1. 15th ICSMFE: Workshop #7 organised by TC2 Centrifuge Testing Some Achievements and Challenges Malcolm Bolton Cambridge 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 swinging platform motor slip rings Acutronic 661 Centrifuge model container perspex window camera lights swinging platform swing hangers tunnel clay sample with targets on front surface

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

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

11. After 2 Shakes Before 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

16. 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…..