On Rate-Dependency of. Gothenburg Clay

Transcription

1 On Rate-Dependency of Gothenburg Clay Mats Olsson Chalmers/NCC Teknik 1

2 Background & Introduction Mats Olsson Outline MAC-s model (anisotropic creep model) New K 0 - triaxial cell Results & Simulations 2 Conclusions

3 Background On-going settlement 7 cm/yr 3

4 Introduction This research has the following: Aims Extend the understanding of Rate- Dependency of soft soils Reduce uncertainties in predicting longterm settlements Objectives To develop and test a new constitutive creep model and a new K 0 -triaxial cell Limitations Model formulation restricted to monotonic loading conditions 4

5 Introduction Behaviour of soft soils Oedometer case Leroueil et al. (2005) Mats Olsson 5

6 Introduction Evaluation of p c from CRS test Swedish standard 0,0024 mm/min Mats Olsson 6

7 Introduction Comparison - CRS and IL 7

8 Undrained triaxial tests Introduction Behaviour of soft soils Leroueil et al. (2005) Länsivaara (1999) Mats Olsson 8

9 Introduction Constitutive models Without creep effects Modified Cam-Clay Model S-CLAY1S (Roscoe & Burland, 1968) (Wheeler et al., 1999, Karstunen et al., 2005) Mats Olsson 9

10 Introduction Constitutive models With creep effects Isotropic Soft Soil Creep model (Vermeer et al., 1998) n-sac model (Grimstad & Degago 2010) CREEP-SCLAY1S (Karstunen et al., 2013) Mats Olsson 10

11 Modified Anisotropic Creep Model with structure (MAC-s model) MAC-s model aims to improve the prediction in OC state by formulating a new flexible normal compression surface (NCS) n-sac => visco-plastic multiplier S-CLAY1S => hardening laws Implemented in FE code COMSOL Multiphysics (today also Plaxis) Mats Olsson 11

12 Influence of parameters 12

13 Influence of parameters 13

14 Model performance 14

15 Model performance 15

16 Model performance 16

17 Model performance 17

18 New K 0 -triaxial cell Input parameters for advanced constitutive models such as MAC-s Strength parameters - Triaxial tests Deformation parameters Oedometer tests (IL/CRS) Creep parameters IL Oedometer K nc 0 new K0 -triaxial cell Mats Olsson 18

19 New K 0 -triaxial cell Measure K 0 value as a function of stress and strain Incremental loading Deformation gauge control zero radial deformation Mats Olsson 19

20 Results & Simulations Performance of the MAC-s model compared to experimental data Stepwise IL oedoemeter Undrained triaxial test Undrained triaxial test OCR=4 Drained p -q stress path tests Experimental results from K 0 -triaxial cell Stress-strain K 0 -time p -q stress path K 0 -normalized stress 20

21 Results & simulations Vertical effective stress (kpa) CC m Time (hr) MAC s Model 5 MAC s Model 5 CC m Axial strain (%) Axial strain (%) Mats Olsson 21

22 Results & simulations 22

23 Results & simulations 23

24 Results Drained p -q stress path tests (constant K 0 ) MAC-s model K = 0.4-5m K = m K = m K = m K = m oedotriax_5m oedotriax_15m failure line 32 deg K = 0.4-5m K = m K = m q/ vc,crs (kpa) K = m K = m p / vc,crs (kpa) Mats Olsson 24

25 Results K 0 triaxial cell 2 tests Depth 5 m and 15 m Conducted in room temperature Index properties depth :5 m w w N L (t/m ) 68% 67% depth :15 m w w N L (t/m ) 78% 70% CC5001 Re.5m CC5001 Re.20m CC5001 5m CC m CC m CC m CC m CC m CH m CH m CH m CH m CH m HH m HH m HH m HH m HH m CH Normalized stress ( / vc,crs ) 17m Creep number, r Mats Olsson 25

26 0% 5% 10% 15% 20% 25% 30% Results K 0 triaxial cell Vertical effective stress (kpa) K0 triax 5m IL test 5m CRS 5m 0% 5% Vertical effective stress (kpa) K0_triax_15m IL test 15m CRS test 15m 10% 15% 20% 25% 26 30% Axial strain, a ( ) Axial strain, a ( ) Depth: 5 m Depth: 15 m

27 Results - K 0 triaxial cell 27

28 Results - K 0 triaxial cell 28

29 Results - K 0 triaxial cell K0_triax 5m sample K0_triax 15m sample 1.2 unload 5m sample reload 5m sample Normalized stress ( v/ vc ) 29 K0

30 Results - Comparison K 0 K0_triax 5m sample K0_triax 15m sample unload 5m sample reload 5m sample Data from Kullingsjö (2007) depth 8m Data from Sällfors (1975) Test C7 4 depth 7m Normalized stress ( v/ vc ) 30 K0

31 Results - Comparison K 0 Predicted with MAC s model K0_triax 5m sample K0_triax 15m sample unload 5m sample reload 5m sample Data from Kullingsjö (2007) depth 8m Data from Sällfors (1975) Test C7 4 depth 7m Normalized stress ( v/ vc ) 31 K0

32 Conclusions A modified creep model with a versatile normal compression surface A newly developed K 0 -triaxial cell The evaluated K nc 0 value is in a range of (Gothenburg Clay) 32

33 Recommendations More experimental testing For validating the model formulation For gathering more data on K nc 0 values for soft soils With load reversals to capture the soils unload and reload behaviour To establish the intrinsic properties of Gothenburg Clay Improve the model to incorporate a small strain formulation 33

34 Financial sponsors, who are greatly acknowledged for their support. 34