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

strong acid/bases, flames including welding sparks, temperature in excess of 71 0 c and any other
environmental condition that maydamage the geotextile.
Steps to be taken if geotextile roll or protective wrapping is damaged
In most cases, damage to a roll of geotextile is limited to the protective wrapping. If the wrapping is
damaged, proper storage of the geotextile is particularly critical. The rolls must be elevated off the
ground surface and securely covered with a tarpaulin or opaque plastic sheet. If the outer layer of the
geotextile itself is damaged, it is permissible during installation to remove the outermost wraps of the
roll and discard the damaged material. The remaining undamaged material is suitable for use.
Removing the outermost wrap of geotextile is also acceptable when a roll is exposed to sunlight for a
period beyond that permitted by the project specifications. The remaining unexposed material is
suitable for construction. Exposing geotextile rolls to moisture or water prior to installation can lead to
serious handling problems. Non-woven geotextiles in particular can absorb water up to three times their
weight. Further, the cores on which the geotextile rolls are wound are manufactured from laminated
paper. When wet, the strength of these cores is seriouslydiminished to the point where the core will not
support the weight of the geotextile.Consequently, it can be extremely difficult to install wet rolls of
geotextile. In addition, it is nearly impossible to unroll wet, frozen geotextile without first allowing it to
thaw. If geotextile rolls become wet, it is permissible to remove the waterproof cover to allow for a few
days of exposure to wind in order to dry the fabric. It is essential that the rolls be elevated during the
process. It is also possible to remove the protective wrapping from one end of the rolland elevate the
opposite end of the roll. The majority of excess water will then flow out of the geotextile. In most
cases, these procedures will not allow the fabric to dry completely. Once unrolled during installation, the
geotextile will dry very quickly in the sun and wind. However, it should be noted that non-woven
geotextiles used in conjunction with bitumen overlays of existing pavements must be completely dry
prior to installation.
702 GEOTEXTILES IN SUB-SURFACE DRAINS
702.1 Scope
This work shall consist of furnishing and placing a geotextile for the following drainage applications:
edge of pavement drains; interceptor drains; wall drains; recharge basins, and relief wells. The
geotextile shall be designed to allow passage of water while retaining in-situ soil without clogging. The
work shall be carried out as per design drawings. The quantities of drainage Geotextiles as shown on
the plans may be increased or decreased at the direction of the Engineer based on construction
procedures and actual site conditions that occur during construction of project. Such variations in
quantity will not be considered as alternatives in the details of construction or a change in the character
of the work.
702.2 Materials
The geotextile fabric shall be a woven or non-woven fabric consisting of long-chain polymeric filaments
or yarns such as polypropylene, polyethylene or polyester or any combination thereof, formed into a
stable network such that the filaments or yarns retain their relative position to each other. These
materials shall conform to the physical requirements of Table 700-3.
All numeric values in Table 700-3 except AOS represent MARV in the weaker principal direction.
Footnote of this Table 700-3 provides for a reduction in minimum property requirements when sufficient
survivability information is available. The Engineer may also specify properties different from those
listed in Table 2 based on engineering design and field experience.
Table 700-3 Geotextile Requirements for Subsurface Drainage
Per cent in-s
itu soil
passing
0.075 mm
sieve
< 15
15 to 50
> 50
Geotextile drainage property
requirement
Permittivity,
per sec ASTM
D 4491
(Minimum ARV)
0.5
0.2
0.1
Apparent opening
size, mm
ASTM D 4751
(Maximum ARV)
0.43
0.25
0.22
Recommended
geotextile *
Type II from
Table 700-1