When excavation is the right call
- Full collapse, where no host pipe remains to line against.
- A section that has lost its fall and holds standing water.
- Severe deformation where the pipe is well out of round.
- A displaced joint where one length has dropped clear of the next.
- A run that needs rerouting, for example around a proposed extension.
- A new chamber or connection that has to be formed properly.
Why lining cannot cure a fall problem
This is the one people find least intuitive. A liner follows the shape of the pipe it is installed inside. If that pipe dips because the ground beneath it settled, the liner dips too, and the finished repair is a smooth watertight dip that will still hold water and still drop solids in the same place.
The only fix is to dig out that section, prepare a properly compacted bed and relay the pipe at the correct gradient, which for a hundred millimetre foul run is typically around one in forty. That is why a survey noting standing water is a more significant finding than a photogenic crack.
How the work is carried out
The line and depth are traced from the surface first so the dig is as small as possible. Surface material is lifted and set aside for reuse where it can be, turf, slabs and block paving all being worth saving. Excavation is by machine where access allows and by hand as the pipe is approached, since the object is to expose the run without breaking sound pipework either side of the fault.
At depth the excavation is shored or battered for safety. The failed section is cut out, new pipe is laid to fall on a properly prepared bed, and couplings are used to join to the existing sound pipe. Depending on depth and loading, the new pipe is surrounded in pea gravel or in concrete.
Backfill and reinstatement
Backfilling is done in layers and compacted as it goes, because a trench that is simply pushed full will settle within a year and you will get a visible depression exactly where the work was done. Under a driveway, compaction and the correct sub base are what stop the surface failing later.
Reinstatement should be specified in the quote. Turf, block paving, slabs and tarmac all have different costs and different matching problems, and an old tarmac drive in particular will show a patch no matter how well it is done. We are straightforward about that in advance rather than after.
What drives the price
Depth is the single biggest factor, followed by the surface being broken out, access for a machine, the length of pipe being replaced and whether spoil has to be carried out by barrow rather than loaded directly. Proximity to other services matters as well, since gas, water and electricity in the same trench mean careful hand digging.
A short shallow repair in an open garden is at the modest end. A deep repair under a block driveway with no machine access is at the other, and the pipe itself is the cheapest part of either.
Doing it once, and proving it
We survey the repaired run on completion and give you the footage, so you have a record that the new section is laid correctly and running clear. Where the excavation exposed other defects nearby, we will tell you rather than backfill over them, since the expensive part of the job is the hole and it is far cheaper to deal with a second fault while it is open.
We carry out excavation, patch lining and full relining in house across West Lothian, Edinburgh, Falkirk, Lanarkshire and Fife, so nothing is subcontracted and the recommendation reflects the pipe rather than the kit on the van.
Safety and site care
Excavation near services and at depth is the part of drainage work with real risk attached, and it is worth knowing what a competent contractor does about it. Services are located before the machine starts, trenches beyond a certain depth are shored or battered, open excavations are barriered and covered outside working hours, and spoil is kept clear of the edge.
We carry five million pounds of public liability cover and provide risk assessments and method statements on request, which matters particularly on commercial sites and where children or livestock are around. Site care also means protecting the route to the work area, because a repaired drain and a ruined lawn is only half a good job.
Questions we get asked
How deep are domestic drains usually?
Commonly between six hundred millimetres and one and a half metres in a garden, and deeper towards the boundary chamber or shared sewer.
Will you need to close my driveway?
For the working area only, and we plan around access so a property is not left without parking any longer than necessary.
Do I need permission to dig up a drain?
Not for private drainage on your own land, but work affecting a public sewer or building over a run needs agreement with the relevant authority.
Is excavation always more expensive than lining?
Usually, but not always. A short shallow repair in open ground can be cheaper than a full liner and will outlast it in a run with fall problems.