where e = void ratio 



W = water content 

 G = specific gravity of particles 



The plasticity index (Equation 5) represented the difference between 

 the liquid limit and the plastic limit, while the liquidity index 

 (Equation 6) equalled the difference between the original water 

 content and the plastic limit divided by the plasticity index. 



PI = LL - PL (5) 



LI ■ ^ (6) 



where LI = the liquidity index 



PL = the plastic limit 



PI = the plasticity index 

 STRENGTH CONSIDERATIONS 



The various classification systems generally distinguish between 

 a cohesive and a cohesionless soil. This distinction arises because 

 the factors affecting the strength of soils in each category differ. 

 The strength of a cohesionless soil depends upon the soil's density, 

 the particle angularity and shape, the particle size, and the particle 

 gradation. The strength of a cohesive soil, in turn, is a function 

 of the particle mineralogy, the particle size, the void ratio, the 

 effective stress in the vertical and horizontal planes, and the soil's 

 stress history. Since the two varieties of soils derive their strength 

 by independent mechanisms, the criteria involved in evaluating the 

 two soils for strength must differ. 



Unfortunately, the vane shear device has been used to test both 

 cohesive and cohesionless sediments. However, the device was designed 

 to measure the undrained strength of cohesive soils. Even in this 

 role, it has limitations which should be understood. 



The first paragraph in this section also mentioned that the 

 strength of a soil varies as certain sediment properties vary. In 

 some cases, these changes correspond to alterations in the depositional 

 environment. A few sentences are, therefore, devoted to the variation 

 of strength with environmental conditions. 



