Question $3$

$($a$)($i$)$ Explain why the dry density of compacted soil is lower for moisture contents smaller and

greater than the optimum moisture content.

$($ii$)$ What is the purpose of control testing after a field soil compaction? State two test methods

to determine the bulk density of a compacted soil in the field.

$($b$)$ The results of a standard energy compaction test on a sample of silty clay are given in the

table below.

$($i$)$ Plot the compaction curve for the above soil on the axes provided on Page $7($bottom$)$ and

hence determine the values of maximum dry density and optimum moisture content.

$($ii$)$ If $Gs=2\mathrm{.}70,$ perform the required calculatiofs and plot the $5\%$ air void curve on the same

graph.

$($c$)($i$)$ Briefly describe the key steps of standard penetration test $($SPT$)$ for estimating basic soil

properties in the field.

$($ii$)$ Briefly describe the process of using hydraulic fracturing technique for geothermal energy

extraction.