Geophysical surveys integrated with rainfall data analysis for the study of soil piping phenomena occurred in a densely urbanized area in eastern Sicily

Graziano Patti,Sebastiano Imposa,Mauro Corrao,Gabriele Morreale,Sabrina Grassi

doi:10.1007/s11069-021-04784-9

Abstract

The occurrence of strong and abrupt rainfall, together with a wrong land use planning and an uncontrolled urban development, can constitute a risk for infrastructure and population. The water flow in the subsoil, under certain conditions, may cause underground cavities formation. This phenomena known as soil piping can evolve and generate the surface collapse. It is clear that such phenomena in densely urbanized areas represent an unpredictable and consistent risk factor, which can interfere with social activities. In this study a multidisciplinary approach aimed to obtain useful information for the mitigation of the risks associated with the occurrence of soil piping phenomena in urban areas has been developed. This approach is aimed at defining the causes of sudden soil subsidence events, as well as the definition of the extension and possible evolution of these instability areas. The information obtained from rainfall data analysis, together with a study of the morphological, geological and hydrogeological characteristics, have allowed us to evaluate the causes that have led to the formation of soil pipes. Furthermore, performance of 3D electrical resistivity surveys in the area affected by the instability have allowed us to estimate their extension in the subsoil and identifying the presence of further areas susceptible to instability.

Highlights

The devastating natural events that have affected the entire Italian peninsula in recent decades have strongly highlighted how the physical vulnerability of the territories increases exponentially due to the urban and infrastructural expansion
A phenomenon that constitutes a real civil protection problem, especially if it occurs in an urban environment, is represented by soil piping
It is clear that the occurrence of sudden subsidence phenomena within a residential area, such as those that occurred between 2015 and 2017 in the Valverde municipality, represent a serious problem for public safety

Summary

Introduction

The devastating natural events that have affected the entire Italian peninsula in recent decades have strongly highlighted how the physical vulnerability of the territories increases exponentially due to the urban and infrastructural expansion. This uncontrolled urban growth involves, after the occurrence of natural phenomena, such as seismic events, landslides, floods, etc., infrastructure damage and loss of human lives. The term soil piping indicates erosion phenomena that lead to the occurrence of land subsidence It is defined as the hydraulic removal of underground soil that causes the underground channels and cavities formation (Boucher 1995), which can cause the collapse of the soil surface layer. This phenomenon, which can have both natural and anthropic origin, depends on various factors such as the lithological and structural nature of the subsoil, the waterproof urban surface connected with the hydrography characteristics, the increasing "urbanization" of the subsoil (undergrounds and tram lines, underground utilities, drainage system, etc.), the weather phenomena, the subsoil hydrogeological nature and its interaction with the mentioned factors (Waltham et al 2005; Kaufmann 2014; Vannoppen et al 2017; Bernatek-Jakiel and Poesen 2018; Bovi et al 2020)

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Conclusion