Time-dependent deformation of small tunnels—II. Typical test data

Abstract

Abstract Process simulation tests have been conducted to investigate the time-dependent deformation processes near tunnels at large depth or in weak rock. The test equipment has been described in Part I together with a presentation of the loading history adopted for the tests. This second Part includes a detailed description of typical test results and a discussion of the time-dependent processes, such as failure propagation and associated stress redistribution, which cause the observed behaviour. Both the time-dependent and time-dependent tunnel convergence and radial strain pattern inside the rock mass are presented in plots of field stress, strain or tunnel closure with time, and strain rate or tunnel closure rate. The performance of the tunnel in the pre-failure stress range, during the transition to an unstable opening and after a yield zone has developed is evaluated. Even though a detailed interpretation of the test results will follow in subsequent publications, several important conclusions can be made with respect to time-dependent processes controlling tunnel convergence, observation of the rock mass response to local yielding, position and type of instrumentation to detect time-dependent processes and propagation of instabilities in overstressed rock.