Slotted drain rehabilitation

Aprons and taxiways at commercial airports are legally classified as surfaces governed by the Ordinance on Facilities for Handling Substances Hazardous to Water (Verordnung über Anlagen zum Umgang mit wassergefährdenden Stoffen – VAwS). This is why slotted drains which collect precipitation from these surfaces should be checked for leaks and rehabilitated if necessary.

Paved surfaces of airports are, insofar as they are used directly by aircraft, potentially at risk from the emission of substances hazardous to water. This applies in particular to those apron areas on which aircraft are refuelled and de-iced. Drainage systems in surfaces of this nature are subject to particularly strict safety regulations pursuant to the Model Ordinance on Facilities for Handling Substances Hazardous to Water (Muster-Verordnung über Anlagen zum Umgang mit wassergefährdenden Stoffen) and designated as VAwS surfaces. This does not only apply to the structural condition of slotted drains which collect and convey precipitation away. It must be verified that they are impermeable. The technical standard (DIN 19580) contains neither testing nor rehabilitation regulations for slotted drains in operational use.

In order to meet official restrictions, Swietelsky- Faber GmbH Kanalsanierung developed its own solutions for visual inspections, leak testing, damage classification and, where required, necessary rehabilitation.

An initial visual assessment of the structure leads to a classification in damage categories (e. g. cracks continuous slight gaping) highlighted by generalized statements relating to impermeability. The “Cracks continuous closed” and “Cracks continuous slight gaping” categories were subjected to reference leak testing at “typical” positions in each case for the purpose of unequivocal assessment. These leak tests were conducted on the basis of DWA M 143 Part 6 as fluid level testing.

Findings: visually ambiguous crack formations were universally designated as permeable and, consequently, in need of rehabilitation. The basis for the visual assessment and classification was the passage of the PANORAMO digital sewer TV system through the drain, with the findings of an above-surface examination being superimposed over the results of this inspection. The second phase of the slotted drain project involved the development and testing of a practical rehabilitation concept for the positions classified as defective.

While slotted drains with structural damage are in all cases replaced, the remaining cases can be rehabilitated on the basis of damage assessment using fibre inner lining, either locally with glass fibre material or through tubular lining of entire positions. In the case of tubular lining, two synthetic fibre-based tubular liner systems were used in the steam cured installation variant, primarily due to the extremely restricted rehabilitation time window available. The key technical problem in tubular lining of slotted drains is the opening of the slots following rehabilitation. All trials involving robots failed. Swietelsky- Faber therefore developed a laser-supported cutting technique with partner companies. Particular attention is given to the creation of economically viable structural sections through “renovation through lining” and “localised repair”.