Seminar - Shakera Khan - Rectification of Tilted Structures Using Soil Extraction Technique
Wednesday 4 June 2008, 1.10 - 1.55 pm
Civil Engineering Lecture Theatre 3
Settlement of a foundation usually results from distortion of the underlying soil mass due to shear stresses imposed by the external loads and also due to volume changes which occur as the soil is consolidated. Tilt and distortion are the two common types of foundation failure. Tilt is more dangerous than distortion because distortion shows some visible effects such as cracks, but tilt may cause larger movement without showing noticeable effects. Remedial action is needed for the tilting of towers and buildings when tilts of magnitude 1/100 or greater are measured. There are several techniques available such as jacking, underpinning, grouting, piling, soil removals, etc. for the restoration of a tilted building of which the soil removal method has been proven to be the most effective and permanent solution for settlement problems as it is less costly, requires less fabrication on the structure itself and does not require advanced technology. The soil extraction technique can also be a viable alternative especially for piled raft foundations where other solution methods like jacking are not effective. The main objective of this research is to investigate the efficacy of implementing the soil removal technique to restore a tilted building which will be done by simulating selective excavation of soil, using the finite element method.
When soil layers are removed, the resulting cavities gently close due to the overburden pressure, which then eventually cause a small subsidence of the leaning structure. Analysis for controlled excavation was performed by digging trenches beside a sample raft foundation and its effects on the tilted structure were observed. Similar analysis was done for taking into account the effects of soil removal in the case of piled raft foundation by digging trenches along the full length of some of the piles. Both of these analyses generated satisfactory results for linear and elastic soils.
This research also aims at simulating excavation for Elasto-Plastic soil materials using Mohr-Coulomb and Cam Clay models and also for poro-elastic and non-linear soils.