Question

As per the compaction specification, a highway fill of 1.5 km length has to be compacted to 90% of Indian standard light compaction test dry density. A borrow pit available near the project site has a dry density of 1.78 g/cc at 100% compaction and a void ratio of 0.63. The volume of borrow pit material required to construct a highway fill of height 5 m and top width of 10.5 with side slope of 1V:2H is (Assume G=2.7)

• A. 153750 m${}^3$
• B. 158937m${}^3$
• C. 148731m${}^3$
• D. 57486m${}^3$

Answer 1

The correct option is C 148731m${}^3$



${\gamma }_{d\left(borrow\right)}=1.78g/cc$
$e_{borrow}=e_b=0.63$
G = 2.7

Base width of highway fill $=2\times (2\times 5)+10.5=30.5$ m
Vol. of highway fill, $V_f=\frac{1}{2}(10.5+30.5)\times 5\times 1500=153750m^3$

Dry density of highway fill (90%)$=0.90\times 1.78=1.602$ g/cc
To find void ratio of fill

${\gamma }_{d\left(fill\right)}=\frac{G{\gamma }_w}{1+e_f}$
$1.602=\frac{2.7\times 1}{1+e_f}$
$e_f=0.685$

Since volume solids remain constant in both borrow pit and fill

$\frac{V_b}{1+e_b}=\frac{V_f}{1+e_f}$

$V_b=\left(\frac{1+e_b}{1+e_f}\right)V_f=\left(\frac{1+0.63}{1+0.685}\right)\times 153750=148731m^3$