ROADS AND BRIDGES 303 



and reinforced with fy-inch corrugated bars, about 20 

 inches center to center. If plain bars are used a some- 

 what larger per cent of reinforcement should be used. 



" For a yard of concrete in the proportions one, three, 

 six there will be required i.n barrels of cement, 0.47 

 cubic yards of sand, and 0.94 cubic yards of stone. At 

 the prices given the materials alone for a yard of con- 

 crete would be in the neighborhood of $3.50, not includ- 

 ing the hauling or mixing. For the one, two, four con- 

 crete 1.57 barrels of cement will be required, 0.44 cubic 

 yards of sand, and 0.88 cubic yards of broken stone. 



" The forms, which are always a costly part of small 

 culverts, should be designed so that they can be used a 

 number of times without wasting the lumber. 



" The shape of the culvert is exactly like a square box 

 with the ends knocked out, and it may or may not have 

 a floor. If it does not, the side walls should be carried 

 down to a good foundation. All culverts should have 

 wing walls built at the ends projecting at an angle of 

 about 30 degrees." 



PHYSICS OF ROADS 



By referring to the discussion of the movement of the 

 water in the soil the reader will understand some of the 

 physical problems in road drainage. In nearly all cases, 

 water softens the road, though in some cases, as in sand, 

 it assists in making the road surface compact. The 

 principles involved in farm drainage apply in a general 

 way to the drainage of a roadbed. Where a roadbed 

 is filled with standing ground water, it is more difficult 

 to keep it solid than where it is well drained, and even 

 an excess of capillary water in and near the surface 

 makes most roadways less solid and less durable. 



It is an advantage to have the roadbed shed the rain 

 to the roadside ditch, not allowing it to penetrate into 



