$13\mathrm{.}4$ During a subsoil exploration program, undisturbed nomally consolidated silty clayy samples were collected in Shelby tubes from location $A$ as shown in Figure $13\mathrm{.}62.$

Following are the results of four drained, direct shear tests conducted on the clay samples with each having a diameter of $63\mathrm{.}5mm$ and height of $32mm.$

Test no$.$

$\frac{1}{25}$

Nomal force $($N$)$

$1$

$84$

$2$

$168$

$4$

$360$

Shear force at fallure

$($N$)$

$28\mathrm{.}9$

$28\mathrm{.}9$

$59\mathrm{.}6$

$89\mathrm{.}1$

$125,3$

a$.$ Determine the drained angle of friction for the silty clay soul.

b$.$ Determine the shear swength of the clay in the field at location $A.$

Problem $13\mathrm{.}4$ Part $($a$)$

The area of the specimen $A=$

$m^2$

$($Express your answer with five decimal places, e$.$g$.,0\mathrm{.}12345$; unit: $m^2)$

Test $1$:

The normal stress at failure, sigma$\_1=$

$k\frac{N}{m^2}$

The shear stress at failure, tau$\_$f$1=$

$k\frac{N}{m^2}$

$($Express your answer with one decimal place$)$