Gravity-induced deformations due to Rock-Mass Creep (RMC) affect the carbonate Peschiera Springs slope (Italy) which hosts the most important drainage plant for the Rome's water supply. This water resource is due to a major regional karst aquifer with an average discharge exceeding 18m3/s. The interaction of the RMC with the karst ground water seepage is responsible for underground failures, including cave collapses which generally occur very close to the spring area. On September 2008, an accelerometric array was installed within the tunnels of the drainage plant for integrating a pre-existing stress-strain monitoring system. The integrated monitoring system provided many data on:

  • continuous deformations due to the RMC which affects the slope;

  • microseismicity due to the underground failures occurring within the slope;

  • underground failures and rock-mass deformations induced by earthquakes.

The up to now collected data, were fundamental for deriving an alarm system devoted to the drainage plant management and based on some characteristic parameters of the seismic records. This alarm system provides three possible levels of alarm, which can be independently reached in the different sectors of the drainage plant: the "ordinary" level; the "alert" level and the "emergency" level. Some recently occurred events of underground failures made it possible to experience the reliability of the adopted alarm system.

1 Introduction

This study used the data from an accelerometric array to record precursors, post-failure events and triggering impulsive events within a karst rock mass hosting the major drainage system of Rome's aqueduct. The prefailure behaviour of rock masses represents a complex geomechanical problem because the stress and jointing conditions as well as the joint setting can strongly constrain pre-failure effects, such as generation of cracks, opening or closing of joints and readjustment of the stress field within the rock mass. Recognizing pre-failure events by geological surveys as well as monitoring natural and anthropogenic systems is a major goal for the mitigation of risks due to the "unexpected" and "rapid" rock failure events (Szwedzicki 2003). More complex scenarios of failure involving rock masses can be associated with impulsive triggers (i.e. explosions, collapses) or earthquakes. In these last cases precursors do not necessarily occur, while the events representing possible triggers can be monitored.

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