The geotechnical design of underground structures deals with the interaction between the ground and the structure. The key element of this behavior is the potential failure mode of the ground, which mainly depends on the ground conditions including ground parameter, water and primary stress condition as well as the excavation geometry. Typical ground behaviors for underground structures are discussed and engineering design methods are presented. To deal with the uncertainties of the ground and the complexity of the subsurface buildings a behavior based design methodology is discussed in combination with the risk management process as described in ISO 31000. The integration of the processes leads to a sound design process, which allows the application of individual and problem-oriented engineering design tools as well as the adaptation of the design during the construction phase to minimize the geological and geotechnical risks if required.
The "geotechnical design of underground structures" can be described as the design dealing with the interaction between the ground and the structure. With focus on an economic construction according to its pre-defined specifications the geotechnical design mainly covers the design of the excavation and the primary support but also additional measures such as lowering of the ground water level or injections to change the ground properties. Generally the geotechnical design includes all aspects, which deal with the ground interactions.
Underground structures are often complex structures with geometrically different elements such as shafts, tunnels or caverns. These structures are excavated in various ground conditions concerning geological units, overburden, primary stresses or ground water with different levels of uncertainties of the predictions. Due to this the geotechnical design of underground structures is often very complex and requires comprehensive understanding of the geological, geotechnical and structural designs and its interactions.
At the moment a comprehensive method for the geotechnical design of underground structures, especially in rock mass, is neither defined in standards nor internationally accepted as state of the art. Various different approaches are applied based on regional experience or specifications of local clients and authorities. The typical methods applied for geotechnical design are discussed by various authors (e.g. Hudson 2001, Palmstrom & Stille 2007 or Feng & Hudson 2011) and can be summarized as