Development in the field of Reinforced Earth Structures

Transcription

1 Development in the field of Reinforced Earth Structures Prof. Ivan Vaníček CTU Faculty of Civil Engineering Geotechnical Department 1

2 CONTENT 1. Basic principles of soil reinforcement 2. Typical examples of reinforced earth structures 3. Fundamental demands on reinforcing geosynthetics 4. Design of reinforced earth structures 5. Direction of new development 6. Conclusion 2

3 Basic principles of soil reinforcement timber, steel, concrete X soil (min. tensile strength) DEVELOPMENT mass concrete reinforced concrete prestressed concrete fibre-reinforced concrete Soil reinforced soil (macro-reinforcement) - pre-stressed reinforced soil - soil with randomly distributed reinforcement (micro-reinforcement) vaniceki@fsv.cvut.cz 3

4 MAIN EFFECT OF SOIL REINFORCEMENT a) Improvement of stability, bearing capacity of earth structure - shear plane passing through reinforcement zone - shear plane outside of reinforcement - cinematically more demanding b) Reduction of total and differential settlement - stiffness of reinforcement - involvement of large part of earth structure on load transfer vaniceki@fsv.cvut.cz 4

5 Typical examples of reinforced earth structures - Transport engineering Comparison of unreinforced and reinforced fill vaniceki@fsv.cvut.cz 5

6 Reinforced slope facing options Independent surface erosion protection element Surface erosion protection element from reinforcement wrap-around 6

7 Reinforcement (1) alternatives of the contact between fill (3) and basement / subsoil (2) vaniceki@fsv.cvut.cz 7

8 Road widening 8

9 Embankment widening 9

10 Noise protection bund 10

11 Bridge abutment 11

12 Retaining walls construction systems casing Concrete prefabricates - gabions casing Temporary supporting system vaniceki@fsv.cvut.cz 12

13 Construction steps of the reinforced wall used in Japan 13

14 Fundamental demands on reinforcing elements Tensile strength and maximum elongation at failure (strength for acceptable elongation) Shear strength of the contact Creep properties of reinforcing materials chemical mechanical resistivity 14

15 Polyester Polyvinylalcohol Aramid High strength for small elongation Excellent creep properties Product - geotextile - geogrids - geocells woven knitted woven extruded vaniceki@fsv.cvut.cz 15

16 TENSILE STRENGTH AND ELONGATION předepnutí Pre-stressed Reinforcing výztuha element Soil zemina ε 16

17 Tensile force T Stress strain behaviour of geosynthetic materials 100 mm f 200 mm d creep T f T f 1200 kn/m ε f 6-12 % T d Celkové Elongation přetvoření vaniceki@fsv.cvut.cz 17

18 Creep n nonstable creep neustálený creep ustálený creep stable creep b n 0 t = 0 + b log t Time t čas t a) b) log t log t vaniceki@fsv.cvut.cz 18

19 Creep coefficient b as a function of load level for basic polymers vaniceki@fsv.cvut.cz 19

20 Level of loading [%] Úroveň napětí [v % tahové pevnosti] Hellenic Geotechnical Society - Athens Creep ,1 h 1 h h 100 h 1000 h h h h Celkové protažení Elongation [%] a) polyester (geogrid Fortrac ) General condition for realized structures: <1% - retaining walls <0,5% - bridge abutments vaniceki@fsv.cvut.cz 20

21 Level of loading [%] Úroveň napětí [v % okamžité tahové pevnosti] Hellenic Geotechnical Society - Athens Creep hour 1 hodina month měsíc 1 year 1 rok 10 years 10 roků 120 roků 120 years Elongation Elongation [%] [%] Celkové protažení [%] b) Polypropylene vaniceki@fsv.cvut.cz 21

22 σ Shear strength along contact Sliding test Pull out test T tg gs tg T Geogrids vaniceki@fsv.cvut.cz 22

23 REINFORCED EARTH STRUCTURES DESIGN Limit state - Loss of overall stability or bearing capacity - Deformation including creep which can cause - lost of serviceability of structure - structural damage of surrounding structures - Surface erosion - Internal erosion - Uplift vaniceki@fsv.cvut.cz 23

24 EC 7 3 G Categories LIMIT STATE DESIGN APPROACH: Numerical modelling different numerical methods Laboratory modelling - centrifuge (Porhaba, Goodings 1996) - stereofotogrammetry (Vaníček 1978, 1980) Modelling 1:1 real structures approval future utilization - analogy vaniceki@fsv.cvut.cz 24

25 Classical methods NUMERICAL MODELLING Stress-strain numerical methods FEM (1 SLS+1 ULS) - deformation Stability (LEM) - ULS Deformation (1D, 3D) - SLS - state of stresses local failures vaniceki@fsv.cvut.cz 25

26 LIMIT STATE OF DEFORMATION From experience / previous projects Estimation according to the accepted elongation of reinforcing elements Laboratory simulation models FEM Classical methods s calc. s real (without reinforcement) vaniceki@fsv.cvut.cz 26

27 Limit equilibrium methods sit. n. c. fai. S act,in stp. fpj. S pas,jn simplified case: LIMIT STATE OF STABILITY S pas,jn / S act,in n / stp S pas,jn / S act,in 1,22-1,33 n - structure significance 1,1-1,2 (risk factor) stp - stability calculation 0,9 (model factor) vaniceki@fsv.cvut.cz 27

28 Soils d, c d Reinforcing element DESIGN STRENGTH T d F tc F comp T F f env F mat F ost, where Partial factors of safety for different standards: Standard F comp F env F tc F mat F ost PET PP PE FHWA (USA) 1,25-3 1,1-2 2,5 5 1,5 - CFGG (F) 1,1-1,5 1,1 2,5 4,5 1,2 - Gourc (F) (NFP 38064) 1,1-1,5 1,1 2,25 4,5 - - DGGT (D) 1,1-1,5 1,1 2,5 4 1,75 - Polyfelt 1,3-1,5 1, ,2 - TP 97 (1997) + ČD (CZ) 1,1-1,5 1,1 2,5 4,5-1,22-1,33 vaniceki@fsv.cvut.cz 28

29 Reinforcement implementation into limit equilibrium methods O O R y T D T D T D y a) b) T D R c) Assumptions for reinforcement implementation into stability calculation a) Moment from T d on lever-arm y (variable) b) Moment from T d on radius R (constant) c) Additional inter-slice force (variable effect) vaniceki@fsv.cvut.cz 29

30 Shear plane passing through reinforcing elements - Internal stability smyková plocha Shear plane } Zone oblast of vyztužení reinforcement vaniceki@fsv.cvut.cz 30

31 Shear plane passing outside of zone of reinforcement - External / overall stability } oblast Zone of vyztužení smyková plocha Shear plane reinforcement vaniceki@fsv.cvut.cz 31

32 Shear plane passing outside of zone of reinforcement - External / local stability smyková plocha Shear plane } Zone oblast of vyztužení reinforcement vaniceki@fsv.cvut.cz 32

33 Critical cases for retaining wall - Internal stability Failure of reinforcing element (overstressing) Pull out Buckling of facing elements vaniceki@fsv.cvut.cz 33

34 Critical cases for retaining wall - External stability Sliding Overturning Loss of Overall bearing capacity stability vaniceki@fsv.cvut.cz 34

35 Method of Janbu software SVARG / GEO4 Limit state equilibrium method General slip surface Automatic determination of design parameters for soil and reinforcing elements Automatic search for the most critical slip surface Automatic control of anchoring length vaniceki@fsv.cvut.cz 35

36 PROBLEMS: FEM Reinforcing element modeling thickness is very small leading to enormous number of elements Modeling of interaction of the contact soil reinforcing element Brown + Poulos (1978) Rowe + Ho (1988) - Composite models - Discrete models vaniceki@fsv.cvut.cz 36

37 FEM Karpurapu + Bathurst (1994) More general constitutive models for soil Special finite elements for contacts: soil reinforcing element soil facing vaniceki@fsv.cvut.cz 37

38 Directions of new development a) Prestressed reinforced earth structures b) FEM inclusion of creep for geosynthetic reinforcement 38

39 Hellenic Geotechnical Society - Athens Directions of new development c) Randomly distributed short synthetic fibres Relative shear stresses Extreme relative shear stress 1,00 vaniceki@fsv.cvut.cz 39

40 Directions of new development d) Monitoring of strength strain behaviour of geosynthetics in Earth structures 40

41 Practical examples RW reconstruction 41

42 Practical examples RW reconstruction 42

43 Practical examples - Overturning vaniceki@fsv.cvut.cz 43

44 Practical examples - Overturning vaniceki@fsv.cvut.cz 44

45 Practical examples - Overturning vaniceki@fsv.cvut.cz 45

46 Practical examples - Overturning vaniceki@fsv.cvut.cz 46

47 Practical examples - Overturning vaniceki@fsv.cvut.cz 47

48 Practical examples - Overturning vaniceki@fsv.cvut.cz 48

49 Practical examples earthquake Koseki 2010 Embankment ma h (Horizontal inertia due to earthquake) Embankments Resultant body force mg (Self weight, g=980 gal) Increase in driving moment Reinforcements Mobilized tensile force Increase in resisting moment vaniceki@fsv.cvut.cz 49

50 Koseki Hyogoken-Nanbu Earthquake Residual disp cm Could be re-used with minor repair No deep foundation GRS RW with FHR facing at Tanata site vaniceki@fsv.cvut.cz 50

51 Koseki - 3 vaniceki@fsv.cvut.cz 51

52 Koseki - 4 Response of GRS RW (R2) model in 1.1 g shaking vaniceki@fsv.cvut.cz 52

53 Koseki - 5 vaniceki@fsv.cvut.cz 53

54 Reinforced soil: CONCLUSION Structure containing two very different materials with sensitive interaction (composite materials) Application of limit state design Deformation Significance of monitoring 54