Clays pore-water characterization

The alluvial and fluvial strata were flooded by meteoric pore water and got cemented prior to faulting. While clay smear and intergranual shear fractures dominate in fine-grained and poorly cemented intervals (Fig. 7a), well cemented intervals cut by faults display fault gouges characterized by brecciation and granulation (Fig. 7b). Within these (brittle) fault... 

Recent advances in the formulation of nonlinear hysteretic soil relationships for soils and the characterization of stiffness degradation for saturated sands and clays have required ever more explicit determinations of soil properties such as the shape of the stress-strain relationship and the nature of pore water buildup. 

Because of their low permeability, flowing groundwaters cannot generally be obtained from clays and mudrocks. Although fracture flows can frequently be induced from crystalline formations, the frequency of features such as open fractures that conduct water flow is normally limited. To evaluate the chemistry within geological and engineered barriers it is necessary, therefore, to characterize matrix pore-waters obtained using speciaUzed extraction techniques. 

The choice of porous media as a model system is dependent on conditions, i.e., a well characterized pore size distribution and surface details. Among the hydrophilic model systems where the structure of confined water has been studied by neutron diffraction, let us mention clay minerals [11,12] and various types of... 

Water in well-characterized pores is a system of general interest because it serves as model system for the non-bulk or inhomogeneous water that is ubiquitous in biological and geological systems, as well as in nano-sfructured materials. Often confined or interfacial water is highly relevant to the properties and functions of entire systems, e.g., those in ion channels and clay minerals. X-ray diffraction studies show that water can fill the inner space of open-ended single-walled carbon nanotubes (SWCNTs) under ambient conditions and freezes into crystalline solids. These are often referred to as ice nanotubes . Ice stmctures in confined systems are characterized as stacked n-membered rings or equivalently as a rolled square-net sheet. The formation of the ice nanotubes in CNTs has also been observed by NMR, neutron diffraction, and vibrational spectroscopy studies. 

The choice of porous media as model systems is dependent on the conditions a well-characterized pore size distribution and surface details. Among the hydrophilic model systems where the structure of confined water has been studied by neutron diffraction, let us mention clay minerals [11,12] and various types of porous silica [14-22]. In the last case, the authors have interpreted their results in terms of a thin layer of surface water with more extensive H-bonding, lower density and mobility, and lower nucleation temperature as compared to bulk water. Recently the structure of water confined in the cylindrical pores of MCM-41 zeolites with two different pore sizes (21 A and 28 A) has been studied by x-ray diffraction [21] over a temperature range of 223-298 K. For the capillary-condensed samples, there is a tendency to form a more tetrahedral-like hydrogen-bonded water structure at subzero temperatures in both pore sizes. 

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