HIGHWAY CONSTRUCTION 47 



The shrinkage in the different materials is about as f'oll< 



Gravel X per cent 



Gravel and sand <) " " 



Clay and clay earths 10 " 



Loam and light sandy earths. . . 



Loose vegetable soil 



Puddled clay 2"> 



Thlis an excavation of loain measuring 1,000 cubic yards will 

 form only about 880 cubic yards of embankment, or an embankment 

 of 1,000 cubic yards will require about 1,120 cubic yards measured 

 in excavation to make it. A rock excavation measuring 1 ,000 yards 

 will make from 1,500 to 1,700 cubic yards of embankment, depending 

 upon the size of the fragments. 



The lineal settlement of earth embankments will be about in 

 the ratio given above; therefore either the contractor should be 

 instructed in setting his poles to guide him as to the height of grade 

 on an earth embankment to add the required percentage to the fill 

 marked on the stakes, or the percentage may be included in the 

 fill marked on the stakes. In rock embankments this is not necessary. 

 Classification of Earthwork. Excavation is usually classi- 

 fied under the heads earth, hardpan, loose rock, and solid rock. For 

 each of these classes a specific price is usually agreed upon, and an 

 extra allowance is sometimes made when the haul or distance to 

 which the excavated material is moved exceeds a given amount. 



The characteristics which determine the classes to which a given 

 material belongs are usually described with clearness in the speci- 

 fications, as: 



Earth will include loam, clay, sand, and loose gravel. 

 Hardpan will include cemented gravel, slate, cobbles, and boul- 

 ders containing less than one cubic foot, and all other matters of an 

 earthy nature, however compact they may be. 



Loose rock will include shale, decomposed rock, boulders, and 

 detached masses of rock containing not less than three cubic feet, 

 and all other matters of a rock nature which may be loosened with a 

 pick, although blasting may be resorted to in order to expedite the 

 work. 



Solid rock will include all rock found in place in ledges and 



