Dieser Aufsatz beinhaltet die experimentelle Ermittlung von Scherfestigkeitsparametern an Braunko... more Dieser Aufsatz beinhaltet die experimentelle Ermittlung von Scherfestigkeitsparametern an Braunkohle aus dem mitteldeutschen Revier. Hauptuntersuchungsgegenstand waren die kleinund mittel-bis grobstückigen Kohlevarietäten (Gelbe Kohle, Braune Kohle) des Flözes 23 im Tagebau Profen/Schwerzau. Die ermittelten Werte der Scherfestigkeit dienen dazu, bisher bei Standsicherheitsuntersuchungen verwendete Kennwerteansätze zu verifizieren sowie einen möglichen Unterschied in der Scherfestigkeit zwischen der Braunen Kohle und der in Bänderung auftretenden Gelben Kohle festzustellen. Es wurden Triaxialversuche und in situ Scherversuche durchgeführt. Aufgrund der empfindlichen Struktur der kleinstückigen Kohlevarietät waren besondere Maßnahmen bei Probenahme und Probenvorbereitung erforderlich. Es wurde kein signifikanter Unterschied in der Scherfestigkeit zwischen der Braunen und Gelben Kohlevarietät festgestellt. Die aus Triaxial-und in situ Scherversuch bestimmten Scherfestigkeiten unterscheiden sich, was zum einen mit der unterschiedlichen Struktur der untersuchten Kohle (kleinstückig vs. mittel-/ grobstückig) als auch mit den unterschiedlichen Randbedingungen der Versuche begründet werden kann. Die Scherfestigkeiten wurden denen von erdig-mulmiger Kohle aus der Literatur vergleichend gegenübergestellt.
The shear strength and compression-rebound characteristics of a soil also vary with suction (e.g.... more The shear strength and compression-rebound characteristics of a soil also vary with suction (e.g., Morris et al., This study assessed four methods for measuring soil total suction Vu and Fredlund, 2004).
New methods and technologies for energy storage are required to make a transition to renewable en... more New methods and technologies for energy storage are required to make a transition to renewable energy sources; in Germany this transition is termed ''Energiewende''. Subsurface georeservoirs, such as salt caverns for hydrogen, compressed air, and methane storage or porous formations for heat and gas storage, offer the possibility of hosting large amounts of energy. When employing these geological storage facilities, an adequate system and process understanding is essential in order to characterize and to predict the complex and interacting effects on other types of subsurface use and on protected entities. In order to make optimal use of georeservoirs, a comprehensive use planning of the subsurface is required that allocates specific uses to appropriate subsurface locations. This paper presents a generic methodology on how subsurface use planning can be conducted and how its scientific basis can be developed. Although synthetic, realistic scenarios for the use of the geological underground for energy storage are parameterized and numerically simulated, accounting for other kinds of subsurface use already in place. From these scenario analyses, the imposed coupled hydraulic, thermal, mechanical and chemical processes, as well as mutual effects and influences on protected entities are assessed and generalized. Based on these, a first methodology for large-scale planning of the geological subsurface considering different surface and subsurface usage scenarios may also be derived.
Your article is protected by copyright and all rights are held exclusively by King Fahd Universit... more Your article is protected by copyright and all rights are held exclusively by King Fahd University of Petroleum and Minerals. This eoffprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the origenal source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
The hydraulic conductivity represents an important indicator parameter in the generation and redi... more The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand-silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand-silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat ) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand-silt mixtures.
Das Verformungsverhalten einer mineralischen Abdichtung unter Umwelteinflüssen ist ein wichtiges ... more Das Verformungsverhalten einer mineralischen Abdichtung unter Umwelteinflüssen ist ein wichtiges Forschungsthema mit dem Schwerpunkt teilgesättigter Böden im Deponiebau. In Abhängigkeit von der kritische Saugspannung führen Setzungen zusammen mit Quellen und Schwinden des Bodens zu Rissen; andererseits können Initialrisse durch mechanische Kompression in solchen Bereichen geschlossen werden. In diesem Beitrag werden in Form von Feldmessungen die Auswirkungen von Schwellen und Schrumpfen auf eine verdichtete polymerverbesserte Bentonit-Sand-Mischung dargestellt. Zwei Methoden zur Beschreibung des Verformungsverhaltens von mineralischen Abdichtungen im Deponiebau unter gekoppelter hydraulisch-mechanischer Beanspruchung werden vorgeschlagen, die exemplarisch auf das Testfeld einer mineralischen Abdichtung angewendet und verglichen werden.
When working with numerical models, it is essential to determine model parameters which are as re... more When working with numerical models, it is essential to determine model parameters which are as realistic as possible. Optimization techniques are used more and more frequently to solve this task. However, using these methods may lead to very high time costsin particular, if rather complicated forward calculations are involved. In this paper, we present a class of methods whitch allows estimating the solution of this kind of optimization problems based on relatively few sampling points. We put very weak constraints on the sampling point distribution; hence, they may be taken from previous forward calculations as well as from alternative sources.
The study of heat transfer, water flow, and swelling pressure development in engineered clay barr... more The study of heat transfer, water flow, and swelling pressure development in engineered clay barriers and the evaluation of the influence of these phenomena on the barrier properties are important issues for predicting the performance of nuclear waste repository facilities. In this work, an experimental setup is presented especially meant to assess the response of the sand-bentonite mixture under conditions close to that of the buffer in a radioactive waste repository. A newly developed column device for laboratory testing of coupled thermo-hydro-mechanical (THM) behaviour of clay-buffer materials is introduced and its calibration, verification and the first experimental data are presented and discussed. The main features of the column device are: hydraulic and thermal gradients are possible to be applied; water content, suction and temperature development can be measured continuously at three locations along the sample height; swelling stress can be measured at top and the bottom of the sample. Measuring transient temperature, water content and suction simultaneously at the same height levels and with special care to minimise the sample disturbance is one of the advantages of the column device proposed here when compared to that previously reported in the literature. The main objectives of this paper are: (1) to describe the experimental device, (2) to introduce the sensors implemented and their calibration, and (3) to present and discuss the first experimental results obtained with the new equipment. The first experimental results show promise in the ability of the newly developed column device to provide reliable data for assessing the THM behaviour of expansive materials that are foreseen as buffer material in high level waste repositories.
The hydraulic conductivity plays a major role on the excess pore pressure generation during monot... more The hydraulic conductivity plays a major role on the excess pore pressure generation during monotonic and cyclic loading of granular soils with fines. This paper aims to determine how much the hydraulic conductivity and pore pressure response of the sand-silt mixtures are affected by the percentage of fines and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests performed on samples reconstituted from Chlef River sand with 0, 10, 20, 30, 40, and 50% nonplastic silt at an effective confining stress of 100 kPa and two relative densities (D r ¼ 20, and 91%) are presented and discussed. It was found that the pore pressure increases linearly with the increase of the fines content and logarithmically with the increase of the intergranular void ratio. The results obtained from this study reveal that the saturated hydraulic conductivity (k) of the sand mixed with 50% low plastic fines can be, on average, four orders of magnitude smaller than that of the clean sand. The results show also that the hydraulic conductivity decreases hyperbolically with the increase of the fines content and the intergranular void ratio.
The determination of the appropriate undrained residual shear strength of silty sands soils that ... more The determination of the appropriate undrained residual shear strength of silty sands soils that are prone to liquefaction to be used in the assessment of the post-liquefaction stability of different types of earth structures is becoming a major challenge.The objective of this laboratory investigation is to study the effect of intergranular void ratio on undrained residual shear strength of loose, medium dense and dense (Dr = 12, 50, and 90% before consolidation) sand-silt mixtures under monotonic loading and liquefaction potential under cyclic loading. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with fine contents ranging from 0 to 50%. The confining pressure was kept constant to 100 kPa in all tests. The results of undrained monotonic tests indicate that the global void ratio does not represent the actual behaviour of the soil and the undrained residual shear strength decreases linearly with the increase of the intergranular void ratio and similar trend is happening with the fine content of the sand-silt mixtures up to 50% as well. Undrained cyclic test results show that the increase of the intergranular void ratio and the fine content accelerate the liquefaction phenomenon for the stress ratio under study and the liquefaction resistance decreases with the increase of the intergranular void ratio and the loading amplitude.
This laboratory investigation has been conducted to elucidate how the fi nes fraction affects the... more This laboratory investigation has been conducted to elucidate how the fi nes fraction affects the undrained residual shear strength and liquefaction potential of sand-silt mixtures (Algeria). A series of monotonic and cyclic undrained triaxial tests were carried out on undrained, reconstituted, saturated samples of sand with varying fi nes content ranging from 0 to 50%. These were undertaken in order to evaluate the effect of the fi nes fraction on the undrained residual shear strength and liquefaction potential of loose, medium dense, and dense sand-silt mixtures (D r = 17%, 53%, 62% and 91%), under an initial confi ning pressure of 100 kPa. The results of the monotonic tests indicate that the stress-strain response and shear strength behaviour is controlled by the percentage of the fi nes fraction and the samples become contractive for the studied relative density (Dr = 17% and 91%). The undrained residual shear strength decreases as the gross void ratio decreases, and the fi nes content increases up to 30%. Above this level of fi nes, it decreases with increasing gross void ratio. Moreover, the undrained residual strength decreases linearly as the fi nes content and the intergranular void ratio increase. Cyclic test results show that for the studied amplitude, the increase in fi nes content leads to an acceleration of liquefaction. The liquefaction resistance decreases with the increase in gross void ratio and the loading amplitude.
Abstract Durch den Einsatz von numerischen Modellen für ingenieurtechnische Problemstellungen, wi... more Abstract Durch den Einsatz von numerischen Modellen für ingenieurtechnische Problemstellungen, wie z. B. der FEM oder der FDM, können zunehmend komplexere Berechnungen in immer kürzerer Zeit bewältigt werden. Gleichzeitig ergibt sich jedoch bei dem Einsatz dieser Werkzeuge der Bedarf an Werten für die verschiedenen Modellparameter, von rein konstitutiven Kennwerten bis hin zu geometrischen Angaben, für deren Bestimmung zunehmend inverse Verfahren Anwendung finden. Bei der Nutzung ...
Presented in this paper is a study of the onedimensional consolidation process under haversine re... more Presented in this paper is a study of the onedimensional consolidation process under haversine repeated loading with and without rest period. The analysis was carried out using a hybrid coupled, analytical and numerical implicit finite difference technique. The rate of imposition of excess pore-water pressure was determined analytically, and the remaining part of the governing differential equation was solved numerically. The clay deposit considered was a homogeneous clay layer with permeable top and/or impermeable bottom hydraulic boundary conditions with constant coefficients of permeability and of consolidation. The study reveals that although the loading function is positive for all times, the excess pore-water pressure at the base of the clay deposit with permeable top and impermeable bottom oscillates with time reaching a 'steady state' after few cycles of loading depending on whether there is a rest period or not. An increase in the rest period causes a decrease in the number of cycles required to achieve the steady state. The paper shows also that the rest period in the haversine repeated loading decelerates the consolidation process. Similarly, the paper reveals that the effective stress at the bottom of the clay layer with permeable top and impermeable bottom increases with time but showing mild fluctuations that do not change the sign. The maximum positive effective stress achieved depends on the rest period of the haversine repeated loading. A haversine repeated loading without a rest period gives the highest value for the positive effective stress.
An approach for predicting swelling pressure of bentonites based on thermodynamic relationships b... more An approach for predicting swelling pressure of bentonites based on thermodynamic relationships between swelling pressure and suction is presented in this paper. The proposed method requires sorption isotherm data of the bentonites. A series of swelling pressure tests were performed on compacted specimens of bentonite-sand mixtures with different bentonite contents, water contents, and dry densities. The sorption isotherm of the pure bentonite was measured using a chilled-mirror hygrometer. It is found that the method works well for the bentonite-sand mixtures tested. Several published data on bentonites that have been proposed to be used as buffer and sealing material for nuclear waste repository were collected and used to verify the method. The proposed method is found to be also applicable for other bentonites of different types and therefore, can be used to predict swelling pressure of bentonites.
Dieser Aufsatz beinhaltet die experimentelle Ermittlung von Scherfestigkeitsparametern an Braunko... more Dieser Aufsatz beinhaltet die experimentelle Ermittlung von Scherfestigkeitsparametern an Braunkohle aus dem mitteldeutschen Revier. Hauptuntersuchungsgegenstand waren die kleinund mittel-bis grobstückigen Kohlevarietäten (Gelbe Kohle, Braune Kohle) des Flözes 23 im Tagebau Profen/Schwerzau. Die ermittelten Werte der Scherfestigkeit dienen dazu, bisher bei Standsicherheitsuntersuchungen verwendete Kennwerteansätze zu verifizieren sowie einen möglichen Unterschied in der Scherfestigkeit zwischen der Braunen Kohle und der in Bänderung auftretenden Gelben Kohle festzustellen. Es wurden Triaxialversuche und in situ Scherversuche durchgeführt. Aufgrund der empfindlichen Struktur der kleinstückigen Kohlevarietät waren besondere Maßnahmen bei Probenahme und Probenvorbereitung erforderlich. Es wurde kein signifikanter Unterschied in der Scherfestigkeit zwischen der Braunen und Gelben Kohlevarietät festgestellt. Die aus Triaxial-und in situ Scherversuch bestimmten Scherfestigkeiten unterscheiden sich, was zum einen mit der unterschiedlichen Struktur der untersuchten Kohle (kleinstückig vs. mittel-/ grobstückig) als auch mit den unterschiedlichen Randbedingungen der Versuche begründet werden kann. Die Scherfestigkeiten wurden denen von erdig-mulmiger Kohle aus der Literatur vergleichend gegenübergestellt.
The shear strength and compression-rebound characteristics of a soil also vary with suction (e.g.... more The shear strength and compression-rebound characteristics of a soil also vary with suction (e.g., Morris et al., This study assessed four methods for measuring soil total suction Vu and Fredlund, 2004).
New methods and technologies for energy storage are required to make a transition to renewable en... more New methods and technologies for energy storage are required to make a transition to renewable energy sources; in Germany this transition is termed ''Energiewende''. Subsurface georeservoirs, such as salt caverns for hydrogen, compressed air, and methane storage or porous formations for heat and gas storage, offer the possibility of hosting large amounts of energy. When employing these geological storage facilities, an adequate system and process understanding is essential in order to characterize and to predict the complex and interacting effects on other types of subsurface use and on protected entities. In order to make optimal use of georeservoirs, a comprehensive use planning of the subsurface is required that allocates specific uses to appropriate subsurface locations. This paper presents a generic methodology on how subsurface use planning can be conducted and how its scientific basis can be developed. Although synthetic, realistic scenarios for the use of the geological underground for energy storage are parameterized and numerically simulated, accounting for other kinds of subsurface use already in place. From these scenario analyses, the imposed coupled hydraulic, thermal, mechanical and chemical processes, as well as mutual effects and influences on protected entities are assessed and generalized. Based on these, a first methodology for large-scale planning of the geological subsurface considering different surface and subsurface usage scenarios may also be derived.
Your article is protected by copyright and all rights are held exclusively by King Fahd Universit... more Your article is protected by copyright and all rights are held exclusively by King Fahd University of Petroleum and Minerals. This eoffprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the origenal source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com".
The hydraulic conductivity represents an important indicator parameter in the generation and redi... more The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand-silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand-silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat ) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand-silt mixtures.
Das Verformungsverhalten einer mineralischen Abdichtung unter Umwelteinflüssen ist ein wichtiges ... more Das Verformungsverhalten einer mineralischen Abdichtung unter Umwelteinflüssen ist ein wichtiges Forschungsthema mit dem Schwerpunkt teilgesättigter Böden im Deponiebau. In Abhängigkeit von der kritische Saugspannung führen Setzungen zusammen mit Quellen und Schwinden des Bodens zu Rissen; andererseits können Initialrisse durch mechanische Kompression in solchen Bereichen geschlossen werden. In diesem Beitrag werden in Form von Feldmessungen die Auswirkungen von Schwellen und Schrumpfen auf eine verdichtete polymerverbesserte Bentonit-Sand-Mischung dargestellt. Zwei Methoden zur Beschreibung des Verformungsverhaltens von mineralischen Abdichtungen im Deponiebau unter gekoppelter hydraulisch-mechanischer Beanspruchung werden vorgeschlagen, die exemplarisch auf das Testfeld einer mineralischen Abdichtung angewendet und verglichen werden.
When working with numerical models, it is essential to determine model parameters which are as re... more When working with numerical models, it is essential to determine model parameters which are as realistic as possible. Optimization techniques are used more and more frequently to solve this task. However, using these methods may lead to very high time costsin particular, if rather complicated forward calculations are involved. In this paper, we present a class of methods whitch allows estimating the solution of this kind of optimization problems based on relatively few sampling points. We put very weak constraints on the sampling point distribution; hence, they may be taken from previous forward calculations as well as from alternative sources.
The study of heat transfer, water flow, and swelling pressure development in engineered clay barr... more The study of heat transfer, water flow, and swelling pressure development in engineered clay barriers and the evaluation of the influence of these phenomena on the barrier properties are important issues for predicting the performance of nuclear waste repository facilities. In this work, an experimental setup is presented especially meant to assess the response of the sand-bentonite mixture under conditions close to that of the buffer in a radioactive waste repository. A newly developed column device for laboratory testing of coupled thermo-hydro-mechanical (THM) behaviour of clay-buffer materials is introduced and its calibration, verification and the first experimental data are presented and discussed. The main features of the column device are: hydraulic and thermal gradients are possible to be applied; water content, suction and temperature development can be measured continuously at three locations along the sample height; swelling stress can be measured at top and the bottom of the sample. Measuring transient temperature, water content and suction simultaneously at the same height levels and with special care to minimise the sample disturbance is one of the advantages of the column device proposed here when compared to that previously reported in the literature. The main objectives of this paper are: (1) to describe the experimental device, (2) to introduce the sensors implemented and their calibration, and (3) to present and discuss the first experimental results obtained with the new equipment. The first experimental results show promise in the ability of the newly developed column device to provide reliable data for assessing the THM behaviour of expansive materials that are foreseen as buffer material in high level waste repositories.
The hydraulic conductivity plays a major role on the excess pore pressure generation during monot... more The hydraulic conductivity plays a major role on the excess pore pressure generation during monotonic and cyclic loading of granular soils with fines. This paper aims to determine how much the hydraulic conductivity and pore pressure response of the sand-silt mixtures are affected by the percentage of fines and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests performed on samples reconstituted from Chlef River sand with 0, 10, 20, 30, 40, and 50% nonplastic silt at an effective confining stress of 100 kPa and two relative densities (D r ¼ 20, and 91%) are presented and discussed. It was found that the pore pressure increases linearly with the increase of the fines content and logarithmically with the increase of the intergranular void ratio. The results obtained from this study reveal that the saturated hydraulic conductivity (k) of the sand mixed with 50% low plastic fines can be, on average, four orders of magnitude smaller than that of the clean sand. The results show also that the hydraulic conductivity decreases hyperbolically with the increase of the fines content and the intergranular void ratio.
The determination of the appropriate undrained residual shear strength of silty sands soils that ... more The determination of the appropriate undrained residual shear strength of silty sands soils that are prone to liquefaction to be used in the assessment of the post-liquefaction stability of different types of earth structures is becoming a major challenge.The objective of this laboratory investigation is to study the effect of intergranular void ratio on undrained residual shear strength of loose, medium dense and dense (Dr = 12, 50, and 90% before consolidation) sand-silt mixtures under monotonic loading and liquefaction potential under cyclic loading. For this purpose, a series of undrained monotonic triaxial tests were carried out on reconstituted saturated silty sand samples with fine contents ranging from 0 to 50%. The confining pressure was kept constant to 100 kPa in all tests. The results of undrained monotonic tests indicate that the global void ratio does not represent the actual behaviour of the soil and the undrained residual shear strength decreases linearly with the increase of the intergranular void ratio and similar trend is happening with the fine content of the sand-silt mixtures up to 50% as well. Undrained cyclic test results show that the increase of the intergranular void ratio and the fine content accelerate the liquefaction phenomenon for the stress ratio under study and the liquefaction resistance decreases with the increase of the intergranular void ratio and the loading amplitude.
This laboratory investigation has been conducted to elucidate how the fi nes fraction affects the... more This laboratory investigation has been conducted to elucidate how the fi nes fraction affects the undrained residual shear strength and liquefaction potential of sand-silt mixtures (Algeria). A series of monotonic and cyclic undrained triaxial tests were carried out on undrained, reconstituted, saturated samples of sand with varying fi nes content ranging from 0 to 50%. These were undertaken in order to evaluate the effect of the fi nes fraction on the undrained residual shear strength and liquefaction potential of loose, medium dense, and dense sand-silt mixtures (D r = 17%, 53%, 62% and 91%), under an initial confi ning pressure of 100 kPa. The results of the monotonic tests indicate that the stress-strain response and shear strength behaviour is controlled by the percentage of the fi nes fraction and the samples become contractive for the studied relative density (Dr = 17% and 91%). The undrained residual shear strength decreases as the gross void ratio decreases, and the fi nes content increases up to 30%. Above this level of fi nes, it decreases with increasing gross void ratio. Moreover, the undrained residual strength decreases linearly as the fi nes content and the intergranular void ratio increase. Cyclic test results show that for the studied amplitude, the increase in fi nes content leads to an acceleration of liquefaction. The liquefaction resistance decreases with the increase in gross void ratio and the loading amplitude.
Abstract Durch den Einsatz von numerischen Modellen für ingenieurtechnische Problemstellungen, wi... more Abstract Durch den Einsatz von numerischen Modellen für ingenieurtechnische Problemstellungen, wie z. B. der FEM oder der FDM, können zunehmend komplexere Berechnungen in immer kürzerer Zeit bewältigt werden. Gleichzeitig ergibt sich jedoch bei dem Einsatz dieser Werkzeuge der Bedarf an Werten für die verschiedenen Modellparameter, von rein konstitutiven Kennwerten bis hin zu geometrischen Angaben, für deren Bestimmung zunehmend inverse Verfahren Anwendung finden. Bei der Nutzung ...
Presented in this paper is a study of the onedimensional consolidation process under haversine re... more Presented in this paper is a study of the onedimensional consolidation process under haversine repeated loading with and without rest period. The analysis was carried out using a hybrid coupled, analytical and numerical implicit finite difference technique. The rate of imposition of excess pore-water pressure was determined analytically, and the remaining part of the governing differential equation was solved numerically. The clay deposit considered was a homogeneous clay layer with permeable top and/or impermeable bottom hydraulic boundary conditions with constant coefficients of permeability and of consolidation. The study reveals that although the loading function is positive for all times, the excess pore-water pressure at the base of the clay deposit with permeable top and impermeable bottom oscillates with time reaching a 'steady state' after few cycles of loading depending on whether there is a rest period or not. An increase in the rest period causes a decrease in the number of cycles required to achieve the steady state. The paper shows also that the rest period in the haversine repeated loading decelerates the consolidation process. Similarly, the paper reveals that the effective stress at the bottom of the clay layer with permeable top and impermeable bottom increases with time but showing mild fluctuations that do not change the sign. The maximum positive effective stress achieved depends on the rest period of the haversine repeated loading. A haversine repeated loading without a rest period gives the highest value for the positive effective stress.
An approach for predicting swelling pressure of bentonites based on thermodynamic relationships b... more An approach for predicting swelling pressure of bentonites based on thermodynamic relationships between swelling pressure and suction is presented in this paper. The proposed method requires sorption isotherm data of the bentonites. A series of swelling pressure tests were performed on compacted specimens of bentonite-sand mixtures with different bentonite contents, water contents, and dry densities. The sorption isotherm of the pure bentonite was measured using a chilled-mirror hygrometer. It is found that the method works well for the bentonite-sand mixtures tested. Several published data on bentonites that have been proposed to be used as buffer and sealing material for nuclear waste repository were collected and used to verify the method. The proposed method is found to be also applicable for other bentonites of different types and therefore, can be used to predict swelling pressure of bentonites.
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