Behavior Of Marine Clay Research Articles

Impact forces of submarine landslides on suspended pipelines considering the low-temperature environment

Submarine pipelines in deep-water oil and gas developments are highly vulnerable to the threat of submarine landslides, which results in enormous, inestimable losses. Currently, the numerical method of computational fluid dynamics (CFD) is often employed to predict the impact of landslides on pipelines. However, a constitutive model based on artificially configured materials instead of natural marine clay is used for the numerical studies. In particular, the effect of the low-temperature environment of the seabed on the behavior of marine clay has not been considered. In this paper, a low-temperature rheological model was established by conducting rheological tests of submarine mud flows from the northern continental slope of the South China Sea and introduced into the CFD numerical simulation. The impact of mud flow on suspended pipelines was then systematically numerically calculated. The effect of the peak and stable loads on the impact force calculation is considered, and the average rate of change of the two quantities can reach 27.9%. Compared with the drag force and lift force of a mud flow impact on pipelines at 22 °C, those at 0.5 °C are increased by 26.0% and 70.3%, respectively. Finally, calculation equations of the peak and stable values of the impact force are established, which can provide a scientific basis for the engineering design of pipelines.

Comparison between Cement and Concrete Waste on the Strength Behaviour of Marine Clay Treated with Coal Ash

This paper aims to compare the strength behaviour of demolished concrete material (DCM) and ordinary Portland cement (OPC) in addition to coal ash for stabilizing marine clay, thus determining the optimum mix. Coal ash with different ratio of bottom ash (BA) and fly ash (FA) were prepared at various percentages (i.e. 3%, 6% and 8%). In addition, limited amount of DCM and OPC of 2% was added at different curing periods of 0, 7 and 28 days respectively. Thus, the percentage of admixture added to the marine clay were 5%, 8% and 10% respectively. Unconfined compressive strength (UCS) test was done and the results revealed that the strength of treated marine clay soil increased significantly with increment percentage of coal ash and also for both DCM and OPC. For admixture with OPC, treated marine clay with 5% admixture shows the highest strength gained, while the effective combination between bottom ash and fly ash is 50:50. At the first 7 days the strength gain was very high but from 7 days to 28 days the gain of strength was reduced. While for DCM, 5% of additive at 30BA:70FA shows the highest strength. In addition, both OPC and DCM provide significant strength gained between 0-7 days and decrease for 7-28 days. In conclusion, when comparing both stabilizer, OPC is a much more efficient secondary stabilizer when reacted with coal ash. As it provide early gain in strength with a much higher strength.

Effect of Fabric on Mechanical Behavior of Marine Clays

A reference void ratio is introduced as a fabric index to characterize the compression and shear behavior of marine clays. The same relations are obtained for compression indices versus the reference void ratio, and the strength versus the normalized void ratio (a ratio of void ratio at failure to the reference void ratio), for both undisturbed and reconstituted marine clays. Based on the above results, it is concluded that when the effective stress is larger than the structural yield stress, most bonding structures within natural clay are destroyed; and the difference in compression and strength characteristics between undisturbed and reconstituted samples is caused only by the fabric.

Behavior of marine clays containing seashell fragments under undrained triaxial loading

Marine clays at Gangavaram port on east coast of India are known to contain seashells which affect the undrained shear strength of the soft clays. This paper reports the results of consolidated undrained triaxial tests (CIU) on undisturbed samples of marine clay collected from the site. The findings from the tests are then compared to the results of the common elasto-plastic soil model used in the back analysis. The results seem to suggest that the presence of seashell fragments influence the measured pore pressure response and the strength especially at low consolidation pressure when stiffness of the clay is less.

Long-Term Consolidation and Strength Behavior of Marine Clay Improved with Fly Ash

This paper presents an investigation of the long-term consolidation and strength behavior with fly ash as an additive in improving soft marine clay in Wando, Korea. 0%, 5%, 10%, 20% and 25% of the soil was replaced with fly ash. Consolidation tests were performed as incremental loaded tests. In addition, unconfined compressive strength were determined after 1, 14, 28 and 90 days. A series of forty-two long-term consolidation tests that lasted for 60 days under the constant loading were also conducted. Creep settlements of the blends decreased significantly with an increase in fly ash content. The shear strength properties increased with an increase in fly ash content. Statistical evaluation reveals an excellent correlation between the measured and predicted undrained shear strengths.

Strength Behavior of Cemented Marine Clay Subjected to Storm Type Loading

Cyclic loading on offshore structures leads to an increase in long term deformations. These deformations will cause additional stresses in structural members. Overloading of offshore structures may have serious consequences and they must be designed to accommodate the increased deformations. During a storm, there is a surge in the mean sea level causing an increase in stress and they are believed to represent critical conditions for offshore foundations. This program encompasses an experimental investigation for establishing the behavior of soil subjected to storm type varied cyclic loading conditions on Indian East coast marine clay samples. In field situations where cyclic loading is imposed on the soil, it can be considered a stress controlled phenomenon. If the effects of cyclic loading on any soil have to evaluated, it is considered more appropriate if the cyclic load test results are compared with reference static strength results obtained from stress controlled tests. To meet these requirements, a series of triaxial shear tests are conducted by adopting different load durations at each load increment. In order to estimate the effect brought in by storm type cyclic loading, it becomes necessary to conduct reference standard tests under uniform cyclic loading at various cyclic stress ratios (CSR) on identical soil specimens and these stress levels are chosen in such a way that there is no failure taking place during testing. This paper presents the behavior of marine clay subjected to uniform and storm type of varied cyclic loading. The effects of this cyclic loading are brought through the comparisons of the results obtained from testing under both strain and stress controlled monotonic loading.

Behavior of Marine Clay Subjected to Cyclic Loading with Sustained Shear Stress

Foundations of offshore structures are designed to withstand a combination of static and cyclic loads due to ocean waves. Wave action on offshore structures can cause a significant amount of cyclic horizontal and vertical forces to be transmitted to the soil through the foundation. In all these cases, these cyclic loads are considered to be superimposed over the initial sustained static stress due to the self-weight of structures. This study considers various factors that influence the development of deformation and pore water pressure in a typical cemented marine clay. These results show that the sustained static shear stress significantly influences the strength and deformation behavior of marine clay under cyclic loading. Up to a certain range of sustained static stress, there is an improvement in strength during cyclic loading and the cyclic strains are greatly reduced.

Sulphate Attack in Lime-Treated Marine Clay

ABSTRACT The use of lime to improve the properties of soft clays is not new. Recently the deep lime mixing technique has been extended to coastal regions for improving the behavior of weak marine clays. But lime treatment technique should be approached carefully for clay containing a high percentage of sodium sulphate. The presence of sulphate in lime-treated clays may result in high swelling due to the formation of the expansive mineral, ettringite. A limited study of lime-treated marine clays has shown a need to further explore the formation of ettringite and its stability with time. In this article, a laboratory investigation was carried out to examine the influence of sodium and calcium sulphates on the behavior of lime column treated marine clay. Scanning electron microscopy (SEM) was used to identify the formation of various reaction products, including ettringite. Test results indicate that the formation of ettringite in the lime-sodium sulphate-clay system adversely affects the engineering behavior of the marine clay, whereas the addition of calcium sulphate significantly improves the engineering characteristics of the soil.

Effect of Pollutants on the Physical and Engineering Behavior of Lime-Treated Marine Clay

Rapid industrial growth and increasing population has resulted in the discharge of wastes into the ocean, wastes which ultimately reach the seabed and contaminate the marine sediments. The soil-contaminants interaction, and their associated physico chemical properties with sediments control the behavior of marine clays. Marine clay deposits of low strength and high compressibility are located in many coastal and offshore areas. There are several foundation problems encountered in these weak marine clays. In this study, experimental work was carried out in the laboratory to stabilize soft marine clays using the lime column technique. Also the lime-induced effects on the physical and engineering behavior of marine clays in sulfate-contaminated marine environment was investigated. Consolidation tests indicate that compressibility of the lime-treated samples was reduced to 1/2–1/3 of the virgin soil after 45 days treatment. The test results also suggest that the lime column technique can be conveniently used to improve the behavior of contaminated marine clay deposits.