Practice of the Doorstopper stress measurement method during the last 30 years in Italy

Abstract

In Italy, during the last decades, most of the in situ stress measurements were carried a shallow depth, in existing geotechnical structures. In these cases, the stress measurements involves concrete or low disturbed rocks material; thus linear, elastic, non-fractured materials. For this reason the stress tests interpretation is straightforward and reliable. In these situations, since the early 90s, the Doorstopper technique became the most used stress measurement technique. It has proven to be effective and cheap. A collection of punctual tests can be interpreted with a suitable numerical model. The numerical model provide the interpolation of the punctual measurements and can give important information about the virgin stress field. After recalling the main features and improvements of the doorstopper method in the last 30 years, this paper illustrates two Italian cases. The first case is the Sparvo Tunnel (Bologna-Firenze highway) where was performed a massive measurement campaign made up of more than six hundred Doorstopper tests in two adjacent tunnels; the results of the two tunnel are compared; the 2d FEM model interpretation is discussed. The second case is a marble quarry in Alta Carnia (Udine): the Doorstopper and stress variation measurements were carried out and interpreted by means of a 2d FEM model, resulting in the definition of the natural stress field.