8 BULLETI1S3' 3*73^ U. S. DEPARTMENT OF AGEIGULTTJRE. 



It is also advisable to require a minimum as well as a maximum 

 percentage of loss which any specified sample of the brick ma}^ sus- 

 tain. This is done in order to insure against too much variation 

 between the softest acceptable brick and the hardest brick which may 

 be supplied. 



CONSTRUCTION. 



PREPARING THE ROADBED. 



In forming a roadbed upon which a brick pavement is to be con- 

 structed, the essential features to be considered are (1) thorough 

 drainage, (2) firmness, (3) uniformity in grade and cross section, 

 and (4) adequate shoulders. 



Thorough drainage can be secured for any particular road only by 

 means of a careful study of the local conditions which affect the 

 accumulation and " run-off " of both the surface and ground water. 

 These conditions vary considerably even in the same locality, and no 

 set of rules can be given which would cover all cases. For example, 

 the material composing the roadbed may be springy, and in this case 

 tile underdrains will probabh^ be necessary. On the other hand, 

 extremely flat topograph}'' may make it necessary to elevate the grade 

 considerably above the surrounding land. The nature of the soil, the 

 topography, and the rainfall must all be considered if a sj^stem of 

 drainage is to be planned properly. 



The second requirement, firmness, can be secured only after the 

 road has been properly drained. Soils which readil}^ absorb moisture 

 can not be properly drained in wet weather and should not be per- 

 mitted to form a part of the subgrade. In order that the subgrade 

 may be unyielding, it is also necessary that the roadbed be thoroughly 

 compacted. In forming embankments the material should be put 

 down in laj^ers not over 8 inches thick, and each layer should be 

 thoroughlj^ rolled. In excavation care should be exercised, if the 

 material is earth, not to permit plows or scrapers to penetrate below 

 the subgrade. The subgrade in both excavation and embankment 

 should be brought to its final shape by means of fine grading with 

 picks and shovels and rolling. 



When completed the subgrade should be uniform in grade and 

 cross section; otherwise the foimclation must be made unnecessarily 

 thick where depressions occur, in order that its grade and cross 

 section may be uniform and its thickness not less at any point than 

 that required. The subgrade should be repeatedly rolled and re- 

 sha^Ded until the desired shape is secured. If curbs are constructed 

 independent of the base they should be set before the final finishing, 

 in order that they may be made to serve as a guide for this work. 



The shoulders should never be less than 4 feet wide and should 

 consist of some material which compacts readily under the roller and 



