Educational session Geosynthetics in reinforced soil structures

Transcription

1 AOR Dipl.-Ing. Gerhard Bräu Univ.-Prof. Dr.-Ing. Martin Ziegler, RWTH Aachen University 1

2 1. Introduction: Functioning of geosynthetic reinforcement in soil (M. Ziegler) 2. Introduction: Overview of EBGEO (G. Bräu) 3. Example: Geosynthetic reinforced retaining wall (M. Ziegler) 4. Example: Earth dam (G. Bräu) 2

3 Functioning of geosynthetic reinforcement in soil Univ.-Prof. Dr.-Ing. Martin Ziegler, RWTH Aachen University 1. Introduction 2. Applications of Ground Reinforcement 3. Interaction between Reinforcement and Soil 4. Summary and Conclusions Supported by 3

4 1. Introduction 4

5 1. Introduction Musiktheater-in-Graz-A_ html?img=3&layout=galerie 5

6 1. Introduction Courtesy Huesker 6

7 1. Introduction Temple Ziggurat in Aqar Quf (Mesopotamia, near Bagdad) B.C. Vogt/TUM Stabilisation of foundation and brick walls with reed mats 7

8 1. Introduction &filetimestamp= Pantheon Rome Segment of the 116km long old Roman Eifel water-channel (1 cent. AD) Invention of Opus Caementitium - ancestor of concrete (1 century AD) 8

9 2. Applications Foundation cushion Steep slopes Bridge abutment Reinforcement of base course Embankments Railway and roadworks Pile foundation Bridging of sinkholes Applications of ground reinforcement 9

10 2. Applications Retaining wall with geogrids (Netlon LTD. UK) 10

11 2. Applications Courtesy Huesker 11

12 2. Applications Courtesy Huesker Slope stabilization in Trento Italy 12

13 2. Applications Foundation cushion Steep slopes Bridge abutment Reinforcement of base course Embankments Railway and roadworks Pile foundation Bridging of sinkholes Applications of ground reinforcement 13

14 2. Applications Bridge abutment at Ullerslev, Denmark, 1991 Maybe the first geogrid reinforced bridge abutment in Europe Courtesy Huesker Bridge abutment 14

15 2. Applications support construction Huesker Fortrac 140/30-30 MP precast concrete girder Huesker Fortrac 140/30-30 MP Geogrid reinforced construction w ith gabion facing First permanent bridge abutment in Germany with geogrid reinforced earth and gabion-facing Ilse bridge, non w oven fabric for separation gabion 80/15 0 Courtesy IBH Herold geogrids filling of reinforced area 0/45

16 2. Applications Foundation cushion Steep slopes Bridge abutment Reinforcement of base course Embankments Railway and roadworks Pile foundation Bridging of sinkholes Applications of ground reinforcement 16

17 2. Applications Courtesy Tensar Stabilization of a site road with geogrids combined with a nonwoven 17

18 2. Applications Courtesy Bräu Courtesy Bräu unreinforced reinforced Stabilization of a site road with geogrids in combination with a nonwoven fabric 18

19 2. Applications Courtesy Huesker Courtesy Huesker Courtesy Naue Courtesy Naue Use of geogrids and geotextiles over soft soil under the base course 19

20 2. Applications Foundation cushion Steep slopes Bridge abutment Reinforcement of base course Embankments Railway and roadworks Pile foundation Bridging of sinkholes Applications of ground reinforcement 20

21 2. Applications Paulinenaue: German Rail 2003 cross section with two geogrid layers Courtesy Huesker Embankment on cemented stone colums in soft soil 21

22 2. Applications Courtesy Huesker Courtesy Huesker Selby Bypass, UK, 2002 Mixed solution Geogrids FORTRAC M (PVA) & FORTRAC (PET) Courtesy Huesker Embankment on reinforced concrete piles in soft soil 22

23 2. Applications Geosynthetic encased sand-columns 23

24 2. Applications courtesy Möbius courtesy Möbius Manufacture of geosynthetic encased sand-columns courtesy Möbius 24

25 2. Applications Foundation of an embankment on geosynthetic encased sand columns land reclamation Deutsche Airbus, Mühlenberger Loch 25

26 2. Applications October 2001, courtesy Airbus Deutschland GmbH Land reclamation Airbus Mühlenberger Loch 26

27 2. Applications Foundation cushion Steep slopes Bridge abutment Reinforcement of base course Embankments Railway and roadworks Pile foundation Bridging of sinkholes Applications of ground reinforcement 27

28 2. Applications Collapse sink phenomena 28

29 2. Applications Highway A 143, Germany, 2004, Fortrac R 1200/ AM Courtesy Huesker Bridging of sinkholes with highstrength geogrids Courtesy Huesker 29

30 2. Applications coverage geogrid ringdyke tailings - pond Courtesy Naue Courtesy Naue Courtesy Naue Coverage of tailings-pond 30

31 3. Interaction Field test at a temporarliy abutment highway A8 (Germany) (Bräu a. Floss, 2000) Stability analysis (global) calculated: h = 1,4 measured: h >> 1,4 31 Enlargement of bearing capacity

32 3. Interaction Enlargement of Jablonec-Střelnice Stadium Jablonec nad Nisou - Střelnice Extensometr No.1 0,50% 0,40% =0,4% 2m over GL courtesy Herle Strain (%) 0,30% 0,20% 0,10% 4m over GL 10m over GL 2,0 4,0 7,0 10,0 0,00% Days (log scale) 3 years Strain - measurement with extensometers in different layers (Herle 2006) courtesy Herle 32 Reduction of deformations

33 3. Interaction reinforcement bar Q crack detail M theoretical stress distribution - + real load transfer T P complete bond l/2 l/2 bending moments Q l M = 4 Load transfer in a reinforced concrete beam 33

34 3. Interaction 1 deviatoric plane 1 = 2 = 3 O 3 D P metal 1 soil 1 limit state surface Z = Principal stress state 34

35 3. Interaction 1 deviatoric plane 1 = 2 = 3 isotropic path: high stresses, low deformation deviatoric path: approaching limit state, high deformation 1 O D P 3 m not possible possible stress-states favourable Z limit state surface 2 = 3 1 = 2 = 3 1 not possible 2 = Principal stress state 35

36 3. Interaction Large triaxial compression test apparatus (Ø 500mm) hydraulic plunger loading plate 3 (vacuum) elastic cover geogrids base course 0/45 H 1,1m measuring band DU D = 0,5m 36

37 3. Interaction 37

38 3. Interaction unreinforced reinforced Geogrids σ 1,unreinf. = σ 1,reinf. ε unreinf. >> ε reinf. 38

39 3. Interaction Radial Strains 39

40 3. Interaction Radial Strains 40 Confining Effect of the Reinforcement

41 3. Interaction Courtesy Naue increasing lateral pressure with increasing load without remarkable deformations Courtesy Huesker 41 Interlocking effect

42 3. Interaction courtesy Naue The effect of interlocking mechanism 42

43 3. Interaction Stress path for unreinforced triaxial testing (CD) σ 1 σ 1 [kn/m²] σ 3 σ 3 σ 1 σ 3 = σ c σ 3 [kn/m²] 43

44 3. Interaction Stress path for reinforced triaxial testing (CD) Δσ 1 σ 1 σ 1 [kn/m²] new failure point Δσ 3 σ 3 σ 3 σ 3 σ 3 Δσ 1 F reinf. F reinf. σ 1 σ 3 σ 3 [kn/m²] Δσ 1 Activation of the Reinforcement σ 3 : Additional Confining Effect σ 1 : Increase of the Load Bearing Capacity 44

45 3. Interaction failure point with reinforcement = tan failure point without reinforcement 3 3 +D D 1 45

46 3. Interaction Test Set-Up for the comparison of a unreinforced and a reinforced bearing layer 0,12m 0,12m Geogitter Geogrid Tragschicht Load Bearing Layer 0,2m Load Tragschicht Bearing Layer 2 x 0,1m Weichschicht Soft Soil Weichschicht Soft Soil 0,8m 0,8m 1,0m 1,0m 46

47 3. Interaction unreinforced reinforced bearing layer soft soil bearing layer soft soil geogrid Better Load Distribution leads to less loading of subsoil 47

48 3. Interaction Fundamentsetzung Footing Settlement [mm] [mm] Fundamentlast Footing Stress [kn/m²] [kpa] Ds 270 kpa unreinforced unbewehrt reinforced bewehrt Different settlements for unreinforced and reinforced subgrade at the same load 48

49 3. Interaction Stress paths under a runnning wheel Q v h v h =K a v v0 1 h =K 0 v v = h h0 h 49

50 3. Interaction Stress paths under a runnning wheel unreinforced subgrade Q D v D h1 v h v vq v0 1 2 h =K a v h =K 0 v v = h h0 hq h 50

51 3. Interaction unreinforced subgrade Stress paths under a runnning wheel reinforced subgrade Q D v D h1 geogrid v h v h v vq 2 h =K a v h =K 0 v v0 1 v = h v0 1 h0 hq h h0 h 51

52 3. Interaction unreinforced subgrade Stress paths under a runnning wheel reinforced subgrade Q Q D v D h1 geogrid D h2 > D h1 D v v h v h v vq 2 h =K a v h =K 0 v vq 2 v0 1 v = h v0 1 h0 hq h h0 hq h 52

53 3. Interaction Test Set-Up σ 1 = 50kPa Development and distribution of the earth pressure on the wall facing Kinematic behaviour of soil grains 53

54 3. Interaction Development of earth pressure -1/3 E a No extra deformation required for geogrid activation! 54

55 3. Interaction Digital Image Correlation (DIC) Particle displacements Particle rotations from: Tropea et al. (2008) 55

56 3. Interaction Sliding Planes rot. 0 Geogrids: unreinforced 56

57 3. Interaction Sliding Planes unreinforced 2 Geogrids 5 Geogrids increasing reinforcement 57 less soil moving less earth pressure!

58 3. Interaction DIC-results (detail section) horizontal displacements max 0 max. displacement no displacment (geogrid not connected to facing) 58

59 3. Interaction Corresponding kinematic model Zone of major failure planes Detail section Geogrids Primary sliding body Secundary sliding body unconfined soil (failure plane of unreinforced soil) 59

60 Illustration of the reinforcing effect 60 road blocks from: Univ.-Prof. Dr.-Ing. M. Ziegler

61 4. Summary and Conclusions Summary and conclusions - Ground reinforcement (with geosynthetics) is an effective way to increase the bearing capacity of different geotechnical constructions - Under equal load the deformations of a reinforced construction are much less than the ones of an unreinforced one -The increase in bearing capacity and the decrease in deformations can be explained by the change of the high deviatoric stress state in the unreinforced case to a more isotropic one in the reinforced state. - This change is caused by the interlocking effect of the geogrid which enables the increase of an equivalent confining stress without remarkable deformations. 61

62 Thank you for your attention Tests in Kyushu, Japan 62