242 



RETAINING WALLS. 



CHAP. V. 



The cost of the necessary sheeting and supports shall be included in the unit price for excavation. 

 The Contractor shall provide all pumps and other equipment incidental to such excavation. 



22. All excavation shall be measured in vertical prisms whose end areas are of sufficient 

 size to include the footing courses, and the sheeting surrounding the same. "Wet excavation" 

 shall include all excavation below the surface of standing water in open pits. 



23. CONCRETE. Machine Mixing. Machine mixers, preferably of the batch type, shall 

 be used except where the volume of concrete to be mixed .is not sufficient to warrant their use. 

 The requirements are that the product delivered shall be of the specified proportions and con- 

 sistency, and thoroughly mixed. 



*r M ^ 



FIG. 15. FORMS FOR ILLINOIS CENTRAL 

 R. R. RETAINING WALL. 



. -^b. ?' ' Concrete Footing 



FIG. 1 6. FORMS FOR C. & N. W. RY. 

 RETAINING WALL. 



24. Mixing by Hand. When it is necessary to mix by hand the mixing shall be done on water 

 tight platforms of sufficient size to accommodate men and materials for the progressive and 

 rapid mixing of at least two batches of concrete at the same time. Batches shall not exceed one- 

 half yard. The mixing shall be done as follows: The fine aggregate shall be spread evenly upon 

 the platform, then the cement upon the fine aggregate and these mixed thoroughly until of an 

 even color. Then add the coarse aggregate which, if dry, shall first be thoroughly wet down. 

 The mass shall then be turned with shovels until thoroughly mixed and all the aggregate covered 

 with mortar, the necessary amount of water being added as the mixing proceeds. 



25. Consistency. The material shall be mixed wet enough to produce a concrete of such 

 consistency that it will flow into the forms and about the metal reinforcement, and which on the 

 other hand can be conveyed from the place of mixing to the forms without the separation of the 

 coarse aggregate from the mortar. 



26. Retempering. Retempering mortar or concrete, i. e., remixing with water after it has 

 partially set will not be permitted. 



