The objective of the present work is the experimental, analytical and numerical investigation of the face instability mechanism of shallow circular cylindrical tunnels that are excavated in frictional geomaterials characterized by small cohe- sion. For the experimental investigation a small scale sandbox model has been constructed. Subsequently, experiments have been carried out at 1g using the same dry sand and changing each time the overburden height above the crown of the tunnel.
The objective of the present work is the experimental, analytical and numerical investigation of the face instability mechanism of shallow circular cylindrical tunnels that are excavated in frictional geomaterials characterized by small cohe- sion. For the experimental investigation a small scale sandbox model has been constructed. Subsequently, experiments have been carried out at 1g using the same dry sand and changing each time the overburden height above the crown of the tunnel. In a first attempt to derive a simple analytical equation relating the maximum subsidence occurring at the various stratigraphic horizons above the tunnel imparted by the horizontal tunnel face retreat, the model test results were analyzed utilizing the Dimensional Analysis and Displacement Diffusion theories. The resulting analytical equation, that is remark- ably simple, could be useful for the design and construction stages of shallow tunnels were the subsidence and face move- ments or face pressure exerted by the TBM are monitored, as well as for the validation of numerical codes. The experi- mental results were also compared with numerical results obtained by virtue of the FLAC3D code. It was found that the best agreement of experimental and numerical data is achieved for elastic modulus of the dry sand equal to 130 MPa that was also inferred independently from triaxial compression test results.
The objective of the present w …
AUTORI: Vardoulakis P., Stavropoulou M., Exadaktylos G. RIG ANNO: 2008 NUMERO: 1 Numero di pagina: 9
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