technology. Thus, in many cases for instance, the sewers often had to undertake the additional duties of a land drainage pipe.

Among others, this was achieved by using pipes with half sockets (Bild 2.2.2.1.3) (Bild 2.2.2.1.3) (Bild 2.2.2.1.3) in which the gasket in the region of the crown was also purposely dispensed with.

The selection of materials and components were, and are, strongly characterised by their respective stresses as well as by the current state of the technology.

Thus, one can assume, for instance, that the sealing materials used earlier (Abschnitt 1.7.1) such as clay, cement mortar, poured asphalt and cold-worked sealers (Bild 2.2.2.1) (Bild 2.2.2.1) no longer meet today's requirements and, if not already replaced, contribute, in a not unsubstantial …

In professional circles the theory was long maintained that seepage of the sewage could not occur because leaks block or seal themselves due to the solids in the sewage [Stein88g].

Another theory is that the exfiltration of sewage from leaking sewers is a desirable and environmentally friendly component of wastewater disposal. The reasoning behind this points to the earlier usual targeted seepage of a portion of the communal sewage and the almost …

If leaking gravity flow sewers or structures of drain and sewer systems are constantly or occasionally in the groundwater (Bild 2.2.3.1), then groundwater infiltration will occur (Bild 2.2.1) (Bild 2.2.1) whereby, at the same time, soil material from the embedment can be flushed in.

Infiltrating water belongs to the category of extraneous water and is thus an unwanted portion of the wastewater to be discharged [ATV82] [Graf84] [Klass85] [Liers85].

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.

Properly integrated components such as reducers, throttling or back-up flaps do not constitute discharge obstructions in the sense of a damage.

Typical flow obstacles often found in practice are [ATVM143-1:1989] :

• Hardened …

The causes of obstacles that project can be:

Poles that enter or pass through the sewer, anchor rods (Bild 2.3.2.2) (Bild 2.3.2.2), injection lances, drillings, among others during building work in the course of the sewer run. The most common projecting flow obstacles are laterals of buildings, properties and street run-offs (Bild 2.3.2.2) (Bild 2.3.2.2) (Bild 2.3.2.2).

Next to deposits, the ingress of roots (Bild 2.3.2.3) (Bild 2.3.2.3) into sewer systems presents a further common form of flow obstacles, although root resistance of all piping materials, sealing media and gasket rings, as well as of the complete pipe joints, has been a requirement of all the effective standards since the …

(Image: Sewer blockage caused by deposits [FI-KMG])

Possible consequences of damage caused by flow obstacles in sewer systems according to [ATVM143-1:1989] are:

• Reduction of hydraulic capabilities;
• Blockage (Bild 2.3.3) ;
• Increase of the maintenance effort.

Furthermore, depositing, according to [Rüttg87], leads to the following disadvantages and damage:

• The deposits and backed up water volumes reduce the usable sewer back up space.
• With strong rainwater …

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.

With sewers, one differentiates the positional deviation according to [ATVM143-1:1989] between:

• Vertical direction (e.g. displacement) (Bild 2.4.1) ;
• Horizontal direction (Bild 2.4.1) ;
• Longitudinal direction (Bild 2.4.1) (Bild 2.4.1).

(Image: Possible positional deviations of manholes)

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 (Abschnitt 2.2.1).

Further causes for settling differences between manholes and pipes are, for instance, [ATV82] (Bild 2.4.2) :

• Due to high ground pressure as a result …