ITEM 501- UNDERDRAINS

501.1 Description

This item shall consist of constructing underdrains, using pipe and granular filter materials, underdrain pipe outlets, and blind drains using granular material in accordance with this Specification and in reasonably close conformity with the lines and grades shown on the Plans or as established by the Engineer.

501.2 Material Requirements

Material shall meet the requirements specified in the following specifications:

Zinc coated (galvanized) corrugated iron or steel Culverts and underdrains     AASHTO M 36

Extra strength and standard strength clay pipe and perforated clay pipe           AASHTO M 65

Perforated concrete pipe                                                                            AASHTO M 175

Porous concrete pipe                                                                                  AASHTO M 176

Bituminized-fiber non-pressure sewer drain and underdrainage pipe systems    AASHTO M 177

Asbestos-cement perforated underdrain pipe                                                       AASHTO M 189

Granular Backfill Filter Material – Granular backfill filter material shall be permeable and shall meet the requirements of AASHTO M 6, except that soundness tests will not be required and minor variation in grading and content of deleterious substances may be approved by the Engineer.

When the location of manufacturing plants allows, the plants will be inspected periodically by compliance with specified manufacturing methods, and material sample will be obtained for laboratory testing for compliance with material quality requirements. This shall be the basis for acceptance of manufacturing lots as to quality.

All material shall be subjected to inspection for acceptance as to condition at the latest practicable time.

501.3 Construction Requirements

501.3.1PipeInstallation

Trenches shall be excavated to the dimensions and grades required by the Plans or as directed by the Engineer. A minimum of 150 mm bedding layer of granular backfill material shall be placed and compacted at the bottom of the trench for its full width and length.

Subdrainage pipe of the type and size specified shall be embedded firmly in the bedding material.

Perforated pipe shall normally, be placed with the perforations down and the pipe sections shall be joined securely with the appropriate coupling fittings or bands.

Non-perforated pipe shall be laid with the bell end upgrade and with open joints wrapped with suitable material to permit entry of water, or unwrapped as may be specified. Upgrade end sections of all sub drainage pipe installations shall be closed with suitable plugs to prevent entry of soil materials.

After the pipe installation has been inspected and approved, granular backfill material shall be placed to a height of 300 mm above the top of pipe. Care shall be taken not to displace the pipe or the covering at open joints. The remainder of the granular backfill material shall then be placed and compacted in 150 mm maximum layers to the required height. Any remaining portion of trench above the granular backfill shall be filled with either granular or impervious material, as may be specified, and thoroughly compacted.

501.3.2UnderdrainOutlets

Trenches for underdrain outlets shall be excavated to the width and depth shown on the Plans or as otherwise directed. Pipes shall be laid in the trench with all ends firmly joined by the applicable methods and means. After inspection and approval of the pipe installation, the trench shall be backfilled in accordance with Item 103, Structure Excavation.

501.3.3BlindDrain

Trenches for blind drains shall be excavated to the width and depth shown on the Plans. The trench shall be filled with granular backfill material to the depth required by the Plans. Any remaining upper portion of trench shall be filled with either granular or impervious material in accordance with Item 103, Structure Excavation.

501.4 Method of Measurement

Underdrains and outlets shall be measured by the linear meter for pipe of the type and size specified. Blind drains shall be measured by the linear meter including all excavation and backfill materials required.

Granular backfill filter material, when specified in the Contract as a pay item shall be measured in place by the cubic meter, completed and accepted. Cross-sectional measurements will not exceed the net dimensions shown on the Plans or as directed by the Engineer.

Excavation for underdrain pipe will be measured and paid for as provided in Item103, Structure Excavation.

501.5 Basis of Payment

The accepted quantities determined as provided in Section 501.4, Method of Measurement, shall be paid for at the contract unit prices.

Payment will be made under:

Pay Item Number	Description	Unit of Measurement
501 (1) 502 (2) 503 (3)	Underdrain –mm Blind drain Granular backfill filter material for underdrains	Linear Meter Linear Meter Cubic Meter