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Question 35.4: Find the skin friction of the 4 ft diameter caisson shown in...

Find the skin friction of the 4 ft diameter caisson shown in Fig. 35.7 using the Meyerhoff equation. The average SPT (N) value along the shaft is 15 blows per foot. Ignore the skin friction in the fill material.

35.7
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Only the skin friction is calculated in this example.
Calculate the skin friction.
For fine sand the unit skin friction can be calculated as

f = N/108 tsf
= 15/108 tsf
= 0.14 tsf
total skin friction = unit skin friction × perimeter surface area
=0.14 × π × D × L
= 0.14 × π × 4 × 32 = 56 tons (498 kN)

allowable skin friction = 56/F.O.S.
Assume a factor of safety (F.O.S.) of 3.0.

allowable skin friction = 56/3.0 = 18.7 tons (166 kN)

 

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