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Cihan Cengiz
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1
Flexural and Cracking Behavior of Clay Plates under Bending
Insights from Novel Tests and New Suction Parameters
This study investigates the flexural and cracking behavior of clay plates under pure bending conditions through a novel experimental framework. The test methodology overcomes limitations of traditional beam flexure and burst tests by employing an inflatable membrane to apply a uniform bending pressure while continuously supporting self-weight of the specimen. Kaolin clay plates of varying thicknesses were prepared by slurry consolidation and subjected to bending tests in an instrumented assembly. The bending stresses and moments, pore water pressures, and displacement of the surface were measured with conventional sensors. Additionally, the deformations of the specimens were captured with a three-dimensional scanner to evaluate the curvature and cracking patterns. Beyond the innovative experimental setup, this study also sheds light into the suction regime in clays subjected to flexure and sets forth novel pore water pressure parameters, which correlate well with the cracking tendencies of the clay material. A distinct curvature threshold is defined, and it is observed that the clay material’s crack opening tendencies are influenced by the suction regime in the specimen. Beyond the novel insights offered in this study, the normalized bending resistances yielded from the tests correlate well with existing research.
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This study investigates the flexural and cracking behavior of clay plates under pure bending conditions through a novel experimental framework. The test methodology overcomes limitations of traditional beam flexure and burst tests by employing an inflatable membrane to apply a uniform bending pressure while continuously supporting self-weight of the specimen. Kaolin clay plates of varying thicknesses were prepared by slurry consolidation and subjected to bending tests in an instrumented assembly. The bending stresses and moments, pore water pressures, and displacement of the surface were measured with conventional sensors. Additionally, the deformations of the specimens were captured with a three-dimensional scanner to evaluate the curvature and cracking patterns. Beyond the innovative experimental setup, this study also sheds light into the suction regime in clays subjected to flexure and sets forth novel pore water pressure parameters, which correlate well with the cracking tendencies of the clay material. A distinct curvature threshold is defined, and it is observed that the clay material’s crack opening tendencies are influenced by the suction regime in the specimen. Beyond the novel insights offered in this study, the normalized bending resistances yielded from the tests correlate well with existing research.
Conference paper
(2026)
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Bas van Dijk, Edo Vink, William Ovalle-Villamil, Cihan Cengiz, Agnes van Uitert
Many embankments of the Dutch railroad network are over a hundred years old and were constructed on very soft clay and peat layers. The weight of the trains and the use of the railway infrastructure have increased over time. A recent assessment of the stability of existing infrastructure revealed that the railway embankment is demonstrably not in compliance with the required standards in several locations. However, although considerable deformations exist in some cases, most of these embankments have remained stable under current use. This may indicate that several aspects of the train loading characteristics in relation to the foundation soil strength are not fully understood in the context of railway embankment stability. To better understand the effect of train loading and increased use of railroads on the soil strength, a geocentrifuge test program was executed through the GEOLAB initiative. During this study a series of centrifuge tests were performed of a railroad system composed of a sandy embankment underlain by a soft clay foundation, aiming to provide a better understanding of the potential effects of train loading characteristics and the increased use of railroads on the foundation soil strength. The models were tested in a geotechnical centrifuge at a gravitational acceleration field of 20g and included reference static monotonic tests to failure and tests modelling different train loading conditions, including different loading frequencies and amplitudes. This paper presents the design of the experimental setup, a description of the behavior’s observed during the execution of the tests and preliminary results and observations of the project SURE performed as part of the transnational access initiative by GEOLAB. Further presentation and analysis of the results will be presented in a future companion article.
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Many embankments of the Dutch railroad network are over a hundred years old and were constructed on very soft clay and peat layers. The weight of the trains and the use of the railway infrastructure have increased over time. A recent assessment of the stability of existing infrastructure revealed that the railway embankment is demonstrably not in compliance with the required standards in several locations. However, although considerable deformations exist in some cases, most of these embankments have remained stable under current use. This may indicate that several aspects of the train loading characteristics in relation to the foundation soil strength are not fully understood in the context of railway embankment stability. To better understand the effect of train loading and increased use of railroads on the soil strength, a geocentrifuge test program was executed through the GEOLAB initiative. During this study a series of centrifuge tests were performed of a railroad system composed of a sandy embankment underlain by a soft clay foundation, aiming to provide a better understanding of the potential effects of train loading characteristics and the increased use of railroads on the foundation soil strength. The models were tested in a geotechnical centrifuge at a gravitational acceleration field of 20g and included reference static monotonic tests to failure and tests modelling different train loading conditions, including different loading frequencies and amplitudes. This paper presents the design of the experimental setup, a description of the behavior’s observed during the execution of the tests and preliminary results and observations of the project SURE performed as part of the transnational access initiative by GEOLAB. Further presentation and analysis of the results will be presented in a future companion article.
Journal article
(2025)
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Cihan Cengiz, Maria Konstantinou, Marien Harkes, Danko Boonstra, Alba Rodríguez Piedrabuena, Arno Talmon
Porosity and pore structure are critical parameters in geotechnical engineering which influence the stiffness and permeability of granular materials. Traditional wave-based techniques, such as bender element testing, often require complex equipment, are susceptible to noise, and rely on stiffness-to-density conversions that introduce uncertainties in porosity inference. This study introduces the Concentration Conductivity Measurement (CCM) technique as a novel, non-destructive alternative for porosity and formation factor measurement using electrical conductivity. The CCM technique was validated through calibration tests on various sands and glass beads where a strong correlation was demonstrated with empirical models and literature data. The findings exhibit CCM sensors ability to provide reliable measurements under different material typologies prepared with varying compaction efforts. The method also alleviates the shortcomings of existing techniques. Unlike wave-based methods, CCM requires simpler equipment and is not susceptible to be affected by background noise which makes the method particularly suitable for geotechnical laboratory applications. This study provides a practical and versatile framework for porosity profiling with CCM and it advances the state of the art on granular media characterization. The study also demonstrates the significant potential of the technique for applications in soil mechanics and geotechnical modelling by comparing the findings to the data in the existing literature.
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Porosity and pore structure are critical parameters in geotechnical engineering which influence the stiffness and permeability of granular materials. Traditional wave-based techniques, such as bender element testing, often require complex equipment, are susceptible to noise, and rely on stiffness-to-density conversions that introduce uncertainties in porosity inference. This study introduces the Concentration Conductivity Measurement (CCM) technique as a novel, non-destructive alternative for porosity and formation factor measurement using electrical conductivity. The CCM technique was validated through calibration tests on various sands and glass beads where a strong correlation was demonstrated with empirical models and literature data. The findings exhibit CCM sensors ability to provide reliable measurements under different material typologies prepared with varying compaction efforts. The method also alleviates the shortcomings of existing techniques. Unlike wave-based methods, CCM requires simpler equipment and is not susceptible to be affected by background noise which makes the method particularly suitable for geotechnical laboratory applications. This study provides a practical and versatile framework for porosity profiling with CCM and it advances the state of the art on granular media characterization. The study also demonstrates the significant potential of the technique for applications in soil mechanics and geotechnical modelling by comparing the findings to the data in the existing literature.
Journal article
(2025)
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Hao Shi, Cihan Cengiz, Giulia Macaro, Mario Martinelli, Jovana Jovanova, Dingena Schott
Monopiles are the dominant foundation type for offshore wind turbines, accounting for approximately 80% of the installed capacity. Installing offshore monopile foundations on seabeds susceptible to scour erosion requires monopiles to penetrate several pre-installed scour protection rock layers before securing them into the seabed. The accurate prediction of the pile penetration resistance is crucial to ensure successful monopile installations. To complement, and potentially reduce the dependence on the costly and labour-intensive experimental small-scale penetration tests, a numerical model has been developed using the Discrete Element Method (DEM) that captures the discrete nature of interactions between rocks and piles and predicts the resistance during the penetration process. The developed DEM model includes armour and filter rocks represented by multispheres and sand particles represented by spheres. A multistage calibration, verification and validation DEM modelling framework is proposed and examined with small-scale penetration tests conducted using plates and piles in a double-layer scour protection configuration. The sand material model is calibrated and verified using penetrometer tests and the rock material models are calibrated and verified using a plate penetration test. The DEM model with three verified materials predicts the penetration resistance well in small-scale pile penetration tests and proves the validity of the proposed framework. The DEM model presented in this paper facilitates the modelling in areas where traditional continuum-based numerical methods give less accurate predictions and provide insights that are difficult or nearly impossible to obtain through experimental methods.
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Monopiles are the dominant foundation type for offshore wind turbines, accounting for approximately 80% of the installed capacity. Installing offshore monopile foundations on seabeds susceptible to scour erosion requires monopiles to penetrate several pre-installed scour protection rock layers before securing them into the seabed. The accurate prediction of the pile penetration resistance is crucial to ensure successful monopile installations. To complement, and potentially reduce the dependence on the costly and labour-intensive experimental small-scale penetration tests, a numerical model has been developed using the Discrete Element Method (DEM) that captures the discrete nature of interactions between rocks and piles and predicts the resistance during the penetration process. The developed DEM model includes armour and filter rocks represented by multispheres and sand particles represented by spheres. A multistage calibration, verification and validation DEM modelling framework is proposed and examined with small-scale penetration tests conducted using plates and piles in a double-layer scour protection configuration. The sand material model is calibrated and verified using penetrometer tests and the rock material models are calibrated and verified using a plate penetration test. The DEM model with three verified materials predicts the penetration resistance well in small-scale pile penetration tests and proves the validity of the proposed framework. The DEM model presented in this paper facilitates the modelling in areas where traditional continuum-based numerical methods give less accurate predictions and provide insights that are difficult or nearly impossible to obtain through experimental methods.
Journal article
(2025)
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Maria Konstadinou, Etienne A. Alderlieste, Cor Zwanenburg, Cihan Cengiz, Anderson Peccin da Silva, Charlotte J.W. van Verseveld
The shear strength and compression properties of stiff Boom clay from Belgium at a depth of about 16.5 to 28 m were investigated by means of cone penetration and laboratory testing. The latter consisted of index classification, constant rate of strain, triaxial, direct simple shear and unconfined compression tests. The Boom clay samples exhibited strong swelling tendencies. The suction pressure was measured via different procedures and was compared to the expected in situ stress. The undrained shear strength profile determined from cone penetration tests (CPTs) was not compatible with the triaxial and direct simple shear measurements, which gave significantly lower undrained shear strength values. Micro-computed tomography (μCT) scans of the samples showed the presence of pre-existing discontinuities which may cause inconsistencies in the comparison of the laboratory test results with in situ data. The experimental data gathered in this study provide useful information for analyzing the mechanical behaviour of Boom clay at shallow depths considering that most investigations in the literature have been carried out on deep Boom clay deposits.
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The shear strength and compression properties of stiff Boom clay from Belgium at a depth of about 16.5 to 28 m were investigated by means of cone penetration and laboratory testing. The latter consisted of index classification, constant rate of strain, triaxial, direct simple shear and unconfined compression tests. The Boom clay samples exhibited strong swelling tendencies. The suction pressure was measured via different procedures and was compared to the expected in situ stress. The undrained shear strength profile determined from cone penetration tests (CPTs) was not compatible with the triaxial and direct simple shear measurements, which gave significantly lower undrained shear strength values. Micro-computed tomography (μCT) scans of the samples showed the presence of pre-existing discontinuities which may cause inconsistencies in the comparison of the laboratory test results with in situ data. The experimental data gathered in this study provide useful information for analyzing the mechanical behaviour of Boom clay at shallow depths considering that most investigations in the literature have been carried out on deep Boom clay deposits.
Centrifuge testing and numerical modelling of cyclically loaded monopiles in clay
Setup and early findings of the MIDASclay project
Conference paper
(2025)
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E. Kementzetzidis, Maria Konstantinou, Debasis Mohapatra, Cihan Cengiz, Rob Zwaan, Astha Sharma, A.S.K. Elkadi, Federico Pisanò , Huan Wang, Hans Petter Jostad, Georgios Christopoulos
The MIDASclay project (Monopile Improved Design via Advanced Cyclic Soil Modelling in Clay) aims to evaluate the cyclic lateral behaviour of monopiles in clays and clay-sand mixtures, focusing on developing a cyclic soil reaction model that captures cyclic ratcheting and operational stiffness in cohesive soils. Together with the MIDAS project – aimed at cyclic behaviour of monopiles in sand, it seeks to establish a comprehensive framework for modelling the cyclic lateral response of monopiles across diverse soil conditions. To address knowledge gaps, the project employs centrifuge testing of monopiles under cyclic lateral loads, aiming to produce a soil reaction model tailored to cohesive soils. This paper outlines the project setup, research plan, and initial findings. Early results from an auxiliary centrifuge test highlight the preparation of highly over-consolidated samples and provide insights into the influence of clay properties on monopile behaviour. MIDASclay is expected to support and advance design methodologies for monopiles in cohesive soils.
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The MIDASclay project (Monopile Improved Design via Advanced Cyclic Soil Modelling in Clay) aims to evaluate the cyclic lateral behaviour of monopiles in clays and clay-sand mixtures, focusing on developing a cyclic soil reaction model that captures cyclic ratcheting and operational stiffness in cohesive soils. Together with the MIDAS project – aimed at cyclic behaviour of monopiles in sand, it seeks to establish a comprehensive framework for modelling the cyclic lateral response of monopiles across diverse soil conditions. To address knowledge gaps, the project employs centrifuge testing of monopiles under cyclic lateral loads, aiming to produce a soil reaction model tailored to cohesive soils. This paper outlines the project setup, research plan, and initial findings. Early results from an auxiliary centrifuge test highlight the preparation of highly over-consolidated samples and provide insights into the influence of clay properties on monopile behaviour. MIDASclay is expected to support and advance design methodologies for monopiles in cohesive soils.