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Papers by Erminio Salvatore

Research paper thumbnail of Improving the Performance of Deep Soil Mixing in Clay with Chemical Additives

Research paper thumbnail of Strain localization in triaxial tests on sand studied with geostatistical analyses of the porosity distribution

Géotechnique Letters, 2019

Strain localisation influences the behaviour of sheared soils in a way that the assumption of the... more Strain localisation influences the behaviour of sheared soils in a way that the assumption of the continuum loses validity and may become inapplicable. This occurrence affects the interpretation of triaxial tests where samples are usually considered as representative elements of an equivalent continuum and a phenomenological interpretation is carried out to calibrate constitutive models. Considering the inherent and stress-induced heterogeneity of the material as a possible precursor of localisation, the evolution of porosity and strain fields is studied interpreting with statistical and geostatistical analyses, the results of X-ray computerised microtomography. The study is performed on sandy samples sheared in triaxial compression and extension. The analysis carried out before shearing shows a meaningful statistical heterogeneity of the porosity with correlation lengths to the order of a few grain diameters. The evolution on shearing reveals the onset of a second statistical popul...

Research paper thumbnail of Conditioning clayey soils with a dispersant agent for Deep Soil Mixing application: laboratory experiments and artificial neural network interpretation

Research paper thumbnail of Critical State of Sand Determined with Triaxial Tests

Research paper thumbnail of Liquefaction risk assessment: lesson learned from a case study

A detailed and comprehensive assessment of risk is the basis to protect communities<br> and... more A detailed and comprehensive assessment of risk is the basis to protect communities<br> and assist decision-making towards the sustainable management of territories. For liquefaction<br> this process implies to simultaneously investigate seismic hazard, susceptibility of the subsoil,<br> vulnerability of structures, economic and social relevance of critical infrastructures and<br> ultimately build a comprehensive multi-level model that considers the interaction among all aspects.<br> Developing a methodology to achieve this goal is the scope of Liquefact, a EU H2020<br> project. A case study pervasively affected by liquefaction damages is here studied as a real scale<br> scenario to identify the main factors of uncertainty. The available data concerning seismic motion,<br> subsoil and building characteristics, damage and economic loss are used to develop a methodology<br> aimed at quantifying and reducing uncertainties in the spa...

Research paper thumbnail of Low Pressure Grouting with Nanosilicates to Reduce the Liquefaction Susceptibility of Sand

The paper reports an experimental laboratory study aimed at investigating the effectiveness of lo... more The paper reports an experimental laboratory study aimed at investigating the effectiveness of low pressure grouting with nano-silica compounds as a remedial against liquefaction of sandy soils and to optimize the technique rendering it more attractive from the technical and economical viewpoint.<br> The grout herein adopted is a three-component mix of an aqueous suspension of sub-micrometric silica particles, water and an aqueous solution of sodium chloride. The latter, raising the pH of the suspension triggers the formation of the silica gel that clogging the soil pores reduces the mobility of the grains and, hopefully, produces a stiffer response and a reduced contractive tendency of the material.<br> A preliminary set of laboratory vane tests is performed to observe the gelling time of the material and fix the curing time of the samples by measuring the increase of shear resistance.<br> Thus, reconstituted samples of a silica sand, manufactured at two different...

Research paper thumbnail of Experimental Evidence of the Effectiveness and Applicability of Colloidal Nanosilica Grouting for Liquefaction Mitigation

Journal of Geotechnical and Geoenvironmental Engineering, 2020

AbstractThe low viscosity and the ability to control solidification rate make colloidal nanosilic... more AbstractThe low viscosity and the ability to control solidification rate make colloidal nanosilica grout an excellent ground-improvement solution which is functional for different engineering purpo...

Research paper thumbnail of Strain Localisation in Sand in Cycles of Triaxial Compression and Extension: Continuum and Grain-Scale Analysis

In this work we present selected results from a recent experimental programme where small sand sp... more In this work we present selected results from a recent experimental programme where small sand specimens are subjected to cycles of triaxial compression and triaxial extension: the material is “yielded” in extension, after which the loading is reversed and the material is “yielded” in compression—a number of cycles are performed. The ways in which extension and compression-like localisation patterns (i.e., dilatant shear banding, and necking respectively) appear, get activated and disactivated on reversal of loading are measured, and discussed—in terms of both (continuum) strain fields and individual grain rotations.

Research paper thumbnail of The Effects of Strain Localization on the Determination of Critical State Seen with Experimental and Numerical Models

The paper aims to study the role of strain localization on the results of triaxial test on sand a... more The paper aims to study the role of strain localization on the results of triaxial test on sand and more particularly on the determination of the Critical State. To this aim, triaxial compression and extension tests have been performed by adopting the tomographic technique and digital image correlation to detect strain localization. Then the tests have been numerically simulated adopting a recent advanced Critical State constitutive model. The simulation, firstly carried out with the classical element test approach, i.e., considering the sample as a single element representative of the soil behaviour, has proven to be unable to capture the soil response under the various loading conditions. Then the analysis has been repeated assuming the triaxial test as a physical model, i.e., introducing the boundary conditions given by the tests and simulating the sample as made of different elements each of different initial porosity, as observed from the tomography. The analysis reveals the im...

Research paper thumbnail of Effect of strain localization on the response of granular materials subjected to monotonic and cyclic triaxial tests

Research paper thumbnail of Non destructive tests to detect the integrity of steel anchors in corrosive environments

Research paper thumbnail of Compression and extension triaxial tests on sand, studied with X-ray microtomography and digital image correlation

Research paper thumbnail of Effects of compaction on the seismic performance of embankments built with gravel

Soil Dynamics and Earthquake Engineering

Abstract The effects of compaction on the seismic performance of gravelly embankments is investig... more Abstract The effects of compaction on the seismic performance of gravelly embankments is investigated transferring the precision of very accurate laboratory tests on the constituent material into the prediction of the large scale response. The stress-strain response observed upon monotonic and cyclic tests is captured by a critical state elastic-plastic model used as a virtual simulator of experiments to determine the influence of the initial state on the soil response. This dependency is introduced in equivalent linear elastic-perfectly plastic models as function of the state variable ψ to study the propagation of shear waves through horizontally layered landfills and embankments. A parametric analysis is performed assigning systematically variable seismic inputs, soil density and geometry to see the role of these factors on the soil response and the sliding resistance of the embankment. The study reveals an exceptionally high resistance of the gravel that enables embankment with steep abutments to resist against severe earthquakes.

Research paper thumbnail of Strength of sandy and clayey soils cemented with single and double fluid jet grouting

Soils and Foundations

Abstract Innovations in jet grouting technology have primarily focused on the cutting efficiency ... more Abstract Innovations in jet grouting technology have primarily focused on the cutting efficiency of the jets, with the aim of creating larger columns and increasing the productivity of construction sites. Relatively little attention has been paid to the consequences of the grouting system on the mechanical properties of the formed material. This paper investigates this aspect by analysing the results of two field trials carried out in both sandy and clayey soils, where single and double fluid jet grouting were simultaneously performed, with varied grout composition and injection parameters. Parallel uniaxial compressive tests on samples cored from the columns show that the material formed with the double system is systematically lower in strength than the material formed using the single fluid system. The mineralogical composition of samples cored from the columns was analysed by performing parallel Scanning Electron Microscopy (SEM), X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA) and Thermo-Gravimetric Analyses (TGA) to determine the reasons for this difference. A lower proportion of cementitious products, an accelerated carbonation of portlandite and a less homogeneous distribution of cement hydration products was found on the surface of the soil particles of the double samples than for the single fluid columns.

Research paper thumbnail of Determination of the critical state of granular materials with triaxial tests

Soils and Foundations

Abstract While the Critical State Locus (CSL) determined from triaxial compression tests is commo... more Abstract While the Critical State Locus (CSL) determined from triaxial compression tests is commonly adopted for the constitutive modelling of soil, the validity of the locus for other stress paths needs to be proved. Several authors have tried to experimentally verify whether the classical CSL representation in the stress invariants – void ratio space could be considered as unique or should depend on the loading direction, but the question is still being debated and a unique conclusion has not been convincingly drawn. In order to clarify this issue, compression and extension triaxial tests are performed on granular materials with different characteristics, namely, two homogeneously distributed sands and an assembly of steel spheres prepared under different initial conditions. The procedure for identifying the CSL is reviewed and indicates the limitations arising from strain localization (shear bands and necking). All the tests show that the materials head to systematically different traces in the e-p′ and p′-q planes when sheared under triaxial compression and extension. Searching for the reasons for this phenomenon, small samples of sand are subjected to the same tests quantifying the whole strain field with X-ray tomography and a digital image correlation. This analysis reveals an inhomogeneous pattern of deformation that is strongly affected by the presence of the two rigid frictional bases and the flexible side membrane, even for the samples deforming in an apparently uniform manner. The different localization observed for the compression and extension tests justifies the dependence of the CSL on the stress path seen on the global scale. On the other hand, a unique trace of the CSL is obtained in the volumetric e-p′ plane when the void ratio is measured limitedly to the zones affected by the largest distortion.

Research paper thumbnail of Experimental measurement of granular fabric and its evolution under shearing

EPJ Web of Conferences

X-ray μ computed tomography (CT) made three-dimensional in-situ imaging of natural granular mater... more X-ray μ computed tomography (CT) made three-dimensional in-situ imaging of natural granular materials possible. Previous work using x-ray μCT and triaxial compression tests has studied the 3D kinematics of individual grains during shear banding [1]. This works aims to supplement these measurements of kinematics with the measurement of different fabric entities, such as particle or contact orientations. It was found that the individual orientations of the different fabric entities pick up on the forming and the direction of the evolving shear band. The evolution of the anisotropy of the bulk of orientations corresponds to the macroscopic behaviour during the shearing test.

Research paper thumbnail of Micromechanical Study of Cyclically Loaded Sands with x-ray Microtomography and Digital Image Correlation

Procedia Engineering, 2016

Research paper thumbnail of Prediction of the effects of compaction on granular materials

Geomechanics from Micro to Macro, 2014

Research paper thumbnail of Improving the Hydrodynamic Performance of Jet Grouting with Chemical Additives

International Journal of Geosynthetics and Ground Engineering

Research paper thumbnail of Improving the Performance of Deep Soil Mixing in Clay with Chemical Additives

Research paper thumbnail of Strain localization in triaxial tests on sand studied with geostatistical analyses of the porosity distribution

Géotechnique Letters, 2019

Strain localisation influences the behaviour of sheared soils in a way that the assumption of the... more Strain localisation influences the behaviour of sheared soils in a way that the assumption of the continuum loses validity and may become inapplicable. This occurrence affects the interpretation of triaxial tests where samples are usually considered as representative elements of an equivalent continuum and a phenomenological interpretation is carried out to calibrate constitutive models. Considering the inherent and stress-induced heterogeneity of the material as a possible precursor of localisation, the evolution of porosity and strain fields is studied interpreting with statistical and geostatistical analyses, the results of X-ray computerised microtomography. The study is performed on sandy samples sheared in triaxial compression and extension. The analysis carried out before shearing shows a meaningful statistical heterogeneity of the porosity with correlation lengths to the order of a few grain diameters. The evolution on shearing reveals the onset of a second statistical popul...

Research paper thumbnail of Conditioning clayey soils with a dispersant agent for Deep Soil Mixing application: laboratory experiments and artificial neural network interpretation

Research paper thumbnail of Critical State of Sand Determined with Triaxial Tests

Research paper thumbnail of Liquefaction risk assessment: lesson learned from a case study

A detailed and comprehensive assessment of risk is the basis to protect communities<br> and... more A detailed and comprehensive assessment of risk is the basis to protect communities<br> and assist decision-making towards the sustainable management of territories. For liquefaction<br> this process implies to simultaneously investigate seismic hazard, susceptibility of the subsoil,<br> vulnerability of structures, economic and social relevance of critical infrastructures and<br> ultimately build a comprehensive multi-level model that considers the interaction among all aspects.<br> Developing a methodology to achieve this goal is the scope of Liquefact, a EU H2020<br> project. A case study pervasively affected by liquefaction damages is here studied as a real scale<br> scenario to identify the main factors of uncertainty. The available data concerning seismic motion,<br> subsoil and building characteristics, damage and economic loss are used to develop a methodology<br> aimed at quantifying and reducing uncertainties in the spa...

Research paper thumbnail of Low Pressure Grouting with Nanosilicates to Reduce the Liquefaction Susceptibility of Sand

The paper reports an experimental laboratory study aimed at investigating the effectiveness of lo... more The paper reports an experimental laboratory study aimed at investigating the effectiveness of low pressure grouting with nano-silica compounds as a remedial against liquefaction of sandy soils and to optimize the technique rendering it more attractive from the technical and economical viewpoint.<br> The grout herein adopted is a three-component mix of an aqueous suspension of sub-micrometric silica particles, water and an aqueous solution of sodium chloride. The latter, raising the pH of the suspension triggers the formation of the silica gel that clogging the soil pores reduces the mobility of the grains and, hopefully, produces a stiffer response and a reduced contractive tendency of the material.<br> A preliminary set of laboratory vane tests is performed to observe the gelling time of the material and fix the curing time of the samples by measuring the increase of shear resistance.<br> Thus, reconstituted samples of a silica sand, manufactured at two different...

Research paper thumbnail of Experimental Evidence of the Effectiveness and Applicability of Colloidal Nanosilica Grouting for Liquefaction Mitigation

Journal of Geotechnical and Geoenvironmental Engineering, 2020

AbstractThe low viscosity and the ability to control solidification rate make colloidal nanosilic... more AbstractThe low viscosity and the ability to control solidification rate make colloidal nanosilica grout an excellent ground-improvement solution which is functional for different engineering purpo...

Research paper thumbnail of Strain Localisation in Sand in Cycles of Triaxial Compression and Extension: Continuum and Grain-Scale Analysis

In this work we present selected results from a recent experimental programme where small sand sp... more In this work we present selected results from a recent experimental programme where small sand specimens are subjected to cycles of triaxial compression and triaxial extension: the material is “yielded” in extension, after which the loading is reversed and the material is “yielded” in compression—a number of cycles are performed. The ways in which extension and compression-like localisation patterns (i.e., dilatant shear banding, and necking respectively) appear, get activated and disactivated on reversal of loading are measured, and discussed—in terms of both (continuum) strain fields and individual grain rotations.

Research paper thumbnail of The Effects of Strain Localization on the Determination of Critical State Seen with Experimental and Numerical Models

The paper aims to study the role of strain localization on the results of triaxial test on sand a... more The paper aims to study the role of strain localization on the results of triaxial test on sand and more particularly on the determination of the Critical State. To this aim, triaxial compression and extension tests have been performed by adopting the tomographic technique and digital image correlation to detect strain localization. Then the tests have been numerically simulated adopting a recent advanced Critical State constitutive model. The simulation, firstly carried out with the classical element test approach, i.e., considering the sample as a single element representative of the soil behaviour, has proven to be unable to capture the soil response under the various loading conditions. Then the analysis has been repeated assuming the triaxial test as a physical model, i.e., introducing the boundary conditions given by the tests and simulating the sample as made of different elements each of different initial porosity, as observed from the tomography. The analysis reveals the im...

Research paper thumbnail of Effect of strain localization on the response of granular materials subjected to monotonic and cyclic triaxial tests

Research paper thumbnail of Non destructive tests to detect the integrity of steel anchors in corrosive environments

Research paper thumbnail of Compression and extension triaxial tests on sand, studied with X-ray microtomography and digital image correlation

Research paper thumbnail of Effects of compaction on the seismic performance of embankments built with gravel

Soil Dynamics and Earthquake Engineering

Abstract The effects of compaction on the seismic performance of gravelly embankments is investig... more Abstract The effects of compaction on the seismic performance of gravelly embankments is investigated transferring the precision of very accurate laboratory tests on the constituent material into the prediction of the large scale response. The stress-strain response observed upon monotonic and cyclic tests is captured by a critical state elastic-plastic model used as a virtual simulator of experiments to determine the influence of the initial state on the soil response. This dependency is introduced in equivalent linear elastic-perfectly plastic models as function of the state variable ψ to study the propagation of shear waves through horizontally layered landfills and embankments. A parametric analysis is performed assigning systematically variable seismic inputs, soil density and geometry to see the role of these factors on the soil response and the sliding resistance of the embankment. The study reveals an exceptionally high resistance of the gravel that enables embankment with steep abutments to resist against severe earthquakes.

Research paper thumbnail of Strength of sandy and clayey soils cemented with single and double fluid jet grouting

Soils and Foundations

Abstract Innovations in jet grouting technology have primarily focused on the cutting efficiency ... more Abstract Innovations in jet grouting technology have primarily focused on the cutting efficiency of the jets, with the aim of creating larger columns and increasing the productivity of construction sites. Relatively little attention has been paid to the consequences of the grouting system on the mechanical properties of the formed material. This paper investigates this aspect by analysing the results of two field trials carried out in both sandy and clayey soils, where single and double fluid jet grouting were simultaneously performed, with varied grout composition and injection parameters. Parallel uniaxial compressive tests on samples cored from the columns show that the material formed with the double system is systematically lower in strength than the material formed using the single fluid system. The mineralogical composition of samples cored from the columns was analysed by performing parallel Scanning Electron Microscopy (SEM), X-ray diffraction analysis (XRD), Differential Thermal Analysis (DTA) and Thermo-Gravimetric Analyses (TGA) to determine the reasons for this difference. A lower proportion of cementitious products, an accelerated carbonation of portlandite and a less homogeneous distribution of cement hydration products was found on the surface of the soil particles of the double samples than for the single fluid columns.

Research paper thumbnail of Determination of the critical state of granular materials with triaxial tests

Soils and Foundations

Abstract While the Critical State Locus (CSL) determined from triaxial compression tests is commo... more Abstract While the Critical State Locus (CSL) determined from triaxial compression tests is commonly adopted for the constitutive modelling of soil, the validity of the locus for other stress paths needs to be proved. Several authors have tried to experimentally verify whether the classical CSL representation in the stress invariants – void ratio space could be considered as unique or should depend on the loading direction, but the question is still being debated and a unique conclusion has not been convincingly drawn. In order to clarify this issue, compression and extension triaxial tests are performed on granular materials with different characteristics, namely, two homogeneously distributed sands and an assembly of steel spheres prepared under different initial conditions. The procedure for identifying the CSL is reviewed and indicates the limitations arising from strain localization (shear bands and necking). All the tests show that the materials head to systematically different traces in the e-p′ and p′-q planes when sheared under triaxial compression and extension. Searching for the reasons for this phenomenon, small samples of sand are subjected to the same tests quantifying the whole strain field with X-ray tomography and a digital image correlation. This analysis reveals an inhomogeneous pattern of deformation that is strongly affected by the presence of the two rigid frictional bases and the flexible side membrane, even for the samples deforming in an apparently uniform manner. The different localization observed for the compression and extension tests justifies the dependence of the CSL on the stress path seen on the global scale. On the other hand, a unique trace of the CSL is obtained in the volumetric e-p′ plane when the void ratio is measured limitedly to the zones affected by the largest distortion.

Research paper thumbnail of Experimental measurement of granular fabric and its evolution under shearing

EPJ Web of Conferences

X-ray μ computed tomography (CT) made three-dimensional in-situ imaging of natural granular mater... more X-ray μ computed tomography (CT) made three-dimensional in-situ imaging of natural granular materials possible. Previous work using x-ray μCT and triaxial compression tests has studied the 3D kinematics of individual grains during shear banding [1]. This works aims to supplement these measurements of kinematics with the measurement of different fabric entities, such as particle or contact orientations. It was found that the individual orientations of the different fabric entities pick up on the forming and the direction of the evolving shear band. The evolution of the anisotropy of the bulk of orientations corresponds to the macroscopic behaviour during the shearing test.

Research paper thumbnail of Micromechanical Study of Cyclically Loaded Sands with x-ray Microtomography and Digital Image Correlation

Procedia Engineering, 2016

Research paper thumbnail of Prediction of the effects of compaction on granular materials

Geomechanics from Micro to Macro, 2014

Research paper thumbnail of Improving the Hydrodynamic Performance of Jet Grouting with Chemical Additives

International Journal of Geosynthetics and Ground Engineering