Location Assessment Process

for Jack-Up Units

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 Table of Contents
1. Introduction................................................................................................................ 5
2. Risks............................................................................................................................... 6
3. Location Assessment................................................................................................ 8
4. Location assessment documents.......................................................................... 9
5. Risks / Control Measures..................................................................................... 11
6. Risk Flow Charts...................................................................................................... 14
Appendix A – Example of Leg Penetration Analysis.....................................................16
Appendix B - Example of Penetration History................................................................17
Appendix C – Example of Footprint overlay on detailed side scan sonar Seabed
survey........................................................................................................................................... 18
Appendix D – Example of Footprint Overlay from History (to be used when
detailed seabed survey not available)..............................................................................19

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 Abbreviations

LPA Leg Penetration Analysis

RPD Rack Phase Difference
RA Risk Assessment
SBS Seabed Survey
SSA Site Specific Assessment
VDL Variable Deck Load

Definitions

Bearing Pressure The Bearing Pressure is the seabed footing

reaction divided by the spudcan footing area. The
higher the Bearing Pressure the more weight is
exerted onto the soil which would most cause
higher penetration in soft soils.
Hang up A ‘Hang up’ situation is where the weight of the
unit should cause the leg(s) to penetrate a
particular layer of soil during preload / predrive
but when the Barges reaches the location one or
more leg does not penetrate this layer. The Unit is
then at risk as the soil layer in question could
break / give way at any time.

In the case of a hang up all predrive / preload

should be suspended and the Master must seek
advise from his company as how to proceed.
Leg Penetration Analysis A Leg Penetration Analysis is a study that is
(LPA) conducted by a Geotechnical Company where a soil
sample is analyzed for that specific unit. The LPA
shows how the soil is expected to react when the
weight and specifications for that Unit is applied.
Pinion loads The pinion loads is the weight excreted onto the
jacking system, this includes the weight of the unit
including all variable deck load but does not
include the weight of the legs.
Preload Preloading is an operation where the weight that
the Unit exerts onto the soil is increased to a
specific weight as defined in the Marine Operations
Manual in order to test the soil beyond the
maximum weight that the unit will face in fully
loaded operational and storm conditions.

Preload can be done by adding preload / Ballast

water on 3-legged units or by using opposing legs
on 4 legged units.
Punch Through A Punch through is when a leg (or legs) penetrate
so quickly that the jacking system cannot maintain
the barge in a level position.

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 Rack Phase Difference Rack Phase Difference is specific to Truss Legs and
(RPD) it is when there is a difference in height between
the chords. When RPD is present there will be
stress on the horizontal braces and could cause
significant damage.

RPD can be caused by an uneven seabed, ex-pin

holes, sliding or any other means where the
spudcan is not fully supported under all chords
when weight / load is increased.
Rapid Penetration A Rapid Penetration is when a leg (or legs)
penetrate quickly but the Barge level can be
maintained by use of the jacking system.
Spudcan footing reaction This is the force exerted onto the seabed in tons.
The leg footing reaction includes the weight of the
unit (including hull, superstructure and the
variable load) and the weight of the legs.
Spudcan Interaction Spudcan Interaction is when the spudcan contacts
the seabed and interacts with ex-pin holes or a
sloping seabed.
Spudcan footing area This is the area on the spudcan that will make
contact with the seabed i.e. the total area of the
underside of the spudcan.

The larger the spudcan footing area the more the

weight will be spread on the seabed which gives a
lower bearing pressure.
Variable Load The Variable Load is all the weights added to the
Unit from the lightship condition. This includes all
deck cargo, liquid cargos / fluids, stores and any
weight in addition to lightship.

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 1. Introduction

Emplacing any Jack-Up Unit at a new location has inherent risks / dangers and
each location must be properly assessed on a case by case basis during the
planning stages before the move.

The location assessment should be approached using the Risk Assessment

methodology where each risk is assessed regarding the level of likelihood and
consequence.

This document is a basic guide and does not cover all cases that could be faced,
this document does not cover cases such as deep penetration where further
studies such as a leg extraction calculation may be required. Also in the case
where there is a risk of leg punch through it may still be possible to proceed to
this location with caution however studies such as a punch through survivability
study may be required.

The below table shows the common risks that should be assessed and also what
effect they could have for the Unit.

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 2. Risks

Risk Cause Effect

Punch Punch through is caused by the soil not being able to A Punch through is the highest risk whilst emplacing a unit at a
through hold the weight applied by the Unit new location

In the case of a punch through heavy damage could be sustained

to the legs, jacking system and jack houses

Rapid Rapid penetration is similar to a punch through A Rapid Penetration normally does not cause damage as the
Penetration where the soil is not able to hold the weight applied jacking system can maintain the unit in a level condition
by the unit however in the case of rapid penetration however if the unit has RPD prone legs a rapid penetration
the Unit can be maintained level (or within allowable could cause damage due to RPD
tolerance) by lowering the leg / legs that are
penetrating

Spudcan Leg sliding is most commonly caused by the presence Leg Sliding can result in the unit sliding towards or impacting a
interaction of ex-spudcan depressions / pin holes, this is known nearby structure / asset
/ Sliding as spudcan interaction.
Spudcan interaction can also cause RPD damage &/or Leg Splay
Leg sliding can also be caused by an uneven seabed

Debris / If any other Unit was previously at that location there The presence of any debris or harmful seabed features pose a
harmful could be debris left behind on the seabed (scaffolding, risk of damage to the Units spudcans
seabed tyre fenders etc).
features If any debris or harmful seabed features exist and cannot be
Even if the location is a virgin location the presence of removed their position must be checked and assessed against
debris may exist such as fishing traps, lost ships the spudcan locations

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 anchors, sunken vessels….

Harmful seabed features include coral outcrops, rock

boulders or any other natural obstruction

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 3. Location Assessment

The location assessment varies depending on the information provided and the
information available for the particular location that the unit is proposed to be
moved too.

Often the information provided can be weak or incomplete, in that case an

assessment should be conducted using the Risk Assessment methodology to
determine if sufficient control measures can be put in place to justify that the
Unit can safely be emplaced at that location or not. If the information is
incomplete or insufficient to make an acceptable assessment then the Master
must inform his Marine Manager and inform the Client.

Each risk should be assessed with regard to consequence and likelihood with all
available control measures in place. By studying all the information available it
should be possible to tell the level of risk and if each risk can be mitigated to a
level where it is acceptable.

Some locations may prove to be relatively safe and will require only normal
preloading operations but some locations may require special precautions
during preload or it may not be possible to fully assess the risk without further
information therefore the location should be postponed until a full study can be
made.

The Master of any unit must have an understanding of how to make the
assessment of each location and in the case that there is a lack of information or
the information shows that the risk is high he must raise his concerns to his
company for further review. The owners / operators of the Unit can engage a
third party geotechnical company to assist in the review. The Master should not
accept the next location until there is sufficient information to assess the location
and to have appropriate control measures in place.

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 4. Location assessment documents

Leg Penetration Analysis

In order to be able to make a Leg Penetration Analysis a soil sample is required,

the soil sample used should be site specific and in the case of locations with
higher risks it may be required to have more than one soil sample (some cases
required soil samples for each leg position).

If site specific soil data is not available but there is soil relatively close by &/or
history in the surrounding areas the Geotechnical Company may be able to make
an ‘indicative’ analysis. This would give a theoretical indication as to the soil
reactions however there is no way to ensure the lateral variability of the soils so
an indicative LPA should be treated with caution.

The LPA will show the expected penetration for that specific unit, expected
penetrations will be within a predicted range known as upper bound and lower
bound curves. The LPA will also show if there is any risk of punch through or a
hang up situation.

If a Risk of Punch Through or Hang up is present then the Master should seek
advise from the Marine Manager as to how to proceed.

See Appendix A for a detailed example of a LPA curve.

Penetration History

If the proposed location has been used by any unit previously then the client
should provide the penetration history, see appendix B of this document for an
example. The details in the penetration history may vary from different clients
but the details should show;

 Name of units that have been at the location

 Water depth
 Heading / Orientation
 Steel to steel distance
 Penetrations achieved
 Date / Year the Unit was at the location
 Any other relevant comments

If there is no detailed seabed survey available it is possible to make an

approximate scale drawing as sown in appendix D of this document in order to
assess the risks of spudcan interaction &/or sliding. This method is not as
accurate as a detailed seabed survey overlay however in the case that previous
penetrations are considerably deep this method can at least show the expected
spudcan overlap / interaction.

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 If any of the units that used the location previously have a higher bearing
pressure than your Barge this gives a good indication that the soils should
withstand your Barge without punch through however without a LPA the
predrive / preload should be made in a cautious manner until the full leg
reaction is achieved.

In the case that the history is used without a LPA then a cautious preload should
be conducted.

Seabed Survey

The level of detail shown in a seabed survey can vary greatly depending on the
means used for the survey to be conducted. Equipment such as a side scan sonar
will produce a very detailed and accurate report however if the survey is
conducted by Divers the level of detail and accuracy will be much less.

The seabed survey is used to show the position and size of any ex-pin holes
which should be used to check for spudcan interaction and also to show that the
area where the legs will engage the seabed is clear from debris &/or subsea
assets.

As shown in Appendix B a detailed seabed survey can be used to check for

spudcan interaction by using a scale overlay of the Barge footprint, this can show
if the ex-pin holes will cause any issues during emplacing the Barge.

If any debris is found that causes concerns for the barge leg positions then the
Master should request a Debris Removal. In some cases, it may not be possible to
remove the debris so provided this is clear from the leg positions the subject
debris can be marked by a marker buoy in order to give the Master a visual
reference to avoid setting the leg on the debris.

Certificate of Approval (CofA) – Location Approval

The Location Approval CofA is required depending on the Companies Insurance,

some Companies are self-insured and do not require any Location Approval
CofA.

If the Location Approval CofA is required then the Unit Owners / Operators will
engage a recognized Marine Warranty Consultancy Company who will review all
the documentation available for the subject location (LPA, seabed survey,
history, bathometry etc).

The Location Approval CofA is a means to give the Insurance Underwriters

assurance that the Unit can safely be emplaced at the proposed location. The
Marine Consultancy Company will make recommendations on the CofA which
must be followed by the Master during the emplacement & preloading of the
unit.

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 5. Risks / Control Measures

Risk Effect Control measure Comments

1 Punch If a punch through 1- The first and most effective control measure 1- In order to conduct a LPA there needs
through / occurs the unit will for the risk of punch through & to see if to be a soil sample available. The soil
Rapid more than likely there is a risk of rapid penetration or punch sample should be from as close to the
Penetration suffer heavy damage through is a leg penetration analysis (LPA). proposed location as possible.

Historical events 2- If the soil data is not site specific (or there is 2- Previous history only shows the
have shown total no soil data available) then an ‘Indictive’ LPA penetration achieved by units
losses in the case of can be considered depending on the previously emplaced at that location. It
heavy punch through information available such as nearby bore does not involve any soil analysis and
holes and surrounding penetration history does not show any soil layers.
records however if such information is used
then it should be treated with caution. 3- Using previous history is only an
assumption that if a unit with similar
3- If a leg penetration analysis (LPA) is not or higher bearing pressure has been at
available or not possible due to the lack of that location previously that the soil
soil data then it may be possible to predict will again withstand that weight /
the expected penetration and to check the bearing pressure with similar results.
soil strength by using previous history, again
this should also be treated with caution and 4- The level of caution implemented into
a cautious preload procedure should be the preload procedure depends on the
implemented. information available i.e. a site-specific
LPA with no risk of punch through can
be considered normal opposed to an
indictive LPA that should be treated
with caution.

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 2 Spudcan Leg Brace Damage 1- Detailed Seabed Survey by side scan sonar 1- A detailed seabed survey used to do
Interaction showing all seabed depressions, ex-pin the overlay as shown in Appendix C of
Leg Splay holes and any gradient difference. this document gives an accurate
picture of how the Barge will react and
Sliding 2- Seabed Survey by Divers, a seabed survey by to show how the Barge should be
divers will not be as accurate as a Side Scan positioned to avoid spudcan
Sonar survey however it should give in interaction.
indication regarding ex-pin holes which
could then be used together with the history 2- The positions of ex-pin holes on divers
to make a scale drawing as show in reports should not be considered
appendix D of this document. accurate, the divers report shows that
there is an ex-pin hole present but a
scale drawing from the history would
give a more accurate picture of the ex-
pin hole locations.

3 Sliding Leg Brace Damage 1- As per the above Risk for Spudcan 1- The assessment for sliding is the same
Interaction the Seabed Survey is the best as per the risk above for Spudcan
Making contact with control measure to evaluate if there will be a Interaction however the Master
the Platform due to risk of sliding or not. should use the overlay to predict if the
sliding barge will slide in any particular
2- The seabed survey together with any direction.
Bathometry surveys and the penetration
history should be used to overlay the barge 2- If it is predicted that the unit may slide
footprint in order to decide how best to towards the Platform then the Master
position the Barge to avoid or reduce any should try to position the Unit further
sliding. away then the target distance.

3- To avoid sliding the Master should aim

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 to position the Unit where the Unit
legs are inside the existing pin hole or
as far away as possible on virgin
seabed.
4 Debris Spudcan Damage 1- The barge should not be emplaced if there is
any debris present in close vicinity to the leg
positions, this includes the location where
the barge will soft pin during the approach.

2- If the seabed survey shows any debris in the

approach areas &/or at the final spudcan
positions the master should request the
debris to be removed he should receive a
debris removal report.

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 6. Risk Flow Charts

Risk 1 – Punch Through / Rapid Penetration

Penetration
LPA Available Yes Similar Unit (or Proceed to Risk 2
No History Available Yes
heavier) in history

Yes No No

Risk of Punch
Through Yes
Further study required

No

Proceed to Risk 2

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 Risk 2 – Spudcan Interaction / Sliding

Detailed Seabed Sufficient history Overlay clear of

Survey (Side No to make rough Yes spudcan Yes Proceed to Risk 3
Scan) Available scale drawing interaction issues

Yes No No

Footprint Overlay
matching or clear No
from pin holes
Further study required

Yes

Proceed to Risk 3

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 Appendix A – Example of Leg Penetration Analysis

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 Appendix B - Example of Penetration History
Penetration Bearing Water
Unit Orientation Stand-off (Meters) Pressure Air Gap depth Date Comments
PLATFORM NAME Rig XX 341 14 ft 2 28.5 10-May-16
Barge XX 347 12 ft 2 53.0 6 20-Dec-18
Barge XX 158 27 ft 1.0/1.0/1.3/1.4 46.0 7.7 22-Nov-18
Barge XX 159 27 ft 0.7/0.8/1.1/1.2 46.0 1.6 29-Mar-19
Barge XX 158 27 ft 1.2/1.2/1.5/1.7 46.0 6.4 21-Aug-19
Rig design 25.9
344 14 ft 1.5/1.8/1.2 28.5 3-Feb-20
MLT-82
Barge design
254 33 ft 1.6/1.8/1.4/1.7 40.9 8.8 2-Dec-20
K-Class

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 Appendix C – Example of Footprint overlay on detailed side scan sonar
Seabed survey

The picture above shows that the Barge overlay has been made to the same scale
as the detailed side scan sonar seabed survey.

This case shows that there is heavy spudcan interaction between the Barge
Footprint and the ex-pin holes on the seabed. In a case like this the Master must
report to his office and

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 Appendix D – Example of Footprint Overlay from History (to be used
when detailed seabed survey not available)

The case above shows that there will be spudcan interaction if a GMS K-Class
Barge is positioned 33 ft from a Platform where the previous unit was a MLT 82-
SD-C Rig as 14 ft stand-off.

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 In this case it would be advisable to reposition the Barge either to Port or
Starboard (offset) so as to have one leg in the previous pin hole from the Rig and
one almost fully on virgin soil. If this was not possible and the Barge must be
positioned to the center of the Platform it would be advisable to position the
barge using the 2 legs furthest from the Platform first as they will be placed on
virgin seabed.

Placing the legs with such spudcan interaction as shown has a high risk for leg
splay, Sliding &/or RPD issues. RPD would be a particular concern on a unit with
lattice legs in this case.

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