Specification Part 3 - Road & Bridge Works - Urban Administration ...

706 GEOSYNTHETICS FOR HIGHWAY PAVEMENTS
706.1 Scope
This work shall consist of furnishing and placing geogrid over existing subbgade or subbase or within
the base layer in accordance with the lines and grades shown on the plans or as directed by the
Engineer. Base/Sub base reinforcement in properly designed paved roads, occur when a geogrid is
placed at the subgrade/subbase interface to provide improved subgrade support for the roadway
structural section; to extend the service life of flexible pavement and/or; to allow the use of a reduced
base section. The selection of the type of geogrid and its strength characteristics shall depend upon the
design of pavement with geogrid reinforced highway pavements.
706.2 Materials
Polymers used in the manufacture of geogrids shall consist of long-chain synthetic polymers, composed
of at least 95 per cent by weight of polyolefins, polyesters or polyamides. They shall be formed into a
stable network such that ribs, filaments or yarns retain their dimensional stability relative to each other
including selvages. The aperture size of geogrid may vary from 25 mm to 50 mm. The per cent open
area of the geogrid shall be minimum 70 percent. The following specifications may be used for Geogrid
for use as reinforcement of base or sub base layers of flexible pavement structures. The values given in
Table 700-6 are default values sufficient from survivability point of view. However, the designer may
specify values other than specified based on design. 706.3 Certification The Contractor shall provide
the Engineer, a certificate stating the name of manufacturer, product name, style number, chemical
composition of the product and other pertinent information to fully describe the geogrid. The certificate
shall state that the furnished geogrid meets MARV requirements of the specifications as evaluated
under the manufacturer’s quality control program. The certification shall be attested by a person having
legal authority to bind the manufacturer.
Table 700-6 Requirements for Geogrid for Sub-Base/Base of Flexible
Pavements
Property
Tensilestrength
@1% strain
Tensilestrength
@2% strain
Tensilestrength
@5% strain
Tensile modulus
@5% strain
Junction Efficiency,
% of rib ultimate
tensile strength
Ultraviolet stability
(after 500 hrs)
Test
Method
Required value,kN/m
Machine CrossDirection Direction
ASTM D6637 4.3 6.6
ASTM D6637 7.3 10.9
ASTM D6637 13.4 19.7
ASTM D6637 437 656
ASTM D4355 70%
90 90
Note 1) All numerical values in the Table represent MARV in the specified direction.
2) All geogrids shall be placed along machine direction parallel to the centre line of roadway
alignment.
3) Junction strength is required to maintain dimensional stability of the geogrid during
deployment. It is not applicable to geogrid/geotextile composite products.
706.4 Installation
All areas immediately beneath the installation area for the geogrid shall be properly prepared as
detailed on the plan and, as per these Specifications or as directed by the Engineer. The geogrid shall
be installed in accordance with the manufacturere’s recommendation. The geogrid shall be placed
within the layers of the compacted soil as shown on the plans or as directed by the Engineer. If the