. Economic Papers. he bottom is good and the puddle wall carefullybuilt, a small hand pump, with the aid of a small sink in one corner,will generally keep the bottom dry. If the bottom is sandy or gravellya gasoline bilge pump will be useful. If the foundation is solid rock and there is no current in the streamthe concrete may be deposited in bags until the water level is reached, nocofferdam being necessary. TYPES OF CULVERTS TIMBER CULVERTS AND BRIDGES. In any timber structure it should be borne in mind that whereverwood is in contact with earth (except when continually under water) itwill d
. Economic Papers. he bottom is good and the puddle wall carefullybuilt, a small hand pump, with the aid of a small sink in one corner,will generally keep the bottom dry. If the bottom is sandy or gravellya gasoline bilge pump will be useful. If the foundation is solid rock and there is no current in the streamthe concrete may be deposited in bags until the water level is reached, nocofferdam being necessary. TYPES OF CULVERTS TIMBER CULVERTS AND BRIDGES. In any timber structure it should be borne in mind that whereverwood is in contact with earth (except when continually under water) itwill decay rapidly. For this reason it is advisable to use heaviermaterial at these points than is required for strength alone. If timberis the only material available it may be advisable in some cases to usecreosoted lumber at these points. In salt or brackish water, creosotedlumber should be used as a protection against the inroads of marinewood-borers. Material: White oak is the most durable lumber to use in road cul-. COUNTRY ROADS IN NORTH CAROLINA 21 verts. Red oak should be avoided, especially when in contact with pine free from large knots is durable and makes satisfactory floorjoists. Rough sawed lumber should be used since there is a considerableloss in planing. Three inch oak flooring should be used where the wear I 5^P V i I
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