Time-independent and time-dependent deformation of small tunnels—III pre-failure behaviour

Abstract Process simulation tests have been conducted to investigate the time-dependent deformation processes near tunnels at large depth or in weak rock. The tests equipment has been described in Part I together with a presentation of the loading history adopted for the tests. In Part II typical test results have been presented to document the behaviour of small tunnels in a jointed rock mass with time-dependent strength and deformation properties. A qualitative interpretation of the observed displacement pattern has been given. In this third part the measured tunnel closure and radial strain patterns are compared with those predicted from simple material models. The time-independent behaviour is compared with predictions assuming linear elastic material properties and the time-dependent tunnel response is compared with solutions assuming linear visco-elastic material properties. It is concluded that excessive deformations can be attributed to softening processes near the tunnel wall. The practical implications of this interpretation are discussed.