A vane shear tester is used to determine an approximate value of the shear strength

of clay $($undrained shear strength$)$ in the field. The field measured shear strength

values need to be corrected for plasticity of clay before using them in the design

calculations. The tester has a blade diameter of $60mm$ and a blade height of $180$

$mm.$ In a field test, the vane required a torque of $42\mathrm{.}5Nm$ to shear the clay, which

has a liquid limit of $70\%$ and a plastic limit of $23\%.$ The undrained shear strength of

clay to be used in foundation design is:

$C_{u(\text{D}\text{e}\text{s}\text{i}\text{g}\text{n})}=C_{u(\text{F}\text{i}\text{e}\text{l}\text{d})}$

$($ correction factor $)=1\mathrm{.}7-0\mathrm{.}54log(\frac{?}{PI}\%)$

$PI-$ Plasticit $y$ Index

$C_u=\frac{T}{(\frac{d^{2}h}{2}+\frac{d^3}{6})}$

$37\mathrm{.}6$kPa

$24\mathrm{.}4$kPa

$30\mathrm{.}0$kPa

$54\mathrm{.}0$kPa