Andrea Diambra

Space–time prediction of rainfall-induced shallow landslides through a combined probabilistic/deterministic approach, optimized for initial water table conditions

In landslide-prone areas the magnitude of events is related to recurring rainfall intensity. In a large sector of the Sannio Apennines (Southern Italy), predictive mapping of recurrent shallow landslides was undertaken by combining deterministic and probabilistic predictive approaches. This, with the aim to minimize the negative influence of the uniform distribution of the initial water table depth in steady condition that usually influence the theoretical instability resulting from the application of methods for large-scale estimation. The deterministic approach was performed by means of the Transient Rainfall Infiltration and Grid-based Regional Slope-stability model to obtain triggering maps in multi-temporal transient pore-water pressures. The optimized physical modeling was validated by back-analysis on large-magnitude landslide events which occurred in 2003 by means of the introduction of two cross-mapping correlation indexes. Subsequently, different predictive scenarios were proposed for different probabilistic return periods of the rainstorm events. The output data permitted the definition of a linear log regression curve to estimate the theoretical instability of the study area. This curve is defined as a function of cumulative precipitation, duration and return periods of the possible rainfall events.

Theoretical Derivation of Artificially Cemented Granular Soil Strength

AbstractThis paper provides a theoretical derivation for the unconfined compression strength of artificially cemented granular soils. The proposed developments are based on the concept of superposi...

Memory Surface Hardening Model for Granular Soils under Repeated Loading Conditions

AbstractThe prediction of the stress-strain response of granular soils under large numbers of repeated loading cycles requires subtle changes to existing models, although the basic framework of kinematic hardening/bounding surface elastoplasticity can be retained. Extending an existing model, an extra memory surface is introduced to track the stress history of the soil. The memory surface can evolve in size and position according to three rules that can be linked with physical principles of particle fabric and interaction. The memory surface changes in size and position through the experienced plastic volumetric strains, but it always encloses the current stress state and the yield surface; these simple rules permit progressive stiffening of the soil in cyclic loading, the accurate prediction of plastic strain rate accumulation during cyclic loading, and the description of slightly stiffer stress-strain response upon subsequent monotonic reloading. The implementation of the additional modeling features re...

A sole empirical correlation expressing strength of fine-grained soils – lime mixtures

This paper advances understanding of the key parameters controlling unconfined compressive strength (qu) of lime stabilized fine-grained soils by considering distinct specimen porosities ( ), different lime types and contents and several curing temperatures and time periods. A sole empirical relationship is proposed establishing the normalized unconfined compression strength for lime stabilized fine-grained materials considering all porosities, lime contents, curing temperatures and curing periods studied. From a practical point of view, this means that a very limited number of unconfined compression tests on specific lime stabilized fine-grained material specimens molded with a given lime type and amount, porosity, moisture content and cured for a given time period at a particular temperature, should be sufficient to estimate the strength for an entire range of porosities and lime contents at any given condition. Examples of the practicality of the proposed relationship are presented.

3D fibre architecture of fibre-reinforced sand

The mechanical behaviour of fibre-reinforced sands is primarily governed by the three-dimensional fibre architecture within the sand matrix. In laboratory, the normal procedures for sample preparation of fibre-sand mixtures generally produce a distribution of fibre orientations with a preferential bedding orientation, generating strength anisotropy of the composite’s response under loading. While demonstrating the potential application of X-ray tomography to the analysis of fibre-reinforced soils, this paper provides for the first time a direct experimental description of the three-dimensional architecture of the fibres induced by the laboratory sample fabrication method. Miniature fibre reinforced sand samples were produced using two widely used laboratory sample fabrication techniques: the moist tamping and the moist vibration. It is shown that both laboratory fabrication methods create anisotropic fibre orientation with preferential sub-horizontal directions. The fibre orientation distribution does not seem to be affected by the concentration of fibres, at least for the fibre concentrations considered in this study and, for both fabrication methods, the fibre orientation distribution appears to be axisymmetric with respect to the vertical axis of the sample. The X-ray analysis also demonstrates the presence of an increased porosity in the fibre vicinity, which confirms the assumption of the “stolen void ratio” effect adopted in previous constitutive modelling. A fibre orientation distribution function is tested and a combined experimental and analytical method for fibre orientation determination is further validated.

Compacted Chalk Putty-Cement Blends: Mechanical Properties and Performance

AbstractCompaction and portland cement addition are among the promising ground improvement procedures to enhance the mechanical properties of chalk putty. The present investigation intends to compu...