Advantages of innovative automatic inclinometers applied to landslides monitoring for early warning activities

Geotechnical monitoring is one of the most important activities aimed to study and understand the evolution of a landslide. Traditionally, surveys have been performed by using different devices specifically developed to measure a parameter of interest. Inclinometers are some of the most commonly used and well-known tools, designed to monitor slope displacements at different depths. These instruments present a series of features typical of the so-called “traditional” approach, including the need for an operator on-site to perform all the passages required to obtain monitoring data, and a sampling rate typically ranging from some day to weeks depending of several factors, including site accessibility and operator’s availability. While these characteristics do not affect the tool’s ability to perform as a survey system, they represent a relevant limitation to their application for early warning purposes. In fact, in a context where it is essential to acquire timely information on the evolution of a critical event, it should be required to provide a monitoring system able to provide a continuous description of the ongoing phenomenon. In particular, features like automatic data acquisition, high sampling frequency and remote control of the on-site instrumentation are typical of monitoring systems designed for early warning applications. The need for tools able to meet these requirements has led to several upgrades of classical inclinometers, resulting into the development of new contact-based tools. These innovative systems include the possibility to integrate different devices typologies (e.g. inclinometers, piezometers and thermometers) creating a single, multi-parametric array of sensors. The exploited technologies allow for the implementation of automatic procedures for data sampling, elaboration and visualization, which can greatly contribute to the design of alert systems for instability phenomena. In particular, larger datasets achievable by these tools are suitable for a more reliable application of failure forecasting models, which are a key component in the development of early warning activities. In order to provide an example of the importance of these considerations, a case study is presented where both traditional and innovative inclinometers were installed on-site. While the monitoring plan was intended as a geotechnical survey activity, the innovative system allowed to identify a series of critical events which interested the monitored area. Thanks to the innovative procedures implemented, it was possible to obtain a good representation of the final collapse of the landslide, which irreversibly damaged all the traditional inclinometer casings and, ultimately, broke the automatic array. Nonetheless, the dataset recorded before the system failure allowed the application of forecasting models, which correctly predicted the landslide collapse several hours before its occurrence.