A cantilever retaining wall is retaining coarse grained sandy backfill as shown below. A standard penetration test was performed within the backfill material, and the average N value for this sand profile was $7($i$.$e$.,$ N $-$value $=7).$ The hammer energy efficiency used to drive the split spoon was $100\%.$

Answer the following questions.

Calculate $N_{60}.[3$ points$]$

Calculate $N_{1,60}$ at the midpoint height $($i$.$e$.,$ at $5$ feet$)$ of the backfill. $[3$ points$]$

What is the average friction angle for this sand? $[3$ points$]$

What is the magnitude of wall top movement $()$ needed to mobilize the full active earth pressure? $[5$ points$]$

Now, assuming that the active earth force is fully mobilized, answer the following.

$5.$ Using Rankine Earth Pressure Theory, what is the active earth pressure coefficient $(K_A)$ for this sand? In estimating $K_A,$ use the friction angle found in part $3.[3$ points$]$

$6.$ Plot the distribution of the active lateral earth pressure behind the backfill. $[6$ points$]$

$7.$ What is the magnitude of the total active force? $[4$ points$]$

$8.$ What other methods $($i$.$e$.,$ other than Rankine's$)$ you could have used to estimate the active earth pressure? $[3$ points$]$

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A cantilever retaining wall is retaining coarse grained sandy backfill as shown below. A standard penetration test was performed within the backfill material, and the average N value for this sand profile was $7($i$.$e$.,$ N $-$value $=7).$ The hammer energy efficiency used to drive the split spoon was $100\%.$

Answer the following questions.

Calculate $N_{60}.[3$ points$]$

Calculate $N_{1,60}$ at the midpoint height $($i$.$e$.,$ at $5$ feet$)$ of the backfill. $[3$ points$]$

What is the average friction angle for this sand? $[3$ points$]$

What is the magnitude of wall top movement $()$ needed to mobilize the full active earth pressure? $[5$ points$]$

Now, assuming that the active earth force is fully mobilized, answer the following.

$5.$ Using Rankine Earth Pressure Theory, what is the active earth pressure coefficient $(K_A)$ for this sand? In estimating $K_A,$ use the friction angle found in part $3.[3$ points$]$

$6.$ Plot the distribution of the active lateral earth pressure behind the backfill. $[6$ points$]$

$7.$ What is the magnitude of the total active force? $[4$ points$]$

$8.$ What other methods $($i$.$e$.,$ other than Rankine's$)$ you could have used to estimate the active earth pressure? $[3$ points$]$