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Plaxis finite element code for soil and rock analyses

issue 23 / March 2008Plaxis Bulletin

Comparison of computed vs. measured lateral load/deflection response of ACIP pilesModelling the behaviour of piled raft applying Plaxis 3D Foundation Version 2

Remarks on site response analysis by using Plaxis dynamic module

2

the Plaxis Bulletin is the combined magazine of Plaxis B.V. and the Plaxis Users

association (nl). the Bulletin focuses on the use of the finite element method in geotech-

nical engineering practise and includes articles on the practical application of the Plaxis

programs, case studies and backgrounds on the models implemented in Plaxis.

the Bulletin offers a platform where users of Plaxis can share ideas and experiences with

each other. the editors welcome submission of papers for the Plaxis Bulletin that fall in

any of these categories.

the manuscript should preferably be submitted in an electronic format, formatted as

plain text without formatting. it should include the title of the paper, the name(s) of the

authors and contact information (preferably email) for the corresponding author(s). the

main body of the article should be divided into appropriate sections and, if necessary,

subsections. if any references are used, they should be listed at the end of the article.

the author should ensure that the article is written clearly for ease of reading.

in case figures are used in the text, it should be indicated where they should be placed

approximately in the text. the figures themselves have to be supplied separately from the

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any correspondence regarding the Plaxis Bulletin can be sent by email to

bulletin@plaxis.nl

or by regular mail to:

Plaxis Bulletinc/o erwin Beernink

Po Box 572

2600 an delft

the netherlands

the Plaxis Bulletin has a total circulation of 13.000 copies and is distributed worldwide.

Editorial Board:

Wout BroereRonald BrinkgreveErwin Beerninkarny lengkeek

Colophon

Editorial

New Developments

Plaxis PracticeComparison of computed

vs. measured lateral load/deflection response of

ACIP piles

Plaxis PracticeModelling the behaviour of

piled raft applying Plaxis 3D Foundation Version 2

Plaxis PracticeRemarks on site response

analysis by using Plaxis dynamic module

Recent Activities

Activities 2008

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4

6

10

14

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20

3

Editorial

in addition to the ‘standard’ columns, it is a pleasure to notice that more and more Plaxis

users are willing to share their modelling experience with other users, and submit inte-

resting articles for the Plaxis Bulletin. this Bulletin contains three articles about the back-

grounds and use of Plaxis 2d and 3d products in practical geotechnical applications.

the first article shows a comparison between the results of a lateral loading test on

cast-in-place piles and a numerical simulation using Plaxis 3d foundation. the Harde-

ning soil model with small-strain stiffness was used to model the behaviour of the stiff

over-consolidated clay. the results seem to match the test data reasonably well, but the

specific behaviour of the piles requires more research and a better modelling of the pile

behaviour.

the second article is again an application of the 3d foundation program. it describes how

3d fem can be used for piled raft foundations. the embedded piles in the foundation pro-

gram prove to be very efficient in the modelling of such complex foundations. neverthe-

less, there is a need for improved modelling facilities, like horizontal interface elements.

the third article describes the results of a research project on the possibilities and limita-

tions of the dynamic module with respect to seismic site response analysis. the research-

ers have varied numerical parameters to evaluate their influence on the results. they

propose a procedure to calibrate the numerical model and conclude that the standard

settings in Plaxis do not always give the best results.

in all of the articles, the authors give suggestions on how Plaxis could be improved to

model various geotechnical applications in a better way. We are very thankful to the au-

thors for these suggestions and will consider them seriously as a part of future Plaxis

developments.

We wish you an interesting reading experience and look forward to receive new articles

for future Bulletins.

the editors

The year 2008 will be a year of many new issues for Plaxis. We started in a new

office in Delft to facilitate a further expansion of activities; we employed new staff

(Delft, asia); we appointed new agents (China); we introduced a new service (special

Projects) and last but not least, we are working on new features and will release

new products. some of these issues are described in more details in this Bulletin or

will come back in the next Bulletin.

Ronald Brinkgreve

4

New Developments

Ronald Brinkgreve

New Developments

the finite element method is well established in the current geotechnical engineering

practice. although most calculations are still 2d, there is a tendency to model compli-

cated situations in more detail using 3d models.

since the new millennium, Plaxis offers 3d models that are relatively easy to create. after

the success of the 3d tunnel program for simplified 3d situations, the recent 3d founda-

tion program version 2 allows for a realistic modelling of complicated foundation and

excavation projects, including multiple piles or ground anchors. since the introduction

of this version halfway 2007, more than 500 licences are being used. for the general

modelling of geotechnical applications, Plaxis will offer two independent solutions with

full geometrical flexibility, depending on the user’s preference:

1. a new-generation geotechnical-oriented input program based on familiar concepts

from 3d foundation, with arbitrary volume object creation and import facilities, avai-

lable from mid 2009 for advanced to expert users.

2. a general cad-like input program, available from mid 2008 for top users with 3d cad

experience.

Both programs enable the creation of arbitrary 3d finite element models composed of

10-node (quadratic) tetrahedron elements, which are calculated with the Plaxis 3d cal-

culation kernel. in both programs the existing Plaxis soil models are available. the diffe-

rence is in the modelling approach, either geotechnical-oriented or cad-like.

the decision to develop this two-leg strategy is based on different work flows in different

companies or different projects: in most companies or projects the geotechnical engineer

has to create a finite element model him/herself based on 1d or 2d (geotechnical) in-

formation whereas in some companies or projects a 3d model is created by cad experts

before a geotechnical finite element analysis is considered. the latter group can soon be

served. the former group has to wait another year before a dedicated product is available,

but in the remainder of this article i will already elaborate some of its details.

the creation of a geotechnical 3d model starts with the composition of the sub-soil. for

this, the borehole feature of the foundation program may be used. soil layer boundaries

may be imported as triangulated surfaces and assigned to the soil layer boundary in the

borehole. in addition to the sub-soil, structures and loads are defined independent from

the sub-soil. arbitrary excavation volumes or other volumes may be created using the

excavation designer, or by importing 3d objects from cad packages. structures and loads

may be defined in a similar way as in the foundation program, but with more flexibility in

vertical direction. during the modelling phase the user is confronted with a 3d view of the

model in which he can directly select the visible objects. alternatively, all objects appear

in a tree view, which can also be used to create objects or assign properties. Programs

like Google sketch up have shown that 3d drawing can be almost as easy as 2d drawing.

the new Plaxis program includes similar 3d drawing facilities and allows import of such

models.

5

New Developments

When proceeding to the definition of calculation phases, all objects are crossed with each

other using a csG (constructive solid Geometry) algorithm and divided into sub-volumes

and sub-structures. different construction stages may be defined in which (sub-)volumes,

(sub-)structures and loads can be activated or de-activated. the 3d meshing, including

global and local refinement, is considered just before the start of the calculation. since

all calculation settings are based on geometric objects, it is not necessary to redefine

calculation phases after mesh regeneration. even minor geometric changes can be made

without the need to redefine the calculation phases. this stimulates improved modelling

and meshing after promising preliminary results have been obtained.

calculations are performed with the existing Plaxis 3d calculation kernel. to allow for

unstructured 3d meshes, 10-node tetrahedron elements have been implemented. more-

over, a 64-bit version of the calculation kernel will be available to enable hundreds of

thousands elements. also the general output program (post-processor), as available with

3d foundation, has been extended with 10-node tetrahedrons and all existing output

facilities have been adapted for this type of element.

a beta version of the new 3d program is expected by the end of 2008. Users interested in

beta-testing of this program, may contact Plaxis bv. We will keep you informed about the

progress of development. meanwhile, for those who are interested in cad-like 3d model-

ling, we can soon provide general modelling facilities to address the reliable Plaxis 3d

calculation kernel.

6

Comparison of computed vs. measured lateral load/deflection response of ACIP piles

Plaxis Practice

K.E. Tand, P.E., Principal Engineer, Kenneth E. Tand & associatesC. Vipulanandan, Ph.D., P.E., Chairman of the U of H Civil Engineering Dept.

Introductionfive auger cast-in-place piles (aciP) were installed at the national Geotechnical experi-

mentation site located at the University of Houston campus in Houston, texas in decem-

ber 1996. lateral load tests were performed on four of the piles in January 1997. the

purpose of these tests was to evaluate the feasibility for design and construction of aciP

piles to support concrete screen walls subjected to large wind forces along highways in

urban areas.

Subsoil Profilethe site is located on a Pleistocene age deltaic deposit known locally as the Beaumont

formation. the Beaumont formation is about 8 meters deep at the test site, and it is un-

derlain by an older geologic formation known as the montgomery formation. the subsoils

in both formations are primarily clay with occasional interbedded seams and layers of

sand and silt. the consistency of the clays is generally stiff to very stiff, and they have

been overconsolidated due to desiccation.

the first major silt/sand stratum occurs at a depth of 14 m (47 ft) which is below the

depth of influence of the test piles. the water level was at a depth of about 2 m (6.5 ft)

below grade at the time of the load tests.

after deposition, vertical fissures were formed due to shrinkage caused by drying, and the

cracks at the surface were probably more than 5 cm (2 in) wide visually estimated from

presently occurring wet/dry cycles. soil from the surface was washed down into these

cracks during periods of heavy rain. the soft sediments in the cracks were then com-

pressed when the clays swelled leaving locked-in horizontal stress. this process was re-

peated throughout Pleistocene to modern geologic times, and ko values of 3.0 and greater

have been measured in the upper 4 m (13 ft) at this site. the process of desiccation

and subsequent rewetting caused cyclic shearing displacements in the clay mass that

produced polished failure planes referred to as slickensides. the slickensides are widely

variable in size and orientation. the clays are spatially inhomogeneous, and exhibit some

anisotropic properties due to their stress history.

the joints and horizontal locked-in stress affect the strength, deformation, and permea-

bility properties of the clays. the soil parameters have been extensively studied at this site

and they are summarized in fig. 1. a more detailed summary of the database can be found

on the web site at www.unh.edu/nges. the laboratory and in situ tests in the database in-

dicate a wide range in the strength/deformation properties of the clays due to the effects

of secondary structure, loading stress path, and possible sample disturbance.

Photo 1: load testing a 0.91 m diameter aciP Pile

fig 1: Generalized subsoil Profile

fig 2: Pile load test layout

7

Plaxis Practice

Test Piles and Instrumentationthe pile load test arrangement is shown on fig. 2. the n pile was 0.91 m (36 in) in dia-

meter and 10.7 m (35 ft) long, and the W pile was 0.46 m (18 in) in diameter and 10.7 m

(35 ft) long. the s pile was 0.91 m (36 in) in diameter and 6.1 m (20 ft) long, and the e

pile was 0.46 m (18 in) in diameter and 6.1 m (20 ft) long.

the piles were installed using a continuous hollow stem flight auger rotated into the

ground at a rate of 400 to 1,200 mm/min (16 to 47 in/min). immediately after reaching

the design depth, the augers were slowly withdrawn while pumping high strength grout

into the pile. Grouting was monitored using a pile integrity recorder, and the ratio of the

pumped versus theoretical grout volume ranged from 1 to more than 2 (average of 1.3).

the soil was stiff to very stiff clay, and most (if not all) of the grout in excess of the pile

volume was lost at the surface when removing the spoils.

the grout mix was comprised of Portland cement, fly ash, sand, water and a fluidizer. the

compressive strength of the field mix was 38 mPa (5,500 psi), and the tensile strength

was 2.0 mPa (280 psi) at 28 days.

fig 3: lateral load-deflection curves for e & W Piles

fig 4: lateral load-deflection curves for s & n Piles

immediately after cleaning the top of the pile heads with a screen, a full length rebar cage

was inserted into the piles. the rebar cages for the 0.46 m diameter piles were comprised

of six number 6 vertical rebars with number 3 ties spaced at 15 cm (6 in) centers. the

cages for the 0.91 m diameter piles were comprised of eight number 10 vertical rebars

with number 4 ties spaced at 23 cm (9 in) centers.

as shown on Photo 1, two aBs tubes were installed in each pile. they were used for sonic

logging to check the integrity of the piles prior to the load tests. Based on results of the

sonic tests, the piles were found to be free of defects such as voids or cracks.

one of the aBs tubes in each pile was later used as a guide to run an inclinometer instru-

ment down the piles during the lateral load tests to measure the rotation during loading.

Pile Load Teststhe piles were load tested 28 days after installation. the lateral load was applied at

about 15 cm (6 in) above the ground level so that only a very small bending moment was

induced into the pile head during loading.

the load was applied using a hydraulic jack, and it was measured using an electronic

load cell. as shown on Photo 1, the jack and load cells were housed inside a steel pipe

strut. lateral deflections at the pile head were measured using an electronic measuring

gauge mounted on the back side of the piles with the tip set to a wooden reference beam.

the below grade deformations were measured using an electronic inclinometer.

the e & W piles (0.46 m diameter) were loaded in 4 increments to about 55 kn (12 kips),

and each load was held for a period of 15 minutes. the piles were then unloaded back to

“0”, and the load was cycled 4 times to simulate wind loading. after cycling, they were

loaded in increments to about 95 kn (21 kips), and then again cycled 4 times. the piles

were finally loaded in increments until the deflections exceeded 90 mm (3.5 in).

the n & s piles (0.91 m diameter) were loaded in 4 increments to about 172 kn (39 kips),

and each load was held for a period of 15 minutes. the piles were cycled as described

above, and then they were loaded to about 300 kn (68 kips) and cycled 4 times again. the

piles were finally loaded in increments to a deflection of 25 mm (1 in).

the load/deflection relationships are shown graphically in figs. 3 & 4. during the initial

cycling, the deflections were so small that they are not shown on the graphs for clarity.

note that non-linear pile deflections started to occur at about 60 kn (14 kips) for the e &

W piles, and at about 200 kn (45 kips) for the n & s piles.

the initial load/deflection response of the n pile was slightly stiffer than the shorter s

pile. However, the initial load/deflection response of the W pile was softer than the e pile

even though it had 4.6 m (15 ft) more embedment. the authors speculate that subsoil

variations were present even though these piles were only 4 m (13 ft) apart. Perhaps, the

slickensides and fissures in the clay were orientated in an unfavorable pattern in front of

the W pile. However, there could have been an undetected defect in this pile.

the inclinometer readings indicated that a plastic hinge formed at a depth of about 2.1 m

(7 ft) in both the e & W piles, even though the W pile had 4.6 m (15 ft) more embedment.

the plastic hinge formed at a depth of about 4.5 m (15 ft) in the larger diameter s pile.

the inclinometer tube in the n pile was plugged during grouting, and thus data was not

available for this pile. However, the load/deflection response was so similar for the n&s

piles that it is assumed that the hinge occurred at the same depth.

8

Plaxis Practice

Continuation

FE Analysisthe numerical model employed in the fe analysis for the s pile (typical for all piles) is

shown in fig. 5. the calculations were performed using PlaXis 3d foundations V.2 with

about 2,000 elements. the small strain hardening soil model was used to model the stiff

to very stiff clay.

- effective stress parameters for the stiff to very stiff clays were used as input, but the

analysis was performed using the undrained mode to simulate the rapid rate of loading.

- initially, soil parameters were selected from tand and o’neill’s article published in the

PlaXis Bulletin 14 (sept. 2003). Parametric studies were then performed until good

agreement was obtained with the field load/deflection response of the piles. the final

soil parameters were in good agreement with the prior parameters, but not exact, be-

cause there were variations in the subsoil stratigraphy and the stress path was diffe-

rent for the horizontally loaded piles than the vertically loaded underreamed piers. the

soil parameters used in the final fe analysis are summarized in fig. 6.

- the initial cycle of loading at small loads was not modeled due to the small elastic

deflections that were measured.

- the second cycle of loading was modeled to check the hysteresis cycles. However, only 2

load/unload cycles were computed due to the fact that the load/deflection curves were

almost linearly elastic.

- after the cycling, the pile was loaded to the last measured field load.

Comparison of computed vs. measured lateral load/deflection response of ACIP piles

fig 5: typical fe mesh

Subsoil

c'

kPa

(ksf)

!'

(deg)!

(deg)

Gref

o

mPa

(ksf)

Eref

50

mPa

(ksf)

Eref

oed

mPa

(ksf)

Eref

ur

mPa(ksf)

m vur If

Stiff clay 19.1

(0.4)

20 1 48

(1000)

9.6

(200)

7.2

(150)

27.5

(575)

8 15 6

Stiff to very stiff

clay

19.1

(0.4)

20 1 96

(2000)

12.0

(250)

9.6

(200)

34.5

(720)

8 15 6

Very stiff clayey

sand

28.7

(0.6)

30 2 144

(3000)

16.8

(350)

14.4

(300)

69.0

(1440)

8 15 6

Very stiff clay 28.7

(0.6)

20 1 192

(4000)

14.4

(300)

12.0

(250)

41.4

(865)

8 15 6

Very stiff sandy

clay

28.7

(0.6)

30 2 240

(5000)

16.8

(350)

14.4

(300)

47.9

(1000)

8 15 6

fig 6: optimized soil Parameters

fig 7: comparison of load/deflection curves for s Pile

Youngs’ Modulus Cohesion φ Tension2.5 x 107 mPa 7.2 mPa 40° 1.9 mPa

(5.2 x 105 ksf) (150 ksf) - (40 ksf)

the authors speculate that the stiffness of the piles affected the load/deflection response

as much as the strength and stiffness of the clay subsoils. to study its’ influence, the

piles were modeled as circular piles with a steel shell. a wall element with the equivalent

ei of the rebar was input to model the stiffness of the rebar.

a mass concrete pile is most often modeled using linear elastic properties of the pile

materials. However, the stiffness will be overestimated if tensile strains are large enough

to crack the concrete. the cracks reduce the moment of inertia, and this is a continuing

process as increasing deflections cause the cracks to propagate. the moment of inertia

must be adjusted to reflect the correct state of stress in the pile whether conventional

methods of analysis such as Brom’s procedure or numerical methods such as finite ele-

ment or beam-on-elastic foundation procedures are used. one objective of this study is

to evaluate whether the pile materials can be modeled so that the moment of inertia is

numerically adjusted during the fe calculations.

the laboratory compression tests that had been performed on the grout cylinders were

modeled using PlaXis 2d Version 8, and the following parameters for the mohr-columb

model were back calculated in our analysis by best fitting the stress-strain data:

the following basic procedures were used during the fe analysis:

- the initial ko conditions were generated using a 0.3 m (1 ft) thick “dummy soil layer”

with a unit weight of 943 kn/m3 (6,000 pcf) in the initial phase. thus, the gravity loa-

ding induced a preconsolidation pressure of 216 kPá (6,000 psf). this layer was then

turned off for the subsequent calculations. the fe computed ko was 2.9 at 1.2 m (4 ft),

and 2.6 at 3.6 m (12 ft). these values correlate reasonably well with those reported in

the U of H database.

9

Plaxis Practice

Resultsa graph of the field and fe computed load/deflection relationships for the s pile is shown

in fig. 7. the n pile was omitted for clarity because both the curves for the field loading

and fe simulation plotted on top of each other. the fe computed load/deflection response

of the pile without the shell is shown for comparison purposes. also, the load/deflection

response computed assuming linear-elastic parameters for the grout are shown.

a graph of the field and fe computed load/deflection curve for the e pile is shown in fig.

8. as previously discussed, the W pile appeared to be an anomaly and is not shown. there

were either subsoil variations in front of this pile, or there was an undetected defect in

the pile.

fig 9: delecftions with depth

fig 8: comparison of load/deflection curves for e Pile

exceeded the tension cut off stress. these observations highlight the advantages of u-

sing a proper constitutive model for the grout so that the effective moment of inertia is

automatically reduced during fe loading.

the good correlations are due to parameter studies, not simply selecting the correct in-

put data for the initial computation. fe cannot be expected to model the load/deflection

response within ±25 percent on a common basis because the stress/strain behavior of

soil is very complex, and the uncertainty of selecting appropriate strength/deformation

properties of the soil when there is considerable data scatter. also, the strength/deforma-

tion properties of the pile materials must be properly accessed. it is possible that there

might be other combinations of soil and pile properties that could result in correlations as

well as those determined in this study.

Conclusionsthe fe computed load/deflection response of the aciP piles bearing in stiff to very stiff

clay correlated well with results of the full scale lateral load tests. the small strain har-

dening soil model in PlaXis 3d foundations can be used in predicting the lateral load/

deflection response of piles. However, additional research needs to be performed to better

model aciP piles with internal reinforcing steel if deflections are large enough to cause

tension cracks in the grout.

References:- k.m. Hassan, m.W. o’neill, and c. Vipulanandan, specifications and design criteria for

the construction of continuous flight auger Piles in the Houston area, fHa report UH

3921-1, 1998.

- l.J. mahar and m.W. o’neill, Geotechnical characterization of desiccated clay, Journal

of Geotechnical engineering, asce, January, 1983, pp. 56-71.

- m.W. o’neill, national Geotechnical experimentation site – University of Houston, Geo-

technical special Publication no. 93, 2000, pp. 72-101.

a graph of the field measured and fe computed horizontal displacements with depth for

the s & e piles is shown in fig. 9. note that fe predicts that a plastic hinge formed at

about the same depth as measured in the field loading tests.

the initial fe computed load/deflection response of the piles using the optimized para-

meters is in excellent agreement with the loading tests. However, fe under predicts the

deflections at the high loads.

the authors speculate that the piles as modeled in the fe analysis are stiffer than the

field piles. the tension stress of the grout had been input so that the grout would crack

and reduce the moment of inertia of the pile during the fe loading phases. However, the

fact that the steel shell modeled in the fe analysis is located at the perimeter of the piles

probably restricted the tension cracks that would be expected form between the rebar and

outer edge of the field piles. also, PlaXis has published a notice that the interface ele-

ments for round piles have corners in the fe geometry that makes the interface behavior

stiffer than would occur under field conditions (see Plaxis website).

the fe computed load/deflection response of the aciP piles without the steel shell was

somewhat softer than for the field piles. this occurs because of the reduced moment of

inertia resulting from neglecting the rebar, and the fact that more deflections occur du-

ring loading increasing the tensile strains.

the fe computed load/deflection response of the aciP piles assuming linear elastic pro-

perties for the grout was considerably stiffer than for the field piles. this occurs because

the effective moment of inertia was not being reduced when the mobilized tensile stresses

10

Plaxis Practice

Modelling the behaviour of piled raft applying Plaxis 3D Foundation Version 2

Yasser El-Mossallamy, associate Prof., ain shams University, Cairo, Egypt c/o aRCaDis GmbH, Berliner allee 6, D - 64295 Darmstadt, Germany y.el-mossallamy@arcadis.de

Introductionthe quick growth of cities in the last two decades all over the world led to a rapid increase

in the number and height of high rise buildings even in unfavourable subground condi-

tions. since the 80's, a new foundation technique, the so-called piled rafts, has been

developed and used extensively in order to reduce the maximum as well as the differential

settlements and the associated tilting of the buildings. the analysis of piled raft is a

very interesting example of the soil-structure interaction that requires the co-operation

between the geotechnical and structural engineers to reach the most economic founda-

tion system. enhanced numerical analyses play a decisive role for the analyses of such

complex foundation system. the piled raft foundation has shown its validity as a very

economic geotechnical foundation type, where the structural loads are carried partly by

the piles and partly by the raft contact stresses. this foundation system was successfully

applied in stiff as well as soft subsoil. an innovative application of the piled raft is its

special adjustment to cases of foundations with large load eccentricities or very different

loaded parts of buildings to avoid the need of complex settlement joints especially below

ground water table.

calculation procedures to model the behavior of such complex three-dimensional prob-

lems have been developed since the 1970s (e.g., by Butterfield and Banerjee 1971, Poulos

and davis 1980 and randolph 1993). But some important requirements concerning the

raft stiffness, the nonlinear behavior of the pile support and the slip developing along the

pile shafts even under working loads were not sufficiently considered in these analyses.

for these reasons improved numerical models based on three dimensional finite element

method are applied taking into account all above mentioned effects (el-mossallamy

1996).

a traditional 3d finite element technique with the appropriate soil constitutive laws pres-

ents a powerful tool to model this complex soil-structure interaction problem. neverthe-

less, the main disadvantage applying the 3d fe analyses is the need of a huge number

of volume elements which can exceed the available computer capacities. to cover this

problem, a new technique combined the so called embedded pile model with the 3d finite

element model was developed by Plaxis B.V. under the name Plaxis 3d foundation version

2. the following sections present an example demonstrating the ability of this program

to deal with a complex piled rafts. a case history in frankfurt will be resolved applying

this program.

the piled raft is a composite geotechnical foundation system consisting of piles, raft

and soil. figure 1 demonstrates the principles of piled raft foundation and the different

interactions (e.g. pile/pile and pile/raft) that govern its behavior.

extensive measurements of the load transfer mechanism of piled raft foundations during

and after the construction were performed to verify the design concept and to prove the

serviceability requirements. the piled raft foundation is extensively applied as suitable

foundation technique of high-rise buildings in frankfurt, Germany to achieve economic

solutions that fulfill the stability as well as the serviceability requirements. the measured

settlements of different case histories of piled rafts in comparison with traditional raft as

well piled foundation are shown in figure 2. the factor αl is a load factor representing the

load taken by the piles relative to the total structural load.

figure 1: Principles of piled raft

figure 2: settlement behavior of high-rise buildings in frankfurt, Germany

11

Plaxis Practice

Frankfurt subground and methodologyto develop the piled raftmost of the high-rise buildings in frankfurt are founded on the so-called frankfurter clay,

which developed 2 to 10 million years ago as a result of the sedimentation in the tertiary

sea in the mainz basin. in the town center, the clay layer measures up to 100 meters and

includes limestone banks, lignite coal lenses and layers of calcareous sand. the ground-

water level is mostly just above the clay surface and circulates in the fissured limestone

banks and sand lenses resulting in different confined aquifer pressures. the clay is geo-

logically overconsolidated through older, already eroded sediments and volcanic rock.

Example of a high-Rise Building on Frankfurt subsoilthe 120 m building with a 4-storey underground basement has an l shape (fig. 3) with

a load eccentricity of about 7.0 m. applying the concept of piled raft foundation it was

possible to construct the foundation without settlement joints between the tower and

the adjacent 4-storey underground garage. the piles were placed eccentrically below the

tower to balance the load eccentricity.

figure 3: General layout

Geometry

the foundation of the building has a total area of about 1930 m². only 25 large diameter

bored piles were constructed beneath the raft as a piled raft foundation. the pile arrange-

ments are shown in figure 4. the rafts are 3.5 meters thick in the middle and 1.0 m at

the edges. the raft base lies at a depth of 15.75 meters below the soil surface. the piles

where designed with a diameter of 1.3 m and a length of 22 m. the total working loads

reach about 900 mn.

figure 4: foundation dimensions and pile arrangement

Foundation and subsoil conditions

General information

Height (m) 114

Foundation area (m!) 1930

Raft thickness (m) 3.5 - 1.0

Foundation depth (m) -15.75

Groundwater - 6.0

Slenderness ratio 3.5

No of piles 25

Pile length (m) 22

Pile diameter (m) 1.3

General information Height (m) 114

foundation area (m2) 1930

raft thickness (m) 3.5 - 1.0

foundation depth (m) -15.75

Groundwater - 6.0

slenderness ratio 3.5

no of piles 25

Pile length (m) 22

Pile diameter (m) 1.3

12

Plaxis Practice

figure 7: foundation settlement under working loads

Numerical modelsoil Parametersthe soil stress-strain relationship was modelled applying the Hardening soil model. the

main advantage of this constitutive law is its ability to consider the stress path and its

effect on the soil stiffness and its behavior. for the concrete piles and raft, a linear elastic

material set was applied using the concrete weight and its stiffness. the ultimate skin

friction of the pile is assumed to start with 60 kPa at the pile head and increased with

depth to reach 120 kPa at the pile tip. the ultimate pile base resistance was taken equal

to 2.0 mPa.

3D Finite element modelWork-planes are defined. the Work-planes are needed at each level where a discontinuity

in the geometry or the loading occurs in the initial situation or in the construction pro-

cess. figure 5 shows the applied three dimensional finite element mesh. the main model

geometries are given in figure 6.

Yasser El-Mossallamy, associate Prof., ain shams University, Cairo, Egypt c/o aRCaDis GmbH, Berliner allee 6, D - 64295 Darmstadt, Germany y.el-mossallamy@arcadis.de

Modelling the behaviour of piled raft applying Plaxis 3D Foundation Version 2

figure 5: 3d fe-model

figure 6: applied loads

inspect outputthe initial conditions should be generated using the k0-procedure. a value of k0 = 0.8 is

applied to consider the effect of overconsolidation. the aim of the calculation is to deter-

mine the average settlement of the rafts under working load (serviceability limit state).

figure 7 demonstrates the raft settlements under working loads.

settlement of about 4 cm is calculated at the raft center. this value agrees well with the

measured value and approves the ability of the three dimensional analyses to predict the

settlement of the piled raft as a main part of the foundation design. figure 8 shows the

load distribution among the individual piles within the pile group. it can be recognized

that the contribution of the edge piles by carrying the loads is very small. this is due to

the presence of the outer wall that works also as shoring system, which is modelled as

fully connected with the foundation raft. the effect of the outer walls can be investigated

by applying a new model in which the outer walls are not modelled.

13

Plaxis Practice

Conclusion and Outlookthe illustrated examples show that understanding of the effects of the interaction be-

tween construction and subsoil based on the appropriate theoretical knowledge and on

experienced application of measurement techniques and numerical modelling are the

necessary qualification for a safe and economic design for such complex foundations.

the piled raft foundation can be modelled using the embedded piles that are available in

Plaxis 3d foundation. the results should be further compared with cases where the piles

are modelled using volume elements. there is still need of horizontal interface elements

to investigate the raft contact stresses in a direct manner. the embedded piles help to

reduce the required number of elements needed to model the complex three dimensional

feature of piled rafts. the experience with this model type should be gathered with time

and shared among the Plaxis users. the effect of the shoring system on the behavior of

piled raft needs further investigation.

figure 8: results of normal force distribution along all piles

outer piles

middle piles

Some related references- Burland, J.B., Broms, B.B., and de mello, V. (1977) Behaviour of foundations and struc-

tures, state-of-the- art report, Proc. 9th icsmfe tokyo, vol. 2, 495 - 546

- Butterfield, r., and Banerjee, P.k. (1971) "the problem of pile group-pile cap interac-

tion." Géotechnique, Vol. 21, no. 2, pp. 135-142.

- din 1054-100 (2005) Baugrund: sicherheitsnachweis im erd- und Grundbau

- dürrwang, r., el-mossallamy, y. und reininger-Behrenroth, m.(2007) neue erkenntnisse

zum Verformungsverhalten des frankfurter tones, Bautechnik, Vol.3, 190-192

- el-mossallamy, y. (1996) ein Berechnungsmodell zum tragverhalten der kombinierten

Pfahl-Plattengründung., dissertation, fachbereich Bauingenieur-wesen der technis-

chen Hochschule darmstadt

- el-mossallamy, y., lutz, B., and richter, th. (2006) innovative application and design

of piled raft foundation. 10th international conference on Piling and deep foundations,

(31 may - 2 June 2006), amsterdam, netherlands

- el-mossalamy, y., el-nahhas, f. and essawy, a. (2006) innovative Use of Piled raft

foundation to optimize the design of High-rise Buildings. 10th arab structural engi-

neering conference, 13-15 november 2006, kuwait

- el-mossallamy, y (2007) Piled raft foundation in frankfurt clay. Validation manual,

Plaxis 3d foundation, Version 2

- franke, e.; el-mossallamy, y.; and Wittmann, P.(2000) calculation methods for raft

foundations in Germany. design applications of raft foundation and ground slabs, edi-

ted by Hemsley, Published by thomas telford ltd, london, 2000, p.p.283-322

- Hanisch, J., katzenbach, r., und könig, G. 2002. kombinierte Pfahl-Plattengründung,

in Zusammenarbeit mit dem arbeitskreis „Pfähle“ der deutschen Gesellschaft für Geo-

technik e.V. (dGGt), ernst & sohn.

- Poulos, H.G., and davis, e.H. (1980) Pile foundation analysis and design. Wiley, new

york.

- randolph, m.f. and clancy, P. (1993) efficient design of piled rafts. Proc. 2nd int. semi-

nar, deep foundation, Ghent, 119-130.

14

Plaxis Practice

Ciro VisONE, Ph.D. student, Department of Geotechnical Engineering, University of Naples Federico ii, Naples, italy, ciro.visone@unina.itEmilio BilOTTa, Research assistant, Department of Geotechnical Engineering, University of Naples Federico ii, Naples, italy, bilotta@unina.itFilippo saNTUCCi de MaGisTRis, lecturer, Department s.a.V.a. – Engineering & Environment Division, University of Molise, Campobasso, italy, filippo.santucci@unimol.it

Remarks on site response analysis by using Plaxis dynamic module

Introductiondynamic fe analyses can be considered the most complete available instrument for the

prediction of the seismic response of a geotechnical system, since they can give detailed

indication of both the soil stress distribution and deformation. However, they require at

least a proper soil constitutive model, an adequate soil characterization by means of in

situ and laboratory tests, a proper definition of the seismic input.

this article discusses how to calibrate a finite element model in order to obtain a realistic

response of the given system subjected to seismic loading. Plaxis 2d v.8.2 (Brinkgreve,

2002) that includes the dynamic module was used in this research. a series of dynamic

analyses of vertical propagation of s-waves in a homogeneous elastic layer was carried

out. this scheme was chosen because a theoretical solution of the problem is available

in literature and some comparisons can be easily done. the influences on the response of

boundaries conditions, mesh dimensions, input signal filtering and damping parameters

was investigated.

the information obtained in this preliminary calibration process can be used thereafter

for the analysis of any geotechnical system subjected to seismic loadings.

Reference theoretical solutionVertical one-dimensional propagation of shear waves in a visco-elastic homogeneous

layer that lies on rigid bedrock can be described in the frequency domain by its amplifica-

tion function. the latter is defined as the modulus of the transfer function that is the ratio

of the fourier spectrum of the free surface motion to the corresponding component of the

bedrock motion. therefore, for a given visco-elastic stratum and a given seismic motion

acting at the rigid bedrock the motion at the free surface can be easily obtained. first, the

fourier spectrum of the input signal is computed. then, this function is multiplied by the

amplification function and after that the motion is given by the inverse fourier transform

of the previous product.

if the properties of the medium (density, ρ or total unit weight of soil, γ; shear wave

velocity, Vs; material damping, d) and its geometry (layer thickness, H) are known, the

amplification function is uniquely defined.

for a soil layer on rigid bedrock with the following parameters:

H =16 m; γ = 14.1 kn/m3; ρ = 1.44 kg/m3; Vs = 361.5 m/s; d = 2 %

the amplification function (roesset, 1970) is:

PHYSICAL PROPERTIES STIFFNESS PARAMETERS

! RAYLEIGH DAMPING E " G Eoed VS VP

[kN/m3] ! " [kN/m2] [kN/m2] [kN/m2] [m/s] [m/s]

141 - - 4.889x105 3 1.88x105 6.581x105 3615 6763

figure 1. amplification function of an elastic layer over rigid bedrock

table 1. material properties of the linear elastic layer

figure 2. seismic input: a) accelerations time-history; b) fourier spectrum

A(f)=

cos2 2π f + 2π fH HDVs Vs

2

1

15

Plaxis Practice

Remarks on site response analysis by using Plaxis dynamic module

figure 1 shows its graphical representation in the amplification ratio-frequency plane.

Here, and in the following similar figures, two vertical red lines indicate the first and the

second natural frequency of the system. in the previous indicated hypotheses, the nth

natural frequencies fn of the layer are:

Numerical modeling3.1 input signalin numerical computation, the earthquake loading was often imposed as an acceleration

time-history at the base of the model.

Here, the input signal chosen for numerical analyses is the accelerometer registration of

tolmezzo station (friuli earthquake, italy, may 6th, 1976). the sampling frequency is 200

Hz, the duration is 36.39 s and the peak acceleration is 0.315 g.

accelerations time-history and fourier spectrum of the signal are reported in figure 2.

3.2 Finite element modelthe finite element model is plotted in figure 3. it is constituted by a rectangular domain

80 m wide and 16 m high and two additional similar lateral domains, in order to place

far enough the lateral boundaries (total width 240 m). this should help minimizing the

influence of the boundaries on the obtained results, even though no clear indications

exist in literature on this aspect. recently, amorosi et al. (2007) have shown a case of

site response analysis in which they have extended the width of the mesh eight times its

height, in order to obtain acceptable results.

the medium is schematized as a linear elastic layer that is implemented in the Plaxis

code. its parameters are indicated in table 1.

the initial stress generation was obtained by the k0-procedure in which the value of the

earth pressure at rest, k0 was chosen by means of the well-known formula for the elastic

medium:

the mesh generation in Plaxis is fully automatic and based on a robust triangulation

procedure, which results in an “unstructured” mesh. in the meshes used in the present

analyses, the basic type of element is the 15-node triangular element. the dimensions

of any triangle can be controlled by local element size. By subdividing the homogeneous

layer in sub-layers with a fixed thickness and by using the local element size, it is possible

to assign to the triangles a maximum size.

an average dimension that is representative for refinement degree of the mesh is the

“average element size” (aes) that represents an average length of the side of the ele-

ments employed.

every time a numerical analysis is performed, the mesh influence must be tested.

kuhlmeyer & lysmer (1973) suggested to assume a size of element not larger than λ/8,

where λ is the wavelength corresponding to the maximum frequency f of interest. in this

case λ/8 = Vs/8 f = 1.81 m, being Vs= 361.5 m/s and f = 25 Hz. in the analyses of the

present work an aes=1.58 m was used.

Results of dynamic analyseschristian et al. (1977) have shown that the right lateral boundaries conditions for s-

waves polarized in horizontal plane and propagating vertically are the vertical fixities.

Horizontal displacements must be allowed. in order to equilibrate the horizontal litho

static stresses acting on lateral boundaries, it is suitable to introduce load distributions

at the left-hand and right-hand vertical boundaries. in this manner, the amplification

function of all points placed on the free surface of the model is the same. figure 4 plots

the graphical lateral boundaries condition utilized in Plaxis.

the use of such boundary conditions instead of adopting lateral dampers as suggested by

kuhlmeyer & lysmer (1973) permits to calibrate the damping parameters of the system

with more accuracy.

in numerical calculations two types of damping exist: numerical damping, due to finite

element formulation, and material damping, due to viscous properties, friction and de-

velopment of plasticity.

in Plaxis (and in most dynamic fe codes), the material damping is simulated with the

well-known rayleigh formulation. the damping matrix c is assumed to be proportional

to mass matrix m and stiffness matrix k by means two coefficients, αr and βr according

to:

different criteria exist to evaluate the rayleigh coefficients (see for instance lanzo et al.,

2004; Park & Hashash, 2004; amorosi et al., 2007). in terms of frequency, the dynamic

response of a system is affected by the choice of these parameters to a large extent.

in the numerical implementation of dynamic problems, the formulation of the time inte-

gration constitutes an important factor for stability and accuracy of the calculation pro-

cess. explicit and implicit integration are two commonly used time integration schemes.

in Plaxis, the newmark type implicit time integration scheme is implemented. With this

method, the displacement and the velocity at the point in time t+Δt are expressed res-

pectively as:

80m80m 80m

16m

figure 3. finite element model utilized in the dynamic analyses

figure 4. free Horizontal displacements (fHd) condition on lateral boundaries of fe model

16

Plaxis Practice

the coefficients αn and βn, which should not be confused with rayleigh coefficients,

determine the accuracy of numerical time integration. for determining these parameters,

different suggestions are proposed, too. typical values are (Barrios et al., 2005):

a) αn =1/6 and βn =1/2, which lead to a linear acceleration approximation (conditionally

stable scheme);

b) αn =1/4 and βn =1/2, which lead to a constant average acceleration (unconditionally

stable scheme);

c) αn =1/12 and βn =1/2, the fox-Goodwin method, which is fourth order accurate (con-

ditionally stable scheme);

in order to keep a second order accurate scheme and to introduce numerical dissipation,

a modification of the initial newmark scheme was proposed by Hilber et al. (lUsas, 2000),

introducing a new parameter γ (α in the notation of the author), which is a numerical

dissipation parameter. the original newmark scheme becomes the α-method or new-

mark HHt modification. the α-method leads to an unconditionally stable integration time

scheme and the new newmark parameters are expressed as a function of the parameter

γ, according to:

where the value of γ belongs to the interval [0, 1/3]. By assuming γ=0 the modified

newmark methods coincides with the original newmark method with constant average

acceleration.

moreover, in order to obtain a stable solution, the following condition must apply in the

Plaxis code:

neither the linear acceleration approximation or the fox-Goodwin method does meet such

requirement.

if no damping, material and/or numerical, is introduced in a dynamic analysis, the model

reaches the resonant conditions at the natural frequencies of the system with a cor-

responding theoretically infinite amplification ratio. figure 5 shows the response at a

control point on the free-surface obtained for an undamped analysis (αn = βn = αr =

βr = 0) in terms of the acceleration time-history and the fourier spectrum as a result of

the input signal shown in figure 2. the numerical results are very close to the expected

theoretical values.

Remarks on site response analysis by using Plaxis dynamic module

Continuation

figure 5. signal at surface of undamped analysis: a) accelerations time-history; b) fourier

spectrum

figure 6. influence of newmark numerical damping coefficients on amplification function

of the model

12

αN ≥ + ßN 14 2

12

12

17

Plaxis Practice

the standard setting of Plaxis is the damped newmark scheme with αn = 0.3025 and βn

= 0.6, that correspond to γ = 0.1.

figure 6 explains the results of numerical analyses for three different values of γ. rayleigh

coefficients were put equal to zero. When γ increases, the peaks amplification at the

natural frequencies of the layer decrease. However, the shape of amplification function is

not essentially modified. the numerical damping coefficients chosen by default in Plaxis

(black curve in figure 6) conduct to an amplification ratio (a=7.97 at f=16.55 Hz) smaller

than the theoretical one (a=10.54 at f =16.95 Hz, see figure 1) in correspondence to the

second natural frequency of the layer.

note also that the value of second natural frequency of the stratum is underestimated

by the time domain analyses. this is due to the finite element formulation with lumped

masses instead of consistent mass matrices (roesset, 1977). the natural frequencies

with a lumped masses formulation, which is implemented in Plaxis, are always smaller

than the true frequencies. consistent mass matrices overestimate them. the accuracy of

the results decreases with the number of vibration modes.

numerical damping has a great influence on the dynamic response of a geotechnical

system and this issue should be particularly considered when an earthquake signal needs

to be preliminarily processed. in fact, to reduce the calculation time, filtered signals at the

frequency of interest (i.e., accelerograms with a reduced number of registration points)

are often used for the input motion. in this case, users should be aware that the analysis

needs an adequate calibration of newmark coefficients, in such a manner to avoid the

loss of important frequency contents of the signal. a comparison of the system response

to a complete signal and a 25 Hz filtered signal is represented in figure 7.

figure 8 shows the different amplification functions for three values of rayleigh damping

coefficient αr. the coefficient βr is given equal to zero for avoiding excessive damping

of the motion at high frequencies. the results are referred to a numerical damping of γ

= 0.055. this value has been worked out to obtain a good agreement between numerical

and theoretical values of the amplification ratio that correspond to the second natural

frequency of the layer as shown in fig. 10.

the solution with free horizontal displacements (fHd) on lateral boundaries is only rea-

sonable for non-plastic material and when local site response is the objective of the study.

if a 2-d configuration of the problem should be examined, horizontal fixities on the left and

on the right hand of the model must to be applied. in these conditions, silent boundaries

are often used to simulate infinite media.

different methods exist to apply a silent boundary (ross, 2004). in Plaxis, viscous adsor-

bent boundaries can be introduced, which are based on the method described by lysmer

& kuhlmeyer (1969). By default, relaxation coefficients c1 and c2 are set to 1.0 and 0.25,

respectively.

By placing the lateral boundaries sufficiently far from the central zone, the effects due to

the reflection of waves on boundaries can be neglected.

a comparison of the results with standard earthquake Boundaries seB (fig. 3) and free

Horizontal displacements fHd (fig. 4) on lateral boundaries is presented in figure 10, by

using default values for c1 and c2. it seems to suggest that better results are obtained by

using fHd rather than seB.

Remarks on site response analysis by using Plaxis dynamic module

figure 7. influence of input signal filtering on amplification function of the model (γ =

0.1)

figure 8. influence of rayleigh material damping coefficients on amplification function

of the model (γ = 0.055)

figure 9. comparison between numerical and theoretical solution for d=2%

18

Recent Activities

Conclusionsthe use of dynamic analyses to calculate the seismic response of a geotechnical system is

dependent on advanced site characterization and numerical knowledge.

it is necessary a good calibration of the numerical model before conducting a dynamic

analysis for any type of 2-d problem. some parameters (equivalent stiffness, numerical

and material damping, etc.) can be chosen by comparing the dynamic response of model

under vertical shear waves propagation to the theoretical solutions. in the present article,

an example of procedure to calibrate the finite element model parameters has been pre-

sented in order to control the system damping.

material damping is often modelled by rayleigh formulation. moreover, numerical dam-

ping is also needed in order to attain a stable calculation. this leads to some difficulty

to control the actual damping of the numerical model. a possible choice in order to limit

such uncertainty is to set the minimum value for newmark γ which allows stability, then

fit the theoretical solution. this can be achieved by assuming rayleigh β=0 and changing

rayleigh α only, in order to model the material damping with reasonable approximation

in the desired range of frequencies. the best-fit criterion can be, for instance, reprodu-

cing the amplification of the seismic signal over the first and second natural frequency

of the system. modelling lateral boundaries and filtering input signal need to be carefully

considered when performing such calibration.

the proposed approach was preliminarily used for the analysis of some geotechnical

earthquake problems as the seismic response of flexible earth retaining structures (Vi-

sone & santucci de magistris, 2007) and the transverse section of a circular tunnel in soft

ground (Bilotta et al., 2007).

Acknowledgmentsthis work is a part of a research Project funded by relUis (italian University network of

seismic engineering laboratories) consortium. the authors wish to thank the coordinator,

prof. stefano aversa, for his continuous support and the fruitful discussions.

References- amorosi a.,elia G., Boldini d., sasso m., lollino P. (2007). sull’analisi della risposta sismica

locale mediante codici di calcolo numerici. Proc. of iarG 2007 salerno, italy (in italian).

- Barrios d.B., angelo e., Gonçalves e., (2005). finite element shot Peening simulation.

analysis and comparison with experimental results, mecom 2005, Viii congreso argen-

tino de mecànica computacional, ed. a. larreteguy, vol. XXiV, Buenos aires, argentina,

noviembre 2005

- Bilotta e., lanzano G., russo G., santucci de magistris f., silvestri f. (2007). methods

for the seismic analysis of transverse section of circular tunnels in soft ground, Work-

shop of ertc12 - evaluation committee for the application of ec8, special session XiV

ecsmGe, madrid, 2007.

- Brinkgreve r.B.J. (2002) , Plaxis 2d version8. a.a. Balkema Publisher, lisse, 2002.

christian J.t., roesset J.m., desai c.s., (1977). two- or three-dimensional dynamic

analyses, numerical methods in Geotechnical engineering, chapter 20, pp. 683-718,

ed. desai c.s., christian J.t. - mcGraw-Hill

- kuhlmeyer r.l, lysmer J. (1973). finite element method accuracy for Wave Propaga-

tion Problems, Journal of the soil mechanics and foundation division, vol.99 n.5, pp.

421-427

- lanzo G., Pagliaroli a., d’elia B. (2004). l’influenza della modellazione di rayleigh dello

smorzamento viscoso nelle analisi di risposta sismica locale, anidis, Xi congresso na-

zionale “l’ingegneria sismica in italia”, Genova 25-29 Gennaio 2004 (in italian)

lUsas (2000). theory manual, fea ltd., United kingdom

- lysmer J., kuhlmeyer r.l. (1969). finite dynamic model for infinite media, asce, Journal

of engineering and mechanical division, pp. 859-877

- Park d., Hashash y.m.a. (2004). soil damping formulation in nonlinear time domain

site response analysis, Journal of earthquake engineering, vol.8 n.2, pp.249-274

- roesset, J.m. (1970). fundamentals of soil amplification, in: seismic design for. nucle-

ar Power Plants (r.J. Hansen, ed.), the mit Press, cambridge, ma, pp. 183-244.

- roesset J.m., (1977). soil amplification of earthquakes, numerical methods in Geotech-

nical engineering, chapter 19, pp. 639-682, ed. desai c.s., christian J.t. - mcGraw-Hill

- ross m., (2004). modelling methods for silent Boundaries in infinite media, asen

5519-006: fluid-structure interaction, University of colorado at Boulder

- Visone c., santucci de magistris f. (2007). some aspects of seismic design methods for

flexible earth retaining structures, Workshop of ertc12 - evaluation committee for the

application of ec8, special session XiV ecsmGe, madrid, 2007.

Remarks on site response analysis by using Plaxis dynamic module

Continuation

figure 10. comparison between seB and fHd on lateral boundaries solutions

19

Recent activities

Recent Activities

Plaxis AsiaPlaxis expands “Plaxis asia” office. since 2006 dr. William cheang was already involved

in pre and after sales activities in asian countries. furthermore William assist our agents

upon request to promote Plaxis products and services via conferences, courses and semi-

nars. from 2008 Plaxis bv appointed mr. eddy tan to have the lead in the business de-

velopment of all local sales and marketing activities for the company’s Plaxis products

and services. the aim is to establish a strong local presence in order to provide optimum

support for all Plaxis users and prospects in the asian market.

Plaxis regards the asian market as strategically important because it exhibits a strong

and constantly growing demand in Plaxis products and service solutions.

Plaxis asia activities in 2008 are;

to assist HQ in managing sales and technical support in asia

- to provide a better service & support to agents in asia

- to provide assistance to agents in sales & marketing

- to provide necessary technical support to agents

- to have direct contact with the local education institutions

- to assist local agents to organise seminars and courses

With the establishment of Plaxis asia, one of her major focus will be the china market

among other emerging countries in asia. although marketing effort has been started

since 5 years ago in china, we notice the application usage are mainly in the higher

educational institutions and research sectors. a recent marketing trip to china in Jan

2008 has elevated us beyond this horizon. We have met and presented our software to

big private corporations such as the Water resource commission, provincial government-

owned electrical Power design consultants and railway design institutes, whom they see

the potential needs on fem application for their work. We also take the opportunities to

understand their projects and problem faced during the various stages of their work.

We are confident that Plaxis will soon be widely used by most private design firms in china

just like any other geotechnical design consultants around the world”.

Plaxis on the moveto be able to continue the increase of staff Plaxis bv moved to a new building. detailed

contact information on Plaxis bv and Plaxis asia can be found at our contact page of our

website.

Plaxis Eventslast year our worldwide expansion of Plaxis courses included also 2 fully booked courses

in latin america (Brazil and colombia). in 2008 we have an extended course Program to

facilitate our knowledge transfer of the background and usage of Plaxis products. Please

visit our agenda on the back cover of this bulletin or on the website to get a full overview

of the upcoming Plaxis events. We hope to meet you soon in our new offices or at one of

the above mentioned events.

Remarks on site response analysis by using Plaxis dynamic module

new Head Quarter Plaxis bv

Photographer Peter de ruigPhotographer Peter de ruig

Plaxis finite element code for soil and rock analyses

Plaxis BVPo Box 572

2600 an delft

the netherlands

tel: +31 (0)15 251 77 20

fax: +31 (0)15 257 31 07

e-mail: info@plaxis.nl

Website: www.plaxis.nl

Activities 2008

8006

758

march 9 – 12, 2008Gi-Geocongress 2008new orleans, Usa

march 10 – 13, 2008international course for experienced Plaxis usersantwerp, Belgium

april 2008seminars in chongqin, shanghai, Beijing and Guangzhouchina

april 10 – 12, 2008tc28 shanghaishanghai, china

april 2008seminars in new dehli & mumbaiindia

april 29, 2008seminars london/ GlasgowUnited kingdom

may 4 – 7, 200813th australian tunneling conference 2008Grand Hyatt, melbourne, australia

may 8 – 9, 20084th conference on advances and applications of Gidibiza, spain

may 14 – 16, 2008 course on computational GeotechnicsPisa, italy

may 18 – 22, 2008Gi-Geesd iVsacramento, ca, Usa

June 2008seminars in VietnamVietnam

June 17 – 19, 2008numerical methods in Geotechnical engineeringmanchester, United kingdom

June 10, 2008course for experienced Plaxis Usersseoul, south korea

June 23 – 25, 2008sat 2008sao Paolo, Brasil

June 2008russian Users conferencest. Petersburg, russia

July 2 – 4, 2008e-Unsat 2008durham, United kingdom

July 2008course on computational GeotechnicsGuadalajara, mexico

July 15, 2008seminars PhilippinesPhilippines

august 2008course on computational GeotechnicsHouston, Usa

august 2008course on computational Geotechnicstaiwan

september 3 – 5, 2008amGiss, 2nd international Workshop on Geotechnics of soft soilsGlasgow, scotland, United kingdom

september 7 – 10, 2008euroGeo4 edinburgh, scotland, United kingdom

september 15 – 18, 200811th Baltic sea Geotechnical conferenceGdansk, Poland

september 2008course on computational Geotechnics new dehli, india

september 22 – 27, 2008ita – aites World tunnel congressagra, india

october 1 – 6, 200812th iacmaGGoa, india

october 8, 2008funderingsdagede, the netherlands

october 13 – 15, 2008nUcGe 2008skikda, algeria

october 2008course on computational GeotechnicsJapan

november 5 – 7, 200815th european Plaxis User meetingkarlsruhe, Germany

november 2008course on computational Geotechnicsshanghai, china

november 2008course on computational GeotechnicsParis, france