Foundations Assignment on Spudcan Foundation
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OT5206 Offshore Foundations Assignment on Spudcan Foundation
Although the submission date is set to be the day before your OT5206 Exam to provide
you flexibility in time management, you are advised to tackle this assignment as early as
possible because this will help you to revise the topic of spudcan foundation.
This assignment will count towards 10% of OT5206 total marks.
Answer both questions. You may make appropriate assumptions if you think there are
missing/incorrect information.
Question 1 (modified from 2021 Exam Q2)
(a) Fig. 1 shows a borehole log from an offshore site. Determine the average
undrained shear strength and submerged unit weight of (i) the upper stiff to very
stiff clay layer from 0.8 m to 3.9 m depth, and (ii) the lower soft to firm clay layer
from 3.9 m to 6.9 m depth. Hence determine whether punch through would occur
during spudcan penetration or not, if the maximum preload is 170 kPa for an 18-
m diameter spudcan. You may ignore the thin upper sand layer and take that
upper clay starts at the mudline (i.e. 0 m depth). You must include the cavity
height in your calculations.
Fig. 1 Borehole Log
(b) A jack-up spudcan foundation has an equivalent diameter of 25 m. The clayey
seabed has an undrained shear strength of 35 kPa and an average submerged unit
weight of 8 kN/m3. If the anticipated preload is 350 kPa, estimate the approximate
penetration depth of the spudcan. You must include the cavity height in your
calculations. [Hint: The penetration depth is greater than 30 m.]
Question 2 (modified from 2019 Exam Q2)
(a) A 20-m diameter spudcan will be installed in a clay overlying sand. The clay has an
undrained shear strength of 35 kPa, a unit weight of 18 kN/m3 and a thickness of 9
m.
(i) Determine the limiting depth of cavity that remains open above the spudcan
during penetration Hcav.
(ii) Estimate the depth of the spudcan penetration when squeezing of the upper
soft clay will start to occur.
(b) An 18-m diameter spudcan has been installed to a penetration depth of 28 m.
Taking that the average shear strength to be 30 kPa and the sensitivity of the soil to
be 2.8, determine the maximum unfactored moment load that the spudcan can resist
using the V-M envelope formulation for spudcan. You may assume Hcav to be
negligible for such deep spudan penetration.