CV$6311$

$4.($a$)$ A Standard Penetration Test $($SPT$)$ using a donut hammer and a standard split$-$spoon sampler is carried out in a coarse sand deposit at $8$ m below the ground surface. The groundwater table $($GWT$)$ is at $3$ m below the ground surface. The total unit weights of the sand deposit above and below the GWT are $17k\frac{N}{m^3}$ and $18\mathrm{.}5k\frac{N}{m^3},$ respectively. The unit weight of water ${}_w=9\mathrm{.}81k\frac{N}{m^3}.$ Given that the number of blows for three consecutive $150$ mm penetration from the SPT test are $3,4$ and $5$ respectively and the borehole diameter is $100$ mm $,$ determine the corrected N value and briefly describe why $C_N$ is needed.

$(8$ Marks$)$

Note: Standard Penetration Test

$N_{eo}=N_{\text{m}\text{e}\text{a}\text{s}}{C}_E{C}_B{C}_S{C}_R$

Coarse$-$grained soil

$(N_1{)}_{60}=C_N{N}_{60}$ where $C_N=(\frac{100}{{}_{v0}}{)}^{0\mathrm{.}5}$ and ${}^{\text{'}}{v}_0$ is in kPa $.$

$($b$)$ A Cone Penetration Test with pore$-$water pressure measurement $($CPTu$)$ is conducted in a soil deposit at $17$ m below the ground surface. The groundwater table is at $3$ m below the ground surface. The total unit weights of the soil deposit above and below the groundwater table are $17k\frac{N}{m^3}$ and $18\mathrm{.}5k\frac{N}{m^3},$ respectively. The unit weight of water ${}_w=9\mathrm{.}81k\frac{N}{m^3}.$ The technical data of the CPTu test are the cone resistance $q_c$ is $0\mathrm{.}6$ MPa $,$ the total cone resistance $q_t$ is $0\mathrm{.}875$ MPa and the $($or a$)$ coefficient of the cone is $0\mathrm{.}58.$ Identify the soil type and calculate the pore$-$water pressure $u_2,$ shear strength and overconsolidation ratio of the soil deposit at the level of the cone tip. Comment on the OCR value.

$(8$ Marks$)$

Note: Cone Penetration Test CPTu

Corrected cone resistance: $q_t=q_c+(1-a)u_2,$ where $a=\frac{d^2}{D^2}$

Penetration pore$-$water pressure ratio: $B_q=\frac{u_2-u_0}{q_t-{}_{v0}}$

Friction ratio: $F_{,}=\frac{f_s}{q_1-{}_{20}}100\%$

$D=$ Outer cone diameter, $d=Ier$ cone diameter.

Note: Question No$.4$ continues on page $5.$