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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.


Sagot :

Solution :

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 [tex]$=1500 \ lb/ft^2$[/tex]

                                              [tex]$= 71.82 \ kN/m^2$[/tex]

                                             [tex]$ \sim 72 \ kN/m^2 $[/tex]

Now,

[tex]$N_1=N_0 \left(\frac{350}{\bar{\sigma}+70} \right)$[/tex]

[tex]$N_1 = $[/tex] corrected N - value of overburden

[tex]$\bar{\sigma}=$[/tex] effective stress at level of test

0 - 6 inch, [tex]$N_1=4 \left(\frac{350}{72+70} \right)$[/tex]

                      = 9.86

6 - 12 inch, [tex]$N_1=6 \left(\frac{350}{72+70} \right) $[/tex]

                        = 14.8

12 - 18 inch, [tex]$N_1=6 \left(\frac{350}{72+70} \right) $[/tex]

                         = 14.8

[tex]$N_{avg}=\frac{9.86+14.8+14.8}{3}$[/tex]

       = 13.14

       = 13

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