An experimental plot for hydrological processes modeling

In this paper we describe the data and some preliminary analysis as the investigations of infiltration process, soil water content profiles dynamic and water movement systems, referring to an experimental plot. The broad aim of the work is to test the usefulness for hydrological modelling of a soil moisture monitoring methodology which is based on capacitance devices and has the benefit to be an easy and low cost system. Collected data are expected to be useful to improve the general understanding at the field scale

A review of the occurrence and causes for wildfires and their impacts on the geoenvironment

Wildfires have short- and long-term impacts on the geoenvironment, including the changes to biogeochemical and mechanical properties of soils, landfill stability, surface- and groundwater, air pollution, and vegetation. Climate change has increased the extent and severity of wildfires across the world. Simultaneously, anthropogenic activities—through the expansion of urban areas into wildlands, abandonment of rural practices, and accidental or intentional fire-inception activities—are also responsible for a majority of fires. This paper provides an overall review and critical appraisal of existing knowledge about processes induced by wildfires and their impact on the geoenvironment. Burning of vegetation leads to loss of root reinforcement and changes in soil hydromechanical properties. Also, depending on the fire temperature, soil can be rendered hydrophobic or hydrophilic and compromise soil nutrition levels, hinder revegetation, and, in turn, increase post-fire erosion and the debris flow susceptibility of hillslopes. In addition to direct hazards, wildfires pollute air and soil with smoke and fire suppression agents releasing toxic, persistent, and relatively mobile contaminants into the geoenvironment. Nevertheless, the mitigation of wildfires’ geoenvironmental impacts does not fit within the scope of this paper. In the end, and in no exhaustive way, some of the areas requiring future research are highlighted

The influence of grass roots on the shear strength of pyroclastic soils

The paper investigates the effects of indigenous vegetation on the shear strength of loose pyroclastic soils of the Campania region (Southern Italy); these soils are frequently affected by shallow landslides 1-2m deep that experience static liquefaction during the post-failure stage. Perennial graminae grasses were seeded in a 1D column 2 m high and filled by pyroclastic soils, allowing the root to grow under atmospheric conditions. A noninvasive sampling procedure was adopted to take the vegetated soil samples, in which the roots were in their natural geometrical distribution. For each rooted sample, the root biomass RM was measured, and the root volume density RVD was calculated. Isotropic consolidated triaxial tests in both drained and undrained conditions were performed on the rooted specimens, as well as on bare specimens as a control. The obtained results showed that the roots generally provided an increment to the soil strength. In drained conditions a reduction in the volumetric deformation was observed, which, under undrained conditions, was reflected in a general reduction of the excess pore water pressures with a possible inhibition of the static liquefaction occurrence. This study highlights the potential role of grass roots as bio-engineering practice for stabilizing shallow covers of pyroclastic soils.The influence of grass roots on the shear strength of pyroclastic soilsacceptedVersio

Penetration tests in shallow layered unsaturated pyroclastic soil deposits of Southern Italy

The paper deals with a recent extensive in-situ and laboratory investigation carried out in a site characterized by thin layered unsaturated air-fall volcanic (pyroclastic) soil deposits, which are very steep and prone to slope failures turning into catastrophic flows (Cervinara, Southern Italy). The field campaign was based on iron-rod drillings, penetration tests and hand-excavated shafts, beside to the collection of undisturbed soil specimens used for laboratory tests. The real sequence of the soil layers was identified in more than two hundreds verticals. In addition, while a series of available literature formulas are detected as unreliable for these soils, the paper propose new reliable empirical correlations between the soil friction angle (of three lithotypes) and both the number of blows of the penetration test and the vertical stress

Shear strength of a pyroclastic soil measured in different testing devices

The paper deals with the shear strength of a Vesuvian pyroclastic soil (southern Italy), sampled in a district, where flowslides frequently occur. Direct shear tests, drained and undrained triaxial tests, as well as simple shear tests were carried out. The use of different testing devices was motivated by an extensive literature, which outlines some differences among the measured shear strength due to different failure mechanisms. The interpretation of the experimental results was made through distinct procedures, specific for each type of device. As main insight, some differences were pointed out for the effective friction angle (ϕ) and for the stress ratio (M) at critical state, as computed in the deviatoric (q–p) plane for triaxial conditions. Particularly, the results of the simple shear tests, whether interpreted in the (t–s) plane, well agree the direct shear and triaxial tests, and the differences were related to the normalized displacement of the specimen at failure

Simple Shear Tests on Unsaturated Soils

Abstract Rainfall induces landslides in several geo-environmental contexts through a variety of triggering mechanisms. In shallow covers of unsaturated silts or loose sands, static liquefaction may occur upon shearing or wetting. The paper proposes simple shear and wetting tests performed on remoulded specimens of air-fall volcanic pyroclastic silty sands from Sarno site (Italy), where huge flowslides occurred. Simple shear wetting tests reproduce the initial stress conditions in the field as well as the stress path of the most common triggering mechanisms which take place during critical rainfalls. The tests are carried out through the Unsaturated Simple Shear apparatus designed at the University of Salerno. First, simple shear tests are performed in dry and saturated conditions and the results compared in terms of shear strength and volumetric response. Then, wetting tests – under constant vertical stress or constant shear stress – are performed. The experimental results are presented and the future research is outlined

One-dimensional consolidation of unsaturated pyroclastic soils: Theoretical analysis and experimental results

This paper synthesizes the results of a study aimed at analyzing the one-dimensional consolidation of unsaturated pyroclastic soils from both theoretical and experimental points of view. In order to pursue this goal, the differential equations governing the problem are firstly derived and their set is solved via the use of the Finite Difference Method. Input data consist of hydraulic and mechanical parameters whereas output data – changing in space and with time – are the settlement, the pore water pressure and the air pressure of the modelled medium. The values of constitutive parameters appearing in the theoretical model are calibrated on the basis of experimental results achieved from laboratory tests carried out, via a suction controlled oedometer, on specimens of unsaturated pyroclastic soils. Considering that consolidation settlements of unsaturated soils are lower than those experienced by the same soils in saturated conditions (changes in boundary conditions being equal), the followed approach – which combines theoretical and experimental results – can be profitably adopted in geotechnical problems in which the quantitative prediction of consolidation settlement values is a requirement of particular concern

Experimental Analysis of the Fire-Induced Effects on the Physical, Mechanical, and Hydraulic Properties of Sloping Pyroclastic Soils

The paper investigates the changes in the physical, mechanical, and hydraulic properties of coarse-grained pyroclastic soils, considered under both wildfire-burned and laboratory heating conditions. The soil samples were collected on Mount “Le Porche” in the municipality of Siano (Campania Region, Southern Italy), hit by wildfires on 20 September 2019. The area is prone to fast-moving landslides, as testified by the disastrous events of 5–6 May 1998. The experimental results show that the analyzed surficial samples exhibited (i) grain size distribution variations due to the disaggregation of gravelly and sandy particles (mostly of pumice nature), (ii) chromatic changes ranging from black to reddish, (iii) changes in specific gravity in low-severity fire-burned soil samples different from those exposed to laboratory heating treatments; (iv) progressive reductions of shear strength, associated with a decrease in the cohesive contribution offered by the soil-root systems and, for more severe burns, even in the soil friction angle, and (v) changes in soil-water retention capacity. Although the analyses deserve further deepening, the appropriate knowledge on these issues could provide key inputs for geotechnical analyses dealing with landslide susceptibility on fire-affected slopes in unsaturated conditions