The Mississippi DOT proposes to construct a $72-$inch outer diameter by

$0\mathrm{.}75$ thick storm drain beneath I$-20$ near the Pearl River in Jackson. The pipeline will be steel

and the crossing will be approximately $300$ feet long. The proposed construction method is

auger boring $($jack and bore$).$ The drawings indicate earth cover above the invert of the storm

drain pipe will vary from $15$ to $20$ feet. A geotechnical investigation was conducted for the

crossing. The logs of the $2$ borings drilled on either side of I$-20$ are attached. The boring logs

indicate loose to medium dense silty sand. Groundwater was encountered at about $12$ feet

below I$-20$ ground surface. Research settlement risk evaluation methods and the auger boring

method. Review provided geotechnical information. Answer the following:

$1.$ Calculate the anticipated systematic settlements associated with closure of the

annular space between the bore and the steel storm drain pipeline. Assume that

the bore diameter is $74$ inches, creating a radial overcut of $1\mathrm{.}0$ around the pipe.

Bracket your results using conservative but realistic assumptions and more realistic

less conservative assumptions regarding closure of the annulus. Assume that the

annulus is completely filled with bentonite lubricant for case $2$ but no bentonite

lubricant is injected for case $1.$ List all assumptions and the calculation

model$/$approach used in your work.

$2.$ Calculate the anticipated settlements associated with $1\%$ and $2\%$ face losses.

$3.$ Combine the results of $1$ and $2$ to Estimate total settlements.

$4.$ Are the estimated total settlements likely acceptable to MSDOT?

$5.$ Is the auger boring method appropriate for the proposed crossing? If not what

would be a more appropriate method to use?

$6.$ What would be the expected settlement if we could $$wish the storm drain pipeline

into place$?$

$7.$ Bonus: If settlements exceed values to MS DOT, what mitigation measures could be

implemented to reduce them?