Q$4.$ At $10m$ depth, a silty sand layer was encountered and the Standard Penetration Test $($SPT$)$ was performed. Blows for the first, second, and third $15cm$ ground penetration were reported as $4,6,$ and $11,$ respectively. The energy rate of the ram is $50\%.$ The borehore diameter is $200mm$ and the SPT sampler without liner is used. The rod length from the bottom of the ram to a depth of $10m$ is $12m.$ Calculate $N_{1,60}$ value. $($GWT is $4m$ below ground surface and unit weight above and below GWT is $19k\frac{N}{m^3}$ and $20k\frac{N}{m^3}$ respectively$)$

TABLE $3-3$

Factors ${}_i$ For Eq$.(3-3)*$