1*0 THE IMPROVEMENT OF RIVERS. 



would produce a surface of excellent appearance. Thus, before the concrete was put 

 in, the sheets would be coated with a thin grease and placed horizontally against the 

 lagging, and the strips would be set with a level and a plumb-line to represent joints, 

 with half-strips at the end of each block as before described. If 36-inch sheets were 

 used (which might be of No. 20 gauge) in lengths of 6 feet, the horizontal strips 

 would be placed about 36 inches apart, covering the longitudinal seams, and vertical 

 strips would be fitted between them about 6 feet apart, staggered in each course and 

 covering the vertical seams, thus giving the appearance of a jointed wall. A some- 

 what similar method, but without the use of iron, has been used for small concrete 

 work, greatly to the advantage of its appearance. The lagging should be dressed as 

 usual, to secure evenness of face. 



This procedure would of course entail some expense, but it would be a very small 

 percentage of the cost of the work, and the gain would probably more than justify 

 the outlay. A certain amount of labor would be saved also, that of having to make 

 good edge and butt joints in the lagging. 



The forms for the culverts and other inside openings may be made of rough 

 plank, i inch in thickness. With stiffening frames 2j feet apart this size will be found 

 strong enough. 



The posts, which may be of 3-inch by 8-inch lumber, should be rigidly braced on 

 the outside, as the ramming has a powerful effect in springing them. With posts of 

 this size a brace should be placed every 7 feet or closer in the vertical plane. Sometimes 

 the tops are tied together with pieces which carry at the same time a track for dump- 

 cars, at other times no ties are used. Where the concrete is deposited by dump-boxes 

 such ties are a good deal in the way. 



The following sizes for braces will be found satisfactory. For spans up to 10 feet, 

 use 2" by 4" lumber; for spans of 10 to 16 feet, use 3" by 4" lumber; for spans of 

 16 to 22 feet, use 3" by 6" lumber; for spans of 22 to 28 feet, use 4" by 6" lumber; 

 for spans above 28 feet, use 4" by 6" lumber stiffened as required. Where long braces 

 are placed almost horizontally, it it usually necessary to shore up their centers. 



This bracing is one of the objections to this type of form, as it takes a large amount 

 of timber. Possibly the eventual solution of the problem will be found in principles 

 similar to those employed in the lock near St. Paul, Minn.,* where the long timbers 

 were trussed with tie-rods instead of being supported by braces. It has also been 

 suggested to use built-up posts of triangular outline, stiffened like the legs of a bridge 

 traveler, thus avoiding the long braces, while another method, which has affordrd 

 successful results where the lock was built in blocks, consists in imbedding in the 

 concrete, about a foot below the top of the block being finished, J-inch bolts, one to 

 alternate posts, and provided with a nut and washer each end. When the block is to 

 be continued, a 4" X 12" timber is passed over the bolts, the posts with dapped ends 

 rested upon it, the bottom course of lagging put on, and the whole screwed tight 



'Annual Report Chief of Engineers, U. S. A., 1900, Appendix BB. 



