§ 11-144. Pipe underdrain.

(a)

Pipe underdrain shall be installed in all sidehill cut sections any area where subsurface water is encountered and other areas as determined by the County Road Superintendent.

(b)

The underdrain shall be located just behind the curb.

(c)

Outlets shall be provided on at least three hundred-foot intervals, or as approved by the County Road Superintendent. To the extent possible, the underdrain pipe should be connected to the drop inlets or box culverts of the storm drainage system.

(d)

The underdrain material and construction procedures shall be in accordance with the AHTD Standard Specifications for pipe underdrain, with the following exceptions:

(1)

Only corrugated polyethylene tubing and acrylonitrile - butadiene - styrene pipe shall be used in the construction of pipe underdrain.

(2)

Granular filter material shall meet the requirements of the AHTD Standard Specifications for coarse aggregate for Class A concrete or the pavement filter blanket material requirements contained in this Article.

(3)

The nonwoven geotextile fabric having the following properties shall be used as a liner for the pipe underdrain:

Properties	Test Procedure	Value
Weight, oz./sq. yd.	ASTM D - 1910	4.1 min.
Thickness, mils	ASTM D - 1777	40 min.
Tensile strength, lbs.	ASTM D - 1682	115 min.
Elongation, percentage	ASTM D - 1682	55 min.
Puncture strength, lbs.	ASTM D - 751	70 min.
	(Modified)
Mullen burst strength, psi	ASTM D - 751	260 min.
Coefficient of permeability,	Constant head	0.10 min.
cm./sec.

 

(4)

Trenches shall be excavated to a minimum depth of twenty-six (26) inches below the top of the curb or as directed by the County Road Superintendent.

(5)

Following excavation of the trench, the nonwoven geotextile fabric line shall be placed in the trench. The liner shall be of sufficient width to cover the bottom and sides of the trench and lap a minimum of one (1) foot across the top of the granular filter material used to backfill above the top of the pipe.

(Ord. No. 91-9, Art. 1, § 5.05, 4-11-91; Ord. No. 99-32, Art. 1, 7-8-99)