The role of rock mechanics in the utilization of underground space is becoming more and more significant as the number of caverns are increasing under the central areas of expanding cities. In these areas rock mechanical aspects have to take into account already in the city planning phase when new underground facilities are introduced in the middle of existing underground infrastructure. Sometimes things can be solved with simple methods, sometimes quite extensive numerical 3D – rock mechanical analysis shall be conducted. However, the amount of data available is dictating the methods which can be used. For numerical analysis there must be enough data about the bedrock and in-situ stresses, among others. It must be kept in mind that the accuracy of the analysis is dependent on the accuracy of the initial data. In any case, rock mechanics should be utilized already in the initial design phases of underground construction.
Rock mechanics is a relatively young science, but the basic ideas of rock mechanics have already been implicitly known to people living in caves. The basic ideas of the safety of caves are still the same as in the Stone Age. The ground type must be at least in some extent intact without any loose layers to be stable. The stability of the cave is controlled by the shape and dimensions of the cave in the condensed ground conditions. In hard rock conditions the stability of rock blocks is controlled by rock joints.
Due to the technological restrictions ancient man-made caves and tunnels have been constructed only into the ground which can be excavated by hand tools without explosives. All large caverns were created by natural processes and during ages their shapes became stable. The development in technology created possibilities to make tunnels for different purposes, but also then the design was based on experience. As the theories of statics and strength of materials developed and were applied in structural and geotechnical engineering also the mechanical behavior of the rock structures could be formulated by analytical equations. Much of this work was carried out in Central Europe where a lot of railway tunnels were constructed sometimes in difficult ground conditions.
However, the real breakthrough in rock mechanical analysis was achieved in 1970's – 1980's when the development of computers allowed the use of finite-element or other numerical analysis in stability calculations, first mainframe computers and then desktops and laptops. Increased calculation power of computers, advanced software and extended knowledge on rock structure, properties and in-situ stresses have enabled to make more reliable estimates on the rock mechanical effects caused by intended new projects.
