Guidelines on the use of inverse velocity method as a tool for setting alarm thresholds and forecasting landslides and structure collapses

Tommaso Carlà,Teresa Nolesini,Nicola Casagli,Emanuele Intrieri,Federico Di Traglia,Giovanni Gigli

doi:10.1007/s10346-016-0731-5

Abstract

Predicting the time of failure is a topic of major concern in the field of geological risk management. Several approaches, based on the analysis of displacement monitoring data, have been proposed in recent years to deal with the issue. Among these, the inverse velocity method surely demonstrated its effectiveness in anticipating the time of collapse of rock slopes displaying accelerating trends of deformation rate. However, inferring suitable linear trend lines and deducing reliable failure predictions from inverse velocity plots are processes that may be hampered by the noise present in the measurements; data smoothing is therefore a very important phase of inverse velocity analyses. In this study, different filters are tested on velocity time series from four case studies of geomechanical failure in order to improve, in retrospect, the reliability of failure predictions: Specifically, three major landslides and the collapse of an historical city wall in Italy have been examined. The effects of noise on the interpretation of inverse velocity graphs are also assessed. General guidelines to conveniently perform data smoothing, in relation to the specific characteristics of the acceleration phase, are deduced. Finally, with the aim of improving the practical use of the method and supporting the definition of emergency response plans, some standard procedures to automatically setup failure alarm levels are proposed. The thresholds which separate the alarm levels would be established without needing a long period of neither reference historical data nor calibration on past failure events.

Highlights

Introduction and rationale for the studyMonitoring slopes potentially affected by instability is an activity of fundamental importance in the field of geomechanics
Gigli et al (2011) made particular reference to distometric base 1-2, since this recorded the longest and most consistent progressive acceleration in the time series of displacements; they calculated a failure forecast according to the linear extrapolation of the trend in the inverse velocity plot, which could be distinguished since 2 August already (Fig. 2a)
The inverse velocity method is a powerful tool for predicting the time of geomechanical failure of slopes and materials displaying accelerating trends of movement

Summary

Introduction

Introduction and rationale for the studyMonitoring slopes potentially affected by instability is an activity of fundamental importance in the field of geomechanics. The interpretation of monitoring data is one of the main point of emphasis when trying to predict the time of geomechanical failure (Tf) or to assess the probability of an imminent rock slope collapse. A universal law which successfully accomplishes this goal for all the types of failure mechanisms and lithology does not exist, a good number of empirically derived methods and equations have been produced in the last decades. These are usually based on the recurrent observation before failure of certain relationships in the strain or displacement data, eventually linked to some intrinsic properties of the rock mass (Ventura et al 2009). The most notorious description of the topic was made by Voight (1988, 1989), who extended the theory to the behaviour of materials in terminal stages of failure and proposed a relation between displacement rate and acceleration, influenced by two dimensionless parameters (A and α): ð1Þ where Ω is the observed displacement and the dot refers to differentiation with respect to time

Methods

Results

Conclusion