Giacomo Pepe

Geomechanical characterization of a highly heterogeneous flysch rock mass by means of the GSI method

Over the last years, several researchers have investigated heterogeneous rock mass behaviour using the Geological Strength Index (GSI) classification system in conjunction with the Hoek–Brown criterion. Because of the variable composition of such rock masses, the availability of both petrographic and mechanical features of the intact rock is essential in order to carry out geomechanical studies. Starting from the detailed evaluation of the strength and deformability of the intact rock, the GSI method was applied to the Sanremo flysch formation, which is widely outcropping in Western Italy and involved in many engineering projects. It is characterized by both a remarkable lithological heterogeneity and a structural complexity. Petrographic analysis and laboratory tests allowed the definition of the main constituent lithotypes and the identification of their mechanical properties, whereas geomechanical surveys were performed in order to estimate the GSI values and the strong/weak ratio. Based on the frequency of strong and weak layers, a “weighted average” of intact rock values was used in estimating the rock mass parameters. Three main rock mass classes were identified, and a basic engineering geological map of the study area was prepared.

Preliminary analysis of the November 10, 2014 rainstorm and related landslides in the lower Lavagna valley (eastern Liguria)

(*) Università di Genova Dipartimento di Scienze della Terra, dell’Ambiente e della Vita Corso Europa, 26 16132 Genova, Italy (**) Università di Pisa Dipartimento di Scienze della Terra Via S. Maria, 53 56126 Pisa, Italy Corresponding author: cevasco@dipteris.unige.it PRELIMINARY ANALYSIS OF THE NOVEMBER 10, 2014 RAINSTORM AND RELATED LANDSLIDES IN THE LOWER LAVAGNA VALLEY (EASTERN LIGURIA)

Relation between crack initiation-damage stress thresholds and failure strength of intact rock

The analysis of a wide literature dataset of mechanical parameters related to intact rocks from more than 480 unconfined compression tests, coupled with new laboratory tests on 132 specimens, is proposed herein with the aim of analyzing the mechanical behavior of a great variety of rock types, mainly focusing on their crack initiation (σci) and crack damage (σcd) stress levels. These thresholds can be employed as warning indicators for rock mass damage and breakouts and represent important input parameters for numerical models. International literature lacks in a detailed analysis on the mutual dependence existing between the main mechanical properties of intact rocks and their crack stress thresholds. In this paper, the study of the correlation between crack initiation-crack damage stress levels and the failure strength of sedimentary, metamorphic and igneous rocks is carried out through single and multiple regression approaches aimed at finding reliable prediction models, which can be useful when time-consuming laboratory experimental procedures need to be avoided. The correlation between predicted and measured values demonstrates that defined models represent a good tool for the empirical estimation of σci and σcd, and can be useful for preliminary engineering design dealing with stress-induced brittle fracturing, especially when the definition of warning indicators for rock mass damage and breakouts is needed. In fact, it is known that underground instability mainly depends on the redistribution of stresses around the excavation, which can produce induced stress concentrations, resulting in sudden release of stored energy and causing stress-induced brittle failure phenomena.

A study on the 10 November 2014 intense rainfall and the related landslides in the lower Lavagna valley (eastern Liguria)

On 10 November 2011 some small coastal basins of the Tigullio gulf and the middle Lavagna and Sturla valleys (eastern Liguria), were hit by an intense rainfall. Flash floods involved the city of Chiavari and shallow landslides were triggered on the slopes, causing severe damage to settlements and road network. Some buildings were destroyed and two casualties occurred at Leivi, in the lower Lavagna valley.This paper synthesizes the results of preliminary surveys carried out few days after the event in the area most affected by shallow landslides. The investigations, which are still in progress, have contributed to understand the characteristics of both triggering rainfall and landslide source areas. These achievements will be helpful in studying rainfall thresholds, shallow landslide modeling, landslide susceptibility and risk assessment for the study area.

Crack initiation and damage thresholds in some brittle metamorphic rock types

In this study 60 unconfined compression laboratory tests performed on three brittle metamorphic rock types were analysed in order to evaluate the stress thresholds associated with the onset of stable and unstable microcracking which are known in literature as the crack initiation stress and the crack damage stress, respectively. The crack initiation stress was identified applying the lateral strain response (LSR) methodology while the crack damage stress was detected where total volumetric strain reversal occurs. Although the mineralogical and textural features were quite similar among the investigated rock types, the results of this study showed that the crack initiation and damage stress values were affected by variability. However, when the normalized stress values ci/UCS and cd/UCS were considered, the scatter in results decrease consistently suggesting that the stable and unstable crack growth begin at similar stress levels in the investigated rock types

Landslide Inventory of the Cinque Terre National Park, Italy

Landslide inventory maps are effective and easily understandable products both for experts, such as engineering geologists, and for nonexperts, including decision-makers, planners, and civil protection managers. At present, the Cinque Terre landscape suffers from the massive abandonment of cultivations on the terraces, with negative consequences for slope stability due to the increasing erosional processes. Each landform was digitized as a polygon using a GIS platform. Landslide detection was performed by a two-step method. The first step consisted of mapping landslides using orthophotos provided by Liguria Region, together with Google Earth imagery; the second step was a field verification study carried out between September and November 2015. Four hundred and five landslides were then identified and grouped into seven main typologies: a percentage distribution analysis of the different landslide types detected in Cinque Terre was then performed. A large number of debris slides (33.3%) indicates the vulnerability of dry-stone walls after large amounts of rainfall. Rockfalls (18.5%) are also frequent and especially concentrated along the eastern sector of the coastline. In addition, debris flows (12.6%) are widely distributed, especially along the western sector of Cinque Terre, among the Monterosso and Vernazza municipalities; these landslides were mainly triggered by the October 25th, 2011, meteorological event (382 mm of rainfall in 24 h recorded by the Monterosso al Mare weather station). Many landslides with complex evolutions (7% of the total) were detected along the coastline between Vernazza and Manarola; these events are historically well-known and extensively described in the literature.

Extreme Flood and Landslides Triggered in the Arroscia Valley (Liguria Region, Northwestern Italy) During the November 2016 Rainfall Event

From November 20th, 2016, to November 25th, 2016, Liguria Region (northwestern Italy) experienced prolonged and intense rainfall. The rainfall sequence occurred following two main phases. The second phase mainly hit the western sector of the region, reaching its peak on November 24th. Rainfall was particularly abundant within the Arroscia valley, where the 5–days cumulative rainfall locally exceeded 50% of the mean annual precipitation. In this paper, we document the rainstorm magnitude, presenting a first inventory of the rainfall–induced ground effects within the Arroscia Valley. The mapping was performed by means of extensive field work that was partly supported by satellite imageries. More than 250 landslides affected the upper sector of the valley, while in the downstream reach, widespread flood-related forms and processes resulting from the abundant precipitation were mapped. The results of this study are expected to be helpful for future research on both landslide– and flood–related channel change susceptibility and risk scenarios evaluation.

Quantitative landslide susceptibility assessment of the Vernazza catchment (Cinque Terre National Park, Italy)

Abstract from 88th Congress of the Italian Geological Society, 2016-09-07 - 2016-09-09, NaplesAbstract from 88th Congress of the Italian Geological Society, 2016-09-07, 2016-09-09, Naplesbook Edited by D. Calcaterra, S. Mazzoli, F.M. Petti, B. Carmina & A. Zuccari doi: 10.3301/ROL.2016.79