Chapter 12, Problem 12.1P

(a)

To determine

State whether the statement “thinner the wall, the higher is the area ratio of a sampling tube” is true or false.

Answer to Problem 12.1P

The given statement is $\underset{\_}{\text{False}}$.

Explanation of Solution

Show the expression for the area ratio.

$\begin{array}{l}{A}_R\left(\%\right)=\frac{D_o^2-D_i^2}{D_i^2}\\ A_R\left(\%\right)\propto D_o^2-D_i^2\end{array}$

Here, $A_R$ is the area ratio, $D_o$ is the outside diameter, and $D_i$ is the inside diameter of the sampler tube.

As per the formula, the area has the direct proportional relationship with the value of $D_o^2-D_i^2$.

The formula denotes if the wall thickness of the sampling tube is high, the area ratio will be higher and vice versa.

Hence, the given statement is $\underset{\_}{\text{False}}$.

(b)

To determine

State whether the statement “samples recovered from the split-spoon samplers are highly disturbed” is true or false.

Answer to Problem 12.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

Split-spoon samplers are used to obtain representative samples suitable for the field examination of soil texture and fabric. The samples obtained by this process are highly disturbed.

Hence, the given statement is $\underset{\_}{\text{True}}$.

(c)

To determine

State whether the statement “$N_{60}$ is greater than $N_{70}$ in a standard penetration test” is true or false.

Answer to Problem 12.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

Express the relationship between standard penetration numbers $N_{60}$ and $N_{70}$.

$\begin{array}{c}{N}_{70}=N_{60}\times \frac{60\%}{70\%}\\ =N_{60}\times \frac{0.6}{0.7}\\ =N_{60}\times 0.86\end{array}$

In $N_{60}$, 60 denotes 60 % hammer efficiency and in $N_{70}$, 70 denotes the 70 % hammer efficiency.

Thus, the value of $N_{70}$ is only 0.86 times the value of $N_{60}$. Thus, $N_{60}$ value is larger than the value of $N_{70}$.

Hence, the given statement is $\underset{\_}{\text{True}}$.

(d)

To determine

State whether the statement “$N_{60}$ can be greater or less than ${\left(N_1\right)}_{60}$ in a standard penetration test” is true or false.

Answer to Problem 12.1P

The given statement is $\underset{\_}{\text{True}}$.

Explanation of Solution

Express the relationship between the effective overburden pressure ${\left(N_1\right)}_{60}$ and $N_{60}$.

${\left(N_1\right)}_{60}=C_N{N}_{60}$

Here, $C_N$ is the correction factor.

The value of $C_N<1$ results in ${\left(N_1\right)}_{60}<N_{60}$.

The value of $C_N>1$ results in ${\left(N_1\right)}_{60}>N_{60}$.

The value of $C_N=1$ results in ${\left(N_1\right)}_{60}=N_{60}$.

Hence, the given statement is $\underset{\_}{\text{True}}$.

(e)

To determine

State whether the statement “vane shear test can be carried out in sands” is true or false.

Answer to Problem 12.1P

The given statement is $\underset{\_}{\text{False}}$.

Explanation of Solution

The un-drained shear strength of soft clay is estimated directly by the Vane shear test. Reliable results only in medium stiff clays and soft clays are obtained from the field vane shear test.

Vane shear test is valid for only cohesive soil and it is not suitable for clays which contain sand or silt laminations in it.

Hence, the given statement is $\underset{\_}{\text{False}}$.