This work shall include the construction, where
required, of underdrains laid in a trench refilled with aggregate.
They shall be constructed in accordance with the dimensions and details
indicated on the plans and in conformity with these specifications.
A.
Pipe for underdrains shall be either perforated corrugated
metal pipe or slotted reinforced concrete pipe. The pipe for underdrains
and the materials for sealing and coupling of joints shall conform
to the requirements of State Form 810, Article M.08.01.
B.
Aggregate for filling the trench shall consist of
clean, tough, durable pieces of broken stone, screened gravel or washed
sand meeting the following gradation requirements:
|
Square Mesh Sieve
|
Percent Passing by Weight
| |
|---|---|---|
|
1/8 inch
|
100
| |
|
1/2 inch
|
85 to 100
| |
|
3/8 inch
|
50 to 100
| |
|
1/4 inch
|
30 to 85
| |
|
No. 4
|
20 to 80
| |
|
No. 10
|
0 to 30
| |
|
No. 100
|
0 to 2
|
A.
The trench for underdrains shall be excavated in conformity with the requirements of Article IV, Trench Excavation.
B.
Where the bottom of the trench is unstable, sufficient
unstable material shall be removed and aggregate added to stabilize
the bottom of the trench.
C.
The pipe shall be laid on the bottom of the trench
with the perforations up. After the pipe has been carefully laid and
aligned, the joint shall be connected and completed.
D.
After the pipe has been installed, the aggregate shall
be placed around and over the pipe to a height of 12 inches above
the top of the pipe, taking care not to displace the pipe. The trench
shall then be filled to the bottom of the subbase, tamped in layers.
E.
Lateral underdrains shall be connected to longitudinal
underdrain systems by the installation of tees or wyes or by providing
a hole in the main line underdrain adequately protected against infiltration
of backfill material.
