Complete phase diagram and required properties.

Sieve analysis

$($U$.$S$.$ Standard sieve$)$

$No.200,100,40,10,4,\frac{3}{8}in.\frac{3}{4}in.3in.$

FIGURE $2\mathrm{.}6$ Typical grain size distributions.

with only one grain size. Very poorly graded soils, such as beach sands, have a $C_u$ of $2$ or $3,$ whereas very

well graded soils may have a $C_u$ of $15$ or greater. Occasionally the $C_u$ can range up to $1000$ or so$.$ As an

example, the clay core material for Oroville Dam in California has a $C_u$ of between $400$ and $500$; the

sizes range from large boulders down to very fine$-$grained clay particles.

Another shape parameter sometimes used for soil classification is the coefficient of curvature,

defined as

$C_c=\frac{D_{30}^2}{D_{10}{D}_{60}}$

where $D_{30}=$ grain diameter $($in mm$)$ corresponding to $30\%$ passing by weight $($or mass$).$ The other

terms were defined previously.

A soil with a coefficient of curvature between $1$ and $3$ is considered to be well graded as long as

the $C_u$ is also greater than $4$ for gravels and $6$ for sands.

Example $2\mathrm{.}11$

Given:

The grain size distributions shown in Fig. $2\mathrm{.}6.$

Required:

Determine $D_{10},C_u,$ and $C_c$ for each distribution.