Whilst only the wetted sewer region is affected by the corrosion resulting from the direct effect of aggressive sewage, the effects of biogenic sulphuric acid corrosion, that is, the microbiological processes, will only be found in the gas space, i.e. above the water level .

The possible consequences of damage resulting from corrosion depend substantially on the type of corrosion, its manifestation and extent and, according to [ATVM143-1:1989] are

• Leakiness
• Reduction of the wall thickness and thus its accompanying reduction of bearing strength with the possible consequential damage of cracks, deformation, pipe break, collapse.

According to the definition in ATV-A 127E [ATVA127a], taking into account EN 1610 [DINEN1610:1997] and EN 1295 [DINEN1295-1], one distinguishes flexible sewage pipes from rigid pipes as follows:

"Rigid pipes are those in which the loading does not produce any appreciable deformation and therefore has no effect on pressure distribution."

"Flexible pipes are those whose deformation considerably influences the loading and pressure distribution as the …

Deformations in the sense of damage can be caused by [ATVM143-1:1989] :

• Non adherence to the standards and regulations (e.g. EN 1610 [DINEN1610:1997] or ATV-A 127 [ATVA127a]), for instance by:
  • Missing or incorrect statics calculations;
  • Laying of unsuitable or defective pipes;
  • Deviating from the load and/or support conditions of the calculation assumptions [ATVA241:1994] ;
  • Unprofessional laying and/or bedding, poor annulus grouting with a trenchless …

The possible consequences of damage of deformation are, according to [ATVM143-1:1989] :

• Reduction of the hydraulic effectiveness;
• Blockages;
• Increase of the maintenance effort;
• Crack danger for form pieces at those points that, due to formed branches, kinks, etc. are stiffer than the unstiffened pipe;
• The danger of bulges with very large deformations;
• Tension crack deformation;
• Leaks;
• Cracks;
• Pipe break;
• Collapse.

The "cracks" type of damage occurs primarily in rigid piping, whereby distinction is made between three main forms which can be the precursors for the pipe break and, finally, for the collapse of the sewer [ATVM143-1:1989].

• Longitudinal cracks;
• Lateral cracks;
• Cracks originating at a point (in some cases also with pipe fracture).

Of the main forms of cracks mentioned, the ones that occur most often in rigid piping are longitudinal cracks .

In most …

Irrespective of the type of crack, the following are mentioned as causes [ATVM143-1:1989] :

• Non-adherence to the standards and regulations, e.g. EN 1610 [DINEN1610:1997], ATV-A 127E [ATVA127a].
• Damage to the pipes during transport, storage, laying, bedding, backfilling or compacting.
• Effects of wear.

Besides the causes mentioned above, lateral cracks can occur especially due to [ATVM143-1:1989] :

• Impermissible influences of individual loads (point loads, supported by the socket, stones in the embedment).
• Inflexible connection to structures.
• As a …

The most important causes of damage for cracks originating at a point which can lead to pipe fracture, besides those mentioned above, are:

• Impermissible influences of individual loads (point loads, supported by the socket, stones in the embedment).
• Incorrect connections of the lateral due to caulking the sewer.
• Extreme …

All shapes of cracks, with the exception of the lateral cracks, carry with them a priori the danger of loss of stability, whereby the time of total failure (collapse) depends on some of the influencing factors mentioned above and can therefore not be predicted with accuracy [Flatt83] [Trott80].

Under advantageous conditions, e.g. small width of crack, no groundwater, good bedding, constant operating conditions (no overloading / flooding), a pipe …

Pipe break is understood to be the missing of more or less large pieces of the pipe walling .

Collapse is understood to be the complete loss of carrying capacity connected with the destruction of the respective component .

A pipe break is caused by an additional malfunction or changed internal or external loading of an already damaged pipe having a crack or being fractured. Furthermore, according to [ATVM143-1:1989], it occurs due to leaks, mechanical wear, corrosion and cracks.

A collapse is the final phase, and the one with the most serious consequences, in the development of the following damage over a period of time.

• Leakiness .
• Mechanical wear .
• Corrosion .
• Deformation .

All cracks that have penetrated through the pipe, thus also the lateral cracks and pipe breaks, are a priori points of leaks with the consequences as mentioned in .

Due to the in- or exfiltration connected with this, the bedding conditions of the affected pipe region are changed so that position deviations connected with new formation of cracks or further deformation of the cracked pipe up to collapse can occur .

The fragments that have fallen into …

The filling, e.g. the injection and soaking of cracks in man-accessible sewers and structures of drain and sewer systems extends exclusively to the materials of concrete, reinforced concrete or brick masonry because of the large nominal sizes.

The filling of cracks must be undertaken when one or more of the following aims are to be achieved [Verkehra] :

• Reducing …

The process that is applied for the filling of cracks is differentiated according to the pressures used for inserting the filler into the crack as follows:

• Soaking (S): filling without pressure to close the crack;
• Injection (I): filling under pressure using filling nozzles (injection packers) for all the application purposes mentioned above.

The filler materials for both types of filling are mostly epoxy resins (EP) and polyurethane resins (PUR).

According to [Verkehra], crack fillers must possess the following properties:

• Sufficiently low viscosity;
• High degree of capillary attraction (for reaction resin);
• Good workability;
• Sufficient mixing stability;
• Low shrinkage caused by the reaction;
• Sufficient adhesive strength at the edges of the crack;
• Sufficient strength or expanding strength;
• High degree of ageing resistance;
• Freedom from corrosion producing components;
• Compatibility …

The successful application of the individual processes depends on the degree of moisture and the degree of contamination of the cracks.

In [DAfStBb] [Verkehra], four conditions of moisture are defined in greater detail as:

• "dry",
• "moist"
• "water flow without pressure and
• "water flow under pressure" .