2535.01 DESCRIPTION.
Crib walls of the bin type will be used to retain earth embankments when lateral clearance will not allow normal earth slopes. These walls may be constructed of precast concrete units in the form of alternate courses of stretchers and headers or may be constructed of formed galvanized sheets so that when assembled, they will form a succession of vertical, rectangular cells which will be backfilled with suitable material. Both precast concrete units and formed galvanized sheets shall conform to the contract documents.

2535.02 MATERIALS.
Materials used in construction of the cell walls shall meet the following requirements for the respective types:

A. Concrete Crib Units.
Concrete crib units of concrete crib walls shall be furnished in two patterns, one of which will be used as stretchers and the other as headers in building the wall. These units shall meet requirements for dimensions and reinforcement, as shown in the contract documents. The units shall be made of precast concrete in accordance with the applicable requirements of Section 2407. The units shall be free from cracks, spalls, or surface depressions on any face. They shall have rectangular cross section and shall be beveled as shown in the contract documents.

B. Formed Galvanized Sheets.
Formed galvanized sheets used in construction of bin type crib walls shall comply with requirements of Section 4141 for the type of base metal and galvanizing. The sheets shall be of the gauge specified in the contract documents and shall be fabricated so they may be assembled and bolted to form cells of the shape and dimensions shown in the contract documents. Sheets may be galvanized before punching and forming.

Bolts used to assemble the sheets shall be unfinished regular bolts meeting requirements of ASTM A 307, Grade A, full diameter body. Threads shall be ANSI B1.1, Unified Coarse Thread Series. Bolt heads and nuts may be either standard square, hexagonal, or heavy hexagonal style and shall meet requirements of ASTM A 307 or ASTM A 563. Bolts and nuts shall be galvanized meeting requirements of ASTM A 153, Class C.

2535.03 EXCAVATION.
The site shall be excavated to provide a firm foundation at the desired elevation and either level or sloped to the heel to provide the required batter of the wall face. Soil beneath the entire bin area shall be compacted by rolling or tamping to provide a firm foundation.

Unless otherwise designated, when construction of bin type crib wall is included in the contract for grading a section of road, all excavation in connection with this construction shall be classified as provided in Article 2102.02, the same as other excavation in the contract. When not included in contracts for grading, all excavation in connection with this construction shall be Class 23 Excavation as provided in Article 2402.11.

2535.04 CONSTRUCTION.
When the total height of wall does not exceed 6 feet (1.8 m), the foundation may be level and wall face vertical. When the height of wall exceeds 6 feet (1.8 m), the wall face shall be battered as indicated in the contract documents but not less than 2 inches in 12 inches (50 mm in 300 mm). The foundation shall be adjusted to provide the required batter in the wall face. Courses of stretchers or plates in the wall face shall be maintained level. When specified in the contract documents the subgrade for the wall shall be covered with special backfill material meeting requirements of Section 4132. When drainage is provided beneath the wall foundation, material used to cover the drain and foundation shall be porous backfill material meeting requirements of Section 4131.

When concrete units are used on the prepared subgrade or granular backfill, a double row of stretchers shall be placed along the line of the toe of the wall and 1 or more rows of stretchers along the heel of the wall, as indicated in the contract documents, according to the height of the wall. The end stretchers shall be of a length that full bearing is provided for the end headers. Headers shall be placed at right angles to the wall face at 6 foot (1.8 m) intervals. A space of 1/4 inch (6 mm) shall be left between the stretcher and the projecting lug of the header to allow for slight movement of the wall. Stretchers for the wall face shall be of the open or closed type, as indicated in the contract documents. The open type will provide approximately a 5 inch (125 mm) vertical opening between courses of stretchers. The closed type will provide approximately 1 inch (25 mm) vertical space between courses of stretchers. Stretcher courses in the wall face shall be maintained level by shimming with layers of heavy asphalt roofing at bearings. End headers, where the wall is stepped up or down, shall be held in place by extra headers placed parallel to and between the rows of stretchers.

Formed galvanized sheets shall be assembled as shown in the contract documents. Sheets may be placed individually and bolted in place, or the transverse walls and posts may be assembled as a unit and sheets of the front and rear walls placed individually. After the plates of each course are in place, all bolts in that course shall be drawn tight. To be assured that all bolts are properly tightened, all bolts in each course shall be tightened at least twice.

2535.05 BACKFILLING.
Promptly after each 3 foot (1 m) lift of crib wall cell is completed, it shall be backfilled with suitable earth or granular material, as specified. The backfill shall completely fill the cell and the space between the cell and any face of natural earth behind the wall. Backfill shall be placed in layers not greater than 6 inches (150 mm), thoroughly compacted by tamping. Granular material may be compacted by vibration. The method of compaction shall neither distort the wall or displace the units.

2535.06 METHOD OF MEASUREMENT.

A. Excavation.
When this construction is a part of a contract for grading a section of road, excavation shall be measured as provided in Section 2102. When this construction is not a part of a contract for grading a section of road, Class 23 excavation will be computed as provided in Section 2402 and the following:

The quantity of excavation will include only material actually removed above the elevation of the subgrade designated in the contract documents and bounded by vertical planes 1 foot (0.3 m) beyond the horizontal projection of the headers at the ends, and by the stretchers at the rear and by the natural ground surface at the top and front.

B. Backfill.
Granular backfill furnished will be measured in cubic yards (cubic meters) or in tons (megagrams), as indicated in the contract documents and as provided in Article 2402.12, D.

Earth backfill will not be measured for payment.

C. Bin Type Crib Wall.
The Engineer will compute in square yards (square meters) the face area of each design of bin type crib wall from measurements of the length of wall and the height from the extreme top and bottom of stretcher units or sheets.

2535.07 BASIS OF PAYMENT.

A. Excavation.
For the quantities of excavation computed as specified above, the Contractor will be paid the respective contract unit prices per cubic yard (cubic meter).

B. Backfill.
For the quantity of granular backfill furnished and placed, the Contractor will be paid the contract unit price per ton (megagram) or per cubic yard (cubic meter).

C. Bin Type Crib Wall.
For the number of square yards (square meters) of crib wall of each design constructed, the Contractor will be paid the contract unit price per square yard (square meter).

These payments shall be full compensation for furnishing all materials, tools, and labor necessary to construct the crib walls complete for the respective type, and for placing and compacting of earth or granular backfill, and for any other operation necessary to the work and not covered by other items.