AbstractCompressibility of a soil mass is among the most important geotechnical properties that is widely used during the design of geotechnical structures. Various regression equations have been ...proposed by numerous researchers in the past to estimate the compression index of a soil specimen with parameters such as void ratio at liquid limit, initial void ratio, liquid limit, or the combination of the specific gravity, void ratio, and liquid limit. Although all researchers concur that the compression index depends on the mineralogical composition of the soil and initial moisture content, very little research has been performed on the mixtures of minerals composing a wide range of activities under consistent initial moisture contents. This research is conducted on 55 different soil specimens prepared in the laboratory by mixing various proportions of montmorillonite, illite, kaolinite, and quartz at initial moisture contents equal to the liquid limit. The intrinsic compression line (ICL) was unique for most of the mixtures used for this study. Very good regressions were obtained between the compression index and initial void ratio, initial porosity, plasticity index, or liquid limit. Two different equations were proposed to estimate the compression indices of remolded clays with liquid limit—one for soils with activities less than one and the other for soils with activities greater than one. The compression indices of 82 different natural samples, reconstituted at liquid limit, were similar to the values estimated with the proposed equations. Furthermore, the compression indices of the soil samples presented in the literature could also be estimated with reasonable accuracy using the proposed equations.
Global warming is causing unprecedented changes to permafrost regions with amplified effects in the Arctic through a phenomenon known as Arctic amplification. This intensified climate warming thaws ...both the discontinuous and continuous permafrost resulting in changes in the mechanical properties of the soils found in these regions. Since permafrost regions constitute nearly 24% of the Northern Hemisphere, understanding the strength of soils in thawed conditions is essential to analyze the stability of existing structures, and to design safer and more economical infrastructure in these regions. Specifically, thawing of the permafrost is causing considerable reductions in its strength of soils, which may lead to massive landslides, foundation failures, and so forth. Since frozen soil is a multiphase structure that consists of soil particles, unfrozen water, ice, and air, each constituent will influence the mechanical properties. This paper reviews the current state of knowledge of the impact of temperature, volumetric ice content, unfrozen water content, and frozen density on the compressive strength, peak shear strength, residual shear strength, undrained shear strength, and tensile strength of soils. The undrained shear strength of soil is said to have a linear correlation with temperature. In addition, the undrained cohesion of soil was found to depend on the temperature, whereas the undrained friction angle of soil was significantly influenced by volumetric ice content. An increase in the volumetric ice content up to 80% to 90% will cause a reduction in the peak and residual deviatoric stresses. In addition, an increase in volumetric ice content resulted in an increase in the compressive strength of the soil. The tensile and compressive strengths were found to be functions of the unfrozen water content.
Core engineering concepts defined with mathematical formulas and diagrams that will support an engineer in courses throughout their student years, as a refresher before certification testing, and as ...a handy reference throughout a professional career. Precise coverage and easy access makes this a valuable six pages in an immensely critical field of study and application. 6 page guide includes:Statics: Vectors, Forces, Moments, Equilibrium, Centroids, Distributed Loads, Centers of Mass, Moments of InertiaDynamics: Particle Kinematics, Particle Kinetics, Energy & Momentum Methods, Kinetics of Rigid Bodies, Plane Motion, Three Dimensional KineticsMechanics of Materials: Intro, Static Failure Theories, Variable Loading Failure Theories, Torsion, Beams, ColumnsFluid Mechanics: Intro, One Dimensional Flows, Steady Incompressible Flow Through Pipes or Conduits, Impulse & Momentum, Multipath Pipelines, Flow in Open Channels, Measurements
AbstractLandslides and slope failures in natural clay-rich materials are frequently observed in coastal areas and other areas where these materials were deposited in a saline water environment. High ...sodium chloride (NaCl) concentration in the pore fluid results from deposition in this environment. As shown by the results of this study, subsequent reduction in the NaCl concentration results in reduction in fully softened shear strength, with potentially significant reduction in slope stability. Fourteen sample materials were collected from seven different landslide areas in Niigata Prefecture, Japan, to evaluate the effect of saline water on fully softened shear strength (FSSS). The sample materials were collected from the intact mudstones and the sliding surface materials. Pore waters from the powdered sliding surface materials exhibited low concentrations of NaCl; however, the pore waters in the powdered intact rock samples exhibited a high concentration of NaCl. Washing of NaCl from the powdered intact rock samples caused a significant drop in FSSS, whereas mixing the sliding surface materials with NaCl at 0.5-M concentration increased the FSSS of the samples significantly. To evaluate the effect of saline water on various types of clay minerals, 12 samples—nine with montmorillonite as the clay mineral and three with kaolinite as the clay mineral—were prepared in the laboratory, and Atterberg limits and FSSS of these mineral mixtures were measured. There was a significant increase in the FSSS when the mineral mixtures with more than 9.5% montmorillonite were tested with saline water. The effect was negligible or negative for mineral mixtures having 9.5% or less montmorillonite content and any amount of kaolinite. An excellent correlation was observed between the liquid limits, plasticity indexes, and corresponding fully softened friction angles irrespective of the type of pore water. Likewise, there was a good correlation between the ratios of the liquid limits and plasticity indexes measured with different pore waters and the corresponding ratios of the fully softened shear strengths. It was observed that the reduction in FSSS of powdered intact rock with NaCl leaching could reduce the calculated factor of safety of the landslides by more than 0.3, demonstrating the negative effect of NaCl leaching from the slope materials on the stability of slopes.
It has been recommended to use “fully softened shear strength” while conducting slope stability analysis of first time slides. Studies pertaining to the influence of the mineral composition of a soil ...mass on the residual shear strength are available in the literature. However, very limited studies are available regarding the effect of clay mineralogy on the fully softened shear strength. This study addresses the effect of mineral composition of a soil mass on the fully softened shear strength and provides correlations between the geotechnical properties of different clay minerals and the fully softened shear strength. In order to accomplish this, thirty six samples were prepared in the laboratory from different pre-defined mixtures of montmorillonite, kaolinite and quartz. The index properties as well as the fully softened friction angles of these mixtures were measured. The fully softened friction angle was largely dependent on the dominating clay mineral and contained good correlations with the clay content, the liquid limit, and the plasticity index. The difference between the fully softened and residual shear strength was normalized, individually with: i) the fully softened friction angle, and ii) the residual friction angle. These values were then related to the corresponding liquid limits and plasticity indices. Using the mineralogical information as well as the fully softened friction angles obtained, a triangular correlation chart was developed by plotting at two sides of the triangle the proportions of montmorillonite and kaolinite, and the third side with the proportions of quartz plus other minerals. The fully softened friction angle was used to develop contours of the fully softened friction angle for various proportions of constituent minerals. These correlations were then verified with the results of the fully softened friction angles of more than eighty natural specimens demonstrating good agreement with the estimated friction angles.
► Information on the fully softened shear strength (FSSS) of soil. ► Even small proportions of montmorillonite increase the plasticity & reduce the FSSS. ► The FSSS can be estimated if the proportion of each clay mineral is known. ► If the mineralogical composition is unknown, the plasticity index can be used to estimate the FSSS. ► The residual shear strength of a soil with known FSSS can be estimated from the plasticity.
AbstractTo evaluate the effect of plasticity characteristics and mineralogical composition on postcyclic shear strength degradation, 18 soils, prepared as different proportions of kaolinite, ...montmorillonite, and ground quartz, were characterized using static simple shear and cyclic simple shear tests with postcyclic monotonic loading. The postcyclic undrained strength ratio (su,pc/σc′) was found to depend on the clay mineral, plasticity index (PI), and cyclic stress ratio. In soils with kaolinite as the clay mineral, a greater reduction in shear strength due to cyclic loading was noted at lower PIs, whereas soils with montmorillonite as the clay mineral typically experienced reductions between 0% and 30% of the static undrained shear strength. A relationship was established between degradation in undrained shear strength and postcyclic effective stress ratio (PC-ESR), which is the ratio of the consolidation stress to the effective vertical stress after cyclic loading and is equivalent to the reciprocal of the difference between the pore pressure ratio and one. A linear relationship between the ratio of su,pc/σpc′ (where σpc′ is the effective vertical stress immediately after cyclic loading) and the undrained strength ratio (su/σc′) of a normally consolidated soil and PC-ESR was also developed. Results from nine natural soils showed good agreement with the relationships developed for mineral mixtures.
One of the most important geotechnical properties of a soil mass is compressibility. Compressibility is widely used in the design of the geotechnical structures including but not limited to ...foundations, embankments, dams and landfills. Previously, various researchers proposed numerous equations to estimate the compression index of a soil mass with other soil properties such as liquid limit, initial void ratio, void ratio at liquid limit, specific gravity or a combination of the above parameters. Almost every article in the literature concluded that the mineral composition and initial moisture content greatly influence the compression index of a soil mass. However, little research has been done on the compression index under an environment of controlled mineralogy and initial moisture content. Fifty-five different soil specimens composed of mixtures of montmorillonite, kaolinite, illite and quartz were prepared in the laboratory at an initial moisture content equal to their corresponding liquid limits. The results showed that the Intrinsic Compression Line (ICL) was unique for each dominating clay mineral. Furthermore, the compression index and swelling index exhibited good correlations with the initial void ratio, the liquid limit, and the plasticity index. Equations were proposed to estimate the compression and the swelling index of a soil mass using the liquid limit. The compression and the swelling indices for eighty-two natural specimens were estimated using the proposed equations and were found to be similar to the measured values. Moreover, triangular correlation charts relating the mineral composition to the compression index as well as the swelling index were developed to estimate the compression and the swelling indices of a soil mass.
► Slope of Intrinsic Compression Line for a dominating mineral is unique. ► Compressibility behavior of kaolinite and illite dominated soils are similar. ► Proportion of montmorillonite significantly controls the compressibility of soil. ► Compression and swelling indices of soil can be estimated with mineral composition. ► Compression and swelling indices of soil can also be estimated with plasticity data.
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7.8 2015 Gorkha earthquake and its aftershocks significantly impacted the lives and economy of Nepal. The consequences of landslides included fatalities, property losses, blockades of river ...flow, and damage to infrastructural systems. Co-seismic landslides triggered by this earthquake were significantly widespread and pose a major geodisaster. There were tens of thousands of landslides triggered by the earthquake, majority of which were distributed in between the epicenter of the main shock and the
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7.3 aftershock. Although 14,670 landslides triggered by this earthquake were identified, only approximately 23% of them were of moderate to large scale with areas greater than 100 m
2
. Of the moderate- to large-scale landslides identified, just over 90% were triggered by the main shock and smaller aftershocks prior to the major (
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7.3) aftershock, while nearly 10% were triggered by the ground shaking induced by the major aftershock. Moreover, the number of landslides triggered by the 2015 Gorkha earthquake, specifically by the main shock, was slightly more than the expected number of landslides for the recorded maximum peak ground acceleration (PGA) in comparison to the co-seismic landslides triggered by 26 earthquakes. Over 90% of those moderate- to large-scale landslides were concentrated within the estimated fault rupture surface. Majority of these moderate- to large-scale landslides were disrupted failures with over 96% of which were classified as earth falls. However, the majority of small-scale landslides were rock or boulder falls. The most number of moderate- to large-scale landslides were triggered in the slate, shale, siltstone, phyllite, and schist of the Lesser Himalayan formation followed by an equally significant number in both schist, gneiss, etc. of the Higher Himalayan formation and the phyllite, metasandstone, schist, etc. of the Lesser Himalayan formation. The sizes (i.e., areas) of the landslides were lognormally distributed, with a mode area of 322.0 m
2
. Slope inclinations of the moderate- to large-scale landslides followed a normal distribution with a mean slope inclination of 32.6° and standard deviation of 13.5°. There exists a strong correlation between the number of landslides and the peak ground acceleration within the study area, specific for different geological formations.
Failures initiated in clay layers during recent earthquakes have emphasized the need to understand the cyclic behavior of clays. To systematically study the cyclic behavior, seventeen soils, prepared ...as mixtures of kaolinite and montmorillonite with quartz, and twelve natural soils were tested in a cyclic simple shear device. Cyclic strength curves were developed for 2.5%, 5% and 10% double amplitude shear strains. These curves were used to examine the influence of mineralogical composition, plasticity characteristics and shear strain on the cyclic resistance of the mixtures. A power function was used to represent the cyclic strength curves. Based on the results of this study, the mixtures were found to become increasingly resistant to cyclic loading as the plasticity index increased. Moreover, the soils with montmorillonite as the clay mineral were noted to have consistently higher cyclic resistance than the soils with kaolinite as the clay mineral. By examining the power functions, it was found that the cyclic strength curve became increasing flatter as the plasticity index increases in soils having kaolinite as the clay mineral. However, the opposite trend is observed in soils having montmorillonite as the clay mineral. The results presented in the literature for 37 soils were compared with those obtained in this study and found to be in good agreement.
•17 mineral mixtures were tested in a cyclic simple shear to study their cyclic behavior.•Cyclic strength curves at different double amplitude shear strains are presented.•Soils were increasingly resistant to cyclic loading as plasticity index increased.•Greater cyclic resistance in soils containing montmorillonite instead of kaolinite.•Curvature of cyclic strength curve depends on mineralogical composition of soils.
