Plaxis Bulletin 22

Plaxis finite element code for soil and rock analyses

Stabilization of vertical cut using soil nailingDesigning a bridge with Plaxis 3D tunnel

Tangiers - Mediterranean harbor

issue 22 / October 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

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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acceptable). if bitmaps or scanned figures are used the author should ensure that they

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figures is encouraged, as the Plaxis Bulletin is printed in full-colour.

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

[email protected]

or by regular mail to:

Plaxis Bulletinc/o erwin Beernink

Po Box 57�

�600 an delft

the netherlands

the Plaxis Bulletin has a total circulation of 1�.000 copies and is distributed worldwide.

Editorial Board:

Wout BroereRonald BrinkgreveErwin Beerninkarny lengkeek

copyright coverphoto: BeeldbankVenW.nl, rijkswaterstaat

Colophon

Editorial

New Developments

Plaxis PracticeStabilization of vertical cut

using soil nailing

Plaxis PracticeDesigning a bridge with

Plaxis 3D tunnel

Plaxis PracticeTangiers -

Mediterranean harbor

Recent Activities

Activities 2007-2008

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6

10

12

18

20

3

the first article describes the ins and outs of a research project on the stabilization of a

vertical cut by means of a soil nail wall. the research has been performed at the indian

institute of science. the factor of safety and the extreme horizontal displacement are

shown for different excavation depths and different shear strengths, for a situation with

and without soil nails. the research results provide valuable insight in the usefulness of

soil nail walls to stabilize excavations.

the second article describes an application that is quite unusual for Plaxis: a support

bridge to prevent excessive deformations in a high-speed railway line as a result of the

construction of two shield tunnels. the article shows the deformations and bending

moments in the support bridge, and how they are obtained from Plaxis. in the end some

interesting conclusions are drawn.

the third article describes a project named “tangiers – mediterranean harbor”, where a

huge breakwater was designed and analysed with Plaxis. in addition to time-dependent

settlements as a result of the construction process, a dynamic analysis was performed to

investigate the effects of seismic loading. the stability and serviceability of the breakwa-

ter seem to meet the design criteria.

Besides the main articles from Plaxis users on practical applications, this Bulletin con-

tains the ‘standard’ contributions on new developments and recent activities. at the end

of the Bulletin, the agenda of Plaxis activities is again filled with interesting events. We

wish you enjoyable reading and we look forward to see you at one of the listed events.

the editors

Ronald Brinkgreve

Editorial

in this 22nd edition of the Plaxis Bulletin you can find again some interesting

applications of projects that have been analysed with Plaxis. More and more users

send us articles that can be published in the Bulletin. On the other hand, many users

do not have time to write such articles, but are still proud of the projects that they

have modelled with Plaxis; especially 3D projects. For these users we now provide the

possibility to send us interesting Plaxis 3D output graphs with a very short description

of the project and the presented graphs, which we will collect and make available to

other Plaxis users. Contributions can be sent to [email protected].

�

New Developments

Ronald Brinkgreve

New Developments

Just before the release of this Bulletin, Plaxis signed a strategic cooperation agreement

with the norwegian Geotechnical institute (nGi). in the last two years, nGi has made a

significant contribution to the validation of the recently released Plaxis 3d foundation

program (version �). the agreement is the acknowledgement of a cooperation that actually

started many years ago. it is also a starting point to cooperate project-wise on advanced

numerical models for offshore geo-engineering applications. through this cooperation we

can better serve our clients in this field. a press release about the cooperation agreement

can be found on the Plaxis web site www.plaxis.nl (news).

this strategic cooperation with nGi fits perfectly in the Plaxis strategy of building close

relationships with world leaders in the field of geotechnical research & development.

Plaxis has for example a long lasting relationship with Geodelft (the netherlands). in

Bulletin 19 the moU with Geodelft was already mentioned. meanwhile, we cooperate with

Geodelft in scientific projects (such as the material Point method project, executed at the

University of stuttgart) and we join forces in commercial activities. another cooperation

is with the German Bundesanstalt für Wasserbau (BaW) on the extended fem project.

BaW also organises the yearly european Plaxis Users meeting in karlsruhe. last but not

least we should mention the cooperations with several universities all over the world, not

only in terms of research projects that eventually lead to new Plaxis features, but also in

testing and validating new features and beta versions of the software, and facilitating

courses and educating geotechnical engineers in the use and backgrounds of Plaxis.

all these cooperations make Plaxis a reliable and well accepted software product for

geo-engineering applications.

intuitiveness and user-friendliness are key-elements in the Plaxis software. However,

according to a user-inquiry some time ago, there is one aspect that Plaxis users find less

user-friendly: after refinement of the finite element mesh or after slight modifications of

the geometry, initial stresses and water pressures need to be regenerated and calculation

phases (construction stages) are reset to the initial phase. this handicap will have been

improved in the next update of the Plaxis �d version.

refinement of the finite element mesh is a common procedure to improve the accuracy of

the computational results. Preliminary results may be obtained using a relatively coarse

mesh, whereas final results may be obtained after global or local mesh refinement. in

this case the geometry model itself is considered not to change; only the distribution of

finite elements is updated. this means that information contained in the geometry must

be reassigned to all elements and stress points (such as material data, initial stresses,

water pressures and active/inactive settings). although after mesh generation only the

calculation settings are already retained in the current Plaxis version, the new �d update

will facilitate this further and will stimulate mesh optimization to obtain more accurate

results.

in some cases slight modifications of the geometric model may be required to introduce

geometric details which have not been considered in a preliminary analysis. in this

respect one can think of introducing a few additional geometry points or lines, which will

also affect the cluster definition, or even introduce new clusters. as long as the Plaxis

input program is able to properly relocate material data sets in the updated geometry (as

in the current version), the new version will also automatically regenerate stresses and

staged construction settings for previously defined calculation phases. this will avoid

manual regeneration of these data. nevertheless, it is strongly recommended to check the

settings when geometric changes have been made.

figure 1. outcome of user-requiry �005 (specific features)

dr. ronald Brinkgreve (Plaxis) and

dr. suzanne lacasse (nGi) signing strategic cooperation

5

New Developments

in addition to the Plaxis �d version, the new general Plaxis 3d model that is currently

being developed will have these facilities from the beginning of its existence. the internal

data structure has been designed such that properties are mainly assigned to the basic

volumes (like soil layers or excavation volumes) and are inherited by the resulting

sub-volumes as soon as basic volumes are crossed with other objects. Volume properties

are maintained when the geometry is modified. mesh generation, generation of element

properties from the (sub-)volumes, and initial stress generation is only considered after

definition of the calculation phases, just before the start of the finite element calculations.

this structure guarantees the consistency of model settings and facilitates the

optimization of the model from a simplified preliminary analysis to a more detailed final

run. more details about the new 3d model will be given in the next Plaxis bulletin.

Because of increasing activities, Plaxis is continuously searching for talented

professionals to join our team in delft. at the moment we have vacant positions

for a back-office manager and for a project manager with a geo-engineering back-

ground to further lead the successful Plaxis �d development line. for details and

applications see the announcement on the Plaxis website.

With the new Plaxis �d update (�008) and the new 3d version (early �009) we will fulfill

strong desires from Plaxis users, as came out of the inquiry (figs. 1 and �). some of

the new features, such as the Hs small-strain stiffness model, simulation of soil tests,

and Parameter variation are already available as part of the ViPlaxis package. for more

information about this package see the Plaxis web site. We trust that the new releases will

further increase the perception of user-friendliness and robustness. more importantly, it

will stimulate the improvement of accuracy of finite element simulations.

ronald Brinkgreve

Plaxis bv

figure �. outcome of user-requiry �005 (general remarks)

6

Stabilization of vertical cut using soil nailing

Plaxis Practice

G. l. sivakumar Babu, associate ProfessorDepartment of Civil Engineering, indian institute of science, Bangalore, Karnataka, indiaVikas Pratap singh, Research scholarDepartment of Civil Engineering, indian institute of science, Bangalore, Karnataka, india

Introductionsoil nailing has been used extensively as an in-situ reinforcement technique in many

parts of the world. the design and analysis are essentially based on limit equilibrium

methods (Gassler and Gudehus, 1981; Juran, 1985). one of the important aspects

of the analysis of in-situ earth reinforcement is in understanding the behaviour of

soil-nailed retaining walls. in a soil-nailed retaining wall, the properties and material

behaviour of three components—the native soil, the reinforcement (nails) and the facing

element—and their mutual interactions significantly affect the performance of

the structure. the behaviour of reinforced soil walls can be understood to some extent by

studying the state of stress within the reinforced zone (rowe and Ho, 1996). in addition,

various factors such as the construction sequence, the installation of nails, the connection

between the nails and the facing are likely to influence the behaviour. these influences

are not adequately addressed in the conventional design procedures based on limit

equilibrium methods, with which the wall in the present study was designed. Hence, for a better

understanding of the behaviour, it is necessary to assess the stability and performance of

soil-nailed walls using numerical simulations.

Applications of soil nail wallssoil nail walls are particularly well suited to excavation applications for ground conditions

that require vertical or near-vertical cuts. they have been used successfully in highway

cuts; end slope removal under existing bridge abutments during underpass widening;

for the repair, stabilization, and reconstruction of existing retaining structures; and tunnel

portals. figure 1a and 1b shows examples of the use of soil nail walls in temporary and

permanent cut applications.

soil nail walls can be considered as retaining structures for any permanent or temporary

vertical or near-vertical cut construction, as they add stabilizing resistance in

situations where other retaining structures (e.g., anchor walls) are commonly used and

where ground conditions are suitable. the relatively wide range of available facing systems

allows for various aesthetic requirements to be addressed. in this application, soil

nailing is attractive because it tends to minimize excavation, provides reasonable

right-of-way and clearing limits, and hence, minimizes environmental impacts within

the transportation corridor.

Objectivethe objective of current study is to emphasize on the feasibility of soil nail wall as an

effective technique of stabilization of vertical cuts. to accomplish this purpose a case

study is referred, wherein, a 6.8m high vertical cut in soil was supported using soil-nail

wall system. the cut was made for the approach road to the subway underneath a busy

highway connecting two sections in an area of considerable importance in Bangalore.

a soil-nail wall system was designed conventionally based on the federal Highway

administration (fHWa, �003) guidelines. an extensive geotechnical investigation

was carried out to assess in-situ soil conditions. the entire soil-nail wall system was

numerically simulated using a finite element code PlaXis. Various design variables

were studied and compared. in particular, emphasis is laid on the effect of nailing

on deformations and global factor of safety.

In-situ soil investigation and reinforcement propertiesthe in-situ ground is a residual soil deposit weathered to a moderate degree.

no groundwater is found within the influence zone. the unit weight of the soil is

approximately 18 kn/m3. Undrained shear tests on undisturbed saturated samples

indicate that the large-strain total friction angle is �5º, and cohesion is in the range

10 – �0 kPa. the spacing and length of reinforcements were worked out based on the

methods of Gassler and Gudehus (1981)and fHWa (1990). the overall factor of safety

was computed as 1.5, and the factor of safety against pullout was �.0. ribbed mild

steel bars �0 mm in diameter and 3500 mm long were used as nails and driven into

the excavated soil.

the interfacial friction angle between soil and nail, ju, was determined from direct

shear tests on representative soil samples, compacted to the field density and moisture

content. the area of ribs/striations over the nail surface was measured as 6 %. this was

represented in the direct shear box test by a mild steel plate (60 mm x 60 mm x � mm)

with equivalent striations at the interface. the steel plate was fixed to a wooden plate

(60 mm x 60 mm x 8 mm) and was used as the bottom half of the sample; the soil

figure 1. examples of use of soil nail walls in temporary and permanent cut applications.

7

Plaxis Practice

facing elements. input parameter definitions in PlaXis require averaging the effect of

a three-dimensional problem to a two-dimensional problem. figure � shows the modelled

state of the soil nailed wall.

Simulation of excavation stagesaccomplishment of physical modelling, including simulation for gravity stresses

using ko -procedure, was followed with the calculation program. simulation of the entire

soil-nail wall construction process was carried out in a sequence of construction stages.

in each construction stage a sufficient number of calculation steps were used to obtain

an equilibrium-state. since the properties of the soil at the location are highly variable,

the representative values of soil cohesion 10, 15 and �0 kPa were used for numerical

analysis. also, factor of safety is determined after each construction stage using strength

reduction technique.

Results and discussionsGlobal factor of safety is obtained using strength reduction technique after each

construction stage. three sets of observations corresponding to cohesion value of 10 kPa,

15 kPa and �0 kPa were obtained and the improvement in factor of safety is observed.

table � indicates the obtained factors of safety. an improvement of about 1.5 – �.5

times in values of factor of safety is observed. also, it could be noticed that a global

factor of safety in the range of 1.�0 – 1.53 is obtained for the entire depth (6.8 m) of

excavation supported using nails. this value reasonably agrees with the minimum range

sample was compacted to the field conditions, and sliding tests were carried out under

different normal pressures of �5 kPa, 50 kPa and 100 kPa. the samples were sheared

at a rate of 0.�mm/min, which could be considered to represent undrained conditions

in the field. Pore water pressure was not measured, and the interface parameters

are expressed in terms of friction angle and cohesion. the interfacial friction angle

between nail and soil, ju, was obtained as �5º, and cohesion was in the range

10–�0 kPa. the interface properties and the soil properties were nearly the same, as

the striations present on the plane surface cause the failure plane to pass through

the soil. the properties of the native soil and the reinforcement are given in table 1.

Construction sequencethe construction procedure consisted of excavation, nailing of the reinforcement, and

construction of rcc facing. first, the soil was excavated to a depth of 1500 mm, and

nails were driven at the desired spacing in both the horizontal and vertical directions.

nominal reinforcement for the rcc facing was provided and rigidly connected to the nails

by welding. subsequently, a 100 mm thick rcc facing was constructed. the process was

repeated until the desired depth of excavation was reached.

Numerical simulation – using Plaxisfor the numerical simulation, two-dimensional finite element code PlaXis was

used. the mohr-coulomb model is used to model soil, and for nails along with facing

elements an elastic model is used. Beam elements were used to model nails and

figure � finite element model for the soil nailed wall

Parameter Value

Wall layout

Height , H (m) 6.80

face batter, a (degrees) 0.0

slope of backfill, β (degrees) 0.0

Soil properties

cohesion, c (kPa) 10 - �0

friction angle, j (degrees) �5

Unit weight, γ (kn/m3) 18

modulus of elasticity, es (kn/m�) �0000

Poisson’s ratio, ν 0.3

Nail properties

length, ln (m) 3.50

diameter, d (m) 0.0�

spacing, sV x sH (m x m) 0.5 x 0.5

modulus of elasticity, en (kn/m�) � x 108

soil-nail interface friction, ju (degrees) �5

RCC facing properties

thickness, t (m) 0.1

modulus of elasticity, ec (kn/m�) � x 107

cross-sectional area, a (m�/m length) 0.1

moment of inertia, i (m�/m length) 8.3 x 10-5

8

Plaxis Practice

Stabilization of vertical cut using soil nailing

1.�0 – 1.30 of recommended factor of safety for global stability, as per fHWa guidelines.

figure 3 shows the graphical representation of variation of factor of safety with the depth of

excavation.

table � factors of safety obtained using strength reduction technique

another important aspect studied is the deformations in the soil nailed wall system.

it could be noticed that a maximum horizontal deformation of 7.60 mm is observed

for the nailed wall, contrary to that of �7.�5 mm for excavation of 6 m without nailing.

this shows a significant reduction (about 70%) in the displacement of the vertical cut.

table 3 shows the comparison of extreme horizontal displacements for different

excavation stages.

figure � represent graphically the variation of extreme horizontal displacements with

the depth of excavation.

in addition to the stability and deformations aspect of soil-nail wall system, various

design parameters with regard to development of axial forces, shear forces,

moments and deformations in individual nail and facing elements were also taken into

account. some of these results are as shown in figure 5 to 8 and are summarized in

table �. earth pressure distribution behind the nailed wall is as shown in figure 9. a

maximum value of 96 kn/m� passive earth pressure is obtained. the trend of variation of

forces and moments are found to conform to theoretical expectations. it also justifies the

effectivene of numerical simulations.

table 3 Horizontal displacements with excavation stages

Continuation

table � factors of safety obtained using strength reduction technique

figure 3 Variation of factor of safety with the depth of excavation

figure � Variation of horizontal displacement of vertical cut with depth of excavation

figure 5 Variation of maximum horizontal displacement of nails with depth

FOS

ux[mm]

ux[mm]

9

Plaxis Practice

figure 6 Variation of maximum axial force in nails with depth

figure 7 Pattern of variation of axial force along nail length (alternate nail from top shown)

Concluding remarksthe results provide an understanding of the effect of soil-nailing on the global

stability of vertical cuts using numerical simulations. the results and analysis

indicate that the soil-nailed wall is stable with respect to both stability and deformation

considerations. further, it could be concluded that soil nailing is a viable and

economical option for supporting vertical cuts particularly in locations where

site-constraints are more predominant and project duration is very limited.

Acknowledgementsthe work presented in this article is a part of the research project Guidelines for soil

nailing technique in Highway engineering (r-86) financed by the ministry of shipping,

road transport and Highways, Government of india, new delhi. the authors express

thanks to the ministry for funding and providing necessary support for the project.

References- dawson e. m., roth W. H. a. and drescher a. (1999) slope stability analysis by strength

reduction. Geotechnique, �9, no. 6, 835–8�0.

- fHWa (�003) carlos a. lazarte, Victor elias,

- r. david espinoza, Paul J. sabatini, Geotechnical engineering circular no. 7, soil nail -

Walls, 0-if-03-017.

- matsui, t. and san, k-c. (199�) finite element slope stability analysis by shear strength

reduction technique, soils and foundations, Vol. 3�, no. 1, pp. 59-70.

- PlaXis (�006) reference manual, PlaXis B.V., the netherlands.

- Babu, G. l. s., murthy, B. r. s. and srinivas, a. (�00�): “analysis of construction factors

influencing the behavior of soil nailed earth retaining walls”, Ground improvement, 6,

no. 3, pp. 137 – 1�3.

table � summary of design parameters for nails and facing element

figure 9 Variation of earth pressures behind the soil nail wall

figure 8 Variations of axial forces, bending moments and shear forces in facing elements

N[kN/M]

10

Plaxis Practice Plaxis Practice

Designing a bridge with Plaxis 3D tunnel

P.G. van Duijnen, Movares The Netherlands

Introductionthe High speed line (Hsl) between amsterdam and Brussels is not yet in operation and

there are plans to cross this railway track by local roads and motorways. movares has

carried out a global research projects over infrastructures crossing an operational Hsl.

one of these research projects concerned the crossing the Hsl by two large shield tunnels

(15 m diameter) without generating any track deformations through tunnelling. an op-

tion to achieve this is to construct a “support bridge” i.e. a concerte plate to avoid local

settlements of the railway track. the purpose of this support bridge is to carry the Hsl

track over the route of both shield tunnels free from eventual settlements. figure 1 gives

a 3d-view of the Hsl and crossing tunnels. the global dimensions of the support bridge

were calculated with the Plaxis 3d tunnel program in an early stage of design.

this article gives a short description of the 3d Plaxis model, the model difficulties and

calculation results.

figure 1: 3d picture of the Hsl track, new support bridge and shield tunnels.

Background information HSLin the netherlands, the Hsl is mainly built on a concrete plate on pile foundation. the

bearing piles are driven to a depth of 15 to �0 m below the surface. the bottom of the

shield tunnel is situated just under the toe of the piles. the tunnelling process will reduce

the bearing capacity of the pile foundation and settlement of railway track is expected.

it’s assumed that such a support bridge should prevent (differential)

settlement of the railway track.

Why Plaxis 3D Tunnel?the support bridge is a complex asymmetrical construction. the question asked is: is the

bridge capable of meeting the Hsl deformation requirements and can this be modelled

with Plaxis 3d? rough calculations by hand do not provide these answers. Plaxis �d has

been used for predictions of settlement caused by the tunnelling process.

The Support Bridgefigure 1 gives a 3d artist impression of the support bridge, shield tunnels and the Hsl.

figure � presents the Plaxis 3d model with the main components of the bridge.

Plaxis 3D Modelsolid elements are used for primary, secondary beams and concrete plate. all abutments

support the main beams in a vertical and rotational direction. Because of rotation sup-

port, every abutment has two fixed-end anchors. the abutment in the middle section

supports the main beam also in a horizontal direction; horizontal fixed-end anchors are

added in longitudinal direction (acceleration and break forces). one fixed-end anchor is

added in transverse direction for numerical integrity.

figure �: Plaxis 3d model with main parts.

some special modelling features need to be taken into account, which are indicated in

table 1

Do’s- add fictitious inactive slices on both ends of the model. fictitious inactive slices

overcome problems with the standard boundary conditions at both ends of the

model.

- define separate material data set for each abutment. separate material sets make it

easier to change the vertical stiffness of the abutment during calculation.

- two fixed-end anchors models each abutment, to provide rotation stiffness for

the main beams.

Remarks

- it was considered including plate elements in the primary and secondary beams.

Plate elements with a fictitious, low bending stiffness, simplifies presentation of

bending moments, normal forces etcetera. the use of plate elements was rejected

because bending moments occur in diverse directions.

table 1 special modelling features

11

Plaxis Practice

Post processing, deformations and reaction forcesduring normal train operations, the key element to consider is global deformations

and differential deformations. settlements of track are obtained in Plaxis 3d through

generating a cross section at track level. numerical deformations are thereafter copied

into an excel sheet for further processing. figure 3 shows the deformed support bridge.

figure � shows the settlements of the main beams, the railway tracks and the reaction

forces of abutments for load case B (load case B being the situation where one train is

on the bridge). figure 5 shows the bending moments in the main beam for the different

load cases.

figure 3: deformed support bridge

figure �: settlements of the main beams

Tunnelling Processsettlements of the abutments as a result of the tunnelling process were expected for

the abutments situated close to the tunnels. settlements of the abutments caused by

the tunnelling process are modelled by reducing the vertical stiffness of the support.

the amount of reduction applied is an iterative process. the calculated settlement of

the abutment had to comply with the predicted settlement induced by the tunnelling

process.

Post processing, bending momentthe plate elements were not included in the model. Bending moments are obtained by

integrating the stresses over the height of the main beam.

Conclusions- the definition of the boundary conditions gave a few difficulties;

- modelling the support bridge with Plaxis 3d posed no difficulties;

- the post processing of the numerical results is a time consuming process;

- the copy option of slides and planes in the calculation model proved to be a useful

timesaver;

- Herewith the structure complies with the deformation requirements;

- there is a good concordance between the results of the Plaxis 3d calculation with other

fem programs such as ansys (not presented here).

Calculation of the bending moments for the cross sections a-a, B-B and c-c

maa(z) = ∑σzz;i(z)⋅ai⋅yi

Bending moment in main Beam:

m(z) = 1/3⋅(maa(z) + mBB(z) + mcc(z))

m(z) Bending moment around X-X.maa, mBB, mcc Bending moment cross section a-a respectively B-B and c-c.ai area for σzz(y,z)σzz(y,z) stress in longitudinal direction in cross section a-a, B-B and c-c.y distance to X-XZ Z-coordinate

figure 5: bending moments in the main beam

reac

tion

forc

e [M

N] S

ettlement [m

m]

Ben

ding

mom

ent

[kN

m]

Bending moment [kN m/m]

1�


sylvie Bretelle, Bruno Demay, agathe Touati, saiPEM-sa


1. Introductionon the south bank of the Gibraltar’s strait �0 km east of tangiers city, the morocco

authorities have launched the construction of a new harbor, to favor the economical

development of the north region and to improve the relationship between morocco and

the euro-mediterranean area. the main functions of the harbor are:

- Getting a part of the traffic of the containers transshipment

- developing the traffic of trucks

- rationalizing the affectation of the cereals traffic

- serving the tangiers hinterland with refined oil products

- clearing the city of tangiers, in order to turn its activity more to the tourism and make

it as a pole of a cultural center.

the works are performed by a joint venture company (srPtm) constituted by:

- BoUyGUes-tP

- saiPem-sa

- Bymaro (morocco subsidiary company of Bouygues-Bi)

2. Project description2.1 Generalthis project, named “tangiers - mediterranean harbor “, was initiated to create a harbor

in deep water, free zones of logistic, industrial, commercial and tourist facilities and

infrastructures of motorways and railways connections.

the harbor of tangiers-mediterranean is protected by a main breakwater of �,050 m

length and a secondary breakwater of 570 m length. Both breakwaters are composed of

one part of rubble mound and the other part of caissons depending upon the sea bed level.

this breakwater will protect terminals to be erected later:

- a container terminal of 1,61� m length, offering a draught of 1� to 18 m and

a reclamation area of 90 hectares.

- a �01 m length of quay, for feeders with a draught of 1� m.

- a cereal terminal with a 366 m length of quay, with a draught of 15 m.

- a ��5 m length utility quay, with a draught of 6 m.

2.2 Description of rubble moundthe rubble mound is realized with materials from quarry, placed by maritime or terrestrial

way (dumping from ship when water depth exceeds 10m, dumping from truck and pushed

from land at shallow water depth). it is located in depths not exceeding �0 m. its total

length is around 1,000 m.

2.3 Description of breakwaterthe Breakwater is constituted of �0 caissons based at level -�0 m and placed one close

to the other, along a total length of around 1,100 m. the horizontal dimensions of one

caisson are �8x�8 m and the height is 3� to 35 m. the caissons are longitudinally

connected by means of concrete keys. the total concrete volume is 3,000 m3 per caisson.

caissons are filled with ballast in order to ensure installation and service stability.

the weight of each unit is 7900 t.

figure 1: tangiers-mediterranen harbor project

figure �: aerial view of the harbor

figure 3: detailed vew of breakwater

13



2.4 Description of the caissonsthe caissons are made of precast reinforced concrete and have � cells shape (sharmrock

shape) filled with sand on a height of �3 m. above this the superstructures are constructed

constituted by three walls.

- a partially opened front wall (in order to reduce the swell energy),

- a rear wall as a screen to the swell

- a transverse wall to link the two previous walls.

General layout of the harbor is shown in the next picture, with caissons dike in the upper

part of the drawing, and turning basin in the middle.

3. Geological contextaccording to detailed site investigation (cPt, boreholes, sPt, laboratory testing), several

basement soils were identified. the geotechnical context is as follow:

Rubble mound breakwater:Based on a bedrock composed of slightly to highly weathered siltstone/sandstone flysch (flysch

is a thick deposit of distinctively interbedded sandstones and shales laid down by turbidity

currents in a deep water marine environment during the early phases of orogenesis).

Caissons breakwater:Based on soils (silts, sands and gravels), with foreseen settlements:

- formation i: is mainly composed of sand,

- formation ii: interbedded gravelly sand, clays and sandy gravel or clayey gravel.

- formation iii: sandstone/siltstone substratum.

4. Simulation with Plaxis 2D4.1 soil ModelPlaxis was used to estimate the settlements (both global and differential) of the caissons.

for this purpose, the different soil layers were considered with the following soil model:

formation i: Hardening soil model, Hsm in drained conditions (parameters defined from

calibration on triaxial tests results). (soils 1-�-3 in table below)

formation ii: soft soil model, ssm for clayey layers with available oedometer tests results

to define cc, cs e0. mohr coulomb elasto-plastic model, ePmc for other gravely layers.

(soils �-5 in table below)

formation iii: mohr coulomb elasto-plastic model, ePmc with non porous conditions.

Parameters are defined from in-situ tests and correlations.

one of the calculated cross section is shown here after, with a detailed table of the

parameters used for the calculation.

figure �: detail of caisson

figure 5: Harbor plan

table 1: soil data

figure 6: cross section of caisson

1�


Continuation

4.2 Construction stages and estimated settlementsconstruction stages are described here after for two sections part of the study.

cereal quay area (Pm 1000 et Pm1��5)

- Preparation of platform for caisson (between sea bed at -�5m and caisson bottom

at -�0 m)

- caisson installation and ballast

- superstructure cast in place

- � month consolidation before backfilling behind the caissons

- Backfilling behind the caissons by 5 m height layers (in the model, to obtain a

representative stress distribution), no consolidation allowed between backfilling

stages

- long term consolidation (up to full dissipation of excess pore pressure).

the Plaxis mesh is as follows:

the table summarizes the main results from the calculation of caisson settlement

(seaside, port side and on caisson axis).

outside cereal quay area (Pm 1�75)

- Preparation of platform for caisson (between sea bed and caisson bottom at -�0 m)

- caisson installation and ballast

- superstructure cast in place

- long term consolidation (up to full dissipation of excess pore pressure).

the Plaxis mesh is as follows:

the table summarizes the main results from the calculation of caisson settlement

(seaside, port side and on caisson axis).

Pm 1��5

Port(cm) axis(cm) sea(cm)

Preparation of platform for caisson

+ 5 months consolidation 7.� 7.8 8.0

caisson installation and ballast

+ 5 months consolidation 39.6 37.1 3�.5

superstructure cast in place

+ � months consolidation �.1 �.� �.8

Backfilling behind the caisson 7.6 5.9 �.�

long term consolidation 11.1 10.0 8.9

Total caisson settlement 60.5 55.4 50.3

Pm 1�75

Port(cm) axis(cm) sea(cm)

Preparation of platform for caisson

+ 5 months consolidation 7.� 7.8 8.0

caisson installation and ballast

+ 5 months consolidation 39.6 37.1 3�.5

superstructure cast in place

Total caisson settlement 60.5 55.4 50.3


seaside

seasidePortside

figure 7: Plaxis model of cereal quay area

table �: calculated displacements (quay)

table 3: calculated displacements (caisson)

figure 8: Plaxis model of caisson

15


5. Observed behavior during construction – comparison with Plaxis calculationthe compared observed behavior and calculated behavior are shown in this page,

resulting in a good agreement. the first part of the curve correspond to the concrete

caisson installation, and the observed step correspond to the ballast installed in

the caisson.

6. Dynamic simulationa dynamic soil structure interaction was performed in order to confirm the validity of

pseudo static calculation and to quantify settlements and rotations of caissons during

seismic event. in addition, the pore pressure increase will be considered with regard to

the liquefaction phenomena.

main data considered for dynamic simulation are:

- soil conditions / substratum position as shown in next picture

- dynamic modulus (6 times static modulus) as laboratory tests shows a ratio between

5 and 8

seismic signal: defined from existing seismic data to represent as much as possible

the frequency content of most probable seism.

- kocaeli (distant) mw 8.5 amax 0.093g

- Umbria (close) mw �.7 amax 0.��g

- signal imposed at rock substratum level.

- dilatancy sensitivity analysis


installed in the caisson.

CAISSON N°11 - PM 1229

Tassements

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

17/06 24/06 01/07 08/07 15/07 22/07 29/07 05/08 12/08 19/08 26/08 02/09 09/09 16/09 23/09 30/09 07/10 14/10 21/10 28/10 04/11 11/11 18/11Date

Ta

ss

em

en

t [m

]

P1

relevé

P2

relevé

P3

relevé

BALLASTAGE EN SABLE DALLE SUPERIEURE

Calculated value

Settlement (cm)


Tassements

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

06/08 13/08 20/08 27/08 03/09 10/09 17/09 24/09 01/10 08/10 15/10 22/10 29/10 05/11 12/11 19/11Date

Ta

ss

em

en

t [m

]

P1

relevé

P2

relevé

P3

relevé

Calculated value

Settlement (cm)

installed in the caisson.


Tassements

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

17/06 24/06 01/07 08/07 15/07 22/07 29/07 05/08 12/08 19/08 26/08 02/09 09/09 16/09 23/09 30/09 07/10 14/10 21/10 28/10 04/11 11/11 18/11Date

Ta

ss

em

en

t [m

]

P1

relevé

P2

relevé

P3

relevé

BALLASTAGE EN SABLE DALLE SUPERIEURE

Calculated value

Settlement (cm)


Tassements

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

06/08 13/08 20/08 27/08 03/09 10/09 17/09 24/09 01/10 08/10 15/10 22/10 29/10 05/11 12/11 19/11Date

Ta

ss

em

en

t [m

]

P1

relevé

P2

relevé

P3

relevé

Calculated value

Settlement (cm)

figure 9: observed vs calculated settlements

figure 10: observed vs calculated settlements

figure 11: Plaxis model

figure 1�: typical short duration seismic event

figure 13: typical long duration seismic event

16

Plaxis PracticePlaxis Practice

ar = βr = 0.01 (default values) and ar = βr = 0.03 are considered for sensitivity analysis

(proposed value in different reference sources).

the dilatancy angle has an influence on the volume change of soil due to shear.

for static analysis, the retained dilatancy angle value was 0° < ψ < 0.5° allowing pore

pressure generation during construction loading. this choice gives a proper correlation of

observed and calculated settlement.

for sensitivity purpose, values of 5° < ψ < 10° (ψ = j - 30°, correspond to the usual

value) were compared to the case with ψ = 1° (correspond to the value retained for static

calculation).

the results show similar displacements.

the results show similar excess pore pressure.

- rayleigh Parameters and sensitivity analysis


Ψ = j - 30° ↑Ψ = 1° ↓

Ψ = j - 30° ↑Ψ = 1° ↓

a and β = 0.01 ↑ dmax = 88 mm,

a and β = 0.03 ↓ dmax = 83 mm,

a and β = 0.01 ↑ extreme pore pressure 130 kPa

a and β = 0.03 ↓ extreme pore pressure 316 kPa

17

Plaxis PracticePlaxis Practice

- number of step sensitivity analysis

for the short duration seismic event, the application time was set to 10s and the time step

to 0.�s (or 500 steps) or 0.01s (or 1000 steps for sensitivity analysis).

the used time step shall be lower than critical time step. the critical time step is

a function of element size, shear moduli, and volumic weight of soils.

the calculation was performed with 500, 700 and 1000 steps in order to control

the critical step number. results shown are displacements.

the results are very similar for 700 to 1000 steps, whereas the results change

dramatically for 500 steps. for 500 steps, the time step is probably lower than critical

time step.

7. Results of the Plaxis dynamic analysisthe main results of this Plaxis dynamic analysis are:

- an accurate choice of the parameters is required (seismic signal, soil models and

parameters) with dedicated soil investigation (both in situ and in laboratory), and

seismic study,

- Precise answers are found related to amplification or attenuation of the seismic signal

between substratum and structure,

- localization of the higher pore pressure increase (zone of possible liquefaction),

- Quantification of the residual displacements after seism.

some sensitivity analysis on different parameters help to define specific parameters for

the dynamic model such as time steps, rayleigh parameters and dilatancy.


nb step = 500 ↑ dmax =1�7 mm

nb step = 700 ↑ dmax =8� mm

nb step = 1000 ↑ dmax =88 mm

18

Product Information3dfoundation is designed for the analysis of raft, pile-raft and offshore foundations.

large arbitrary 3d soil geometries and meshes can easily be generated by the definition

of one or more boreholes. structures or structural parts and piles can be defined

independent of non-horizontal soil stratigraphy by well defined dedicated wizards.

Version � of the PlaXis 3dfoUndation program offers additional functionality compared

to previous releases. new features include embedded piles, ground anchors, user defined

soil models, vertical mesh refinement, Phi/c reduction user defined boundary conditions

for consolidation. further features include multiselect and grouping, the hardware

accelerated display of graphical output data and the possibility to create animations

of the results. Via the V.i.Plaxis service Program of 3dfoundation users can also have

access to the new small strain stiffness model (Hssmall) and the soil test facility. see

also our movies at www.plaxis.nl

in the process of adapting our products and services to a particular language, culture,

and desired local features we started a few years ago to unicodify our products.

in �006 we released the Japanese and chinese Plaxis V8 and in the framework of

these localization we recently announced a russian language website www.plaxis.ru

and the indonesian Plaxis V8. from the Japanese and chinese V8 we also released

an introductory version. these are part of a completely refreshed Plaxis introductory. this

introductory Version is intended to show (new) users most of the available options of the

Plaxis programs and includes:

- Plaxis at Work movies

- Plaxis V8 introductory

- chinese Plaxis V8 introductory

- Japanese Plaxis V8 introductory

- 3dtunnel introductory

- 3dfoundation introductory

the introductory version is workable like the full versions but limited in some ways.

Recent activities

Recent Activities

19

Recent Activities

Users Servicesso far �007 is a successful year with respect to courses as most courses have reached

the maximum amount of participants. next to the yearly courses in Holland, Belgium,

Germany and the Uk a new course has been held in india. this course in

chennai was conducted in cooperation with the indian institute of technology – madras.

the course was very well attended with over 50 participants. in south-east asia there

have been workshops and seminars in Vietnam, thailand and malaysia. furthermore

the iem organized a course in malaysia with almost 100 participants. the annual courses

in the Usa were this year in Berkeley (January) and chicago (July) with especially the latter

one well visited. australia saw in �007 its first advanced course. this 3 days course

in sydney had �5 enthusiastic participants.

for the remaining part of the year the first advanced course in turkey was planned and

to our surprise and delight this course was already full more than � months before the

course was actually held. at about the time of the release of this Plaxis bulletin after a 5

years period since the first course in Brazil (�00�, sao carlos) another course in Brazil will

take place. this time it will be more an intermediate level course of � days. other courses

this year are planned in indonesia and colombia.

as extension of the advanced course in sydney, on the evening of thursday �6 June

the first australian-new Zealand Users meeting was held. though the group of attendants

was not very large there where some interesting presentations and discussions.

a dam design was discussed, focusing on the use of different advanced soil models

for this particular case. the evening was closed with a presentation on future Plaxis

developments with respect to 3d. considering the positive reactions of the attendants

more user meetings are planned as part of future courses in australia or new Zealand.

a �-day russian Users conference with about 85 participants was organized as a

successor of last year User day in st. Petersburg.

We look forward to meet you in our upcoming events.

for the 1�th european Plaxis Users meeting you can register online via our agenda on

www.plaxis.com

russia (top)

malaysia (middle)

india (bottom)

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

Activities 2007-2008

7006

301

1 – 4 October 2007Plaxis seminar and Workshops

thailand

1 – 4 October 2007course computational Geotechnics

rio de Janairo, Brazil

4 October 2007Geotechniekdag �007

Breda, the netherlands

16 October 2007oil and Gas seminar

aberdeen, United kingdom

17 - 18 October 2007Plaxis seminar and Workshop

taipei, taiwan

21 - 24 October 200710th anZ smGe,

Brisbane, australia

1 November 2007launch indonesian Plaxis V8

Jakarta, indonesia

1 – 4 November 200710th chinese Geotechnical conference

chongqin city, china

5 – 9 November 2007course computational Geotechnics

Bogotá, colombia

6 November 2007Plaxis Workshop

Jakarta, indonesia

7 - 9 November 20071�th european Plaxis User meeting

karlsruhe, Germany

14 – 16 November 20075th international symposium

on earth reinforcement

fukuoka, JaPan

21 –23 November 2007course computational Geotechnics

Paris, france

26 – 28 November 20071� african regional conference smGe,

yaounde, cameroon-africa

6 – 7 December 2007international symposium on

Geotechnical engineering

Bangkok, thailand

10 – 14 December 200713th asian regional conference on

soil mechanics and Geotechnical engineering

kolkata, india

January 2008course computational Geotechnics

Boston, U.s.a.

21 – 23 January 2008international course on computational

Geotechnics

schiphol, the netherlands

4 – 8 February 2008course computational Geotechnics

Brisbane, australia

12 – 13 February 2008Workshop “Plaxis: advanced soil models and

3d modelling”

Perth, australia

10 – 13 March 2008international course on computational

Geotechnics

antwerp, Belgium

9 – 12 March 2008Geo congres 08

new orleans, Usa

Plaxis Bulletin 22

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