According to Stützel et al. [Stütz2004], pipe joints should meet the following requirements in order to prevent root ingrowth:

• Appropriate counter-pressure of the sealant by using mechanically effective sealants with a high structural safety against external pressure loads

• Repelling geometry of the pipe joint (e.g. use of socket and spigot joints with a lower tendency of gap formation)

• The anti-stick surface structure of the pipes in order to avoid …

Possible causes of defect in the category root ingrowth are:

• non-root-proof sealants or pipe joints
• non-professionally created pipe joints
• fissures (BAB)
• pipe break (BAC)
• defective masonry (BAD)
• missing mortar (BAE)
• defective connections (BAH)
• porous pipe (BAN)

Among the possible consequences of defect caused by roots growing into sewer systems, there exist:

• reduction of the hydraulic performance capacity

• risk of clogging / congestion

• backwater

• infiltration (BBF) / exfiltration (BBG) (leakages)

• increased operating expenditure

Furthermore, ingrown roots can also lead to an increase in the causal damage or a partial destruction of the pipes or structures.

According to EN 13508-2, types of defect categorized into the main code “Attached deposits (BBB)” are also called agglomerations. In accordance with EN 14654-1, agglomerations are defined as material that, due to chemical or physical bonding, adheres to the walls of parts of the drain and sewer system. According to EN 13508-2, depending on the type of attached deposits, agglomerations include:

The defect is always quantified by a specification of the cross-sectional reduction in percent [%]. In addition, the position of defect at the circumference shall be recorded [EN13508-2:2011].

(Table: Encrustation in the area of a pipe joint)

(Table: Encrustation in the area of a pipe joint)

(Table: Encrustation in the area of a connection)

The causes of defect for attached deposits differ depending on the type of attachment.

According to an encyclopaedia [Berte1991], encrustation is defined as “a formation of a crust on top of a natural or artificial object due to chemical depositions from water”. In the given case of application, this always refers to a secondary form of defect that shall be assigned to the causal primary defect in the defect coding process.

Because of the difference …

The following consequences may result from attached deposits, for example:

• reduction of the hydraulic performance capacity

• risk of congestion

• backwater

• increased operating expenditure

DIN EN 13508-2 characterises deposits exclusively according to their material composition as follows:

• Fine material - e.g. sand, silt (code specification A)

• Coarse material - e.g. gravel, rubble (code specification B)

• Hard or compacted material - e.g. concrete (code specification C)

• Other material (code specification Z; further remark supposed to be recorded)

The design of sewer systems to date has been based on the premise that ingress of solids in combined and surface water sewers along with the waste-, precipitation, and infiltration water cannot be prevented. Thus, it is also often inevitable that deposits are formed in sewer systems whenever the limiting velocity of the mixed flow falls below the required value.

Deposits in sewer systems occur whenever a required minimum flow velocity cannot be met …

Deposits have several negative operational effects for the affected drain and sewer networks and all of them also involve economic disadvantages. 

The following cons apply to both the operation and maintenance of sewer systems [SteinR08]:

• Increased expenditure for sewer cleaning measures

• Increase of the risk of biogenic sulphuric acid corrosion (BSC) for partly filled sewers and structures made of cement-bound material with the consequence of reduced …

This form of defect is characterised according to the type of soil that has penetrated:

• Sand (code specification A)

• Peat (code specification B)

• Fine material e.g. clay or silt (code specification C)

• Gravel (code specification D)

• Other (code specification Z; further remark supposed to be recorded)

The following images show the behaviour of silts and sands in a leaking area. When groundwater or extraneous water infiltrates (e.g. from leaking water service pipes in the vicinity), fine soil particles are flushed out for as long as a stable filter has formed on top of the leaking area.

(Video: Erosion behaviour of non-cohesive ground for leaks)

(Image: Erosion behaviour of cohesive ground for leaks with reference to [Jones84a] [Image: S&P GmbH])For cohesive soils (clays, clayey silts, and silts as well as their mixtures with non-cohesive types of soil, given that the weight percentage of the components with particle sizes < 0.06 mm amounts to more than 15 %), the ingress of solids in the leaking area mainly occurs due to soil erosion as a consequence of
internal loads. This phenomenon occurs …

The following consequences of defect caused by the ingress of soil material are possible, for example:

• damaging effects on adjacent pipelines, structures, and road surfaces (void formation, road collapse)

• change in the bedding conditions with consequential types of defect such as Pipe break/Collapse (BAC), Deformation (BAA), or Fissures (BAB)

• deposits up to congestion

• increased operating expenditure