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Influence of geosynthetic reinforcement on the shear strength characteristics of two-layer sub-grade
Mehrad Kamalzare, Reza Ziaie-Moayed, 2011, original scientific article

Abstract: Due to the low bearing capacity of soft clayey soils in places that because of economic, military or geological conditions we are oblige to build a structure on, geosynthetics will be used to reinforce the soil and improve its bearing capacity. Particularly, A good example is roadways, where geosynthetics are placed between the interface of the granular materials and the soft-soil sub-grade to improve the bearing capacity of the composite layers. In previous research the behavior of one-layer soils that were reinforced with different kinds of geosynthetics were studied by experimental and analytical methods and some numerical models have been developed. In this paper the behavior of two-layer soils (granular base and clayey sub-grade) that were reinforced with some geosynthetics are investigated. Large-scale direct shear tests were performed on unreinforced and reinforced samples with different geosynthetics. The results show that depending on the characteristics of the geosynthetics, the inclusion of these materials may increase or decrease the shear strength parameters of the interface of two-layered soils. It implies that the geosynthetic-reinforced soils in the sub-base layer of roads are so sensitive to the characteristics of geosynthetics and will perform better than non-reinforced soils and consequently the load-carrying capacity of the basement will improve only if the appropriate geosynthetics are used. However, geogrid shows more reinforcement efficiency under higher vertical stresses. Increasing the relative density of the clayey sub-grade would also cause the geogrid reinforcement to be more effective.
Keywords: shear strength, geosynthetic, large scale direct shear test, soft clay, subgrade
Published: 13.06.2018; Views: 441; Downloads: 43
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The dynamic properties of the snail soil from the Ljubljana marsh
Bojan 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: 18.05.2018; Views: 886; Downloads: 58
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