Terrestrial laser scanning for rockfall stability analysis in the cultural heritage site of Pitigliano (Italy)

Riccardo Fanti,Giovanni Gigli,Deodato Tapete,Luca Lombardi,Paolo Canuti

doi:10.1007/s10346-012-0329-5

Abstract

Traditional surveying methods are often not sufficient to achieve a complete geomechanical characterization of the rock mass, to analyze the instability mechanisms threatening the cultural heritage of hilltop historic towns. In Pitigliano (Tuscany, Central Italy), terrestrial laser scanning was employed complementarily to conventional geomechanical techniques. The overall 3D survey of the exposed surfaces was combined with scanlines of the inner walls of the subterranean cavities running underneath the historic centre. The rock mass discontinuities geometry was extracted, and the most critical instability mechanisms were mapped, with particular interest in the potential impacts on the ancient buildings located along the cliff edge. The geomechanical analysis of the surveyed joint sets confirmed a structural control on the cliff morphology by two main joint sets. Thanks to the laser scanner-based kinematic analysis, flexural toppling and wedge failure were found as the main hazardous instability mechanisms in Pitigliano. Finally, the conservation criticalities were identified and a pilot monitoring system was installed in a sector highly susceptible to block detachment.

Highlights

The impact of landslide hazard on the immovable cultural heritage represents a multi-disciplinary theme, which requires several different approaches (Canuti et al 2009)
The geomechanical characterization of discontinuities has been carried out starting from a traditional geomechanical survey of the rock mass, following prescriptions of ISRM (1978) in a significant number of scanlines along the cliff
In Pitigliano some additional data on the rock mass geometry can be gathered from a geomechanical survey in the cave network, whose presence points out the following issues: (a) The underground network allows an unusual inner look-out of the rock mass, from which some additional data on joints geometry can be obtained; (b) The role of the underground tunnels and chambers in the general behaviour of the rock slab could be assessed, considering these elements as non-persistent discontinuities, in particular if their spatial distribution showed some preferential directions; and (c) The position of the caves could form an obstacle in the realization of stabilisation measures as anchors, which efficiency could be strongly diminished if the tie bar went through an unexpected hollow

Summary

Introduction

The impact of landslide hazard on the immovable cultural heritage represents a multi-disciplinary theme, which requires several different approaches (Canuti et al 2009). In Italy, ancient buildings, archaeological sites and even entire historic towns are frequently threatened by slope instability phenomena (Canuti et al 2000; Fanti 2005; Lollino and Audisio 2006). The case of Orvieto (Tommasi et al 2006) is the most famous, but in the same geological province there are many towns built on the top of volcanic slabs overlying normal- or over-consolidated clays. In these conditions, some landslide mechanisms can develop: slow movements in the clays, toppling and rockfalls of the marginal zones of the slab, deepseated gravitational slope deformations (Ribacchi et al 1988)

Methods

Results

Conclusion