Impact identification on flexible rockfall barriers: on site test of a wireless monitoring system

Abstract

Flexible rockfall barriers represent an effective measure to mitigate hazard related to falling boulders. The monitoring activity of these protection structures is essential to guarantee their functionality, and usually aims to verify the barrier conditions and to identify any impact on the net. The system here presented, called D-Fence, was specifically developed for the realtime monitoring of flexible rockfall barriers. It consists of a series of separate battery-powered devices installed on the uprights of the monitored structure and transmit data to the elaboration center through a wireless local network. Each module includes a 3D tilt sensor, allowing the near real-time monitoring of the rotation of the uprights, while the integration of a shock sensor makes it possible to measure in real-time the accelerations experienced by the barrier. The onsite test of the D-Fence system involved the installation of four modules on a prototype barrier located in a pilot site in Northern Italy. Each device was placed on a different upright and was connected to a local Wi-Fi network. In this configuration, two different concrete boulders were dropped on the barrier in order to test the D-Fence ability to measure the tilt variation of the uprights and identify the overcoming of a predefined acceleration threshold.