Mechanical Characteristics of Ningbo Marine Deposit Soft Clay under Different Stress Paths

2011 ◽  
Vol 250-253 ◽  
pp. 2093-2097
Author(s):  
Chen Bin ◽  
Jun Neng Ye ◽  
Gan Bin Liu
Keyword(s):  
Effective Stress ◽  
Mechanical Characteristics ◽  
Axial Strain ◽  
Soft Clay ◽  
Stress Path ◽  
Shear Mode ◽  
Test Results ◽  
Total Stress ◽  
Consolidation Pressure ◽  
Marine Deposit

Based on a series of consolidated-undrained stress path tests, the mechanical characteristics of Ningbo marine deposit soft clay under K0 consolidation condition are systematically studied for different consolidation pressure, i.e.,60, 120 and 200kPa, in the GDS stress path triaxial system. Three kinds of stress path, i.e., DE (increase p), DG(constant p) and DF(reduce p), are carried out, and the characteristics of stress-axial strain relation, stress path and strength under different stress paths are compared. The test results show that the effective stress paths under consolidated-undrained shear are mainly related to initial consolidation, and the controlled shear mode has evident effect on the effective stress paths. In addition, the stress path has a certain influence on both the total stress and the effect stress strength.

Deformability and consolidation characteristics of soft Bangkok clay using screw plate tests

1990 ◽  
Vol 27 (5) ◽  
pp. 531-545 ◽  
Author(s):  
D. T. Bergado ◽  
K. C. Chong ◽  
P. A. M. Daria ◽  
M. C. Alfaro
Keyword(s):  
Graphical Method ◽  
Soft Clay ◽  
Stress Path ◽  
Soil Parameters ◽  
Test Results ◽  
Coefficient Of Consolidation ◽  
Plate Test ◽  
Settlement Time ◽  
Oedometer Tests ◽  
Test Embankment

This study centred on the performance of the screw plate test (SPLT) to determine the deformability and consolidation characteristics of soft Bangkok clay. For comparison, a series of stress-path-controlled triaxial consolidation tests (tri) were carried out on good quality samples of Bangkok clay taken from the same testing sites and imposed with the same loading conditions as the screw plate tests. Undrained and drained moduli and coefficients of consolidation were obtained from the stress-path-controlled triaxial consolidation tests and were compared with the corresponding values of the screw plate test. In addition, the ultimate bearing capacity was derived from the pressure–deformation relationships of the screw plate test results. A graphical method was used to compute the coefficient of consolidation from the screw plate tests and from stress-path-controlled triaxial consolidation test results. The compressibility data were also obtained from conventional oedometer tests (oed). Both cv (SPLT)/cv (tri) and cv (SPLT)/cv(oed) ratios compared favorably with the cv (field)/cv (laboratory) ratio obtained from past investigations. The data from pressure–settlement–time relationships of the screw plate tests were used to successfully predict values that compared favorably with the measured values at each stress level. The pressure–deformation–time relationship from stress-path-controlled triaxial consolidation tests were also evaluated, and they indicated behaviour similar to that of the screw plate test results. Soil parameters obtained from screw plate tests were subsequently used to predict the settlement of two test embankments, giving fairly close agreement with the observed values. Key words: soft clay, settlement, deformation, consolidation, screw plate test, triaxial test, embankment, prediction, stress path.

Effective stress paths and yielding in soft clays below embankments

1985 ◽  
Vol 22 (3) ◽  
pp. 357-374 ◽  
Author(s):  
D. J. Folkes ◽  
J. H. A. Crooks
Keyword(s):  
Pore Water ◽  
Effective Stress ◽  
Strain Softening ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Clay ◽  
Stress Path ◽  
Excess Pore Water Pressure ◽  
Soft Clays ◽  
Effective Stress Path

Current methods of predicting the response of soft clays to surface loading are often unsuccessful because the assumed constitutive relationships, including effective stress path behaviour, are incorrect. In particular, the transition from small-strain to large-strain behaviour (i.e. yielding) is frequently not taken into account. Recent laboratory testing has demonstrated that the behaviour of soft clays is largely controlled by yielding. The locus of effective stress states causing yield is known as the yield envelope (YE).The effective stress paths (ESP's) in soft clay foundations below the centre of six fills were determined from computed total stresses and measured pore-water pressures. Yield behaviour is clearly indicated by ESP shapes. The yield envelopes inferred from analyses of field data are similar to those obtained from laboratory testing. Effective stress path shapes vary widely, depending on a variety of factors, including imposed stress level, rate of construction, and boundary drainage conditions. This finding contradicts an earlier conclusion that soft clay behaviour can be characterized by a single ESP. Because of the wide range of possible ESP shapes, the parameters [Formula: see text] does not provide an adequate basis for determining the effective stress state in a soft clay.The ESP/YE analyses indicate that yield can occur either during loading or during excess pore-water pressure dissipation following completion of loading. Yield of sensitive soils during loading is usually followed by strain softening. However, in some soils, dilatant behaviour appears to occur. Yield during dissipation of excess pore-water pressure is characterized by a dramatic change in cv and increased compressibility. Key words: soft clay, yield, effective stress paths, field behaviour, strain softening, rate of consolidation.

Analysis of Nonlinear Stress and Strain in Clay under the Undrained Condition

2011 ◽  
Vol 27 (2) ◽  
pp. 201-213 ◽  
Author(s):  
P.-G. Hsieh ◽  
C.-Y. Ou
Keyword(s):  
Soft Clay ◽  
Stress Path ◽  
Small Strain ◽  
Model Parameters ◽  
Soil Behavior ◽  
Total Stress ◽  
Soil Stiffness ◽  
Nonlinear Stress ◽  
Strength Tests ◽  
Laboratory Stress

ABSTRACTThough the total stress undrained analysis approach in geotechnical engineering is widely utilized by practicing engineers, it has some intrinsic imperfections that cause the obtained parameters to have unavoidable empirical correlations. In this study, an undrained soft clay model is developed, which overcomes the imperfections of the conventional total stress undrained approach. In addition, the high soil stiffness at small strain and the concept of yield surface are employed to realistically simulate actual soil behavior. The model parameters can be obtainable directly from conventional laboratory tests. The model is validated through different laboratory stress path tests and strength tests in this paper.

An embankment failure on soft fissured clay

1986 ◽  
Vol 23 (4) ◽  
pp. 528-540 ◽  
Author(s):  
J. H. A. Crooks ◽  
K. Been ◽  
B. W. Mickleborough ◽  
J. P. Dean
Keyword(s):  
Effective Stress ◽  
Soft Clay ◽  
Monitoring Program ◽  
Stress Path ◽  
Performance Criterion ◽  
The North ◽  
Empirical Performance ◽  
Average Shear ◽  
Translational Mode ◽  
Effective Stress Path

Construction at the Genesee Power Project near Edmonton required 13 m high approach fills on soft clay for a roadway overpass structure. During construction, the north approach fill failed at a height of about 12 m. An investigation of the failure was carried out and a monitoring program instigated for further fill construction and piling for the overpass structure.The in situ mass strength of the soft clay was found to be controlled by defects such as slickensides rather than the intact strength. A translational mode of failure is considered most likely to have occurred, with computations based on c′ = 0 and [Formula: see text] determined from normally consolidated samples yielding the appropriate factors of safety to account for the failure. "Tearing" of the fill and overconsolidated crust due to the translational failure mechanism, with associated reduced average shear strengths, also occurred.Monitoring data for construction after the failure are presented and discussed. The effective stress path/yield envelope approach was used to assess the data. An empirical performance criterion for the site was developed for the overpass structure based on the observed deformation rates and computed factors of safety. Key words: embankment, stability, clay, failure, translational failure, effective stress path, fissured.

On the undrained unloading behaviour of gassy sands

2009 ◽  
Vol 46 (11) ◽  
pp. 1267-1276 ◽  
Author(s):  
A. Amaratunga ◽  
J. L.H. Grozic
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Marine Sediments ◽  
Stress Condition ◽  
Saturation Pressure ◽  
Stress Path ◽  
Pressure Change ◽  
Dissolved Gas ◽  
Total Stress ◽  
Dissolved Form

Soils that contain large amounts of dissolved gas within the pore fluid are called gassy soils. Gassy soils are common in marine environments and it is important to further our understanding of the unloading behaviour of gassy soils because of their potential to initiate and propagate submarine slope failures. This paper focuses on the pore-pressure responses and volumetric strains of loose gassy sands under different undrained unloading stress paths in laboratory specimens. Special attention was given to the constant deviatoric stress (q-constant) undrained unloading stress path as it simulates the stress condition imposed by tidal drawdown — one of the potential triggers of landslides in gaseous marine sediments. Gas exsolution was observed when the pore pressure was reduced below the liquid gas saturation pressure. Upon further decreases in total stress, the resulting pore-pressure change was much less than the total stress change; hence, effective stress decreased rapidly and at a certain point the samples tested under the q-constant stress path collapsed. This paper has experimentally and theoretically shown that gas in free and (or) dissolved form is detrimental in undrained unloading stress paths.

Experimental Study on the Time Effect of the Jacked Pile

2013 ◽  
Vol 353-356 ◽  
pp. 125-129
Author(s):  
Rui Cai Wang ◽  
Jian Yong Shi ◽  
Sheng Chen ◽  
Hua Jie Chen
Keyword(s):  
Initial Stress ◽  
Pore Water ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Stress Path ◽  
Test Results ◽  
Stress Increment ◽  
Excess Pore Water Pressure ◽  
Triaxial Apparatus

Based on the strain-holding test by using GDS stress path triaxial apparatus, the changes of pore water pressure and stress of soil around the pile were simulated during and after pile jacking. Test results show as follows: excess pore water pressure and effective stress increment increase with strain and initial stress rising at the stage of strain applied. And at the stage of strain holding, effective stress increment increases with rising of strain and initial stress. For the total effective stress increment, the proportion of effective stress increment is large at the stage of strain applied. And at the stage of strain holding, the proportion of effective stress increment is small.

Pore Pressure Build-up of Silt Soft Clay under Dynamic Loading at Zhoushan Islands

2012 ◽  
Vol 594-597 ◽  
pp. 460-464
Author(s):  
Qian Shi ◽  
Kui Zhou ◽  
Qiang Li
Keyword(s):  
Pore Pressure ◽  
Dynamic Loading ◽  
Dynamic Load ◽  
Soft Clay ◽  
Test System ◽  
Dynamic Responses ◽  
Minor Effect ◽  
Consolidation Pressure ◽  
Anisotropic Consolidation ◽  
Pore Pressure Build Up

The mechanism of dynamic tri-axial test is introduced in this paper and the dynamic responses of silt soft clay at Zhoushan are studied using a dynamic tri-axial test system. The laws of pore pressure build-up of the silt clay are obtained which are affected by the consolidation pressure and dynamic load. The greater the consolidation pressure and the dynamic loading is, the more the build-up of pore pressure is. However, the dynamic load has minor effect on pore pressure build-up under the anisotropic consolidation.

Experimental Study on the Combined Effect of Cyclic and Static Loads on the Mechanical Properties of the Saturated Soft Clay Material

2016 ◽  
Vol 723 ◽  
pp. 843-848
Author(s):  
Yi Wei ◽  
Ying Zhu ◽  
Jing Ni
Keyword(s):  
Mechanical Properties ◽  
Cyclic Load ◽  
Stress Ratio ◽  
Axial Strain ◽  
Soft Clay ◽  
Cyclic Stress ◽  
Excess Pore Pressure ◽  
Static Loads ◽  
Cyclic Stress Ratio ◽  
Excess Pore

The combined effect of cyclic and static loads on the mechanical properties of the soft clay was experimentally investigated by conducting undrained cyclic triaxial tests on Shanghai clay. The results show that an increment in either static or cyclic load increases excess pore pressures and axial strains. For a given value of combined cyclic and static loads, the mechanical properties of the soft clay are more sensitive to the cyclic load. Furthermore, the accumulated excess pore pressure and axial strain for a larger cyclic stress ratio and a lower combined stress ratio might overcome that for a lower cyclic stress ratio and a higher combined stress ratio. The mechanical properties of the soft clay after the cyclic load was unloaded were also discussed. It was observed that the excess pore pressure and axial strain under the static load alone decrease gradually with time. The trend of them largely depends on the ratio of cyclic load to static load.

Effects of Laumontite Hydration/Dehydration on Swelling Deformation and Slake Durability of Altered Granodiorite

2020 ◽  
Vol 26 (4) ◽  
pp. 507-516
Author(s):  
Junsong Yan ◽  
Junhui Shen ◽  
Kaizhen Zhang ◽  
Jianjun Xu ◽  
Weifeng Duan ◽  
...  
Keyword(s):  
Axial Strain ◽  
Test Results ◽  
X Ray Diffraction ◽  
Dam Foundation ◽  
Hydro Power ◽  
Slake Durability Index ◽  
Slake Durability ◽  
Dehydration Reactions ◽  
Short Period ◽  
Durability Index

ABSTRACT The mineral laumontite can undergo hydration/dehydration reactions at room temperature. The hydration/dehydration produces a 3 to 6 percent volume change in the unit cell. The effects of laumontite hydration/dehydration on swelling and slake durability were investigated using altered granodiorite containing laumontite from the dam foundation of Yangfanggou Hydro Power Station, Sichuan, China. The occurrence of laumontite in altered rocks was first determined by petrological analysis. Typical samples were then collected for laboratory X-ray diffraction (XRD) analyses, free swelling tests, and slake durability index (SDI) tests. The test results were analyzed to determine the quantitative relationships between laumontite content, maximum axial strain, and slake durability index. We found that hydration of laumontite led to rock swelling. As laumontite content increased, maximum axial strain increased linearly; if water penetrated the rock quickly, swelling occurred over a short period. The hydration/dehydration of laumontite decreased slake durability of the rock; the SDI decreased approximately linearly as laumontite content increased.

A Change of Undrain Shear Strength of Soft Ground during Consolidation Process

2014 ◽  
Vol 513-517 ◽  
pp. 269-272
Author(s):  
Yeong Mog Park ◽  
Ik Joo Um ◽  
Norihiko Miura ◽  
Seung Cheol Baek
Keyword(s):  
Shear Strength ◽  
Soft Clay ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Test Results ◽  
Exponential Equation ◽  
Consolidation Process ◽  
Degree Of Consolidation ◽  
Clay Ground ◽  
Strength Increment

The purpose of this study is to investigate the undrain shear strength increment during consolidation process of soft clayey soils. Thirty kinds of laboratory triaxial tests have been performed using undisturbed and remolded Ariake clay samples with different degree of consolidation and 5 kinds of confining pressure. Test results show that well known linear equation proposed by Yamanouchi et al.(1982) is overestimated the strength of undisturbed soft clay ground in the process of consolidation. A new simple and reasonable exponential equation proposed in this paper.

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