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1.
The influence of porosity on geomechanical characteristics of snail soil in the Ljubljana Marsh
Bojan Žlender, Ludvik Trauner, 2006, izvirni znanstveni članek

Opis: 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.
Ključne besede: geomechanics, properties of soils, snail soil, triaxial testing, porosity, permeability, consolidation, Young`s modulus, Poisson`s ratio, shear angle
Objavljeno: 17.05.2018; Ogledov: 386; Prenosov: 27
.pdf Celotno besedilo (486,06 KB)
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2.
Methods for control of seepage in RCC dams with wathertight and drainage measures
Yueming Zhu, Stephan Semprich, Erich Bauer, Cuiping Yuan, Dongmei Sun, 2006, izvirni znanstveni članek

Opis: The technologies for construction of roller-compacted concrete (RCC) dams have been considerably developed during recent years in China. At the time being, they have been successfully applied to the constructions of even extreme-high gravity dams and medium to high arch dams. There are a few of hundreds of RCC dams (RCCD) under design and/or construction in China. One of the main concerned technical problems according to the construction is about the understanding of the property of seepage in RCCDs and the relevant theory and methods for the control of the seepage. In order to overcome the problem, the senior author has been engaged in a wide study on the property and methods for control of seepage in RCCDs for more than 10 years. The property of seepage, measures for watertightness and drainage, optimal design and construction schemes for control of seepage in the dams have been essentially understood either in theory and practice. The results have been applied for the construction and the backanalysis of several dams. The paper describes the research findings in detail with respect to the theoretical fundament and their application for a high RCC gravity dam.
Ključne besede: gravity dam, Roller-compacted concrete, RCC, seepage, anisotropic permeability, drainage
Objavljeno: 17.05.2018; Ogledov: 285; Prenosov: 20
.pdf Celotno besedilo (209,12 KB)
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3.
The dynamic properties of the snail soil from the Ljubljana marsh
Bojan Žlender, Ludvik Trauner, 2007, izvirni znanstveni članek

Opis: 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.
Ključne besede: snail soil, cyclic triaxial test, porosity, permeability, consolidation, Young’s modulus, shear modulus, damping ratio, Poisson’s ratio, friction angle
Objavljeno: 18.05.2018; Ogledov: 654; Prenosov: 39
.pdf Celotno besedilo (479,11 KB)
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4.
A new method for testing the anti-permeability strength of clay failure under a high water pressure
Fu-wei Jiang, Ming-tang Lei, Xiao-zhen Jiang, 2015, izvirni znanstveni članek

Opis: It is difficult to judge the failure of clay seepage under a high water pressure.This paper presents a new method to assess clay failure based on the anti-permeability strength, which is the critical water pressure to destroy the clay. An experiment is designed to test the value that avoids the problem of the time-consuming, traditional method to test clay seepage deformation. The experimental system and the process of testing are introduced in this paper. With a self-designed experimental system and method, 18 groups of sample were tested. The results show that the clay thickness and the seepage paths influence the anti-permeability strength. It also indicates that water infiltrates into the clay under the condition that its pressure exceeds a minimum value (P0).
Ključne besede: clay failure, seepage deformation, anti-permeability strength, high water pressure
Objavljeno: 15.06.2018; Ogledov: 300; Prenosov: 14
.pdf Celotno besedilo (249,24 KB)
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