EARTH, SAND-CLAY, AND GRAVEL ROADS. 19 



and compact when placed in a road surface, and in some localities 

 this material is used extensively for road surfacing. 



Gumbo is essentially loam containing a high percentage each of 

 clay and decayed vegetable matter and a very low percentage of sand. 

 Gumbo has a strong tendency to absorb and hold water, and there- 

 fore is hard to drain. It is harder to handle in a road surface 

 than clay, because the vegetable matter is an added weakness, but if 

 protected from surface water by a proper system of drainage, it may 

 be used to construct a fair subgrade for supporting some type of 

 impervious road crust. Gumbo has a relatively high capillary 

 power, and for this reason its occurrence in a road bed often will 

 necessitate the use of subdrainage, even under conditions favorable 

 for surface drainage. 



CONSTRUCTION OF EARTH ROADS. 



The work of constructing an earth road, after the general location 

 and design have been decided upon, may be separated into six more 

 or less distinct operations, viz : 



(1) The work is staked out in accordance with previously pre- 

 pared plans; (2) the right of way is cleared of all trees, brush, 

 stumps, etc., which would interfere in any way with the work; (3) 

 all necessary bridges, culverts, drains, and other structures which 

 extend under the road surface are constructed in accordance with 

 proper designs; (4) the roadbed is brought to the required width 

 and grade by making excavations and constructing embankments; 

 (5) the surface is finished to the required cross section and so main- 

 tained until compacted thoroughly; (6) all necessary outlet ditches, 

 gutters, guard rails, fences, etc., are constructed in accordance with 

 the plans. 



STAKING OUT THE WOKK. 



Before any construction work is started on a road the limits of 

 the work should be marked clearly by setting line and grade stakes 

 at convenient intervals. The same stakes generally are made to 

 serve for both line and grade, and the space between successive 

 stakes is made 100 feet. Heavy reference stakes are driven on 

 each side of the center line sufficiently far out not to be disturbed 

 during the progress of the work. Then, as the work proceeds, such 

 supplementary stakes as are necessary for marking the tops and 

 bottoms of slopes, ditch lines, etc., may be set from the reference 

 stakes by means of a string level and a metallic tape. 



Culvert locations usually are fixed on the ground by means of two 

 stakes in the line of the culvert, one near each end. 



