84 MECHANICAL ANALYSIS OF SOIL 



shallow layer, to a depth of 9 inches, as representing 

 the soil proper. Three methods are in general use, 

 the surface vegetation being first removed in each 

 case. 



{a) A surface 6 inches square is marked out with a 

 spade, and the sides of the square cut down to a depth 

 6f 9 inches. The surrounding soil is cut away and the 

 block removed with the spade, either at the 9-inch depth 

 or at the line where the subsoil commences. 



[b) A more accurate way is to use a steel box 

 without top or bottom, 6 inches square in section and 9 

 inches deep. The box is placed in position and 

 hammered down until the top is flush with the 

 surrounding soil The contents are then carefully 

 removed and conveyed to the laboratory. 



ic) Samples are most conveniently taken by means 

 of an auger, many types of which exist. The auger is 

 forced gently into the soil to the required depth, the 

 tool removed and the core extracted. The advantage 

 of this method is that the boring may be continued into 

 the subsoil to any depth if necessary. 



64. Preparation of the Sample. 



The well-mixed borings are spread out on shallow 

 trays to dry. This may be expedited by heating in the 

 oven to a temperature not exceeding 40° C. About i 

 lb. of dry material is weighed out and then transferred to 

 a sieve with 3 mm. diameter round meshes, and separated 

 as much as possible. The portion which does not pass 

 the sieve is rubbed in a mortar with a wooden pestle, 

 care being taken not to crush the stones, pieces of chalk, 

 etc., and the material again sieved. The portion 

 remaining upon the sieve is well washed in a stream of 

 water until all the fine soil is removed, any portions 



