An overview of the geological and morphological constraints in the excavation of artificial cavities

The habit of man to excavate artificial cavities began a very long time ago. Man’s efforts were initially moved by the need to have a safe place to live, to control the surrounding territory, to collect and transport water, to exploit the natural resources. For all these purposes, he had to face a number of geological and morphological constraints that, depending on site characteristics, guided, favored or complicated the excavation. Therefore, all the phases in the “life” of an artificial cavity, from the original idea, to planning and realization, up to its later evolution and possible conservation, depend in some ways on geology and morphology. Lithology of hosting rock is the first aspect to consider: the rock mass must allow hand excavation but, at the same time, it should present physical-mechanical characteristics such to support the newlyformed cavity. The geological and structural setting, including the main faults and the discontinuity systems in the rock mass, have to be particularly taken into account. Choice of the site where to locate an artificial cavity is also dictated by morphology, the morphological factors being, in turn, strictly related to land management and control. When safety reasons were considered to be the main priority, for instance, those sites that apparently were extremely difficult to excavate and to settle in were chosen. Morphology is also strictly related to slope instability. Several rock settlements situated at the borders of deep valleys and ravines are directly involved in mass movements, due to natural evolution of the slopes and to open cracks produced by the tensional release in the unsupported rock mass. Inside the artificial cavities, in turn, problems of instability may be observed. Locally, these may become so significant to compromise the overall stability of the structure. Slope instability processes deserve a greater attention from cavers and scientists, since their effects might be extremely dangerous for people visiting and working in artificial cavities, and for the cultural heritage therein contained as well. Availability of water resources is a further factor that controlled during historical times the choice of sites for settlements and towns. As a consequence, the hydrogeology plays a crucial role for artificial cavities, and particularly for those works intended to collect and transport water to settlers and inhabitants. Aqueducts, tunnels, fountains are, for the reasons above, very important to study in the context of the geological and hydrogeological setting, considering at the same time the social and historical aspects of the community that designed and realized them. The present contribution is an attempt in categorizing the aforementioned factors that play a role in the realization of artificial cavities. The topic is very wide, covering several interrelated disciplines and field of research, and should deserve to be treated with much greater detail and thoroughness. Our goal is therefore to stimulate with this article cavers and interested scientists in carrying out studies about the crucial role that geology and morphology have in the development of artificial cavities