Clay Microfabrics Research Articles

Analysis of Clay Mineral Transformation in Plambik Village, Central Lombok Using X-Ray Diffraction and Scanning Electron Microscope Methods

Analysis of minerals and microfabric changes during the burning process of clay in Plambik village, Central Lombok has been carried out using 2 methods: X-Ray Diffraction and Scanning Electron Microscope. A brick of dimension (10 x 20 x 5) mm was prepared which was formed through a gypsum mould. After drying it is burned using an electric furnace with temperatures: 800oC, 1000oC and 1100oC. The results show that using the X-ray diffraction method when burned at 800oC there are quartz minerals with several illite peaks, at 1000oC there is only quartz, the illite peaks disappear while at 1100oC the quartz mineral peaks remain accompanied by the appearance of mullit peaks. Then the effect of the firing temperature on the clay microfabric was analyzed by observing the sample with a Scanning Electron Microscope. This test aims to obtain information about the changes in structure and texture that develop during the combustion process and more specifically on the morphology of the particles and their interaction with the development of the vitrification process and the distribution of the shape and size of the pores. The results showed that before burning, the kaolinite and illite particles were randomly distributed with porous aggregates and the grain size was between 1 – 5 microns. During firing at 800oC some parts have undergone melting and welding phases with the development of secondary porosity. Meanwhile, when burning with a temperature of 1100oC, it appears that the welding and smelting processes that occur are wider and the emergence of mullite crystals from the glass matrix.

Experimental investigation on the tribological behavior and surface damage due to embedment of ceramic proppant – analog mudrock composite systems

The analysis of interface problems involving proppants and rocks is of major interest in unconventional reservoir exploitation and modeling as well as in geophysics, mining engineering and rock mechanics. Despite the significant progresses that have been reported in hydraulic fracturing, there has been given less attention in the fundamental understanding of the interactions between proppants and rocks, which can provide enhanced input parameters in computational-based analyses involving complex multi-phase processes. In this study, the tribological behavior of three types of contacts including ceramic-ceramic (analog) proppants, kaolinite-kaolinite blocks (analog mudrock) and ceramic-kaolinite composite interfaces was investigated performing laboratory tests using a custom-developed loading apparatus and the experiments involved force and displacement measurements by the application of high-precision transducers. Based on a series of normal loading tests, it was observed that the ceramic beads exhibited a completely elastic behavior, whereas the kaolinite blocks showed a softer response with, predominantly, plastic deformations. The results of the shearing tests indicated that for the ceramic-kaolinite composite contacts, the arrangement of the clay microfabric significantly affected the shearing load-displacement response in terms of the post-peak softening behavior, the development of the microslip regime as well as the dynamic friction. It was also shown that even though the interface friction was controlled, predominantly, by the softer kaolinite block, the interface tangential stiffness had different involved mechanisms, in which case the kaolinite blocks showed the highest stiffness specifically at greater magnitudes of normal load, whereas the ceramic-kaolinite composite interfaces had the lowest values of stiffness.

The mineralogy and fabric of ‘Brickearths’ in Kent, UK and their relationship to engineering behaviour

Mineralogical and petrographical investigation of two loessic brickearth profiles from Ospringe and Pegwell Bay in north Kent, UK have differentiated two types of brickearth fabric that can be correlated with different engineering behaviour. Both sequences comprise metastable (collapsing) calcareous brickearth, overlain by non-collapsing ‘non-calcareous’ brickearth. This study has demonstrated that the two types of brickearth are discretely different sedimentary units, with different primary sedimentary characteristics and an erosional junction between the two units. A palaeosol is developed on the calcareous brickearth, and is associated with the formation of rhizolithic calcrete indicating an arid or semi-arid environment. No evidence has been found for decalcification being responsible for the fabric of the upper ‘non-calcareous’ brickearth. Optically-stimulated dates lend further support for the calcareous and ‘non-calcareous’ brickearth horizons being of different age or origins. The calcareous brickearth is metastable in that it undergoes rapid collapse settlement when wetted under applied stresses. It is characterised by an open-packed arrangement of clay-coated, silt-sized quartz particles and pelletised aggregate grains (peds) of compacted silt and clay, supported by an inter-ped matrix of loosely packed, silt/fine-grained sand, in which the grains are held in place by a skeletal framework of illuviated clay. The illuviated clay forms bridges and pillars separating and binding the dispersed component silt/sand grains. There is little direct grain-to-grain contact and the resultant fabric has a very high voids ratio. Any applied load is largely supported by these delicate clay bridge and pillar microfabrics. Collapse of this brickearth fabric can be explained by a sequence of processes involving: (1) dispersion and disruption of the grain-bridging clay on saturation, leading to initial rapid collapse of the loose-packed inter-ped silt/sand; (2) rearrangement and closer stacking of the compact aggregate silt/clay peds; (3) with increasing stress further consolidation may result from deformation and break up of the peds as they collapse into the inter-ped regions. Smectite is a significant component of the clay assemblage and will swell on wetting, further encouraging disruption and breaking of the clay bonds. In contrast, the ‘non-calcareous’ brickearth already possesses a close-packed and interlocking arrangement of silt/sand grains with only limited scope for further consolidation under load. Minor authigenic calcite and dolomite may also form meniscus cements between silt grains. These have either acted as “scaffolds” on which illuviated clay has subsequently been deposited or have encrusted earlier-formed grain-bridging clay. In either case, the carbonate cements may help to reinforce the clay bridge fabrics. However, these carbonate features are a relatively minor feature and not an essential component of the collapsible brickearth fabric. Cryoturbation and micromorphological features indicate that the calcareous brickearth fabric has probably been developed through periglacial freeze–thaw processes. Freezing could have produced the compact silt/clay aggregates and an open porous soil framework containing significant inter-ped void space. Silt and clay were remobilised and translocated deeper into the soil profile by water percolating through the active layer of the sediment profile during thawing cycles, to form the loosed-packed inter-ped silt matrix and grain-bridging meniscus clay fabrics. In contrast, the upper ‘non-calcareous’ brickearth may represent a head or solifluction deposit. Mass movement during solifluction will have destroyed any delicate grain-bridging clay microfabrics that may have been present in this material.

Development of Intermediate Microfabric in Kaolin Clay and Its Consolidation Behaviour

The effect of microfabric on the mechanical behaviour of clays has been explored previously based on the response of dispersed and flocculated microfabrics only. However, the natural clays often have the geometric arrangement of particles between these two extreme cases which can be termed as intermediate microfabric. This paper explores the formation of intermediate microfabric of kaolin clay and its impact on soil’s consolidation behaviour by performing self-weight consolidation, slurry consolidation and 1-D consolidation tests. The effect of calgon content (dispersing agent) on geometric arrangement of the particles has been evaluated through cluster size distribution by performing double hydrometer tests. Then these clay slurries have been used to perform the AFM (Atomic Force Microscopy) test to obtain the variation in average angle of particle orientation with respect to the calgon content present in the slurry. AFM technique provides 3D image of the clay sample and 2D image with Z-information with the potential of measuring intermediate microfabric of clayey soil quantitatively including dispersed and flocculated microfabrics. Other traditional techniques such as SEM, TEM & XRD are limited to only qualitative analysis of soil’s microfabric, thus, having no capability to measure intermediate microfabric of clay. A methodology of preparing bulk specimens of clay with intermediate microfabric has been developed using slurry consolidation technique; and then these specimens have been consolidated under 1-D loading to evaluate the effect of intermediate microfabric on compressibility and permeability of clay. In this study, all the experiments reports that the dispersed type geometric arrangement increases with the increase in calgon content in soil up to 2 % and then the reverse behaviour is observed at 3 %; which may depend on the required amount of sodium cations to neutralize the negatively charged faces of the clay platelets present in the slurry.

Clay fabrics in SAFOD core samples

With optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements, we analyzed clay microfabrics in ultracataclastic/gouge and cataclastic core samples obtained from the main bore hole of the San Andreas Fault observatory at depth (SAFOD). The analysis reveals a significant contrast between weak clay fabrics observed in the core samples with synchrotron X-ray fabric measurements and strong degree of preferred alignment for clay particles documented with the optical microscope. TEM and SEM observations also show distinct zones of locally aligned and randomly oriented clay minerals. The lack of a strong fabric may be attributed to randomly oriented matrix sheet silicates dominating the fault rocks. The presence of weak fabrics in intensely strained ultracataclasites/fault gouges is attributed to 1) newly formed clay minerals that grew in many orientations, 2) folded and kinked clay minerals, and 3) clay particles that are wrapped around grains. In addition, the locally aligned clay particles may act as barriers to fluid flow, which in turn decrease porosity, expel intergranular pore fluids, and consequently, may increase fluid pressure.

Stratigraphic and microfacies analysis of the Kaili Formation, a candidate GSSP for the Cambrian Series 2–Series 3 boundary

The Kaili Formation of South China is a ~ 200–300 m thick succession of fine-grained siliciclastic sediments with minor carbonates that spans the proposed Cambrian Series 2–Series 3 boundary interval, formerly the Early-Middle Cambrian boundary. It was deposited at low latitude on a slope lying between the Yangtze carbonate platform to the northwest and deep-water outer shelf facies of the Jiangnan Basin to the southeast. Because the Kaili Formation contains abundant and well-preserved fossils throughout, most importantly oryctocephalid trilobites that have a broad geographic distribution, and because it appears to be less condensed than other contemporaneous sections found on other paleocontinents, a section near Balang Village, Jianhe County, Guizhou Province, has been proposed as a candidate Global Stratotype Section and Point (GSSP) for the Cambrian Series 2–3 boundary. However, because the Kaili Formation is mudstone-dominated, it is not possible to determine from outcrop study whether a change in depositional regime or a condensed interval may be present around the proposed boundary. Because the proposed boundary interval coincides with the maximum flooding stage of a global transgression, it is possible that subtle, yet significant facies changes may occur within the mudstones that comprise the proposed boundary interval, rendering its utility as a potential GSSP questionable. Here, we present an analysis of a composite section of the complete Kaili Formation exposed along two ridges and in a road cut near Balang Village. The section was measured at the cm-scale and sampled every 1 m throughout the complete thickness of the unit, except where covered. Microfacies analysis of 138 samples, using thin sections, polished slabs, acetate peels, X-radiographs and scanning electron microscopy was conducted in the laboratory. These analyses confirm that depositional processes within the Kaili Formation were consistent and unshifting throughout complete thickness of the formation. Event-driven deposition was maintained across the Kaili Formation with no evidence for condensation present, even at the 5–20 μm scale. The signal of the global transgression in the boundary interval is manifest as a slight thinning of individual millimeter-scale event-deposited lamina from 50 to 55 m above the base of the formation, around the proposed GSSP boundary at 52.8 m. The entire Kaili Formation appears to have been deposited below storm wave base, as no silt-sized or coarser clastic particles are present, and no evidence of cross-bedding or graded bedding occurs within any of the facies present within it. The great majority of its thickness, including the entirety of the proposed boundary interval, is comprised of mm-laminated calcareous claystones that exhibit randomly oriented clay microfabrics characteristic of deposition from turbid suspension by sediment-gravity flows.

Burial Consolidation Processes of Deep-Sea Sediments: An Example of Core Sediments Collected from the Labrador Sea in the Northwest Atlantic

ABSTRACT Progressive change of microfabrics of deep-sea sediments during early diagenesis was analyzed using two drill cores collected from the Sites U1305 and U1306 of the Integrated Ocean Drilling Program Expedition 303 in the Labrador Sea in the northwest Atlantic Ocean. Microfabrics were analyzed by scanning electron microscope and deduced from anisotropy of magnetic susceptibility. Different microfabrics in three layers were distinguished in both cores: Surface layer with general void ratio >2.5, subjacent layer with void ratio 2.5-1.5, and deep layer with void ratio 2.5 and 2) change of clay microfabrics in the layer with the void ratio

Effect of Shear Deformation on Microfabric of Clay Using XRD Technique

The present paper deals with the impact of shear deformation on the geometric arrangement of particles within the soil specimen, which is termed as the microfabric of soil. A series of compression and extension lubricated end triaxial tests are performed on cylindrical specimens of Kaolinite clay with two extreme microfabrics; dispersed and flocculated, which are obtained using slurry consolidation technique. Flocculated microfabric has random orientation of particles within the soil mass having face-to-edge particle contacts; however, dispersed microfabric has parallel orientation of particles containing face-to-face particle contacts. When the specimen is subjected to large stress levels during its shear deformation, the particle orientation and the geometric arrangement within the soil specimen gets affected due to the force acting on the clay platelets. The variation in microfabric of soil before and after shear deformation process is evaluated by obtaining X-ray diffraction patterns of the clay specimen at three different locations using standard X-ray diffractometer. The discussion includes an analysis of the orientation of soil particles located at shear banding zones of the clay specimens, which may be useful for understanding the strain localization development in clays.

Variability of Physical and Consolidation Test Results for Relatively Uniform Clay Samples Retrieved from Osaka Bay

ABSTRACT Samples collected from both Holocene and Pleistocene layers in Osaka Bay were examined in this study. The objective of this study is to evaluate variations of soil parameters in a sample length of about one meter. The retrieved samples from EL. (elevation) -37.5 to -38.5 m and from EL.-125.5 to -126.5 m with a length of about one meter were divided into every 25 mm long to trim consolidation specimens. Variations of soil parameters obtained from laboratory tests were evaluated. Clay microfabric was also evaluated by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The clay layers are relatively homogeneous with variation coefficient CV in a range of 0.025 to 0.12 for the consolidation parameters (e, p′c, Cc and cv). CV of void ratio e is only 0.025 to 0.056. In contrast, CV values of the other consolidation parameters are significantly greater than this, but the average is less than 0.1. It can be concluded that CV of soil consolidation parameters for the homogeneous natural clay deposits dealt in this study is less than about 0.1. These variations are mainly influenced by sedimentary environment. Even the soil is said to be homogeneous, because the specimen size for the laboratory tests is sufficiently large in consideration of microscopic heterogeneity obtained from SEM and MIP.

Undrained cyclic behavior of bentonite–sand mixtures and factors affecting it

In this work, the cyclic behavior of bentonite–sand mixtures and factors affecting it were studied by means of a ring-shear apparatus and a scanning electron microscope. It was found that bentonite content had a significant influence on the liquefaction potential of the studied soils. A small amount of bentonite in the mixtures would cause the formation of “loose” microstructures, resulting in the occurrence of rapid liquefaction under cyclic loading, while a high bentonite content would cause the formation of clay matrixes, thus raising the soil resistance to liquefaction. In addition, the effect of pore water chemistry on the cyclic behavior of a high plasticity bentonite–sand mixture was carefully examined. It was also found that the presence of ions in pore water would change the clay microfabric, making it more open and thus more vulnerable to liquefaction. Finally, the effects of loading frequency on the cyclic behavior of mixtures with different amounts of bentonite were investigated. It was found that as the bentonite content increased, the influence became more pronounced.

Origin of Shale Fabric by Mechanical Compaction of Flocculated Clay: Evidence from the Upper Devonian Rhinestreet Shale, Western New York, U.S.A.

ABSTRACT Most workers attribute the preferred grain orientation that defines the shale fabric to the mechanical collapse of a high-porosity clay microfabric under increasing overburden pressure. Scanning electron microscope analysis of samples of the Upper Devonian (Frasnian) Rhinestreet shale of western New York State collected from near early diagenetic carbonate concretions provides further evidence of this mechanism. Specifically, mudstones recovered from pressure shadows immediately adjacent to lateral edges of concretions are characterized by an open fabric of randomly arranged clay domains--the cardhouse fabric. Laterally equivalent shale samples collected only 0.2 to 0.3 m distant the pressure shadows, however, reveal a low-porosity, strongly oriented shale fabric in which clay particles mold around incompressible quartz silt and euhedral pyrite grains and pyrite framboids. These observations suggest that the organic Rhinestreet shale accumulated as water-rich flocculated clay. The open clay fabric observed in pressure-shadow mudstones was preserved by the incompressible concretions during burial. Flocculated clay beyond the shielding effect of the concretions, however, collapsed during progressive burial to form the strongly oriented shale fabric.

Deformation structures in Plio- and Pleistocene sediments (NW Bohemia, Central Europe)

Abstract The small intracratonic Cheb (Eger) Basin in NW Bohemia (Central Europe) is characterized by swarm earthquakes, many mineral springs and mofettes with upper mantle CO 2 degassing and by neotectonic graben and basin structures. Especially in non-lithified Upper Pliocene clay formations of the basin, a variety of deformation patterns is exposed. They include non-tectonic and tectonic activity and comprise faulting and folding from µm- to km-scale. Previously unrecognized N-S- and ENE-striking faults are sites of mantle degassing and seismic activities. Confined-layer deformation and liquefaction structures hint to palaeoseismic events and gas escape activity. Cleavage-like arranged clay mineral plates represent the microfabric of clay within fault zones. For the first time the degassing channels of Upper Mantle fluids/gases through the Pliocene clay sediments can be documented: µm-scale micro-tubes were produced by the opening of Riedel shear planes induced by fault movements.

Evaluating Clay Microfabric Using Scanning Electron Microscopy and Digital Information Processing

Several aspects related to the qualitative and quantitative evaluation of clay microfabric are presented. A digital image processing technique called “intensity gradient analysis” is used in evaluating clay microfabric from scanning electron micrographs. Details are given of three computer programs (histogram.c, average.c and ellipse.c) that provide for the quantitative analysis of the orientation of clay particles. The important aspects related to sample and surface preparation, digital image acquisition, and analysis are explained. Two natural clays, Pennsylvanian fire clay and Pleistocene varved glacial lake clay, considered in the analysis show well-defined preferred and random fabric. The polar histograms of the intensity gradient analysis for the two clays are compared at varying magnifications, and conclusions were drawn. The output data was conveniently reduced to a few parameters that indicate the strength and magnitude of a given orientation. The concept of fabric index is used to quantitatively describe the preferential or randomness of clay microfabric. A simple scheme is proposed by which clay microfabric is classified as preferred when the fabric index is less than a value of 0.75 and random otherwise. The advantages of the signal intensity gradient method are that it is based on intensity changes rather than absolute values, the rosette diagrams of several micrographs can simply be added to get an overall idea, and it provides a common frame of reference for description of microfabric. The disadvantages are that it requires careful surface preparation, and the technique is valid for linear features. With the advent of inexpensive and powerful image processing tools, the technique has the potential to become a routine tool for the orientation analysis of clay micrographs seen in scanning electron microscopy.

Evaluating Clay Microfabric Using Scanning Electron Microscopy and Digital Information Processing

Several aspects related to the qualitative and quantitative evaluation of clay microfabric are presented. A digital image processing technique called gradient is used in evaluating clay micro-fabric from scanning electron micrographs. Details are given of three computer programs (histogram.c, average.c and ellipse.c) that provide for the quantitative analysis of the orientation of clay particles. The important aspects related to sample and surface preparation, digital image acquisition, and analysis are explained. Two natural clays, Pennsylvanian fire clay and Pleistocene varved glacial lake clay, considered in the analysis show well-defined preferred and random fabric. The polar histograms of the intensity gradient analysis for the two clays are compared at varying magnifications, and conclusions were drawn. The output data was conveniently reduced to a few parameters that indicate the strength and magnitude of a given orientation. The concept of fabric index is used to quantitativel...

Microstructural modeling of clay sediments in Eckernfoerde Bay

A finite-element microstructure analysis code was used to model the geoacoustic properties of shallow marine clay sediments in Eckernfoerde Bay which has been the subject of an intensive geoacoustic and geotechnical study (Coastal Benthic Boundary Layer—Special Research Program). Uniaxial strain and pure shear were applied to two-phase microstructure models with generalized, periodic plane-strain boundary conditions to generate anisotropic bulk and shear moduli. Analyses were carried out on two length scales: clay microfabric (μm) and gas-filled inclusions (mm). The clay microstructure was modeled as a random lattice of Illite platelets with a density and porosity equivalent to average values observed in shallow Eckernfoerde Bay sediments. Saturated and dry framework moduli were calculated and the effective medium velocities were compared with observed velocities. The analysis suggests that shear wave propagation in these sediments is not supported by the framework structure but by differential compression of fluid-filled pores. Radiographic images of pressurized cores containing gas-filled inclusions with dimensions of a few millimeters were also analyzed. The analysis indicates a shear wave velocity anomaly related to the inclusion structure. The calculated effective medium velocities are compared with analytical models of spheroidal inclusions. [Work supported by ONR.]

The Progression from Optical Light Microscopy to Transmission Electron Microscopy in the Study of Soils

AbstractThe use of electron microscopy to study clay microfabrics in thin-sections is discussed. A technique is described to isolate undisturbed microparts of pedofeatures from thin-sections, which are subsequently used for TEM analysis. Re-embedding with a polyester resin of undisturbed, in situ, neoformed clay microfabrics, obtained by microdrilling and preparation of ultrathin sections by microtoming with a diamond knife are emphasized; these steps enable micromorphology, clay mineralogy, microchemical and HRTEM analysis to be performed on one unique microsample of clay fabrics, with conserved micro-organization. Two examples on clay neoformation are presented to demonstrate that this technique can successfully be applied to unravel the impact of mineral alteration and clay neoformation in undisturbed soil samples on a micro- and a nanometer scale.

The role of roots, fungi and bacteria on clay particle organization. An experimental approach

Experimental studies were conducted to investigate the role of different living organisms (roots, fungi, bacteria) on clay microfabric. For this purpose various microorganisms (bacteria, fungi) and roots were allowed to grow on kaolinite or montmorillonite pastes under controlled hydric conditions (−0.01 to −10 2 MPa). Microstructures were studied with a cold-stage SEM, that allowed the preservation of the organizations that characterized the wet states. With fungi, three main effects were observed in moist conditions: orientation of clay particles around the cells; secretion of extracellular polysaccharides that induced local binding of clay particles, and a general packing effect by hyphae. These effects lead to a new microstructure, in the immediate surrounding of the cell, designated as a microenvironment. A modified microstructure was recognized with all species, the size depending on the size of organism. With bacteria, polysaccharide-mediated aggregation was predominant. With grass roots, modifications of the microstructure were more complex than with fungi and occurred at a larger scale. The present results thereby confirm and complete the existing models on biologically mediated aggregation in soils.

Automatic X-ray analysis of clay microfabrics : Borokina, MM Centr. Scient. Res. Inst. Metall. Moscow, SU Osipov, VI Centr. Scient. Res. Inst. Metall. Moscow, SU Internat. Symp. on Soil Structure, Gothenburg, 1973. 2F, 9R. Swedish Geotechnical Society, Stockholm, 1973, P15–20

Automatic X-ray analysis of clay microfabrics : Borokina, MM Centr. Scient. Res. Inst. Metall. Moscow, SU Osipov, VI Centr. Scient. Res. Inst. Metall. Moscow, SU Internat. Symp. on Soil Structure, Gothenburg, 1973. 2F, 9R. Swedish Geotechnical Society, Stockholm, 1973, P15–20