Xdisp – How can I model the excavation of a shaft in Xdisp?
There are two potential methods to model shafts in Xdisp. Both have limitations/drawbacks.
The first method is to define a shaft in the ‘embedded wall excavation’ function. An approximate shaft shape is defined in the excavation details tab. The user then specifies an appropriate relationship for surface and sub-surface ground movement. This could be based upon measured data, for example New and Bowers (1994), or from carrying out other analyses.
The alternative method is to specify a number of very short tunnel sections (say 1m length) stacked vertically on top of each other to the proposed depth of the shaft. The total volume of the tunnel sections should equal the total volume excavated for the shaft. Reasonably close matches have been achieved between measured settlement data from New and Bowers (1994) and the results from Xdisp. Generally a high k value and low volume loss has been used to achieve these correlations. No validation has been carried out to check whether sub-surface displacements or horizontal displacements are appropriate.
- New B. M. and Bowers K. H. (1994). Ground movement validation at the Heathrow Express Trial Tunnel, Proc. IMM Tunnelling ’94, Chapman and Hall, pp 301-327