Evaluation of the internal stability of well-graded silty sand through the long-term seepage test

Suffusion is the phenomenon responsible for internal erosion, and is the process by which finer soil particles are moved through the constrictions between the larger soil particles by seepage forces. Generally, gap-graded soil is known to be susceptible to suffusion. Meanwhile, suffusion of well-graded silty sand and the resulting soil behavior are not well understood. Moreover, the previous researches on laboratory suffusion tests focused on the study of the critical hydraulic gradient, which triggers the internal instability of the soils within a short period of time. Therefore, in this study, long-term suffusion tests were conducted on well-graded silty sand under a hydraulic gradient lower than the critical value. As a result, abrupt increases in permeability and amount of soil discharged were observed due to the progressive migration of the soil particles, resulting in suffusion even at a relatively low hydraulic gradient

Assessing the internal erosion sensitivity of earth-fill-dam soils based on the phenomena of suffusion and suffosion

© 2022, The Author(s), under exclusive licence to Springer Nature B.V.Suffusion and suffosion are the process of internal instability which involves the migration of finer soil particles by the seepage forces, and it is known as a major cause of dam failures. Internal instability of the soils has been studied by a number of researchers, and through the laboratory seepage tests, criteria on grain size distribution to evaluate the internal stability were suggested. Seepage tests conducted by early researchers, however, are different in terms of the details, fine contents, relative density of the soils, applied hydraulic gradients and boundary conditions (filter system). Such discrepancies can lead to a problem of applicability of existing criteria on fill-dams. Therefore, in this study, laboratory seepage tests were conducted on fill-dam materials in Korea with the consideration of various testing conditions, and based on the test results, potential behavior of internal instability was evaluated. Test results showed that the soils with small fraction of fines (10%, passing sieve no. 200) are susceptible to suffusion. On the other hand, soils with significant amount of fine contents (40%) are vulnerable to suffosion, and it is dependent on the relative density. Thus, the susceptibility of fill-dam materials in Korea to internal erosion is highly affected by the fines and relative density of the soils.N

Effect of directional stress history on anisotropy of initial stiffness of cohesive soils measured by bender element tests

This paper describes the initial stiffness of reconstituted kaolinite clay in both vertical and horizontal planes under three different stress histories. The initial shear stiffness was obtained from bi-directional bender element tests during isotropic and K 0 stress loading and unloading. An empirical correlation was established based on the initial stiffness of normally consolidated soils. Unlike the unique relationship of the initial vertical stiffness of normally consolidated clays, the initial stiffness in the horizontal plane is dependent on the stress ratio and previous stress history; thus, three different relationships of the initial horizontal stiffness were obtained for the three loading programs. The effect of the stress history on the initial horizontal stiffness can be considered properly by defining the degree of overconsolidation in terms of the horizontal effective stress. The change in the initial stiffness has a directional dependency on the stress history in the direction of the particle motion and wave propagation in the bender element tests.Link_to_subscribed_fulltex

Association between Metabolic Syndrome and the Number of Remaining Teeth in Postmenopausal Women: A Cross-Sectional Analysis Using the Korean National Health and Nutritional Examination Survey

There are very few studies on metabolic syndrome (MetS) and oral health in postmenopausal women. The purpose of this cross-sectional study was to determine the association between MetS and its components and the number of remaining teeth in postmenopausal women in Korea. The study selected 3320 menopausal women (40–79 years old) from those who participated in the seventh Korea National Health and Nutrition Survey (2016–2018). Multiple regression and multiple logistic regression analyses were performed to determine the association between MetS and its components and the number of remaining teeth. According to the multiple regression analysis, the regression coefficient (B) values were −1.62 (p < 0.05), −1.31 (p < 0.05), −1.60 (p < 0.05), and −2.28 (p < 0.05) in the hypertension group, hyperglycemia group, low high-density lipoprotein (HDL) cholesterol group, and MetS prevalence group, respectively. This indicates that the number of remaining teeth was lower in the MetS prevalence group as compared to the non-prevalence groups. As observed in the multiple logistic regression analysis, the odds ratio of the number of remaining teeth (less than 20) was higher in the MetS prevalence group (1.82 (p < 0.05)) as compared to the non-prevalence groups (1.25 (p < 0.05) in the abdominal obesity group, 1.50 (p < 0.05) in the hypertension group, 1.36 (p <0.05) in the hyperglycemia group, and 1.72 (p < 0.05) in the low HDL cholesterol group). Therefore, our results indicate that abdominal obesity, hypertension, diabetes, dyslipidemia, and prevalence of MetS are associated with tooth loss in postmenopausal women

Hydraulic Conductivity Variation of Coarse-Fine Soil Mixture upon Mixing Ratio

This paper presents the theoretical and experimental investigations of the hydraulic conductivity variation of the soil mixture that contains two distinct particle size distributions, coarse and fine soils. A new model for the hydraulic conductivity is introduced that focuses on the relationship between the coarse-fine soil mixing ratio and the hydraulic conductivity of the mixture. For the model verification, permeability tests were conducted. The glass beads and quality-controlled standard sand and soils obtained from fields were used for the specimen. The experiment results showed that the hydraulic conductivity of the soil mixture strongly depends on the mixing ratio. As the amount of the coarse soil contained in the fine soil increased, the hydraulic conductivity of the mixture decreased from that for the fine soil until the critical mixing ratio. This ratio is defined as the fine soils perfectly fill the voids between the coarse soils without remains. When the ratio is greater than the critical mixing ratio, the hydraulic conductivity is drastically increased with the mixing ratio up to that of the coarse soil. The comparison between the computed values and the test results shows that the introduced model successfully describes the measurements

Patterns of Nonlinear Shear Stiffness Degradation of Reconstituted Clay with Different Stress Histories

This paper describes patterns of nonlinear shear stiffness degradation with respect to the stress history of clay. An experimental study using undrained triaxial compression tests was conducted on specimens cut from reconstituted clay samples of kaolinite. The nonlinear pattern of stiffness degradation was analyzed within the frameworks of both the conventional overconsolidation ratio (OCR) and the stress path rotation angle. The experimental data were subsequently interpreted based on the concept of the kinematic sub-yield surface. The pattern of stiffness degradation is more relevant to the rotation angle of the current stress path than the OCR value. The sizes of the sub-yield surfaces are variable. Results show that the kinematic movements of sub-yield surfaces within the overall bounding surface may provide an insufficient tool to fully describe the pattern of stiffness degradation. © 2013 Copyright Taylor and Francis Group, LLC.Link_to_subscribed_fulltex

Effect of pre-shear stress path on nonlinear shear stiffness degradation of cohesive soils

The nonlinear degradation of soil stiffness from very small to small strain is a key consideration for reliable prediction of ground behavior and its interactions with structures under dynamic excitation and working load conditions. Despite high sensitiveness of stiffness measurement to testing conditions, the effect of the pre-shear stress path on the stiffness degradation has not been properly discussed. Here we investigate the effect of pre-shear stress path on nonlinear shear stiffness degradation of cohesive soils. Reconstituted kaolinite specimens were consolidated to be the overconsolidation ratio (OCR)=1, 2, and 4 along K 0 and isotropic stress paths. The shear stiffness degradations of the specimens during undrained shear were measured using on-specimen linear variable differential transformers (LVDTs). Experimental results show that the pre-stress stress path has a strong influence on the degree of shear stiffness degradation at different OCRs. This influence is interpreted within the context of the rotation angle of shear stress path, which provides a good qualitative explanation of the inconsistent observations in the literature. Copyright © 2013 by ASTM International.Link_to_subscribed_fulltex

Experimental Study on Relationship Between Critical State Line and Zero Creep Volume Change Zone in Engineered Silty Sand

Volume change during creep is one of the important factors to explain various time-dependent problems such as the pile set-up effect. Park [1] and Park et al. [2] experimentally measured creep volume characteristics under various stress conditions using engineered silty sand obtained from weathered granite soil in Korea. They found that a zero-creep volume change zone (ZCVZ) exists on the e-log p' plane. If the void ratios at the beginning of the creep are above the ZCVZ on the e-log p' plane, the volume decreases during creep; if they are below the ZCVZ, the volume increases during creep. In this study, a series of simple critical state (CS) tests which can simply determine the critical state parameters in sandy soils were performed to estimate the critical state line (CSL) and compared with ZCVZ. In addition, the CSL obtained using the method proposed by Santamarina and Cho [3] was compared with those obtained by the triaxial test. The CSL for Jumunjin sand and engineered silty sand is close to ZCVZ. Therefore, the CSL can be used as a reference line to determine the volume change pattern by creep