- 751 - SECTION 914 -- PIPE UNDERDRAINS
914.01 Description
1.The Contractor shall furnish an d install pipe underdrains, filter fabric, and underdrain headwalls as described in the contract.
914.02 Material Requirements
1.All materials shall conform to the requirements in Table 914.01. Table 914.01 Material Requirements Applicable Materials Section Corrugated Pipe Underdrains 1035 Plastic Pipe 1038
2.Gravel aggregate placed in the trench shall conform to the gradations shown in Table 914.02. The material shall have a Los Angeles Abrasion loss percentage (AASHTO, T-96) of not more than 40. The material shall also have a soundness loss of not more than 12% by weight at the end of 5 cycles using sodium sulfate solution. Table 914.02 Granular Backfill Material Percent Passing English Sieve Size (Metric) Target Value Tolerance 1 inch (25 mm) 100 0 1/2 inch (12 mm) 94 ±4 No. 4 (4.75 mm) 65 ±25 No. 10 (2.00 mm) 20 ±20 No. 50 (300 m) 5 ±5 No. 200 (75 m) 3 ±3
3.Granular backfill material shall be compacted to optimal stiffness as defined by a deflection target value established by the Engineer.
4.The trench should be lined with an approved filter fabric before filling with aggregate. The filter fabric shall be installed according to the contract details.
5.Filter fabric shall be on the Department’s Approved Products List.
6.The filter fabric material will be chosen to accommodate the type of in-situ soils and within the manuf acturer’s requirements and limits.
914.03 Construction Methods
1.a. The trench for laying pi pe underdrains shall be excavated beginning at the outlet end and proce eding toward the upper end, true to the required line and grade.
b.Trenches shall be of sufficient width to provide working space on each side of the pipe and in no case shall the width of the trench be less than 12 inches (300 mm).
914.03 Pipe Underdrains
- 752 - c. Any material excavated below the proper grade shall be restored in kind to proper bearing capacity.
2.The perforated pipe shall be laid directly upon the floor of the trench. All loose material lying on the floor of the trench shall be removed prior to the placing of the perforat ed pipe. Grade and alignment shall not vary from the described grade by more than 0.03 foot (9 mm) at any point. The joints between sections of pipe shall be connected in a fashion acceptable to the Engineer.
3.Dead ends of pipe shall be tightly closed with satisfactory plugs. Discharge ends shall be protected with a suitable rodent screen.
4.If unsuitable foundation soils ar e present, other suitable material shall be placed under the pipe to prevent displacement.
5.a. Once the pipe is in place, it shall be covered immediately with Granular Backfill Material.
b.The Granular Backfill Material shall be of uniform depth on either side of the pipe.
6.Special inlets and special devices at the outlet end of the pipe shall be constructed as shown in the contract.
7.a. The underdrain headwalls shall be constructed as shown in the contract.
b.The concrete for the headwalls shall be Class 47B-3000 (47B- 20 MPa) or BX-3000 (BX-20 MPa).
8.The Contractor shall place filter fabric as shown in the contract.
914.04 Method of Measurement
1.Each size of pipe underdrains shall be measured in linear feet (meters) along the centerline of the pipe.
2.Headwalls will be measured by the each.
914.05 Basis of Payment
1.P a y I t e m P a y U n i t _____ Perforated Pipe Underdrain Linear Foot (LF) [Meter (m)] _____ Perforated _____ Pipe Linear Foot (LF) Underdrain [Meter (m)] _____ Nonperforated Pipe Underdrain Linear Foot (LF) [Meter (m)] _____ Nonperforated _____ Pipe Linear Foot (LF) Underdrain [Meter (m)] Underdrain Headwall Each (ea) 2. Filter fabric is subsidiary to the appropriate underdrain pay item.
3.Granular backfill is subsidiary to the appropriate underdrain pipe pay item.
4.Payment is full compensation for all work described in this Section. - 753 - SECTION 915 -- GRANULAR SUBDRAINS
915.01 Description
1.The Contractor shall construct granular subdrains as described in the contract.
915.02 Material Requirements
1.Aggregate that is used in gra nular subdrains shall conform to the gradation requirements for Gravel Su rfacing shown in Table 1033.07 of Subsection 1033.02.
915.03 Construction Methods
1.The Contractor shall excavate subdrain trenches to the dimensions and the elevations show n in the contract.
2.The Contractor shall provide and place aggregate in the trench as described in the contract.
3.After the aggregate has been pl aced, the trench shall be backfilled to the shoulder surface.
4.All backfill material shall be compacted to a density equal to the density of the adjacent shoulder.
5.Surplus material shall be disposed of on adjacent slopes.
915.04 Method of Measurement
1.The "Granular Subdrain" shall be measured by the each.
915.05 Basis of Payment
1.P a y I t e m P a y U n i t Granular Subdrain, Type ______ Each (ea) Granular Subdrain Each (ea) 2. Payment is full compensation for all work described in this Section.
Source: Nebraska Standard Specifications for Highway Construction, 2017 Edition. Pages 785–786 of 1,048.