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Landslide dams are a common hazard which threaten downstream human settlement or infrastructure, as their collapse may result in a flash flood. The danger is compounded by the amount of water accumulated; therefore, estimation of the time to failure becomes crucial for assessing engineering risk mitigation procedures. Dam dimension indices, descriptive multivariate analysis and logistic regression have been used to produce a static image of the dam conditions, estimating the probability of failure, but they provide no information of when a failure might occur. We propose a Bayesian model to predict the time to failure of landslide dams, based on imputing missing dam and reservoir measurements via an analysis of their covariate structure. The resulting data is then used in a Bayesian survival model which links the (censored) failure time to dam and reservoir variables. A case study on heterogeneous Italian events is presented, on which our model is tested. Results show that it is possible to produce a probabilistic model of time to failure. The length and height of dams, and the catchment area behind them, are identified as the most important covariates controlling the time to failure. The addition of area-based intercepts confirms the robustness of the methodology. Examples of potential results (forecasting) and possible generalizations of the model are presented.

Natural hazards can be initiated by different types of triggering events. For landslides, the triggering events are predominantly earthquakes and rainfall. However, risk analysis commonly focuses on a single mechanism, without considering possible interactions between the primary triggering events. Spatial modeling of landslide susceptibility (suppressing temporal dependence), or tailoring models to specific areas and events are not sufficient to understand the risk produced by interacting causes. More elaborate models with interactions, capable of capturing direct or indirect triggering of secondary hazards, are required. By discretising space, we create a daily-spatio-temporal hazard model to evaluate the relative and combined effects on landslide triggering due to earthquakes and rainfall. A case study on the Italian region of Emilia-Romagna is presented, which suggests these triggering effects are best modeled as additive. This paper demonstrates how point processes can be used to model the triggering influence of multiple factors in a large real dataset collected from various sources.

A reliable modeling of a landslide activation and reactivation requires a representative geological and engineering geological characterization of the affected materials. Beyond the material strength, landslide reactivation is sensitive to groundwater pressure distributions, that are generated by some external perturbation (recharge) and by the hydraulic properties of the materials. Drainage stabilization works generally involve drilling of a large number of drains and, therefore, minimize the total length is of primary concern to reduce the costs.Aim of this work was the calibration of material properties for the optimization of drainage elements to be built for the slope stabilization and the construction of a shallow tunnel crossing a landslide. The case study is represented by the 4.0 · 105 m3 Carozzo landslide (La Spezia, Liguria, Italy) which affects some marly and sandstone formation. During the tunnel excavation a monitoring network consisting of five DMS columns for displacements and piezometric head multilevel measurements was installed. The monitoring provided a series of piezometric head recession curves following some recharge events. The series of data generated in response of a unique perturbation (rainfall recharge event) were chosen to calibrate the material properties through a multi-step approach, starting from a 1D model and progressively approaching a complete 3D model.The 1D simplified approach applies the solution by Troch et al. (2003) that considers a homogeneous landslide material, with constant slope and a progressive change in the slope width. In this model a storage function considers the amount of water stored in a slope section. By imposing the continuity equation and the Darcy law a second order of partial differential equation is solved by integration in space and time. By taking the initial conditions from piezometric measurements and assuming a constant rainfall recharge, the piezometric level and the outflow rate were computed and compared with the local piezometric level time history, by changing the hydraulic conductivity and the storage function value.Successively, a groundwater flow FEM numerical model (in 2D and 3D) was developed considering the landslide geometry and internal zonation, including the presence of the excavated part of the tunnel. The model domain was divided into sub-zones according to the available geological surveys to account for internal variations of the material properties. The steady-state simulation of the water flow allowed to estimate the equivalent hydrogeological parameters of each subdomain. The hydraulic head distribution obtained under steady-state conditions was used as initial condition for the transient-state simulation. The recharge from precipitation was also included in the water balance by means of daily rainfall time-series. Finally, the model parameters were calibrated in transient state by comparing measured data and simulated results.The minimum error between simulated and measured piezometric heads under transient conditions was obtained through the 3D configuration. Calibrated hydraulic conductivities in the 3D solution are up to an order of magnitude lower than the 1D solution because of the homogenous assumption of the model. The internal zonation of the landslide body and the modeling of a low-conductivity shear zone were essential to explain the pressure differences inside the body.

In spite of the increasing diffusion of tunnel boring machines, conventional tunnelling is still preferred for economic reasons in case of short tunnels, unconventional cross sections or irregular tunnel trajectories. In conventional tunnelling, the mechanical response of the tunnel front is a main concern and, when tunnels are excavated in cohesive soils, this is dominated by the time factor, related to geometry, to the mean excavation rate and to the hydro-mechanical properties of the materials involved. This is particularly evident during excavation standstill: front displacements progressively increase with time and, in many cases, the system response under long-term conditions becomes unstable. In conventional tunnelling, a common technique employed to improve the system response (under both short- and long-term conditions) is the installation of fibreglass tubes within the advance core. In this paper, the mechanical response of both unreinforced and reinforced deep tunnel fronts in cohesive soils is experimentally analysed. In particular, the results of a series of 1g small-scale tests, taking into account both the influence of the excavation rate (the unloading time) on the system response and the evolution with time of the tunnel face displacements, induced by a rapid reduction in the horizontal stress applied on the tunnel face, are reported.

In spite of the increasing diffusion of tunnel boring machines, conventional tunnelling is still largely employed in the excavation of both deep and shallow tunnels characterized by a particularly irregular tracing. Under difficult ground conditions, in conventional tunnelling, the front is frequently reinforced by using fibreglass tubes partially removed during the excavation. This technique is expensive, time-consuming and its design is based on either empirical or very simplified theoretical formulas. Thus, the ultimate objective of the research developed by the authors is to introduce a more sophisticated design approach for this front reinforcement technique. A first step in this direction is this numerical study, in which the mechanical response of deep tunnel faces under undrained conditions is analysed by employing the front characteristic curve: a useful tool largely employed in the literature in analogy with what done for the cavity. The main result of this paper is the “Front Mother Characteristic” curve, obtained by introducing appropriate non-dimensional variables, allowing the designer, once both the system geometry and the soil mechanical properties are assigned, to assess the displacements of tunnel fronts without performing any numerical analysis.

Piled foundations are largely employed as settlement reducers in the design of artificial embankments on soft soil strata. The commonly employed design methods are, however, based on simplified approaches not allowing the assessment of average and differential settlements at the top of the embankment. With this objective, the authors introduce a generalised constitutive relationship capable of accounting for irreversibilities stemming from both geometrical evolution and soil yielding. The model derives from the interpretation of the results of a campaign of three-dimensional elastic–plastic finite-difference numerical analyses describing the embankment construction process. Numerous simplifying assumptions (for instance smooth pile shaft, drained conditions) have been employed. Nevertheless, this does not compromise the theoretical value of the proposed approach. From a practical point of view, this model is a useful tool for geotechnical engineers to employ with a displacement-based design perspective.

Chalks are highly porous rocks formed of mainly carbonate grains bonded together by calcite bridges. From a microstructural point of view they are very similar to calcarenites. The above characteristics make them prone to water induced weathering, frequently featuring large caverns and inland natural underground cavities. This study is aimed to determine the main physical processes at the base of the short - and long-term weakening experienced by these rocks when interacting with water. We present the results of microscale experimental investigations performed on calcarenites from different sites in Southern Italy. SEM, thin sections, X-ray CT observations and related analyses are used for both the interpretation - definition of the structure changes and the identification - quantification of the degradation mechanisms. Two distinct types of bonding could be identified within the rock: depositional bonds and diagenetic bonds. The diverse mechanisms linked to these two types of bonding explain both the observed fast decrease in rock strength when water fills the pores (shortterm effect of water), identified with a short-term debonding (STD), and a long-term weakening of the material, when the latter is persistently kept in water saturated conditions (long-term effect of water), identified with a long-term debonding (LTD). To highlight the microhydro-chemo mechanical processes of formation and annihilation of the depositional bonds and their role in the evolution of the mechanical strength of the material, mechanical tests on samples prepared by drying partially saturated calcarenite powder, or a mix of glass ballotini and calcarenite powder were conducted. Finally the use of transparent chemical consolidants as a more sustainable alternative to grouting is explored experimentally.

During the last decade, a large rockslide along the NW slope of the Mont de la Saxe (Courmayeur, AO—Italy) showed a significant increase in the rate of activity in conjunction with snow melting periods and more recently with important amount of rainfall. The ca 8 mm3 rockslide affects a heavily tectonised and intensely fractured mass of black schists, for a surface area of about 150,000 m2. The rockslide failure surface is typically located at depths of 60–80 m b.g.l. Because of the highly valuable exposed elements regional authorities commissioned a comprehensive ground investigation and monitoring campaign, as well as theoretical and numerical analyses, in order to assess slope stability conditions, the possible evolution and the suitable stabilization and mitigation countermeasures. Here we present the recent rockslide evolution till spring 2014 when a major seasonal reactivation of a 400,000 m3 mass occurred. Finally, with the aim to develop a possible tool for displacement prediction, the results of a series of 1D visco-plastic simulations are presented, discussing the possible role of each of the main controlling factors (e.g. groundwater recharge and piezometric level oscillation, rock degradation). .

Soft and highly porous rocks such as calcarenites are very common in all Mediterranean region. Due to their porous calcareous structure these rocks are prone to water induced weathering mechanisms. Natural onshore and inland underground cavities are evidence of such phenomena. The collapse of cliffs and underground cavities is usually the long-term result of a complex hydro-chemo mechanical process taking place at the micro-scale. Experimental results mainly give evidence of: (a) a marked and instantaneous reduction in strength and stiffness for these porous rocks when macro-pores are filled with water, (b) a slow successive reduction in strength and stiffness occurring in the long-term due to dissolution processes; (c) a more pronounced weakening of the rock material as a consequence of wetting and drying cycles. In the present work a methodological path to cope with deterministic assessment of the stability of natural and anthropic caves will be presented. The following steps will be adopted: (i) experimental study: execution of an experimental campaign to identify the physics of the processes taking place at both the micro-scale and the macro-scale; (ii) theoretical study: extend the concept of strain hardening-non mechanical softening to the time evolution of c-fi reduction; (iii) numerical study: present the 3D numerical results of a real case-study showing the capability of the proposed methodology to cope with risk assessment in complex geomechanical situations concerning weathering, as for underground cavities.

Earth pyramids are tall tapered spires, slender or stocky, made of rock or soil material. This type of features have been marginally studied. Even if they are often included in parks and geosites. We start from this lack of studies to analyse the geometrical and physical-mechanical characteristics considering some case studies in northern Italy. Because of their geometrical characteristics these elements are intrinsically weak and can be used as indicators of past external perturbations. We performed laboratory characterization and numerical modelling to analyse the involved actions, the stability and the reaction to dynamic perturbations.

To model the temporal evolution of complex landslides, a 1D pseudo-dynamic visco-plastic approach, based on Perzyna’s theory, has been modified. In the original version of the model, the viscous nucleus has been assumed to be bi-linear: where irreversible deformations develop uniquely for positive yield function values whereas, in a more general case, it can also develop for negative values. In this work the model has been enriched by considering: (1) an exponential viscous nucleus, (2) a strain-rate softening to reduce friction angle as the sliding velocity increases and (3) block interaction forces to cope with complex 3D geometries for the sliding mass.

To model the evolution with time of the Bindo-Cortenova translational landslide (Italian Prealps, Lombardy, Italy), a 1D pseudo-dynamic visco-plastic approach, based on Perzyna's theory, has been conceived. The viscous nucleus has been assumed to be bilinear: in one case, irreversible deformations develop uniquely for positive yield function values; in a more general case, visco-plastic deformations develop even for negative values. The model has been calibrated and subsequently validated on a long temporal series of monitoring data and it seems quite reliable in simulating the in situ data. © Springer-Verlag Berlin Heidelberg 2013.

After the abandonment occurred in the '70s, the mining system (rooms and pillars) located in S. Lazzaro di Savena (BO, Italy), grown on three levels with the method rooms and pillars, has been progressively more and more affected by degradation processes due to water infiltration. The mine is located underneath a residential area causing significant concern to the local municipality. On the basis of in situ surveys, laboratory and in situ geomechanical tests, some critical scenarios were adopted in the analyses to simulate the progressive collapse of pillars and of roofs in the most critical sectors of the mine. A first set of numerical analyses using 3D geotechnical FEM codes were performed to predict the extension of the subsidence area and its interaction with buildings. Secondly 3D CFD analyses were used to evaluated the amount of water that could be eventually ejected outside the mine and eventually flooding the downstream village. The predicted extension of the subsidence area together with the predicted amount of the ejected water have been used to design possible remedial measurements.