Question $2$

$2\mathrm{.}1$ You are the technologist at a road construction site. The laboratory report shows that for the subbase material, the maximum Dry Density $($MDD$)$ is $1900k\frac{g}{m^3}$ with an Optimum Moisture Content $($OMC$)$ of $11\%.$ The road drawings indicate a requirement of $"93\%$ MOD" for the subbase layer. An average in$-$situ density of $1800k\frac{g}{m^3}$ was determined by conducting sand replacement tests.

$2\mathrm{.}1\mathrm{.}1$ Determine if the subbase layer is adequately compacted.

$(3)$

$2\mathrm{.}1\mathrm{.}2$ What is the significance of the OMC value in the subbase construction?

$(3)$

$2\mathrm{.}1\mathrm{.}3$ What other method can be used to assure subbase compaction?

$(2)$

$2\mathrm{.}1\mathrm{.}4$ Explain the mechanism by which compaction increases the soil density.

$(2)$

$3$ of $12$

TPG$3700-$ Major Test $2-06/09/2024$

$2\mathrm{.}2$ Hand$-$augured technique is utilised to obtain soil samples along the centre line of a proposed Category $($B$)$ road in a cut section. The road is in a wet region, between chainages $0+000$ and $1+200.$ The samples were taken to UNISA Civil Engineering laboratory in Florida, Johannesburg. The tested CBR values are as follows:

$\backslash$table$[[$Chainage$,$CBR $(\%),$Chainage,CBR

Given that the subgrade is delineated into three uniform sections: Area to $0+400,$ Area to $0+700,$ and Area to $1+200.$ Determine the design CBR for the specified subgrade areas. Additionally, provide neat, labelled crosssectional sketches to display your subgrade designs.

$(20)$

$[30$ marks$]$