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.
This open access book provides an overview of the progress in landslide research and technology and is part of a book series of the International Consortium on Landslides (ICL). The book provides a ...common platform for the publication of recent progress in landslide research and technology for practical applications and the benefit for the society contributing to the Kyoto Landslide Commitment 2020, which is expected to continue up to 2030 and even beyond to globally promote the understanding and reduction of landslide disaster risk, as well as to address the 2030 Agenda Sustainable Development Goals.
This open access book provides an overview of the progress in landslide research and technology and is part of a book series of the International Consortium on Landslides (ICL). The book provides a ...common platform for the publication of recent progress in landslide research and technology for practical applications and the benefit for the society contributing to the Kyoto Landslide Commitment 2020, which is expected to continue up to 2030 and even beyond to globally promote the understanding and reduction of landslide disaster risk, as well as to address the 2030 Agenda Sustainable Development Goals.
This open access book provides an overview of the progress in landslide research and technology and is part of a book series of the International Consortium on Landslides (ICL). It gives an overview ...of recent progress in landslide research and technology for practical applications and the benefit for the society contributing to understanding and reducing landslide disaster risk.
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.
