572Slope Underdrains

572.1 General Description

This Work consists of the construction of slope underdrains, including placement of Geogrid reinforcement, Geocomposite wall drains, plastic filter fabric and other materials in slope excavations or fills where encountering high groundwater. Perform this Work in accordance with the Specifications and details, lines and grades shown on the Plans, or as directed by the Engineer.

572.1.01 Definitions

General Provisions 101 through 150.

572.1.02 Related References

A. Standard Specifications General Provisions 101 through 150 Section 500—Concrete Structures Section 603—Sand-cement Bag Rip Rap Section 806—Aggregate for Drainage Section 809—Geogrid Materials Section 839—Corrugated Polyethylene Underdrain Pipe Section 853—Reinforcement and Tensioning Steel Section 881—Fabrics B. Referenced Documents QPL 28 QPL 47

572.2 Materials

Ensure that materials meet the requirements of the following Specifications: Material Specification Concrete 500 Sand-cement Bag Rip Rap 603 Coarse Aggregate for Underdrains 806.2.01 Geogrid 809 Corrugated Polyethylene Underdrain Pipe 839 Material Specification Reinforcing Steel 853 Woven Plastic Filter Fabric 881.2.05 Use approved geocomposite wall drain listed on QPL 47. See QPL 28 for acceptable woven fabrics that meet the requirements of this Specification.

572.3 Construction Requirements

572.3.01 Personnel

General Provisions 101 through 150.

572.3.02 Equipment

General Provisions 101 through 150.

572.3.03 Preparation

General Provisions 101 through 150.

572.3.04 Fabrication

General Provisions 101 through 150.

572.3.05 Construction

Arrange the work schedule so that the slope underdrain installations will coincide with other operations on the Project in a manner that will prevent damage to completed work or may cause and/or allow soil contamination of materials. A. Excavation Excavate in accordance with the details and elevations shown on the Plans or to an additional depth as directed by the Engineer to intercept the water-bearing strata encountered during construction. Begin the excavations with the topmost bench and proceed to the bottom of the slope. Excavate as necessary to provide continuous slope underdrain coverage from the top of the water-bearing strata to the bottom of the slope. When encountering unstable conditions in the bottom of the excavation, remove unstable material as directed by the Engineer and replace with approved granular material and compact so as to provide a stable foundation for the excavation and placement of pipes. B. Placement of Geocomposite Wall Drains Place the Geocomposite wall drains the full height and width of the vertical bench cuts and secure the drains with metal staples or wooden stakes. Do not allow any horizontal joints or splices to remain in the drains. Abut adjoining drain strips to make vertical joints between drain strips. C. Placement of Plastic Filter Fabric Place plastic filter fabric of sufficient length to cover the drainage aggregate at the bottom of the bench excavation adjacent to the geocomposite wall drain. Overlap the fabric with a minimum of 3 feet (914 mm) of material. Sewing of the fabric will not be required. The fabric may be cut at the locations of the solid underdrain pipe to allow for wrapping around the drainage aggregate. D. Placement of Pipe and Aggregate Place perforated pipe continuous with the bench excavation adjacent to the Geocomposite wall drain in accordance with the details shown on the Plans. Place solid pipe at 200-foot (61-meter) intervals with a minimum of 2 solid pipes at each bench excavation, joined to perforated pipe with “T” connections. Connect all joints securely. Place drainage aggregate to a level of 6 inches (152 mm) above the pipes without disturbing the pipe alignment. Wrap the plastic filter fabric over the drainage aggregate prior to backfilling with soil. E. Backfilling and Placement of Geogrid Reinforcement Place soil to be used as backfill material with the same lift and compaction requirements as normal embankment construction. Do not disturb the pipe alignment. Place layers of Type B geogrid reinforcement 4 feet (1.22 m) long beginning at a level 2 feet (600 mm) above the bottom of each bench, and at 1-foot (300 mm) intervals thereafter as each bench excavation is backfilled. F. Markers Mark each outlet end of the drainage pipe in accordance with Plan details. G. Protection from Contamination Protect all materials from contamination by foreign matter. In the event that the drainage aggregates, plastic filter fabric or Geocomposite wall drains become contaminated, remove the contaminated portion and replace with clean material at no additional cost to the Department. Placement of soil backfill over the fabric is incidental to the Work and is not considered to be contamination. H. Type B Concrete Flume After the slope is backfilled, construct a Type B concrete flume at each solid drain location as indicated on the Plans. Extend each flume from the topmost solid drain pipe to the bottom of the slope.

572.4 Measurement

Slope underdrains will be measured for payment by the linear foot (meter) of accepted perforated underdrain in place at each bench excavation. No separate measurement will be made for bench excavation, drainage aggregate, Geocomposite wall drain, solid drain pipe, connections, geogrid, plastic filter fabric, or backfill required by the Plan Details. Additional depth bench excavation required beyond the limits of the Plan details and directed by the Engineer will be measured according to Subsection 205.4 of the Specifications. No separate measurement will be made for disposing of any unsuitable material encountered. Replacement material will not be measured separately. When the contract includes Item 210-Grading Complete, additional depth bench excavation required beyond the limits of the Plan details, and as directed by the Engineer, will be measured according to Subsection 210.4.C. of the Specifications. No separate measurement will be made for backfilling the additional depth bench excavation.

572.5 Payment

Slope underdrains will be paid for at the Contract Price per linear foot (meter), complete and in place. Payment is full compensation for excavation, furnishing all materials, including drainage aggregate, Geocomposite wall drain, solid drain pipe, perforated drain pipe, connections, geogrid and plastic filter fabric, backfill, placing all materials and for all labor, equipment, tools and incidentals necessary to perform the Work. Payment for concrete flumes will be according to the Plans. Additional depth bench excavation required beyond the limits of the Plan details, and as directed by the Engineer, will be paid for at the Contract Price per cubic yard for Unclassified Excavation. When the contract includes Item 210-Grading Complete, additional depth bench excavation will be paid for according to Subsection 210.5.C, Undercut Excavation. Payment will be made under: Item No. 572 Slope Underdrains Per linear foot (meter)

572.5.01 Adjustments

General Provisions 101 through 150.