THE STANDARD SPECIFICATIONS, SERIES 2001, ARE AMENDED BY THE FOLLOWING MODIFICATIONS AND ADDITIONS. THESE ARE SUPPLEMENTAL SPECIFICATIONS AND THEY SHALL PREVAIL OVER THOSE PUBLISHED IN THE STANDARD SPECIFICATIONS.

01052.01 DESCRIPTION.

This work includes furnishing and installing modular block retaining wall units, wall fill, and granular backfill to the lines and grades shown on the plans. Modular block retaining walls are defined as systems that usually do not require mesh or strips in the backfill behind the wall facing to limit backfill stresses by reinforcing the soil structure.

01052.02 DESIGN.

A. Wall Design Engineer.
The wall design shall be performed by a Professional Engineer licensed in the State of Iowa that prepares and seals the design submittals as defined in this Supplemental Specification.

B. Submittals.
Prior to the beginning of the wall construction, Tthe Contractor shall, in accordance with Article 1105.03 of the Standard Specifications, submit for approval to the Engineer detailed design calculations including soil bearing pressure, construction drawings, and shop drawings prepared and sealed by the Wall Design Engineer for approval at least 30 days prior to the beginning of the wall construction. If required, a detailed explanation of the design properties and quality control test limits for the geogrid reinforcement shall be submitted with the design.

01052.03 MATERIALS.

The wall shall be manufactured by a company on the approved manufacturer’s list in Materials I.M.445.04 , Appendix E.

A. Concrete Units.
Exterior dimensions may vary. Each unit is required to have a minimum of 0.5 square foot (0.046 m²) of face area and an 8 inch (200 mm) maximum vertical dimension.  The face of the block shall be straight with split face texture.

Units shall have angled sides and capable of attaining concave and convex alignment curves minimum radius of 5.0 feet (1.5 m).

Units shall be interlocked with connector pins recommended by the supplier/manufacturer or by integrally cast shear lugs.

Units shall be interlocked as to provide minimum of 1/4 inch (6 mm) of setback per each course of wall height.

Connector pins shall be of the type, size, and design recommended by the supplier/manufacturer for the type of masonry unit and backfill reinforcement material used in the wall.

B. Leveling Pad.
The type of materials used for the leveling pad shall be as recommended by the supplier/manufacturer.  If granular material is recommended for the leveling pad, it shall be specific backfill meeting the requirements of Section 4132 of the Standard Specifications.  If unreinforced concrete is recommended for the leveling pad, it shall be Class C concrete meeting the requirements of the Materials I.M. 529 and Section 2403 of the Standard Specifications.

C. Unit Fill.
Unit fill is defined as the granular material that is within the concrete facing units.

Fill for units shall be porous backfill meeting the requirements of Section 4131 of the Standard Specifications.

D. Backfill.
If required, backfill shall be granular backfill, meeting the requirements of Section 4133 of the Standard Specifications.

E. Tieback Reinforcement.
Tieback reinforcement, when required, shall be of type, size, and design recommended by the supplier/manufacturer.

01052.04 CONSTRUCTION.

A. Excavation.
The Contractor shall excavate in accordance with Section 2102 of the Standard Specifications. This includes benching of the existing roadway foreslopes and the excavation area under the pad line. The Contractor shall be careful not to disturb existing embankment materials beyond what is needed to construct the wall.

At locations where the wall is to be constructed adjacent to a fill section, the fill shall be constructed and compacted to 95% Standard Proctor Density prior to beginning wall construction. After the fill has been constructed, the cut shall be made to permit a minimum of 12 inches (300 mm) beyond the wall to be backfilled with granular materials that meet the requirements of Section 4131 of the Standard Specifications.  Granular material shall be placed and compacted on a course-by-course basis.

B. Foundation Soil Preparation.
The Contractor shall prepare foundation soil as required for the leveling pad.

Foundation soil shall be examined by the Engineer to assure that the actual foundation soil strength meets or exceeds the assumed design bearing strength. Soils not meeting required strength shall be removed and replaced with soil meeting the design criteria.

The earth foundation shall have a density equal to or greater than 90% Standard Proctor Density. The earth foundation shall be stepped at the required intervals to keep it a minimum 1 foot (300 mm) below the finished grade.

The Contractor shall place granular backfill as replacement material for over excavation in the foundation soil. The Contractor shall compact the replacement material in accordance with Article 2107.08 of the Standard Specifications.

C. Leveling Pad.
The Contractor shall place the leveling pad a minimum of 6 inches (150 mm) in thickness.

The Contractor shall construct the leveling pad to insure complete contact of the retaining wall unit with the leveling pad. Gaps will not be allowed between the retaining wall unit and the leveling pad.

D. Unit Installation.
The Contractor shall ensure that units are in full contact with the leveling pad.

The Contractor shall place units side by side for the full length of wall alignment.  Alignment may be done by means of a string line or offset from the base line.

The Contractor shall install connecting pins and fill units, and tamp fill.

The Contractor shall sweep all excess material from top of units and install the next course. The Contractor shall ensure each course is completely filled prior to proceeding to the next course.

The Contractor shall place each course so that pins protrude into adjoining courses a minimum of 1 inch (25 mm) or to tolerances recommended by the supplier/manufacturer. Two pins are required per unit. The Contractor shall repeat the above procedure for each course to the top of wall height.

At the end of each course where the wall changes elevation, the Contractor shall turn the units into the backfill. The Contractor shall place units to create the minimum radius possible. The Contractor shall install a minimum of 3 units into the grade. Only the front face of the units shall be visible from the side of the wall.

E. Backfill Placement.
Granular backfill placement for the reinforcing wall shall closely follow the erection of each lift of wall. At each level for reinforcing, backfill shall be roughly leveled before placing and connecting reinforcement. Reinforcing shall be placed normal to the face of the wall. The placement of the lifts shall closely follow panel erection. The Contractor shall decrease this lift thickness, if necessary, to obtain the specified density.

At the end of each day's operations, the Contractor shall shape the last level of backfill to permit runoff of rainwater away from the wall face.

The Contractor shall compact granular backfill in accordance with Article 2107.08 of the Standard Specifications. The moisture limits shall be from 3% under optimum moisture to not more than the optimum moisture content.

The Contractor shall place and compact backfill without disturbing or distorting the tieback reinforcement or the wall. The Contractor shall not use tamping type rollers or other rollers that may damage the reinforcing. The Contractor shall use light mechanical tampers to achieve the required compaction in a strip 3 feet (1 m) wide adjacent to the backside of the wall, however, compaction within this strip will not be subjected to density testing.

F. Tieback Reinforcement Installation For Retaining Walls, Where Specified.
The Contractor shall place the tieback reinforcement horizontally on compacted backfill, connect it to the concrete wall units and embed it a minimum of 12 inches (300 mm). The Contractor shall hook reinforcement over pins, pull taut, and anchor before backfill is placed on the tieback reinforcement.

The Contractor shall remove slack in the tieback reinforcement at the wall unit connections.

The Contractor shall place tieback reinforcement at the proper elevation and orient it as recommended by the supplier/manufacturer.

The Contractor shall correct orientation (roll direction) of the tieback reinforcement, if applicable, as recommended by the supplier/manufacturer.

The Contractor may secure the tieback reinforcement in‑place with staples, pins, sand bags, or backfill depending on the fill properties, fill placement procedures, and weather conditions.

Overlaps:

1. The Contractor does not need to overlap uniaxial tieback reinforcement in the across-the-roll direction, except to contain the fill at the slope face when wrap-around facing is used. The Contractor shall overlap uniaxial tieback reinforcement a minimum of 48 inches (1.2 m) in the roll direction.

2. The Contractor shall spread a layer of compacted backfill, a minimum of 4 inches (100 mm) in thickness, between uniaxial tieback reinforcement layers in the area to be overlapped.

01052.05 METHOD OF MEASUREMENT.

The Engineer will measure the area of Modular Block Retaining Wall in square feet (square meters), from measurements of the front face of the wall in place. The height will be measured from the top of the leveling pad to the top of the wall, including cap block.

01052.06 BASIS OF PAYMENT.

For the quantity of Modular Block Retaining Wall constructed, the Contractor will be paid the contract unit price per square foot (square meter). This payment shall be full compensation for furnishing and erecting the modular block retaining wall, including the design, excavation, foundation soil preparation, leveling pads, concrete units, connector pins, unit fill for inside the blocks, granular backfill, and tieback reinforcement if required, in accordance with the contract documents.