Deformations analysis and monitoring in underground constructions: automatic systems to measure convergence and preconvergence effects

Due to the considerable number of uncertainties and to the anisotropic nature of rock masses, tunnel design assumptions should be always validated during the construction phase. This procedure could be performed by means of a regular monitoring of the rock mass deformation around the tunnel face, with particular attention to convergence and preconvergence phenomena. This paper presents the experimental data obtained through an automatic monitoring system composed of two devices, called PreConv Array and Cir Array, respectively developed for the direct monitoring of pre-convergence ahead of the excavation front, and the convergence of the tunnel profile in a specific section. Each device is connected to an acquisition control unit that queries the sensors and automatically sends the data to an elaboration center at predefined time intervals. The automated elaboration approach provides a complete and immediate description of the rock mass behavior.