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SUMMARY:The response of buildings to tunnelling - Ruaidhri Farrell\, CUED
DTSTART:20101015T160000Z
DTEND:20101015T170000Z
UID:TALK26410@talks.cam.ac.uk
CONTACT:Zelda Stuck
DESCRIPTION:An understanding of the response of surface and subsurface str
 uctures to tunnelling is crucial to avoid undesirable safety\, legal or fi
 nancial issues. Current assessment procedures\, which are based on greenfi
 eld distortions\, can be very conservative as in reality the presence of b
 uildings can modify and reduce these greenfield distortions.\n\nThis resea
 rch investigates mechanisms associated with soil structure interaction whe
 n tunnelling beneath buildings\, using both case study data and centrifuge
  modelling. Field observations of the soil structure interaction have been
  obtained from the response of two buildings to the construction of a 12m 
 diameter tunnel with extensive jet grouting in fluvial deposits. Centrifug
 e modelling has been carried out on the 8m diameter beam centrifuge at the
  University of Cambridge. Buildings are modelled as aluminium\, masonry an
 d micro concrete beams on fine dry sand. By varying the building materials
  and geometry\, the response of buildings with a range of stiffnesses is i
 nvestigated. Observed mechanisms showed good agreement with those identifi
 ed from the case study\, demonstrating the benefits of centrifuge modellin
 g. These results demonstrate that buildings can significantly modify and r
 educe the greenfield ground distortions\, in both the vertical and horizon
 tal planes. Based on these observations a new empirical approach for quant
 ifying the soil structure interaction is proposed. The centrifuge modellin
 g and field data have\, however\, shown that settlements beneath rigidly r
 esponding buildings can be larger than greenfield values. This arises from
  a redistribution of the building weight and may have implications for adj
 acent infrastructure.\n\nLarge volume losses were observed (5%) in the cas
 e study. An investigation of the settlement and pore pressure response to 
 the tunnelling works indicates that a significant proportion of the volume
  losses were caused by the installation of horizontal jet grout columns fr
 om the tunnel face. It is postulated that low grout fluid pressure along t
 he jet grout columns resulted in relatively unstable cavities and conseque
 ntly\, large volume losses for each column. While ground movements associa
 ted with individual jet grout columns were relatively small\, the cumulati
 ve effect of multiple columns resulted in significant settlements.
LOCATION:Engineering Department - Lecture Room - LR6
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