B.
Quality assurance.
(1)
(2)
Inspections. Inspection by the municipality will, at a minimum, be
made of the subgrade prior to placement of the base course, and of
the base course prior to placement of the binder surface.
A.
Acceptable materials.
(1)
Roadway fill areas: as specified previously under Site Excavation and Placement of Fill Material, Article VI.
(2)
Embankment fill areas: as specified previously under Site Excavation and Placement of Fill Material, Article VI.
(3)
Excavated areas. Suitability of material for subgrade purposes shall
be determined by nonmovement of the material under compaction equipment.
A.
Subgrade.
(1)
Perform soil erosion control work in accordance with the approved
soil erosion plan.
(2)
Roadway excavation. Excavate or otherwise remove and satisfactorily
dispose of materials located within the limits indicated on the drawings
for roadways.
(a)
Excavate to roadway subgrade depths required, and cut drainage
channels and waterways as detailed on the drawings. Proof roll subgrade
to the satisfaction of the municipality.
(b)
Remove rock encountered in roadway excavation to a depth six
inches below finished subgrade elevation.
(c)
Excavate unsuitable subgrade material. Refill such areas to
required elevation with acceptable materials.
(3)
Roadway grading. Shape subgrade of roadways, intersections, approaches,
entrances and adjoining pedestrian walkways to no more than 0.10 foot
above or below the design elevations.
(4)
Roadway fill. Construction requirements for roadway fill shall be
as follows:
(5)
Roadway embankment. Construction requirements for roadway embankment
shall be as follows:
(a)
Break up shale and other rock-like materials formed by natural
consolidation of mud, clay, silt and fine sand into a maximum size
that can be readily placed and compacted in loose eight-inch layers.
(b)
Place rock to form the base of roadway embankments. Place in
uniform loose layers not exceeding in depth the approximate average
size of the larger rock, but not exceeding eight inches deep.
(c)
Smooth and level each layer adding soil or granular material conforming to Article VI, in sufficient quantity to supplement the smaller rock pieces, filling the voids and pockets.
(d)
Form the top 18 inches of roadway embankments with soil or granular material conforming to Article VI.
(e)
Compact embankment material to a minimum final density of not
less than 95% of the maximum dry weight density at its optimum moisture
content plus or minus 2%. Proof roll embankments to the satisfaction
of the municipality.
(f)
During foreign borrow excavation operations, keep the borrow
area graded to ensure free water drainage. Following completion of
work in the borrow area, grade the area to present a uniformly trim
appearance merging into the surrounding terrain and to prevent erosion.
B.
Base courses.
(1)
Subbase course.
(a)
Compact subgrade material to a minimum final density of not
less than 95% of the maximum dry weight density at its optimum moisture
content plus or minus 2%. Perform finish rolling on roadway subgrade
just prior to installation of aggregate subbase or base course.
(b)
When indicated on the drawings, construct subbase in accordance
with Publication 408 Specifications, Section 350.
(2)
Crushed aggregate base course, standard.
(a)
Compaction shall be achieved by means of approved static or
vibratory equipment as specified in Publication 408, Section 108.05(c)3.
If static roller is used, base course of more than eight inches shall
be constructed in two lifts. If approved vibratory roller is used,
base course up to 10 inches in compacted thickness may be constructed
in one course.
(b)
On prepared subgrade (or subbase if required), spread limestone
screenings (AASHTO No. 10) to a depth of one inch and compact.
(c)
Construct stone base of AASHTO No. 1 aggregate to the compacted
depth specified in the standard details.
(d)
Spreading coarse material. The coarse material shall be spread
uniformly on the initial layer of fine material by approved mechanical
stone spreaders to the full width of the base unless otherwise specified
for part-width construction. Spreaders shall be adjusted to spread
the loose material to obtain a layer of the required depth after compaction.
In areas inaccessible to spreading equipment, the material may be
spread directly from trucks provided the distribution is equivalent
to that achieved by the spreader. All segregated material shall be
removed and replaced with well-graded material. The coarse material
shall not be spread for a distance of more than an average day's
work ahead of choking and compacting.
(e)
Compacting coarse material. Immediately after surface corrections
have been made to the spread coarse material, it shall be thoroughly
compacted. The rolling shall begin at the sides and progress to the
center, except on superelevated curves where the rolling shall begin
on the low side and progress to the high side. The rolling shall be
parallel with the center line of the roadway, uniformly lapping each
preceding track, covering the entire surface with the rear wheels
ahead of the roller wheels. After each layer of material has been
spread and compacted, it shall be checked with approved templates
and straightedges, and all irregularities shall be satisfactorily
corrected. Red flags shall be placed at the limits of satisfactorily
compacted coarse material. The flags shall be moved ahead as additional
material is compacted, and no filler shall be applied to the coarse
material in advance of the flag-marked sections.
(f)
Application of fine material. After the coarse material has
been set and keyed by compaction, dry limestone screenings (AASHTO
No. 10), in an amount equal to approximately 50% of that required
to fill the voids in the coarse material, shall be spread uniformly
over the surface. The vibratory compaction equipment shall then be
operated over the surface to cause the screenings to settle into the
voids. The remaining screenings shall be spread and vibrated in one
or more applications to satisfactorily fill the voids; however, the
quantity of screenings used and the operation of filling shall not
cause floatation of the coarse aggregate. Areas not completely filled,
in the foregoing operations, shall be filled by manual methods and
need not be further vibrated.
(g)
Compacting and bonding. After completing the vibration of the
fine material, the surface of single-layer construction, or the surface
of each layer of multilayer construction, shall be sprinkled with
water and rolled. All excess screenings forming in piles or cakes
upon the surface shall be loosened and scattered by sweeping, exercising
care that the fine material is not removed below the top of the coarse
aggregate. On the surface of single-layer construction or the top
layer of multilayer construction, the sprinkling and rolling shall
be continued and additional screenings applied where necessary until
all voids are filled and until a slight wave of grout forms in front
of the roller wheels. Brooms attached to the roller, and hand brooms,
shall be used to distribute the grout uniformly into the unfilled
voids. After the wave of grout has been produced over the entire section
of the base course, this portion shall be left to dry. The surface
shall be sprinkled and rerolled as required to bond it thoroughly
and to secure a satisfactory surface. The quantity of screenings and
water used shall be sufficient to produce a smooth, hard monolithic
surface.
(h)
Maintenance and traffic. The contractor shall maintain the completed
base course until the placement of the surface course. No traffic
shall be allowed on the base course other than necessary local traffic
and that developing from the operation of essential construction equipment.
Any defects which may develop in the construction of the base course
or any damage caused by the operation of local or job traffic is the
responsibility of the contractor and shall be immediately repaired
or replaced at no expense to the municipality.
(3)
Crushed aggregate base course, alternate.
(a)
Compaction shall be achieved by means of approved static or
vibratory equipment. If static roller is used, base course of more
than eight inches shall be constructed in two lifts. If approved vibratory
roller is used, base course up to 10 inches compacted thickness may
be constructed in one course.
(b)
On prepared subgrade (or subbase if required), construct stone
base of PennDOT 2A coarse aggregate to the compacted depth specified
on the standard details.
(c)
Spreading coarse material. The aggregate material shall be spread
uniformly by approved mechanical stone spreaders to the full width
of the base unless otherwise specified for part-width construction.
Spreaders shall be adjusted to spread the loose material to obtain
a layer of the required depth after compaction. In areas inaccessible
to spreading equipment, the material may be spread directly from trucks,
provided the distribution is equivalent to that achieved by the spreader.
All segregated material shall be removed and replaced with well-graded
material. The aggregate material shall not be spread for a distance
of more than an average day's work ahead of compacting.
(d)
Compacting coarse material. Immediately after surface corrections
have been made to the spread material, it shall be compacted. The
rolling shall begin at the sides and progress to the center, except
on superelevated curves where the rolling shall begin on the low side
and progress to the high side. The rolling shall be parallel with
the center line of the roadway, uniformly lapping each preceding track,
covering the entire surface with the rear wheels and continuing until
the material does not creep or wave ahead of the roller wheels. After
each layer of material has been spread and compacted, it shall be
checked with approved templates and straightedges, and all irregularities
shall be satisfactorily corrected. Red flags shall be placed at the
limits of satisfactorily compacted material. The flags shall be moved
ahead as additional material is compacted.
(e)
Maintenance and traffic. The contractor shall maintain the completed
base course until the placement of the surface course. No traffic
shall be allowed on the base course other than necessary local traffic
and that developing from the operation of essential construction equipment.
Any defects which may develop in the construction of the base course
or any damage caused by the operation of local or job traffic is the
responsibility of the contractor and shall be immediately repaired
or replaced at no expense to the municipality.
C.
Field quality control.
(1)
Surface tolerance. After the base course has been completed as specified,
the surface smoothness shall be checked with approved templates, string
lines, or straightedges.
(a)
Templates. The contractor shall furnish and use approved templates
of required length and cut to the required crown of the finished surface
of the base course, for checking the crown and contour thereof. The
templates shall be equipped with metal or other approved vertical
extensions attached to each end, so that the bottom of the template
will be at the elevation of the top of the aggregate. At least three
such templates shall be furnished and used at intervals of not more
than 25 feet.
(b)
String lines. String lines, for controlling the finished elevation
of the proposed base course, shall be furnished with ample supports
and offset along each side of the base course, and shall be maintained
until all irregularities have been satisfactorily corrected.
(c)
Straightedges. Approved straightedges 10 feet in length shall
also be furnished and used for testing longitudinal irregularities
in the surface of the base course.
(d)
Surface irregularities. Any surface irregularities that exceed
1/2 inch shall be remedied by loosening the surface and removing or
adding material as required, after which the entire area, including
the surrounding surface, shall be rolled until satisfactorily compacted.
(2)
Tests for depth of finished base course. During the progress of the
work, the depth of the base course will be measured by the municipality
and unsatisfactory work shall be repaired, corrected, or replaced.
The municipality will not be liable for payment for any excess depth
of base course. The initial layer of fine material placed as a bed
and filler will be measured and considered as part of the base course
in determining the compacted depth of the finished base course.
(a)
The depth will be determined by cutting or digging holes to
the full depth of the completed base course. One depth measurement
shall be made for each 1,500 square yards, or less, of completed base
course. Any section in which the depth is 1/2 inch or more deficient
in specified depth shall be satisfactorily corrected at no expense
to the municipality.
(b)
All test holes shall be backfilled with similar material and
satisfactorily compacted by and at the expense of the contractor.
This operation shall be performed under the observation of the municipality
who will check the depth for record purposes.
