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SUMMARY:Slopes: can centrifuge models contribute to improved design? - Pro
 fessor Malcolm Bolton\, Head\, Geotechnical and Environmental Group\, CUED
DTSTART:20090508T153000Z
DTEND:20090508T163000Z
UID:TALK17752@talks.cam.ac.uk
CONTACT:Zelda Stuck
DESCRIPTION:Geotechnical engineering research can span from science (How d
 oes the ground behave?)\, through technology (How can we intervene to impr
 ove things?) to the formation of Codes of Practice (What is best practice?
 )\, and ultimately to the development of national policies (What is sustai
 nable\, and can we afford it?).\n\nThe failure of slopes can have a severe
  impact on local communities and regional transport corridors. Examples in
 clude mining waste heaps\, and road or railway embankments. Two strands of
  centrifuge model research on the stability of slopes will be described. \
 n\nThe first relates to the catastrophic failure of uncompacted fill slope
 s subjected to heavy rainfall\, which are often described as liquefaction 
 flowslides. Examples include the 1966 catastrophe in Aberfan\, Wales\, whi
 ch killed 144 people\, and a number of failures in Hong Kong which used to
  take an annual toll of lives until their Geotechnical Engineering Office 
 took the matter in hand. Centrifuge models conducted here by GEO engineers
  seconded as MPhil students cast doubt on “static liquefaction” as the
  most probable mechanism\, and suggested an alternative. Of course\, new i
 deas are not easily digested by those who have been successful applying ol
 der ideas. But it is nevertheless the role of the University to suggest ne
 w guidelines based on new thinking.\n\nThe second strand of research relat
 es to the creep and progressive failure of clay slopes\, especially releva
 nt to road and railway embankments. The accepted mechanism of progressive 
 failure is the fatigue-like growth of a shear rupture along which the soil
  strength has dropped from its peak friction angle for dilatant shearing t
 o its residual friction angle for sliding on a polished surface. The avera
 ge soil strength along the failure surface at the point of a delayed failu
 re of this sort is generally found to be an intermediate value – given b
 y the critical state friction angle for turbulent shearing. Adherents of t
 he peak-residual concept regard this as a coincidence. Centrifuge tests co
 nducted by Andy Take in an atmospheric chamber indicated a quite different
  mechanism\, in which a large region of overconsolidated clay beneath a sl
 ope could incrementally soften towards its critical state angle of frictio
 n every time it had to mobilise any more than that value in a succession o
 f wet and dry seasons. This naturally points to the critical state angle a
 s the appropriate design value. This new evidence has proved to be controv
 ersial\, and the work has only recently been approved for publication subj
 ect to minor revisions. The main contribution to good design may be clarit
 y of thought.\n\nThe relevance in the field of new mechanisms found in a l
 aboratory can always be challenged. And the question of whether practise a
 nd policy can respond to research insights always remains open. But the dr
 ive to simplify and verify our understanding of geotechnical engineering r
 emains a strong motivation.\n\n
LOCATION:Engineering Department - LR6
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