Settlement prediction of a pile foundation for bridge abutment

Transcription

1 Settlement prediction of a pile foundation for bridge abutment A large scale 3D modelling using ZSoil Rafal OBRZUD Claude CHAPPUIS robrzud@geomod.ch

2 Content Project overview Project: Replacement of the existing bridge with a new one Junction A9 motorway and N9 road in Villeneuve (Vaud) Client: Federal Roads Office (CH) General project manager: IUB Engineering (CH) Numerical modelling: GeoMod (CH) FE modelling of a pile foundation for the new bridge

3 Bridge replacement at A9 motorway in Villeneuve Dents du midi Existing bridge Villeneuve

4 Existing old overpass at A9 motorway in Villeneuve Facts: - 2 spans - abutment founded on micropiles

5 Concept of pile foundation for the new bridge Precast concrete elements Single-span deck

6 Concept of pile foundation for the new bridge

7 3D FE mesh at initial state Abutement of existing bridge N09 NB. All natural soils were described with the Hardeninig Soil model with small strain stiffness extension Drainage along the motorway

8 T=1 Initial state NB. Weight of existing bridge neglected Soil overconsolidation taken into account Existing micropiles neglected

9 T=2 Demolition of the upper part of the existing abutment

10 T=3 Demolition of the existing abutment and realisation of 1 st row of nails Shotcrete h = 10cm NAILS Ø20mm interval=2.0m, length =8.0m

11 T=4 Demolition of the existing abutment and realisation of 2 nd row of nails Shotcrete h = 10cm NAILS Ø20mm interval=2.0m, length =6.0m

12 T=5 Demolition of the existing abutment and realisation of 3 rd row of nails Shotcrete h = 10cm NAILS Ø20mm interval=2.0m, length =2.0m

13 T=6 Realisation of secant piled wall and bored piles Work platform Bored piles Ø1200mm L=16m (under footing level) Bored piles Ø1200mm L=18m (under footing level) Secant piled wall (Ø750mm) ELASTIC SHELLS h eq =0.65cm f = 2.7m

14 T=7 1 st stage of excavation and installation of anchors Excavation 1.2m Anchors: A s = 450 mm 2 F 0 = 100 kn L f = 11.0 m L v = 4.0 m Borehole diameter 0.18 mm Interval= 1.3 m

15 T=8 Excavation down to the bottom of the excavation Bottom of the excavation

16 T=9 Realisation of the footing and pillars Foundation NB. Weightless structural elements because loads related the selfweight were applied at the foundation level Plastic hinge (connection ensured by NODAL LINK)

17 T=10 Filling inside the excavation 1 st filling subgrade

18 T=11 Filling inside the excavation 2 nd filling subgrade

19 External load applied at the foundation level T-11.5: Self weigth of the bridge (SLS) T-12.0 :Traffic load (SLS) T-13.5: Wind load (SLS) T-14.0: All loads with ULS security coefficients Loads at the footing pillar joint level provided by bridge s designer (reactions from structural model)

20 T=13 Final backfilling Final backfill

21 View on structural elements Nails Ø20mm e=2.0m, L=8.0m Secant piled wall (Ø750mm) h eq =0.65cm f = 2.7m in alluvium fluvial Bored piles Ø1200mm L = 18.0 m Anchors: A s = 450 mm 2 F 0 = 100 kn L f = 11.0 m L v = 4.0 m Borehole diameter 0.18 mm Interval= 1.3 m Bored piles Ø1200mm L = 16.0 m

22

23 Groud water level at initial state Drainage along the motorway GWT 1.0m below soil surface

24 Groud water level lowering due to pumping Pumping below the excavation 1.3m

25 Main results Excavation stage

26 DT = 8-6 Horizontal displacement due to excavation ( average soil parameters scenario) u z = 1.5cm Z X Y

27 DT = 8-6 Horizontal displacement due to excavation ( unfavourable parameters scenario) u z = 3.3cm Z Y

28 DT = 8-6 Horizontal displacement due to excavation ( unfavourable parameters scenario) with a strut in the middle u z = 0.6cm u z = 1.1cm Z X Y

29 DT = 8-6 Horizontal displacement due to excavation ( unfavourable parameters scenario) u n = 2.0cm u n = 3.3cm Y

30 DT = 8-6 Horizontal displacement due to excavation ( unfavourable parameters scenario) with a strut in the middle u z = 0.6cm u z = 1.1cm Strut Z Y X

31 DT = 8-6 Horizontal displacement due to excavation ( unfavourable parameters scenario) with a strut in the middle f c 235MPa F HEB kN A HEB mm 2 F HEB MPa A HEB400 NB. P 0 =100kN MPa < f c 214MPa 1.1

32 T = 8 Horizontal displacement due to excavation ( unfavourable parameters scenario) M max = 204 knm / m M max = -132 knm / m

33 T = 8 Horizontal displacement due to excavation ( unfavourable parameters scenario) with a strut in the middle M max = 318 knm / m M max = 230 knm / m

34 Main results Construction of bridge and external loads stages

35 DT = 11 8 Filling accomplished

36 DT = Self weigth of the bridge 36

37 DT = 12 8 Traffic load

38 DT = 13 8 Backfilling

39 DT = Wind load

40 DT = 14 8 Load increment from SLS to ULS level

41 DT = 11 8 Filling accomplished

42 DT = Self weigth of the bridge

43 DT = 12 8 Traffic load

44 DT = 13 8 Backfilling

45 DT = Wind load

46 DT = 14 8 Load increment from SLS to ULS level

47 DT = 12 8 Traffic load

48 Self weight of bridge Traffic load Realisation of footing Wind load Load increment from SLS to ULS Settlement at the pillars footing level Settlement [m] Filling up to the motorway level Realisation of final backfilling 0.45cm Min J11 J11 J17 J27 Max J16

49 Realisation of footing Self weight of bridge Traffic load Wind load Load increment from SLS to ULS Horizontal displacement at the pillars footing level [m] Filling up to the motorway level Realisation of final backfilling Min J27 J11 J17 J27 Max J14

50 T=13.5 Ground water level (all SLS loads applied) Drainage GWT 1.0m below soil surface Pore pressure excess after stopping pumping

51 T=13.5 Ground water lowering (all SLS loads applied) 2.0m of ground water lowering

52 Self weight of bridge Traffic load Realisation of footing Wind load «Drought» scenario: 2.0m of GWT lowering Settlement at the pillars footing level (GWT lowering scenario for unfavourable parameters ) Settlement [m] Filling up to the motorway level Realisation of final backfilling 0.65cm

53 Settlement at the pillars footing level (overloading scenario) Settlement [m] Vertical load / Vertical load ULS [%] 100 % of ULS load % of ULS load

54 Bending moments M z max = 1043 knm Local axes for piles X Y Z Z Y X

55 Bending moments M y max = 1171 kn Local axes for piles X Y Z Z X

56 Normal forces Local axes for piles X Y Z Z Y X

57 Shear forces T y max = 545 kn Local axes for piles X Y Z

58 Summary Numerical model allowed to account for : Actual geometry of both, excavation and foundation Actual subsoil stratigraphy and hydro-geological conditions Realistic behaviour of soil (HSS) Earthwork and construction stages Soil-structure interaction FE modelling revealed : Small horizontal displacements at the foundation level Expected bridge settlements: 1.7 et 2.2cm (3.0cm) Internal forces in the piles are not excessive

59 Thank you for your attention GeoMod 2013