K. Fujisawa, A. Murakami, S. Nishimura and T. Shuku

ABSTRACT: Thus far, the focus of studies on seepage failure, known as sand boiling or the piping phenomenon, has been to determine the critical hydraulic gradient or the critical seepage flow velocity. However, the transport of soil after seepage failure also needs to be well investigated in order to estimate the damage to soil structures or the ground. The purpose of this study is to experimentally investigate the relationship between the seepage force and the velocity of the sand particles during sand boiling induced by upward and horizontal seepage flows. In the experiments, silica sand is used as the test material and the migration velocities of the seepage water and the sand particles are calculated from the measured amounts of their discharge. The test results reveal that the equilibrium of the forces exerted on the sand particles, i.e., gravity, buoyancy and fluid-particle interaction, can be successfully used to estimate the velocity of the sand particles subjected to upward seepage flow and that the seepage force needed for the horizontal transport of the sand tends to decrease as the velocity of the sand particles increases.

A density-and stress-dependent elasto-plastic model for sands subjected to monotonic undrained torsional shear loading

G. Chiaro, J. Koseki and L.I. Nalin De Silva

ABSTRACT: A density- and stress-dependent elasto-plastic model for saturated sands undergoing monotonic undrained torsional shear loading is presented in this paper. The model is developed under an extended general hyperbolic equation (GHE) approach, in which the void ratio and stress level dependence upon stress-strain response of sand is incorporated. Most importantly, a state-dependent stress-dilatancy relationship is introduced to account for the effect of density on the stress ratio. Such a stress-dilatancy relation is used for modeling the excess pore water pressure generation in undrained shear conditions as the mirror effect of volumetric change in drained shear conditions. In this paper, details of the model formulation and soil parameters calibration are described. By using the proposed model, numerical simulation of monotonic undrained torsional shear tests have been carried out on Toyoura sand. The model predictions show that undrained shear behavior, described in terms of stress-strain relationship and effective stress path for both loose and dense sands, can be modeled satisfactorily by using a single set of soil parameters.

1-G model test with digital image analysis for seismic behavior of earth dam

Y. Miyanaga, A. Kobayashi and A.Murakami

ABSTRACT: This paper proposes a new experimental method using small 1-G shaking table tests to investigate the seismic behavior of an earth dam. In this research, a digital image analysis was applied to observe strain distributions during excitation. White gauge points were placed on the surface of the model and the movements of these points were analyzed via successive digital image pictures. From the displacements of the gauge points, the distributions of shear strain and volumetric strain were examined as the functions of the acceleration response of the dam body. As a result of the volumetric strain distributions, it was found that vertical tension and compression zones exist in turn, and that tensile stress was observed at the top of the model. It was estimated that the crack at the crest of the earth dam, brought about by the earthquake, was attributed to the tensile stress.

X-ray CT imaging of 3-D bearing capacity mechanism for vertically loaded shallow foundations

D. Takano, J. Otani, M. Nakamura, and R. Mokwa

ABSTRACT: The three-dimensional bearing capacity of shallow foundations has not been fully investigated because of the difficulty in visualizing and understanding the complex three-dimensional failure mechanism. In this paper, a series of model loading tests were conducted on shallow foundations with square and rectangular shaped footings X-ray CT scanning techniques were utilized to nondestructively visualize and investigate the soil behavior during the loading tests. Based on the tomographic results for four different footing geometries, both surface deformations and below ground deformations along the failure surface cross section are described and three-dimensional failure mechanisms illustrated. A gradual change or progression of the bearing capacity failure pattern was observed and quantified as the footing aspect ratio changed from a square foundation to a rectangular shape that approached plane strain conditions. It is anticipated that the process and technique developed in this study could be beneficial in understanding and quantifying the mechanics associated with other soil-structure interaction problems, especially complex problems in which the failure mechanism is difficult or impossible to predict using conventional geotechnical engineering principles.

Modeling and bending test simulations of cement treated soil

K. Kaneda, T. Tanikawa and S. Onimaru

ABSTRACT: Cement treated soil, which is commonly utilized to prevent liquefaction and/or to increase the bearing capacity of soft clay foundations, is characterized by four basic properties: 1) its strength is greater than that of untreated soil, yet less than that of concrete, 2) it exhibits nonlinear behavior close to its peak strength, 3) softening occurs after its peak strength has been exceeded, and 4) the extension strength is found while the soil is not considered. In this study, the subloading surface model introduced by Hashiguchi was incorporated into a modified Drucker-Prager criterion, and undrained triaxial compression tests of cement treated soil were performed under constrained pressures of 0.1 and 0.4 MN/m2, after which bending tests and simulations were performed. The numerical results of these tests agreed well with the actual results of element wise and boundary condition testing.

Modelling viscous effects during and after construction in London Clay

S. D. Clarke and C. C. Hird

ABSTRACT: A new approach to allow the modelling of the viscous behaviour of clay soils has recently been developed (Clarke & Hird, 2012) based on the BRICK constitutive model (Simpson, 1992). In this approach viscous effects, such as creep and stress relaxation, and the effects of strain history on soil stiffness are modelled within a single conceptual framework. The developed model, SRD (strain-rate dependent) BRICK, has been incorporated in a finite element program, allowing boundary value problems to be analysed. In this paper two case histories involving London Clay, where viscous effects possibly had an influence on the observed displacements, are back-analysed. These cases are the Jubilee Line extension at St James’s Park (Standing et al., 1996, Nyren et al., 2001) and a deep basement at Horseferry Road (May, 1975, Chapman, 1999). The results of the numerical modelling show that, in each case, the SRD BRICK model is able to achieve closer agreement with the recorded displacements when compared with the unmodified BRICK model.

Modelling viscous effects during and after construction in London Clay

S. D. Clarke and C. C. Hird

ABSTRACT: A new approach to allow the modelling of the viscous behaviour of clay soils has recently been developed (Clarke & Hird, 2012) based on the BRICK constitutive model (Simpson, 1992). In this approach viscous effects, such as creep and stress relaxation, and the effects of strain history on soil stiffness are modelled within a single conceptual framework. The developed model, SRD (strain-rate dependent) BRICK, has been incorporated in a finite element program, allowing boundary value problems to be analysed. In this paper two case histories involving London Clay, where viscous effects possibly had an influence on the observed displacements, are back-analysed. These cases are the Jubilee Line extension at St James’s Park (Standing et al., 1996, Nyren et al., 2001) and a deep basement at Horseferry Road (May, 1975, Chapman, 1999). The results of the numerical modelling show that, in each case, the SRD BRICK model is able to achieve closer agreement with the recorded displacements when compared with the unmodified BRICK model.

Vol. 44 No.2 June 2013

Soil-water-air coupled finite element analysis of model test on slope failure in unsaturated soil

Y. L. Xiong, X. H. Bao, F. Zhang

ABSTRACT: In this paper, a program of finite element method named as SOFT, using finite element-finite difference scheme (FE-FD) in soil-water-air three-phase coupling problem has been developed based on a rational constitutive model for unsaturated soil proposed by Zhang and Ikariya (2011), which can properly take into consideration of moisture characteristics of unsaturated soils. In the program, the FEFD formulation in saturated condition proposed by Oka et al. (1994) has been extended to unsaturated condition. In order to verify the availability of the program, a model test on slope failure of unsaturated soil, carried out by Kitamura et al. (2007), is simulated by the proposed numerical method. From the results, it is known that the test results can be described in a satisfactory accuracy on the whole.

KEYWORDS: Soil-water-air Coupled; Finite Element Analysis; Slope Failure; Unsaturated Soil

DOI: 10.14456/seagj.2013.24

Vol. 44 No.2 June 2013

Relation between seepage force and velocity of sand particles during sand boiling

K. Fujisawa, A. Murakami, S. Nishimura and T. Shuku

ABSTRACT: Thus far, the focus of studies on seepage failure, known as sand boiling or the piping phenomenon, has been to determine the critical hydraulic gradient or the critical seepage flow velocity. However, the transport of soil after seepage failure also needs to be well investigated in order to estimate the damage to soil structures or the ground. The purpose of this study is to experimentally investigate the relationship between the seepage force and the velocity of the sand particles during sand boiling induced by upward and horizontal seepage flows. In the experiments, silica sand is used as the test material and the migration velocities of the seepage water and the sand particles are calculated from the measured amounts of their discharge. The test results reveal that the equilibrium of the forces exerted on the sand particles, i.e., gravity, buoyancy and fluid-particle interaction, can be successfully used to estimate the velocity of the sand particles subjected to upward seepage flow and that the seepage force needed for the horizontal transport of the sand tends to decrease as the velocity of the sand particles increases.

KEYWORDS: Relation; Seepage force; Velocity; Sand particles; Sand boiling

DOI: 10.14456/seagj.2013.25

Vol. 44 No.2 June 2013

A density-and stress-dependent elasto-plastic model for sands subjected to monotonic undrained torsional shear loading

G. Chiaro, J. Koseki and L.I. Nalin De Silva

ABSTRACT: A density- and stress-dependent elasto-plastic model for saturated sands undergoing monotonic undrained torsional shear loading is presented in this paper. The model is developed under an extended general hyperbolic equation (GHE) approach, in which the void ratio and stress level dependence upon stress-strain response of sand is incorporated. Most importantly, a state-dependent stress-dilatancy relationship is introduced to account for the effect of density on the stress ratio. Such a stress-dilatancy relation is used for modeling the excess pore water pressure generation in undrained shear conditions as the mirror effect of volumetric change in drained shear conditions. In this paper, details of the model formulation and soil parameters calibration are described. By using the proposed model, numerical simulation of monotonic undrained torsional shear tests have been carried out on Toyoura sand. The model predictions show that undrained shear behavior, described in terms of stress-strain relationship and effective stress path for both loose and dense sands, can be modeled satisfactorily by using a single set of soil parameters.

KEYWORDS: A density- and stress-dependent; Elasto-plastic model; Sands; Monotonic undrained torsional shear loading

DOI: 10.14456/seagj.2013.26

Vol. 44 No.2 June 2013

1-G model test with digital image analysis for seismic behavior of earth dam

Y. Miyanaga, A. Kobayashi and A.Murakami

ABSTRACT: This paper proposes a new experimental method using small 1-G shaking table tests to investigate the seismic behavior of an earth dam. In this research, a digital image analysis was applied to observe strain distributions during excitation. White gauge points were placed on the surface of the model and the movements of these points were analyzed via successive digital image pictures. From the displacements of the gauge points, the distributions of shear strain and volumetric strain were examined as the functions of the acceleration response of the dam body. As a result of the volumetric strain distributions, it was found that vertical tension and compression zones exist in turn, and that tensile stress was observed at the top of the model. It was estimated that the crack at the crest of the earth dam, brought about by the earthquake, was attributed to the tensile stress.

KEYWORDS: 1-G Model Test; Digital Image Analysis; Seismic Behavior; Earth Dam

DOI: 10.14456/seagj.2013.27

Vol. 44 No.2 June 2013

X-ray CT imaging of 3-D bearing capacity mechanism for vertically loaded shallow foundations

D. Takano, J. Otani, M. Nakamura, and R. Mokwa

ABSTRACT: The three-dimensional bearing capacity of shallow foundations has not been fully investigated because of the difficulty in visualizing and understanding the complex three-dimensional failure mechanism. In this paper, a series of model loading tests were conducted on shallow foundations with square and rectangular shaped footings X-ray CT scanning techniques were utilized to nondestructively visualize and investigate the soil behavior during the loading tests. Based on the tomographic results for four different footing geometries, both surface deformations and below ground deformations along the failure surface cross section are described and three-dimensional failure mechanisms illustrated. A gradual change or progression of the bearing capacity failure pattern was observed and quantified as the footing aspect ratio changed from a square foundation to a rectangular shape that approached plane strain conditions. It is anticipated that the process and technique developed in this study could be beneficial in understanding and quantifying the mechanics associated with other soil-structure interaction problems, especially complex problems in which the failure mechanism is difficult or impossible to predict using conventional geotechnical engineering principles.

KEYWORDS: X-ray CT imaging; 3-D bearing capacity mechanism; Vertically loaded; Shallow foundations

DOI: 10.14456/seagj.2013.28

Vol. 44 No.2 June 2013

Modeling and bending test simulations of cement treated soil

K. Kaneda, T. Tanikawa and S. Onimaru

ABSTRACT: Cement treated soil, which is commonly utilized to prevent liquefaction and/or to increase the bearing capacity of soft clay foundations, is characterized by four basic properties: 1) its strength is greater than that of untreated soil, yet less than that of concrete, 2) it exhibits nonlinear behavior close to its peak strength, 3) softening occurs after its peak strength has been exceeded, and 4) the extension strength is found while the soil is not considered. In this study, the subloading surface model introduced by Hashiguchi was incorporated into a modified Drucker-Prager criterion, and undrained triaxial compression tests of cement treated soil were performed under constrained pressures of 0.1 and 0.4 MN/m2, after which bending tests and simulations were performed. The numerical results of these tests agreed well with the actual results of element wise and boundary condition testing.

KEYWORDS: Modeling; Bending Test; Simulations; Cement Treated Soil

DOI: 10.14456/seagj.2013.29

Vol. 44 No.2 June 2013

Modelling viscous effects during and after construction in London Clay

S. D. Clarke and C. C. Hird

ABSTRACT: A new approach to allow the modelling of the viscous behaviour of clay soils has recently been developed (Clarke & Hird, 2012) based on the BRICK constitutive model (Simpson, 1992). In this approach viscous effects, such as creep and stress relaxation, and the effects of strain history on soil stiffness are modelled within a single conceptual framework. The developed model, SRD (strain-rate dependent) BRICK, has been incorporated in a finite element program, allowing boundary value problems to be analysed. In this paper two case histories involving London Clay, where viscous effects possibly had an influence on the observed displacements, are back-analysed. These cases are the Jubilee Line extension at St James’s Park (Standing et al., 1996, Nyren et al., 2001) and a deep basement at Horseferry Road (May, 1975, Chapman, 1999). The results of the numerical modelling show that, in each case, the SRD BRICK model is able to achieve closer agreement with the recorded displacements when compared with the unmodified BRICK model.

KEYWORDS: Modelling; Viscous Effects; During and after Construction; London Clay

DOI: 10.14456/seagj.2013.30

The 4th International Young Geotechnical Engineers Conference (4iYGEC) was held at the Hotel El Mahrousa on the sea front in Alexandria on the 3 and 4 October 2009. The organizing committee was chaired by Prof. Fatma Baligh. The event gathered 89 papers, and 83 of the authors – representing 42 countries on five continents ‐ travelled to Alexandria to present their papers. Eleven participants came from Africa, 7 from the Americas, 21 from Asia, 2 from Australia and 42 from Europe. The conference began with an opening ceremony where Prof. Fatma Baligh, Prof. Mamdouh Hamza, Prof. Neil Taylor and Prof. Pedro Seco e Pinto welcomed the participants.

Delegates and organizing committee of the 4th International Young Geotechnical Engineering Conference.

Following the opening ceremony, a plenary lecture presented by Prof. Ahmed Elgamal (University of California, San Diego, USA) preceded the technical sessions that addressed these themes:
‐ Soil Behaviour and Properties, New Concepts and Correlations
‐ Ground Improvement: Chemical, Mechanical and Reinforcement
‐ Seepage Flow, Contaminated Soil Treatment and Response
‐ Landslide and Slope Stability, Case Studies
‐ Deep Foundation Design and Practice
‐ Performance of Different Types of Earth Retaining Structures
‐ Soil Structure Interaction, Risk Management
‐ Underground Construction

At the end of each session, a symbolic prize was awarded for the best presentation.

Delegates and organizing committee of the 4th International Young Geotechnical Engineering Conference.

As the 4iYGEC is held within the framework of the 17th International Conference on Soil Mechanics and Geotechnical Engineering (17th ICSMGE), all of the young participants of 4iYGEC were invited to attend the 17th ICSMGE held in the Library of Alexandria (Bibliotheca Alexandrina). During the two first days of the 17th ICSGME (5‐6 October 2009) the participants attended five State‐of‐The‐Art lectures, a Heritage Lecture and two lectures on Great Projects. On 6 October in the session “Thoughts and Observations,” the 4iYGEC conference chairperson and three chosen participants presented a briefing of what had taken place at the 4iYGEC. An optional Technical Visit to the San‐Stefano Hotel Harbour was also scheduled this day.

A Cultural Evening of Egyptian Folk Dancing was held around the swimming pool at El‐Mahrousa Hotel where traditional oriental food and beverages were served to the 4iYGEC participants.

The 4iYGEC was a great contribution to the sharing of scientific knowledge in the field of soil mechanics and geotechnical engineering.

Reported by Prof. Fatma Baligh

Read more from ISSMGE Bulletin – Volume 3 Issue 4 December 2009 (pp.22-24)
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The 2nd Thai Young Geotechnical Engineers Meeting

Following on the success of the 1st Thai Young Geotechnical Engineers Meeting (tYGEM) held at Khon Kaen City in 2006, the 2nd tYGEM was held in Kanchanaburi Province, Thailand from 20 to 21 October 2007. The venue was at Srinagarind Dam, located 120 km west side from the capital Bangkok. The meeting was organized by the Geotechnical Engineering Subcommittee, the Engineering Institute of Thailand under H.M. the King’s Patronage (EIT), in cooperation with the Geotechnical Engineering Research and Development Center of the Kasetsart University. 130 delegates from Universities in Thailand registered for this meeting.

The purpose and objective of this meeting was to bring together both senior and young geotechnical engineers from various universities to stay together so that they could meet and interchange ideas in an informal atmosphere. The organizing committee would like to encourage the young geotechnical delegates to develop a wider scope of thinking in the geotechnical engineering field. Attendees will not only be comfortable in exchanging technical leanings, but the organizing committee wishes to form personal linkages with peers across universities.

In the opening ceremony, the Chairman of the Geotechnical Engineering Subcommittee Dr.Watcharin Gasaluck described the significance and aims of this meeting and then the Chairman expressed that the Geotechnical Engineering Subcommittee of EIT is always supporting the activity of younger generations who will bear the future of the geotechnical engineering in Thailand.

The meeting was started with the technical sessions. In 5 technical sessions chaired by junior lecturers from various universities, each participant had the opportunity to make a 10 minutes presentation on a project or research topic which they were currently or had been recently involved in the graduate study. The fruitful discussions and comments from the senior members give a good idea and encourage the younger members in continuing a good research work. The summary session was conducted in the main conference room after a whole day and long presentations by a senior geotechnical engineer, Dr.Warakorn Mai-Rieng, the Head of Civil Engineering Department, Kasetsart University. Dr. Warakorn stated the high success of this meeting with the full achievement of the objective.

All audiences agreed that this kind of meeting should be continued as long as possible under the support from EIT and from the local universities. The next meeting will tentatively be organized next year by the Ubonratchatani University which is located in the Northeastern part of Thailand and located about 500 km from Bangkok. The academic part of the meeting was completed by the official dinner with a variety of local foods and drinks. The 2nd tYGEM has finally finished with a technical excursion. A technical visit to the Srinagarind Dam– One of major dams in Thailand which is located on the active faults and with many geotechnical works, was organized for the conference delegates.

Reported by Dr.Pongsakorn Punrattanasin, the Engineering Institute of Thailand

From ISSMGE Bulletin: Volume 1 Issue 4 (p.2)
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