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

applicable to a temperature of 15°C using published data on variation iin viscosity of
water with temperature.
d) have a minimum puncture resistance of 200 N when determined in accordance with
BS:6906 (Part 4) or ASTM D 4833.
e) have a minimum tear resistance of 150 N when determined in accordance with ASTM
Standard D 4533.
703.2.4 The composite drain shall have flow rate through each face of the drain of more than
75 per cent of the value specified in sub-Clause 702.2.3.(c), determined by direct measurement of the
composite drain using BS:6906 (Part 3). The composite drain shall have values of long-term in-plane
flow rates as stated in the design
703.3 Installation
The installation of fin drains shall be as per the design drawings. Where fin drains are assembled on
site, the assembly area shall be clean and dry and free of any wind-borne pollutants. No geotextile or
core material shall be exposed to daylight (or any source of ultraviolet radiation) for a period exceeding
a cumulative total of 50 hours. Where fin drains are laid in trench, the bottom of the trench shall be free
of irregularities and shall be brought to the required level. Rock and other hard protrusions shall be
removed and any excess cut in the trench bottom filled and compacted back to the required grade with
suitable excavated or imported material as directed by the Engineer. Fin drains shall be capable of
being jointed longitudinal or laterally into pipe systems or chambers for inflow and outflow purposes.
Joints parallel to the direction of flow and any exposed edge shall be protected from the ingress of soil
by a geotextile wrapping with a minimum overlap of 150 mm or other measures as agreed by the
Engineer.
703.4 Narrow filter drains consisting of a porous or perforated pipe and in a narrow trench surrounded
by a layer of geotextile filter shall have the same properties of geotextile as specified in Clause 703.2.
The spicing of lengths of geotextile and minimum overlap shall be as per the design drawing or as
approved by the Engineer. Such drains shall be installed as per the design drawing to Clauses 703.3
and 309.3.5. 703.5
Measurement for Payment
Measurement for fin drain/narrow filter drains shall be per running metre length of the drain.
703.6 Rate
The Contract unit rates for subsurface drains shall be payment in full for all items such as excavation,
dressing the sides and bottom, providing geotextile composites, laying and jointing pipes etc. including
full compensation for all materials, labour, tools equipment incidental to complete the work as shown on
drawings with all leads and lifts including removal of unsuitable material. Provision of inlets, outlet
pipes, bedding, etc., wherever required shall be incidental to construction of drain.
704 GEOTEXTILES FOR EROSION CONTROL
704.1 Scope
This work shall consist of furnishing and placing a geotextile for erosion control application’s such as
cut and fill slope protection, protection of various small drainage structures and, ditches, wave
protection for causeways and shore line roadway embankments, and scour protection for structures
(bridge piers and abutments). The geotextile shall be designed to allow passage of water while
retaining in situ soil without clogging. The quantities of erosion control geotextiles as shown on the
plans maybe increased or decreased at the direction of the Engineer based on construction procedure
and actual site conditions that occur during construction of the project. Such variations in quantity will
not be considered as alterations in the details of construction or a change in the character of the wok.
704.2 Materials
704.2.1 Fibers used in the manufacture of geotextile, and the threads used in joining geotextiles by
sewing, shall consist of long-chain synthetic polymers, composed of at least 85% by weight polyolefins,
polyesters, or polyamides. They shall be formed into a network such that the filaments or yarns retain