EXCESS PORE WATER PRESSURE ACCUMULATION AND RECOMPRESSION OF SATURATED SOFT CLAY SUBJECTED TO UNI-DIRECTIONAL AND MULTI-DIRECTIONAL CYCLIC SIMPLE SHEARS

2013 ◽  
Vol 07 (04) ◽  
pp. 1250027 ◽  
Author(s):  
HIROSHI MATSUDA ◽  
TRAN THANH NHAN ◽  
RYOHEI ISHIKURA
Keyword(s):  
Shear Strain ◽  
Pore Water ◽  
Strain Amplitude ◽  
Phase Difference ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shear Direction ◽  
Cyclic Shear ◽  
Number Of Cycles ◽  
Shear Strain Amplitude

This paper is to investigate the effect of cyclic shear direction (or phase difference) on the accumulation of excess pore water pressure during cyclic shear and on the recompression after cyclic shear. Several series of uni-directional and multi-directional cyclic simple shear tests under undrained condition were carried out for normally consolidated Kaolin. From the test results it is shown that the accumulation of pore water pressure and the post-cyclic settlement increase with the shear strain amplitude and the phase difference. The values of the shear strain amplitude at which the effect of cyclic shear direction is most significant, decrease with the increase of the number of cycles. The change of the void ratio in the recompression stage increases approximately in proportion to the logarithm of the stress reduction ratio and is not affected by the shear strain amplitude. For multi-directional cyclic shear, this change of the void ratio depends on the phase difference and the number of cycles. The cyclic recompression indices in the recompression stage were obtained for uni-directional and multi-directional cyclic shears. The cyclic shear induced settlement can be calculated by using these indices.

scholarly journals Pore water pressure responses of saturated sand and clay under undrained cyclic shearing

2021 ◽  
Author(s):  
An ◽  
Hiroshi ◽  
Nhan ◽  
Nhan ◽  
Tien ◽  
...  
Keyword(s):  
Shear Strain ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Silty Clay ◽  
Shear Tests ◽  
Sand Liquefaction ◽  
Cyclic Shear ◽  
Wide Range ◽  
Number Of Cycles

In this study, changes in the pore water pressure were observed for saturated specimens of a loose fined-grain sand (Nam O sand) and a soft silty clay (Hue clay) subjected to undrained cyclic shearing with different testing conditions. The cyclic shear tests were run for relatively wide range of shear strain amplitude (g = 0.05%-2%), different cycle numbers (n = 10, 50, 150 and 200) and various shear directions (uni-direction and two-direction with phase difference of q = 0o, 45o and 90o). It is indicated from the experimental results that under the same cyclic shearing condition, the pore water pressure accumulation in Hue clay is at a slower rate, suggesting a higher cyclic shear resistance of Hue clay than that of Nam O sand. Liquefaction is reached easily in nominally 50% relative density specimens of Nam O sand when g ³ 0.4%, meanwhile soft specimen of Hue clay is not liquefied regardless of the cyclic shearing conditions used in this study. The threshold number of cycles for the pore water pressure generation generally decreases with g meanwhile, the threshold cumulative shear strain for such a property mostly approaches 0.1%. In addition, by using this new strain path parameter, it becomes more advantageous when evaluating the pore water pressure accumulation in Nam O sand and Hue clay subjected to undrained uni-directional and two-directional cyclic shears.

scholarly journals Pore water pressure accumulation and settlement of clays with a wide range of Atterberg’s limits subjected to multi-directional cyclic shear

2020 ◽  
Vol 42 (1) ◽  
pp. 93-104
Author(s):  
Tran Thanh Nhan ◽  
Hiroshi Matsuda
Keyword(s):  
Shear Strain ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Pressure Ratio ◽  
Kaolinite Clay ◽  
Cyclic Shear ◽  
Wide Range ◽  
Number Of Cycles ◽  
Cyclic Settlement

In this study, normally consolidated specimens on four clays with a wide range of Atterberg’s limits were tested by applying several series of undrained multi-directional cyclic shear followed by drainage. The cyclic shear tests were carried out under the shear strain amplitudes (γ = 0.05%-2.00%), number of cycles n = 200 and the phase difference θ = 90o. Then the accumulation of cyclic shear-induced pore water pressure and the post-cyclic settlement in strain (εv, %) were observed and discussed. In conclusion, it is clarified that the pore water pressure ratio (Udyn/σ’vo) increases with g and the soils with higher Atterberg’s limits show lower Udyn/σ’vo, and under the multi-directional cyclic shear strain at γ > 0.4%, Hue clay and Kaolinite clay with relatively low plasticity suffer from cyclic failure. In addition, the post-cyclic settlement has a tendency of decreasing with the Atterberg’s limits in the range of plasticity index from Ip = 25.5 to 63.8, meanwhile when Ip < 25.5, different tendencies were observed e.g., Hue clay (with lower Ip) shows a smaller settlement compared with those on Kaolin (with higher Ip). Furthermore, the threshold number of cycles (ntp) and cumulative shear strain (G*tp) for pore water pressure buildup were then clarified.

scholarly journals A LIQUEFACTION CRITERION FOR FINE-GRAINED SAND CONSTITUTING NAM O FORMATION SUBJECTED TO UNI-DIRECTIONAL AND MULTI-DIRECTIONAL CYCLIC SHEARS

2018 ◽  
Vol 127 (1D) ◽  
pp. 37
Author(s):  
Tran Thanh Nhan ◽  
Hoang Thi Sinh Huong ◽  
Tran Ngoc Tin ◽  
Ho Trung Thanh ◽  
Le Thi Cat Tuong
Keyword(s):  
Shear Strain ◽  
Strain Amplitude ◽  
Effective Stress ◽  
Stress Reduction ◽  
Shear Direction ◽  
Liquefaction Resistance ◽  
Cyclic Shear ◽  
Fine Grained ◽  
Number Of Cycles ◽  
Shear Strain Amplitude

In this paper, fine-grained samples at nominally 50% relative density of Nam O sand were tested by several series of uni-directional and multi-directional cyclic shears. The changes of cyclic shear-induced effective stress reduction were observed for a wide range of shear strain amplitudes and various cyclic shear directions and number of cycles. The effects of such cyclic shearing conditions on the liquefaction resistance of the soil were then clarified. It is indicated from experimental results that the effective stress in Nam O sand reduces quickly by the application of the cyclic shear and that the soil is liquefied even when the cyclic shear strain is at small amplitude (<em>g</em> = 0.1%). The effects of cyclic shear direction on the effective stress reduction and also on the liquefaction resistance of the soil are evident at small shear strain amplitude, these effects however decrease with <em>g</em> and become negligible when <em>g</em> ³ 1.0% at which the soil is liquefied after a very few number of cycles. The occurrence of liquefaction in Nam O sand can be observed precisely for various cyclic shear directions by using relations between the shear strain amplitude and the number of cycles. Liquefaction criterion of Nam O sand was finally obtained and discussed for both cases of uni-directional and multi-directional cyclic shears.

LIQUEFACTION AND PORE WATER PRESSURE GENERATION IN SAND — A CYCLIC STRAIN APPROACH

2008 ◽  
Vol 02 (03) ◽  
pp. 227-240 ◽  
Author(s):  
T. G. SITHARAM ◽  
B. V. RAVISHANKAR ◽  
J. S. VINOD
Keyword(s):  
Relative Density ◽  
Shear Strain ◽  
Laboratory Investigation ◽  
Pore Water ◽  
Strain Amplitude ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Shear Strain Amplitude

This paper presents the results of laboratory investigation carried out on Ahmedabad sand on the liquefaction and pore water pressure generation during strain controled cyclic loading. Laboratory experiments were carried out on representative natural sand samples (base sand) collected from earthquake-affected area of Ahmedabad City of Gujarat State in India. A series of strain controled cyclic triaxial tests were carried out on isotropically compressed samples to study the influence of different parameters such as shear strain amplitude, initial effective confining pressure, relative density and percentage of non-plastic fines on the behavior of liquefaction and pore water pressure generation. It has been observed from the laboratory investigation that the potential for liquefaction of the sandy soils depends on the shear strain amplitude, initial relative density, initial effective confining pressure and non-plastic fines. In addition, an empirical relationship between pore pressure ratio and cycle ratio independent of the number of cycles of loading, relative density, confining pressure, amplitude of shear strain and non-plastic fines has been proposed.

Evaluation of a simplified soil constitutive model considering implied strength and pore-water pressure generation for one-dimensional (1D) seismic site response

2020 ◽  
Vol 57 (7) ◽  
pp. 974-991 ◽  
Author(s):  
Xuan Mei ◽  
Scott M. Olson ◽  
Youssef M.A. Hashash
Keyword(s):  
Constitutive Model ◽  
Shear Strain ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Site Response ◽  
Water Pressure ◽  
Generation Model ◽  
Cyclic Shear ◽  
Centrifuge Tests ◽  
Spectral Accelerations

Pore-water pressure (PWP) generation can lead to soil softening and liquefaction of sandy soils during earthquakes, with potential influence on site response and seismic design. The authors evaluated the generalized quadratic/hyperbolic (GQ/H) constitutive model, which captures small-strain stiffness, large-strain shear strength, and is coupled with a widely used cyclic strain–based PWP generation model (termed GQ/H+u). A suite of cyclic direct simple shear tests with a range of relative densities (∼30%–80%) and effective vertical stresses (∼25–200 kPa) and dynamic centrifuge tests with liquefiable sands were used to evaluate the ability of the GQ/H+u model to simulate cyclic soil behavior. Results indicate that GQ/H+u provides reasonable estimates of PWP increase during cyclic shear, with differences between measured and computed excess PWP ratios (ru) for both element and centrifuge tests generally smaller than 0.1. Computed spectral accelerations are comparable to centrifuge test measurements, with almost no bias at medium to long periods (T > 0.4 s) when the computed maximum shear strain (γmax) was smaller than the limit shear strain (γlimit). When computed ru > 0.8 and computed γmax > γlimit, spectral accelerations may be underestimated at both short and long periods as dilative behavior is not captured by GQ/H+u.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Stress–strain pattern–based criterion to assess cyclic shear resistance of soil from laboratory element tests

2016 ◽  
Vol 53 (9) ◽  
pp. 1460-1473 ◽  
Author(s):  
Dharma Wijewickreme ◽  
Achala Soysa
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shear Stiffness ◽  
Large Strains ◽  
Fundamental Parameter ◽  
Stress Strain ◽  
Cyclic Shear ◽  
Excess Pore Water Pressure ◽  
Excess Pore

The cyclic shear response of soils is commonly examined using undrained (or constant-volume) laboratory element tests conducted using triaxial and direct simple shear (DSS) devices. The cyclic resistance ratio (CRR) from these tests is expressed in terms of the number of cycles of loading to reach unacceptable performance that is defined in terms of the attainment of a certain excess pore-water pressure and (or) strain level. While strain accumulation is generally commensurate with excess pore-water pressure, the definition of unacceptable performance in laboratory tests based purely on cyclic strain criteria is not robust. The shear stiffness is a more fundamental parameter in describing engineering performance than the excess pore-water pressure alone or shear strain alone; so far, no criterion has considered shear stiffness to determine CRR. Data from cyclic DSS tests indicate consistent differences inherent in the patterns between the stress–strain loops at initial and later stages of cyclic loading; instead of relatively “smooth” stress–strain loops in the initial parts of loading, nonsmooth changes in incremental stiffness showing “kinks” are notable in the stress–strain loops at large strains. The point of pattern change in a stress–strain loop provides a meaningful basis to determine the CRR (based on unacceptable performance) in cyclic shear tests.

Earthquake-induced deformation analyses of the Upper San Fernando Dam under the 1971 San Fernando Earthquake

2001 ◽  
Vol 38 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Guoxi Wu
Keyword(s):  
Finite Element ◽  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Ground Deformation ◽  
Water Pressure ◽  
Soil Liquefaction ◽  
Shear Stresses ◽  
Cyclic Shear ◽  
San Fernando

A nonlinear effective stress finite element approach for dynamic analysis of soil structure is described in the paper. Major features of this approach include the use of a third parameter in the two-parameter hyperbolic stress-strain model, a modified expression for unloading–reloading modulus in the Martin–Finn–Seed pore-water pressure model, and an additional pore-water pressure model based on cyclic shear stress. The additional pore-water pressure model uses the equivalent number of uniform cyclic shear stresses for the assessment of pore-water pressure. Dynamic analyses were then conducted to simulate the seismically induced soil liquefaction and ground deformation of the Upper San Fernando Dam under the 1971 San Fernando Earthquake. The analyses were conducted using the finite element computer program VERSAT. The computed zones of liquefaction and deformation are compared with the measured response and with results obtained by others.Key words: effective stress method, finite element analysis, Upper San Fernando Dam, earthquake deformation, VERSAT.

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