1. General

Geocomposite is a generic name used to define a factory-fabricated geosynthetic product consisting of combination of two or more geosynthetic material like geotextiles, geogrids, geonets, and/or geomembranes. The application areas of geocomposites are numerous and growing steadily. They encompass the entire range of functions performed by geosynthetics: separation, reinforcement, filtration, drainage and containment.

2. Application of Geocomposites

Geocomposites, consisting of a geonet bonded with geotextile layer(s) on one or both sides (Fig.01) are used for drainage from a basal layer in case of embankments and for drainage behind retaining walls and/or bridge abutments. They have very high in-plane drainage capacity vis-a-vis cross plane drainage, thereby making them highly suitable as drainage elements.

Fig. 01 : Typical Geocomposite Drain
2.1 As Basal layer (Horizontal Direction)

In case of embankments over soft soils and in the areas with high water table, it is a good practice to provide a sand layer at the base of embankment (at the junction of subsoil and subgrade). This separator-cum-drainage layer of sand prevents fouling of subgrade with fine grained subsoil, reduces excess pore water pressure in the bank thereby increasing its' stability and ensures uniform distribution of load over subsoil. In areas having scarcity of requisite quality of sand, requirement of sand can be reduced by laying a geocomposite layer, sandwiched between two sand layers of lesser thicknesses (about 75mm each), as basal layer of embankment (Fig.02).

Video on Use of Geocomposite as Basal Layer
Fig. 02
2.2 As Vertical/Chimney Drain

In case of bridge abutment and/or retaining walls, or behind Reinforced Earth Retaining walls, they replace the natural graded filters (consisting of different sizes of boulders and gravels etc.) and also eliminate the need for weep holes in bridge abutment and/or retaining walls (Fig.03, Fig.04 and Fig.05).

Fig. 03
Fig. 04: Geocomposite drain behind Abutment or Retaining Wall
Fig. 05: Geocomposite drain behind Bridge Abutment

As per Railway Board's letter no. 2017/CE-IV/RUB/88 dated 24.09.2018, in lieu of Graded Filter (in the form of boulders/cobbles) on the vertical walls of Road Under bridges (RUB)/Limited Height Subways (LHS)/Subway, geo-composite drains may be used for trial purpose.

Video on Vertical Geocomposite Drain
3. Specifications for Geo-composite Drain
3.1 As basal layer (Horizontal Direction)

RDSO Specifications for Geocomposite Drain to be used at the base of Embankment for Railway Formation, are contained in Specification no. RDSO/2018/GE:IRS-0004 Part-II (March'2019).

Specification no. RDSO/2018/GE:IRS-0004 Part-II (March'2019)."

3.2 As Vertical/Chimney Drain

RDSO Specifications for Geocomposite Drain to be used behind Bridge Abutment/retaining Wall are contained in Specification no. RDSO/2018/ GE:IRS-006 (March'2019).

Specification no. RDSO/2018/GE:IRS-0006 (March'2019)."