Thesis Chapters by Michele Iodice
The increased demand for non-destructive evaluation of the shear wave profiling, condition
monit... more The increased demand for non-destructive evaluation of the shear wave profiling, condition
monitoring and performance assessment of soils and roads in a dynamic state has made seismic
methods the most desirable and effective non-destructive techniques. Surface wave methods have
gained popularity over the last decades since they monitor the propagation of the surface wave with
non-invasive transducers working from the surface. Nonetheless, their use is restricted by resolution
problems and their ability to assess the actual dispersive behaviour of Rayleigh wave. Nondestructive,
in-situ methods for characterizing existing infrastructures require the ability to detect
structural damage and features such as cracking and discontinuities. The proper assessment of the
location and of the extension of such discontinuities is crucial for the determination of the level of
deterioration of an infrastructure and for planning the maintenance interventions. Damage in a
pavement structure is usually initiated in the asphalt layers, making the Rayleigh wave ideally suited
for the detection of shallow surface defects. Nonetheless, the practical application of crack detection
methods in asphalt is hampered due to the heterogeneous and dispersive nature of the material tested.
This thesis describes new signal processing methods and the novel application of existing methods
to tackle the problems that hinder the non-destructive surface wave methods.
The spectral convolution method proposed in this thesis, based on the simultaneous exploitation of
the vertical and the horizontal components of a seismic event, improved the resolution and the overall
accuracy of the spectral image in the frequency-wavenumber (f-k) domain. Hence, it led to more
accurate seismic inversion by reducing the amount of uncertainty coming from a seismic survey.
This research investigated the use of this new proposed method in soils and asphalts for the measurement of surface wave dispersion through conceptual analysis and numerical investigation
alongside experimental investigation on soil and asphalt.
The application of spectral wave methods and the transformation of the wavefield into the frequencywavenumber
domain allowed the identification of the position and the extension of vertical defects.
The joint use of the Multichannel Analysis of Surface Waves and the Multiple Impact of Surface
Waves methods in numerical and experimental investigations presented in this thesis proved to be
effective for crack detection and sizing. Moreover, the space-normalised seismogram helped in the
interpretation of f-k spectra for cracks detection.
Here, the wave decomposition method for crack interrogation consisted of a signal processing
algorithm capable of computing the direct and reflected waves’ amplitudes and phase angles from
the signals of a deployment of sensors. It solved linear systems with a number of measurements much
bigger than the number of unknowns. It tackled the measurement errors naturally present in
experimental data by finding a least square approximate solution with the help of the pseudo-inverse
matrix for overdetermined systems. The results coming from numerical simulations and experimental
investigations showed the effectiveness of the wave decomposition method for the assessment of the
location and of the depth of surface-breaking cracks in the half-space and in layered systems.
Contrary to other techniques, it was able to cope with the heterogeneities and the dispersive nature
of layered system, thus making possible to detect and assess the depth of surface-breaking cracks in
roads.
All’interno della nuova filosofia progettuale delle pavimentazioni stradali, basata sulla
valutaz... more All’interno della nuova filosofia progettuale delle pavimentazioni stradali, basata sulla
valutazione delle prestazioni, che ha permesso un approccio molto più flessibile in termini di
progetto, scelta dei materiali ed esecuzione dei lavori, c’è la forte necessità di sviluppare
metodi veloci e affidabili per la misurazione delle grandezze prestazionali fondamentali (su
tutte la capacità portante e il livello di addensamento) durante le fasi costruttive.
Il Light Weigth Deflectometer è considerato a livello mondiale come lo strumento più adatto
a tale scopo, con enormi potenzialità ancora parzialmente inespresse.
Il seguente lavoro si è basato su una preliminare analisi e caratterizzazione della grandezza
deformativa energy loss e sui vantaggi derivabili da un suo utilizzo come parametro di tipo
prestazionale, attraverso la costruzione di un modello matematico che aiuti, simulandone il
comportamento, a comprenderne le caratteristiche. Nel seguente lavoro le analisi si sono
concentrate su strati di sottofondo e fondazione, quindi su aggregati di tipo naturale e inerti
riciclati.
Lo studio ha approfondito anche l’influenza posseduta dalla rigidezza dei buffer, e
l’importanza di una corretta configurazione dello strumento, in termini di rigidezza degli
smorzatori e quindi di durata dell’impulso di carico trasmesso al terreno (load pulse length).
L’obiettivo finale di questa tesi è stato quello di riuscire a trovare una corrispondenza tra i
parametri di deflessione misurabili dal LWD e il livello di addensamento, limitatamente a
sottofondi e a strati di fondazione costituiti da materiali non legati. Il livello di addensamento
è una misura tradizionale per il controllo prestazionale durante le fasi costruttive, ed è di
fondamentale importanza raggiungere determinati livelli di compattazione per assicurare
durabilità e funzionalità della struttura, minimizzare eventuali cedimenti differenziali e quindi
gli oneri collegati ai lavori di sistemazione e ripristino. Tuttavia i metodi classici per la misura
della densità in sito sono lenti e imprecisi.
Le corrispondenze trovate all’interno di questo studio, tra i valori misurabili mediante il LWD
e il livello di addensamento, potrebbero consentire una valutazione molto più veloce e
affidabile della resistenza alle deformazioni permanenti di strati costituiti da materiali non
legati.
Papers by Michele Iodice
ArXiv, 2018
Ultrasonic acoustic fields have recently been used to generate haptic effects on the human skin a... more Ultrasonic acoustic fields have recently been used to generate haptic effects on the human skin as well as to levitate small sub-wavelength size particles. Schlieren imaging and background-oriented schlieren techniques can be used for acoustic wave pattern and beam shape visualization. These techniques exploit variations in the refractive index of a propagation medium by applying refractive optics or cross-correlation algorithms of photographs of illuminated background patterns. Here both background-oriented and traditional schlieren systems are used to visualize the regions of the acoustic power involved in creating dynamic haptic sensations and dynamic levitation traps. We demonstrate for the first time the application of back-ground-oriented schlieren for imaging ultrasonic fields in air. We detail our imaging apparatus and present improved algorithms used to visualize these phenomena that we have produced using multiple phased arrays. Moreover, to improve imaging, we leverage an...
Rayleigh waves are surface seismic waves, which can be produced by a disturbance applied to the s... more Rayleigh waves are surface seismic waves, which can be produced by a disturbance applied to the surface of a half-space. The dispersive behaviour of Rayleigh waves in real multi-layered media is widely utilized for near-surface acoustic characterization, e.g. in Spectral Analysis of Surface Waves (SASW), and more recently, in Multi-channel Analysis of Surface Waves (MASW). These methods, along with the associated field testing, result in the construction of a dispersion curve. However, it is often difficult to measure the speed of Rayleigh waves in a consistent manner. Other interference, such as direct, reflected and refracted body waves, backscatter from nearby objects, are unwanted and could contaminate the dispersion curve (i.e. the phase velocity) in a significant way. Thus, shear or compression wave energy is undesirable. Furthermore, additional surface waves coming from other sources and background noise can compound the problems. A wide range of different active sources have been utilized for decades in surface wave-based methods, but the reliability and the differences among these have not been properly assessed. The main focus of this paper is to compare different types of soil excitation, in order to identify and quantify seismic waves generated by each different type and to find a feasible Rayleigh wave source for the survey of shallow depths. This will be in terms of type of energy generated, range of frequencies excited, and amount of Rayleigh wave energy with respect to the total. Particularly, in this paper, the excitations caused by inertial shakers, oscillating in both the horizontal and vertical direction, and by transient sources like sledgehammers and mallets, are examined. For each different type of excitation, two key aspects are varied: the magnitude of the impact and the coupling of the source to the soil. The transmission of the energy from the source to the soil will be investigated using rigid platforms of different size, shape and material. This paper investigates the limitations of each type of active source to be utilized. These goals are pursued with experimental tests, digital processing of data, and by comparison with analytical and numerical models.
The increased demand for non-destructive evaluation of the shear wave profiling, condition monito... more The increased demand for non-destructive evaluation of the shear wave profiling, condition monitoring and performance assessment of soils and roads in a dynamic state has made seismic methods the most desirable and effective non-destructive techniques. Surface wave methods have gained popularity over the last decades since they monitor the propagation of the surface wave with non-invasive transducers working from the surface. Nonetheless, their use is restricted by resolution problems and their ability to assess the actual dispersive behaviour of Rayleigh wave. Non-destructive, in-situ methods for characterizing existing infrastructures require the ability to detect structural damage and features such as cracking and discontinuities. The proper assessment of the location and of the extension of such discontinuities is crucial for the determination of the level of deterioration of an infrastructure and for planning the maintenance interventions. Damage in a pavement structure is usua...
The dispersion behaviour of ground roll has been ex ploited in recent decades for the imaging and... more The dispersion behaviour of ground roll has been ex ploited in recent decades for the imaging and acous tic characterization of the shallow subsurface, often u si g the Multichannel Analysis of Surface Waves (MA SW) method. The effectiveness of the method in providin g a accurate shear wave profile of a soil deposit and the identification of seismic event largely depends on the degree of interference from other noise sources , unrelated to the primary signal of interest. In MASW a wavefi eld transformation in the frequency-wavenumber ( f-k) domain is usually performed exploiting vertical com ponents of a seismic event, picked up at different positions, theoretically allowing the identification of differ nt wave-types and higher Rayleigh wave (R-wave) mo des. In this work a multi-component approach to seismic characterization of the shallow subsurface is propo sed. The body wave content is lowered and the Rayleigh wave content is enhanced by simultaneously exploiting th e vertical an...
Multi-channel Analysis of Surface Waves (MASW) is a seismic wave propagation method which involve... more Multi-channel Analysis of Surface Waves (MASW) is a seismic wave propagation method which involves the measurement of Rayleigh waves propagating along the surface of a medium. The method is non-intrusive, fast and practical and it has been successfully utilized for the in-situ evaluation of shear modulus and layer thicknesses of soils and, more recently, pavement systems. The method is also widely utilized as a tool for monitoring stiffness during construction, for maintenance inspections and even for the detection of voids and sinkholes. Time Domain Reflectometry (TDR) is an electromagnetic method based on the measurement of the propagation velocity of a step voltage pulse along a probe inserted in the soil. Electrical properties of the soil, i.e. dielectric permittivity and bulk electrical conductivity, are determined and can be related to some geotechnical properties, e.g. the volumetric water content and potentially the soil density. Seismic wave propagation methods such as MASW...
Extended Abstracts of the 2019 CHI Conference on Human Factors in Computing Systems
Rayleigh waves are surface seismic waves, which can be produced by a disturbance applied to the s... more Rayleigh waves are surface seismic waves, which can be produced by a disturbance applied to the surface of a half-space. The dispersive behaviour of Rayleigh waves in real multi-layered media is widely utilized for near-surface acoustic characterization, e.g. in Spectral Analysis of Surface Waves (SASW), and more recently, in Multi-channel Analysis of Surface Waves (MASW). These methods, along with the associated field testing, result in the construction of a dispersion curve. However, it is often difficult to measure the speed of Rayleigh waves in a consistent manner. Other interference, such as direct, reflected and refracted body waves, backscatter from nearby objects, are unwanted and could contaminate the dispersion curve (i.e. the phase velocity) in a significant way. Thus, shear or compression wave energy is undesirable. Furthermore, additional surface waves coming from other sources and background noise can compound the problems. A wide range of different active sources have been utilized for decades in surface wave-based methods, but the reliability and the differences among these have not been properly assessed. The main focus of this paper is to compare different types of soil excitation, in order to identify and quantify seismic waves generated by each different type and to find a feasible Rayleigh wave source for the survey of shallow depths. This will be in terms of type of energy generated, range of frequencies excited, and amount of Rayleigh wave energy with respect to the total. Particularly, in this paper, the excitations caused by inertial shakers, oscillating in both the horizontal and vertical direction, and by transient sources like sledgehammers and mallets, are examined. For each different type of excitation, two key aspects are varied: the magnitude of the impact and the coupling of the source to the soil. The transmission of the energy from the source to the soil will be investigated using rigid platforms of different size, shape and material. This paper investigates the limitations of each type of active source to be utilized. These goals are pursued with experimental tests, digital processing of data, and by comparison with analytical and numerical models.
Multi-channel Analysis of Surface Waves (MASW) is a seismic wave propagation method which involve... more Multi-channel Analysis of Surface Waves (MASW) is a seismic wave propagation method which involves the measurement of Rayleigh waves propagating along the surface of a medium. The method is non-intrusive, fast and practical and it has been successfully utilized for the in-situ evaluation of shear modulus and layer thicknesses of soils and, more recently, pavement systems. The method is also widely utilized as a tool for monitoring stiffness during construction, for maintenance inspections and even for the detection of voids and sinkholes. Time Domain Reflectometry (TDR) is an electromagnetic method based on the measurement of the propagation velocity of a step voltage pulse along a probe inserted in the soil. Electrical properties of the soil, i.e. dielectric permittivity and bulk electrical conductivity, are determined and can be related to some geotechnical properties, e.g. the volumetric water content and potentially the soil density. Seismic wave propagation methods such as MASW are sometimes used in conjunction with electromagnetic methods, in an attempt to reduce the uncertainty associated with each individual method, and to provide an enhanced characterization of the investigated soil. It is still unknown however, whether they are mostly complementary methods or whether they share the assessment of common mechanical/geotechnical properties. In this work the potential and the limitations of the joint use of the MASW and TDR techniques were investigated through an in-situ near-surface programme measurement at two different soil sites, up to a depth of 1 metre. A Dynamic Cone Penetrometer test was performed and the Particle Size Distribution curve determined to extend the soil characterization, and where possible soil samples were taken at various depths in order to measure the dry density and the volumetric water content. The two techniques measured similar trends, augmenting the results obtained by each method and showing the potential for an enhanced and more complete assessment of the soil properties. In addition, bulk electrical conductivity was shown to be related to the shear modulus for the soils studied. Keywords: Multichannel Analysis of Seismic Waves (MASW), Time Domain Reflectometry (TDR), dry density, volumetric water content (VWC), Dynamic Cone Penetrometer (DCP), phase velocity, shear wave velocity, dielectric permittivity, bulk electrical conductivity.
The dispersion behaviour of ground roll has been exploited in recent decades for the imaging and ... more The dispersion behaviour of ground roll has been exploited in recent decades for the imaging and acoustic characterization of the shallow subsurface, often using the Multichannel Analysis of Surface Waves (MASW) method. The effectiveness of the method in providing an accurate shear wave profile of a soil deposit and the identification of seismic event largely depends on the degree of interference from other noise sources, unrelated to the primary signal of interest. In MASW a wavefield transformation in the frequency-wavenumber (f-k) domain is usually performed exploiting vertical components of a seismic event, picked up at different positions, theoretically allowing the identification of different wave-types and higher Rayleigh wave (R-wave) modes. In this work a multi-component approach to seismic characterization of the shallow subsurface is proposed. The body wave content is lowered and the Rayleigh wave content is enhanced by simultaneously exploiting the vertical and horizontal components of the seismic event in the direction of propagation of the ground roll (i.e. the direction of the receivers array), in the time domain. The effects of this multi-component approach are investigated in detail by finite element modelling and with respect to an in-situ experimental study. In general, the approach was found to be beneficial in enhancing the Rayleigh wave content of the seismic signal, hence improving mode separation in the f-k domain. It augments the range of detectable frequencies actually excited by ground roll and improves the resolution of the f-k transformation by a factor of two.
Assessment of the location and of the extension of cracking in road surfaces is important for det... more Assessment of the location and of the extension of cracking in road surfaces is important for determining the potential level of deterioration in the road overall and the infrastructure buried beneath it. Damage in a pavement structure is usually initiated in the tarmac layers, making the Rayleigh wave ideally suited for the detection of shallow surface defects. This paper presents an investigation of two surface wave methods to detect and locate top-down cracks in asphalt layers. The aim of the study is to compare the results from the well-established Multichannel Analysis of Surface Waves (MASW) and the more recent Multiple Impact of Surface Waves (MISW) in the presence of a discontinuity and to suggest the best surface wave technique for evaluating the presence and the extension of vertical cracks in roads. The study is conducted through numerical simulations alongside experimental investigations and it considers the cases for which the cracking is internal and external to the deployment of sensors. MISW is found to enhance the visibility of the reflected waves in the frequency wavenumber (f-k) spectrum, helping with the detection of the discontinuity. In some cases, by looking at the f-k spectrum obtained with MISW it is possible to extract information regarding the location and the depth of the cracking. 1. Introduction Non-destructive, in-situ methods for characterizing existing infrastructures require the ability to detect structural damage and features such as cracking and discontinuities. Damage in a pavement structure is usually initiated in the asphalt layers, making the Rayleigh wave ideally suited for the detection of shallow surface defects. The proper assessment of the location and of the extension of such discontinuities is crucial for the determination of the level of deterioration of an infrastructure and for decisions regarding maintenance, strengthening and rebuilding of existing infrastructures. Detection of vertical cracking is normally based on the study of the reflections and refraction caused by the boundaries of the crack, even though reflections from cavity surfaces have weak energy and limited frequency range, making this process difficult to implement [1]. Numerical approaches to near-surface discontinuity detection show that the dispersion curve, and hence the wavefield, changes if the signal travels across a vertical discontinuity, which can be a crack or a slot [2]. The finite depth blocks shorter-wavelength Rayleigh waves, allowing only the longer wavelength to proceed and hence it acts as a low-pass filter. In general, cracks are likely to generate reflections and to change both the time history and the frequency content (the spectrum response) of a surface signal [1]. Moreover the edges of surface defects like cracks act like a source that excites surface waves which propagate along the crack surface [3, 4].
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Thesis Chapters by Michele Iodice
monitoring and performance assessment of soils and roads in a dynamic state has made seismic
methods the most desirable and effective non-destructive techniques. Surface wave methods have
gained popularity over the last decades since they monitor the propagation of the surface wave with
non-invasive transducers working from the surface. Nonetheless, their use is restricted by resolution
problems and their ability to assess the actual dispersive behaviour of Rayleigh wave. Nondestructive,
in-situ methods for characterizing existing infrastructures require the ability to detect
structural damage and features such as cracking and discontinuities. The proper assessment of the
location and of the extension of such discontinuities is crucial for the determination of the level of
deterioration of an infrastructure and for planning the maintenance interventions. Damage in a
pavement structure is usually initiated in the asphalt layers, making the Rayleigh wave ideally suited
for the detection of shallow surface defects. Nonetheless, the practical application of crack detection
methods in asphalt is hampered due to the heterogeneous and dispersive nature of the material tested.
This thesis describes new signal processing methods and the novel application of existing methods
to tackle the problems that hinder the non-destructive surface wave methods.
The spectral convolution method proposed in this thesis, based on the simultaneous exploitation of
the vertical and the horizontal components of a seismic event, improved the resolution and the overall
accuracy of the spectral image in the frequency-wavenumber (f-k) domain. Hence, it led to more
accurate seismic inversion by reducing the amount of uncertainty coming from a seismic survey.
This research investigated the use of this new proposed method in soils and asphalts for the measurement of surface wave dispersion through conceptual analysis and numerical investigation
alongside experimental investigation on soil and asphalt.
The application of spectral wave methods and the transformation of the wavefield into the frequencywavenumber
domain allowed the identification of the position and the extension of vertical defects.
The joint use of the Multichannel Analysis of Surface Waves and the Multiple Impact of Surface
Waves methods in numerical and experimental investigations presented in this thesis proved to be
effective for crack detection and sizing. Moreover, the space-normalised seismogram helped in the
interpretation of f-k spectra for cracks detection.
Here, the wave decomposition method for crack interrogation consisted of a signal processing
algorithm capable of computing the direct and reflected waves’ amplitudes and phase angles from
the signals of a deployment of sensors. It solved linear systems with a number of measurements much
bigger than the number of unknowns. It tackled the measurement errors naturally present in
experimental data by finding a least square approximate solution with the help of the pseudo-inverse
matrix for overdetermined systems. The results coming from numerical simulations and experimental
investigations showed the effectiveness of the wave decomposition method for the assessment of the
location and of the depth of surface-breaking cracks in the half-space and in layered systems.
Contrary to other techniques, it was able to cope with the heterogeneities and the dispersive nature
of layered system, thus making possible to detect and assess the depth of surface-breaking cracks in
roads.
valutazione delle prestazioni, che ha permesso un approccio molto più flessibile in termini di
progetto, scelta dei materiali ed esecuzione dei lavori, c’è la forte necessità di sviluppare
metodi veloci e affidabili per la misurazione delle grandezze prestazionali fondamentali (su
tutte la capacità portante e il livello di addensamento) durante le fasi costruttive.
Il Light Weigth Deflectometer è considerato a livello mondiale come lo strumento più adatto
a tale scopo, con enormi potenzialità ancora parzialmente inespresse.
Il seguente lavoro si è basato su una preliminare analisi e caratterizzazione della grandezza
deformativa energy loss e sui vantaggi derivabili da un suo utilizzo come parametro di tipo
prestazionale, attraverso la costruzione di un modello matematico che aiuti, simulandone il
comportamento, a comprenderne le caratteristiche. Nel seguente lavoro le analisi si sono
concentrate su strati di sottofondo e fondazione, quindi su aggregati di tipo naturale e inerti
riciclati.
Lo studio ha approfondito anche l’influenza posseduta dalla rigidezza dei buffer, e
l’importanza di una corretta configurazione dello strumento, in termini di rigidezza degli
smorzatori e quindi di durata dell’impulso di carico trasmesso al terreno (load pulse length).
L’obiettivo finale di questa tesi è stato quello di riuscire a trovare una corrispondenza tra i
parametri di deflessione misurabili dal LWD e il livello di addensamento, limitatamente a
sottofondi e a strati di fondazione costituiti da materiali non legati. Il livello di addensamento
è una misura tradizionale per il controllo prestazionale durante le fasi costruttive, ed è di
fondamentale importanza raggiungere determinati livelli di compattazione per assicurare
durabilità e funzionalità della struttura, minimizzare eventuali cedimenti differenziali e quindi
gli oneri collegati ai lavori di sistemazione e ripristino. Tuttavia i metodi classici per la misura
della densità in sito sono lenti e imprecisi.
Le corrispondenze trovate all’interno di questo studio, tra i valori misurabili mediante il LWD
e il livello di addensamento, potrebbero consentire una valutazione molto più veloce e
affidabile della resistenza alle deformazioni permanenti di strati costituiti da materiali non
legati.
Papers by Michele Iodice
monitoring and performance assessment of soils and roads in a dynamic state has made seismic
methods the most desirable and effective non-destructive techniques. Surface wave methods have
gained popularity over the last decades since they monitor the propagation of the surface wave with
non-invasive transducers working from the surface. Nonetheless, their use is restricted by resolution
problems and their ability to assess the actual dispersive behaviour of Rayleigh wave. Nondestructive,
in-situ methods for characterizing existing infrastructures require the ability to detect
structural damage and features such as cracking and discontinuities. The proper assessment of the
location and of the extension of such discontinuities is crucial for the determination of the level of
deterioration of an infrastructure and for planning the maintenance interventions. Damage in a
pavement structure is usually initiated in the asphalt layers, making the Rayleigh wave ideally suited
for the detection of shallow surface defects. Nonetheless, the practical application of crack detection
methods in asphalt is hampered due to the heterogeneous and dispersive nature of the material tested.
This thesis describes new signal processing methods and the novel application of existing methods
to tackle the problems that hinder the non-destructive surface wave methods.
The spectral convolution method proposed in this thesis, based on the simultaneous exploitation of
the vertical and the horizontal components of a seismic event, improved the resolution and the overall
accuracy of the spectral image in the frequency-wavenumber (f-k) domain. Hence, it led to more
accurate seismic inversion by reducing the amount of uncertainty coming from a seismic survey.
This research investigated the use of this new proposed method in soils and asphalts for the measurement of surface wave dispersion through conceptual analysis and numerical investigation
alongside experimental investigation on soil and asphalt.
The application of spectral wave methods and the transformation of the wavefield into the frequencywavenumber
domain allowed the identification of the position and the extension of vertical defects.
The joint use of the Multichannel Analysis of Surface Waves and the Multiple Impact of Surface
Waves methods in numerical and experimental investigations presented in this thesis proved to be
effective for crack detection and sizing. Moreover, the space-normalised seismogram helped in the
interpretation of f-k spectra for cracks detection.
Here, the wave decomposition method for crack interrogation consisted of a signal processing
algorithm capable of computing the direct and reflected waves’ amplitudes and phase angles from
the signals of a deployment of sensors. It solved linear systems with a number of measurements much
bigger than the number of unknowns. It tackled the measurement errors naturally present in
experimental data by finding a least square approximate solution with the help of the pseudo-inverse
matrix for overdetermined systems. The results coming from numerical simulations and experimental
investigations showed the effectiveness of the wave decomposition method for the assessment of the
location and of the depth of surface-breaking cracks in the half-space and in layered systems.
Contrary to other techniques, it was able to cope with the heterogeneities and the dispersive nature
of layered system, thus making possible to detect and assess the depth of surface-breaking cracks in
roads.
valutazione delle prestazioni, che ha permesso un approccio molto più flessibile in termini di
progetto, scelta dei materiali ed esecuzione dei lavori, c’è la forte necessità di sviluppare
metodi veloci e affidabili per la misurazione delle grandezze prestazionali fondamentali (su
tutte la capacità portante e il livello di addensamento) durante le fasi costruttive.
Il Light Weigth Deflectometer è considerato a livello mondiale come lo strumento più adatto
a tale scopo, con enormi potenzialità ancora parzialmente inespresse.
Il seguente lavoro si è basato su una preliminare analisi e caratterizzazione della grandezza
deformativa energy loss e sui vantaggi derivabili da un suo utilizzo come parametro di tipo
prestazionale, attraverso la costruzione di un modello matematico che aiuti, simulandone il
comportamento, a comprenderne le caratteristiche. Nel seguente lavoro le analisi si sono
concentrate su strati di sottofondo e fondazione, quindi su aggregati di tipo naturale e inerti
riciclati.
Lo studio ha approfondito anche l’influenza posseduta dalla rigidezza dei buffer, e
l’importanza di una corretta configurazione dello strumento, in termini di rigidezza degli
smorzatori e quindi di durata dell’impulso di carico trasmesso al terreno (load pulse length).
L’obiettivo finale di questa tesi è stato quello di riuscire a trovare una corrispondenza tra i
parametri di deflessione misurabili dal LWD e il livello di addensamento, limitatamente a
sottofondi e a strati di fondazione costituiti da materiali non legati. Il livello di addensamento
è una misura tradizionale per il controllo prestazionale durante le fasi costruttive, ed è di
fondamentale importanza raggiungere determinati livelli di compattazione per assicurare
durabilità e funzionalità della struttura, minimizzare eventuali cedimenti differenziali e quindi
gli oneri collegati ai lavori di sistemazione e ripristino. Tuttavia i metodi classici per la misura
della densità in sito sono lenti e imprecisi.
Le corrispondenze trovate all’interno di questo studio, tra i valori misurabili mediante il LWD
e il livello di addensamento, potrebbero consentire una valutazione molto più veloce e
affidabile della resistenza alle deformazioni permanenti di strati costituiti da materiali non
legati.