Primary and secondary compression behavior of dredged clay at low effective stresses

Sabkha soils are coastal and inland saline deposits of arid climates consisting mainly of loosely cemented sandy silt to silty clay particles. Invariably the soils contain an appreciable amount of organic material and are characterized as being highly compressible. Despite increased interest in various aspects of sabkha soil behavior, little is yet known about the nature and magnitude of secondary compression of these distinct sediments. In this paper, the secondary compression behavior of a typical sabkha formation from the southwestern coast of Saudi Arabia was investigated. Series of conventional and long-term, one-dimensional consolidation tests were conducted on natural and preloaded undisturbed samples taken from the compressible sabkha layer. The results of the laboratory investigation, substantiated by existing field data, indicated that a significant portion of sabkha settlements takes place as a secondary compression. The coefficient of secondary compression, Cα, was found to be constant, and the ratio of Cα to the compression index, Cc, is within the range reported in the published literature for various geotechnical materials. The applicability of the Cα /Cc concept to sabkha soils was further ascertained by comparing the secondary settlements estimated based on this concept with those measured directly in the field under an instrumented test embankment. Reasonable agreement was found between predictions and field observations.Key words: sabkhas, consolidation, coefficient of secondary compression, preloading, test embankment.

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Experimental Study on Axial Compression Behavior on Circular Timber Columns Strengthened with CFRP Strips and Near-Surface Mounted Steel Bars

Journal of Structural Engineering ◽

10.1061/(asce)st.1943-541x.0002931 ◽

2021 ◽

Vol 147 (3) ◽

pp. 04021003

Author(s):

Siha A ◽

Changdong Zhou ◽

Ligan Yang

Keyword(s):

Experimental Study ◽

Axial Compression ◽

Near Surface ◽

Compression Behavior ◽

Steel Bars ◽

Near Surface Mounted

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Compression behavior of press felts and wet webs

Nordic Pulp & Paper Research Journal ◽

10.3183/npprj-1990-05-01-p028-032 ◽

1990 ◽

Vol 5 (1) ◽

pp. 28-32 ◽

Cited By ~ 6

Author(s):

Farouk El-Hosseiny

Keyword(s):

Compression Behavior

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DEM analyses of cemented hydrate’s effect on the compression behavior of fine-grained sediments

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/643/1/012111 ◽

2021 ◽

Vol 643 ◽

pp. 012111

Author(s):

Tao Li ◽

Liqing Li

Keyword(s):

Compression Behavior ◽

Fine Grained

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A comparative study on methods for determining the hydraulic properties of a clay shale

Geophysical Journal International ◽

10.1093/gji/ggaa532 ◽

2020 ◽

Vol 224 (3) ◽

pp. 1523-1539

Author(s):

Lisa Winhausen ◽

Alexandra Amann-Hildenbrand ◽

Reinhard Fink ◽

Mohammadreza Jalali ◽

Kavan Khaledi ◽

...

Keyword(s):

Pore Pressure ◽

Effective Stress ◽

Ion Beam ◽

Applied Pressure ◽

Pressure Oscillation ◽

Stress Conditions ◽

Data Set ◽

Clay Shale ◽

Permeability Coefficients ◽

Effective Stresses

SUMMARY A comprehensive characterization of clay shale behavior requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: (i) pore pressure oscillation, (ii) pressure pulse decay and (iii) pore pressure equilibration. Based on a comprehensive data set obtained on one sample under well-defined temperature and isostatic effective stress conditions, we discuss the sensitivity of permeability and storativity on the experimental boundary conditions (oscillation frequency, pore pressure amplitudes and effective stress). The results show that permeability coefficients obtained by all three methods differ less than 15 per cent at a constant effective stress of 24 MPa (kmean = 6.6E-21 to 7.5E-21 m2). The pore pressure transmission technique tends towards lower permeability coefficients, whereas the pulse decay and pressure oscillation techniques result in slightly higher values. The discrepancies are considered minor and experimental times of the techniques are similar in the range of 1–2 d for this sample. We found that permeability coefficients determined by the pore pressure oscillation technique increase with higher frequencies, that is oscillation periods shorter than 2 hr. No dependence is found for the applied pressure amplitudes (5, 10 and 25 per cent of the mean pore pressure). By means of experimental handling and data density, the pore pressure oscillation technique appears to be the most efficient. Data can be recorded continuously over a user-defined period of time and yield information on both, permeability and storativity. Furthermore, effective stress conditions can be held constant during the test and pressure equilibration prior to testing is not necessary. Electron microscopic imaging of ion-beam polished surfaces before and after testing suggests that testing at effective stresses higher than in situ did not lead to pore significant collapse or other irreversible damage in the samples. The study also shows that unloading during the experiment did not result in a permeability increase, which is associated to the persistent closure of microcracks at effective stresses between 24 and 6 MPa.

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Experimental study on the axial compression behavior of columns confined by BFRP ties

Composite Structures ◽

10.1016/j.compstruct.2020.113302 ◽

2021 ◽

Vol 258 ◽

pp. 113302

Author(s):

Pu Zhang ◽

Bowen Chen ◽

Ye Liu ◽

Yazheng Tu ◽

Danying Gao ◽

...

Keyword(s):

Experimental Study ◽

Axial Compression ◽

Compression Behavior

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Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes

Rock Mechanics and Rock Engineering ◽

10.1007/s00603-021-02420-3 ◽

2021 ◽

Author(s):

Serge A. Shapiro ◽

Carsten Dinske

Keyword(s):

Stress Drop ◽

Induced Seismicity ◽

Quantitative Characteristic ◽

High Stress ◽

Operation Time ◽

Average Stress ◽

Induced Earthquakes ◽

Effective Stresses ◽

Seismicity Rates

AbstractSometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.

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