GENERAL
The scope of
work under this section covers the furnishing of all materials, labour,
equipment, transportation and installation service to prepare the sub grade for
roads placing the crushed stone base and surface courses as shown on the
drawings or as directed by the Owner.
SUBGRADE PREPARATION
Excavate sub grade of fill, as required, and then
graded and compacted to provide a firm foundation of uniform density
throughout. Completed sub grade shall be true to alignment, grade and cross
section, including the required crown as shown on the drawings. CBR test on the
furnished level of completed sub grade shall have a minimum value of 6 in the
condition 98 % dry density.
Prior to
placing of any fill required to bring the sub grade to its finished level,
strip areas to be covered of any loose or otherwise unapproved fill materials,
organic materials, or any foreign or deleterious matter.
Holes, ruts and
similar defects shall be filled with approved materials. Unstable areas, projecting
stone or rock, and similar defects shall be cut out and the hole areas shall be
filled.
All required
fill shall be compacted as specified in
Book III Technical Specification refers to Earth Work.
Sub base
preparation for roads shall be started only when the required of CBR sub grade
has been achieved.
Drainage
culvert under the sub grade shall have been constructed before the sub grade
works is carried out.
To enable the
Contractor carry out the work during wet season, temporary drainage shall be
provide to drain the under smoothly.
SUBBASE AND BASE COURSES.
GENERAL
The Contractor
shall prepare the sub grade and apply the sub base and base course materials
for roads as shown on the drawings and as specified herein.
MATERIAL
Material used
for the sub-base, and base course shall consist of materials as specified
below.
Sub-base
Material
Material shall be obtained from a source
approved by the Owner.
This material shall consist of well graded
crushed stone with hard, strong, durable rock pieces having the following
gradation (size No 5-ASTM D693).
Sieve
Size Percentage Passing
by Weight
37.5 mm 100
25.00 mm 90
- 100
19.00 mm 40
- 75
12.50 mm 15
- 35
9.5 mm 0
- 15
4.75 mm 0
- 5
Base Course
This material shall consist of well
graded crushed stoned with hard, strong, durable pieces having the following
gradation :
ASTM
Standard Sieve Percentage
Passing by Weight
1.5” 100
1.0” 60
- 100
¾” 55
- 85
4 35
- 60
10 25
- 50
40 15
- 30
200
8 - 15
CONSTRUCTION OF SUB-BASE COURSE (30
CM THICK)
Immediately before placing the sub-base
material, the surface shall be proof rolled and compacted to a dry density not
less than 98 percent of the maximum dry density as determined by the method
specified in ASTM D698, Method D.
Any soft,
unsound areas, encountered during the preparation and compaction of the
surfaces, shall be removed. The unsound areas, pockets or cavities, shall be
excavated and backfilled with approved material to the depth and extend beyond
the neat lines and elevations shown on the drawings or as may be directed by
the Owner.
Shaping and compaction shall be carried out
concurrently so that upon completion, the surfaces shall be smooth and
everywhere within plus or minus 30 mm of the required grade, but not uniformly
high or low.
The surface shall be regarded and re-compacted
at the Contractor expense of if disturbs for any reason before or during the
placing of the base course material.
CONSTRUCTION
BASE COURSES (20 cm thick)
After the
sub-base for the road has been completed, the Contractor shall place the base
course as designated on the drawings, in layers not less than 100 mm of
compacted thickness.
Road bases and
surfaces shall be compacted to a dry density not less than 98 percent of the
maximum dry density as determined by the method specified in ASTM D698, Method
D. Water shall be added during compaction as required to achieve the specified
dry density.
Road surfaces
shall be shaped and compacted to the lines, grades and dimensions shown on the
drawings by equipment designed for that purpose. Such shaping and compaction
shall be carried out concurrently so that upon completion the surfaces shall be
smooth and everywhere within plus or minus 15 mm of the required grade, and
shall be compacted to the degree specified for the full depth. Any local
depressions which do not meet the above tolerances shall be filled with
approved granular surface materials.
ASPHALT
PRIMER/PRIME COAT
The
crushed rock base course shall be dried, swept clean of all dust, dirt and
loose particles and prepared for surfacing.
A prime coat of
asphalt primer ASTM D2027 GRADE MC70 shall be sprayed over to the base course
at a rate 0.90 litre per sq m required to fill all voids and interstices and
uniformly coat the base course surface.
Asphalt paving
will be constructed on the section of Finishing.