Ingrown roots
Root ingrowth is a biological process that can take place in supply or disposal lines, such as sewer pipes or sewer manholes . Root ingrowth occurs because roots within lines and their pipe connections have space available that is not available in the backfill and bedding material of the lines due to its compaction.
The basis for the occurrence of root ingrowth is the presence of the root cap cells of the root tip and their reaction to the soil conditions occurring at the respective place of growth . The cell walls inside the root cap partially dissolve, the cells lose their cohesion and can be moved against each other. The root tip is therefore not a rigid drill, but has a soft, gelatinous tip. The root tip is pushed into the substrate by the root pressure from the initials. By sliding the root tip on the canopy cells, the root tip acts like a hydrostatic drill that is driven into the pores between soil particles. The root cap forms and widens a canal into which theRoot is forced into it. The path of the roots to the pipe is determined by the fact that the elastic root cap is changed in shape as the roots grow through the soil. The root cap and thus also the root is deflected in the direction from which the root is exposed to the lowest pressure from the soil particles. The root creates space where the surrounding soil is most flexible. Earlier specialist literature (up to approx. 1999) wrongly assumed that the root's search for moisture or nutrients was the sole cause of root ingrowth.
Ingrown roots in urban agglomeration
The surface sealing in the urban environment can have the consequence that the entry of oxygen into the soil is reduced. Like all parts of plants, roots are dependent on a functioning respiration ( oxidation ) of carbohydrate-rich compounds for energy production. The required oxygen is in a natural soil structure in the soil air and can be taken up there by the roots. By compaction of a soil at its pore space and the amount of oxygen contained therein decreases. The growth of roots in pipes is prevented by low-pore filling materials such as flowable filling materials, which in the case of a product are referred to as liquid soil .
Technical background
The most common technical solution for connecting sewer pipes is plug-in connections. In this system, the spigot ends of the pipes in question are connected to the socket of the next pipe or to separate sleeve sleeves . Compared to other systems, they offer the advantage that they are comparatively easy to manufacture even under difficult construction site conditions. Lines affected by ingrown roots were usually laid underground by digging a trench, then backfilling and compacting the backfill material introduced [DIN EN 1610]. Due to the geometry required for the plugging together, an annular gap remains in all plug-in connections, which forms the entry opening for roots into the annular space behind. In the case of glued or welded pipe connections, as are typical for supply lines, for example, ingrown roots only rarely occur because the annular gaps that occur in this case are not accessible due to the gluing or welding work. In general, however, root ingrowth can also occur with glued and welded pipe connections.
Testing of root resistance according to DIN 4060 / DIN EN 681
From a technical point of view, all pipe connections sold in Germany today are resistant to root ingrowth. In Germany, the resistance to roots of pipe connections is considered to be proven in accordance with DIN 4060 if the pipe connection passes a tightness test under shear load in the event of overpressure or underpressure. The mechanical properties of the seal are tested in accordance with DIN EN 681. However, the geometry of the seal and the resulting influence on the contact pressure generated in the pipe connection are not taken into account. Biological aspects are not taken into account when assessing the strength of the roots, so that only highly idealized mechanical methods are used to verify the strength of the roots in pipe connections. The test criteria described in DIN 4060 are to be regarded as minimum requirements. Depending on the pipe materials and their pipe connection or load class, the same or higher requirements exist in further pipe standards than in DIN 4060.
Consequences of root ingrowth in sewer pipes
Roots grow into the annulus and ultimately into the line cross-section of the lines concerned. Root cushions (obstacles to drainage), leaks, breaks and damage to the pipe can occur as a result of root ingrowth in sewer pipes . The error-free operation of the sewage system in question is no longer possible in many cases, since the growth of the roots continues as long as the tree in question continues to grow .
Mechanical removal of root ingrowth
In accessible canals, roots can be removed manually. The ingrown roots are removed using tools ( chisels , knives or spades ). Mechanical processes are used in non-accessible canals. Roots usually protrude from the pipe connections into the cross-section of the respective pipe. In many cases they have grown through the pipe connection in the area of the apex and remain fixed there. The roots hang down in the form of a curtain in the pipe. They can be removed with the help of rotating tools such as chain knives or milling machines. The mechanical removal of ingrown roots is suitable for removing acute problem areas (blockages in sewer pipes). Renewed growth is stimulated by severing roots during mechanical root removal. The only permanent solution to the problem is the removal of the ingrown roots in connection with a professional rehabilitation of the pipe concerned.
Chemical removal of root ingrowth
The removal of ingrown roots in sewer pipes is possible with the help of herbicides , but not permitted in Germany.
Avoidance of root ingrowth
The connections between root growth and the conditions on underground lines were first described in a research report. Roots not only grow into pipe connections that are not tight according to the state of the art, but they also overcome “tight” pipe connections and the hypothesis “If a pipe connection is tight , then it is also root-proof” does not apply. Soil areas with few pores, such as those created by the installation of flowable backfill materials, cannot be penetrated by roots. The targeted installation of low-pore filling materials can prevent ingress of roots on pipes or manholes. As a rule, roots grow preferentially in areas that can easily be penetrated by roots. These areas meet the needs of the roots in terms of water availability (soil water), oxygen supply (soil air) and low mechanical resistance (soil structure). Root growth is optimal when these requirements are met. Roots, which find ideal conditions at the location of the tree, do not grow into the pipeline and thus do not lead to ingrown roots.
literature
- Th. Stützel; B. Bosseler, C. Bennerscheidt, H. Schmiedener: "Ingrown roots in sewage pipes and sewers", final report. IKT - Institute for Underground Infrastructure, in cooperation with the Chair of Special Botany at the Ruhr University Bochum with the participation of various NRW network operators on behalf of the Ministry of the Environment of North Rhine-Westphalia (MUNLV), August 2004.
- Th. Stützel, M. Straßenbach, B. Bosseler, C. Bennerscheidt, H. Schmiedener: "Ingrown roots in sewers and sewers - supplementary projects", final report. IKT - Institute for Underground Infrastructure, in cooperation with the Department of Special Botany at the Ruhr University Bochum on behalf of the Ministry of the Environment of North Rhine-Westphalia (MUNLV), June 2007.
- Markus Linienbach: Interactions between roots and underground technical infrastructure - basics and strategies for problem avoidance. (English title: Interactions between roots and technical subterranean infrastructure - fundamentals and possibilities to avoid damage. ) Dissertation, Ruhr-Universität Bochum, 2009 ( PDF file; 14 MB ).
Web links
- IKT - Institute for Underground Infrastructure (research and services on underground infrastructure)