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Last updated 7 January, 2014
draindmain.com > site map > drainage system parts > dropshafts
Drainage Dropshafts
A drop shaft is a vertical length of pipe work taking a drain or pipe down to the level of a deeper drain, pipe or sewer, given that most of the early systems were hand dug it is no surprise that they took the path of least resistance. So a drain running from a property would be installed at the minimum workable depth before passing through a drop shaft which would take the waste or storm water down to the level of the main line drainage.
The image to the right shows a vertical drainage line as it enters a drop shaft and then discharges into a main sewer through a lateral junction, though it is not uncommon to find drop shafts discharging directly into the crown of a sewer dependant on its size, construction and age.
If the drop shaft is prior to a particularly deep sewer several properties at a time would be connected so as to save on pipe work, labour and unnecessary deep excavation works, the top of the drop shaft would be either a 90 degree bend as shown or a square junction would be installed with the shaft being extended up to surface level for future access.
These shafts are not confined to connections onto main sewers and they are often found around domestic properties, a typical property with a cellar will have a deep drain run from a cellar gully running directly into a main sewer, all the ground level gullies and toilet runs would then be installed at a minimum depth before entering the deeper drainage via a shaft within the boundaries of the property.
Its not uncommon to find drop shafts on properties without cellars if the main line drainage from the house is a metre or so deep waste and storm water gullies at ground level will often outfall directly into a small shaft before discharging
into the main run as shown in the image to the right.
Problems Associated With Drainage Dropshafts
From a drain clearing point of view they are restrictive to drain rods as you typically have a 90 degree bend at the top and base of the shaft, drain jetters and mechanical rods however should pass through the shaft easily enough.
Structurally drop shafts are prone to the usual defects such as root ingress, undue loading from vehicular movement and its common to find the back of the top bend broken and damaged from somebody attempting to get a set of drain rods around that first bend.
If the shaft is prior to the connection onto a main sewer beneath a highway or road this can cause major problems, the sheer weight of the shaft along with vehicle movement and any water loss or soil erosion can cause the shaft to drop, often leaving the rest bend at the base of the shaft lower than the level of the sewer.
Repairing Defective Dropshafts
If a shaft is accessible from a manhole and the problem is due to root ingress of fracturing then there are a couple of drain relining methods available, if however there has been severe movement then excavation is often the only answer.
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