Rainwater Drainage

Are you aware of the legislation that came into force on 1st October 2008 which affects the drainage of front drives? www.communities.gov.uk/ publications/planningandbuilding/ pavingfrontgardens gives government advice on driveway planning which you may find useful.

Front drives larger than 5 square metres are no longer allowed to discharge water onto the public road or into the domestic drainage without planning permission.

If you don't want to apply for planning permission at a cost of £150, the drive must be constructed of porous paving or a system such as channel and drain used to catch all surface flow and discharge it to a soak away or other SUDS compliant facility.

The following drive collected all the water and drained it to climbing roses alongside the drive. Even though the subsoil is clay, there has been no complaints of the system getting overloaded during the last 16 years.

Gravel Stabilisation System nidagravel product is a unique gravel stabilisation system that transforms loose gravel driveways and access areas into a firm gravel surface. The gravel stabiliser provides an excellent low maintenance finish that is ideal, not just for cars and bicycles but also for disabled, wheelchair and pushchair access to private, public and commercial premises. The base sheet of polypropylene honeycomb is filled with gravel to achieve a stabilised gravel surface. With an appropriate sub-base, this system will support vehicles weighing up to 100 tonnes.

I have used this product for paths, driveways and patios. In order to provide a patio without losing a section of lawn, I have laid Plantex with NidaGravel on top, filled it with loose earth, watered it, spread grass seed, filled again with earth and watered it. It then became a lawn that outside chairs and tables could be laid on without deforming this new lawn.

Drive Foundations

If the foundation for a drive is incorrect, then vehicular access can deform it. If there is no foundation under a pedestrian path or patio, the surfacing layer can be raised/lowered by the weather.

Spon's Landscape Handbook provides an overview for those involved in landscape planning, design, construction and management:-

The layers of material that make up a full-scale road are:-

Substrate or Subgrade: natural or engineered ground level.

Sub-base: main structural and levelling layer.

Road Base: secondary structural and levelling layer ( not usually neccessary in domestic drive, pedestrian path or patio work)

Surfacing: the finished surface that carries the traffic.

 

 

Substrate

When dealing with sub-bases, the soil (substrate) can be divided into 6 types and 2 categories depending on the level of the water-table. Each type and category is given a California Bearing Ratio percentage number (CBR). A geotextile (like Plantex) filter membrane should be laid between the substrate and the sub-base.

See below this plan and photos for remainder of this technical note.

Concrete and rainwater soakaway trench excavated. Weatherboarded fence removed.

The perforated drainage pipe was surrounded by 8mm peashingle (supplied by Allsand Supplies Ltd), which was enveloped in Plantex (Plantex is a geotextile used to separate materials from combining with each other and is available from Travis Perkins builders merchants). 6 Gully covers with chamber risers filled with planting compost were placed on top of this drainage pipe, so that the climbing roses inserted in that compost would have a water supply from below.

Clay excavated. Perforated Drainage pipe installed in trench with 1:40 fall from garage to drive entrance.

Concrete edging and foundation was installed

Concrete edging was installed to stop the sand from migrating. It was haunched with concrete on each side for strength. 6" deep of Type I Roadstone was placed on top of Plantex as foundation. The fence was created and installed by Jacksons Fine Fencing to my specification. I installed the gree plastic coated chainlink fence to provide a climber support system for the Zephirin Druin thornless climbing roses.

Zephirin Druin climbing rose installed in planting compost and mulched with peashingle.

Small Child-proof side gate and path installed by Jacksons Fine Fencing.

Coarse Sand was laid and compacted before the pavers were installed, kiln dried paving sand was used to fill the gaps between the pavers and these were then vibrated down.

The completed drive.

The completed drive in June of the following year

Sub-base

The sub-base is the main layer of material that forms the structural foundation for the drive, and establishs the pedestrian paving or drive level. For domestic use, the sub-base material alternatives are: a solid concrete base, a cement bound sub-base, or a granular sub-base.

A granular sub-base as used for this drive (and I use under paths and patios as well) consists of aggregate to the specification of Department of Transport Type I. I use the crushed rock alternative, which must pass a 75mm sieve, and be free from dust or any pollutant such as oil or other chemicals.

The thickness of the sub-base is determined by using the California Bearing Ratio percentage number (CBR) from the table below in the

Estimated sub-base Thickness Table.

Soil Type

Plasticity index

CBR for Water-Table more than 600mm down

Heavy Clay

70

2

2

Silty Clay

30

4

5

Sandy Clay

20

6

7

Silt

...

2

2

Sand

...

30

30

Sandy Gravel

...

60

60

2

230

4

160

6

120

7% and over

100

I used a 150mm thick sub-base for average clay conditions, then 50mm thick of compacted sharp washed sand complying with Table 2 of BS 6717 Part 2 (BS is British Standard) followed by laying 60mm thick concrete pavers on top. These were then vibrated down with 6 bags of dry paving sand to lock the pavers together.

Construction Notes:-
19 cubic yards of clay, concrete and fence required 6 six cubic yard skips. These are currently £151 each.

These materials had to be excavated by hand and removed by wheelbarrow due to the clay main drain 6" below the concrete surface, with brick manhole walls, lead mains water pipe alongside the house wall and yellow gas pipe across the drive and 1 foot below and no access allowed from next door's drive.

Instead of using 10" wide joists as a skip ramp, I would recomend the use of Load-Eze for safety reasons.