1,721,197 research outputs found
Development of a Citywide Real-time Landslide Warning System in Busan, Korea
No full textRainfall-induced landslides have been one of major disasters in Korea where 70% of territory is covered by mountainous regions. As magnitude and frequency of extreme rainfall events has increased due to the global climate change, the number of landslide has significantly enlarged that results in casualties and property damages. In order to mitigate the landslide risk and to provide with an effective tool for public officials to manage the landside disasters, a citywide real-time landslide warning system has been developed by taking into account for situations in Busan, the second largest metropolitan city in Korea, as an application target area. The system provides with warning information based on five-alert levels that are classified as Normal, Attention, Watch, Alert, and Emergency. The warning level is determined by applying several thresholds developed by statistical, and physically-based as well as direct measurement-based approaches using forecasted/observed rainfall data or data obtained from a ground monitoring system. As a first step, the target area at ‘normal’ state is upgraded to an ‘attention’ state if the statistical thresholds are exceeded. Subsequently, the area delineated in the previous step can be updated to the next warning levels (watch and alert) by applying an infiltration-slope stability analysis when the safety factor of slope failure is less than 1.3 and 1.0, respectively. Finally, the ‘emergency’ state is determined by applying a debris-flow mobilization criterion and the subsequent potential debris-flow risk at specific local-scale areas are evaluated by conducting runout analyses. In order to validate the system applicability, landslide historical data and previous rainfall data during rainy seasons from 2009 to 2016 have been used. The system performance demonstrates a good agreement with the past landslide events. The developed system, therefore, will serve as a powerful tool to decision makers for landslide disaster preparedness
An Improved Search Strategy for the Critical Slip Surface using Finite Element Stress Fields
No full textThe finite element method can be used to advantage in slope stability problems. This paper proposes a technique to search for the critical slip surface as well as to define and calculate the factor of safety for the slope, when the finite element method is used to model its formation. First, stresses are estimated at each Gaussian point from the finite element analysis. Then, the global stress smoothing method is applied to get a continuous stress field. Based on this stress field, the factor of safety is calculated for a specified slip surface by a stress integration scheme. An improved search strategy is proposed for a noncircular critical surface which starts with a search method for a circular critical surface. During the search process, points defining a trial slip surface can freely move in the finite element mesh subject to some kinematical constraints. This method can be applied to both the limit equilibrium method and the finite element method. Effects of the slope stress history and soil parameters on the resulting critical surface are investigated. (C) 1998 Elsevier Science Ltd. All rights reserved
Formulation of implicit stress integration and consistent tangent modulus for an anisotropic hardening constitutive model
No full textAn anisotropic hardening constitutive model based on the generalized isotropic hardening (GIH) rule was implemented into the nonlinear finite element method. The GIH rule describes discrete formation of homology centers and simultaneous hardening of both inner and outer yield surfaces. Consequently, yielding in the field of reverse loading can be accurately modeled by this rule. In order to preserve the accuracy of nonlinear finite element analysis, an implicit stress integration technique employing the generalized trapezoidal rule was applied to the GIH constitutive equation. Furthermore, the consistent tangent modulus was formulated and coded into a nonlinear FEA program, which has the advantage of the quadratic rate of convergence in Newton's iteration. Accuracy and convergence were successfully verified through examples, and thus the anisotropic hardening constitutive model could assess the plastic straining mobilized in overconsolidated state and versatile loading sequences. (C) 2001 Elsevier Science B.V. All rights reserved
Long-term settlement behaviour of MSW landfills with various fill ages
No full textMSW landfill settlement characteristics are peculiar because a considerable amount of settlement occurs due to the decomposition of waste organic solids for very long duration. The total amount of settlement that occurs due to this decomposition in a MSW landfill is mainly dependent upon the amount of biodegradable solid waste and hence the fill age of the MSW landfill. The settlement stabilisation period is also dependent upon the decomposition condition. In order to investigate the settlement characteristics of MSW landfills, a mathematical model was proposed and applied to settlement data of MSW landfills which have various fill ages. A data bank of model parameters were obtained and the trends were analysed. The long-term settlement behaviour of MSW landfills can be fairly well estimated by the proposed model. It is supposed that the total remaining amount of settlement might be predicted on the basis of the fill age with two appropriate design parameters
AN ANISOTROPIC HARDENING CONSTITUTIVE MODEL-BASED ON GENERALIZED ISOTROPIC HARDENING RULE FOR MODELING CLAY BEHAVIOR
No full textAn anisotropic hardening description is proposed on the basis of the Generalized Isotropic Hardening (GIH) rule. The key concept of the GIH rule is that any proper stress state inside or on an yield surface can be the homologic center of isotropic hardening. A concrete constitutive relationship was formulated by utilizing a simple hardening function. For verification, three sets of triaxial test results obtained from drained and undrained tests on overconsolidated clays and K-0 consolidated clays were evaluated. Consequently, it was determined that the proposed model can represent any plastic deformation in reverse loading
Temperature effect on migration of Zn and Cd through natural clay
No full textTo investigate the effect of temperature on effective diffusion coefficients and retardation factors for Zn and Cd, combined diffusion and sequential extraction analyses were conducted at 15 degrees C and 55 degrees C. The effective diffusion coefficients of the metals increased up to ten times according to the increased temperature. On the other hand, the effect of temperature on the retardation factor depended on the retention mechanisms of the metals. The distribution coefficient for Zn, which was mainly partitioned in the carbonate phase, increased up to two times with the increase in temperature. On the other hand, the distribution coefficient for Cd, which was mainly partitioned in the exchangeable phase, was hardly affected by the temperature change. Results of combined diffusion and sequential extraction analysis showed that the effect of temperature on the heavy metals' (Zn and Cd) migration through the compacted natural clay was influenced by the combined effects of the diffusion coefficient and the retardation factor. Additionally, we could also observe the change in retention mechanism for the metals with the change in pore water concentration
Uplift capacity of fixed shallow anchors subjected to vertical loading in rock
No full textThis paper presents the results of full-scale loading tests performed on 54 passive anchors and 4 group-anchored footings grouted to various lengths at several sites in Korea. Various rock types were tested, ranging from highly weathered shale to sound gneiss. In many tests, rock failure was reached and the ultimate loads were recorded along with observations on the shape and extent of the failure surface. Laboratory tests were also conducted to investigate the influence on the bond strength of the corrosion protection sheath. Based on test results, the main parameters governing the uplift capacity of the rock-anchor system were determined. Through evaluation of the ultimate uplift capacity of anchor foundations in a wide range of in situ rock masses, a rock classification suitable for a transmission tower foundation was developed. Finally, a very simple and economical design procedure is proposed for rock-anchor foundations subjected to uplift tensile loads
Effect of temperature on single and competitive adsorptions of Cu(II) and Zn(II) onto natural clays
No full textThis study conducted a combined adsorption-sequential extraction analysis (CASA), by which five phases (i.e., exchangeable, carbonate, Mn-Oxide, organic, and Fe-Oxide phases) of adsorbed heavy metals were analyzed, to investigate temperature effects on single and competitive adsorptions of Zn(II) and Cu(II) onto natural clays. In the case of single adsorption of Zn, the exchangeable phase adsorption decreased from 65 to 40%, but the carbonate phase adsorption increased from 30 to 40%, with an increase in temperature from 15 to 55 C. However, in its competitive adsorption with Cu, Zn was mostly present in the exchangeable phase (over 90%), and with an increase in temperature, the exchangeable phase adsorption decreased only 10%. In the case of Cu, over 50% among the total amount of adsorption was present in the carbonate phase in both cases of single and competitive adsorptions. The carbonate phase adsorption of Cu increased from 56 to 61% and from 60 to 66% in single and competitive adsorptions, respectively, with a temperature increase. These results show that in the case of Zn, the major mechanism of retention in natural clay soils might be exchangeable phase adsorption, especially in the case of competitive adsorption with Cu. However, in the case of Cu, the major mechanism might be carbonate phase adsorption, which is known to be a more immobile phase than exchangeable phase adsorption. It seems that the adsorption of Zn and Cu onto natural clays is an endothermic reaction, which represents that the adsorption equilibrium constants and capacities increase with a temperature increase, with the exception of exchangeable phase adsorption
Effects of Equipment Loadings on Geosynthetic Lined Slope Behavior
No full textWhen combined in the lining and covering of waste-containment facilities, soil and geosynthetic components protect the environment by acting as a hydraulic barrier. Equipment loading may significantly increase the tensile stress induced in geosynthetic components, leading to a potential stability problem. Large equipment loadings may also result in a localized circular slip surface during construction operations. New analytical method based on discrete element modelling is proposed for estimating the distribution of tensile force developed in the individual geosynthetic components of the lining system and for evaluating the safety factor of slope failure due to equipment loading. The analytical results of an example are presented to demonstrate the applicability of the analytical method for the lining system of a waste landfill. The analyses of the example show that equipment loading provide a substantial increase in the tensile forces of the geosynthetic components of a lining system and that the possibility of shallow failure due to equipment loading increases as the slope becomes steeper. This method is a useful tool for analysing the lining system of waste landfills with complex lining components
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