FULL SCALE PILE TESTING RANDERS HARBOUR

Transcription

1 FULL SCALE PILE TESTING RANDERS HARBOUR A study into the influence of bitumen coating on the development of negative skin friction on driven concrete piles

2 CONTENT Introduction and Background Full Scale Pile Test Setup In-situ Monitoring Supplementary Lab Tests Results and Interpretation of Field Data Preliminary Conclusions

3 INTRODUCTION AND BACKGROUND

4 NEGATIVE SKIN FRICTION / DOWN DRAG Results from relative settlement between pile and soil Neutral point Increases the load in the pile and the settlement of the pile Briaud and Tucker1996 Development of shaft resistance and settlement profile of pile/soil

5 INFLUENCE OF BITUMEN COATING Current Danish practise 1mm bitumen 10 kn/m 2 (max. 75% reduction), undrained analysis Guideline in the Danish foundation code of 1984 / not mentioned in Eurocode 7! Previous case studies (none DK): typically >80% reduction in skin friction with bitumen coating Bitumen: viscous material / shear strength is rate dependent Coating of concrete pile with bitumen at Centrum Pæle A/S

6 PROJECT DESCRIPTION Study and document the influence of bitumen coating on the development of negative skin friction in relation to driven concrete piles in soft soils Timeline: Jan Project start Jan. Aug 2013 Preliminary study Sep. Nov Design test setup Nov Full-scale setup June 2014 Loading of ground level Field monitoring

7 FULL SCALE PILE TEST SETUP

8 TEST LOCATION Test site Map data 2015 Google

9 GROUND CONDITIONS AND SOIL PROPERTIES Layer thickness Soil type m FILL, clayey 6.5 to 9.5 m GYTJA, Ma. P.g. >5.5 to 8 m SAND, with gravel, Ma. P.g. Artesian water in sand: (~ +1.0 m. above g.l.), Ground level: ~ 0 m.o.d Soil layer CPT q c / f s [MPa] c fv [kpa] FILL (71) GYTJA 0.15 / (17) c v [m 2 /s] g [kn/m 3 ] w [%] C ce [%] (6*10-8 ) (14) (95) (27) SAND

10 FIELD TEST LAYOUT FILL GYTJA SAND Driven concrete piles: 0.25x0.25 m 2 Test piles T1 & T3 are coated with bitumen Reaction piles are embedded in sand Cross-section of setup and ground conditions prior to terrain loading Terrain loading m fill (additional) - ~ 16 kpa T4 T3 (B) T2 T1 (B) R5 R4 R3 R2 R1 ~16 m c/c 3 m Field test layout

11 FULL SCALE PILE TEST SETUP Full-scale setup before terrain loading Free hanging test pile

12 SIMPLIFIED FORCE SYSTEM F P F load cell t neg F NEG = F load cell - G pile F NEG Free hanging test pile

13 IN-SITU MONITORING

14 INSTRUMENTATION FILL GYTJA SAND Monitoring equipment: Piezometers (4) Magnetic Extensometer (4) Settlement plates (3) Pile strain gauges (16) T4 T3 (B) T2 T1 (B) R5 R4 R3 R2 R1 ~16 m c/c 3 m Magnetic Extensometer VW Multipoint Strain gauge VW Settlement piezometer plate

15 SUPPLEMENTARY LAB TESTING

16 SOIL AND PILE PARAMETERS Interface direct shear testing: Interface friction between pile and soft soil (6 tests) Tension tests on reinforced pile sections: E-modulus (2 tests) 1D consolidation tests on gytja: deformation and consolidation parameters (7 tests)

17 STRENGTH AND DEFORMATION BEHAVIOUR OF CEMENT BENTONITE GROUT Strength development and stress-strain behaviour Lab vane tests (4 tests) Fall cone tests (67 tests) UU triaxial tests (99 tests) CU triaxial tests (13 tests) 1D compression behaviour IL consolidation tests (9 tests) Permeability (Summer and Autumn 2015 ) Falling head permeability tests Permeability testing using triaxial cell Microstructure (Autumn 2015 ) SEM photos

18 RESULTS AND INTERPRETATION OF FIELD DATA

19 Excess pwp [kpa] Settlement [mm] SETTLEMENT AND EXCESS POREWATER PRESSURE -10 Time [days] after loading Extensometer measurements Depth 10.1m Depth 7.1 m Depth 4.1 m Depth 1.1 m Settlement: Indicate stiff reloading behaviour Approx. linear in log time after 6 days Little settlement below 7 m depth Excess pore water pressure: Max. observed 0-6 days after loading Gradual reduction Depth 1.5 m Depth 4.5 m Depth 7.5 m Consolidation time: Observed: approx. 260 days? Predicted: > 2 yrs (up to 10 yrs) Time [days] after loading

20 T1&T2 T3&T4 Depth [m] Depth [m] SETTLEMENT AND POREWATER PRESSURE Relative settlement [mm] Fill 2 Gytja Loading day 0 Loading day +6 Loading, day +315 Sand Pore water pressure [KPa] Fill Gytja Sand Hydrostatic water pressure Installation, day +223 / loading day 0 Max pressure after loading, day +0-6 Loading, day +315 Non-hydrostatic water pressure profile Influence on negative skin friction: Little relative settlement around lower end of piles, i.e. t max (drained) will gradually increase due to consolidation t mob < t max and F neg,mob < F neg,max

21 Total down drag force [kn] NEGATIVE SKIN FRICTION / DOWN DRAG Time [days] after loading No coating T1 T3 T2 T4 Significant reduction seen in total down drag force due to bitumen coating Similar change in down drag force seen immediately after terrain loading on all test piles (14-18 kn) Max. down drag force on uncoated piles is still increasing! F neg, measured < F neg, calc based on c u Bitumen coated Test pile no. F neg +1 yr [kn] Mob. t neg +1 yr [kn/m 2 ] No T2 & T4 > > 5-9 Yes T1 & T Ratio F neg.coated / F neg.uncoated < % F Neg, calc. undrained [kn] F Neg, calc. drained [kn]

22 Total down drag force [kn] Total down drag force [kn] NEGATIVE SKIN FRICTION / DOWN DRAG Settlement in top layer [kpa] Avr. excess pwp in top layers [kpa] Bitumen 10 coated T1 T3 T2 No coating Data after loading from day +6 to day +315 T4 T1 T3 T2 T4 Changes in down drag force are seen to be proportional to changes in excess pore water pressure / effective normal stress on the pile (uncoated)

23 Microstrain [-] DTotal down drag force [kn] INTERNAL PILE STRAINS Tension Time [days] after loading Test pile 1 1m depth 3m depth 6m depth 9m depth Strongly influenced by shrinkage of concrete difficult to interpret! Bitumen coating allows more shrinkage Elastic behaviour observed after terrain loading (day 0 to 6) Data after loading from day 0 to day +6 Dmicrostrain_top level in pile [-] T3 T2 T1-10 Range of E from tension test on test specimens

24 T1&T2 T3&T4 Depth [m] INTERNAL PILE STRAINS_DERIVED SKIN FRICTION Avr. change in mob. negative skin friction [kn/m 2 ] Fill Gytja 2 4 Tension 6 T1 T2 T3 T4 8 Compression Sand Data immediately after loading (day 0) Immediately after loading; tension in top part (t mob 4-6 kn/m 2 ~residual strength) and compression in bottom part coated piles.

25 PRELIMINARY CONCLUSIONS Bitumen coating has significant effect >80% reduction The negative skin friction appears to be controlled by the consolidation of the soil surrounding the pile If coated, the negative skin friciton is also significantly influenced by the rate of loading (due to viscous properties of bitumen) The negative skin friction may be significantly overestimated - when using undrained parameters! (use either drained parameters or reduced undrained maybe r=0.4) Observations continue conclusions may be subject to change!

26 ACKNOWLEDGEMENTS Previous BSc. students at Aarhus School of Engineering; Glen K. Nielsen Casper S. Jensen Elin H. Myhrman Mikkel J. Nielsen Current BSc. students at Aarhus School of Engineering; Jesper A. Haugaard Emil S. Brandt Nikolaj B. Nielsen Per Aarsleff A/S, Centrum pæle A/S Randers Havn Stevedore Randers Aps COWI A/S

27 Thanks for listening! Any questions? 28 MAJ 2015

28 THE GEOTECHNICAL RESEARCH NAVITAS Soil element testing Stress path triaxial (2), Direct shear (2), IL oedometer (9+), CRS oedometer (2), CBR (1), permeability (2) m.m. Field testing/monitoring Inclinometer, in-situ monitoring of pore pressure, settlement, pile strains etc. Numerical Analysis Plaxis 2D/3D, OASYS suite, WINSPOOKS Page 28