Effect of initial pore pressure on undrained shear behaviour of fine-grained gassy soil

2017 ◽  
Vol 54 (11) ◽  
pp. 1592-1600 ◽  
Author(s):  
Y. Hong ◽  
L.Z. Wang ◽  
Charles W.W. Ng ◽  
B. Yang
Keyword(s):  
Pore Pressure ◽  
Fossil Fuels ◽  
Oil And Gas ◽  
Shear Behaviour ◽  
Excess Pore Pressure ◽  
Triaxial Tests ◽  
Fine Grained ◽  
Wide Range ◽  
The Stability ◽  
Undrained Shear

Many of the world reserves of fossil fuels are located at various water depths in fine-grained sediment under the seabed. The fine-grained sediment contains relatively large biogas bubbles, which has been posing challenges to the stability of offshore foundations supporting oil and gas platforms. Although fine-grained gassy soil was found to exhibit different undrained shear strengths (cu) by altering the initial pore pressure, ui (relevant to water depth), systematic studies concerning the effect of ui on undrained shear behaviours of the soil are still lacking. This study reports a series of undrained triaxial tests aiming to compare and investigate the responses of reconstituted fine-grained gassy soil with the same consolidation pressure ([Formula: see text]), but at a wide range of varying ui (0–1000 kPa). The shearing-induced excess pore pressure (Δu) in the gassy specimens highly depends on ui. It can be either smaller than that of the saturated specimen with the same [Formula: see text] (due to partial dissipation of Δu into relatively large bubbles at low ui) or larger than that of the saturated specimen (related to collapse of relatively small bubbles at high ui). Consequently, the presence of bubbles had beneficially increased cu at relatively low ui (ui/[Formula: see text] < 0.6), and vice versa. The critical stress ratio of the reconstituted fine-grained gassy soil, however, did not appear to be altered by ui.

scholarly journals How deep does sand deposits in the Alentejo basin (Gulf of Cadiz) reach? Evaluating slope stability from bottom-current activities through time

2020 ◽  
Author(s):  
Davide Mencaroni ◽  
Roger Urgeles ◽  
Jonathan Ford ◽  
Jaume Llopart ◽  
Cristina Sànchez Serra ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Sediment Supply ◽  
Excess Pore Pressure ◽  
Bottom Current ◽  
Gulf Of Cadiz ◽  
Strait Of Gibraltar ◽  
Gulf Of Cádiz ◽  
The Stability ◽  
Iberian Margin ◽  
Excess Pore

&lt;p&gt;Contourite deposits are generated by the interplay between deepwater bottom-currents, sediment supply and seafloor topography. The Gulf of Cadiz, in the Southwest Iberian margin, is a famous example of extensive contourite deposition driven by the Mediterranean Outflow Water (MOW), which exits the Strait of Gibraltar, flows northward following the coastline and distributes the sediments coming from the Guadalquivir and Guadiana rivers. The MOW and related contourite deposits affect the stability of the SW Iberian margin in several ways: on one hand it increases the sedimentation rate, favoring the development of excess pore pressure, while on the other hand, by depositing sand it allows pore water pressure to dissipate, potentially increasing the stability of the slope.&lt;/p&gt;&lt;p&gt;In the Gulf of Cadiz, grain size distribution of contourite deposits is influenced by the seafloor morphology, which splits the MOW in different branches, and by the alternation of glacial and interglacial periods that affected the MOW hydrodynamic regimes. Fine clay packages alternates with clean sand formations according to the capacity of transport of the bottom-current in a specific area. Generally speaking, coarser deposits are found in the areas of higher MOW flow energy, such as in the shallower part of the slope or in the area closer to the Strait of Gibraltar, while at higher water depths the sedimentation shifts to progressively finer grain sizes as the MOW gets weaker. Previous works show that at present-day the MOW flows at a maximum depth of 1400 m, while during glacial periods the bottom-current could have reached higher depths.&lt;/p&gt;&lt;p&gt;In this study we derived the different maximum depths at which the MOW flowed by analyzing the distribution of sands at different depths along the Alentejo basin slope, in the Northern sector of the Gulf of Cadiz.&lt;/p&gt;&lt;p&gt;Here we show how changes in sand distribution along slope, within the stratigraphic units deposited between the Neogene and the present day, are driven by glacial &amp;#8211; interglacial period alternation that influenced the hydrodynamic regime of the MOW.&lt;/p&gt;&lt;p&gt;By deriving the depositional history of sand in the Alentejo basin, we are able to correlate directly the influence that climatic cycles had on the MOW activity. Furthermore, by interpreting new multi-channel seismic profiles we have been able to derive a detailed facies characterization of the uppermost part of the Gulf of Cadiz.&lt;/p&gt;&lt;p&gt;An accurate definition of sand distribution along slope plays an important role in evaluating the stability of the slope itself, e.g. to understand if the sediments may be subjected to excess pore pressure generation. As sand distribution is a direct function of the bottom-current transport capacity, the ultimate goal of this study is to understand how climate variations can affect the stability of submarine slope by depositing contourite-related sand.&lt;/p&gt;

Energy dissipation and dynamic behaviour of clay under cyclic loading

1992 ◽  
Vol 29 (1) ◽  
pp. 103-111 ◽  
Author(s):  
Y. L. Cao ◽  
K. T. Law
Keyword(s):  
Shear Modulus ◽  
Pore Pressure ◽  
Dynamic Behaviour ◽  
Dynamic Strength ◽  
Excess Pore Pressure ◽  
Triaxial Tests ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
Energy Concept ◽  
Excess Pore

A laboratory study has been conducted to investigate the dynamic behaviour of Champlain Sea clay from two locations in the Ottawa River valley region. The test program includes cyclic triaxial tests and resonant-column tests. The soil samples were consolidated at a range of pressures before the dynamic shear in order to cover the dynamic behaviour under both the overconsolidated and the normally consolidated states. An energy concept is introduced to interpret the test results. Mathematical relationships have been established for describing the various aspects of dynamic behaviour. These aspects include excess pore pressure, dynamic strength, dynamic shear modulus, and plastic strain. The study shows that the energy concept provides a promising way to analyze dynamic soil behaviour. Key words : energy, dynamic behaviour, clay, cyclic test, earthquake, excess pore pressure, shear modulus, strength.

A Study on the Weldability of INCOLOY 825 Alloys and STS316L Alloys

2015 ◽  
Vol 1110 ◽  
pp. 118-124 ◽  
Author(s):  
Pyung Su Kim ◽  
So Young Choi ◽  
Young Sik Kim ◽  
Jong Do Kim
Keyword(s):  
Low Temperature ◽  
Alternative Energy ◽  
Fossil Fuels ◽  
Oil And Gas ◽  
Waste Treatment ◽  
Pressure Sensors ◽  
Low Carbon ◽  
Wide Range ◽  
Treatment Facilities ◽  
Incoloy 825

Bellows are widely used as parts in industrial machinery such as ships, valves, automotive, semiconductor equipment, flow and pressure sensors, and even in aircraft. Due to the recent depletion of conventional fossil fuels, natural liquified petroleum is increasingly demanded as an alternative energy, which in turn increases the demand for bellows on LNG ships. As the material used the bellows of LNG ships, the STS316L and INCOLOY 825 alloy, resistant to low-temperature embrittlement and corrosion, are used. STS316L is low-carbon stainless steel with a carbon content of less than 0.03%, preventing intergranular corrosion by welding work and maintaining its toughness and strength at a low temperature. In addition, Ni-Fe-Cr-based INCOLOY 825 alloy, containing Mo, Cu and Ti, is an alloy material resistant to general local corrosion in various atmospheres. INCOLOY 825 alloy is widely used for the creation of chemical processing equipment and in pollution-treatment facilities, oil and gas reduction equipment, acid manufacturing plants, pickling plants, nuclear fuel reprocessing and radioactive waste treatment facilities as well as in the bellows of LNG ships. Furthermore this material maintains good mechanical properties across a wide range of temperatures from ultra-low temperatures up to temperature approaching 500 °C. In this study, to assess its quality as a LNG ship bellows material, the STS316L and INCOLOY 825 alloy, used at an ultra-low temperature, the optimal welding conditions were established and its formability was analyzed by conducting an Erichsen test.

scholarly journals Application of Pickering emulsion in oil drilling and production

2021 ◽  
Vol 11 (1) ◽  
pp. 26-39
Author(s):  
Lipei Fu ◽  
Qianli Ma ◽  
Kaili Liao ◽  
Junnan An ◽  
Jinmei Bai ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Petroleum Industry ◽  
Pickering Emulsion ◽  
Pickering Emulsions ◽  
Gas Field ◽  
Oil Drilling ◽  
Wide Range ◽  
Reservoir Conditions ◽  
Oil And Gas Field ◽  
The Stability

Abstract When surfactant is used as emulsifier, the stability of emulsion is often greatly reduced with the influence of reservoir conditions (temperature, pressure, salinity, etc.), which shortens the validity period of emulsion. Pickering emulsion has a wide range of applications in the oil and gas field due to its advantages of good stability and easy regulation. In this article, the formation, stabilization mechanism, and influencing factors of Pickering emulsions were introduced, and the application status and prospects of Pickering emulsions in oil and gas field were summarized. It was pointed out that Pickering emulsion has many advantages and important research value when applied in deep strata and complicated reservoirs. It is expected that this article can effectively reflect the application value of Pickering emulsion in oil and gas field and promote the application of Pickering emulsion in petroleum industry.

Stability threshold for cyclic loading of saturated clay

1989 ◽  
Vol 26 (1) ◽  
pp. 122-131 ◽  
Author(s):  
Guy Lefebvre ◽  
Denis LeBoeuf ◽  
Benoît Demers
Keyword(s):  
Shear Strength ◽  
Cyclic Loading ◽  
Strain Rate ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Repeated Loading ◽  
Loading Test ◽  
Stability Threshold ◽  
The Stability ◽  
Undrained Shear

This paper presents the results of an experimental investigation performed to study the stability threshold under cyclic (repeated) loading, and the postcyclic static strength of a sensitive clay from the Hudson Bay region. The strain rate and structure effects were also studied by carrying out monotonic and cyclic triaxial tests at both slow and rapid strain rates or frequencies, and at confining pressures above and below the apparent preconsolidation pressure. The stability threshold for both structured and normally consolidated Grande Baleine clay is about 60–65% of the original undrained shear strength measured at the same strain rate as that used in the repeated loading test. The undrained shear strength and the failure envelope remain essentially unchanged if the repeated preloading is kept below the threshold. The clay structure remains unaltered by this preloading. Key words: clay, stability threshold, cyclic loading, earthquake, postcyclic strength.

Evaluating the sealing potential of young and thin mass-transport deposits: Lake Villarrica, Chile

2019 ◽  
Vol 500 (1) ◽  
pp. 129-146 ◽  
Author(s):  
Jasper Moernaut ◽  
Gauvain Wiemer ◽  
Achim Kopf ◽  
Michael Strasser
Keyword(s):  
Shear Strength ◽  
Mass Transport ◽  
Pore Pressure ◽  
Sediment Cores ◽  
Free Fall ◽  
Undrained Shear Strength ◽  
Excess Pore Pressure ◽  
Minor Role ◽  
Mass Transport Deposits ◽  
Undrained Shear

AbstractSubaqueous mass-transport deposits (MTDs) can be important elements in hydrocarbon systems, forming potential reservoirs or seals. Most research has targeted outcrops or moderately to deeply buried MTDs and, therefore, the petrophysical properties of near-seafloor MTDs, and their influence in the trapping and release of shallow fluids, is poorly studied. Here, we investigate shallow MTDs in Lake Villarrica (Chile) by combining sub-bottom profiles, free-fall penetrometer data, pore pressure dissipation tests and geotechnical properties of sediment cores. Low undrained shear strength under a surficial MTD indicates underconsolidation caused by sudden loading and rapid sealing. Larger, buried MTDs show acoustic signatures of free gas at their base, indicating effective sealing. This is supported by degassing core gaps just below MTDs and by excess pore pressure ratios c. 30–70% within MTDs. Acoustic windows below rafted blocks suggest local fluid escape. MTDs exhibit elevated undrained shear strength and reduced porosity compared to surrounding sediments, but are comparable to upslope source sequences. This suggests that MTD sealing capacity in Villarrica relates to the apparently overconsolidated nature of the slope sequence, leaving a minor role for shear densification. This study shows that shallow MTDs can form a relatively rapid seal for fluid migration, locally degraded by rafted blocks.

Behavior of a Cemented Plastic Clay as an Embankment Foundation

1974 ◽  
Vol 11 (1) ◽  
pp. 46-58
Author(s):  
Guy Lefebvre ◽  
Liguori M. Lefebvre ◽  
Peter Rosenberg
Keyword(s):  
Shear Strength ◽  
Pore Pressure ◽  
Applied Pressure ◽  
Undrained Shear Strength ◽  
Glacial Lake ◽  
Triaxial Tests ◽  
High Plasticity ◽  
Degree Of Consolidation ◽  
Undrained Shear ◽  
Varved Clay

A 32 ft (10 m) high embankment has been built at Matagami, Quebec, on a varved clay deposit of the glacial lake Barlow–Ojibway. This paper reports on some aspects considered in the design, mainly the cementation and the high plasticity of the clay. The variation of settlements and pore pressure is presented and indicates that, 8 months after construction, the pore pressure dissipation is very small while the measured settlements reach 18 in. (45 cm).Triaxial tests, with various consolidation times, were carried out on specimens cut from undisturbed block samples obtained in the same area, in order to study the effect of consolidation on the shear strength of these cemented clays. Results indicate that the undrained shear strength decreases during consolidation until the degree of consolidation reaches 50%. This phenomenon together with the non-dissipation of pore pressure in the field is attributed to the collapse of the cemented structure when the applied pressure exceeds Pc.Similar behavior reported for two other cases of embankments built on deposits of the same origin, leads to the conclusion that the stage construction method is not suitable for embankment on cemented clays, at least those from the glacial lake Barlow–Ojibway, because no gain in shear strength is recorded over a normal consolidation period.

Effect of load shape on relationship between dissipated energy and residual excess pore pressure generation in cyclic triaxial tests

2013 ◽  
Vol 50 (11) ◽  
pp. 1118-1128 ◽  
Author(s):  
Carmine Polito ◽  
Russell A. Green ◽  
Erin Dillon ◽  
Changbum Sohn
Keyword(s):  
Pore Pressure ◽  
Water Pressure ◽  
Laboratory Data ◽  
Excess Pore Pressure ◽  
Triaxial Tests ◽  
Dissipated Energy ◽  
Generation Model ◽  
Cyclic Triaxial ◽  
Cyclic Triaxial Tests ◽  
Load Shape

The energy dissipated in soil during cyclic loading can be used to predict the change in the pore-water pressure developed in the soil. To examine whether the energy required to cause liquefaction is dependent on or independent of the load shape applied, a series of 28 cyclic triaxial tests were performed using five different load shapes having a range of cyclic stress ratios. The five load shapes were applied to identically prepared specimens of clean sand and the dissipated energy – pore pressure generation characteristics examined. It was found that that the dissipated energy to cause initial liquefaction was normally distributed and independent of the load shape, although it is seemingly somewhat dependent on duration of loading. A corollary to this finding is that laboratory data from specimens tested using sinusoidal loadings can be used to calibrate the Green, Mitchell, and Polito (GMP) energy-based pore pressure generation model for use in predicting in situ pore pressures in soils subjected to nonsinusoidal loadings (e.g., earthquake loadings). Given the relative simplicity of the GMP model, these findings make the model an attractive alternative to implement in effective stress dynamic response codes.

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