De 



SPECIFICATIONS FOR CONCRETE RETAINING WALLS. 



241 



MVIT, Colo., the gravel and sand were taken from the cut, the concrete waa mixed in mixers 

 installed at the foot of movable towers, and the concrete was raised in a skip elevator and chuted 

 into place. 



On railroad work the mixer may be mounted on a flat car, the materials may be delivered on 

 other cars, and the concrete is dumped or chuted directly into place. 



FIG. 13. RETAINING WALL, C. B. 

 & Q. R. R. 



FIG. 14. F OEMS FOR RETAINING WALL, C. 

 B. & Q. R. R. 



SPECIFICATIONS FOR CONCRETE RETAINING WALLS. The following extracts 

 have been taken from the specifications prepared by Crocker and Ketchum, Consulting Engineers, 

 for the concrete retaining walls for the West Alameda Avenue Subway, Denver, Colo. 



16. MATERIALS. Cement. The cement shall be furnished by the Companies on board 

 cars or in store houses at the site of the work as required. The cement shall be Portland, and 

 shall meet the requirements of the Standard Specifications of the American Society for Testing 

 Materials. 



17. Concrete Aggregate. The fine aggregate shall pass a screen with J in. mesh, while the 

 coarse aggregate shall all be retained on a screen with J in. mesh and all shall pass a screen with 

 3 in. mesh. The sand and gravel shall be obtained from the excavation of the open cut of the 

 Subway. The Consulting Engineers reserve the right to change the proportions of sand and 

 screened gravel (34 and 35) from time to time, as may be necessary to secure a dense concrete 

 of desired consistency. Payment to trie Contractor for the screening will be made on the basis 

 of unit price per cubic yard of gravel measured after screening. 



1 8. Water. The water used in mixing concrete shall be clean and reasonably clear, free 

 from acids and injurious oils, alkalies or vegetable matter. 



19. Lumber. Lumber for forms shall have a nominal thickness of 2" before surfacing, and 

 shall be of a good quality of Douglas fir or Southern long leaf yellow pine. Lumber used for 

 forms of face work shall be dressed on one side and both edges to a uniform thickness and width. 

 Lumber for backing and other rough work may be unsurfaced and of an inferior grade of the 

 kinds above specified. 



20. Reinforcing Steel. All reinforcing steel shall be plain bars, and shall comply with the 

 specifications for structural steel as given in the Standard Specifications of the American Railway 

 Engineering Association. 



21. EXCAVATION. The subway is being excavated by the Companies but the contractor 

 shall make all necessary excavations for wall and pedestal footings, and shall furnish all necessary 

 sheeting and supports and bracing to hold the forms in place during the construction of the work. 



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