Problem Statement

A $5-$m$-$high highway embankment is to be constructed over a landfill that has a fine$-$grained soil

cover underlain by a soil mixture with a total thickness ranging from $5\mathrm{.}0$ to $8\mathrm{.}2$ m $.$ This soil

mixture includes primarily silts and clays with construction waste $($concrete blocks, brick

fragments, etc.$).$ At certain locations, there are voids and loose pockets within the landfill.

Standard penetration tests performed prior to ground improvement indicate SPT values ranging

from about $5$ to $20$ with an average of $10.$ The predicted settlement ranged from $140$ to $274$

mm $.$ Dynamic compaction is selected to reduce the anticipated total and differential settlements.

The required SPT $N$ value after improvement should be at least $20.$ The surface of the

landfill is strong enough to support the dynamic compaction equipment. Leachate inside the

landfill was at a relatively shallow depth $($approximately $2\mathrm{.}5$ m from the existing surface$).$

To minimize the generation of excess pore water pressure, multiple pass construction may be

needed. The contractor has an $18\mathrm{.}2-$ ton tamper that has a diameter of $1\mathrm{.}5$ m and a height of

$1\mathrm{.}5$ m $.$ You are requested to provide a preliminary design for the dynamic compaction project

and estimate the settlement after compaction.