A study on the dynamic behavior of the Meuse/Haute-Marne argillite

Excavation of underground tunnels can be conducted by tunnel boring machines (TBM) or drill-and-blast. TBMs cause minimum damage to excavation walls. Blasting effects on excavation walls depend on the care with which the blasting is executed. For blast-induced damage in excavation walls, two issues have to be addressed: rate of loss of confinement (rate of excavation) and dynamic loading from wave propagation that causes both intended and unintended damage. To address these two aspects, laboratory dynamic tests were conducted for the determination of the dynamic properties of the Meuse/Haute-Marne argillite.In the present study, 17 tensile (Brazilian) and 15 compression split Hopkinson pressure bar (SHPB) tests were conducted. The test revealed that the dynamic strengths of the argillite are strain rate dependent. The average dynamic increase factors (ratio of dynamic strength to static strength) for tensile and compressive strength are about 3.3 and 2.4, respectively. A high-speed video camera was used to visualize the initiation of failure and subsequent deformation of the specimens. The direct compression specimens were found to deform and fail uniformly around the circumference of the specimen, by a spalling process. The SHPB Brazilian tests indicated that failure occurred in tension along the line of load application. Radial fractures were also observed. The test results can be used for the development of a dynamic constitutive model for the argillite for the prediction of damage in underground excavation utilizing the drill-and blast method.