Simonetta Cola

Use of an up-scaled DEM model for analysing the behaviour of a shallow foundation on a model slope

This paper presents a methodological approach for the DEM modelling of geotechnical problems. The approach is based on quite general principles, which are illustrated with reference to a specific problem, i.e. the reproduction of a physical model of a foundation on a sandy slope. The approach mainly consists in the reproduction of the involved soil using a small, but statistically representative, assembly of spheres characterized by the same porosity and a slightly simplified grain-size curve. The DEM parameters are calibrated on the base of some standard compression tests on the same material utilised in the physical model. The thus calibrated DEM model is finally utilised to reproduce the tests on the model foundation, but, to limit the computational effort in this latter phase, an up-scaled grain-size curve is adopted and the corresponding DEM parameters are determined using the scaling rules provided with the approach. The performance of the numerical model in predicting the experiments is assessed by comparing both global results (foundation load–settlement curves) and local measurements (strain field). Moreover, the DEM model is finally used to test the foundation behaviour in some different loading conditions that could not be investigated in the laboratory.

Applicability of piezocone and dilatometer to characterize the soils of the Venice Lagoon

The effectiveness of two geotechnical investigation tools—the piezocone and the dilatometer—to characterize the soils forming the shallowest deposits of the upper quaternary basin of the Venice lagoon soil is examined in this study. For this purpose, the results of a comprehensive site and laboratory investigation carried out recently over a small lagoon area—the Malamocco Test Site—are used to evaluate the applicability of the most widely used charts or correlative equations to characterize soil profile and estimate the main geotechnical properties of these soils, when applied to the interpretation of CPTU and DMT results. The particular interest of this site—apart from its unquestionable historical relevance—is the presence, apparently without any regular pattern in depth and site, of a predominantly silty fraction combined with clay and/or sand, thus forming an erratic interbedding of various types of sediments. This case represents therefore the opposite condition of that which has been normally utilized in the past to calibrate the two devices, namely the presence of particularly homogeneous natural deposits or artificially sedimented homogeneous layers of sand or clay. The Malamocco Test Site may therefore be considered as test benchmark for the applicability of the two devices to characterize highly heterogeneous silty deposits.

Landslide Displacement Monitoring from Multi-Temporal Terrestrial Digital Images: Case of the Valoria Landslide Site

This work presents a low-cost method to measure the displacement of some points on the landslide surface. The method uses a sequence of terrestrial digital images. The Image Acquisition System (IAS) consists in a remote connected DSLR camera and controlled by software. The camera is fixed on a stable pillar, inside a transparent box and it periodically takes the pictures of the landslide. In order to rectify the image and to correct the little natural displacement of the image plane with respect to the landslide some fixed reference points are selected in the images. Moreover, some “well recognizable” optical targets are used in order to evaluate the displacement field. The image sequence is analyzed with a home-made digital image correlation code. The colour and size of the optical targets were evaluated in order to get the maximum accuracy of measurements and to improve the auto-matching function between the images. Taking pictures with bracketing function was proved to help the target searching phase for different weather conditions. The possibilities of the method are evaluated with reference to a sequence of images taken at the Valoria landslide site (Northern Apennines, Italy).

Overconsolidation and Stiffness of Venice Lagoon Sands and Silts from SDMT and CPTU

AbstractThis study is part of an extensive research program carried out at the Treporti test site (Venice, Italy), where a cylindrical trial embankment was constructed and monitored from the beginning of its construction until complete removal, 4 years later. This paper concentrates mainly on the evaluation of overconsolidation and stiffness of the Venice lagoon sands and silts. The possibility of estimating the overconsolidation ratio (OCR) in sand by the combined use of seismic dilatometer (SDMT) tests and piezocone (CPTU) tests is investigated. A tentative correlation for estimating the OCR in sand from the ratio MDMT/qt is constructed. Field compression curves have been back-figured from 1-m field oedometer curves reconstructed from local vertical strains measured by a sliding deformeter under the embankment center. The SDMT and CPTU soundings performed before embankment application and postremoval have permitted analyzing how the OCR caused by the embankment was reflected by the before/after SDMT and...

Collapse of quasi-two-dimensional wet granular columns

This paper deals with the experimental characterization of the collapse of wet granular columns in the pendular state, with the purpose of collecting data on triggering and jamming phenomena in wet granular media. The final deposit shape and the runout dynamics were studied for samples of glass beads, varying particle diameter, liquid surface tension, and liquid amount. We show how the runout distance decreases with increasing water amount (reaching a plateau for

Adapting a Generalized Plasticity Model to Reproduce the Stress-Strain Response of Silty Soils Forming the Venice Lagoon Basin

w>1 \%

Discrete particle simulations and experiments on the collapse of wet granular columns

) and increases with increasing Bond number, while the top and toe angles and the final deposit height increase with increasing water amount and decrease with decreasing Bond number. Dimensional analysis allowed to discuss possible scalings for the runout length and the top and toe angles: a satisfying scaling was found, based on the combination of Bond number and liquid amount.

A new data assimilation procedure to develop a debris flow run-out model

A Generalized Plasticity model, originally developed for the analysis of sandy soil behaviour, is modified in order to properly simulate the stress-strain response of a wide class of non-active natural soils, forming the upper profile of the Venice Lagoon basin. The main modification consists in introducing a state-dependent dilatancy, which allows proper modelling of granular soils over a wide range of pressures and densities, fulfilling at the same time basic premises of critical state soil mechanics. Moreover, according to recent developments on the isotropic compression of granular soils, few adjustments are introduced in the plastic modulus expression. The approach is validated by comparing the model predictions with experimental data obtained from drained triaxial compression tests on natural and reconstituted samples of soils having different fine contents.

Induced thermal compaction in cohesive sediments around a borehole heat exchanger: laboratory tests on the effect of pore water salinity

Small quantities of liquid in a granular material control the flow dynamics as well as the triggering and jamming phases. In order to study this problem, some experimental collapse tests conducted in a rectangular box were reproduced with a 1:1 scale numerical model using the Discrete Element Method. In simulations the effect of the capillary bridges has been investigated implementing a mid-range attractive force between particles based on the minimum energy approach. Also a bonding-debonding mechanism was incorporated in the algorithm and the volume of each sessile drop on the particle surface was considered during its motion. The influence of some variables was investigated with respect to the final slope profiles and the runout lengths: the initial liquid content, the particle size, the solid density, the liquid surface tension, and the liquid-solid contact angle. Also the crucial effect of the confinement walls on the collapse phenomenon was investigated: wet particles adhere to the lateral walls prov...

Applicability of Two Propagation Models to Simulate the Rotolon Earth-Flow Occurred in November 2010

Parameter calibration is one of the most problematic phases of numerical modeling since the choice of parameters affects the model’s reliability as far as the physical problems being studied are concerned. In some cases, laboratory tests or physical models evaluating model parameters cannot be completed and other strategies must be adopted; numerical models reproducing debris flow propagation are one of these. Since scale problems affect the reproduction of real debris flows in the laboratory or specific tests used to determine rheological parameters, calibration is usually carried out by comparing in a subjective way only a few parameters, such as the heights of soil deposits calculated for some sections of the debris flows or the distance traveled by the debris flows using the values detected in situ after an event has occurred. Since no automatic or objective procedure has as yet been produced, this paper presents a numerical procedure based on the application of a statistical algorithm, which makes it possible to define, without ambiguities, the best parameter set. The procedure has been applied to a study case for which digital elevation models of both before and after an important event exist, implicating that a good database for applying the method was available. Its application has uncovered insights to better understand debris flows and related phenomena.