Shotcrete: Large Scale Testing of Thin Liners with a Flat Arch Geometry: Fid-Bau Portal

Shotcrete: Large Scale Testing of Thin Liners with a Flat Arch Geometry

G. Fernandez-Delgado / J. Mahar / E. Cording / H. Parker

This report presents the results of model tests on thin shotcrete layers similar to those potentially used as initial tunnel support in flat roofed tunnels. The structural behavior and maximum carrying capacity of these layers were determined in this testing program. The large-scale test facility used in previous work was modified to simulate a flat roofed tunnel. Preliminary tests, using thin mortar layers, were conducted in order to assess the performance of the test device and to evaluate the principal variables controlling the capacity of a thin lining. Results obtained from these tests were used in the planning and evaluation of the shotcrete test program. Three principal modes of failure were observed: diagonal tension in the shotcrete, separation of the layer from the wall, and thrust-moment interaction in the separated portion of the layer. The failure mode was governed mainly by the thickness and boundary conditions of the layer, as well as the adhesive characteristics along the shotcrete wall contact. Other parameters, such as the strength of the shotcrete also affected the maximum carrying capacity of the layers. A conceptual model has been developed to be used as a theoretical framework in the analysis of these and future tests results. Recommendations for future studies of thin shotcrete linings are also given in this report.