Civil Engineering Reference
In-Depth Information
The safety factors against bearing-capacity failure recommended herein are
2.0 for on-bottom gravity loads alone and 1.5 for the design environmental con-
dition applicable for the installation period.
Allowable steel stresses may be increased by one-third when wave loading
is included. In the event of rough seas or if the installation equipment must
leave the site for other reasons before the jacket has been adequately secured
with piles, the effective weight on bottom may require adjustment to minimize
the possibility of jacket movement due to skidding, overturning or soil failure.
Settlement of the mud mat is often predicted by the method of comparison
between the applied pressure and the ultimate bearing capacity. This method is
simple and easy to apply in the analysis. In the actual case, settlement of the
mud mat could be a very important aspect to investigate, especially when the
topsoil is weak. Therefore, a proper method should be identified to provide
this information as part of the design practice. A check list for on-bottom
stability analysis is given in
Table 3.15
.
TABLE 3.15
Check List for Jacket On-Bottom Stability Analysis
Check
(yes/no)
Items
Check Point
I
Computer Model
1
It is assumed that the model is checked for dimensions, elevations,
member group and section properties in the in-service analysis and is
upgraded to suit the current analysis. Check for LDOPT, OPTIONS,
UCPART in the input file Model modifications to suit the current
analysis
(a) remove pile, appurtenances
(b) revise
C
d,
C
m with member and group overrides as for clean
members in the entire structure
(c) Remove marine growth card from the input file
(d) Check for flooded members and support conditions
II
Loads
1
It is assumed that the load calculations are verified in the in-service
analysis and only relevant load cases are picked for the current
analysis
2
Wave parameters
—
Installation wave conditions and directions
3
Weight of lead and add-on pile sections (before driving in)
4
Load contingencies
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