Paolo Simonini

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.

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...

Analysis of Piezocone Penetration under Different Drainage Conditions with the Two-Phase Material Point Method

AbstractThe piezocone penetration test (CPTU) is commonly used to identify a soil’s profile and estimate its material properties. Depending on the soil type, ranging from clay to sand, undrained, partially drained, or drained conditions may occur during cone penetration. In silt and sand–clay mixtures, the CPTU penetration is characterized by partially drained conditions, which are often neglected in data interpretation. The effect of drainage on CPTU measurements has been mainly studied experimentally. Numerical analyses are rare because taking into account large soil deformations, soil–water and soil–structure interactions, and nonlinear soil behavior is still a challenging task. This paper presents and discusses numerical simulations of CPTU in saturated soils with the two-phase material point method. Soil behavior is described with the modified cam clay model. This study investigates the effects of pore pressure dissipation during penetration, cone roughness, and horizontal stress state, comparing the...

Evaluation of secondary compression of sands and silts from CPTU

The estimate of secondary compression behaviour of sandy and silty deposits is not routinely taken into account in the classical settlement calculation, due to its generally limited contribution to the total amount of strains. However, such soils exhibit a non-negligible time-dependent behaviour and the prediction of their long-term response may sometimes be important. This paper explores the capability of the piezocone test as an effective tool to estimate the one-dimensional secondary compression characteristics of sands and silts. The approach is mainly based on the observation that frictional response essentially governs both secondary compression of granular soils and cone resistance, hence it seems reasonable to establish a valid correlation among them. The study uses part of the field data assembled over the last years at the Treporti Test Site (Venice, Italy), within an extensive research project aimed at analysing the stress-strain-time response of the predominantly silty sediments forming the Venetian lagoon subsoil. Empirical, site-specific correlations for estimating the secondary compression coefficient from cone resistance are proposed. The regression analyses indicate that the estimate is slightly improved if the cone resistance-based correlations include a variable accounting for the different pore pressure response associated to the drainage conditions around the advancing cone.

The effect of the front inclination on the impact forces transmitted by granular flows to rigid structures

Open image in new window The assessment of the damage of existing structures caused by flow landslides, as well as the design of sheltering structures, requires the evaluation of the forces arising during the impact. In particular, the peak force depends on several factors such as the impact velocity, the material bulk density, the flow thickness, and the material compressibility. The effect of the front shape on the force evolution has rarely been taken into account because it is experimentally very difficult to consider. The aim of this paper is to study numerically the impact process evaluating the effect of the material constitutive parameters and shape of the flow front. Large deformations of the granular material are simulated by employing a 3D numerical approach based on the Material Point Method (MPM). The granular material mechanical behavior is simulated by means of an elastic perfectly plastic model with a Mohr-Coulomb failure criterion. The soil mass is initially positioned in front of the wall with a prescribed uniform velocity and the evolution of the impact force is monitored. The results show that the front shape not only influences the peak pressure, but also the evolution of the impact force with time.

Effect on the Structure in Elevation of Wood Deterioration on Small-Pile Foundation: Numerical Analyses

ABSTRACT Wooden pile foundations are quite common in Venice historical building. Very short, small-diameter piles are embedded into the soft shallowest soil layer under the groundwater level, but wood degradation is not prevented as anaerobic bacteria can flourish even in anoxic condition. This study couples the behavior of the masonry structure and the foundation as result of pile degradation. The numerical analyses, relative to the ancient piling, consider wood decay and secondary settlement of soil. The effect of deterioration as a function of the pile spacing and the possible presence of a stiff layer under pile tips are also investigated. The geotechnical results are then used as input for the structural model. The behavior of the masonry as result of different states of wood conservation along the wall is studied numerically.

Microstructural and Mineralogical Evaluation of the Effectiveness of Mixing Treatments in Stabilized Clays

This paper shows and discusses the results of a comprehensive mineralogical and microstructural investigation carried out on several samples collected from diaphragm walls obtained treating a deposit of overconsolidated clay with the cutter soil mixing (CSM) technology, one of the most recent methods for deep mixing. To this purpose, scanning electron microscopy, X-ray powder diffraction analysis, mercury intrusion porosimetry, and X-ray computed micro-tomography were extensively used to measure soil properties at the micro-scale. In addition, unconfined compression tests and permeability tests were conducted to evaluate the effectiveness of CSM also at the macro-scale. The capability of CSM to treat cohesive soils seems to be confirmed by the experimental investigation carried out so far, considering, particularly, the degree of mixture homogeneity achieved at the end of the mixing procedure, together with the growth of several hydration products in the cemented matrix.

High density distributed strain sensing of landslide in large scale physical model

This paper describes the application of a commercial distributed optical fiber sensing system to a large scale physical model of landslide. An optical fiber cable, deployed inside the landslide body, is interrogated by means of optical frequency domain reflectometry with very high spatial density. A shallow landslide is triggered in the physical model by artificial rainfall and the evolution of the strain is measured up to the slope failure. Precursory signs of failure are detected well before the collapse, providing insights to the failure dynamic.

Effects of Grain-Size Composition Examined in Laboratory and Numerical Tests on Artificial Mud-Flows

This paper deals with a laboratory and numerical research on mudflows performed in with the aim to study the interrelations between the grain-size composition of the mud and its rheological properties at different solid concentrations. Furthermore, the predicting capability of a new numerical model in reproducing the flow of viscous materials is evaluated.

Site Monitoring and Numerical Modelling of a Trial Embankment's Behaviour on Venice Lagoon Soils

Mineralogical and mechanical characterization of Venice lagoon soils is required for design and construction of movable floodgates that aim to safeguard the city of Venice against recurrent floods. An instrumented circular test embankment was constructed in the lagoon area, enabling accurate measurement of relevant ground displacements. In situ stress-strain-time measurements were carried out in order to investigate the viscous behaviour of Venice lagoon soils during and after embankment loading. Site monitoring was kept up also during embankment removal so that information on soil behaviour in unloading is available, too. This paper illustrates key results from embankment monitoring and also focuses on modelling of creep behaviour. A recently developed anisotropic constitutive model was calibrated for Venice lagoon soils and is used in back analysis of the embankment construction and removal process. The constitutive parameters of the model were calibrated from in situ and laboratory tests.