6 Materials and product

6.1 General

6.1.1 Vertical drainage involves the use of prefabricated drains and/or sand drains.

NOTE A variety of prefabricated drains exists on the market. Most of them consist of the core and a geotextile filter.

6.1.2 Prefabricated drains consisting of a core and a geotextile filter are subjected to CE marking. The following specific properties shall be given.

  • a) tensile strength, in kN according to EN ISO 10319;
  • b) elongation at maximum tensile force, in % according to EN ISO 10319;
  • c) tensile strength of filter, in kN/m according to EN ISO 10319;
  • d) tensile strength of seams and joints, in kN/m according to EN ISO 10321;
  • e) velocity index of filter (vh50), in mm/s according to EN ISO 11058;
  • f) characteristic opening size of filter (O90), in µm according to EN ISO 12956;
  • g) discharge capacity of the drain, in m3/year according to EN ISO 12958 (see also Annex A);
  • h) durability, in years (EN 13252:2000, Annex B).

NOTE The dynamic perforation resistance (cone drop test, EN 918) as mentioned in EN 13252 is not compulsory for this application.

6.2 Raw materials of prefabricated drains

6.2.1 A prefabricated drain usually comprises a geotextile or geotextile-related product.

6.2.2 The product is used in applications that do not involve reinforcement of soil and where long-term strength is not a significant parameter and in natural soils with a pH-value between 4 and 9 and at a soil temperature less than 25 °C according to EN 13252. A service lifetime of up to 5 years is applicable.

6.2.3 The use of 5 % internal regenerate (e.g. raw material made out of unused core) for the production of the core is permitted. The composition should be known and the material be processed in the same way as the original product. The use of recycled material is only permitted provided that it can be verified that it is not causing pollution of the soil or ground water.

6.2.4 Materials used to manufacture the drains shall not cause pollution of the soil or the groundwater.

6.2.5 Biodegradable drains can be used if they fulfil the drainage requirements during the lifetime of the project.

6.3 Band drains

6.3.1 Shape and structure of band drains The band drain is a prefabricated drain with a rectangular cross-section, usually consisting of a central core with a channel system surrounded by a filter. The width of the core of the band drains is typically 100 mm and the thickness is between 2 mm and 10 mm. The core should consist of a profiled strip, with or without perforation, or a profiled mat with an open or closed structure. It should have a structure that provides regular hydraulic flow capacity. Tears and/or other defects shall not be allowed to occur. Visual inspections for damage shall be made regularly as part of the production quality control.

6.3.2 Measurements The roll length, width and thickness of the core at any given place should comply with the dimensions given by the manufacturer (within allowable deviations given by the manufacturer). See accompanying document for CE-marking (EN 13252). The measurements should comply with EN ISO 9863-1.

6.3.3 Durability The durability of the drain shall comply with the durability aspects given in EN 13252 (weathering, required service lives up to five years or more when the drains are installed to mitigate soil liquefaction). The drains should be protected against weathering during storage on the site. The product shall not be exposed longer than the time announced by the producer for CE Marking (EN 13252) unless the product is protected by a wrapping material or stored in-house. The recommendations of the supplier shall be followed.

6.3.4 Tensile strength and elongation The required tensile strength of the band drain is very dependent upon the type of installation machine, installation technique and depth of the drain. Tensile strength of the band drains in the longitudinal direction shall be high enough to prevent breakage during and after installation. Testing of tensile strength and elongation of the band drain should be made in accordance with EN ISO 10319 (to be modified with regard to the width of the product). The following characteristics of a band drain are recommended:

  • a) elongation ≥ 2 % at failure of the weakest element;
  • b) elongation ≤ 10 % at a tensile force of 0,5 kN (20 % if exposed to frost);
  • c) minimum tensile force > 1,5 kN at failure of the weakest element. The seam should not fail during the test.

NOTE These values depend on the installation equipment and procedure and may need to be adjusted accordingly. The strength of the seam, measured according to EN ISO 10321 in a range of temperatures, which apply to the project site, shall be at least 1 kN/m.

EN 15237:2007 Execution of special geotechnical works — Vertical drainage