Application of unsaturated shear strength properties in slope stability analysis

It is very important to study applications of unsaturated soil properties in slope stability analysis due to the additional shear strength an unsaturated soil possesses. Shear strength of an unsaturated soil is strongly related to the amount of water in the voids of the soil, and therefore to the matric suction. It is postulated that the shear strength of an unsaturated soil should also bear a relationship to the soil-water characteristic curve. In this thesis, the effect of unsaturated shear strength properties on stability of slopes is investigated by analysing for the stability of hypothetical cut slopes. The effect of the position of water table below the failure surface of hypothetical cut slopes were analysed using Slope/w software for different water table positions for three different cut slope angles. For this work, analyses were done by replacing the cohesion by the apparent cohesion values. Apparent cohesion values were increased by increasing the depth of water table and increasing the effect of negative pore water pressure. Different apparent cohesion values corresponding to the different percentage of negative hydrostatic pressures were utilized. Spreadsheets prepared by a previous research were used to analyse the hypothetical cut slopes by the Modified Janbu’s Method of slices for unsaturated soils. The negative pore water pressure could be directly taken into account in this method, and the Factors of Safety (FOS) derived by this method are compared with the results from SLOPE/W software. Variation of FOS with slope angle and position of water table are investigated. The parametric study done here gives an insight into the problem of landslides. Lowering of the Water Table is been to increase the FOS against sliding failure, as expected

Including Ratio of Platelets to Liver Stiffness Improves Accuracy of Screening for Esophageal Varices That Require Treatment

International audienceBackground & aims: Based on platelets and liver stiffness measurements, the Baveno VI criteria (B6C), the expanded B6C (EB6C), and the ANTICIPATE score can be used to rule out varices needing treatment (VNT) in patients with compensated chronic liver disease. We aimed to improve these tests by including data on the ratio of platelets to liver stiffness.Methods: In a retrospective analysis of data from 10 study populations, collected from 2004 through 2018, we randomly assigned data from 2368 patients with chronic liver disease of different etiologies to a derivation population (n = 1579; 15.1% with VNT, 50.2% with viral hepatitis, 28.9% with nonalcoholic fatty liver disease, 20.8% with alcohol-associated liver disease, with model for end-stage liver disease scores of 9.5 ± 3.0, and 93.0% with liver stiffness measurements ≥10 kPa) or a validation population (n = 789). Test results were compared with results from a sequential algorithm (VariScreen). VariScreen incorporated data on platelets or liver stiffness measurements and then the ratio of platelets to liver stiffness measurement, adjusted for etiology, patient sex, and international normalized ratio.Results: In the derivation population, endoscopies were spared for 23.9% of patients using the B6C (VNT missed in 2.9%), 24.3% of patients using the ANTICIPATE score (VNT missed in 4.6%), 34.5% of patients using VariScreen (VNT missed in 2.9%), and 41.9% of patients using the EB6C (VNT missed in 10.9%). Differences in spared endoscopy rates were significant (P ≤ .001), except for B6C vs ANTICIPATE and in missed VNT only for EB6C vs the others (P ≤ .009). VariScreen was the only safe test regardless of sex or etiology (missed VNT ≤5%). Moreover, VariScreen secured screening without missed VNT in patients with model for end-stage liver disease scores higher than 10. This overall strategy performed better than a selective strategy restricted to patients with compensated liver disease. Test performance and safety did not differ significantly among populations.Conclusions: In a retrospective study of data from 2368 patients with chronic liver disease, we found that the B6C are safe whereas the EB6C are unsafe, based on missed VNT. The VariScreen algorithm performed well in patients with chronic liver disease of any etiology or severity. It is the only test that safely rules out VNT and can be used in clinical practice