HIGHWAY CONSTRUCTION 



49 



represents the natural surface of the ground, C K B the excavation, 

 and ADC the embankment, resting on steps which have been cut 

 between A and C. The best position for these steps is perpendicular 

 to the axis of greatest pressure. If A D is inclined at the angle of 

 repose of the material, the steps near A should be inclined in the 



Fig. 23. Method of Construction on Hillsides. 



opposite direction to AD, and at an angle of nearly 90 degrees 

 thereto, while the steps near C may be level. If stone is abundant, 

 the toe of the slope may be further secured by a dry wall of stone. 

 On hillsides of great inclination the above method of construc- 

 tion will not be sufficiently secure; retaining walls of stone must 

 be substituted for the side slopes of both the excavations and em- 

 bankments. These walls may be made of stone laid dry, when stone 



Fig. 24. Hillside Road with Retaining and Revetment Walls. 



can be procured in blocks of sufficient size to render this kind of con- 

 struction of sufficient stability to resist the pressure of the earth. 

 When the stones laid dry do not offer this security, they must be laid 

 in mortar. The wall which forms the slope of the excavation should 

 be carried up as high as the natural surface of the ground. Unless 

 the material is such that the slope may be safely formed into steps 

 or benches as shown in Fig. 23, the wall that sustains the embank- 

 ment should be built up to the surface of the roadway, and a parapet 



