Outline. Efficient modelling of pile foundations in the Finite Element Method. Introduction. Embedded pile (3D) Embedded pile row (2D)

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Embedded pile (3D) Embedded pile row (2D)

1 Efficient modelling of pile foundations in the Finite Element Method Ronald B.J. Brinkgreve Plaxis / Delft University of Technology 1 / 40 Outline Introduction Embedded pile (3D) Embedded pile row (2D) Applications of embedded piles Ongoing research Conclusions 2 / 40 1

Introduction Finite Element Method (FEM) in

boundary value problems: - Deformation (stress,

Groundwater flow analysis - (Geo)thermal analysis

simulation of soil, structure, soil-structure

2 Introduction Finite Element Method (FEM) in geotechnical engineering: Numerical solution of boundary value problems: - Deformation (stress, strain) analysis (SLS) and ULS design - Groundwater flow analysis - (Geo)thermal analysis - Thermo-Hydro-Mechanical coupling Realistic simulation of soil, structure, soil-structure interaction and construction process 3/ 40 Introduction Dancing Towers, Dubai 4/ 40 2

3 Introduction FEM modelling piles: 2D: - Axisymmetry: Axially loaded single pile - Plane strain: Pile (beam) becomes a wall - New: Embedded pile row in 2D Most practical applications involving pile foundations require a 3D model! 5/ 40 Introduction Modelling options of piles in 3D FEM: Solid elements: Expensive Poor mesh quality No structural forces Beam elements: No pile volume No surface area Unrealistic pile-soil interaction 6 / 40 3

feature: Embedded pile elements Pile as beam elements Pile-soil

4 Introduction? (Courtesy of Prof. H.F. Schweiger) 7 / 40 Embedded pile (3D) Efficient 3D modelling feature: Embedded pile elements Pile as beam elements Pile-soil interaction (shaft friction, end bearing) Arbitrary crossing of soil elements pile t skin F foot soil 8 / 40 4

5 Embedded pile (3D) k t F foot pile t skin soil k n k t k n k t k n k s k s k s Skin stiffness: k s : axial stiffness K n,k t : lateral stiffness Skin tractions: t s = q s /length =k s (u s pile -u s soil ) t max t n = q n /length = k n (u n pile -u n soil ) t t = q t /length = k t (u t pile -u t soil ) t tmax k 1 urel t s Base stiffness: k b : base/foot stiffness (Engin et al, 2007) n k b Base/Foot force: F b = k b (u b pile -u b soil ) F max 9/ 40 Embedded pile (3D) Embedded pile: Beam nodes: Real nodes; 6 d.o.f. s per node (u x u y u z r x r y r z ) Interface nodes: Virtual nodes, 3 d.o.f. s per node (u x u y u z ), expressed in volume element shape functions 10 / 40 5

Embedded pile (3D) Bearing capacity = ½ (T top +T bot ) L pile + F max T top L pile T bot F max 11 / 40 Embedded pile Deformation behaviour Pile bearing capacity is input and

6 Embedded pile (3D) Bearing capacity = ½ (T top +T bot ) L pile + F max T top L pile T bot F max 11 / 40 Embedded pile Deformation behaviour Pile bearing capacity is input and not result of FEM calculation F Global t Local Specified bearing capacity tmax k 1 urel Global pile response from soil modelling and pile-soil interaction F Fmax u k 1 urel 12/ 40 6

7 Embedded pile Elastic region Around shaft Around foot Soil stress points inside elastic region are forced to remain elastic 13 / 40 Embedded pile Output Displacements, bending moments, axial forces, shaft friction, foot force u N Ts C B A 14/ 40 7

8 Embedded pile Validation by TUGraz (Tschuchnigg, 2009) 15 / 40 Embedded pile Validation 3D model - volume piles: 70 mm 2D model: 72 mm 3D model - embedded piles: 74 mm 16 / 40 8

Embedded pile Validation by TUDelft (Dao,

9 Embedded pile Validation by TUDelft (Dao, 2011) Lateral movement of pile in horizontal soil slice: Embedded pile almost behaves as volume pile due to elastic region 17 / 40 Embedded pile Validation by TUDelft (Dao, 2011) Lateral force at pile top: 18 / 40 9

Embedded pile (3D) Conclusions embedded pile: Efficient 3D modelling of pile foundations (bored piles, piled rafts) Realistic pile-soil interaction (shaft friction, end bearing, group effects) Pile

10 Embedded pile (3D) Conclusions embedded pile: Efficient 3D modelling of pile foundations (bored piles, piled rafts) Realistic pile-soil interaction (shaft friction, end bearing, group effects) Pile capacity is Input (not a result) Since 2005 many applications in practice (pile foundations, ground anchors) 19 / 40 Embedded pile row (2D) How to model a row of piles (out-of-plane) in 2D? 20/ 40 10

option: Ls Embedded pile row: Continuous soil mesh Pile as a superimposed beam element (axial stiffness, bending stiffness)

11 Embedded pile row (2D) Conventional 2D options: Beam (plate): Continuous out-of-plane Prevents soil flow between piles Two-node spring (N2N anchor): No bending stiffness No pile-soil interaction 21/ 40 Embedded pile row (2D) New 2D modelling option: Ls Embedded pile row: Continuous soil mesh Pile as a superimposed beam element (axial stiffness, bending stiffness) Pile and soil can move independently Pile-soil interaction (interface) (shaft friction, end bearing) Out-of-plane spacing (Ls) 22/ 40 11

12 Embedded pile row (2D) (Sluis, 2012) 23/ 40 Embedded pile row (2D) Calibration of interface stiffness from 3D calculations (Sluis, 2012) 24/ 40 12

13 Embedded pile row (2D) Calibration of interface stiffness from 3D calculations (out-of-plane) (Sluis, 2012) 25/ 40 Embedded pile row (2D) 150 kn/m N 10m 26/ 40 13

Embedded pile row (2D) Case study: Bridge abudment Bridge deck Piled

sand (foundation layer) 27/ 40 Embedded pile row (2D) Case study:

3D 3D detail 2D 10 Q 2d emb [kn] M 2d emb [knm] N 2d emb [kn] 5 N 3D

14 Embedded pile row (2D) Case study: Bridge abudment Bridge deck Piled abutment Road/railway freeboard Embankment Soft layers (peat/clay) Deep sand (foundation layer) 27/ 40 Embedded pile row (2D) Case study: Bridge abudment Comparison 2D vs. 3D 3D detail 2D 10 Q 2d emb [kn] M 2d emb [knm] N 2d emb [kn] 5 N 3D [kn] M_2 3D [knm] 0 Q_13 3D [kn] vertical height [m] First pile row: M/Q/N 28/ 40 14

Embedded pile row (2D) Conclusions embedded pile row: Efficient 2D modelling of pile rows (out-of-plane) Pile and soil can move independently Realistic pile-soil interaction (shaft friction, end

15 Embedded pile row (2D) Conclusions embedded pile row: Efficient 2D modelling of pile rows (out-of-plane) Pile and soil can move independently Realistic pile-soil interaction (shaft friction, end bearing) Calibration of interface stiffness, based on out-of-plane spacing (Ls) Successful validation Since 2012 several applications in practice (piles and ground anchors) 29/ 40 Applications of embedded piles Quay wall 30/ 40 15

16 Applications of embedded piles Foundation of high-rise building in Frankfurt (Japan Centre) (Courtesy of Prof. Y. El-Mossallamy) 31/ 40 Applications of embedded piles Foundation of high-rise building in Singapore 32/ 40 16

Applications of embedded piles Railway station in

view) 615 Piles Different pile lengths Different pile

17 Applications of embedded piles Railway station in Vienna ~ 500m ~500 m ~ 400m ~400 m elements (Courtesy of Prof. H.F. Schweiger) 33/ 40 Applications of embedded piles Railway station in Vienna Model without soil (bottom view) 615 Piles Different pile lengths Different pile inclinations (Rest is modelled as blocks) 34/ 40 17

18 Applications of embedded piles Railway station in Vienna axial force shaft friction 35/ 40 Applications of embedded piles Excavation in Monaco (Odeon Towers) (i.c.w. Terrasol, France; Plaxis Bulletin 29, 2011) 36/ 40 18

19 Ongoing research Research on installation effects of driven piles at TUDelft: Idea: Impose modified stress and density on wished-in-place pile (Engin, 2013) 37 / 40 Ongoing research Research on large deformation analysis (MPM) due to pile installation 38 / 40 19

20 Conclusions Efficient modelling of piles in FEM: - Embedded pile row (2D) - Embedded pile (3D) Realistic pile-soil interaction (shaft friction, end bearing) Pile capacity is Input (not a result) Meanwhile many applications in practice (piles and ground anchors) Ongoing research: - Installation effects - Pile penetration using MPM 39 / 40 References 1. Engin H.K., Septanika E.G. and Brinkgreve R.B.J. (2007). Improved embedded beam elements for the modelling of piles. In: G.N. Pande & S. Pietruszczak (eds.), Int. Symp. on Numerical Models in Geomechanics NUMOG X, London: Taylor & Francis group. 2. Engin H.K., Septanika E.G., Brinkgreve R.B.J., Bonnier P.G. (2008). Modeling piled foundation by means of embedded piles. 2nd International Workshop on Geotechnics of Soft Soils - Focus on Ground Improvement. 3-5 September 2008, University of Strathclyde, Glasgow, Scotland. 3. Septanika E.G., Brinkgreve R.B.J., Engin H.K. (2008). Estimation of pile group behavior using embedded piles, the 12th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG), 1-6 October, 2008, Goa, India. 4. Tschuchnigg F. (2009). Embedded piles 1. Report. CGG_IR021_2009. Technische Universität Graz. 5. Tschuchnigg F. (2009). Embedded piles 2. Report. Improvements. Technische Universität Graz. 6. Dao T.P.T. (2011). Validation of PLAXIS embedded piles for lateral loading. MSc thesis. Delft University of Technology. 7. Brinkgreve R.B.J., Engin E., Dao T.P.T. (2012). Possibilities and limitations of embedded pile elements for lateral loading. IS-GI Brussels. 8. Sluis J. (2012). Validation of embedded pile row in PLAXIS 2D. MSc thesis. Delft University of Technology. 9. Engin H.K. (2013). Modelling pile installation effects A numerical approach. PhD thesis. Delft University of Technology. 40 / 40 20

21 Efficient modelling of pile foundations in the finite element method Ronald B.J. Brinkgreve 21

Modeling Foundations in RS

Modeling Foundations in RS 3 Piled Raft Modeling in RS 3 Deep foundation piles are commonly used to increase foundation stability and to increase the bearing capacity of structural systems. The design