Sandbox modeling of-the shallow tunnel face collapse

摘要

The objective of the present work is the experimental, analytical and numerical investigation of the face instabilitymechanism 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, experimentshave been carried out at 1g using the same dry sand and changing each time the overburden height above the crown of thetunnel. In a first attempt to derive a simple analytical equation relating the maximum subsidence occurring at the variousstratigraphic horizons above the tunnel imparted by the horizontal tunnel face retreat, the model test results were analyzedutilizing 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 FLAC~(3D)code. It was found that the bestagreement of experimental and numerical data is achieved for elastic modulus of the dry sand equal to 130 MPa that wasalso inferred independently from triaxial compression test results.