ANALYSES YSES PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANAL
Plaxis Bulletin issue 22 / October 2007
Stabilization of vertical cut using soil nailing Designing a bridge with Plaxis 3D tunnel Tangiers - Mediterranean harbor
Colophon
Editorial
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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 geotechnical engineering practise and includes articles on the practical application of the Plaxis
New Developments
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programs, case studies and backgrounds on the models implemented i n Plaxis. The Bulletin offers a platform where users of Plaxis can share ideas and experiences with
Plaxis Practice
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Stabilization of vertical cut using soil nailing
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,
Plaxis Practice 10
Designing a bridge with Plaxis 3D tunnel
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 text in a common graphics format (e.g. tif, gif, png, jpg, wmf, cdr or eps formats are all
Plaxis Practice 12
Tangiers Mediterranean harbor
acceptable). If bitmaps or scanned figures are used the author should ensure that they have a resolution of at least 300 dpi at the size they will be printed. The use of colour in figures is encouraged, as the Plaxis Bull etin is printed in full -colour. Any correspondence regarding the Plaxis Bulletin can be sent by email to
[email protected]
Recent Activities 18 or by regular mail to:
Activities 2007-200 2007-2008 8 20
Plaxis Bulletin c/o Erwin Beernink PO Box 572 2600 AN Delft The Netherlands The Plaxis Bulletin has a total circulation of 12.000 copies and is distributed worldwide. Editorial Board: Wout Broere Ronald Brinkgreve Erwin Beernink Arny Lengkeek
Copyright coverphoto: BeeldbankVenW.nl, Rijkswaterstaat
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Editorial
Ronald Brinkgreve
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].
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 breakwater seem to meet the design criteria. Besides the main articles from Plaxis users on practical applications, this Bulletin contains 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
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New Developments
New Developments Ronald Brinkgreve
Just before the release of this Bulletin, Plaxis signed a strategic cooperation agreement
Intuitiveness and user-friendliness are key-elements in the Plaxis software. However,
with the Norwegian Geotechnical Institute (NGI). In the last two years, NGI has made a
according to a user-inquiry some time ago, there is one aspect that Plaxis users find less
significant contribution to the validation of the recently released Plaxis 3D Foundation
user-friendly: After refinement of the finite element mesh or after slight modifications of
program (version 2). The agreement is the acknowledgement of a cooperation that actually
the geometry, initial stresses and water pressures need to be regenerated and calculation
started many years ago. It is also a starting point to cooperate project-wise on advanced
phases (construction stages) are reset to the initial phase. This handicap will have been
numerical models for offshore geo-engineering applications. Through this cooperation we
improved in the next update of the Plaxis 2D version.
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).
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
This strategic cooperation with NGI fits perfectly in the Plaxis strategy of building close
mesh, whereas final results may be obtained after global or local mesh refinement. In
relationships with world leaders in the field of geotechnical research & development.
this case the geometry model itself is considered not to change; only the distribution of
Plaxis has for example a long lasting relationship with GeoDelft (the Netherlands). In
finite elements is updated. This means that information contained in the geometry must
Bulletin 19 the MOU with GeoDelft was already mentioned. Meanwhile, we cooperate with
be reassigned to all elements and stress points (such as material data, initial stresses,
GeoDelft in scientific projects (such as the Material Point Method project, executed at the
water pressures and active/inactive settings). Although after mesh generation only the
University of Stuttgart) and we join forces in commercial activities. Another cooperation
calculation settings are already retained in the current Plaxis version, the new 2D update
is with the German BundesAnstalt für Wasserbau (BAW) on the Extended FEM project.
will facilitate this further and will stimulate mesh optimization to obtain more accurate
BAW also organises the yearly European Plaxis Users Meeting in Karlsruhe. Last but not
results.
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
In some cases slight modifications of the geometric model may be required to introduce
testing and validating new features and beta versions of the software, and facilitating
geometric details which have not been considered in a preliminary analysis. In this
courses and educating geotechnical engineers in the use and backgrounds of Plaxis.
respect one can think of introducing a few additional geometry points or lines, which will
All these cooperations make Plaxis a reliable and well accepted software product for
also affect the cluster definition, or even introduce new clusters. As long as the Plaxis
geo-engineering applications.
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.
Dr. Ronald Brinkgreve (Plaxis) and Dr. Suzanne Lacasse (NGI) signing strategic cooperation
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Figure 1. Outcome of user-requiry 2005 (specific features)
New Developments
In addition to the Plaxis 2D version, the new general Plaxis 3D model that is currently
With the new Plaxis 2D update (2008) and the new 3D version (early 2009) we will fulfill
being developed will have these facilities from the beginning of its exi stence. The internal
strong desires from Plaxis users, as came out of the inquiry (Figs. 1 and 2). Some of
data structure has been designed such that properties are mainly assigned to the basic
the new features, such as the HS small-strain stiffness model, Simulation of soil tests,
volumes (like soil layers or excavation volumes) and are inherited by the resulting
and Parameter variation are already available as part of the VIPlaxis package. For more
sub-volumes as soon as basic volumes are crossed with other objects. Volume properties
information about this package see the Plaxis web site. We trust that the new releases will
are maintained when the geometry is modified. Mesh generation, generation of element
further increase the perception of user-friendliness and robustness. More importantly, it
properties from the (sub-)volumes, and initial stress generation is only considered after
will stimulate the improvement of accuracy of finite element simulations.
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
Ronald Brinkgreve
run. More details about the new 3D model will be given in the next Plaxis bulletin.
Plaxis bv
Figure 2. Outcome of user-requiry 2005 (general remarks)
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 background to further lead the successful Plaxis 2D development line. For details and applications see the announcement on the Plaxis website.
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Plaxis Practice
Stabilization of vertical cut using soil nailing G. L. Sivakumar Babu, Associate Professor Department of Civil Engineering, Indian Institute of Science, Bangalore, Karnataka, India Vikas Pratap Singh, Research Scholar Department of Civil Engineering, Indian Institute of Science, Bangalore, Karnataka, India
Introduction
Objective
Soil nailing has been used extensively as an in-situ reinforcement technique in many
The objective of current study is to emphasize on the feasibility of soil nail wall as an
parts of the world. The design and analysis are essentially based on limit equilibrium
effective technique of stabilization of vertical cuts. To accomplish this purpose a case
methods (Gassler and Gudehus, 1981; Juran, 1985). One of the important aspects
study is referred, wherein, a 6.8m high vertical cut in soil was supported using Soil-Nail
of the analysis of in-situ earth reinforcement is in understanding the behaviour of
wall system. The cut was made for the approach road to the subway underneath a busy
soil-nailed retaining walls. In a soil-nailed retaining wall, the properties and material
highway connecting two sections in an area of considerable importance in Bangalore.
behaviour of three components—the native soil, the reinforcement (nails) and the facing element—and their mutual interactions significantly affect the performance of
A Soil-Nail wall system was designed conventionally based on the Federal Highway
the structure. The behaviour of reinforced soil walls can be understood to some extent by
Administration (FHWA, 2003) guidelines. An extensive geotechnical investigation
studying the state of stress within the reinforced zone (Rowe and Ho, 1996). In addition,
was carried out to assess in-situ soil conditions. The entire soil-nail wall system was
various factors such as the construction sequence, the installation of nails, the connection
numerically simulated using a finite element code PLAXIS. Various design variables
between the nails and the facing are likely to influence the behaviour. These influences
were studied and compared. In particular, emphasis is laid on the effect of nailing
are not adequately addressed in the conventional design procedures based on limit
on deformations and global factor of safety.
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.
In-situ soil investigation and reinforcement properties The in-situ ground is a residual soil deposit weathered to a moderate degree.
Applications of soil nail walls
No groundwater is found within the influence zone. The unit weight of the soil is
Soil nail walls are particularly well suited to excavation applications for ground conditions
approximately 18 kN/m3. Undrained shear tests on undisturbed saturated samples
that require vertical or near-vertical cuts. They have been used successfully in highway
indicate that the large-strain total friction angle is 25º, and cohesion is in the range
cuts; end slope removal under existing bridge abutments during underpass widening;
10 – 20 kPa. The spacing and length of reinforcements were worked out based on the
for the repair, stabilization, and reconstruction of existing retaining structures; and tunnel
methods of Gassler and Gudehus (1981)and FHWA (1990). The overall factor of safety
portals. Figure 1a and 1b shows examples of the use of soil nail walls in temporary and
was computed as 1.5, and the factor of safety against pullout was 2.0. Ribbed mild
permanent cut applications.
steel bars 20 mm in diameter and 3500 mm long were used as nails and driven into
Soil nail walls can be considered as retaining structures for any permanent or temporary
the excavated soil.
vertical or near-vertical cut construction, as they add stabilizing resistance in
ju, was determined from direct
situations where other retaining structures (e.g., anchor walls) are commonly used and
The interfacial friction angle between soil and nail,
where ground conditions are suitable. The relatively wide range of available facing systems
shear tests on representative soil samples, compacted to the field density and moisture
allows for various aesthetic requirements to be addressed. In this application, soil
content. The area of ribs/striations over the nail surface was measured as 6 %. This was
nailing is attractive because it tends to minimize excavation, provides reasonable
represented in the direct shear box test by a mild steel plate (60 mm x 60 mm x 2 mm)
right-of-way and clearing limits, and hence, minimizes environmental impacts within
with equivalent striations at the interface. The steel plate was fixed to a wooden plate
the transportation corridor.
(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.
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Plaxis Practice
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 - 20
Friction angle, j (Degrees)
25
Unit weight, γ (kN/m3)
18 2
Modulus of elasticity, ES (kN/m )
20000
Poisson’s ratio, ν
0.3
Nail properties Length, LN (m)
3.50
Diameter, D (m)
0.02
Spacing, SV x SH (m x m)
0.5 x 0.5 2
Modulus of elasticity, EN (kN/m )
2 x 108
Soil-nail interface friction, ju (Degrees)
25
RCC facing properties Thickness, t (m)
0.1 2
Modulus of elasticity, EC (kN/m )
2 x 107
Cross-sectional area, A (m 2 /m length)
0.1
Moment of inertia, I (m4 /m length)
8.3 x 10-5
Figure 2 Finite element model for the soil nailed wall
sample was compacted to the field conditions, and sliding tests were carried out under
facing elements. Input parameter definitions in PLAXIS require averaging the effect of
different normal pressures of 25 kPa, 50 kPa and 100 kPa. The samples were sheared
a three-dimensional problem to a two-dimensional problem. Figure 2 shows the modelled
at a rate of 0.4mm/min, which could be considered to represent undrained conditions
state of the soil nailed wall.
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
Simulation of excavation stages
ju, was obtained as 25º, and cohesion was in the range
Accomplishment of physical modelling, including simulation for gravity stresses
10–20 kPa. The interface properties and the soil properties were nearly the same, as
using Ko -procedure, was followed with the calculation program. Simulation of the entire
the striations present on the plane surface cause the failure plane to pass through
soil-nail wall construction process was carried out in a sequence of construction stages.
the soil. The properties of the native soil and the reinforcement are given in Table 1.
In each construction stage a sufficient number of calculation steps were used to obtain
between nail and soil,
an equilibrium-state. Since the properties of the soil at the location are highly variable,
Construction sequence
the representative values of soil cohesion 10, 15 and 20 kPa were used for numerical
The construction procedure consisted of excavation, nailing of the reinforcement, and
analysis. Also, factor of safety is determined after each construction stage using strength
construction of RCC facing. First, the soil was excavated to a depth of 1500 mm, and
reduction technique.
nails were driven at the desired spacing in both the horizontal and vertical directions. Nominal reinforcement for the RCC facing was provided and rigidl y connected to the nails
Results and discussions
by welding. Subsequently, a 100 mm thick RCC facing was constructed. The process was
Global factor of safety is obtained using strength reduction technique after each
repeated until the desired depth of excavation was reached.
construction stage. Three sets of observations corresponding to cohesion value of 10 kPa, 15 kPa and 20 kPa were obtained and the improvement in factor of safety is observed.
Numerical simulation – using Plaxis
Table 2 indicates the obtained factors of safety. An improvement of about 1.5 – 2.5
For the numerical simulation, two-dimensional finite element code PLAXIS was
times in values of factor of safety is observed. Also, it could be noticed that a global
used. The Mohr-Coulomb model is used to model soil, and for nails along with facing
factor of safety in the range of 1.20 – 1.53 is obtained for the entire depth (6.8 m) of
elements an elastic model is used. Beam elements were used to model nails and
excavation supported using nails. This value reasonably agrees with the minimum range
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Plaxis Practice
Stabilization of vertical cut using soil nailing Continuation
Table 2 Factors of Safety obtained using strength reduction technique
1.20 – 1.30 of recommended factor of safety for global stability, as per FHWA guidelines.
Table 3 Horizontal displacements with excavation stages
FOS
Figure 3 shows the graphical representation of variation of factor of safety with the depth of excavation. Table 2 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 27.25 mm for excavation of 6 m without nailing. This shows a significant reduction (about 70%) in the displacement of the vertical cut.
Figure 3 Variation of factor of safety with the depth of excavation
Table 3 shows the comparison of extreme horizontal displacements for different
ux[mm]
excavation stages. Figure 4 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
Figure 4 Variation of horizontal displacement of vertical cut with depth of excavation
account. Some of these results are as shown in Figure 5 to 8 and are summarized in Table 4. Earth pressure distribution behind the nailed wall is as shown in Figure 9. A
ux[mm]
maximum value of 96 kN/m2 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.
Figure 5 Variation of maximum horizontal displacement of nails with depth
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Plaxis Practice
N[kN/M]
Figure 6 Variation of maximum axial force in nails with depth
Table 4 Summary of design parameters for nails and facing element
Concluding remarks The 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 Figure 7 Pattern of variation of axial force along nail length (alternate nail from top shown)
economical option for supporting vertical cuts particularly in locations where site-constraints are more predominant and project duration is very limited.
Acknowledgements The 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 Figure 8 Variations of axial forces, bending m oments and shear forces in facing elements
- Dawson E. M., Roth W. H. A. and Drescher A. (1999) Slope stability analysis by strength reduction. Geotechnique, 49, No. 6, 835–840. - FHWA (2003) 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. (1992) Finite element slope stability analysis by shear strength reduction technique, Soils and Foundations, Vol. 32, No. 1, pp. 59-70. - PLAXIS (2006) Reference Manual, PLAXIS B.V., The Netherlands. - Babu, G. L. S., Murthy, B. R. S. and Srinivas, A. (2002): “Analysis of construction factors influencing the behavior of soil nailed earth retaining walls”, Ground Improvement, 6, No. 3, pp. 137 – 143.
Figure 9 Variation of earth pressures behind the soil nail wall
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Plaxis Practice
Designing a bridge with Plaxis 3D tunnel P.G. van Duijnen, Movares The Netherlands
Introduction
The Support Bridge
The High Speed Line (HSL) between Amsterdam and Brussels is not yet in operation and
Figure 1 gives a 3D artist impression of the support bridge, shield tunnels and the HSL.
there are plans to cross this railway track by local roads and motorways. Movares has
Figure 2 presents the Plaxis 3D m odel with the main components of the bridge.
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
Plaxis 3D Model
(15 m diameter) without generating any track deformations through tunnelling. An op-
Solid elements are used for primary, secondary beams and concrete plate. All abutments
tion to achieve this is to construct a “support bridge” i.e. a concerte plate to avoid local
support the main beams in a vertical and rotational direction. Because of rotation sup-
settlements of the railway track. The purpose of this support bridge is to carry the HSL
port, every abutment has two fixed-end anchors. The abutment in the middle section
track over the route of both shield tunnels free from eventual settlements. Figure 1 gives
supports the main beam also in a horizontal direction; horizontal fixed-end anchors are
a 3D-view of the HSL and crossing tunnels. The global dimensions of the support bridge
added in longitudinal direction (acceleration and break forces). One fixed-end anchor is
were calculated with the Plaxis 3D tunnel program in an early stage of design.
added in transverse direction for numerical integrity.
This article gives a short description of the 3D Plaxis model, the model difficulties and calculation results.
Figure 2: Plaxis 3D model with main parts.
Figure 1: 3D picture of the HSL track, new support bridge and shield tunnels.
Some special modelling features need to be taken into account, which are indicated in table 1
Background information HSL
Do’s
In the Netherlands, the HSL is mainly built on a concrete plate on pile foundation. The
- Add fictitious inactive slices on both ends of the model. Fictitious inactive slices
bearing piles are driven to a depth of 15 to 20 m below the surface. The bottom of the
overcome problems with the standard boundary conditions at both ends of the
shield tunnel is situated just under the toe of the piles. The tunnelling process will reduce
model.
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.
- 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.
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 2D has been used for predictions of settlement caused by the tunnelling process.
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
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Plaxis Practice
Post processing, deformations and reaction forces
Tunnelling Process
During normal train operations, the key element to consider is global deformations
the abutments situated close to the tunnels. Settlements of the abutments caused by
and differential deformations. Settlements of track are obtained in Plaxis 3D through
the tunnelling process are modelled by reducing the vertical stiffness of the support.
generating a cross section at track level. Numerical deformations are thereafter copied
The amount of reduction applied is an iterative process. The calculated settlement of
into an Excel sheet for further processing. Figure 3 shows the deformed support bridge.
the abutment had to comply with the predicted settlement induced by the tunnelling
Figure 4 shows the settlements of the main beams, the railway tracks and the reaction
process.
Settlements of the abutments as a result of the tunnelling process were expected for
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
Post processing, bending moment
load cases.
The plate elements were not included in the model. Bending moments are obtained by integrating the stresses over the height of the main beam.
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) MAA, MBB, MCC Ai
σzz(y,z) y Z
Figure 3: deformed support bridge
Bending moment around X-X. Bending moment cross section A-A respectively B-B and C-C. Area for σzz(y,z) Stress in longitudinal direction in cross section A-A, B-B and C-C. Distance to X-X Z-coordinate
Bending moment [kN m/m]
] N M [ e c r o f n o i t c a e r
S e t t l e m e n t [ m m ]
] m N k [ t n e m o m g n i d n e B
Figure 5: bending moments in 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; Figure 4: settlements of the main beams
- 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).
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Plaxis Practice
Tangiers - Mediterranean harbor Sylvie Bretelle, Bruno Demay, Agathe Touati, SAIPEM-SA
1. Introduction On the south bank of the Gibraltar’s Strait 40 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 description 2.1 General This project, named “Tangiers - Mediterranean harbor “, was initiated to create a harbor
Figure 2: Aerial view of the harbor - A 225 m length utility quay, with a draught of 6 m. 2.2 Description of rubble mound The 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 20 m. Its total length is around 1,000 m.
in deep water, free zones of logistic, industrial, commercial and tourist facilities and infrastructures of motorways and railways connections.
Figure 3: Detailed vew of breakwater
Figure 1: Tangiers-Mediterranen harbor project
2.3 Description of breakwater The Breakwater is constituted of 40 caissons based at level -20 m and placed one close
The harbor of Tangiers-Mediterranean is protected by a main breakwater of 2,050 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 1,612 m length, offering a draught of 12 to 18 m and a reclamation area of 90 hectares. - A 201 m length of quay, for feeders with a draught of 12 m. - A cereal terminal with a 366 m length of quay, with a draught of 15 m.
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to the other, along a total length of around 1,100 m. The horizontal dimensions of one caisson are 28x28 m and the height is 32 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.
Plaxis Practice
2.4 Description of the caissons
3. Geological context
The caissons are made of precast reinforced concrete and have 4 cells shape (sharmrock
According to detailed site investigation (CPT, boreholes, SPT, laboratory testing), several
shape) filled with sand on a height of 23 m. Above this the superstructures are constructed
basement soils were identified. The geotechnical context is as follow:
constituted by three walls. - A partially opened front wall (in order to reduce the swell energy),
Rubble mound breakwater:
- a rear wall as a screen to the swell
Basedonabedrockcomposedofslightly tohighlyweatheredsiltstone/sandstoneflysch(flysch
- a transverse wall to link the two previous walls.
is a thick deposit of distinctively interbedded sandstones and shales laid down by turbidity currents in a deep water marine environment duri ng 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 2D 4.1 Soil Model Plaxis 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: Figure 4: Detail of caisson General layout of the harbor is shown in the next picture, with caissons dike in the upper
Formation I: Hardening Soil Model, HSM in drained conditions (parameters defined from calibration on triaxial tests results). (soils 1-2-3 in table below)
part of the drawing, and turning basin in the middle. Formation II: Soft Soil Model, SSM for clayey layers with available oedometer tests results to define C c, Cs e0. Mohr Coulomb elasto-plastic model, EPMC for other gravely layers. (soils 4-5 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 5: Harbor plan
Table 1: Soil data
Figure 6: Cross section of caisson
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Plaxis Practice
Tangiers - Mediterranean harbor Continuation
4.2 Construction stages and estimated settlements Construction stages are described here after for two sections part of the study.
Outside cereal quay area (PM 1475) - Preparation of platform for caisson (between sea bed and caisson bottom at -20 m)
Cereal quay area (PM 1000 et PM1225)
- Caisson installation and ballast
- Preparation of platform for caisson (between sea bed at -25m and caisson bottom
- Superstructure cast in place
at -20 m)
- Long term consolidation (up to full dissipation of excess pore pressure).
- Caisson installation and ballast - Superstructure cast in place
The Plaxis mesh is as follows: Portside
- 2 month consolidation before backfilling behind the caissons
Seaside
- 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: Seaside
Figure 8: Plaxis model of caisson The table summarizes the main results from the calculation of caisson settlement (seaside, port side and on caisson axis).
PM 1475 Figure 7: Plaxis model of cereal quay area
(seaside, port side and on caisson axis).
Port(cm)
Axis(cm)
Sea(cm)
7.8
8.0
39.6
37.1
34.5
60.5
55.4
50.3
Caisson installation and ballast
Total caisson settlement Table 3: Calculated displacements (caisson)
7.2
7.8
8.0
39.6
37.1
34.5
Caisson installation and ballast Superstructure cast in place
14
7.2
+ 5 months consolidation
Superstructure cast in place
Preparation of platform for caisson
+ 2 months consolidation
2.1
2.4
2.8
Backfilling behind the caisson
7.6
5.9
4.2
Long term consolidation
11.1
10.0
8.9
Total caisson settlement
60.5
55.4
50.3
Table 2: Calculated displacements (quay)
Sea(cm)
+ 5 months consolidation PM 1225
+ 5 months consolidation
Axis(cm)
Preparation of platform for caisson
The table summarizes the main results from the calculation of caisson settlement
+ 5 months consolidation
Port(cm)
Plaxis Practice
5. Observed behavior during construction – comparison with Plaxis calculation
Main data considered for dynamic simulation are:
The compared observed behavior and calculated behavior are shown in this page,
- Dynamic modulus (6 times static modulus) as laboratory tests shows a ratio between
- Soil conditions / substratum position as shown in next picture
resulting in a good agreement. The first part of the curve correspond to the concrete
5 and 8
caisson installation, and the observed step correspond to the ballast installed in the caisson.
CAISSON N°11 - PM 1229 Tassements
Settlement (cm) Date
17/0 6
24/0 6
01/07
08/0 7
15/07
22/07
29/07
05/0 8
12/0 8
19/0 8
26/0 8
02/0 9
09/0 9
16/0 9 23/09
30/09
07/10
14/1 0 21/10
28/1 0 04/11
11/1 1 18/11
0.0 -0.1
-0.2
-0.3 ] m [ -0.4 t n e m-0.5 e s s a -0.6 T
-0.7
-0.8
-0.9
Figure 11: Plaxis model
Calculated value
Seismic signal: defined from existing seismic data to represent as much as possible the frequency content of most probable seism.
-1.0
P1
P2
P3
relevé
relevé
relevé
BALLASTAGEENSABLE
- Kocaeli (distant) Mw 8.5 amax 0.093g
DALLESUPERIEURE
- Umbria (close) Mw 4.7 amax 0.24g
Figure 9: Observed vs calculated settlements
- Signal imposed at rock substratum level. - Dilatancy sensitivity analysis
CAISSON N°20 - PM 1481 Tassements
Settlement (cm)
0 6/ 08
1 3/ 08
2 0/ 08
2 7/ 08
0 3/ 09
1 0/ 09
1 7/ 09
2 4/ 09
0 1/ 10
0 8/ 10
1 5/ 10
2 2/ 10
2 9/ 10
0 5/ 11
1 2/ 11
1 9/ 11
Date
0.0
-0.1 -0.2
-0.3 ] m-0.4 [ t n e m-0.5 e s s a -0.6 T -0.7
Calculated value
-0.8
-0.9 -1.0
P1
P2
P3
relevé
relevé
relevé
Figure 12: Typical short duration seismic event Figure 10: Observed vs calculated settlements
6. Dynamic simulation A 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.
Figure 13: Typical long duration seismic event
15
Plaxis Practice
Tangiers - Mediterranean harbor
The dilatancy angle has an i nfluence on the volume change of soil due to shear. For static analysis, the retained dilatancy angle value was 0° <
ψ < 0.5° allowing pore
aR = βR = 0.01 (default values) and aR = βR = 0.03 are considered for sensitivity analysis (proposed value in different reference sources).
pressure generation during construction loading. This choice gives a proper correlation of observed and calculated settlement.
ψ < 10° (ψ = j - 30°, correspond to the usual value) were compared to the case wi th ψ = 1° (correspond to the value retained for static For sensitivity purpose, values of 5° < calculation). The results show similar displacements.
Ψ = j - 30° ↑ Ψ = 1° ↓ a and β = 0.01 ↑ Dmax = 88 mm, a and β = 0.03 ↓ Dmax = 83 mm,
The results show similar excess pore pressure.
- Rayleigh Parameters and sensitivity analysis
16
Ψ = j - 30° ↑ Ψ = 1° ↓
a and β = 0.01 ↑ extreme pore pressure 130 kPa a and β = 0.03 ↓ extreme pore pressure 316 kPa
Plaxis Practice
- Number of step sensitivity analysis
The results are very similar for 700 to 1000 steps, whereas the results change
For the short duration seismic event, the application time was set to 10s and the time step
dramatically for 500 steps. For 500 steps, the time step is probably lower than critical
to 0.2s (or 500 steps) or 0.01s (or 1000 steps for sensitivity analysis).
time step.
The used time step shall be lower than critical time step. The critical time step is
7. Results of the Plaxis dynamic analysis
a function of element size, shear moduli, and volumic weight of soils.
The main results of this Plaxis dynamic analysis are: - An accurate choice of the parameters is required (seismic signal, soil models and
The calculation was performed with 500, 700 and 1000 steps in order to control
parameters) with dedicated soil investigation (both in situ and in laboratory), and
the critical step number. Results shown are displacements.
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 dil atancy.
Nb step = 1000
↑ dmax =88 mm
Nb step = 700
↑ dmax =82 mm
Nb step = 500
↑ dmax =147 mm
17
Recent Activities
Recent activities
Product Information 3DFoundation 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 2 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 2006 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.
18
Recent Activities
Users Services So far 2007 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 2007 its first Advanced course. This 3 days course in Sydney had 25 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 2 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 (2002, Sao Carlos) another course in Brazil will take place. This time it will be more an intermediate level course of 4 days. Other courses this year are planned in Indonesia and Colombia. As extension of the Advanced course in Sydney, on the evening of Thursday 26 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 2-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 14th European Plaxis Users Meeting you can register online via our Agenda on www.plaxis.com
Russia (top) Malaysia (middle) India (bottom)
19
PLAXIS FINITE ELEMENT CODE FOR SOIL AND ROCK ANALYSES
Activities 2007-2008 1 – 4 October 2007 Plaxis Seminar and Workshops
21 –23 November 2007
Thailand
Course Computational Geotechnics Paris, France
1 – 4 October 2007 Course Computational Geotechnics
26 – 28 November 2007
Rio de Janairo, Brazil
14 African Regional Conference SMGE, Yaounde, Cameroon-Africa
4 October 2007 Geotechniekdag 2007
6 – 7 December 2007
Breda, The Netherlands
International Symposium on Geotechnical Engineering
16 October 2007
Bangkok, Thailand
Oil and Gas Seminar Aberdeen, United Kingdom
10 – 14 December 2007 13th Asian Regional Conference on
17 - 18 October 2007
Soil Mechanics and Geotechnical Engineering
Plaxis Seminar and Workshop
Kolkata, India
Taipei, Taiwan January 2008 21 - 24 October 2007
Course Computational Geotechnics
10th ANZ SMGE,
Boston, U.S.A.
Brisbane, Australia 21 – 23 January 2008 1 November 2007
International Course on Computational
Launch Indonesian Plaxis V8
Geotechnics
Jakarta, Indonesia
Schiphol, The Netherlands
1 – 4 November 2007
4 – 8 February 2008
10th Chinese Geotechnical Conference
Course Computational Geotechnics
Chongqin City, China
Brisbane, Australia
5 – 9 November 2007
12 – 13 February 2008
Course Computational Geotechnics
Workshop “Plaxis: Advanced Soil Models and
Bogotá, Colombia
3D Modelling” Perth, Australia
6 November 2007 Plaxis Workshop
10 – 13 March 2008
Jakarta, Indonesia
International Course on Computational Geotechnics
7 - 9 November 2007
Antwerp, Belgium
14th European Plaxis User Meeting Karlsruhe, Germany 14 – 16 November 2007
Plaxis BV PO Box 572 2600 AN Delft
9 – 12 March 2008
The Netherlands
Geo Congres 08
Tel: +31 (0)15 251 77 20
New Orleans, USA
Fax: +31 (0)15 257 31 07
5th International Symposium
E-Mail:
[email protected]
on Earth Reinforcement
Website: www.plaxis.nl
Fukuoka, JAPAN
1 0 3 6 0 0 7
