The evaluation of the internal stability of a granular soil in contact with a filter is a very im... more The evaluation of the internal stability of a granular soil in contact with a filter is a very important aspect for the design of a filtering system. The erosion of the base soil takes place when the size of the constrictions of the filtering transition are too large and therefore are not able to retain the particles of the base soil entrained in the flow. This phenomenon produces significant volume changes within the soil and the resulting deformation may not be admissible with the limit state of the structure. In some cases, the phenomenon can lead to failure of the granular structure in contact with the filter with the consequent associated damage. In the paper, the main methods available in the literature to evaluate the internal stability of granular soils are described and critically discussed. Therefore, the recent research developments on internal stability achieved by the authors are illustrated. In particular, two methods, considering the grain size distribution of granular base soil, both validated by long term filtration tests, are described in detail
In this paper, a numerical model to simulate the hydraulic conductivity reduction observed during... more In this paper, a numerical model to simulate the hydraulic conductivity reduction observed during long-term laboratory column tests is proposed. The column tests are carried out to study dissolved heavy metals removal by using granular zero valent iron (ZVI). The proposed model is also used to analyse the main causes of hydraulic conductivity reduction observed during laboratory column tests. Expansive iron corrosion, precipitation of reaction products, and gas formation are the processes considered in the proposed model. Numerical simulation results show that to reproduce hydraulic behaviour of the experimental systems, the change of pores geometry due to expansive iron corrosion and precipitation of reaction products, which determines a possible stoppage of gas bubbles, should be considered. Furthermore, model results show that only a small percentage of the iron available is corroded during the tests (from 0.4% to 1.9%). According to the model, the average diameter of gas bubbles...
The geotextile filters design is based on the retention and the permeability criteria. In particu... more The geotextile filters design is based on the retention and the permeability criteria. In particular, the retention criterion, that a filter must satisfy in comparison to the base soil, is commonly expressed as O F D 85 , where O F is the geotextile characteristic opening size and D 85 is the soil particle diameter corresponding to the 85% of the passing soil mass grain size distribution. As consequence, the filter should retain only the larger particles of the base soil. This criterion works if the larger particles retain the smaller particles and this condition is verified when these particles form the solid skeleton (constituted by interconnected particles that transfer the stresses). When the granular soil has a broadly grain size distribution, with uniformity coefficient greater than 3, the larger particles generally do not belong to the solid skeleton but they are "immersed" in the smaller particles matrix that constitutes the solid skeleton (Giroud, 2010). So, for broadly granular soils, if the retention criterion previously defined is satisfied, this condition does not guarantee that the whole base soil is retained. In fact, the base soil could be subjected to an internal erosion phenomenon if the geotextile filter characteristic opening size is too large and the larger particles retained by the filter are not able to retain the smaller particles of the base soil and a hydraulic flow of dragging exists. The paper focuses on the development of a new theoretical method that, starting from the base soil mass grain size distribution and from its relative density, determines the upper limit value of the geotextile filter characteristic opening size, O F , to be used in the retention criterion in order to avoid the internal erosion of broadly granular base soil.
The knowledge of the internal stability of granular soils is a key factor in the design of granul... more The knowledge of the internal stability of granular soils is a key factor in the design of granular or geotextile filters. To evaluate the internal stability of granular soils, different semi-empirical methods are generally used. Nevertheless, the results of these methods, on the same soil, can lead to different internal stability evaluations. In this paper, to evaluate the reliability of the semi-empirical methods available in literature, the internal stability of different granular soils, reconstituted by the authors and by other researchers, has been studied by means of theoretical and experimental approaches. In particular, the theoretical analysis of the internal stability was performed using the Simulfiltr method, developed recently by the authors, while the experimental evaluation of the internal stability was carried out by means of long-term filtration tests. The comparison of the internal stability analysis performed by means of semi-empirical, theoretical, and experimenta...
The geotextile filter design is particularly complex when granular base soils are internally unst... more The geotextile filter design is particularly complex when granular base soils are internally unstable. In these conditions, the design criteria available in literature are not always reliable. This paper deals with a new theoretical method developed to evaluate the internal stability of granular soils. To simulate, theoretically, the filtration process inside these soils, a set of spherical particles and different soil relative densities have been considered. The soil has been represented by means of a sequence of parallel layers, containing constrictions and particles, placed upon each other at a distance, in the direction of hydraulic flow, which is a function of the soil relative density. The movement of the fine particles through the different soil layers has been simulated by means of a mechanism that compares each particle contained in the i layer with the constrictions contained in the next i + 1 layer. The results of the numerical simulations were used to evaluate the intern...
Antibiotic resistance poses an important threat to global public health and has become a challeng... more Antibiotic resistance poses an important threat to global public health and has become a challenge to modern medicine. The occurrence of antibiotic-resistant bacteria in a broad range of foods has led to a growing concern about the impact that food may have as a reservoir of antibiotic resistance genes. Considering Minas Frescal Cheese (MFC)-a typical Brazilian white soft cheese-and its economic and cultural values, in this study, medically relevant antimicrobial-resistance genetic markers (AR genes) were screened, and the occurrence of integrons were evaluated in manufactured MFC using culture-independent approaches. Through a fingerprinting analysis, the tested MFCs were brand-clustered, indicating reproducibility along the production chain. A common core of resistance markers in all brands evaluated and related antimicrobials such as β-lactams, tetracyclines, quinolones, and sulfonamide was detected. Several other markers, including efflux pumps and aminoglycosides-resistance were distributed among brands. Class 1 and 2 integrons were observed, respectively, in 77% and 97% of the samples. The presence of AR genes is of special interest due to their clinical relevance. Taken together, the data may suggest that the production chain of MFC might contribute to the spread of putative drug-resistant bacteria, which could greatly impact human health. Furthermore, detection of class 1 and class 2 integrons in MFC has led to discussions about resistance gene spread in this traditional cheese, providing evidence of potential horizontal transfer of AR genes to human gut microbiota.
The evaluation of the internal stability of a granular soil in contact with a filter is a very im... more The evaluation of the internal stability of a granular soil in contact with a filter is a very important aspect for the design of a filtering system. The erosion of the base soil takes place when the size of the constrictions of the filtering transition are too large and therefore are not able to retain the particles of the base soil entrained in the flow. This phenomenon produces significant volume changes within the soil and the resulting deformation may not be admissible with the limit state of the structure. In some cases, the phenomenon can lead to failure of the granular structure in contact with the filter with the consequent associated damage. In the paper, the main methods available in the literature to evaluate the internal stability of granular soils are described and critically discussed. Therefore, the recent research developments on internal stability achieved by the authors are illustrated. In particular, two methods, considering the grain size distribution of granular base soil, both validated by long term filtration tests, are described in detail
In this paper, a numerical model to simulate the hydraulic conductivity reduction observed during... more In this paper, a numerical model to simulate the hydraulic conductivity reduction observed during long-term laboratory column tests is proposed. The column tests are carried out to study dissolved heavy metals removal by using granular zero valent iron (ZVI). The proposed model is also used to analyse the main causes of hydraulic conductivity reduction observed during laboratory column tests. Expansive iron corrosion, precipitation of reaction products, and gas formation are the processes considered in the proposed model. Numerical simulation results show that to reproduce hydraulic behaviour of the experimental systems, the change of pores geometry due to expansive iron corrosion and precipitation of reaction products, which determines a possible stoppage of gas bubbles, should be considered. Furthermore, model results show that only a small percentage of the iron available is corroded during the tests (from 0.4% to 1.9%). According to the model, the average diameter of gas bubbles...
The geotextile filters design is based on the retention and the permeability criteria. In particu... more The geotextile filters design is based on the retention and the permeability criteria. In particular, the retention criterion, that a filter must satisfy in comparison to the base soil, is commonly expressed as O F D 85 , where O F is the geotextile characteristic opening size and D 85 is the soil particle diameter corresponding to the 85% of the passing soil mass grain size distribution. As consequence, the filter should retain only the larger particles of the base soil. This criterion works if the larger particles retain the smaller particles and this condition is verified when these particles form the solid skeleton (constituted by interconnected particles that transfer the stresses). When the granular soil has a broadly grain size distribution, with uniformity coefficient greater than 3, the larger particles generally do not belong to the solid skeleton but they are "immersed" in the smaller particles matrix that constitutes the solid skeleton (Giroud, 2010). So, for broadly granular soils, if the retention criterion previously defined is satisfied, this condition does not guarantee that the whole base soil is retained. In fact, the base soil could be subjected to an internal erosion phenomenon if the geotextile filter characteristic opening size is too large and the larger particles retained by the filter are not able to retain the smaller particles of the base soil and a hydraulic flow of dragging exists. The paper focuses on the development of a new theoretical method that, starting from the base soil mass grain size distribution and from its relative density, determines the upper limit value of the geotextile filter characteristic opening size, O F , to be used in the retention criterion in order to avoid the internal erosion of broadly granular base soil.
The knowledge of the internal stability of granular soils is a key factor in the design of granul... more The knowledge of the internal stability of granular soils is a key factor in the design of granular or geotextile filters. To evaluate the internal stability of granular soils, different semi-empirical methods are generally used. Nevertheless, the results of these methods, on the same soil, can lead to different internal stability evaluations. In this paper, to evaluate the reliability of the semi-empirical methods available in literature, the internal stability of different granular soils, reconstituted by the authors and by other researchers, has been studied by means of theoretical and experimental approaches. In particular, the theoretical analysis of the internal stability was performed using the Simulfiltr method, developed recently by the authors, while the experimental evaluation of the internal stability was carried out by means of long-term filtration tests. The comparison of the internal stability analysis performed by means of semi-empirical, theoretical, and experimenta...
The geotextile filter design is particularly complex when granular base soils are internally unst... more The geotextile filter design is particularly complex when granular base soils are internally unstable. In these conditions, the design criteria available in literature are not always reliable. This paper deals with a new theoretical method developed to evaluate the internal stability of granular soils. To simulate, theoretically, the filtration process inside these soils, a set of spherical particles and different soil relative densities have been considered. The soil has been represented by means of a sequence of parallel layers, containing constrictions and particles, placed upon each other at a distance, in the direction of hydraulic flow, which is a function of the soil relative density. The movement of the fine particles through the different soil layers has been simulated by means of a mechanism that compares each particle contained in the i layer with the constrictions contained in the next i + 1 layer. The results of the numerical simulations were used to evaluate the intern...
Antibiotic resistance poses an important threat to global public health and has become a challeng... more Antibiotic resistance poses an important threat to global public health and has become a challenge to modern medicine. The occurrence of antibiotic-resistant bacteria in a broad range of foods has led to a growing concern about the impact that food may have as a reservoir of antibiotic resistance genes. Considering Minas Frescal Cheese (MFC)-a typical Brazilian white soft cheese-and its economic and cultural values, in this study, medically relevant antimicrobial-resistance genetic markers (AR genes) were screened, and the occurrence of integrons were evaluated in manufactured MFC using culture-independent approaches. Through a fingerprinting analysis, the tested MFCs were brand-clustered, indicating reproducibility along the production chain. A common core of resistance markers in all brands evaluated and related antimicrobials such as β-lactams, tetracyclines, quinolones, and sulfonamide was detected. Several other markers, including efflux pumps and aminoglycosides-resistance were distributed among brands. Class 1 and 2 integrons were observed, respectively, in 77% and 97% of the samples. The presence of AR genes is of special interest due to their clinical relevance. Taken together, the data may suggest that the production chain of MFC might contribute to the spread of putative drug-resistant bacteria, which could greatly impact human health. Furthermore, detection of class 1 and class 2 integrons in MFC has led to discussions about resistance gene spread in this traditional cheese, providing evidence of potential horizontal transfer of AR genes to human gut microbiota.
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Papers by Domenico Ielo