TC211 Workshop CALIBRATION OF RIGID INCLUSION PARAMETERS BASED ON. Jérôme Racinais. September 15, 2015 PRESSUMETER TEST RESULTS

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1 Jérôme Racinais September 15, 215 TC211 Workshop CALIBRATION OF RIGID INCLUSION PARAMETERS BASED ON PRESSUMETER TEST RESULTS

2 Table of contents 1. Reminder about pressuremeter tests 2. General behaviour of rigid inclusions 3. Rigid inclusions design based on Finite Elements Models 4. Semi-empirical mobilization laws of 5. Calibration of FEM input parameters on s laws 6. Example: Plate Load Tests in Venette, France 7. Conclusion Jérôme RACINAIS 2/23

3 1. Reminder about pressuremeter tests Determination of E m and p l V V S : initial volume of probe V S + 2V 1 Reloading after hole preparation Pseudo-elastic range Plastic behaviour Pressuremeter curve V 2 (V 1 + V 2 ) /2 E m V 1 Creep curve p 1 p 2 p l p E m = ν V S + V 1 + V 2 2 p 2 p 1 V 2 V 1 Jérôme RACINAIS 3/23

4 2. General behaviour of rigid inclusions q Q P () Q P () Load transfer platform q S q S Q P (z) Rigid inclusions Soft soil hc N F N N Q max = Q P () + F N F P Dense soil z Q P (L) z Q P (L) Load-bearing layer Q P () + F N = Q max = F P + Q P (L) Jérôme RACINAIS 4/23

5 3. Rigid inclusions design based on Finite Element Models Jérôme RACINAIS 5/23

6 3. Rigid inclusions design based on Finite Element Models Use of linear elastic perfectly plastic law with Mohr-Coulomb s failure criterion Main basic parameters Young s modulus E Y Poisson s ratio ν Unit weight γ Effective cohesion c Effective friction angle φ Which values should be input? E Y = E m α? c and φ determined from lab tests? Jérôme RACINAIS 6/23

7 4. Semi-empirical mobilization laws of Frank and Zhao Behaviour at the inclusion bottom Stress at the inclusion bottom Limit value of end-bearing pressure of an inclusion (determined in this case based on pressuremeter method) q s b s b Vertical displacement of the inclusion bottom k q = 11E M B for fine-grained soils, k q = 4.8E M B for granular soils B : inclusion diameter Jérôme RACINAIS 7/23

8 4. Semi-empirical mobilization laws of Frank and Zhao Estimation of the limit end-bearing pressure: q b (as per Appendix F of Standard NF P94-262) q b = k p p le p le * : equivalent net limit pressure into the anchoring layer k p : pressuremeter bearing factor 4 Inclusion with soil displacement a = max B ;.5 =.5 m 2 b = min a; h =.5 m p le = 1 D+3a p b + 3a l z dz D b k p D ef /B Clay, Silt, Transitional soils Sand, Gravel, Transitional soils Chalk Marl, Marly limestone, Weathered and fragmented tock 3 Inclusion with soil extraction 2 k p D ef = 1 p le D D h D p l z dz h D = 1B (is comprised between 3 m to 4.2 m) Clay, Silt, Transitional soils Sand, Gravel, Transitional soils Chalk, Marl, Marly limestone Weathered and fragmented tock D ef /B Jérôme RACINAIS 8/23

9 4. Semi-empirical mobilization laws of Frank and Zhao Behaviour along the interface soil/inclusion Skin friction Limit value of skin friction (determined in this case based on pressuremeter method) s s-i s s-i Relative displacement soil-inclusion k τ = 2E M B for fine-grained soils, k τ =.8E M B for granular soils B : Inclusion diameter Jérôme RACINAIS 9/23

10 q s [kpa] q s [kpa] 4. Semi-empirical mobilization laws of Frank and Zhao Estimation of the limit skin friction: q s (as per Appendix F of Standard NF P94-262) q s = min α pieu sol f sol p l ; q s;max α pieu-sol : dimensionless parameter depending on pile type and soil type f sol : function depending on soil type and p l* value 25 Inclusion with soil displacement 25 Inclusion with soil extraction p l * [MPa] Clay, Silt, Transitional soils Transitional soils predominantly sandy or gravelly Sand, Gravel Chalk Marl, Marly limestone p l * [MPa] Clay, Silt, Transitional soils Transitional soils predominantly sandy or gravelly Sand, Gravel Chalk Marl, Marly limestone Jérôme RACINAIS 1/23

11 Load at the inclusion bottom Load at the inclusion bottom Load at the inclusion bottom Skin friction Skin friction Skin friction 5. Calibration of FEM input parameters on s laws Skin friction (along the inclusion in surrounding soil) increase increase Relative displacement soil-inclusion Relative displacement soil-inclusion Relative displacement soil-inclusion Effective cohesion c Friction angle φ Young s modulus E Y Load at the inclusion bottom (in the anchoring layer) vs Plaxis vs Plaxis vs Plaxis increase increase increase Vertical displacement of the inclusion bottom Vertical displacement of the inclusion bottom Vertical displacement of the inclusion bottom Effective cohesion c Friction angle φ Young s modulus E Y Jérôme RACINAIS 11/23

12 5. Calibration of FEM input parameters on s laws E Y = E m /α c = q s (q s determined based on pressuremeter method) φ E Y = 1.5 to 6 x E m /α c = q b /9 (q b determined based on pressuremeter method), API (1991) φ Jérôme RACINAIS 12/23

13 6. Example: Plate Load Tests in Venette, France Pressuremeter tests E m Pl α γ c φ MPa MPa - kn/m 3 kpa 1 m Existing fill / m Soft silts / m Sands and gravels / From lab tests Jérôme RACINAIS 13/23

14 6. Example: Plate Load Tests in Venette, France Presentation of the finite element model initial parameters Skin friction Inclusion bottom behaviour γ c φ E Y R inter [kn/m 3 ] [kpa] [ ] [MPa] [-] Fill = E M /α = 3 1 Silts = E M /α = 11 1 Interface Sands = E M /α = 15 1 Inclusion 32 mm diameter 5 cm anchoring length Existing fill q s = 8 kpa Soft silts q s = 6 kpa γ c φ E Y [kn/m 3 ] [kpa] [ ] [MPa] Sands = E M /α = 15 Sands and gravels q s = 17 kpa q b = 5.8 MPa Based on pressuremeter method Jérôme RACINAIS 14/23

15 Load at the inclusion bottom [kn] 6. Example: Plate Load Tests in Venette, France Load test curve with initial parameters Comparison with Frank and Zhao s mobilization laws vs Plaxis Plaxis - initial parameters Vertical displacement of the inclusion bottom [mm] At inclusion bottom Jérôme RACINAIS 15/23

16 Load at the inclusion bottom [kn] Skin friction [kpa] 6. Example: Plate Load Tests in Venette, France Load test curve with initial parameters Comparison with Frank and Zhao s mobilization laws vs Plaxis Plaxis - initial parameters Vertical displacement of the inclusion bottom [mm] At inclusion bottom vs Plaxis (example for silt) Plaxis - initial parameters m deep Plaxis - initial parameters - 3 m deep Relative displacement soil-inclusion [mm] Along interface soil/inclusion Jérôme RACINAIS 16/23

17 Cumulated settlement [mm] Load at the inclusion bottom [kn] Skin friction [kpa] 6. Example: Plate Load Tests in Venette, France Load test curve with initial parameters Comparison with Frank and Zhao s mobilization laws vs Plaxis Plaxis - initial parameters Vertical displacement of the inclusion bottom [mm] At inclusion bottom adjust modelling parameters to calibrate the Plaxis curve on Frank & Zhao s semi-empirical laws vs Plaxis (example for silt) Plaxis - initial parameters m deep Plaxis - initial parameters - 3 m deep Relative displacement soil-inclusion [mm] Along interface soil/inclusion Curve Load / deformation Plaxis - initial parameters Load [kn] At inclusion head Jérôme RACINAIS 17/23

18 6. Example: Plate Load Tests in Venette, France Calibrated parameters Skin friction γ c φ E Y R inter [kn/m 3 ] [kpa] [ ] [MPa] [-] Fill Silts Interface Sands Fill Silts Inclusion bottom behaviour γ c φ E Y [kn/m 3 ] [kpa] [ ] [MPa] Sands x E M /α, 1.5 x E M /α, 3 x E M /α? Sands Jérôme RACINAIS 18/23

19 Load at the inclusion bottom [kn] 6. Example: Plate Load Tests in Venette, France Load test curve with calibrated parameters Comparison with Frank and Zhao s mobilization laws vs Plaxis Plaxis - initial parameters Plaxis - calibrated parameters 1xEm/α Plaxis Plaxis - - initial calibrated parameters parameters 1.5xEm/α Plaxis --calibrated parameters 1.5xEm/α 3xEm/α Vertical displacement of the inclusion bottom [mm] At inclusion bottom γ c φ E Y [kn/m 3 ] [kpa] [ ] [MPa] Sands = 1.5 x E M /α = Jérôme RACINAIS 19/23

20 Load at the inclusion bottom [kn] Skin friction [kpa] 6. Example: Plate Load Tests in Venette, France Load test curve with calibrated parameters Comparison with Frank and Zhao s mobilization laws vs Plaxis Plaxis - initial parameters Plaxis - calibrated parameters 1xEm/α 1 Plaxis Plaxis - - initial calibrated parameters parameters 1.5xEm/α 5 Plaxis --calibrated parameters 1.5xEm/α 3xEm/α Vertical displacement of the inclusion bottom [mm] At inclusion bottom vs Plaxis (example for silt) Plaxis - initial parameters m deep Plaxis - initial parameters - 3 m deep Plaxis - calibrated parameters Relative displacement soil-inclusion [mm] Along interface soil/inclusion γ c φ E Y [kn/m 3 ] [kpa] [ ] [MPa] Sands = 1.5 x E M /α = Jérôme RACINAIS 2/23

21 Settlement (mm) Load at the inclusion bottom [kn] Skin friction [kpa] 6. Example: Plate Load Tests in Venette, France Load test curve with calibrated parameters Comparison with Frank and Zhao s mobilization laws vs Plaxis Plaxis - initial parameters Plaxis - calibrated parameters 1xEm/α 1 Plaxis Plaxis - - initial calibrated parameters parameters 1.5xEm/α 5 Plaxis --calibrated parameters 1.5xEm/α 3xEm/α Vertical displacement of the inclusion bottom [mm] At inclusion bottom γ c φ E Y [kn/m 3 ] [kpa] [ ] [MPa] Sands = 1.5 x E M /α = vs Plaxis (example for silt) Plaxis - initial parameters m deep Plaxis - initial parameters - 3 m deep Plaxis - calibrated parameters Relative displacement soil-inclusion [mm] Along interface soil/inclusion Curve load / deformation Plaxis - initial parameters Plaxis - calibrated parameters Load (kn) At inclusion head Jérôme RACINAIS 21/23

22 Settlement (mm) 6. Example: Plate Load Tests in Venette, France Load test curve with calibrated parameters Comparison with insitu load test Curve load / deformation Plaxis - initial parameters Plaxis - calibrated parameters In-situ load test Load at inclusion head (kn) Jérôme RACINAIS 22/23

23 7. Conclusion Classical determination of the FE input parameters is often very conservative The calibration of the input parameters on the empirical curves from allows to better simulate the rigid inclusion behaviour The curves require the use of the pressuremeter test parameters E m et p l Three modelling parameters need to be calibrated: Effective cohesion Effective friction angle Young s modulus Thank you for your attention Jérôme RACINAIS 23/23