Subsurface drains

A subsurface drainage system in PVC means a non-structural drainage element used to "drain" and therefore "improve" ground subject to landslip.

The functional element of the subsurface drainage system in PVC is composed of:
- PVC tubing of various diameters with microscopic holes covered in non-woven material.
- The possible cementation of the circular gap at the head of the drain.

Fields of application

The use of perforated drainage tubes is indicated in all situations in which an excess of water causes the ground to subside or reduces the resistance characteristics.
The most classic case, which is by far the field of widest application of drainage tubes, is the stabilization of natural and artificial slopes.
A series of tubes are inserted in the ground at suitable positions below the surface (with an incline of 1+2%), with artificial channels at the lower end to collect the water which filters through the tubes. An intervention of this type can resolve various problems of earth slope and building instability.
In more complex cases of instability, for example in the creation of very steep artificial slopes, subsurface drains can be used together with other surface and subsurface drainage work (trenches, sumps, galleries/shafts) and with consolidation and support works (walls, buttresses, stays).
PWhen stability is ensured essentially by support works, subsurface drains perform the important function of not allowing the interstitial water pressure to rise above a certain level uphill from the support works.

Means of execution

- drilling: drilling using a rotary percussion head or rotary head with diameters Ø variable from 100 mm to 200 mm with a drilling rig and with or without a temporary lining according to the stability of the walls of the bore hole. The tools used are continuous flight augers, jackhammers or triple blade, triple cone or tipped cutters with pointed tools in widia (bits) and with the possible use of temporary linings to prevent the bore hole from breaking up. The bore hole is cleared by using compressed air or by a mechanical conveyor in the case of a continuous flight auger.
laying of the PVC tubes: of suitable diameter from 1" to 3" or 4"; the tubes have microscopic holes protected by a cladding of non-woven material (NWM).

Depending on the diameter of the bore hole and the PVC drainage tube we can determine the following table:

Bore hole ( mm )

PVC drainage tube ( “ )

100 – 130 mm

1”; 1”1/4; 1”½; 1”3/4; 2”

130 – 160 mm

2”1/4; 2”½; 2”3/4; 3”

160 – 200 mm

3”1/4; 3”½; 3”3/4; 4”


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