1. A general analytical solution to the one-dimensional consolidation problem for unsaturated soil under various loading conditionsJiwei Li, Changfu Wei, Yanlin Zhao, 2018, original scientific article Abstract: A general analytical solution is developed for the onedimensional consolidation problem of unsaturated soil under various time-dependent loading conditions based on a differential transformation method (DTM). In particular, analytical solutions are obtained for different relationships between the coefficients in the governing equations for unsaturated soil consolidation. The Fourier series expansion technique is adopted to account for both the continuous differentiable loading and the periodic piecewise loading. A comparison between the results of the current solution and the existing theoretical solution indicates that the proposed solution yields excellent results, while it is straightforward to obtain the analytical solution of the unsaturated consolidation problems. It was also found that the variations in the coefficients in the governing equations can significantly influence the dissipation of both the excess pore-air pressure and the excess pore-water pressure, though the magnitudes of their variations are different. Keywords: one-dimensional consolidation problem, unsaturated soil, analytical solution, time-dependent loading Published in DKUM: 11.10.2018; Views: 1092; Downloads: 485 Full text (814,44 KB) This document has many files! More... |
2. An overview of medical malpractice law in the United States including legislative and the health care industry's responses to increased claimsThomas Allan Heller, 2017, review article Abstract: Medical Malpractice claims are frequently asserted in the United States. At various time and places, an extraordinarily high number of claims and payouts led to what some have called medical malpractice crises. Consequently, in some geographical locations physicians either could not purchase malpractice insurance as carriers withdrew from the market, or, insurance became increasingly expensive and the overall costs associated with the delivery of health care continued to rise. Other undesirable consequences of these crises included a shortage of qualified physicians in certain parts of the country. Many of the states responded to these problems legislatively through a long series of tort reform measures. The health care industry itself has evolved in numerous ways. In particular, many health care providers have turned away from traditional private insurance models to self-insured models such as captives. Further, the industry has continued to consolidate, with fewer, but larger hospitals and clinics, and with an increasing number of physicians employed directly by hospitals and large clinics. The results of all of these changes have had mixed results. Keywords: medical malpractice, defensive medicine, medical malpractice crises, tort reform, consolidation of health care industry, group captives Published in DKUM: 09.10.2018; Views: 1131; Downloads: 147 Full text (488,42 KB) This document has many files! More... |
3. Shear modulus of a saturated granular soil derived from resonant-column testsH. Patiño, E. Martínez, Jesús González, A. Soriano, 2017, original scientific article Abstract: This paper presents the results of 120 determinations of the shear modulus (G) of a saturated granular soil (20–40 Ottawa sand) in different conditions of relative density (Dr), effective consolidation pressure (σ’ c) and level of torsional excitation (Te). The equipment used was a resonant-column apparatus manufactured by Wykeham Farrance and the tests were performed with relative density values of 20, 40, 60 and 80%, effective consolidation pressures of 50, 100, 150, 200, 250 and 300 kPa, and torsional excitations of 0.025, 0.05, 0.1, 0.2 and 0.4 volts (V), leading to shear strains (γ) between 0.002% and 0.023%. The results led to very simple empirical expressions for the shear modulus as a function of the angular strain for different effective consolidation pressures and void-ratio values. Keywords: resonant column, resonant frequency, shear modulus, relative density, effective consolidation pressure, dynamic shear modulus Published in DKUM: 18.06.2018; Views: 1010; Downloads: 78 Full text (1,31 MB) This document has many files! More... |
4. Experimental research on variation of pore water pressure in constant rate of strain consolidation testHojjat Ahmadi, Hassan Rahimi, Abbas Soroush, Claes Alén, 2014, original scientific article Abstract: Constant rate of strain (CRS) consolidation is a rapid test method which is used for determination of compressibility of clayey soils. In a CRS test, the appropriate strain rate is selected based on pore water pressure ratio, i.e. the ratio of pore pressure to total stress. In the present study, to investigate the effect of strain rate on variation of pore water pressure ratio, four different clay samples of different plasticity were tested by CRS apparatus. The results of the experiments showed that the trend of variation of pore water pressure is dependent on the drained water flow regime which may be either Darcy or non-Darcy. The results also indicated that the plasticity of clay does not have considerable effect on variation of pore water pressure. Keywords: constant rate of strain, consolidation, pore water pressure ratio, soil plasticity, Darcy and non-Darcy flow Published in DKUM: 14.06.2018; Views: 837; Downloads: 66 Full text (576,58 KB) This document has many files! More... |
5. Numerical modeling of floating prefabricated vertical drains in layered soilIkhya Ikhya, Helmut Schweiger, 2012, original scientific article Abstract: This paper presents a comparison of field measurements and a numerical model of settlements based on the construction of an embankment on soft soil for the Cirebon Power Plant Project in Indonesia, where prefabricated vertical drains (PVDs) were installed. In the numerical model, floating PVDs in two soil layers for two- and one-way drainage conditions are examined in order to determine the optimum penetration depth. In this study, good agreement between the field measurements of the settlements and the numerical prediction could be achieved. An interesting result of this study is that the differences in the stiffness and/or the permeability in the unimproved area below the PVD tip have a significant influence on the optimum penetration depth (L/H) in the two-soil-layer condition. The numerical study showed that it is possible to use floating PVDs in single drainage conditions if the second layer is stiffer and/or more permeable than the first layer. Keywords: two soil layers, floating prefabricated vertical drain, double and single drainage, numerical model, soft clay, consolidation Published in DKUM: 13.06.2018; Views: 954; Downloads: 74 Full text (727,36 KB) This document has many files! More... |
6. The dynamic properties of the snail soil from the Ljubljana marshBojan Žlender, Ludvik Trauner, 2007, original scientific article Abstract: A series of cyclic triaxial tests was performed on snail-soil samples with different porosities. The cyclic loading was performed with a Wykeham Farrance cyclic triaxial system. The investigation was based on a series of tests in which the following conditions were varied: the initial effective pressures (50, 100, and 150 kPa), the void ratio after consolidation (2.0–1.2) and the cyclic loading expressed by the cyclic stress ratio CSR (0.1–1.0). Measurements were made of the stress, the deformation and the pore-water pressure.
The results of the tests show that interdependency exists between the geomechanical characteristics and the porosity. These relationships can be expressed as functions of the density, the porosity or the water content. It is evident from the results that the changes in the coefficient of permeability, the coefficient of consolidation, and the coefficient of volume compressibility are non-linear with respect to the changes in the porosity. However, the changes at high porosity are much greater than the changes at low porosity, and the changes of the mechanical parameters, such as the Young’s modulus, Poisson’s ratio, and the friction angle, are indistinct and almost linear at lower changes of porosity, and after that become non-linear.
The initial void ratio e is extremely high and the snail soil is liquid after consolidation; a volume strain of εvol > 16 % is needed for the plastic limit state.
The chemical and mineral composition, the particle size distribution and the remains of micro-organisms in the snail soil are constants. In addition, the specific surface is independent of the porosity and the density or unit weight, the porosity and the volume strain are in the well-known correlation.
The performed cyclic triaxial tests show the dynamic characteristics of the snail soil and the influence of the porosity on the cyclic loading strength. The snail soil was recognized as a highly sensitive material. A large strain appears after the initial cycles. The pore pressure, increases already during the first cycle, to the hydrostatic part of the cyclic loading, or more (depending on CSR).
The damping ratio increases exponentially with strain, after some cycles it reach its maximum value, and after that it decreases to the asymptotic value. The reason for such behaviour is the large deformation. The maximum and asymptotic values of the damping ratio are a changed minimum with a void ratio. There is obviously no influence of the porosity on the damping ratio.
The shear modulus is described in relation to shear strain. The increasing of the pore pressure is independent of the porosity until it reaches some value of the pore-pressure ratio (>0.7). Similarly, the increasing of the shear strain becomes dependent on the void ratio until it reaches some particular value of the shear strain (>3%).
The deformation and failure lines for the different porosities are determined from the relationship between the shear stress and the effective stress at some shear strain, after 10 cycles.
The relationships between the shear stress and the effective stress at some value of the pore-pressure ratio are expressed in a similar way.
Two kinds of criteria were used to determine the triggering of liquefaction during the cyclic triaxial tests: first, when the pore pressure becomes equal to the effective confining pressure, and, second, when the axial strain reaches 5% of the double amplitude. Keywords: snail soil, cyclic triaxial test, porosity, permeability, consolidation, Young’s modulus, shear modulus, damping ratio, Poisson’s ratio, friction angle Published in DKUM: 18.05.2018; Views: 1377; Downloads: 82 Full text (479,11 KB) This document has many files! More... |
7. The influence of porosity on geomechanical characteristics of snail soil in the Ljubljana MarshBojan Žlender, Ludvik Trauner, 2006, original scientific article Abstract: This article focusses on mineralogical and physical characteristics of snail soil and their influence on parameter values of geomechanical characteristics.Snail soil, which got its name from fossil remains, is a typical layer observed in the Ljubljana marsh. It is distincltly porous, saturated and in a liquid consistency state. Snail soil was investigated for mineralogical and physical characteristics in the Laboratory of Soil Mechanics, Faculty of Civil Engineering of the University in Maribor. Mineral and chemical composition, visual appearance, specific surface and grain property were determined. Physical characyteristics show that snail soil is saturated in nature, highly porous and almost liquid. Geomechanical characteristics were investigated for their interdependency on physical characteristics. A series of triaxial tests were performed on snail soil samples of different porosity, density and water content. Cylindrical samples of the height of 100 mm and the diameter of 50 mm were tested using three-axial testing apparatus. The results of the tests show that interdependency exists between geomechanical characteristics and porosity. These relationships can be expressed as functions of density, porosity or water content. It is evident from the results that changes of the coefficient of permeability, the coefficient of consolidation, and the coefficient of volume compressibility are nonlinear with respect to changes in porosity. Changes of mechanical parameters, such as Young`s modulus, Poisson`s ratio andfriction angle are indistinct and almost linear at lower changes of porosity. Keywords: geomechanics, properties of soils, snail soil, triaxial testing, porosity, permeability, consolidation, Young`s modulus, Poisson`s ratio, shear angle Published in DKUM: 17.05.2018; Views: 1300; Downloads: 71 Full text (486,06 KB) This document has many files! More... |