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SUMMARY:Monitoring and Numerical Modelling of a Deep Circular Excavation -
  Tina Schwamb
DTSTART:20131128T160000Z
DTEND:20131128T170000Z
UID:TALK47408@talks.cam.ac.uk
CONTACT:Jen Fusiello
DESCRIPTION:The high uncertainty in current design practice of deep circul
 ar excavations may lead to overdesign or underdesign. For the estimation o
 f ground movements New and Bowers’ (1994) empirical formula is used – 
 this has not been confirmed by other studies and is based on specific grou
 nd conditions and geometry. Circular excavations rely on the beneficial ho
 op forces and are therefore structurally stable. However\, very deep shaft
 s are often built with diaphragm walls which are of discontinuous nature 
 – this may reduce the circumferential stiffness and hence influence the 
 excavation's overall performance.\n\nTo extend the data base\, learn about
  ground movements and structural forces\, an extensive monitoring scheme w
 as implemented at the Thames Water Shaft F at Abbey Mills which is approxi
 mately 30 m in diameter and 70 m deep – one of the largest every constru
 cted shafts in the UK. The scheme included innovative fibre optic sensors\
 , conventional soil instrumentation (manual inclinometers\, magnet and rod
  extensometers) and optical surveys.\n\nWhen comparing the measurements wi
 th the initial PLAXIS design some discrepancies are oberserved. To investi
 gate these a parametric study is conducted with FLAC2D. The influence of s
 everal parameters (soil models\, wall stiffness/anisotropy\, wall thicknes
 s/verticality and chalk stiffness) was investigated.\n\nThe monitoring and
  numerical results show the following:\n(1)​ ​Small vertical ground mo
 vement during shaft excavation (≈ 1 mm) – the majority of movement occ
 urs during diaphragm wall construction (≈ 6 mm)\n(2)​ ​Small lateral
  wall movements during shaft excavation (< 4 mm)\n(3)  ​ ​Large bendin
 g moments and hoop forces are measured in the wall during excavation – t
 he measurements are significantly larger than the PLAXIS design suggests\n
 (4)  ​ ​It appears that the cohesion of the chalk was assumed very low
  (20 kPa) which was ‘unsafe’ for the diaphragm wall
LOCATION:Engineering Department - Lecture Room 6
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