Diana Salciarini

Thermomechanical Effects Induced by Energy Piles Operation in a Small Piled Raft

AbstractIn this work, a series of fully coupled three-dimensional thermomechanical finite-element analyses has been carried out to investigate the mechanical and thermal interaction effects induced in a small piled raft equipped with energy piles during the operation of an air-conditioning system based on ground source heat pumps (GSHPs). In particular, attention has focused on (1) the axial-load redistribution among the various piles of the raft as a result of differential thermal dilations occurring in the pile and the soil during the transient heat conduction process and (2) the thermal interaction effects that may affect the heat exchange process when multiple energy piles are placed at short distances within the same piled raft. The results of the numerical simulations, which are in qualitative agreement with the limited experimental observations from full-scale tests on energy piles currently available in the literature, show that significant (positive and negative) axial-load changes can be experie...

Spatially distributed rainfall thresholds for the initiation of shallow landslides

The evaluation of the combined influence of rainfall patterns (in terms of mean intensity and duration) and the geomorphological and mechanical characteristics of hillslopes on their stability conditions is a major goal in the assessment of the shallow landslide triggering processes. Geographic Information Systems (GIS) represent an important tool to develop models that combine hydrological and geomechanical analyses for the evaluation of slope stability, as they allow to combine information concerning rainfall characteristics with topographic and mechanical properties of the slopes over wide areas. In this paper, a GIS-based code is developed to determine physically based intensity/duration rainfall thresholds at the local scale. Given the rainfall duration and the local geometric, hydrological and mechanical characteristics of the slopes, the code evaluates the spatial distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given area. The key feature of the code is the capability of evaluating the time tp required to reach the peak pore pressure head on the failure surface and computing the corresponding critical intensity/duration thresholds based on post-event peak pore pressures. The reliability of the model is tested using a set of one-dimensional analyses, comparing the physically based thresholds obtained for three different slopes with some empirical rainfall thresholds. In a log–log scale, the thresholds provided by the model decrease linearly with increased rainfall duration and they are bracketed by the empirical thresholds considered. Finally, an example of application to a study area of the Umbria region in central Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios.

A probabilistic model for rainfall—induced shallow landslide prediction at the regional scale

This paper presents a new probabilistic physically-based computational model (called PG_TRIGRS) for the probabilistic analysis of rainfall-induced landslide hazard at a regional scale. The model is based on the deterministic approach implemented in the original TRIGRS code, developed by Baum et al. (USGS Open File Report 02–424, 2002) and Baum et al. (USGS Open File Report 08–1159, 2008). Its key innovative features are: (a) the application of Ordinary Kriging for the estimation of the spatial distributions of the first two statistical moments of the probability density functions of the relevant soil properties over the entire area, based on limited available information gathered from available information from limited site investigation campaigns, and (b) the use of Rosenblueth’s Point Estimate method as a more efficient alternative to the classical Monte Carlo method for the reliability analysis performed at the single-cell level to obtain the probability of failure associated to a given rainfall event. The application of the PG_TRIGRS code to a selected study area located in the Umbria Region for different idealized but realistic rainfall scenarios has demonstrated the computational efficiency and the accuracy of the proposed methodology, assessed by comparing predicted landslide densities with available field observations reported by the IFFI project. In particular, while the model might fail to identify all individual landslide events, its predictions are remarkably good in identifying the areas of higher landslide density.

Landwarn: An Operative Early Warning System for Landslides Forecasting Based on Rainfall Thresholds and Soil Moisture

The Umbria Region is one of the Italian areas that are most prone to landslides and floods. For early-warning procedures aimed at the reduction of the hydrogeological risk, the rainfall thresholds represent the main component of the Italian Civil Protection System. To improve the performances of the alert system for landslide risk, the Umbria Region CFD, in cooperation with the Research Institute for Geo-Hydrological Protection (IRPI-CNR), developed and tested a continuous physically-based soil water balance model, addressed to the estimation of soil moisture conditions over the whole regional territory prior to severe landslide events. The relationship established between the maximum cumulative rainfall values and the soil moisture preceding the triggering of landslides allows to dynamically adjust the rainfall thresholds as a function of the estimated soil moisture values. The main components of the new early-warning system (named LANDWARN) for landslide risk prevention operating at the CFD are: (1) the observed and 72 h-predicted cumulative rainfall from the dense regional hydrometeorological network; (2) a local area meteorological model, known as COSMO ME; (3) the soil water balance model by Brocca et al. 2008; and (4) a web-based Information System. All these elements are arranged in a MATLAB-based flux of operations. Nowadays, the system is still under development and implemented at three different scales: (1) for a specific rockslide site, where a real-time extensometer network is available; (2) for 110 high-risk landslide sites located across the whole regional territory; and (3) for the whole regional territory over a regular grid. Further steps of the implementation are currently in progress. In particular, a GIS-based physically-based model that combines the hydrological information with a simple slope stability analysis is being validated in a test-area of the Umbria Region (Salciarini et al. Nat Hazards 9739–9742, 2011), with the aim of evaluating the possibility of developing an early-warning system capable to take into account the mechanical and physical characteristics of the slopes, besides rainfall and soil moisture.

Physically – Based Critical Rainfall Thresholds for Unsaturated Soil Slopes

In this work, a physically based model for the definition of the critical rainfall thresholds for shallow landslide initiation at regional scale is presented. The model is capable of considering unsaturated conditions in the soil volume, by taking into account the effect of partial saturation in: a) the balance of mass for the pore water; b) the deformability of the solid skeleton; and, c) the soil shear strength. Starting from the simplified hypothesis of infinite slope, a series of numerical simulations was conducted in parametric form to determine the functional relationship between the critical rainfall intensity leading the slope to failure to rainfall duration, in terms of dimensionless variables. This has allowed to identify the functional dependence of the critical rainfall intensity on: a) event duration; b) slope geometry; c) mechanical properties of the soil cover; and, d) initial conditions in terms of pore water pressure distribution. The function thus obtained can be easily and efficiently implemented in GIS–based codes for the evaluation of physically–based, spatially–distributed critical rainfall thresholds.

Physically Based Rainfall Thresholds for Shallow Landslide Initiation at Regional Scales

In this work, a physically based model that allows for the evaluation of rainfall thresholds for shallow landslide initiation at regional scales is applied to a study area in central Italy. The model is able to consider unsaturated conditions in the soil volume, by taking into account separately the evolution of pore water pressure below the water table and in the vadose zone. Starting from the simplified hypothesis of infinite slope, a series of numerical simulations were conducted in parametric form for the solution of the Richards equation, generalized to the case of deformable soil and formulated in terms of dimensionless variables. For the application of the model, an extended database of physical and mechanical properties of the soils within the study area was created by collecting data from the archives of the Civil Protection Provincial Office, considering the results of about 2,000 site investigations. This allowed us to identify the functional dependence of the critical rainfall intensity on the duration of the event, the geometric characteristics of the slope, the mechanical properties of the soil and the initial pore pressure regime. The study also shows that results are not sensitive to the deformation parameters.

Mapping earthquake-induced landslide susceptibility in central Italy

In this work, a model to forecast the spatial distribution of earthquake-induced landslide hazard at the regional scale has been developed. The model adopts a displacement–based approach, solving the Newmark equation for the infinite slope problem for each cell of a regular grid discretizing the study area. In Newmark’s approach, seismic slope stability is measured in terms of the ratio of accumulated permanent displacement during the earthquake and the maximum allowable one, depending—in principle—on the definition of tolerable damage level. The computed permanent displacement depends critically on the actual slope stability conditions, quantified by the critical acceleration, i.e. the seismic acceleration bringing the slope to a state of (instantaneous) limit equilibrium. Given the slope features (physical and mechanical properties, geometrical and topographical settings and pore pressure regime) for each cell and the earthquake characteristics, the model is able to predict the potentially unstable zones over the study area. The 1997 Umbria-Marche earthquake has been selected as a benchmark for the model. The model predictions have been compared with an available database of actually occurred landslides after the considered earthquake, and a good correspondence between the predictions and actual field observations has been obtained.

Defining Physically-Based Rainfall Thresholds for Early Warning Systems

Empirical rainfall thresholds compiled on correlations between recorded data show that precipitation intensities and durations required to trigger shallow landslides vary with climatic, geotechnical and topographic conditions; consequently, thresholds exhibit a high degree of spatial variability, even across relatively small geographic areas (see, e.g., Baum and Godt (Landslides 7:259–272, 2010; Guzzetti et al. Landslides 5:3–17, 2008). In order to define intensity/duration rainfall thresholds capable of considering the site-specific hillslope characteristics, GIS-based modelling techniques have been developed and successfully applied starting from Iverson’s theory (Baum et al. TRIGRS – a Fortran program for transient rainfall infiltration and grid–based regional slope–stability analysis, version 2.0, 2008; Godt et al. Rev Eng Geol 20:137–152, 2008; Salciarini et al. Eng Geol 102:227–237, 2008). In this work A GIS-based code is presented which permits the assessment of the spatial distribution of the minimum rainfall intensity that triggers shallow landslides and debris flows over a given study area, based on the rainfall duration and the local geometric, hydrologic and mechanical characteristics of the slopes. Such an approach is used for predicting landslide scenarios produced by short-duration rainfalls. An example of application to a study area of the Umbria Region in central Italy is presented, describing the capability of the model of providing site-specific thresholds for different rainfall scenarios and issuing different levels of hazard warning. The application illustrates some challenges on the technically feasibility of shallow-landslide early warning systems, capable of including specific information on the affected areas, probability of landslide occurrence and expected timing.

MULTIPHYSICS MODELING OF ELECTROKINETIC PHENOMENA IN UNSATURATED FINE-GRAINED SOILS

A multiphysics model for the analysis of coupled deformation and reactive flow of pore fluids, chemical species and electric current has been developed to assess the influence of the geochemical reactions taking place within the soil mass on the effectiveness of electrokinetic remediation treatments. The results of FE simulations have shown that the presence of carbonates in the solid phase may give rise to gas production, significant changes in the degree of saturation and buffering effects with respect to the pore water pH. Under such conditions, the efficiency of the electrokinetic treatment can be significantly reduced.