Deep Marine Clay Research Articles

Macroscopic effects of nano and microscopic phenomena in clayey soils and clay rocks

Based on long term investigations of the microstructure of various geomaterials as different as sensitive low plastic clays from Eastern Canada, unsaturated compacted silt from the Paris area, highly plastic compressible deep marine clay from the gulf of Guinea, compacted MX80 bentonite and the Callovo–Oxfordian claystone, considered as possible barriers in deep geological radioactive waste disposal, two fundamentals and distinct nano and micro mechanisms governing their macroscopic volume changes have been identified. In low plastic structured clays and dry compacted soils, in which an aggregate microstructure has been evidenced, the decrease in volume under mechanical compression result from the collapse of inter-aggregates pores in an ordered manner, from the larger to the smaller, with no effect on the intra-aggregate porosity. The soil skeleton can hence be modelled as an elastic fragile porous matrix, affected by the ordered collapse of its pores. Things are different in plastic soils, due to the significant reactivity of the montmorillonite minerals to changes in water content that results in significant changes of the initial porous matrix. The ordered adsorption of layers of water molecules in clay platelets with respect to the suction or stress applied, evidenced long time ago in Soil science through X-ray diffraction techniques, appear to be able to help better understanding various phenomena like the compression of plastic compressible soils and the hydration of compacted bentonites. Interestingly, it also applies to understand the effects of smectite minerals in the volume changes behaviour of the Callovo–Oxfordian claystone. These two mechanisms at nano and microscopic scales hence provide a better understanding of the macroscopic volume changes of a large variety of natural and compacted clayey soils and rocks.

Experimental evidence about misconception of Terzaghi's 1-D consolidation theory in terms of degree of consolidation

Terzaghi's 1-D consolidation theory is commonly used for prediction of embankment settlement in soft fine-grained soil. Application of this theory is not always effective due to the simplifications of assumed soil behavior under load. This paper examines relationship between the degrees of consolidation determined by pore water pressure measured at the base of the sample and one-dimensional strain. Theoretically, this relationship should be unique, however experimental relationships correlating the degrees of consolidation are found to be non-linear. The article presents the results of multistage consolidation tests with pore water pressure measurements, carried out on intact and reconstituted deep marine clay. Consolidation tests were conducted with uniform stress distribution and single-sided drainage conditions. It was observed that the relationship between degrees of consolidation for intact and reconstituted samples largely divergent from theoretical unique line.

New approach of vacuum preloading with booster prefabricated vertical drains (PVDs) to improve deep marine clay strata

This paper presented a new approach for ground improvement of deep marine clay in which the conventional booster tube in the current air booster vacuum preloading technology was replaced by a booster prefabricated vertical drain (PVD). In comparison to the ordinary PVD, the booster PVD could provide inflow channels for the compressed air when the booster pump was in operation. To examine the performance of this new air booster vacuum preloading technology, in situ field tests were conducted at Oufei sluice project in Wenzhou, China, where the thickness of the soft soil layers (i.e., marine clay) was more than 20 m. An extensive monitoring system was implemented to measure the vacuum pressure, pore-water pressure, settlement, and lateral displacement at this reclamation site. With the collected field monitoring data, a comprehensive data analysis was carried out to evaluate the extent of ground improvement. The study results depicted that this new air booster vacuum preloading technology was more effective for the ground improvement of the deep marine clay layers, in comparison to the conventional vacuum preloading technology.

Stratigraphic architecture of the upper Messinian deposits of the Adana Basin (Southern Turkey): implications for the Messinian salinity crisis and the Taurus petroleum system

This paper is mainly based on field work carried out on the Messinian deposits of the Adana Basin (southern Turkey), as well as on the interpretation of seismic reflection profiles to understand 3D geometries of the basin fill. Chronostratigraphic constraints for the Messinian deposits are from micropaleontological studies on foraminifera, ostracods, and calcareous nannofossils, recently carried out on the Messinian deposits of the Adana Basin.Our results indicate that this basin developed in a marginal area strictly related to the Mediterranean realm. The Messinian deposits of the Adana Basin record all the main steps ofthe Messinian Salinity Crisis (MSC) that affected the Mediterranean area at the end of the Miocene.The new stratigraphic model for the Messinian deposits of the Adana Basin provided in thiswork gives new insights into both the MSC and the Taurus petroleum system. Despite their complete correspondence with the MSC, the Messinian deposits of the Adana Basin show some differences with respect to the current conceptual model for the MSC. For example, inthe current conceptual model for the MSC, only one regional erosional surface (MES) characterizes the MSC deposits. In the Adana Basin, two regional erosional surfaces, named MES1 and MES2, separate the Messinian deposits related to the MSC in Lower Evaporites, Resedimented Lower Evaporites (RLE), and upper Messinian continental deposits containinga late Lago-Mare ostracod assemblage (mainly fluvial coarse-grained and fine-grained sediments). In some places, Brecciated Limestones lie just above the MES1 and beneath the RLE. In addition, the RLE are thought to be related to the same step that brought to the Messinian halite deposition throughout theMediterranean, pointing to a hyperhaline environment. In contrast, the fine-grained deposits of the RLE of the Adana Basin show the occurrence of Parathetyan brackish ostracod fauna (early Lago-Mare ostracod assemblages), which defines an oligohalinedepositional environment for the RLE. In terms of hydrocarbon prospecting, the Messinian evaporates of the Adana Basin have been considered as a perfect seal for the active Taurus petroleum system. Our results show that due to the complex stratigraphic architecture of the basin fill and the occurrence of two regional erosional surfaces (MES1 And MES2), the Messinian evaporates are discontinuously present both in surface and in the Subsurface of the Adana Basin. However, seal properties in the Adana Basin could be found in the Lower Pliocene deep marine clays of the Avadan Formation. This work leads to suggest a new stratigraphical model for the Messinian deposits of the Adana Basin, allowing us to amend the classical scheme with respect to the Messinian, and to officially define some New formations within the stratigraphy of the Adana Basin.

Centrifugal test and numerical assessment for settlement of a large-scale artificial island constructed on deep marine clays

This paper presents a testing and numerical study on the deformation behaviours of marine clays from Jinzhou Bay, China, where a large-scale artificial island is under construction for the Dalian offshore airport. The mechanical behaviours of marine clays were investigated by laboratory tests, triaxial creep tests and centrifugal test. An elasto-viscoplastic constitutive model (Adachi-Oka model) and a finite element programme (CFEM 2D) were used to calculate the deformation of the marine clays. The validation of the elasto-viscoplastic model and finite element programme was initially verified by the numerical simulation of triaxial creep test and the centrifugal test. In addition, the settlement of the large-scale artificial island was calculated by the verified programme, which accounted for the effect of non-linear hydraulic conductivity. The calculated results show that differential settlement exists between functional areas, with the greatest post-construction settlement attaining 288 cm in 100 years. Uneven distribution of excess pore water pressure also exists, and does not fully dissipate in 100 years. It can be concluded that the settlement of the artificial island will continue, hence enough attention should be paid.

Strain-rate effects in deep marine clays from the Gulf of Guinea

Current developments in deepwater offshore oil production in the Gulf of Guinea (GoG) make it necessary to characterise the mechanical behaviour of the GoG deepwater sediments better. This paper examines some aspects of the strain-rate-dependent behaviour of intact and reconstituted GoG clay specimens. Results from isotropic compression and undrained shearing laboratory tests with changing rates of stress and strain are presented. They show that the soil generally follows an isotach behaviour, with clear strain-rate dependence of the stress–strain behaviour and pore pressure response in the undrained shear tests. The effects of structure and its degradation on the time-dependent response of the sediments seem to confirm general trends observed in other structured clays.

The Tertiary of Norden

This chapter provides a lithostratigraphic correlation and the present knowledge of the depositional history of the Tertiary succession of the Scandinavian countries. The succession records an initial phase of carbonate deposition in the early Paleocene. This was succeeded by deposition of deep marine clays with intercalation of sand-rich mass-flow deposits during most of the Paleocene and Eocene. Volcanic activity in the North Atlantic was extensive at the transition from the Paleocene to the Eocene resulting in widespread sedimentation of ash-rich layers in the North Sea area. During the Oligocene, the first prograding deltaic complex developed, sourced from the Fennoscandian Shield. Late Oligocene‐Early Miocene inversion and uplift of Norway and the Shetland Platform resulted in major progradation of coastal and delta plain systems. At the end of the Tertiary most of the North Sea basin was filled and the Fennoscandian Shield was flanked to the west by a broad, coalesced coastal plain.

An active, deep marine strike‐slip basin along the North Anatolian fault in Turkey

The Tekirdağ depression within the Marmara Sea in the Mediterranean region is an active, rhomb‐shaped strike‐slip basin along the North Anatolian fault with a basin floor at a water depth of −1150 m. New multichannel seismic reflection data and on‐land geological studies indicate that the basin is forming along a releasing bend of the strike‐slip fault and is filled with syntransform sediments of Pliocene‐Quaternary age. The basin is bounded on one side by the North Anatolian fault and on the other side by a subparallel normal fault, which forms the steep submarine slope. In cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2.5 km adjacent to the North Anatolian fault. Seismic sections also show that the slope‐forming normal fault connects at depth to the North Anatolian fault, implying that the basin is completely detached from its substratum. The whole structure can be envisaged as a huge, rather flat, negative flower structure. The releasing bend of the North Anatolian fault, responsible for the formation of the basin, is flanked by a constraining bend. Along the constraining bend, the syntransform strata are being underthrust, implying a recent change in the direction of the regional displacement vector. This thrusting is responsible for the uplift of the submarine slope to a height of 924 m, possibly by a mechanism of elastic rebound. Regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays. The anomalous present depth of the Tekirdağ depression is due to reduced Quaternary sedimentation coupled with high rates of displacement along the North Anatolian fault, which amounts to 20 mm/yr in the Marmara Sea region.

Naturally cemented sensitive soils

Many extremely sensitive or quick clay soils, particularly but not only those found in Canada, show characteristics of natural cementation bonding between particles. These soils include not only the brackish-marine Leda-type clay deposits but also fresh water varved clays, deep marine clays and others. Although the causes of cementation may vary, the mechanical behaviour of these soils is similar. The unique strength characteristic of naturally cemented soils is a yield curve, defined by breakdown of cementation, which is independent of the classical effective stress patterns of yielding or failure for soils. At low stresses the influence of cementation is to increase strength and resistance to deformation. The cementation yield curve can be generalized in sections, a limit at a constant value of mean normal stress intersecting a limit of shear stress or stress difference. This part of the yield curve is often at a constant value of shear stress over a large range of normal stress. Tensile strength is small. Strains up to yield, both volumetric and distortional, are small and approximately linear functions of mean normal stress and shear stress respectively. Examples for a variety of naturally cemented soils demonstrate that anisotropy and nonhomogeneous effects such as fissures and varves are important. De nombreux sols d'argile fluide ou extremement sensibles, et en particulier—mais non pas exclusivement—ceux que l'on trouve au Canada, montrent des caractéristiques de liaisons de cémentation interparticulaires. Ces sols comprennent non seulement les dépôts saumâtres marins argileux Leda, mais également les argiles stratifiées d'eau deuce, les argiles marines profondes, et d'autres. Bien que les causes de la cémentation puissent varier, ces sols se comportent d'une manière très semblable au point de vue mécanique. La caractéristique unique de résistance de ces sols naturellement cémentés consiste en une courbe d'écoulement, définie par une rupture de la cémentation, indépendante des schémas classiques des contraintes efficaces lors de 1'écoulement ou de la rupture des SOIS. Sous de faibles contraintes, l'influence de la cémentation est d'augmenter la résistance à la déformation. La courbe d'écoulement de cémentation peut être généralisée en des sections où une limite à valeur constante de la contrainte normale movenne couoe une limite de la contrainte de cisaillement ou he la différence des contraintes. Cette partie de la courbe d'écoulement est souvent atteinte pour des valeurs constantes de la contrainte de cisaillement sur un large domaine de contraintes normales. La résistance à la tension est faible. Les déformations jusau'à l'écoulement—aussi bien volumétriques que distortionelles—sont faibles et sont des fonctions approximativement 1inéaires de la contrainte normale moyenne et de la contrainte de cisaillement moyenne, respectivement. Des exemples couvrant une variété de sols naturellement cémentés démontrent que les effets d'anisotropie et d'hétérogénéité telles que les fissures et les strates, sont importants.

Texture of Modern Deltaic Sediments of Godavari River (India): ABSTRACT

Textures of modern sediments collected from distributary and tidal channels, lagoon, mangrove swamps, coastal beach and dunes, offshore barrier, and deep-marine facies of the Godavari delta differ significantly from place to place. Distributary-channel sediments are characterized by textures ranging from well-sorted sand to poorly sorted mud, and from positively skewed to negatively skewed sediments. The lagoonal sediments generally are poorly sorted and positively skewed. Their texture is believed to have resulted from mixing small amounts of present-day poorly sorted silt and clay with a well-sorted primary sand mode which is inferred to have been deposited earlier in a littoral environment. Coastal beach sands are moderately sorted and slightly negatively skewed. The d ne sands are well sorted and slightly positively skewed. In contrast, the barrier sands are very well sorted and the skewness curve is nearly symmetrical. Beach sands differ from dune sands by having relatively larger amounts of silt plus clay-size particles. Mangrove swamps have silty clay to clay sediments, whereas all sediments from the deep-marine facies of the Godavari delta are clay. The difference between the paludal and deep-marine clays End_Page 733------------------------------ is the relatively high content of particles of less than 1µ size in the latter. It is concluded that the observed variations in the texture of the sediments from various environments of the Godavari delta may serve as criteria in the recognition of environments of deposition of a paleodelta. End_of_Article - Last_Page 734------------