$1\mathrm{.}3$ Exercise $3$

An excavation work between retaining walls for an underground passage project was carried out

in a soil with an initial $4-$meter$-$thick gravel stratum, followed by an intermediate $10-$meter thick

sand stratum, and finally, a $15-$meter thick stratum of very dense clay. The phreatic level was $2,5$

meters below ground surface.

The excavation height is $8$ meters and was implemented in $2-$meter$-$high load steps. In the case

of the retaining walls, they are made of $1-$meter$-$thick and $12-$meter$-$high reinforced concrete. For

the construction of these retaining walls, three perpendicular tubular steel struts were installed,

with a $70cm$ diameter and $60mm$ thickness, with vertical and horizontal spacings of $2$ meters;

the first strut was installed one meter from the wall head. At the end of the excavation works, a

$70-$ cm$-$thick reinforced concrete floor slab was laid at the bottom and a $60-$ cm$-$thick concrete

slab was set at the head of the retaining wall to cover the underground passage. Next, the steel

struts were pulled out.

Currently, a $5-$floor residential building project is intended to be carried out $15$ meters from the

existing retaining walls, whereas each floor represents a $30$kPa load on the soil with a length of

$30$ meters length.

As a geotechnical engineer, you have been tasked with conducting an analysis on the possible

impact the construction works will have on the passage's retaining walls and slabs. In order to

conduct tis analysis, you must create a Plaxis $2$D numerical model, and consider the following

questions:

What elements would you use to model the problem's components $($retaining walls, steel

struts, slabs, loads, etc.$)?$

What construction phases should the model use?

What mechanical calculation types should be performed to analyze the problem correctly?

What essential results should be rigorously analyzed?