Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Innovative Design and Technology Solutions for Development of Port andOffshore Pressed-in Piled Structures
Michael DOUBROVSKYProfessor and Head of Sea and River Ports Department, Odessa National Maritime University, Odessa, Ukraine.
International Press-In Association, Director
Email: doubr@tm.odessa.ua

Andrey GERASHCHENKOPhD Student, Sea and River Ports Department, Odessa National Maritime University, Odessa, Ukraine

Igor DOBROVPhD Student, Sea and River Ports Department, Odessa National Maritime University, Odessa, Ukraine

Olga DUBROVSKA
Senior Project Engineer, DeepOcean, Haugesund, NorwayABSTRACT
Deep water piled clusters and structures supported by large mono-piles are designed to take up significant lateral andpressing loads. In particular, it relates to offshore structures whose foundations need long piled supports of high bearing
capacity. Correspondingly one meets high level of stresses and significant deformations in such constructions. It isespecially important for port or offshore engineering to avoid environmental problems caused by traditional pile driving
technologies. From this point of view, the Press-in Method is the most appropriate approach. Two improved structures
and technologies have been worked out to optimize stress-strain state of such piled clusters and mooring/fender
dolphins. (1) Developed is an effective and less resource-demanding design when connection of all pipe piles with large
diameter steel casing provides their joint work and favorable distribution of stresses and deformations in pile clusters. It
is foreseen that both casing and pipes are installed by pressing into bottom soil. (2) To increase energy-absorbing
capacity of mooring/fender dolphins, a new design of combined tubular mono-pile structure was worked out andresearched. It incorporates internal flexible pile and damping element (cushion) placed between external and internal
piles’ heads. For both innovative and patented solutions, laboratory tests and numerical modeling were fulfilled andcompared.
Key words: Pressed-in Piles, Piled Cluster, Fender/Mooring Dolphin, Model Tests

1. Introduction
Deep water piled clusters and structures supported bydriving technologies. From this point of view, the Press-in

large mono-piles are designed to take up significant lateralstructures and technologies have been worked out toand pressing loads. In particular, it relates to offshore

optimize stress-strain state of piled clusters andstructures whose foundations need long piled supports ofmooring/fender dolphin. To study peculiarities of thesehigh bearing capacity [Doubrovsky & Poizner, 2016].

innovative design solutions model testing in laboratory

Correspondingly one meets high level of stresses andconditions have been produced in Odessa Nationalsignificant deformations in such constructions. It isMaritime University. Physical modeling was provided forespecially important for port or offshore engineering totwo stages. The first one was simplified by testing of theavoid environmental problems caused by traditional pilemodel without soil media (instead of piles embedded into

Method is the most appropriate approach. Two improved- 91 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

the soil piles with tips fixed by special clamps were

Such a structure has been tested on 3-D physicalconsidered (console scheme). The aim of this firstmodel (scale appr. 1:100). The layout of the structure and(simplified) stage was to determine the most appropriate

the location of the displacement indicators are presented

calculation model in order to reflect innovative structuralon the Fig. 2. In the model central steel cylindrical casing

peculiarities and to select proper software. The second(shell) was presented by steel tube of diameter D=50 mmstage was aimed to test the same models in the soil box(shell-wall thickness 1 mm); 4 piles equally spaced along

without artificial fixing of piles’ tips by clamps (piles were

the shell perimeter were modeled by steel bars of d=8 mm

embedded into sandy soil). For model’s installation of thediameter. The total length of the model piles wasboth innovative solutions we applied pressing of the piled

preliminarymodels into sandy soil by hydraulic jack.

recommendations of actual national design codes (770determinedaccordingtotheknownmm).
2. Innovative piled cluster and its model testing
Developed is effective and less resource-demanding
design when connection of all piles with large diameter
casing provides their joint work and favorable distributionof stresses and deformations in pile cluster (Fig. 1)[Doubrovsky, Gerashchenko & Dobrov, 2018]. Mentioned
large diameter casing (shell) is installed both above andbelow the sea bottom level relieving piles and decreasingstresses in them. Connection between casing and piles
may be provided similar to sheet piles interlocks.

Fig. 2

Layout of the structural elements:

D1 and D2 – location of displacement indicators (marked bystars); F – applied lateral force; Z1 and Z3 – length of piles
above and below the central shell; z2 – length of shell; z4 –embedment of the central shell..
Fig. 1 Piled cluster of innovative designa – cross-section; b – 3D view:At the first stage of experiments, pile supports werefixed by clamps to exclude their tips’ displacements and1 – bearing piles; 2 – steel cylindrical casing; 3 – interlock
connections; 4 – superstructure; 5 – water level; 6 – bottom level

central shell length was 350 mm (Photo 1).

All bearing structural elements of this innovative
piled cluster may be installed at the sea (in the sea port orat the offshore oil or gas field) by the Press-in Method
driving both central shell and peripheral piles into thebottom soil. If designed shell diameter is larger than
2.5-3.0 m, the shell may be installed by driving of required
number of straight web sheet piles along the shell’sperimeter.

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The model (Photo 2) has been loaded by the same
horizontal forces as at the first stage. The main aims ofthis stage were to investigate influence of new structuralelement on the piled cluster, i.e. the central shell: its length
along the peripheral piles (size Z2 on the Fig. 2) and its
embedment into the soil (Z4 on the Fig. 2). Provided test
series A corresponded to increase of the shell length Z2
due to enlargement of the embedment Z4. Test series B
considered constant value of the shell length Z2 andincrease of shell pressing depth Z4.

Photo 1.

Piled cluster model at the first stage of testing

The same model was analyzed by a 3-D numericalsimulation (FEM) using different programs in order todetermine the most proper calculation model andsoftware regarding peculiarities of the structure (i.e.
Photo 2. Piled cluster model at the second stage of testing

interaction between the central shell and the peripheral
piled elements). Three programs were applied todetermine the stress-strain state of the model: AxisVM,Displacements of the model were obtained by direct

Lira-SAPR and Midas-Gen. The closest data to themeasurements during horizontal load application; stresses

experimental results have been demonstrated by programin the piles and shell as well as soil reactions wereMidas-Gen (Fig. 3).

calculated by previously tested (at the stage 1) program
Midas-Gen. Some measured and calculated results ofthis experiment are presented on the diagrams (Fig. 4-11).

Fig. 3 Displacement diagrams from experiment andcalculated data using different software (lateral force 350 N)

At the second stage of the experiment, the samestructural model was tested in the sand box (internalfriction angle 32 degrees; Young’s modulus 18-28 MPa
depending on pressure interval; unit weight 19,7 kN/m3).

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Displacements at the level of indicator D1 (test seriesA)

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 5 Maximal stresses in the most stressed peripheral pile andFig. 8 Maximal stresses in the most stressed peripheral pile andcentral shell (series A, applied lateral force F= 40 N and F=80 N)

central shell (series B, applied lateral force F= 40N and F= 80 N)

Fig. 6

Maximal soil reactions (test series A, applied lateralFig. 9 Stresses distribution in the peripheral piles

force F= 40 N and F= 80 N)(test series B)

Fig. 7 Displacements at the level of indicator D1 (test series B)
Fig. 10 Stresses distribution in the central shell (test series B)- 94 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

central shell of increasing length Z2) shows excessive
safety parameters and worse material utilization (Fig. 4and Fig. 6).
3. Innovative structure of combined mooring/fender
dolphin and its model testing
To facilitate construction of deepwater mooring/fender
dolphins and to increase their energy-absorbing capacity,
a new design of combined tubular mono-pile structure wasworked out and researched [Doubrovsky,Dobrov &Gerashchenko, 2018]. It incorporates internal flexible pileand damping element (cushion) placed at the zone of pilehead (Fig. 12).

Fig. 11 Stresses distribution in the soil (test series B)

Sequencesofinstallation

operations

foreseespressing of the internal pile into the bottom soil, mounting
Obtained results and above mentioned diagrams givethe bottom soil and assembling of fender/mooring

us possibility to make some important conclusions:of the damping element, pressing of the external pipe intomeasured and calculated values of model
displacements
demonstratesatisfactoryequipment.

precision (Fig. 3, Fig. 4); so applied calculation

bollard of via fender) initially is taken by internal pile.

External force provoked by ship mooring (either via
While bending the internal pile presses the damping

model works good

considered system “structure-soil” shows
sensitivity to the increase of the central shellelement and through this cushion transfers the decreased

pressing into the soil starting from theof three elements (internal and external piles and damping

embedment depth exceeding approximately

cushion between them) the dolphin may take essential

1.5D. After reaching this driving depth weship load. It can be expected to make needless use of large

registered essential reduction of all stress-strain

diameter (3-4 m) heavy-walled (40-60 mm) tubular pile ofparameters: displacements, stresses in the piles

ruggedness strength (and, correspondingly, of high cost).

force to the external tubular pile. Thus, due to joint work

In such a case combined dolphin made of two

and in the shell as well as soil reaction along thestructure’s supports (Fig. 5 – Fig. 9)

comparatively small diameter piles (of about 1 m forthe better distribution of the stresses in thesystem “structure-soil” corresponds to theexternal pipe and 0.5 m for core one) may be profitably

increase of the embedment depth by pressing in

damping element is correlated with bending strain

the sand of the central shell of constant lengthparameters of combined mono-pile elements.

applied to withstand large operational force. Work of(size Z2 on the Fig. 2). In such a case, theAt the first stage of the experiment (i.e. no soil in the

bearing capacity of piles, shell and soil issystem) pile supports of the physical model were fixed byutilized in the optimal way (Fig. 7 and Fig. 8).

special clamps to exclude their tips’ displacements (PhotoAnother3).

testedoption(increaseof

theembedment depth by pressing in the sand of the- 95 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

d2d1

l=15 mm
L=550 mmFig. 13 Simplified scheme of the dolphin’s model inhorizontal position (d1 and d2 – location of displacementindicators)

External tubular pile was of 50 mm diameter (wallthickness 1 mm) and internal pile was made of steel bar of12 mm diameter.
This model was also analyzed by a 3-D numericalsimulation (as above) in order to determine the mostFig. 12 Mooring/fender dolphin

proper calculation model and software regardinga – cross-section; b – 3D view

peculiarities of the structure and interaction between its

1 – internal pile; 2 – external tubular pile; 3 – damping

elements. The most appropriate results were obtained byelement (cushion); 4 – bollard; 5 - superstructure; 6 – fender; 7

use of program Midas-Gen when, for description of- water level; 8 – bottom level.

damping

element

work,

elastic-plastic

modelofDruker-Prager has been applied (discrepancy between test
and calculations reaches up to 17 %).
At the second stage of the experiment, this structuralmodel was tested in the sand box (Photo 4, soil
parameters as above in Chapter 2).
To clarify advantages of the proposed combined
mono-pile structure in comparison with usual (withoutinternal pile) mono-pile, both models (of the same
external diameter 50 mm) were tested by application of
the same lateral forces. Main results of the displacement
measurements are presented on the Fig. 14, 15.
Comparison of the experimental diagrams forexternal tubes shows that horizontal displacements of thePhoto 3.

combined mono-pile are up to 30% less than horizontal

Dolphin model (1st stage of the test)

displacements of the usual mono-pile in the considered

Total length of the piles was preliminary determinedinterval of applied lateral forces.

according to the known recommendations of actual local
design codes (Fig. 13). For initial calibration of the system
it was convenient to place the dolphin’s model inhorizontal position.

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Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Similar correlation of the studied parameters isdemonstrated also by corresponding calculated curves on
the Fig. 14, 15. This fact confirms effectiveness of use of
the applied calculation model and software.
From the point of view of structure’s operation
reliability, it is important to compare horizontal
displacements of external force application point for bothmodels: at the upper end of the usual mono-pile model(similar to the point d2 on the Fig. 13) and at the level ofpoint d1 of external pile of the combined model).
Measured horizontal displacements in the external force
application point differ up to 20% (reduction corresponds
Photo 4.

Mooring/fender dolphin model for the second stage

to the case of combined model). It confirms better energyof the experiment in the sandy box

absorbing ability of the proposed combined mono-pile.
Illustrations to the numerical modeling (FEM) of theconsidered models are presented on the Fig. 16-20.

Fig. 14 Lateral load - horizontal displacement diagram forusual mono-pile modelFig. 16 Stresses distribution in the usual mono-pile structure.

Fig. 15 Lateral load - horizontal displacement diagram for
Fig. 17 Stresses distribution in the soil for usual mono-pilecombined mono-pile modelstructure.

- 97 -Proceedings of the First International Conference on Press-in Engineering 2018, KochiMPa) and for combined structure (145 MPa) demonstrates
19% of stresses reduction. Correspondingly the external
pile may be produced of smaller diameter or of smaller
wall thickness, or made of weaker steel.
In the considered situation of maximal loading, thebending stress in the internal pile (steel bar) of the
combined model does not exceed 91 MPa (about 30% ofthe yield stress), so internal pile also may be done
light-weight (i.e. more flexible, at least in the interval ofinvestigated displacement disparity in comparison withusual mono-pile as above).
Soil reactions are less in the case of combined
Fig. 18 Stresses distribution in the external tube of combined

mono-pile due to more favorable stress-strain state ofpressed into soil external and internal piles.

mono-pile structure.

4. Conclusions
Study of peculiarities of two innovative structuraland technological solutions of piled cluster andmooring/fender dolphin on combined mono-pile wasfulfilled by testing on physical models in laboratory
conditions and by numerical modeling (FEM). Fulfilled
tests occurred to be useful for study of structural behaviorof both new designs as well as for determination of theappropriate calculation program (by comparison ofmeasured and calculated data). Experiments in the sandbox gave interesting results demonstrated advantages ofFig. 19 Stresses distribution in the internal pile of combined

proposed solutions.

mono-pile structure.

References
Doubrovsky, M. P., Poizner, M. B. 2016. Innovative
development of coastal, port and marine engineering.
Lambert Academic Publishing, Germany, 125p.
Doubrovsky, M.P., Gerashchenko, A.V.. Dobrov, I.Yu. 2018.
Method of installation of the mooring structure on piled
foundation. Patent of Ukraine # 116296. Bulletin #4/2018.
Doubrovsky, M.P., Dobrov, I.Yu., Gerashchenko, A.V. 2018.
Mooring-fender dolphin. Patent of Ukraine # 116708.
Bulletin # 8/2018.
Fig. 20 Stresses distribution in the soil for combined mono-pilestructure.

Comparison of the stresses maximal calculated
values (corresponding to maximal applied lateral force
F=180 N) in the external tube for usual mono-pile (222- 98 -