21 PLAXIS Bulletin

Plaxis finite element code for soil and rock analyses

Simulation of a volcano in PlaxisStructural reliability analysis of deep excavations

Numerical simulation of a trial wall on expansive soil in Sudan

Application of the ground anchor facility in Plaxis 3D Foundation

issue 21 / March 2007Plaxis Bulletin

�

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

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Editorial Board:

Wout BroereRonald BrinkgreveErwin Beerninkarny lengkeek

coverphoto: Building Pit sixhaven, noord/Zuidlijn metro, amsterdam

Colophon

Editorial

New Developments

Plaxis PracticeSimulation of a

volcano in Plaxis

Plaxis PracticeStructural reliability

analysis of deep excavations

Plaxis PracticeNumerical simulation

of a trial wall on expansive soil in Sudan

Plaxis PracticeApplication of the ground

anchor facility in Plaxis 3D Foundation

Recent Activities

Activities 2007

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4

8

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3

the first application involves a study after the stability of the cumbre Vieja volcano

at the island of la Palma. in contrast to what has been suggested in a world famous

television documentary, the results of this study show that there is no danger for a big

slide or resulting tsunami in the near future.

talking about ‘dangers’, the second application shows how Plaxis can be used in

structural reliability calculations using probabilistic methods. in this respect, failure is

not primarily defined as collapse of the soil structure, but may also be defined in terms

of structural forces or displacements obtained from the finite element calculations. the

article shows that probabilistic analysis using Plaxis is quite feasible.

the third application demonstrates the use of a new model for partially saturated soil.

the application involves a combination of transient groundwater flow calculations using

Plaxflow, and deformation analysis using Plaxis version 8. it is concluded that care must

be taken with the use of suction in deformation or stability calculations.

the fourth application is a validation example of the ground anchor facility in the new

Plaxis 3d foundation program that will be released soon. the results show that it is

an efficient way to model ground anchors under working load conditions. However, it is

emphasized that the ground anchor facility should not be used to evaluate a pull-out

force. When going towards failure, results become quite mesh dependent.

all together, we think that the current Bulletin contains enough interesting information,

which may also encourage you to submit your own contribution next time. We wish you a

fruitful reading experience and look forward to receive more documented projects for the

coming bulletins.

the editors

Editorial

in the last year we have seen a continuing increase of Plaxis-related activities.

The prospect for 2007 is even better; see the agenda at the end of this Bulletin.

The increase in 2D and 3D geotechnical finite element calculations has led to

some interesting innovative applications in this Bulletin.

�

New Developments

Ronald Brinkgreve, Plaxis BV

New Developments

the development of advanced but practical models to simulate soil behaviour has always

played an important role in the Plaxis developments. over the years, advanced models

have become available, while maintaining the Plaxis philosophy that such models must

have clear and understandable parameters. subsequently, more and more users have

made the step to learn about these advanced models, to select the corresponding model

parameters and to apply them in practical finite element calculations. all together it has

led to an improvement of the predictive capabilities of the finite element method in the

geotechnical engineering practice.

in fact, model development is an ongoing activity. the latest model that has been added

to the family is the Hardening soil model with small-strain stiffness [1]. this addition

is not only relevant for dynamic applications (wave propagation, hysteretic damping),

but it also improves the prediction of settlements as a result of excavations. moreover,

using small-strain stiffness makes finite element results less dependent on the precise

position of the model boundaries, provided that a sufficiently large part of the geometry

is taken into account in the finite element model [�]. all this is obtained for only two extra

(compared to the standard Hsm) model parameters: the small-strain shear stiffness, G0,

and the shear strain at which the secant shear stiffness has reduced to 70% of G0. the

Hssmall model is available for all users that participate in the Plaxis renewable license

programmes.

in the remainder of this column i like to mention some other material model

developments that are going on and that we consider to make available in the (near)

future for those who are interested. first of all, in addition to the Hssmall model, we will

be working on a real cyclic loading model. this model will include the accumulation of

volumetric straining in multiple load cycles. in combination with undrained behaviour it

will also lead to liquefaction type of behaviour, although real liquefaction would require a

more complicated model with softening. moreover, within the network of universities and

institutes where Plaxis collaborates with, work is being performed on unsaturated soil

models, anisotropic creep models, anisotropic undrained strength models,

structured clay models, hypo-plastic models and other small-strain models. some of

these have already been developed as user-defined soil models and are available on

special request. for further details see the Plaxis web site (services > Udsm).

Historically speaking, Plaxis has always been strong in the modelling of soft soils.

nevertheless, since Plaxis is used nowadays all over the world under different

geological conditions (see for example the la Palma application further in this

Bulletin) there is an increasing demand for rock models. in this respect, the well-known

generalized Hoek-Brown model has been recently implemented as a user-defined model.

a particular feature of the Hoek-Brown model is the curved failure envelope with increasing

confining pressure, in combination with a tensile strength for strong cohesive materials.

this leads to difficulties to make the model compatible with typical Plaxis features like phi-c

reduction, but this difficulty has been overcome, as demonstrated by Benz et.al. [3]. later

this year, the Hoek-Brown model will be made operational as a standard model in Plaxis.

to give users insight in the behaviour of new models we will integrate them in

Plaxis courses on computational Geotechnics and in the new soil test facility.

We are convinced that this will lead to a further improvement of the quality of

geotechnical finite element calculations.

References[1] Benz, t. (�006). small-strain stiffness of soils and its numerical consequences.

Ph.d. thesis. institut für Geotechnik, Universität stuttgart.

[�] Brinkgreve r.B.J., Bakker k.J., Bonnier P.G. (�006). the relevance of small-strain

stiffness in excavation and tunnelling projects. in: H.f. schweiger (ed.) numerical

methods in Geotechnical engineering. taylor & francis. 133-139.

[3] Benz t, kauther r., schwab r (�006). simulation of a large excavation using a

Hoek-Brown model. in: H.f. schweiger (ed.) numerical methods in Geotechnical

engineering. taylor & francis. 513-518.

corrected reference on embedded beam element in previous new developments column

(Bulletin �0): [1] sadek m., shahrour i. (�00�). a three-dimensional embedded beam

element for reinforced geomaterials. int. J. num. anal. meth. Geomech. �8, 931-9�6.

σ σ

figure 1 Hoek-Brown failure criterion

5

Plaxis Practice

Simulation of a volcano in Plaxis

Janneke van Berlo, M. sc. student, Delft University of Technology

Introductionmodelling of slope stability is a common practice in Plaxis. modelling of a volcanic edifice of

16 km wide and � km high however, required some pioneering in the familiar finite element

package. for geological processes such as magma intrusion and water expansion, Plaxis

offers no ready made features. nevertheless this article will show that with creative use of

the program one can accomplish more than might be expected on first sight.

the island of san miguel de la Palma is the most north-western island of the canary

islands archipelago, situated about �00 km from the coast of central morocco.

the south-western part of the island, which is formed by the cumbre Vieja volcano has

been considered to be more or less unstable by various authors (ancochea et all, 199�;

carracedo et al, 1999; day et al, 1999). (figure 1) Ward and day (�001) even forecast that

an effective collapse of the island may cause a tsunami in the altantic ocean.

this research emcompassed quantifying the likelyness that the supposed la Palma

landslide will actually take place. the (boundary) conditions under which the West flank

of the cumbre Vieja volcano could start sliding have been investigated. moreover the time

lapse from the present day to the day such mass movement would occur was assessed.

the purpose of this article is to inform the reader about the specific problems encountered

during the modelling of a volcano and the applied solutions. at the same time the results

of the research objectives will be discussed briefly.

figure 1 satellite view of la Palma with indication of modelled area

The geometry of the mountainin order to construct a full cross-section through the mountain, at least 16 km of

modelling space was required. on the other hand, the drawing space is limited to

10 km. But with the origin in the centre, both positive and negative coordinates up

to 10 km can be used. Because modelling was carried out in �d, a least stable cross

section through the edifice was chosen. figure � shows the layout of the cross section.

the asymmetry of the cross section stands out: a significant part of the eastern flank has

not been modelled. this is because the eastern flank contains a relatively weak layer of

sediments that were deposited there after a previous giant collapse of the island about 560

thousand years ago. this layer is called ‘Post collapse sequence’ or ‘Post collapse

sediment’ (Pcs) and is depicted in yellow in figure �. it is to be expected that this layer

governs the failure mechanism. earlier modelling in a fully symmetric cross section

confirmed this prospect.

figure � the layout of the model

Geotechnical properties of the rocksdue to its volcanic character la Palma almost entirely consists of rocks. But the one

major soil unit present at the island (the Pcs, indicated in yellow in figure �) indeed

governs the stability situation. the rocks on the island are often characterized by a mixed

character on scales too small for modelling. examples are found on the volcano flanks

in the geotechnical unit ‘cumbre Vieja lava & Breccia’ and in the riftzone rocks (figure

�). the parameters representing these zones have been chosen to be averaged values of

the rocks present there. modelling has been carried out with the use of two datasets. the

first one representing an average or ‘standard’ state of rock mass properties, the second

one representing a ‘worst case’ of rock mass properties. from these data appropriate

parameters for the mohr-coulomb model were selected. table 1 depicts a summary of the

‘worst case’ rock mass parameters.

6

Continuation


Plaxis Practice

table 1. summary of worst case parameter data set

Parameter Unit lava & PCs Pyroclasts Dykes Volcaniclasts Breccia (submarine)d mn/m3 0.0177 0.016 0.01� 0.0�5 0.0133

w mn/m 0.0180 0.017 0.016 0.0�6 0.0136

n - 0.�5 0.35 0.�5 0.�5 0.�5

e50 mPa - 1�5 1�95 �9867 -

º 30 �5 �5 37 �6

c mPa 5.8 0.01 �.1 9 3.9

σtm mPa -0.07� -0.006 -0.016 -0.13� -0.039

em mPa 7913 - - 13335 �519

σtm and em are parameters according to the Hoek-Brown formulation

σtm = tensile strength

em = deformation modulus

Modelling of geological and volcanological processesthe program has been made fit to address volcano growth, varying ground water

levels, extreme pore pressure or explosions and dike-shaped magma intrusions. the

next paragraphs will briefly describe the way these processes and structures have been

incorporated.

Volcano Growththe historical growth of the cumbre Vieja volcano has been simulated in stages. in each

stage, about 100m of magmatic rocks are put on top of the edifice. the growth has

been simulated this way, because the influence of the loading path on the final stress

distribution in the edifice was not known. thus the volcano has been slowly built up, up to

the height that it currently has. from this point on the model was extended with possible

future processes and future growth. the height of the water table is updated along with

every stage of growth.

Pore pressures and explosions due to heating of pore water around intrusion in the riftzonea volcanic dyke is a tabular intrusion of magma that cuts across the bedding of

the country rock. an intruding dyke can heat up surrounding water which is trapped

between vertical impermeable dykes. subsequently the water may expand and when

experiencing little counter pressure, cause explosions. although it is plausible that

some of the produced forces are deviated in horizontal direction, experience shows that

great amounts of heated pore water escape in vertical direction through the riftzone. after

all, the vertically zoned pyroclastic rocks in the riftzone will expose less resistance to

pressure than the dykes and lavas that are governing the horizontal direction.

in reality pressurized pore water will move, escape vertically and not be bounded

inside a specific area. When expanding and migrating water cannot dissipate and when

counter pressure is small, explosions occur. Plaxis cannot simulate the migration of water.

instead the pressures are imposed on the model by means of insertion of manually

defined pore pressures on top of the normal hydrostatic pore pressures. the increased pore

pressures have been placed in a limited space in the subsurface. the material data sets

in the pressurized areas have been temporarily replaced by material sets with a very low

elastic modulus. thus pressures can be transmitted to surrounding rocks through

occurring deformations. Hence, a worst case approach has been adapted (as if it

were that the water is blocked in vertical direction e.g. by a sill). two of these limited

areas have been investigated; one simulating a heat source above sea level and another

simulating a heat source below sea level. a range of these pressures have been modelled

in Plaxis until failure of the model occurred.

Dyke intrusiona strong dyke intrusion could fill a fissure from the sea bottom to about 100 m below

the crest of the riftzone. in lateral sense, it is known that during an eruprion of the

cumbre Vieja volcano in 19�9, a fissure of at least 800 m, but more likely �000m

existed (day et al, 1999). When a dyke intrudes into the riftzone, two mechanisms

contribute to a weakening of the volcanic edifice. firstly the weight of the magma exerts a

magmastatic pressure on its surroundings (figure 3). secondly, the magma cannot resist

shear stress and will therefore immediately be the weakest material unit in the model,

thus introducing a potential zone of failure.

figure 3 illustration of the stress difference in a fluid and in a rock mass

in a modelled representation of an intrusion the dyke would ideally be introduced as a

“fluid cluster” instead of a soil cluster. this “fluid cluster” would contain the proper

features to both simulate the equi-directional pressure forces of the magma fluid and

the specific weight of the magma. However the only fluid available in the Plaxis software

is water, so a real magma material cannot be introduced in the program. therefore the

area of the dyke has been assigned an infill of water only. at the same time, a horizontal

prescribed load of 0.017 mn/m�/m has been imposed on the sides of the dyke in order to

make up for the density difference between water and magma (γmagma is approximately

0.0�7 mn/m3.

check: Pwater + magmastatic = γmagma; 0.010 + 0.017 = 0.0�7 mPa). see figure �.

7

Plaxis Practice

figure �. layout of the prescribed load system that simulates a magmastatic dyke pressure

Future volcano growthapart from eruption mechanisms that may destabilize the western flank of the volcano

any further, a process of different nature would be a more steady and certain destabilizer.

this mechanism is further accumulation of lavas at the top part of the volcano. former

landslides at la Palma have been estimated to occur at greater heights and slopes than

the cumbre Vieja has currently reached. heights of �000-3000 m, with flanks consistently

exceeding �0° and frequently even 30-35°. for comparison: the cumbre Vieja volcano is

now 1900 m high at its peak, but on average 1700 m. the dips of its slopes vary from 16°

to �0°. the possible future growth has simply been added in the model by a continuation

of lava streams on top of the topography of the current cumbre Vieja volcano.

Resultsin a situation where gravity only acts on the volcano body in its current configuration,

the factor of safety is 1.70 under a standard parameter set and decreases to 1.��

under a worst case parameter set. similar results were also obtained earlier using a

conventional limit equilibrium method. Hence under its own weight the edifice is not prone

to collapse. the failure mechanism along the weak sediments under the western

volcano flank, however, is already clearly visible (figure 5). even in this situation of

relative stability, about 9 m of displacement has taken place along the volcano crest.

a mayor fissure which formed in 19�9 at the crest of the volcano, may be the result of

such accomodative displacement. formerly scientists have postulated that this 19�9

fissure was an indication of instability. from the results of this work however, one

may conclude differently. the presence of the fissures has been confirmed by the

calculations, but they are more likely the result of deformation only than of a collapse

situation. future growth of the cumbre Vieja is the most effective agent to trigger

the potential landslide. on average, the factor of safety is decreased with 0.1 with every

�00 m of growth. according to this model, due to growth only it would take in the order

of magnitude of tens of thousands of years to trigger a massive flank collapse.

figure 5. total displacements due to historical growth only. the plane of weakness is

formed by a sequence of Post collapse sediments.

the pore water heating mechanism is an effective agent to disrupt the volcano.

nevertheless it does not cause the landslide as feared by many. instead, as may be

expected, this mechanism causes a collapse of the top of the volcano that is blown

upward, in the same way as often observed during volcanic eruptions that involve

water. figure 6 shows how mohr-coulomb and tensions cut-off points are concentrated in

the riftzone. Under the extreme pressures that have been modelled here, the flank also

develops an almost interconnected chain of mohr-coulomb points. yet, the preferential

path of rupture develops in the central zone.

the magmastatic pressure of an intruding dyke can have a significant influence on the

factor of safety (fs) of the potential landslide body, with a reduction of the fs up to 0.�.

Conclusion on modelling and research goalsPlaxis has proven to be suitable to simulate a volcano of significant size and complex

rock structure. in particular, two volcanic processes have been simulated: thermal

pore pressure development due to heat radiation of an intruding magma body and

magmastatic pressure of a dyke. the former can be simulated by a combination of

the manual pore pressure feature working on a fully elastic infill material. the density

of the latter has been simulated by a prescribed load acting on a body of water.

an eruption during the next several human generations is not expected to cause a

landslide hazard at the cumbre Vieja volcano. the eruption forces cannot generate enough

momentum to trigger failure in a 3d situation. However, after further volcano growth in

the far future, when significant extra gravity forces act on the edifice, the eruption forces

may be able to trigger a landslide. this will, however, take place in a time span of not

less than 10.000 years.

W E

8

Plaxis Practice

figure 6 failure points in the riftzone as a result of thermal pore pressures. the thermal

pore pressures form due to heat radiation of deep seated magma intrusions.

Continuation


Referencesancochea e et all. (199�) constructive and destructive episodes in the building of a young

oceanic island, la Palma, canary islands, and genesis of the caldera de taburiente,

Journal of Volcanology and Geothermal research, 60, ��3-�6�

carracedo Jc et all. (1999) later stages of volcanic evolution of la Palma, canary islands:

rift evolution, giant landslides, and the genesis of the caldera de taburiente, Geological

society of america Bulletin, 111 (no. 5), 755-768

day sJ et all. (1999) recent structural evolution of the cumbre Vieja volcano,

la Palma, canary islands: volcanic rift zone reconfiguration as a precursor to volcano flank

instability?, Journal of volcanology and geothermal research, 9� (issues 1-�), 135-167

masson dG et al (�00�) slope failures on the flanks of the western canary islands,

earth-scx. reviews, 57, 1-35

Ward sn, day s (�001) cumbre Vieja Volcano -- Potential collapse and tsunami at

la Palma, canary islands, Geophysical research letters, �8 (17), 3397-3�00

White Jdl; schmincke HU (1999) Phreatomagmatic eruptive and depositional

processes during the 19�9 eruption on la Palma (canary islands), Journal of volcanology

and geothermal research, 9�, �83-30�

9

Plaxis Practice

Structural reliability analysis of deep excavations

Timo schweckendiek, TU Delft,Wim Courage, TNO Built Environment and Geosciences

Introductionthe finite element method is nowadays widely used in structural design, both for the

servicebility limit state (sls) and also for the Ultimate limit state (Uls). especially

the Uls design rules are based on the idea of ensuring sufficient structural reliability,

which is usually expressed in a maximum admissible failure probability. this is commonly

achieved by prescribing design rules and establishing partial safety factors. these

load and resistance factors are calibrated for a wide range of typical cases with typical

dimensions. for more extraordinary cases it could be that the application of these

concepts leads to extremely conservative or possibly also to unconservative designs.

the presented approach enables us to use the optimization potential for these

case. furthermore, the determination of failure probabilities is a substantial and

indispensable element in modern risk-based design strategies (see fig. 1).

figure 1. risk-based design concepts

in this article we present a way of determining the structural reliability respectively

the failure probability by means of probabilisitic calculations directly. to this end

Plaxis is coupled with the generic probabilistic toolbox ‘ProBox’, developed by tno Built

environment and Geosciences. ProBox enables us to carry out a reliability analysis

using Plaxis in a fully automatized manner. We will also show that, in contrast to common

prejudices, probabilistic analysis does not necessarily require thousands or millions of

calculations as e.g. the monte carlo method, if we use more advanced and more efficient

reliability techniques.

Structural Reliabilitythe task of the engineer in structural design is to ensure that the resistance (r) of the

structure is larger than the load (s) it is exhibited to. Both quantities usually imply several

variables, e.g. soil parameters, geometrical dimensions or forces. the magnitude of most

of these quantities is uncertain. to ensure the safety of a structure it is common nowadays

for most types of structures to apply partial safety factors to the load and resistance

variables (lrfd: load and resistance factor design). this design approach is meant

and calibrated to ensure a certain minimum reliability level, i.e. that the probability of

structural failure is sufficiently low.

figure �. Partial safety factors vs. fully Probabilistic

an essential task in structural reliability analysis is thus the determination of failure

probabilities. to this end the first thing to do is the definition of failure. this failure

definition does not necessarily have to mean structural collapse, but an unwanted event

or state of the structure. in general, failure is defined as the load exceeding the strength.

an example for an excavation with a sheet pile retaining wall would be the that the

bending moment exceeds the elastic or plastic moment of the sheet pile, respectively that

the stresses in the pile exceed the yield strength or the ultimate strength of the steel.

for the analysis we have to define a limit state function (Z). this function is the

mathematical description of our failure definition. it implies all relevant load and

resistance variables. a negative Z-value (Z<0) corresponds to failure, whereas a positive

value (Z>0) to the desired state. a simple example for a limit state function is

Z = R - swhere r is the structural resistance and s is the load. consequently, when the load

10

Plaxis Practice Plaxis Practice

exceeds the strength (s>r -> Z<0) we obtain failure.

to obtain the failure probability we have to use furthermore the statistical information of

the variables. in essence, we integrate the probability density over the failure domain:

the reliability is the converse of the probability of failure. it is often expressed in terms

of the reliability index:

where Φ-1 is the inverse cumulative normal distribution. for low values of b one can

approximate the failure probability by Pf = 10b.

Functionality of Proboxthe program ProBox allows us to carry out this complex operation of determining the

failure probability with advanced and efficient methods of high accuracy (level ii and

level iii), amongst which:

- form / sorm

- crude monte carlo

- directional sampling / dars

- increased Variance sampling

- numerical integration

figure 3. screenshot Probox


Continuation

for the model input statistics several distribution types can be used, like e.g. normal,

lognormal or extreme value distributions. the correlations among the variables can be

accounted for in form of a correlation matrix.

the strength of ProBox is the possibility of using external models for reliability analysis.

for example the influence of corrosion on a sheet pile structure can be analyzed by using

a corrosion model for the strength reduction part, whilst the load on the wall would be

determined by Plaxis.

ProBox has already been used in combination with:

- fem-codes (diana, PlaXis, catpro)

- matlab

- excel

- other stand-alone applications (sobek, ozone, etc.)

- user-defined dll’s (fortran, c, c++, Java)

the most relevant results of an analysis with ProBox are the probability of failure Pf ,

the reliability coefficient and the influence coefficients expressing the influence of each

stochastic variable on the analyzed limit state b. the results can also be visualized in

form of scatter plots, histograms or line plots.

Coupling Probox - Plaxisthe reliability analysis is fully controlled by ProBox. Plaxis is used to evaluate the

limit state function for a parameter combination which is determined by the reliability

algorithm. in other words, the Plaxis analysis allows us to decide wether a certain

parameter combination would lead to structural failure or not.

figure �. coupling scheme ProBox-Plaxis

11

Plaxis Practice

the scheme in figure � illustrates how the coupling between ProBox and Plaxis works.

in first instance one has to build the structural model in Plaxis. in ProBox you assign

statistical properties to material properties like e.g. soil parameters or load

characteristics that reflect their uncertainty. the reliability algorithm defines for each

limit state function evaluation the parameter combination that has to be evaluated with

the Plaxis model. the according Plaxis input files are manipulated, before the calculation

is started. after the fem-analysis ProBox reads the relevent results from the output files.

this procedure is repeated until the convergence or stop criteria of the chosen reliability

method are reached.

Examplethe following example of a sheet pile wall with one anchor layer in soft soil will illustrate

the presented ideas.

figure 5. example Geometry

the soil properties and the distributions of the soil parameters are listed in table 1. Based

on the problem geometry and these soil parameters a deterministic design was made,

based on the dutch technical recommendations for sheet pile structures (cUr 166). the

obtained structural dimensions are also indicated in figure 5.

the choice of distribution functions in table 1 is partially based on avoiding illposed

problems. a lognormal distribution cannot assume values smaller than 0 and a Beta

distribution has a lower and an upper limit and is therefore well suited for parameters

such as the Poisson ratio.

in this example we want to determine the probability of failure of the sheet pile

itself. the simplest way to do so would be to determine the probability that the design

moment md is exceeded. the according limit state function would be:

Z = Md - M = Wel * fy - M

where Wel is the elastic section modulus, fy is the yield strength and m is the bending

moment calculated in Plaxis. one could also use a plastic moment, when plastic hinges

are allowed.

this expression can be refined by accounting for the axial forces in the wall as well.

in this case we can determine the probability that the yield strength fy is exceeded using

the limit state function:

Z = fy - σ = fy - (M/Wel + F/a)

where the stress σ is composed of the bending moment m, the section modulus Wel ,

table 1. soil Parameter distributions

1,328 [kPa] 733.2 [kPa]0.396 [-]0.335 [-]18.64 [kN/m³]13.58 [kN/m³]20.48 [deg]23.78 [deg]33.90 [deg]13.69 [kPa]7.36 [kPa]0.474 [-]0.608 [-]

table �. results reliability analysis sheet Pile failure

1�


the axial force f and the cross sectional area a. this expression has the additional

advantage that e.g the influence of corrosion can be accounted for via changes in the

geometrical properties of the sheet pile Wel and a easily.

the results of a reliability analysis, in which the relevant soil properties were treated as

stochastic quantities, are listed in table �. the analysis was carried out with a form

algorithm. 99 evaluations of the limit state function were carried out, i.e. the Plaxis model

was evaluated 99 times. for this relatively simple model this resulted in a calculation

time of only approximately 30 minutes. the results were furthermore checked against

‘exact’ level three calculations, which gave similar results. these were carried out with

directional sampling and required 655 model evaluations. considering the low failure

probability a crude monte carlo simulation would not be feasible within reasonable time,

since the required number of Plaxis calculations would be in the order of 10+7.

the target reliability index of class ii

structure designed with the cUr 166

recommendations is b = 3.�. Using

this approach we calculate a higher

reliability (b =�.�). the structural design

is thus conservative for this limit state.

there might be room for optimization. the

influence coefficients in table � and

figure 6 give us information about the

importance of the parameters involved.

there are two contributions in this

influence measure, the sensitivity of

the model to a certain variable and the

amount of uncertainty in the same

parameter. a positive value of indicates

a positive influence on the limit state

(and the reliability index), whereas a

negative value indicates a negative

influence. the design point is the most

likely combination of parameters leading

to failure (highest probability density).

for this specific example the stiffness

parameters of the clay layer apparently

dominate the load on the wall. the

influence factors α² from figure 6 give

information about the contribution of

the variables to the total uncertainty.

considering the definition of the

influence factor that means that


Continuation

e.g. decreasing the uncertainty in these stiffness properties by additional soil

investigation could increase the reliability considerably.

figures 7 and 8 show the principal effective stresses in the design point. the design

point is the parameter combination with highest probability density that leads to failure.

especially from figure 8 can be concluded that the shear strength in the soil behind

the wall is mobilized to a very low degree. the problem is thus still fully elastic

(the calculations were carried out with the mohr-coulomb model.). that explains why the

strength parameters of the soil play a minor role for this limit state.

this was just an example of results of a reliability analysis and possible conclusions

for the optimization of the problem. the outcomes of such an analysis contain a lot of

useful information that can be used either for design refinements or in risk-based design

approaches.

figure 6. influence factors α�

13


figure 7. Principal effective stresses (design Point sheet Pile failure)

figure 8. relative shear (design Point sheet Pile failure)figure 6. influence factors α�

Conclusionsfully probabilistic reliability analysis can be carried

out with the presented framework with reasonable

modeling and computational effort.

this type of analysis allows us to calculate the

reliability of a structure directly. this information

can be used for optimization purposes, in risk-based

design concepts and for the calibration of partial

safety factors in design codes.

- the influence coefficients as result of the analysis

provide useful information for optimization purposes

and also for the physical understanding of the model

behavior close to failure.

AcknowlegdementsWe want to thank Plaxis bv, especially dr. Paul

Bonnier, for their support during this research.

ReferencesBrinkgreve, Broere, Waterman, ‘Plaxis 8.� manual,

�006.

ditlevsen, o.d., ‘stuctural reliability methods’,

John Wiley & sons, chichester, Uk, 1996, edition 1.

ProBox, ‘a Generic Probabilistic toolbox’, more

information and trial-version availbale on:

www.tno.nl/probox

schweckendiek, t., ‘structural reliability applied

to deep excavations’, msc-thesis, tU delft,

the netherlands, �006. (www.citg.tudelft.nl)

Waarts, P.H., ‘structural reliability Using finite

element methods’, Phd thesis, tU delft,

the netherlands, �000.

1�



ayman abed, stuttgart University

Introductionthe expansive soil shows obvious volumetric changes under changing moisture

conditions. these volumetric deformations usually result in differential movements

of shallow foundations resting on it. consequently, structural damages could happen

if no special measures would have been taken during the design process. this article

illustrates the possibility to predict such movements using PlaXis provided that a

suitable constitutive model for unsaturated soil behaviour is used.

Trial Wall on Expansive Soilnine trial walls were built on swelling soil in Barakat site in sudan. the area is known for

its highly expansive soil. the test were carried out in order to investigate the effect of soil

replacement on the walls vertical movement [saeed �00�]. the walls are made of brick

(1 1/� brick) with a length of 1.� m and a height of 1.9 m above the ground level. the

foundation depth is 0.6 m. a schematic representation of the walls with their dimensions

is given in figure 1. the expansive soil underneath the walls was replaced with different

materials namely a1, a�, a3, B1, B�, B3, c1, c� and c3 where:

a1: plain concrete, a�: reinforced concrete with �0 % voids, a3: Big stones, B1: �5 cm of

cohesive nonexpansive soil (cns), B�: 50 cm of cns, B3: 75 cm of cns, c1: natural soil,

c�: natural soil with 6 % lime, c3: sand.

the soil was then exposed to two successive wetting-drying cycles for a period of

about 18 months. detailed data about the vertical displacements of the trial walls is

reported by [saeed �00�], figure � presents only the displacements of the wall c1 with no

replacement as the purpose of this study is to simulate the behaviour of the expansive

soil itself. on investigating the measurements one finds that the test has four stages.

the first one is a wetting phase of about �70 days resulting in a total heave of about

6.0 cm. the wetting phase was followed by a drying phase of 90 days resulting in �.5 cm

of shrinkage. the second wetting stage lasted 1�7 days and resulted in �.5 cm of heave,

which indicates an elastic behaviour by recovering the settlement in the previous drying

phase in almost similar time. the final phase was relatively short of about 50 days and

resulted in 0.5 cm of shrinkage.

figure 1. Geometrical details of the walls

15


figure �. measured displacements of the wall c1 as provided by [saeed �00�]

Soil Propertiesthe soil is classified as a clayey silt with a liquid limit ll = 68% and a plastic index

Pi = 36%. the 1-d compression results in figure 3 shows that the soil is overconsolidated

and it has a modified compression index l* = cc / �.3 = 0.098 and a modified swelling

index k* ≈ cs / �.3 = 0.03. the high k value is typical for an expansive soil. other available

soil properties are listed in table 1.

figure 3. one dimensional compression results

table 1. other soil properties

f’ c’ σ’p ksat γb

30o 0.0 105 kPa 0.0� m/day 17.6 kn/m3

where f’: soil friction angle

c’: effective cohesion

ksat: saturated permeability

γb: humid unit weight

σ’p: preconsolidation pressure

Material Model for SoilBarcelona Basic model [alonso & Gens 1990] is used as a constitutive model in this

work. the model adopts the idea of two independent stress measures namely, the net

stress σ* and the suction s. the net stress is defined as the difference between the total

stress σ and the pore air pressure ua whereas suction is the difference between pore air

pressure ua and pore water pressure uw. in what follows the air pressure is assumed to be

atmospheric everywhere in the soil which means that the net stress in this special case

is simply the total stress and the suction is equal to -uw. the model is an extension of the

modified cam clay model by adding the effect of suction on soil strength and stiffness.

at full saturation, when suction = 0, the model coincides with the modified cam clay

model.

on drying the soil (increasing the suction), a capillary cohesion develops and

consequently the yield ellipse grows into the tension region with a rate equal to the model

parameter a as it shown in figure �.a. the soil preconsolidation pressure pp increases

as well. it can be related to the preconsolidation pressure at full saturation ppo through

the following formula

ppo

lo - k

pp = pc . ( pc ) l - k (1)

where pc is a reference pressure and

l=l∞-(l∞-lo).e-b.s (�)

(a) (b)

figure �. the yield surface of Barcelona Basic model

16

Plaxis PracticePlaxis Practice

l is the suction dependent compression index. Hence, for full saturation we have

s = 0, l = lo and pp = ppo. the larger the suction, the smaller the compression index l. in

the limit for s = ∞ the above expression yields l=l∞. the constant b controls the rate

of decrease of the compression index with suction.

When the deviatoric stress q = 0, the yield surface of Barcelona Basic model degenerates

to the so-called loading-collapse curve as it clear in figure �.a where p* and q are the

stress invariants being defined as

1

p* = 3 (σ*1+σ*�+σ*3)-ua ;

1q = � (σ*1 -σ*�)

� + (σ*� -σ*3)� + (σ*3 -σ*1)

� (3)

for the elastic behaviour, the model assumes that the soil has different stiffness

parameters for changes of net stress and changes of suction. for example starting from

stress state a in figure �.b the soil shows different stiffness depending on whether it is

exposed to net stress change or suction change. in the latter case the soil swelling index

with respect to suction ks controls the soil response while the normal swelling index k

dominates the other case. this model has been implemented into PlaXis finite element

code as a user defined model by [aBed & Vermeer �006] where the full mathematical

description of the model is also presented. the swelling index with respect to suction ks is

the most important parameter in the trial wall case as suction is the only variable during

the test. it is assumed that the reader is aware of the fact that the change of moisture

content and the change of suction are synonym.

Finite Element Calculationsthe calculations involve transient unsaturated flow as well as deformation analyses.

as the calculations are done in an uncoupled way, the unsaturated ground water flow

analyses are done first and the resulted suction fields are used for later deformation

calculations. the PlaXfloW finite element code [BrinkGreVe et al. �003] is used to

simulate the unsaturated groundwater flow and to determine the suction variation

with time. the deformation analyses are done using the Barcelona Basic model as

implemented in the PlaXis finite element code.

Geometry, Boundary and Initial Conditionsfigure 5.a shows the boundary conditions, the initial conditions and the finite element

mesh being used. the ground water calculation is found to be decisive for choosing the

depth of the mesh. no local deformations are expected to take place around the wall

footing, for that reason no further mesh refinement is needed in that region. the ground

water table lies at a depth of 30 m below the ground level. the initial pore water pressure

is assumed to be hydrostatic, with tension above the phreatic line. according to [saeed

�00�], the soil was always soaked with water during wetting phase, which suggests an

infiltration rate equal to the saturated soil permeability ksat. a high evaporation rate of 10

mm/day is applied during the drying phase to account for the observed severe shrinkage.

the applied surface discharge with time is illustrated in figure 5.b. PlaXfloW requires

information about the suction-degree of saturation and the suction-relative permeability


Continuation

relationships. the first one is known as the soil Water characteristic curve while the

second is the relative permeability function. the term relative permeability stands for

the ratio between soil permeability k at a certain suction level and ksat. Both curves are

shown in figure 6.

(a)

(b)

figure 5. Geometry, boundary and initial conditions

17


figure 6. soil Water characteristic curve and relative permeability function

PLAXFLOW outputfigure 7 illustrates the variation of suction and degree of saturation with time underneath

the wall as calculated by PlaXfloW. the suction drops from 300 kPa to about 30 kPa at

the end of the first wetting phase. then it increases again to ��0 kPa at the end of the

first drying phase. then behaviour is repeated in the next wetting-drying cycle. it is also

interesting to see how the degree of saturation is increasing with the decrease of suction

and vice versa. figure 8 presents the calculated suction profiles at the end of the first

wetting phase as well as at the end of the first drying phase. they resembles typical

suction distributions under infiltration and evaporation boundary conditions

figure 7. suction and degree of saturation underneath the wall

figure 8. suction profile at different time steps

Deformation analysessuction values resulted from ground water flow calculations are transferred to PlaXis for

deformation calculations. the material properties in table � are used for the Barcelona

Basic model.

no information is provided about the soil swelling index with respect to suction ks, for

that reason it is the calibration parameter in these calculations. its value is varied

between 0.005 to 0.03 which covers the most common values for this index as mentioned in

literature [fredlUnd & raHardJo 1993]. a value of ks = 0.015 is found to give the best

fit to the field measurements. indeed this value is satisfactory in the sense that it also

reflects the expansive nature of the soil being studied.

on using the material properties as listed in table � the calculated deformations are in

good agreement with measured data as shown in figure 9. the deviation at the end of the

first drying phase suggests that one should use a higher swelling index during shrinkage.

as the model uses the same index for both swelling and shrinking it would be better for

further improvement to use the idea of yielding on the shrinkage path as it proposed also

by the Barcelona Basic model [alonso & Gens 1990] where after a certain suction level

the soil tends to yield with lower stiffness and giving more shrinkage.

table �. Barcelona Basic model parameters

strength parameters stiffness parameters stiffness parameters with respect to suctionf’ 30o lo 0.098 ks 0.015

c’ 0.0 k 0.03 l∞ 0.07

a 0.5 n 0.� b 0.013 kPa-1

pco 97 kPa pc 50 kPa

where n: soil Poisson’s ratio for unloading-reloading

0.0

50. 0

100. 0

150. 0

200. 0

250. 0

300. 0

0 100 200 300 400 500 600

Time [days]

0

10

20

30

40

50

60

70

Deg

ree

of sa

tura

tion

Sr %

Suct

ion

[kPa

]

degree of saturationsuction

considered point

18


figure 9. calculated versus measured data

Conclusionsthe PlaXfloW-PlaXis interaction offers a nice tool to simulate the mechanical behaviour

of unsaturated soil. in this study PlaXfloW is used to solve suction variation in time

whereas the Barcelona Basic model as implemented in PlaXis is used to calculate the

deformations. it shows clearly how much this procedure is efficient. However, one should

always emphasize on the comprehensive understanding of the constitutive model being

used and its limitations. the use of suction in deformation or stability calculation is

always critical and need special model to handle it. Using it with the wrong model or

without full awareness leads in most cases to a non-conservative estimation.

figure 10. deformed mesh at the end of calculations


Continuation

References[aBed & Vermeer �006] a. a. aBed, P. a. Vermeer: foundation analyses with

unsaturated soil model for different suction profiles: in proc. sixth european conference

on numerical methods in Geotechnical engineering, Graz, austria.

[alonso & Gens 1990] e. e. alonso, a. Gens, and a. Josa: a constitutive model for

partially saturated soils: Géotechnique (�0), 1990

[BrinkGreVe et al. �003] PlaXfloW User manual: Balkema, rotterdam, �003

[fredlUnd & raHardJo 1993] soil mechanics for Unsaturated soils: John Wiley & sons,

1993

[saeed �00�] i. m. a. saeed: evaluation of improvement techniques for strip foundation

on expansive clay soils in Gezira: master thesis: University of khartoum: sudan, �00�

[Vermeer & BrinkGreVe 1998] PlaXis – finite element code for soil and rock analysis:

Balkema, rotterdam, 1998

19



Franz Tschuchnigg, Helmut schweiger, Graz University of Technology

Introductionthe ground anchor in Plaxis 3d foundation consists of two different parts. the first part

represents the free anchor length and the second part the grout body. the free length

is modelled as a node-to-node anchor, which represents the connection between the

grout body and e.g. a diaphragm wall, and the grout body consists of embedded beam

elements, which are line elements with a special interface to model the grout-soil interaction.

for the definition of the ground anchor eight input values are required (fig. 1).

figure 1: system layout and input values for a ground anchor

the soil-interaction is defined with the two separate values for skin resistance along the

grout body. thus it is possible to define a constant, linear or trapezoidal distribution of

skin resistance. the maximum interaction force between the soil and the grout body is

directly applied in the “interface” of the embedded beam.

it is pointed out that this represents the skin resistance at failure (i.e. when the pull

out force is reached) and that the skin traction distribution below full mobilisation is

influenced by the specified limiting distribution. in reality mobilisation will start at the

top of the grout body and only close to the pull out force (failure) the skin traction at the

bottom should be mobilised. in the embedded pile the mobilisation follows the predefined

shape from the beginning (also at the bottom). However, tests have shown that this does

not have a noticeable influence on the global behaviour of an anchored structure under

working load conditions.

another important point is, that for forces close to the theoretical pull out force numerical

failure may occur due to plasticity in the soil adjacent to the grout body. although this is of

course possible in reality, in the model it may be artificial and caused by the fact that the

grout body is a line element. to overcome this problem in ultimate limit state conditions

it is necessary to work with an enlarged diameter of the grout body. this virtual diameter

of the grout body is defined as follows:

Dvirtual = f * Dreal

in this equation f is the factor for the enlargement, and a value of f in the range of � – �

is suggested. this does not affect the pull out force (this is an input due the input of the

limiting skin resistance and the length of the grout body) and has minor effect on the

behaviour under working load conditions. it follows, and the user must be aware of this,

that when using this option in Plaxis 3d foundation the maximum pull out force is an

inPUt and cannot be oBtained from the analysis.

Deep excavation with prestressed ground anchorsin order to demonstrate the application of the ground anchors in Plaxis 3d foundation,

some results from a practical example, namely a deep excavation in Berlin sand, are

presented. this example was chosen for testing the ground anchor facility under working

load conditions because a �d reference solution was available. the model dimensions and

material sets for the soil layers have been taken from the �d reference solution (fig. �).

figure �: Geometry and subsoil conditions

the diaphragm wall has been modelled as a continuum element (fig. 3), with linear

elastic material behaviour and a stiffness eref=3.0*e7 kn/m�. the hydraulic cut off does

not act as a structural element, the properties are the same as for the soil (sand �0

– �0m).

figure 3: 3d view of the model (�09�� elements)

�0

Plaxis Practice


Continuation

to obtain the current porewater distribution inside the excavation the porewater

pressure was defined after each groundwater lowering (with user defined pore pressure

distribution). the ground anchors have different spacing and prestress forces in the

different layers and therefore the anchor rods have different properties. the properties of

the grout body are the same in all rows (table 1).

table 1: Ground anchor properties

aim of the test was to see if the embedded pile model (employed for the grout body) works

well in working load conditions and therefore the skin resistance in the grout body has

been defined about two times the expected axial load in the node-to-node anchor.

in the different calculations the material model, the shape of the limiting skin resistance

and the enlargement of the grout body have been varied (table �).

in the following tables the soil properties for the mc and the Hs-model are summarized.

in calculation 5 the stiffness of the grout body has been changed according to the ratio of

the real diameter (0.1�5m) to the fictitious enlarged diameter (0.1�5*f=0.5m).

Resultsit follows from figure � that neither the variation of the predefined limiting skin

resistance of the grout body nor the f-factor for the enlargement of the grout diameter

have a significant influence on the axial forces predicted under working load conditions.

However the distribution of the mobilised skin traction along the grout body is not what

one would expect in reality (fig. 5). if the mohr coulomb model is employed the results are

slightly different (fig 6).

figure �: axial forces in the first anchor row (calculation 1, �, 3, �, 5)

figure 5: mobilised skin friction and axial force – first anchor row (after excavation �,

calculation 1)

With respect to the horizontal displacements there is a trend that wall deflection

with a linear predefined shape of the skin friction is slightly higher than the one with

constant skin traction distribution. it is also notable that by increasing the f-factors for

the virtual grout body diameter displacements in horizontal direction become smaller.

the differences are in the order of 10%. With the mc-model the highest deformations in

horizontal direction are located around the grout body (fig. 7), whereas with the Hs-model

this is not the case. this effect also occurs with the assignment of a high f-factor.

the settlements behind the diaphragm wall are in the range of 11mm (almost the same

for the different variations) with the Hs model, but with the mc model there is a heave of

more than 1�mm, an effect which is well known.

table �. soil parameters for the Hs-model

table 3. soil parameters for the mc-model

table �. Variations in the different calculations

�1

Plaxis Practice

figure 6: axial forces in the first anchor row – calculation � vs calculation 6

figure 7: Horizontal displacements – left calculation � (Hs-model), right calculation

6 (mc-model)

Comparison of 3d results with 2d reference solutionin figure 8 axial forces in the first anchor row from calculation � (Hs-model and

f-factor=1) are compared with the axial forces from the �d reference solution. in

Plaxis V8 the grout body of a ground anchor is modelled with geogrid elements. these

elements have an axial stiffness but no bending stiffness. the axial forces from Plaxis

V8 are in the dimension [kn/m] and to compare these results with the 3d analysis it is

necessary to divide the axial forces from Plaxis 3d foundation by the anchor spacing of the

different rows. one can see that the axial forces from the 3d calculations are in a very good

agreement to the reference solution. the deviation of the forces in the node-to-node

anchor between both calculations is less than �%. also the vertical displacements

behind the diaphragm wall from the 3d calculation (fig.9) are very similar to the ones

obtained from the �d solution (both maximum value and distribution).

figure 8: axial forces calculation � vs. �d reference solution

figure 9: Vertical displacements behind the diaphragm wall – comparison reference solu-

tion with calculation �

Conclusionsa deep excavation supported by a diaphragm wall and three rows of anchors has been

analysed utilizing Plaxis 3d foundation with the ground anchor option.

the results from the 3d calculation with the Hs-model compare well to the �d reference

solution (both with respect to anchor forces and displacements) and as a consequence

from the parametric study it can be concluded that it is not necessary to artificially

increase the diameter of the grout body for working load conditions.

concerning the distribution of the skin friction along the grout body, it is obvious that

the mobilisation is not realistic. the reason is, that also at working load conditions the

distribution of the skin friction is strongly influenced by the distribution in the failure

state, which is an input. due to the fact that the limiting skin friction is an input the grout

body length has no or minor influence on the result and therefore the length cannot be

determined from the analysis.

compared to the Hs-model the mc-model predicts significantly larger deformations

around the grout body. the virtual enlargement of the grout body diameter (f-factor) does

not change the results significantly for working load conditions.

However for ultimate limit state calculations the f-factor becomes important, because in

these calculations a premature failure (i.e. a failure below the theoretical pull out force)

may occur when f=1.0. to overcome this problem it is essential to work with a virtual

grout body enlargement.

it follows from this study that the ground anchor concept in Plaxis 3d foundation is

efficient for working load conditions, but for ultimate limit state analysis assumptions

such as the f-factor, mesh coarseness and stiffness parameters of the soil (adjacent to

the grout body) may have a significant influence on the result. it is emphasized again the

maximum pull out force is an inPUt to the analysis and not a resUlt.

��

Recent Activities

Recent Activities

Product updatesrecently we introduced a new Plaxis introductory cd. Besides the Plaxis V8 introductory

this cd includes:

- 3dfoundation introductory

- 3dtunnel introductory

- Japanese Plaxis V8 introductory

- chinese Plaxis V8 introductory

- Updated and new animations

if you are interested to receive this new introductory you can fill in the request form at

the service page of www.plaxis.com

Plaxis StaffWe are pleased to announce that we extended our staff with Pranesh chaterjee and luc

Bijsterbosch. Pranesh has a master degree in Geotechnical engineering from Bengal

engineering college, Howrah and Ph. d. in seismic soil-structure interaction analysis from

Jadavpur University, kolkatta both from india. furthermore he worked as a post doctoral

at the k.U. leuven (Belgium) on tunnel-soil interaction analysis and worked in industry

in the U.k. and india. His main responsibility at Plaxis developments will be 3d dynamics

and soil-structure interaction analysis. luc graduated at the tU delft with a hydraulics

background, looking at the influence of sea-level rise on tidal inlets. Besides his study

civil engineering, he also followed several didactical courses. His work will consist of

quality control, support and marketing activities. He will start working on new tutorials

and a 3d example book related to the release of 3d foundation V�.

additional to contracting this promising staff Plaxis bv will continuously strengthen

its team and has currently a key-position available for a senior software development

engineer.

User days and seminarsthe dutch Plaxis Users association or Plaxis Gebruikersvereniging (PGV) had their annual

meeting on october 18, �006. this is one of the yearly activities. in the meeting, the board

presents the plans for the next year and the bookkeeping. the annual meeting was held

at the new metro line (noord/Zuidlijn) in amsterdam. in addition, the program included

a presentation about the design of immersed tunnel and an excursion in the building

pit. the building pit has two functions, one as construction dock for the concrete tunnel

elements and finally as insitu tunnel for the approach of the immersed tunnel under the

river iJ.

furthermore the dutch Plaxis Users association has organised a workshop on

“Geotechnical modelling” which was attended by 30 enthusiastic Plaxis Users. a total

of 10 speakers presented topics ranging from determination from geotechnical

parameters, geometrical modelling, constitutive and numerical modelling to reliability

and safety approach. the speakers and their topics are presented below:

- otto Heeres, “Geotechnical modelling”, Public Works department of rotterdam/ delft

University of technology

- timo schweckendiek, “are safety factors safe?”, tno/ delft University of technology

- Jelke dijkstra, “modelling of pile foundations”, delft University of technology/ Geodelft

- richard de Jager, “modelling of static liquefaction”, delft University of technology/

Boskalis

- ronald Brinkgreve, “modelling in �d or 3d?”, Plaxis bv

- abjan Jacobse, “settlements of high-rise buildings in den Haag“, icPluse

- chris dykstra, “the isotachen model from a practical perspective”, Boskalis

- daan Vink, “the rijksmuseum in amsterdam”, crUX

- dirk luger, “modelling of pre-tensioned friction piles”, Geodelft

- cor Zwanenburg, “experimental testing from up-close”, Geodelft

the topics dealt with in the symposium were very diverse and after each presentation

a stimulating discussion resulted. a more detailed perspective on the topics will follow

since several authors will present their work and/or views in an article in this and future

bulletins.

Plaxis in Russiarelated to the rapid growth of Plaxis users in russia and as a spin-off from the

discussions during the 1st russian Users meeting last year we will soon introduce the

russian Plaxis website (www.plaxis.ru) on this website you will have access to all relevant

Plaxis information in russian language and also fully described papers of presentations

�3

topview of the building pit

of russian User meetings. one paper which can be found is from mr. e. Zakharov. Below

you can find an abstract and some pictures of his presentation. the full paper in russian

language will be posted soon on the russian Plaxis Website.

mr. e. Zakharov of ooo “lengiproengproject”.

“subsoil deformation analysis in the course of underground structures building.”

in this paper the Plaxis programs are used for subsoil deformation analysis in case of

underground collector failure simulation. the procedure suggested makes it possible

to understand surface constructions operation in accident and present an optimum

collector placing scheme. the procedure under consideration has been successfully

used in a number of construction projects in st.-Petersburg. on the bases of the

analysis, recommendations of reinforcement measures are given, concerning

st.-Petersburg historical centre buildings.

Recent Activities

Plaxis in Hong Kongon January 19 a seminar was held at the scoPe lecture theatre city University of Hong

kong. the activity was well attended by 60 participants and they were mainly from

the geotechnical fraternity in Hong kong. dr. andy Pickles gave an interesting and

informative presentation on his experience of using finite element analysis in daily routine

engineering design work. dr. lee siew Wei described and presented some of the

analytical and design problems using Plaxis �d and 3d programs. the technical manager

of Plaxisasia, William cheang delivered presentations that touch on current and future

developments of Plaxis programs. discussions were held at the end of the presentations.

a half-day workshop was held at clifftons, a day after the seminar. in this workshop, the

aim was on the familiarization of �d and 3d finite element analysis using Plaxis. most of

the participants were new to the Plaxis programs. the 3d foundation program generated

the most interest and questionnaires were related to the modelling of deep excavations,

piled foundations and reinforced structures.

Plaxis finite element code for soil and rock analyses

Plaxis BVPo Box 57�

�600 an delft

the netherlands

tel: +31 (0)15 �51 77 �0

fax: +31 (0)15 �57 31 07

e-mail: [email protected]

Website: www.plaxis.nl

19 - 21 March 2007 course computational Geotechnics (German)

stuttgart, Germany

26 - 29 March 2007international course for experienced

Plaxis users

antwerpen, Belgium

1 - 4 april5th international Workshop on applications

of computational mechanics in Geotechnical

engineering

Guimaraes, Portugal

18 - 19 april 2007Plaxis user meeting Uk

london, manchester, United kingdom

25 - 27 april 2007nUmoG X

tenth international symposium on

numerical models in Geomechanics

rhodes, Greece

5 - 10 May 2007ita-aites World tunnel congress �007

Prague, czech republic

8 - 11 May 200716th southeast asian Geotechnical

conference

selangor darul ehsan, malaysia

12 - 14 June 2007 course computational Geotechnics

manchester, United kingdom

25 - 28 June 2007course on advanced computational

Geotechnics

sydney, australia

16 - 20 July 2007Xiii PcsmGe �007

isla de margarita, Venezuela

24 - 27 July 2007course on computational Geotechnics

and dynamics

chicago, Usa

10 - 14 september 2007course on advanced computational

Geotechnics

ankara, turkey

24 - 27 september 2007XiV ecsmGe

madrid, spain

21 - 24 October 200710 anZ smGe,

Brisbane, australia

7 - 9 November 20071�th european Plaxis User meeting

karlsruhe, Germany

26 - 28 November 20071� african regional conference smGe,

yaounde, cameroon-africa

10 - 14 December 200713th asian regional conference on soil me-

chanics and Geotechnical engineering

calcutta, india

Activities 2007

7005

910

21 PLAXIS Bulletin

Documents

ground anchor

caldera de

finite element

tno built

limit state

structural

cumbre vieja

rock mass