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15th ICSMFE: Workshop #7 organised by TC2 Centrifuge Testing Some Achievements and Challenges Malcolm Bolton Cambridge U

15th ICSMFE: Workshop #7 organised by TC2 Centrifuge Testing Some Achievements and Challenges Malcolm Bolton Cambridge University. What are the “unique selling points” of centrifuge testing?. Cheap replication of the response of geo-structures Weight-induced stresses; gradients and rotations

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15th ICSMFE: Workshop #7 organised by TC2 Centrifuge Testing Some Achievements and Challenges Malcolm Bolton Cambridge U

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  1. 15th ICSMFE: Workshop #7organised by TC2Centrifuge TestingSome Achievements and ChallengesMalcolm BoltonCambridge University

  2. What are the “unique selling points” of centrifuge testing? • Cheap replication of the response of geo-structures • Weight-induced stresses; gradients and rotations • Coupling of intergranular and pore fluid pressures • Access to severe distortions, drainage of clay, 3D • Realistic boundary conditions; • free surface, cracks • soil-structure compatibility • seismic shaking

  3. Some achievements: actuators • CITY University tunnelling kit • TIT excavator • NUS compaction sand piler • UWA-COFS drag anchor deployment • TUD wave generator • CCORE static liquefaction actuator • UCD earthquake simulator • CU-SC atmospheric chamber

  4. CITY U. tunelling slip rings swinging platform motor Acutronic 661 Centrifuge model container clay sample with targets on front surface swinging platform swing hangers perspex window camera lights tunnel

  5. 3D Surface settlements from digital image analysis (a) left camera (b) centre camera (c) right camera

  6. TIT excavator

  7. (a) Casing and sand hopper. (a) SCP model on centrifuge. Figure 16a – b. In-flight SCP installer. NUS sand piler

  8. UWA - COFS drag anchor deployment

  9. TUD wave generator

  10. Liquefaction Event Geometry and Instrumentation Settlement Gauge Piezometer Clay Embankment Contained Compacted Sand DAS Sand BBW Sand Deposit BAW Sand Deposit Tilt Sections CANLEX CCORE static flowslide actuator

  11. Before After 2 Shakes UCD earthquake shaker

  12. Some challenges • Replicating the mechanics of processes • Broadband data stream to characterise soil response • Realistic soil profiles - grading, layering, OCR etc • Assessment of size and rate effects • The atmospheric boundary condition

  13. Atmospheric loading of embankments: boundary conditions

  14. Atmospheric loading of embankments: boundary conditions

  15. Atmospheric loading of embankments: boundary conditions

  16. Atmospheric loading of embankments: pore water pressures

  17. Atmospheric loading of embankments: pore water pressures

  18. Atmospheric loading of embankments: pore water pressures

  19. Atmospheric loading of embankments: cyclical deformations

  20. Modes I and II fracture mechanics

  21. PIV reveals slope deformation mechanisms And remember - this was not “collapse”

  22. Rubblisation

  23. Discussion point • We must not make complex models just for fun • Our task is to reproduce essential complexity • And then observe events intensively • Ground layering is sometimes essential • Anisotropy may be essential, and is automatic • Construction process is essential • In clays, the atmospheric boundary may be essential • We need to make simple mechanistic models • Numerical simulation would be useful but lags behind, and can not therefore be considered essential…..

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