Abstract Models for forecasting rainfall-induced landslides are mostly based on the identification of empirical rainfall thresholds obtained exploiting rain gauge data. Despite their increased availability, satellite rainfall estimates are scarcely used for this purpose. Satellite data should be useful in ungauged and remote areas, or should provide a significant spatial and temporal reference in gauged areas. In this paper, the analysis of the reliability of rainfall thresholds based on rainfall remote sensed and rain gauge data for the prediction of landslide occurrence is carried out. To date, the estimation of the uncertainty associated with the empirical rainfall thresholds is mostly based on a bootstrap resampling of the rainfall duration and the cumulated event rainfall pairs ( D , E ) characterizing rainfall events responsible for past failures. This estimation does not consider the measurement uncertainty associated with D and E . In the paper, we propose (i) a new automated procedure to reconstruct ED conditions responsible for the landslide triggering and their uncertainties, and (ii) three new methods to identify rainfall threshold for the possible landslide occurrence, exploiting rain gauge and satellite data. In particular, the proposed methods are based on Least Square (LS), Quantile Regression (QR) and Nonlinear Least Square (NLS) statistical approaches. We applied the new procedure and methods to define empirical rainfall thresholds and their associated uncertainties in the Umbria region (central Italy) using both rain-gauge measurements and satellite estimates. We finally validated the thresholds and tested the effectiveness of the different threshold definition methods with independent landslide information. The NLS method among the others performed better in calculating thresholds in the full range of rainfall durations. We found that the thresholds obtained from satellite data are lower than those obtained from rain gauge measurements. This is in agreement with the literature, where satellite rainfall data underestimate the “ground” rainfall registered by rain gauges.

Statistical approaches for the definition of landslide rainfall thresholds and their uncertainty using rain gauge and satellite data

Integrated GPR and laboratory water content measures of sandy soils: From laboratory to field scale

Influence of Layer Transition Zone on Rainfall-Induced Instability of Multilayered Slope

A probabilistic approach for the assessment of the influence of the dielectric constant of pore fluids on the liquid limit of smectite and kaolinite

Atrazine (ATZ) is one of the most heavily used herbicides in the world, particularly in the United States and Australia. This study evaluated the compressibility and permeability characteristics of two Western Australia natural clays contaminated with varying ATZ contents. A series of one-dimensional consolidation tests using fixed-ring oedometer device were conducted, and the final hydraulic conductivity was calculated at the end of each loading stage. At the first stage, the strain–time graphs at 1,280 kPa effective overburden pressure (σ′n) were evaluated, and the results indicated that the specimens with a greater ATZ content have higher values of final vertical strain (ϵv). Then, the compression index (Cc) values were computed from the void ratio–effective overburden pressure curves (e−σ′n), and the results showed that the compression index (Cc) increased as the ATZ content of the tested clays increased. At the next stage, the coefficient of consolidation (cv) was calculated using the Casagrande method and the Taylor method. The results showed that the computed coefficient of consolidation (cv) using the Taylor method was slightly greater than those calculated using the Casagrande method in both tested clays. Also, the hydraulic conductivity (k) values of the tested clays increased as the contamination content increased (i.e., 3.1 × 10-7 ≤ k ≤ 129 × 10-7 cm/s and 4.49 × 10-9 ≤ k ≤ 95.3 × 10-9 cm/s). This behavior, which was attributed to promotion of the agglomeration and aggregation between clay particles, promoted formation of the tiny voids in the soil. Finally, the secondary compression ratio (Rα) and secondary compression index (Cα) were computed, and the results showed that the specimens containing higher ATZ content had greater values of Rα and Cα.

Effect of Atrazine Contamination on Compressibility and Permeability Characteristics of Clay

Shallow landslide failures are distributed worldwide and cause economic losses and fatalities. A proper evaluation of the possible occurrence of shallow landslides requires reliable characterization of water content. Volumetric water content (θ) is commonly estimated using dielectric sensors, which use manufacturers’ calibration curves developed for specific soil types. In this study, we present the experimental results achieved during a laboratory calibration of a capacitance probe (PR2/6 probe), tested on two sandy soils widely outcropping in Central Italy. The proposed equations demonstrate a more reliable estimation of θ with respect to the generalized soil equation provided by the manufacturer, which overestimates θ by up to 10 percentage points. Such overestimation could affect the evaluation of suction stress in partially saturated shallow soils affecting the slope stability analysis. Although the use of θ from correct calibration equations provides less precautionary factor of safety values, a reliable evaluation of the soil moisture condition is fundamental when mapping and predicting the spatial and temporal occurrence of shallow landslides. The use of the PR2/6 probe with the appropriate soil calibration equations in early warning monitoring systems will provide a more reliable forecast, minimizing the number of false alarms.

Reliability of water content estimation by profile probe and its effect on slope stability

Low plasticity clays are commonly present in compacted soils such road embankments: in this context, prolonged spillage from storage tanks (e.g., refueling stations) containing conventional and alternative fuels (biofuels) may trigger changes in the hydrogeological and geotechnical properties of the soil structure, influencing its overall stability. Moreover, these changes may facilitate migration of pollutants into the environment. This article examines the effect of bioethanol-based fluids on the coefficient of permeability of kaolinitic clay, experimentally investigated by means of an oedometer set up for a falling-head permebilty test. Test results indicate that the addition of high fractions of ethanol in gasoline substantially increases the permeability up to two orders of magnitude with respect to water: changes are produced by the formation of clusters (flocculation) and the development of cracks and pores identifiable at both a macro and micro scale using a high-resolution scanning electron microscope. Although the intrinsic permeability increases with increasing fractions of ethanol in water, no appreciable changes were observed when pure ethanol or a mixture of ethanol/water up to 50 % were used as pore fluids. This work is to be considered as a starting point for further studies, to be extended to other clayey soils with low plasticity used in road engineering: results may be also useful in designing remediation techniques in areas potentially affected by ethanol spillage from refineries or pipelines.

Permeability of remoulded low-plasticity clay contaminated by bioethanol-based fluids

This paper is aimed to illustrate and discuss new data from the clayey deposits collected in the Dunarobba area (Umbria, central Italy), and to better understand some features of the “Fosso Bianco” Unit lacustrine stage inside the South Tiberino Basin, during its latest (presumably Early Pleistocene) phases. Data come from a newly cultivated quarry area (Cava Nuova), only partly considered in previous works; the new section extends well inside the deep lake depositional stage of Fosso Bianco Unit, previously not directly described in outcrop in the Dunarobba area, but only reported from well logs. Selected samples from the Cava Nuova section were analyzed from sedimentological, geotechnical, chemical, mineralogical and biostratigraphical point of view. Sedimentological and geotechnical analyses, including density measurements, particle-size analysis, Atterberg limits and organic matter content, as well as XRF and XRPD analyses, resulted the most suitable techniques to identify the main features, at least for prevailing clayey deposits. Facies analysis and sedimentological data lead to recognize a clear depositional transition from relatively deep to shallow lacustrine deposits, which was only rarely documented formerly through a single section. On the other hand, both geotechnical and mineralogical data indicate a compositional homogeneity for clay sediments, which does not correspond with facies lateral and vertical variability nor with palaeoenvironmental complexity. Despite its preliminary nature, this integrated method looks very promising to characterize the paleodepositional context, and some hypotheses on sediment source were also evaluated. Integrated data from Cava Nuova section, as well as minor well-logs in the immediate surroundings, were discussed and compared with existing data outcoming from the whole Dunarobba area. On the heels of the recent literature, this paper is aimed to put a new light on the complexity of the Fosso Bianco paleoenvironment.

Giuseppe Vinti

Papers

Reliability of water content estimation by profile probe and its effect on slope stability

Permeability of remoulded low-plasticity clay contaminated by bioethanol-based fluids

New integrated data from clay lacustrine deposits of the Dunarobba Area (Umbria, Central Italy)