164 THE IMPKOVKMI-XT OF RIVERS. 



The design for a lock of this class should provide outlines as simple as possible, 

 and offsets, curved surfaces, and difficult intersections, which are rarely necessary, 

 either in the walls or in the culverts, should be avoided. This is desirable as it lessens 

 the expense of the forms, and also permits them to be set up more rapidly. A good 

 deal of delay anl extra work may be caused by having to stop concreting in order to 

 change or set up forms for changes of surface. Similarly the number of bolts, castings, 

 or other parts requiring to be set during construction should be reduced to a mini- 

 mum, as it is more difficult (contrary to the usual belief) to place them properly in a 

 concrete wall than in a wall of stone. 



Square corners on exposed surfaces should be avoided, as they are easily chipped off. 



The walls should be divided into sections not much over 30 feet in length, other- 

 wise they will crack open with shrinkage in drying and with temperature. Where 

 long walls have been built in one length such cracks have appeared at intervals of 25 

 to 50 feet, and even where sections 45 feet long have been used a slight crack has 

 appeared close to the center. While such partings are no more weakening than 

 artificial joints, they are far more unsightly. These joints, when exposed to a con- 

 siderable head of water, usually leak for some months after construction, as will also 

 the main walls; but the action of the water on the carbonates in the cement, and the 

 finer sediment of the river, will gradually seal them up. The leakage through the 

 joints can be reduced by using mortar between the old and new surfaces as the wall is 

 built. 



Where the natural foundation can be easily drained, so that trouble from leakage 

 or from caving material can be overcome without difficulty, the main outlines of the 

 walls may be designed to start from the bottom, without offsets. Where, however, 

 this condition is absent, as is usually the case with a rock foundation, it is an excel- 

 lent plan to provide a footing course a few feet high, and a foot wider all around than the 

 main body of the walls. Its top will thus provide a platform above the leakage, and 

 the forms can be set up without fear of displacement from caving excavation, and 

 with the leisure necessary for accurately lining them in. 



Proportions and Materials. The proportions of the mixture in the earlier locks 

 were considerably richer than those in later ones. On the Illinois and Mississippi 

 Canal (1894) they were one part of Portland cement to seven or eight parts of sand 

 and gravel or broken stone. On Locks Numbers i and 2, Big Sandy River, Ky., and 

 W. Va. (1902), they were one part of Portland cement, three parts of sand, and six parts 

 of mixed gravel or mixed broken stone; while on Lock No. 9, Kentucky River, Ky. 

 (1902), they were one barrel of Portland cement, 15 cubic feet of common river sand, 

 and 33$ cubic feet of mixed broken stone, from $" to 2\" in diameter, giving a mix- 

 ture of about i to 12. The last mixture possessed when hardened an abundance of 

 strength. 



At Lock No. 2, on the Mississippi, near St. Paul (1900), sand cement was used 

 instead of pure cement, the proportions for grinding being one part of cement to one 



