Question

A standard penetration test has been conducted on a coarse sand at a depth of 16 ft below the ground surface. The blow counts obtained in the field were as follows:

0-6 in. 4 blows; 6-12 in.: 6 blows; 12-18 in.: 6 blows. The tests were conducted using a USA-style donut hammer in a 6-in diameter boring using a standard sampler with the liner installed. The vertical effective stress at the test depth was 1500 lb/ft^2. Determine N1.60.

Answer 1

Given :

The number of blows is given as :

0 - 6 inch = 4 blows

6 - 12 inch = 6 blows

12 - 18 inch = 6 blows

The vertical effective stress
`$=1500 \ lb/ft^2$`

`$= 71.82 \ kN/m^2$`

`$ \sim 72 \ kN/m^2 $`

Now,

`$N_1=N_0 \left(\frac{350}{\bar{\sigma}+70} \right)$`

`$N_1 = $` corrected N - value of overburden

`$\bar{\sigma}=$` effective stress at level of test

0 - 6 inch,
`$N_1=4 \left((350)/(72+70) \right)$`

= 9.86

6 - 12 inch,
`$N_1=6 \left((350)/(72+70) \right) $`

= 14.8

12 - 18 inch,
`$N_1=6 \left((350)/(72+70) \right) $`

= 14.8

`$N_(avg)=(9.86+14.8+14.8)/(3)$`

= 13.14

= 13