Xanthan biopolymer-based soil treatment effect on kaolinite clay fabric and structure using XRD analysis.

In this study, we evaluated the impact of xanthan gum biopolymer (XG) on kaolinite fabrics using X-ray diffraction (XRD) and the ensuing changes in the compaction behavior and shear resistance of kaolinite soils. The XRD peak analysis revealed that XG changed kaolinite fabrics into face-to-face associations. Moreover, environmental scanning electron microscopy showed the formation of XG-bridges between kaolinite particles, resulting in the change in fabrics and subsequently improving the resistance of kaolinite to external forces. Consequently, as XG content increased, the maximum dry density decreased, and the undrained shear strength increased. The viscous XG hydrogels produced a higher optimal moisture content and increased resistance to shear force. This study showed that XG affects the mechanical properties of kaolinite through changing kaolinite fabrics (up to 0.5% of the XG-to-kaolinite mass ratio) and absorbing pore-fluids (excess XG over 0.5% of the XG-to-kaolinite mass ratio).

Durability and strength degradation of xanthan gum based biopolymer treated soil subjected to severe weathering cycles.

Biopolymer-based soil treatments have shown effectiveness in soil improvement, with successful field-scale implementation. In this study, we explored the effect of cyclic wetting-drying (W-D) and freezing-thawing (F-T) on the strength durability of biopolymer-treated soils. The results indicate that cyclic W-D and F-T gradually degrade soil strength owing to water adsorption and local biopolymer dilution. Poorly graded sand was highly vulnerable to these weathering effects; however, this problem was mitigated when the soil contained a fines content of 15-25%. These biopolymer-treated soils effectively resisted numerous cycles of both W-D and F-T, indicating that biopolymer-treated soils are suitable for earthen slope reinforcement.

Effects of Gouge Fill on Elastic Wave Propagation in Equivalent Continuum Jointed Rock Mass.

The presence of gouge in rock joints significantly affects the physical and mechanical properties of the host rock mass. Wave-based exploration techniques have been widely used to investigate the effects of gouge fill on rock mass properties. Previous research on wave propagation in gouge-filled joints focused on analytical and theoretical methods. The lack of experimental methods for multiple rock joint systems, however, has limited the verification potential of the proposed models. In this study, the effects of gouge material and thickness on wave propagation in equivalent continuum jointed rocks are investigated using a quasi-static resonant column test. Gouge-filled rock specimens are simulated using stacked granite rock discs. Sand and clay gouge fills of 2 and 5 mm thicknesses are tested to investigate the effects of gouge material and thickness. Comprehensive analyses of the effects of gouge thickness are conducted using homogeneous isotropic acetal gouge fills of known thickness. The results show that gouge fill leads to changes in wave velocity, which depend on the characteristics of the gouge fill. The results also show that particulate soil gouge is susceptible to preloading effects that cause permanent changes in the soil fabric and contact geometry and that increased gouge thickness causes a more significant stiffness contribution of the gouge material properties to the overall stiffness of the equivalent continuum specimen. The normal and shear joint stiffnesses for different gouge fill conditions are calculated from the experimental results using the equivalent continuum model and suggested as input parameters for numerical analysis.

Electrical Resistivity Measurement with Spherical-Tipped Cylindrical Electrode Embedded on Two Layers.

Complex geological processes form multiple layers and change pore water chemistry, saturation level, and temperature. Eventually, the strata hinder interpreting electrical resistivity data. There are no studies that theoretically explore the effects of electrode geometries and multiple layered systems on laboratory electrical resistivity measurements. This study formulates a theoretical electrical resistance between half spherical-tipped cylindrical electrodes embedded on two horizontal layers. The electrical resistivity of each layer is considered separately in the general electrical potential equation with different equipotential surface areas. The finite element analysis is conducted to validate the theoretical equation. Further interpretation provides insights into the distribution of electrical current flow under electrical resistivity mismatch for discussion.

Experimental Characterization of Stress- and Strain-Dependent Stiffness in Grouted Rock Masses.

Grouting of fractured rock mass prior to excavation results in grout-filled discontinuities that govern the deformation characteristics of a site. The influence of joint characteristics on the properties of grouted rocks is important in assessing the effects of grouting on jointed rock mass. However, grouting remains a predominantly empirical practice and the effects of grouting on rock joint behavior and material properties have yet to be accurately assessed. Granular materials, including jointed rocks, typically display nonlinear strain-dependent responses that can be characterized by the shear modulus degradation curve. In this study, the effects of grouting on the strain-dependent shear stiffness of jointed rock mass were investigated at the small-strain (below 10-5) and mid-strain (10-5 to 10-3) ranges using the quasi-static resonant column test and rock mass dynamic test devices. The effects of curing time, axial stress, initial joint roughness, and grouted joint thickness were examined. The results show that (1) grouting of rock joints leads to decreased stress sensitivity and increased small-strain shear stiffness for all tested samples; (2) the grouted rock samples display similar modulus degradation characteristics as the applied grout material; (3) the initial joint roughness determines the stress-dependent behaviors and general stiffness range of the jointed and grouted rocks, but the strain-dependent behaviors are dependent on the properties of the grout material; (4) increased grouted joint thickness results in larger contribution of the grout properties in the overall grouted rock mass.

Dissociation behavior of CO2 hydrate in sediments during isochoric heating.

As CO2 is sequestered into sediments in the oceanic environment, CO2 hydrate can form as a byproduct. This study explored the dissociation behavior of CO2 hydrate in sediments in relation to pore fluid pressure evolution and sediment particle size. We synthesized CO2 hydrate in three types of particulate sediments: glass beads, fine sand, and crushed silt. We then dissociated them through isochoric heating. We observed the excess pore fluid pressure build-up and self-preservation behavior, in which the pressure-temperature state evolves along the hydrate phase boundary until either it reaches the second quadruple point or all hydrates dissociate. The pore fluid pressure evolution is limited, however, by the CO2 vapor-liquid phase equilibrium boundary due to the liquefaction of CO2. The presence of CO2 liquid in sediments forces the pressure-temperature evolution to follow the CO2 vapor-liquid phase equilibrium boundary, regardless of hydrate formation and dissociation processes. CO2 hydrate in fine-grained sediments experiences capillary pressure-induced melting point depression, but this effect vanishes when the pores exceed approximately 1 microm, such as in coarse-grained sediments. In particular, any fracture generation in sediments which involves the local release of confinement eliminates the melting point depression induced by the capillary effect.