applied sciences Article Towards A Geo-Hydro-Mechanical Characterization of Landslide Classes: Preliminary Results Federica Cotecchia 1 , Francesca Santaloia 2 and Vito Tagarelli 1,* 1 DICATECH, Polytechnic University of Bari, 4, 70126 Bari, Italy; [email protected] 2 IRPI, National Research Council, 4, 70126 Bari, Italy; [email protected] * Correspondence: [email protected]; Tel.: +39-3928654797 Received: 21 September 2020; Accepted: 4 November 2020; Published: 10 November 2020 Abstract: Nowadays, landslides still cause both deaths and heavy economic losses around the world, despite the development of risk mitigation measures, which are often not effective; this is mainly due to the lack of proper analyses of landslide mechanisms. As such, in order to achieve a decisive advancement for sustainable landslide risk management, our knowledge of the processes that generate landslide phenomena has to be broadened. This is possible only through a multidisciplinary analysis that covers the complexity of landslide mechanisms that is a fundamental part of the design of the mitigation measure. As such, this contribution applies the “stage-wise” methodology, which allows for geo-hydro-mechanical (GHM) interpretations of landslide processes, highlighting the importance of the synergy between geological-geomorphological analysis and hydro-mechanical modeling of the slope processes for successful interpretations of slope instability, the identification of the causes and the prediction of the evolution of the process over time. Two case studies are reported, showing how to apply GHM analyses of landslide mechanisms. After presenting the background methodology, this contribution proposes a research project aimed at the GHM characterization of landslides, soliciting the support of engineers in the selection of the most sustainable and effective mitigation strategies for different classes of landslides. This proposal is made on the assumption that only GHM classification of landslides can provide engineers with guidelines about instability processes which would be useful for the implementation of sustainable and effective landslide risk mitigation strategies. Keywords: landslide mechanism; phenomenological interpretation; numerical modelling; landslide risk; landslide classification; sustainable mitigation measures 1. Introduction Landslides are still one of the main sources of risk for civil society [1–3], despite the widening of knowledge about their processes and the multiple initiatives aimed at risk mitigation. Landslides still cause numerous deaths and huge economic losses, impacting the socio-economic development of several regions, as is the case for large areas of the Italian peninsula (Figure1;[ 4]). Given the current scenarios of the effects of landslides across the world, the most important international agendas (e.g., the Sendai Framework; Global Assessment Report 2019—GAR19) categorize landslides as natural processes which may cause ‘disasters’ for the civil society, and request the adoption of scientific methods in the assessment of the landslide risk and in the selection of mitigation measures, in order to guarantee the sustainability of the landslide risk management. Appl. Sci. 2020, 10, 7960; doi:10.3390/app10227960 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 7960 2 of 41 Appl. Sci. 2020, 10, x FOR PEER REVIEW 2 of 42 Figure 1. Landslide susceptibility map of Europe [[4].4]. The background of the present paper is long-term research addressing the definitiondefinition of design strategies for for sustainable sustainable landslide landslide risk risk mitigation mitigation [5–11]. [5–11 The]. The results results of the of background the background research research have haveshown shown that thatsustainable sustainable landslide landslide risk riskmitigation mitigation measures measures need need to tobe be based based on on an an objective characterization of the landslide mechanism, i.e., of the slope failure processesprocesses and of their causes (either predisposingpredisposing or or triggering; triggering; [10 –[10–13]).13]). Accordingly, Accordingly, the resultsthe results of the of background the background research research provide evidenceprovide evidence of why: (i)of thewhy: characterization (i) the characterization of landslide of mechanismslandslide mechanisms is useful for is geo-hydro-mechanicaluseful for geo-hydro- (GHM)mechanical studies (GHM) of the studies slope featuresof the slope and equilibriumfeatures and conditions; equilibrium (ii) conditions; the routine (ii) selection the routine of sustainable selection landslideof sustainable risk mitigationlandslide measuresrisk mitigation would measures greatly benefit would from greatly the availability benefit from of athe general availability framework of a ofgeneral landslide framework mechanisms. of landslide This framework mechanisms. should This result framework from a systematic should characterization result from a ofsystematic landslide casecharacterization histories through of landslide GHM case studies histories and mightthrough develop GHM intostudies a GHM and might classification develop of into landslides. a GHM Thisclassification would represent of landslides. an important This would step forward represent with an respect important to the step geomorphological forward with classificationrespect to the of landslidesgeomorphological (e.g., [14 classification–16]; Figure2 ),of which landslides is, to (e.g., date, the[14–16]; most Figure complete 2), andwhich widely is, toused date, approach. the most Suchcomplete classifications and widely have used resulted approach. from comprehensiveSuch classifications field studieshave resulted of landslide from processes,comprehensive carried field out fromstudies the of 1970s landslide to 1990s, processes, and have carried been of out great from significance the 1970s to engineering1990s, and have practices, been of providing great significance engineers withto engineering hints about practices, the possible providing typology engineers of the landslide with hints process about taking the possible place on typology a given slope.of the However,landslide theprocess authors taking of thisplace classifications on a given slop clearlye. However, stated that the theauthors landslide of this classes classifications were characterized clearly stated mainly that the landslide classes were characterized mainly through geomorphological studies and, as such, they did not provide comprehensive information concerning the hydro-mechanical causes and processes Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 42 determining the progression of slope failure. Therefore, such classifications cannot provide objective assessments of landslide causes which may be accounted for in the design of mitigation strategies. Hence, the integration of such geomorphological landslide classifications with GHM characterizations of landslide mechanisms would prove to be a powerful support to the professional community involved in the selection and design of landslide risk mitigation measures. With these notions in mind, this paper presents the preliminary results of research seeking to address, in the long term, the above-mentioned integration of the available geomorphological classification of landslides, and should ultimately result in a system which could be defined Appl. Sci. 2020, 10, 7960 3 of 41 according to GHM classifications of landslides. Accordingly, the paper reports a first tentative GHM characterization of some of the landslide classes of the Cruden DM and Varnes DJ geomorphological classificationthrough geomorphological [16] (Figure 2): studies (1) rotational-rototranslational and, as such, they did not slides provide (box comprehensive 1 in Figure 2); information (2) lateral spread-flowslidesconcerning the hydro-mechanical (box 2 in Figure causes2); (3) compound and processes landslides determining [15], not the shown progression as a class of slope in Figure failure. 2, butTherefore, which could such classifications be a subset of cannotthe complex provide landslides objective depicted assessments in the of Figure; landslide (4) causes earthflows which (box may 4 bein Figureaccounted 2); (5) for deep in the mixtilinear design of mitigationslides (box strategies. 5 in Figure Hence, 2); and the (6) integration debris flows of such and geomorphologicaldebris flowslides (boxlandslide 6 in Figure classifications 2). Such a with characterization GHM characterizations was based on of the landslide results mechanisms of several studies would reported prove to in be the a literaturepowerful supportwhich toprovided the professional GHM community interpretations involved of in thelandslide selection andcase design histories, of landslide through risk phenomenological,mitigation measures. conceptual, or numerical models of the mechanism. FigureFigure 2. 2. LandslideLandslide classification classification ([16]; ([16]; https://www.bgs.ac.uk-Britishhttps://www.bgs.ac.uk-British Geological Survey). With these notions in mind, this paper presents the preliminary results of research seeking to address, in the long term, the above-mentioned integration of the available geomorphological classification of landslides, and should ultimately result in a system which could be defined according to GHM classifications of landslides. Accordingly, the paper reports a first tentative GHM characterization of some of the landslide classes of the Cruden DM and Varnes DJ geomorphological classification [16] (Figure2): (1) rotational-rototranslational