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This 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 1–2 m deep that experience static liquefaction during the post-failure stage. Perennial graminae grasses were seeded in a one-dimensional 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. [ABSTRACT FROM AUTHOR]

This paper reports the main results of an extensive piezocone testing campaign performed over the last years at the Treporti test site (Venice, Italy) within a long-lasting and comprehensive research project aimed at developing a reliable geotechnical model of the heterogeneous and highly stratified Venetian lagoon basin. The project included the construction of a full-scale vertical-walled cylindrical test bank, together with a detailed monitoring system of surface settlements, pore-water pressures, subsoil strains, and stresses beneath the loaded area. The analysis of the large amount of data thus available, referring to different phases of the loading history, confirms the great potential of piezocone as an in situ testing technique, especially for stratigraphic profiling of the predominantly silty subsoil of the Venetian lagoon, but at the same time reveals some limitations of widely used empirical correlations for the relevant soil characterization, with special reference to compressibility and consolidation properties of such intermediate sediments. Indeed, partial drainage effects during cone penetration, as well as potentially dilative behaviour of these soils, should be taken into careful consideration to derive reliable soil parameters from in situ measurements. More suitable site-specific correlations have been introduced, according to the recent findings on piezocone data interpretation. [ABSTRACT FROM AUTHOR]

In situ, seasonal changes expose soils to frequent wetting–drying–freezing–thawing cycles. Such processes can favour and trigger shallow instabilities controlled by the weathering process. This paper presents an experimental study carried out to investigate the effects of the weathering process, caused by the wetting–drying–freezing–thawing cycles, on the compressibility and shear strength of a natural clay. Several specimens were trimmed from block samples of overconsolidated clays taken from a slope in south Calabria, Italy. Specimens were subjected to wetting–drying–freezing–thawing cycles of different durations and then tested with standard equipment (oedometer and direct shear). Test results show that the wetting–drying–freezing–thawing cycles caused a change in the initial microstructure that produced a decrease in the compression index and an increase in the swelling index. Moreover, the direct shear test results show a decrease in the peak shear strength and demonstrate that a larger reduction occurs in the first month of weathering cycles. The intense cycles performed in the laboratory produced a decay of compressibility and a shear strength approaching reconstituted values. The conclusions are important when choosing the shear strength parameters required when studying shallow landsliding in clay slopes. [ABSTRACT FROM AUTHOR]