Any additional drainage facilities not shown
on the approved plan and which may be ordered by the Highway Superintendent
or the Town Engineer shall be constructed by the developer at his
expense and in accordance with this chapter.
A.
The width of the trench in which the pipe is placed shall be equal to, as a minimum, the outside diameter of the pipe plus an additional two feet. The trench excavation shall conform to Figure VI-1.
B.
Where soft, spongy or other unstable soil is encountered
at the grade established, all such unstable soil up two feet under
the pipe and for the total width of the trench shall be removed and
replaced with run of bank gravel or other acceptable material.
C.
Where rock (see § A197-32D) or boulders are encountered, all such rock, and boulders larger than six inches diameter, shall be excavated at least eight inches clear of the pipe. The excavation shall be backfilled with run-of-bank gravel or other acceptable material and properly compacted.
D.
In all cases the bed and the fill on both sides of
the pipe shall be thoroughly compacted and shall provide a firm support
for the pipe.
E.
In general, material removed from the trench during
excavation is suitable for final backfill; provided, however, that
such material is free of sod, roots, spongy material, pieces of pavement,
frozen clumps, lumps or clods of soil, mush, clay, cinders, slag,
ashes, rubbish, rocks or pieces of rock measuring more than six inches
of diameter.
A.
Pipe shall be laid to a true line and grade on the
prepared bed of the trench. Pipe laying shall begin at the downstream
end and progress upstream.
B.
Reinforced concrete pipe shall be sealed with flexible,
watertight, elastomeric gaskets, approved bituminous sealers or plastic
sealers applied at the time the pipe is being laid to line and grade.
Such sealants shall be installed in accordance with the sealant manufacturer's
instruction so that the joint is completely filled with the sealant.
Mortar joint pipe shall not be used.
C.
Corrugated pipe and pipe arch field connections shall
be constructed so that the corrugated band laps equally on each culvert
section.
D.
Smooth interior corrugated polyethylene pipe shall
be installed on a minimum of six inches of suitable bedding material
with one inch of suitable run-of-bank gravel placed on both sides
and on the top of the pipe. Proper compaction must be achieved. The
remainder of the trench shall be backfilled with suitable material
having no stone exceeding six inches in diameter.
E.
When a drainage pipe ends in an open ditch, the ditch
shall be excavated as shown on the plan and the excavated area shall
be entirely filled with rip-rap.
F.
The underdrains should be placed as shown on the plan or as ordered by the Highway Superintendent or the Town Engineer. Underdrains shall be placed in trenches and surrounded by material which is both pervious to water and capable of protecting the pipe from infiltration by the surrounding soil (See Figure VI-2). Underdrains shall outlet in a ditch or shall be connected to a basin or manhole.
A.
Holes for catch basins shall be excavated to a depth
of at least 29 inches below the plan elevation of the invert of the
outlet pipe. Excavation for the catch basin shall be made at least
two feet in the clear around the structure. Crushed stone or run-of-bank
gravel shall be placed in the hole to a uniform depth of nine inches
and shall be leveled and compacted over the entire area under the
base.
B.
Excavation for the manhole and the manhole foundation
shall be made at least two feet in the clear around the structure.
Crushed stone or run-of-bank gravel shall be placed in the hole to
a uniform depth of nine inches and shall be leveled and compacted
over the entire area under the base.
C.
In areas of high groundwater, minimum four-inch diameter
underdains shall be placed to drain into the basin or manhole, in
order to relieve hydrostatic pressure. The backfill around the basin
or manhole shall be coarse granular material for at least one-foot
thickness around the perimeter.
D.
Assembly of sections.
(1)
The interior and exterior of catch basins shall
be parged at all seams and joints, unless sealed with flexible, watertight,
elastomeric gaskets, approved bituminous sealers or plastic sealers.
Bituminous or plastic sealants shall be applied at the time the basin
is set. Such sealants shall be installed in accordance with the sealant
manufacturer's instruction so that the joint is completely filled
with sealant. Brick or block shall be mortared in place and parged
both inside and outside the basin.
(2)
Bituminous or plastic joint sealants shall be
applied at the time a manhole is set. Such sealants shall be installed
in accordance is with the sealant manufacturer's instruction so that
the joint is completely filled with the sealant. Rubber gaskets shall
be installed per the manufacturer's instructions, especially relating
to location, lubrication and setting of manhole sections.
(3)
All steps in each section shall be aligned to
form a continuous ladder with steps being spaced vertically in the
assembled basin or manhole at twelve-inch intervals.
E.
Installation of pipes.
(1)
The openings around all pipes entering or leaving
catch basins (or manholes) shall fit the contours of the pipes as
closely as possible. Remaining interstices shall be solidly filled
with mortar for the full thickness of the wall. All pipes shall be
mortared inside and outside of each basin or manhole.
(2)
The ends of all pipes shall be flush with the
inside surfaces of the catch basin or manhole walls and shall project
outside a sufficient distance to allow for the proper connection with
an adjoining pipe section. No piping shall extend into the catch basin
or manhole.
(3)
When the diameter of the effluent pipe is greater
than that of an influent pipe, the elevation of the crown of the influent
pipe shall be no lower than the elevation of the crown of the effluent
pipe.
(4)
When the diameter of the effluent pipe is the
same as or smaller than that of an influent pipe, the elevation of
the invert of the influent pipe shall be 0.1 foot higher than the
elevation of the invert of the effluent pipe.
(5)
There shall be a minimum 0.1 foot difference
in elevation between inlet invert and the outlet invert at each basin
or manhole.
F.
Setting frames and grates or covers.
(1)
Frames shall be set in a full bed of mortar.
(2)
The frame shall be set to match the pavement
cross slope and to match the roadway profile. Special care shall be
taken at intersections to assure that no ponding will occur.
(3)
The grate or cover shall rest evenly in the
frame. If necessary, the parts shall be filed or ground to assure
even bearing.
(4)
Where the curb inlet shape does not match the
asphalt curb shape, the gutter lines shall match and the asphalt curb
shall be blended/shaped to make a transition between three feet and
five feet long.
B.
In addition, all open ditches shall be cleared of
all trees, shrubs, rock, boulders and excess material to ensure proper
flow of water and ease of maintenance.
B.
The largest stones shall be placed first and smaller
pieces shall be fitted to chink the voids. The stones shall be placed
on a slope not steeper than two to one and so laid that the weight
of the larger stones is carried by the soil and not by the adjacent
stones.
C.
It is intended to have a rough surface, but a generally
uniform shape conforming to the swale cross section.
