A Basic Study on the Large-Scaled Model Test. On the mechanical phenomena accompanying with underground excavation.

To make and maintain deep underground openings, it is important to predict the mechanical phenomena accompanying their excavations in terms of the rockmass properties and the geological structures. In this paper, a large-scaled two dimensional strata model testing method has been developed to approach these problems. In the adopted system, it is possible to excavate cavities in the model under loading condition.At first, some preliminary tests were performed to ensure the stress state created in the model by the loading system as well as the sensitivities of the built-in type sensors employed. Then, the test for a closely located two parallel excavations was performed. Two types of fractures were developed from the openings, which are interpreted, based on the corresponding finite element calculations, to be shear and tensile failures. The stress sensors recorded the local changes (increase and relief) in the model, with accompanying progress of excavation. P-wave velocity and the amplitude of its first motion increased with stress, and decreased on failure.It is concluded that this testing method can almost simulate various circumstances for the underground openings.