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V.-t. Kuokkala - One of the best experts on this subject based on the ideXlab platform.

  • Effects of strain rate and Confining Pressure on the compressive behavior of Kuru granite
    International Journal of Impact Engineering, 2016
    Co-Authors: Mikko Hokka, John T. Black, Dmitry Tkalich, M. Fourmeau, Alexandre Kane, N.-h. Hoang, Weinong Chen, V.-t. Kuokkala
    Abstract:

    Abstract Understanding the influence of hydrostatic Pressure and loading rate on the strength and fracture behavior of rocks is very important for the development of deep drilling technology. This paper presents a systematic study on the mechanical properties and behavior of Kuru Gray granite at Confining Pressures up to 225 MPa and at strain rates of 10 −6  s −1 and 600 s −1 . The low strain rate compression tests were carried out with a servo-controlled hydraulic testing machine with a radial Confining chamber, and the dynamic tests with a special split Hopkinson Pressure bar device with axial and radial Confining Pressure chambers. The results show that the rock strength increases significantly with strain rate and Confining Pressure. At confinements below 20 MPa, the strength of the material increases faster at the higher strain rate, but at confinements higher than this, the effect of Confining Pressure is stronger at the lower strain rate. The strain rate sensitivity increases when even a small Confining Pressure is applied. However, the rate sensitivity remains rather constant when the Confining Pressure is increased above 10 MPa. The parameters of the Hoek–Brown model and an alternative power-law model were calibrated for low and high rate data. Also, the fracture behavior of the rock was found to be strongly dependent on strain rate and Confining Pressure. At the low strain rate, the samples fail by axial splitting in the unconfined tests, whereas the dynamic unconfined tests result in a complete pulverization of the samples. At high Confining Pressures the fracture behavior is shear fracture for both studied strain rates.

Jun Wang - One of the best experts on this subject based on the ideXlab platform.

  • effect of variable Confining Pressure on cyclic behaviour of granular soil under triaxial tests
    Canadian Geotechnical Journal, 2017
    Co-Authors: Qi Sun, Quanyang Dong, Yuanqiang Cai, Jian Chu, Jun Wang
    Abstract:

    Previous studies were performed to use combined cyclic deviatoric stress and Confining Pressure to simulate cyclic vertical and horizontal normal stresses under traffic loading. The effect of variable Confining Pressure (VCP) on the permanent deformation of soils was investigated. However, some studies concluded VCP could promote the development of permanent deformation compared to the tests with constant Confining Pressure (CCP), while others drew the opposite conclusions. In this study, three types of CCP and VCP tests with identical maximum stress, identical average stress, and identical initial stress were conducted. Test results showed VCP tests accumulated more permanent strains when CCP and VCP tests had identical maximum or average stress, and the permanent strains increased with the decrease in the inclinations of stress paths, while similar permanent strains were generated when CCP and VCP tests had identical initial stress. In addition, larger permanent strains were generated with the increase ...

  • deformation characteristics of overconsolidated clay sheared under constant and variable Confining Pressure
    Soils and Foundations, 2016
    Co-Authors: Chuan Gu, Jun Wang, Peng Wang, Quanyang Dong
    Abstract:

    Abstract The traffic-induced settlements of clay subgrade are usually investigated based on one-way cyclic triaxial tests. Most one-way triaxial cyclic tests on clays have been carried out on normally-consolidated samples, with a constant Confining Pressure and under undrained conditions. However, it has been found that the varying stress field induced by traffic loading consists of not only cyclic axial stresses, but also cyclic horizontal stresses and shear stresses. Sometimes part of the subgrade soil is overconsolidated, rather than normally-consolidated, and the drainage of pore water is usually allowed under long-term traffic loading. Recognizing this, a series of one-way cyclic triaxial tests was performed on 30 specimens under partially-drained conditions, and the emphases were placed on the coupling effects of the overconsolidation ratio, the cyclic stress ratio, and the cyclic Confining Pressure on the deformation characteristics of the saturated clay. The test results show that increasing the amplitudes of cyclic Confining Pressure will cause a remarkable acceleration in the accumulation of both the permanent volumetric strain and the axial strain, whether the sample is overconsolidated or normally-consolidated. A linear relationship is found between the permanent axial strains from tests with variable Confining Pressure and their counterparts obtained from tests with constant Confining Pressure, regardless of the OCR and CSR values. A quantitative relationship, which considers the effects of the OCR values, is also established between the increments in cyclic Confining Pressure amplitudes and the increments in permanent axial strain.

  • one way cyclic triaxial behavior of saturated clay comparison between constant and variable Confining Pressure
    Journal of Geotechnical and Geoenvironmental Engineering, 2013
    Co-Authors: Chuan Gu, Jun Wang, Hsein C Juang, Changjie Xu, Xiuqing Hu
    Abstract:

    AbstractThe one-way cyclic triaxial test has been recognized as a useful tool for solving many engineering problems, such as the prediction of deformation in subsoils under traffic loading. Most studies of the one-way cyclic behavior of soils are performed in triaxial tests with constant Confining Pressure (CCP), which can apply cyclic compressive deviatoric stress only. However, the real stress field in subsoils under traffic loading includes varying normal stresses in three directions. Therefore, it is more desirable to simulate the in situ loading conditions induced by passing vehicles through a combination of the varying deviatoric stress and varying Confining Pressure. Recognizing this, two series of one-way cyclic triaxial tests on remolded saturated clay were conducted in this study; one in undrained conditions and the other in partially drained conditions. In each series, both tests with the CCP and variable Confining Pressure (VCP) were carried out. Comparisons between the results of the VCP and ...

  • undrained cyclic triaxial behavior of saturated clays under variable Confining Pressure
    Soil Dynamics and Earthquake Engineering, 2012
    Co-Authors: Jun Wang, Yuanqiang Cai, Z X Yang, Yufeng Gao
    Abstract:

    A laboratory study on the undrained dynamic behavior of saturated clays in cyclic triaxial tests with a variable Confining Pressure (VCP tests) is presented. Tests were performed on remolded clayey samples using a dynamic triaxial device where the deviatoric stress and Confining Pressure can be varied simultaneously. Various cyclic stress paths have been applied on the specimens through varying the ratios or phase differences between the cyclic deviatoric stress and cyclic Confining Pressure. Specifically, the stress paths used in the present study were designed to simulate the coupling effects of simultaneously varying shear and normal stresses in clays due to earthquakes and other vibration sources. Test results obtained from this study show that the undrained response of saturated clays is strongly influenced by the variation of Confining Pressure, in terms of pore water Pressure, development speed of cyclic strain and magnitude of cyclic strength. It is found that when strong P-waves are propagating in soil layers, VCP tests are more appropriate for the simulation of in situ stress fields than the conventional cyclic triaxial tests with a constant Confining Pressure (CCP tests).

Quanyang Dong - One of the best experts on this subject based on the ideXlab platform.

  • effect of variable Confining Pressure on cyclic behaviour of granular soil under triaxial tests
    Canadian Geotechnical Journal, 2017
    Co-Authors: Qi Sun, Quanyang Dong, Yuanqiang Cai, Jian Chu, Jun Wang
    Abstract:

    Previous studies were performed to use combined cyclic deviatoric stress and Confining Pressure to simulate cyclic vertical and horizontal normal stresses under traffic loading. The effect of variable Confining Pressure (VCP) on the permanent deformation of soils was investigated. However, some studies concluded VCP could promote the development of permanent deformation compared to the tests with constant Confining Pressure (CCP), while others drew the opposite conclusions. In this study, three types of CCP and VCP tests with identical maximum stress, identical average stress, and identical initial stress were conducted. Test results showed VCP tests accumulated more permanent strains when CCP and VCP tests had identical maximum or average stress, and the permanent strains increased with the decrease in the inclinations of stress paths, while similar permanent strains were generated when CCP and VCP tests had identical initial stress. In addition, larger permanent strains were generated with the increase ...

  • deformation characteristics of overconsolidated clay sheared under constant and variable Confining Pressure
    Soils and Foundations, 2016
    Co-Authors: Chuan Gu, Jun Wang, Peng Wang, Quanyang Dong
    Abstract:

    Abstract The traffic-induced settlements of clay subgrade are usually investigated based on one-way cyclic triaxial tests. Most one-way triaxial cyclic tests on clays have been carried out on normally-consolidated samples, with a constant Confining Pressure and under undrained conditions. However, it has been found that the varying stress field induced by traffic loading consists of not only cyclic axial stresses, but also cyclic horizontal stresses and shear stresses. Sometimes part of the subgrade soil is overconsolidated, rather than normally-consolidated, and the drainage of pore water is usually allowed under long-term traffic loading. Recognizing this, a series of one-way cyclic triaxial tests was performed on 30 specimens under partially-drained conditions, and the emphases were placed on the coupling effects of the overconsolidation ratio, the cyclic stress ratio, and the cyclic Confining Pressure on the deformation characteristics of the saturated clay. The test results show that increasing the amplitudes of cyclic Confining Pressure will cause a remarkable acceleration in the accumulation of both the permanent volumetric strain and the axial strain, whether the sample is overconsolidated or normally-consolidated. A linear relationship is found between the permanent axial strains from tests with variable Confining Pressure and their counterparts obtained from tests with constant Confining Pressure, regardless of the OCR and CSR values. A quantitative relationship, which considers the effects of the OCR values, is also established between the increments in cyclic Confining Pressure amplitudes and the increments in permanent axial strain.

Chuan Gu - One of the best experts on this subject based on the ideXlab platform.

  • deformation characteristics of overconsolidated clay sheared under constant and variable Confining Pressure
    Soils and Foundations, 2016
    Co-Authors: Chuan Gu, Jun Wang, Peng Wang, Quanyang Dong
    Abstract:

    Abstract The traffic-induced settlements of clay subgrade are usually investigated based on one-way cyclic triaxial tests. Most one-way triaxial cyclic tests on clays have been carried out on normally-consolidated samples, with a constant Confining Pressure and under undrained conditions. However, it has been found that the varying stress field induced by traffic loading consists of not only cyclic axial stresses, but also cyclic horizontal stresses and shear stresses. Sometimes part of the subgrade soil is overconsolidated, rather than normally-consolidated, and the drainage of pore water is usually allowed under long-term traffic loading. Recognizing this, a series of one-way cyclic triaxial tests was performed on 30 specimens under partially-drained conditions, and the emphases were placed on the coupling effects of the overconsolidation ratio, the cyclic stress ratio, and the cyclic Confining Pressure on the deformation characteristics of the saturated clay. The test results show that increasing the amplitudes of cyclic Confining Pressure will cause a remarkable acceleration in the accumulation of both the permanent volumetric strain and the axial strain, whether the sample is overconsolidated or normally-consolidated. A linear relationship is found between the permanent axial strains from tests with variable Confining Pressure and their counterparts obtained from tests with constant Confining Pressure, regardless of the OCR and CSR values. A quantitative relationship, which considers the effects of the OCR values, is also established between the increments in cyclic Confining Pressure amplitudes and the increments in permanent axial strain.

  • one way cyclic triaxial behavior of saturated clay comparison between constant and variable Confining Pressure
    Journal of Geotechnical and Geoenvironmental Engineering, 2013
    Co-Authors: Chuan Gu, Jun Wang, Hsein C Juang, Changjie Xu, Xiuqing Hu
    Abstract:

    AbstractThe one-way cyclic triaxial test has been recognized as a useful tool for solving many engineering problems, such as the prediction of deformation in subsoils under traffic loading. Most studies of the one-way cyclic behavior of soils are performed in triaxial tests with constant Confining Pressure (CCP), which can apply cyclic compressive deviatoric stress only. However, the real stress field in subsoils under traffic loading includes varying normal stresses in three directions. Therefore, it is more desirable to simulate the in situ loading conditions induced by passing vehicles through a combination of the varying deviatoric stress and varying Confining Pressure. Recognizing this, two series of one-way cyclic triaxial tests on remolded saturated clay were conducted in this study; one in undrained conditions and the other in partially drained conditions. In each series, both tests with the CCP and variable Confining Pressure (VCP) were carried out. Comparisons between the results of the VCP and ...

Jilin Qi - One of the best experts on this subject based on the ideXlab platform.

  • a new criterion for strength of frozen sand under quick triaxial compression considering effect of Confining Pressure
    Acta Geotechnica, 2007
    Co-Authors: Jilin Qi
    Abstract:

    The strength of frozen soils has been one of the most extensively studied aspects in frozen soil mechanics. When carrying out deep excavations using freezing methods, high stress states are often encountered. Therefore, the strength of frozen soils under high Confining Pressures is of major concern. This paper first reviews the present failure criteria for frozen soils, especially with regard to the effect of Confining Pressure on the strength. It is suggested that the strength consists of two components, cohesion and friction, and can be expressed by the Mohr–Coulomb criterion and in the framework of the Drucker–Prager criterion. However, these two components are both dependent on the stress state. Duncan’s equation for the friction angle is extended to frozen soils. A frozen Lanzhou fine sand is taken as study subject. The frozen sand is compressed at a high strain rate under three different temperatures and under a wide range of Confining Pressure. Experimental results have confirmed the generally recognized principle that the strength increases with the Confining Pressure up to certain value. Thereafter, it decreases with continued increase in Confining Pressure. Experimental data from our own tests and literature are fitted to the new criterion, which shows its validity.