• Title/Summary/Keyword: Overconsolidated clay

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The Effects of Stress History on the Behaviour of Overconsolidated Clay (과압밀점토의 응력이력 의존성에 관한 연구)

  • 김병일;신현영;김용수;김수삼
    • Proceedings of the Korean Geotechical Society Conference
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    • 2001.03a
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    • pp.161-166
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    • 2001
  • Overconsolidated clays have a different stress history according to the deposit environment. The stress history is classified into (i) rotation angle of stress path, (ii) overconsolidation ratio, and (iii) magnitude of length of recent stress path. Stress-strain behaviour of overconsolidated clays strongly depends on these stress history. In this study a series of drained stress path tests were carried out. Test results indicated that stress-strain behaviour of overconsolidated clay(focused on strain rate) depends on OCR and length of recent stress path, especially rotation angle.

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Stress-Strain Behaviour of Overconsolidated Clay with Loading Rate (하중재하속도에 따른 과압밀점토의 응력-변형 거동)

  • 김병일;신현영;이승원;김수삼
    • Proceedings of the Korean Geotechical Society Conference
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    • 2001.03a
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    • pp.239-244
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    • 2001
  • Natural clayey soils or improved grounds are in a overconsolidated conditions due to changes in vertical stress and pore pressures, desiccation, ageing and so on. These grounds show inelastic stress-strain behaviour characteristics within all range of strain except very small strain (${\gamma}$$\_$s/$\leq$10 ̄$^3$∼10 ̄$^4$%) when construction, such as excavations and retaining walls, is performed. Also it strongly depends on loading rate of current stress path and recent stress path. This study carried out drained stress path tests by varying loading rate of current and recent stress path. Test results indicated that stress-strain behaviour of overconsolidated clay depends on loading rate, especially loading rate of current stress path.

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Study on the Undrained Shear Strength Characteristics (반월지역 해성점토의 비배수 전단강도 특성에 관한 연구)

  • 장병욱;박영곤
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.36 no.3
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    • pp.90-99
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    • 1994
  • To investigate the undrained shear strength characteristics of marine soils with high water content, high compressibility and weak bearing capacity, a series of undrained triaxial tests with pore pressure measurements on undisturbed and disturbed Banwol marine clay in normally consolidated and overconsolidated states is carried out. The results and main conclusions of this study are summarized as follows : 1 . When the consolidation pressure is increased, the maximum deviator stress of disturbed and undistubed clay in normally consolidated state is increased. Pore pressure parameters and internal friction angle of undisturbed clay are greater than those of disturbed clay. 2. The relationship between pore pressure and axial strain of undisturbed clay in normally consolidated state can be expressed as a hyperbolic function like stress-strain relation proposed by Kondner. 3. In the pore pressure-axial strain relation of disturbed clay in normally consolidated state, failure ratio R'f is greatly deviated in the range of 0.7~0.9 proposed by Christian and Desai. 4. For overconsolided clay, when overconsolidation ratio (OCR) is increased, normalized maximum deviator stress is increased and maximum pore pressure is decreased gradually. 5. Cohesion of overconsolidated clay is greater than that of nomally consolidated clay and internal friction angle slightly is decreased. 6. Pore pressure parameter at failure (Af) of overconsolidated clay is varied with OCR, Af becomes negative values with increment in OCR

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Influence of the Intermediate Principal Stress on Behavior of Overconsolidated Clay (중간주응력(中間主應力)이 과압밀점토(過壓密粘土)의 거동(擧動)에 미치는 영향(影響))

  • Hong, Won Pyo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.8 no.2
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    • pp.99-107
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    • 1988
  • A limited number of cubical triaxial tests with independent control of the three principal stresses were performed on an overconsolidated clay. The cubical undisturbed specimens with overconsolidation ratio of 5 were prepared in triaxial chamber after sampling in field. It was found that the intermediate principal stress influences on the stress-strain, undrained strength effective strength, effective friction angle and pore pressure of the overconsolidated clay. When the magnitude of the intermediate principal stress is not same as the minimum principal stress, the failure strength of the overconsolidated clay is underestimated by use of Mohr-Coulomb failure criterion while it can be estimated quite well by use of Lade failure criterion. And the undrained strength of the overconsolidated clay does not coincide with that obtained by Tresca failure criterion.

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V%drained Creep Rupture of an Anisotropically Overconsolidated Clay (이방과압밀점토의 비배수크리프파괴)

  • 강병희;오선호
    • Geotechnical Engineering
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    • v.12 no.6
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    • pp.153-162
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    • 1996
  • The undrained creep tests with isotropically and anisotropically overconsolidated clays were performed to investigate the effects of anisotropic consolidation on the undrained creep rupture behavior. Results of tests showed that the undrained creep rupture behaviors were iuluenced significantly by stress history including overconsolidation ratio and consolidation pressure ratio$(\sigma_{3c}/\sigma_{le})$. That is. the creep strength of clay increases with the increase of both overconsolidation ratio and consolidation pressure ratio. It, therefore, is dangerous to decide the possibility of creep rupture of clay by the isotropically consolidated creep rupture test in the case of the coefficient of earth pressure lower than 1.0. And the creep strength of clay could be obtained by the equation of the upper yield strength suggested by Finn and Shead(1973) irrespective of both overconsolidation ratio and consolidation pressure ratio.

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Constitutive Equation for Clay in Overconsolidation State and Under Cyclic Loading (과압밀상태 및 반복하중을 받는 점토지반에 대한 구성모델)

  • 이승래;김주용
    • Geotechnical Engineering
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    • v.10 no.1
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    • pp.7-18
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    • 1994
  • A new model for describing the behavior of clay under monotonic and cyclic loading is proposed. This model uses the hyperbolic representation for the stress -strain relationship in overconsolidated state and it describes undrained effective stress path on the basis of the critical state theory. The developed constitutive model by using an energy dissipation equation can describe the behavior of clay in heavily overconsolidated state as u.ell as lightly overconsolidated state under monotonic loading. In order to extend the model for the behavior of clay under cyclic loading, a shift function of undrained stress spacing ratio is introduced in the constitutive model developed for monotonlc loading. A single additional parameter is required to represent the cyclic effect and it can be reasonably deter mined from the test results. The measured behavior in undrained cyclic triaxial tests has been easily and precisely predicted by the newly developed constitutive model.

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Distribution of Excess Porepressure caused by PCPT into OC clay

  • Lee, Woo-Jin
    • Proceedings of the Korean Geotechical Society Conference
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    • 2006.10a
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    • pp.312-333
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    • 2006
  • This paper presents the results of an analysis of the excess porewater pressure distribution due to piezocone penetration in overconsolidated clays. From piezocone test results for moderately and heavily overconsolidated clays, it was observed that the excess porewater pressure increases monotonically from the piezocone surface to the outer boundary of the shear zone and then decreases logarithmically to the outer boundary of the plastic zone. It was also found that the size of the shear zone decreases from approximately 2.2 to 1.5 times the cone radius with increasing OCR, while the plastic radius is about 11 times the piezocone radius, regardless of the OCR. The equation developed in this study based on the modified Cam clay model and the cylindrical cavity expansion theory, which take into consideration the effects of the strain rate and stress anisotropy, provide a good prediction of the initial porewater pressure at the piezocone location. The method of predicting the spatial distribution of excess porewater pressure proposed in this study is based on a linearly increasing ${\Delta}u_{shear}$. In the shear zone and a logarithmically decreasing ${\Delta}u_{oct}$, and is verified by comparing with the excess porewater pressure measured in overconsolidated specimens at the calibration chamber.

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Thermal volume change of saturated clays: A fully coupled thermo-hydro-mechanical finite element implementation

  • Wang, Hao;Qi, Xiaohui
    • Geomechanics and Engineering
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    • v.23 no.6
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    • pp.561-573
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    • 2020
  • The creep and consolidation behaviors of clays subjected to thermal cycles are of fundamental importance in the application of energy geostructures. This study aims to numerically investigate the physical mechanisms for the temperature-triggered volume change of saturated clays. A recently developed thermodynamic framework is used to derive the thermo-mechanical constitutive model for clays. Based on the model, a fully coupled thermo-hydro-mechanical (THM) finite element (FE) code is developed. Comparison with experimental observations shows that the proposed FE code can well reproduce the irreversible thermal contraction of normally consolidated and lightly overconsolidated clays, as well as the thermal expansion of heavily overconsolidated clays under drained heating. Simulations reveal that excess pore pressure may accumulate in clay samples under triaxial drained conditions due to low permeability and high heating rate, resulting in thermally induced primary consolidation. Results show that four major mechanisms contribute to the thermal volume change of clays: (i) the principle of thermal expansion, (ii) the decrease of effective stress due to the accumulation of excess pore pressure, (iii) the thermal creep, and (iv) the thermally induced primary consolidation. The former two mechanisms mainly contribute to the thermal expansion of heavily overconsolidated clays, whereas the latter two contribute to the noticeable thermal contraction of normally consolidated and lightly overconsolidated clays. Consideration of the four physical mechanisms is important for the settlement prediction of energy geostructures, especially in soft soils.

Stress-Strain-Strain Rate of Overconsolidated Clay Dependent on Stress and Time History (응력이력과 시간이력에 따른 과압밀점토의 응력-변형-변형률 속도)

  • 한상재;김수삼;김병일
    • Journal of the Korean Geotechnical Society
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    • v.19 no.1
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    • pp.143-150
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    • 2003
  • This study deals with the stress-strain-strain rate behaviour of overconsolidated clay. Consolidated-drained stress path tests were performed on the stress-time dependent condition. Stress history consists of rotation angle of stress path, overconsolidation ratio, and magnitude of length of recent stress path. Time history includes loading rate of recent and current stress path. Test results show that all influence factors have an increasing strain rate with time, and the strain rate varies with the change of the rotation angle of stress path. With the increase of overconsolidation ratio and loading rate of current stress path, the strain rate also increases. For the stress history, correlation between stress-strain and strain rate is indicated but the time history is not.

An Experimental Study on Silty Clay Subjected to Repeated Loads (반복하중을 받는 실트질 점토에 관한 실험적 연구 -과압밀 점토를 중심으로-)

  • Kim, Pal-Gyu;Kim, Gyeong-Jin;Song, Jeon-Seop
    • Geotechnical Engineering
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    • v.5 no.4
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    • pp.37-46
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    • 1989
  • The object of this paper is to study the general characteristics of overconsolidated silty clays subjected to repeated loading. The samples are first remolded. overconsolidated and a series of strain - controlled triaxial repeated tests are carried out. Generally the relationship of deviator stress - axial strain of overconsolidated clay is similar in pattern to the normally consolidated clay under single load. But the behavior of the pore water pressure build up in the sample subjected to repeated loading is dependent upon the consolidation history and the level of repeated stress. Therefore through the series of the tests, the characteristics of stress -strain relationship of soils which are differentlly overconsolidated are investigated, analysed and then compared with each soils. And also, from the relationship of test results, the strength and strain characteristics of soils are obierved. The equilibrium lines which presents the critical repeated stress and equilibrium state in the sample under repeated loading, are often straight, but may be curved. And the tendency of the equilibrium lines is observed as to the variation of overconsolidation ratio.

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