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Papers by Giovanni Ciardi

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Colloidal silica (CS) grouting is a soil improvement technique introduced as an innovative remedi... more Colloidal silica (CS) grouting is a soil improvement technique introduced as an innovative remedial measure against seismic liquefaction. It consists of injecting soils with a time-hardening, nanosilica-based solution forming a silica gel among soil particles. This paper presents the results of an experimental study on the effects of an initial static shear stress on the behaviour of a cyclically loaded clean sand stabilised with 5% CS. Undrained cyclic triaxial tests were performed to analyse the cyclic response of loose untreated and stabilised sand specimens, isotropically or anisotropically consolidated at the same initial mean effective stress. The consolidation stage was used to provide insight on the compressibility of stabilised soil. Stress-strain behaviour, pore water pressure response and cyclic shear resistance were investigated. The results showed that: (i) stabilised sand exhibits higher compressibility than the untreated one during isotropic consolidation; (ii) cyclic strength is higher for stabilised sand than for the untreated one, increasing as the degree of anisotropic initial stress increases; and (iii) extra pore water pressure development does not depend on the degree of initial anisotropy for stabilised sand, while the same does not hold for untreated sand. Simplified relationships are proposed to describe the consolidation process and the residual extra pore water pressure build-up process.

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Geotechnics, 2021

Colloidal silica (CS) is a kind of nanomaterial used in soil/rock grouting techniques in differen... more Colloidal silica (CS) is a kind of nanomaterial used in soil/rock grouting techniques in different branches of civil engineering. Many studies have recently been performed to investigate the potential of CS in improving the mechanical behavior of cohesionless soils and mitigating the risk of seismic liquefaction in urbanized areas. CS grout is chemically and biologically inert and, when injected into a subsoil, it can form a silica gel and stabilize the desired soil layer, thus representing an attractive, environmentally friendly alternative to standard chemical grouting techniques. This paper firstly describes the characteristics of CS grout, the gelation process and the main features of the behavior of the pure gelled material. The grout delivery mechanisms through porous media are then explained, pointing out the crucial issues for practical application of CS grouting. All the grouting-induced effects on the soil behavior, which have been investigated by laboratory tests on small-sized soil elements, are reviewed, including the modifications to soil strength and stiffness under both static and seismic loading conditions, to soil compressibility and hydraulic conductivity. Published results from physical model tests and in situ applications are also presented. Finally, some aspects related to the mechanism of soil improvement are discussed. A critical discussion of each topic is presented, drawing particular attention to the controversial or not yet fully examined aspects to which future research on colloidal silica grouting should be directed.

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Geotechnical Research, 2020

The effectiveness of colloidal silica (CS) treatment in increasing the liquefaction resistance of... more The effectiveness of colloidal silica (CS) treatment in increasing the liquefaction resistance of sandy soils is by now amply demonstrated. However, the best value of the CS content to achieve high performance, minimising economic cost and impact on buildings and the environment, has not yet been quantified. This paper presents the results of a laboratory study aimed to evaluate the influence of different CS contents on the behaviour of a liquefiable sand. The investigation included direct shear, cyclic triaxial, hydraulic conductivity and oedometer tests. CS contents 0, 2 and 5% (by weight) were used for all tests, except for direct shear tests (CS contents 0 and 2%) and oedometer tests (CS contents 0, 2, 3, 5, 10 and 13%). The test results showed that 2% CS content was enough to increase the soil strength under cyclic and monotonic loading conditions. The hydraulic conductivity of treated soil decreased significantly as CS content increased. Oedometer tests pointed out that the main disadvantage of CS treatment is the soil compressibility increase. On the basis of the obtained results, 2% CS content seems to be recommended because it shows effectiveness and capability to improve the liquefaction resistance of sand while minimising the soil compressibility increase.

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Conference Presentations by Giovanni Ciardi

Proceedings of the VII International Conference on Earthquake Geotechnical Engineering, 2019

It has recently been demonstrated that colloidal silica (CS) can be successfully used to stabiliz... more It has recently been demonstrated that colloidal silica (CS) can be successfully used to stabilize liquefiable soils. However, the effects of high-diluted CS mixtures have not been exhaustively investigated yet. This paper presents the results of an experimental testing campaign pointing out how CS dilution modifies the mechanical properties of a liquefiable sand. Cyclic and monotonic triaxial tests for untreated sand, as well as for sand treated with different CS contents, were carried out. Oedometer tests were performed to explore additional effects of the CS treatment on soil properties. The effects of a 5% CS by weight concentration were evaluated and taken as the reference for comparison with the results of previous studies. Furthermore, different CS contents, lower than 5% CS by weight, were used to prepare stabilized specimens. As a result, experimental evidence revealed that these dilutions can also be used to improve the behavior of the material against liquefaction.

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Bookmarks Related papers MentionsView impact

Colloidal silica (CS) grouting is a soil improvement technique introduced as an innovative remedi... more Colloidal silica (CS) grouting is a soil improvement technique introduced as an innovative remedial measure against seismic liquefaction. It consists of injecting soils with a time-hardening, nanosilica-based solution forming a silica gel among soil particles. This paper presents the results of an experimental study on the effects of an initial static shear stress on the behaviour of a cyclically loaded clean sand stabilised with 5% CS. Undrained cyclic triaxial tests were performed to analyse the cyclic response of loose untreated and stabilised sand specimens, isotropically or anisotropically consolidated at the same initial mean effective stress. The consolidation stage was used to provide insight on the compressibility of stabilised soil. Stress-strain behaviour, pore water pressure response and cyclic shear resistance were investigated. The results showed that: (i) stabilised sand exhibits higher compressibility than the untreated one during isotropic consolidation; (ii) cyclic strength is higher for stabilised sand than for the untreated one, increasing as the degree of anisotropic initial stress increases; and (iii) extra pore water pressure development does not depend on the degree of initial anisotropy for stabilised sand, while the same does not hold for untreated sand. Simplified relationships are proposed to describe the consolidation process and the residual extra pore water pressure build-up process.

Bookmarks Related papers MentionsView impact

Geotechnics, 2021

Colloidal silica (CS) is a kind of nanomaterial used in soil/rock grouting techniques in differen... more Colloidal silica (CS) is a kind of nanomaterial used in soil/rock grouting techniques in different branches of civil engineering. Many studies have recently been performed to investigate the potential of CS in improving the mechanical behavior of cohesionless soils and mitigating the risk of seismic liquefaction in urbanized areas. CS grout is chemically and biologically inert and, when injected into a subsoil, it can form a silica gel and stabilize the desired soil layer, thus representing an attractive, environmentally friendly alternative to standard chemical grouting techniques. This paper firstly describes the characteristics of CS grout, the gelation process and the main features of the behavior of the pure gelled material. The grout delivery mechanisms through porous media are then explained, pointing out the crucial issues for practical application of CS grouting. All the grouting-induced effects on the soil behavior, which have been investigated by laboratory tests on small-sized soil elements, are reviewed, including the modifications to soil strength and stiffness under both static and seismic loading conditions, to soil compressibility and hydraulic conductivity. Published results from physical model tests and in situ applications are also presented. Finally, some aspects related to the mechanism of soil improvement are discussed. A critical discussion of each topic is presented, drawing particular attention to the controversial or not yet fully examined aspects to which future research on colloidal silica grouting should be directed.

Bookmarks Related papers MentionsView impact

Geotechnical Research, 2020

The effectiveness of colloidal silica (CS) treatment in increasing the liquefaction resistance of... more The effectiveness of colloidal silica (CS) treatment in increasing the liquefaction resistance of sandy soils is by now amply demonstrated. However, the best value of the CS content to achieve high performance, minimising economic cost and impact on buildings and the environment, has not yet been quantified. This paper presents the results of a laboratory study aimed to evaluate the influence of different CS contents on the behaviour of a liquefiable sand. The investigation included direct shear, cyclic triaxial, hydraulic conductivity and oedometer tests. CS contents 0, 2 and 5% (by weight) were used for all tests, except for direct shear tests (CS contents 0 and 2%) and oedometer tests (CS contents 0, 2, 3, 5, 10 and 13%). The test results showed that 2% CS content was enough to increase the soil strength under cyclic and monotonic loading conditions. The hydraulic conductivity of treated soil decreased significantly as CS content increased. Oedometer tests pointed out that the main disadvantage of CS treatment is the soil compressibility increase. On the basis of the obtained results, 2% CS content seems to be recommended because it shows effectiveness and capability to improve the liquefaction resistance of sand while minimising the soil compressibility increase.

Bookmarks Related papers MentionsView impact

Proceedings of the VII International Conference on Earthquake Geotechnical Engineering, 2019

It has recently been demonstrated that colloidal silica (CS) can be successfully used to stabiliz... more It has recently been demonstrated that colloidal silica (CS) can be successfully used to stabilize liquefiable soils. However, the effects of high-diluted CS mixtures have not been exhaustively investigated yet. This paper presents the results of an experimental testing campaign pointing out how CS dilution modifies the mechanical properties of a liquefiable sand. Cyclic and monotonic triaxial tests for untreated sand, as well as for sand treated with different CS contents, were carried out. Oedometer tests were performed to explore additional effects of the CS treatment on soil properties. The effects of a 5% CS by weight concentration were evaluated and taken as the reference for comparison with the results of previous studies. Furthermore, different CS contents, lower than 5% CS by weight, were used to prepare stabilized specimens. As a result, experimental evidence revealed that these dilutions can also be used to improve the behavior of the material against liquefaction.

Bookmarks Related papers MentionsView impact