SEISMIC EXPLORATION FOR UNDERGROUND DEVELOPMENT (SOUND)

The current rapid progress in tunneling and underground construction entails the planning and realization of large-scale projects of long distances (tunnels >50km) and large diameters (>13m). Many of these projects are located in geologically complex areas or under a thick overburden so that the realization of detailed geotechnical exploration in the run-up to the construction work is limited. However, during the constructional phase information about the mechanical stability of the tunnel or adit wall and face may be provided by high-resolution seismic measurements in a fast and non-destructive way. In recent years the technical pre-conditions for the realization of efficient seismic measurements during underground constructions have been established. The seismic results show high resolution and broad coverage and are also applicable in damp and reinforced (TBM, reinforced concrete lining) environments. To this end elasto-dynamic properties of the rock can be determined via wave propagation velocities of the P- and S-wave that in turn are estimated by analyzing the direct wave or surface waves. The seismic methods enable us to map existing tunnel walls with relatively small effort and to identify potentially risky sectors before damage occurs. Pilot surveys in different European tunnel construction projects have shown the general applicability of these approaches. In the collaborative project SOUND we will focus on three main topics that build upon a common basis of acquisition and interpretation techniques: (1) Seismic and geotechnical exploration in tunneling, (2) Investigation of the acquired data by means of inversion techniques and (3) Enhancement of the seismic sources developed in previous projects. Those sources are also applicable for long-term continuous monitoring of underground construction and are tested with the aim to monitor the changing local stress regime in the vicinity of a freshly excavated adit. The survey covers the drill-and-blast excavation of an adit in the Underground Laboratory of the GFZ at the Education and Research Mine Reiche Zeche (Freiberg/Germany) by using a permanently installed seismic acquisition system.