Determining small strain shear modulus (G) of Viasvesi sand : Resonant column - Bender elements
Smeets, Tom (2022)
2022
Rakennustekniikan DI-ohjelma - Master's Programme in Civil Engineering
Rakennetun ympäristön tiedekunta - Faculty of Built Environment
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Hyväksymispäivämäärä
2022-06-15
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202205175003
https://urn.fi/URN:NBN:fi:tuni-202205175003
Tiivistelmä
Six samples are tested with bender element and eight samples are tested with resonant column, to respectively determine maximum shear modulus (Gmax) and shear modulus reduction curves (G/Gmax) for Viasvesi sand, which is a uniform sand. The stiffness is determined for increasing cell pressure from 50, to 100 and 300 kPa. Afterwards, the cell pressure is decreased again to 100 and 50 kPa to see if overconsolidation has any influence on Viasvesi sand. It is noticed overconsolidation has an important influence on both maximum shear stiffness and the stiffness reduction. Consolidation causes a deformation of the particle structure. Therefore, when the tested soil is unloaded, a stiffer response occurs. This stiffer response can be attributed to better localized restraints, but can also be attributed to more contacts which occur between the sand particles.
The values of the maximum shear modulus and shear modulus reduction curves during loading can be important in static loadings in respectively the very small and small strain area. Additionally, during dynamic loadings, for example on- and off shore wind mills, in railway construction and during service, etc. these parameters can be useful too. Therefore it is important these parameters get determined. Additionally, the effect of overconsolidation can be useful when Viasvesi sand gets preloaded. In this case, after the preload is taken away, the soil will react stiffer and deform less. Additionally, it can be useful during excavations, where the soil body will react stiffer compared to the original soil body.
The collected data with the bender elements is compared to equations of other authors during this study. During analysing the data it is noticed previously published equations are not suitable for Viasvesi sand. These equations underestimated the maximum shear stiffness. This safer estimation can be attributed to the wide range of uniformity coefficients wherefor these equations are proposed for. While the tested Viasvesi sand has a uniformity coefficient Cu of 2, the proposed equations by the other three authors are for much wider ranges of Cu, from 1.5 to 15. Therefore, a possibility exists these equations are not applicable for every type of sand.
To predict the maximum shear modulus of Viasvesi sand, two equations are proposed. The reason of proposing two equations is because of some irregularities in the measurements, some data was not comparable with each other. Therefore a decision is made to propose two equations. Eventually, it is noticed both equations have an R² above 0.90 which is an acceptable accuracy. Additionally, both equations are more correct on Viasvesi sand, compared to previous noticed equations.
After conducting tests, the maximum shear stiffness obtained via bender element and resonant column are plotted against each other. It is noticed the data differed not too much from each other, with R² above 0.98. Additionally, it is noticed bender element measurements estimate the maximum shear stiffness in most cases higher compared to resonant column tests.
The values of the maximum shear modulus and shear modulus reduction curves during loading can be important in static loadings in respectively the very small and small strain area. Additionally, during dynamic loadings, for example on- and off shore wind mills, in railway construction and during service, etc. these parameters can be useful too. Therefore it is important these parameters get determined. Additionally, the effect of overconsolidation can be useful when Viasvesi sand gets preloaded. In this case, after the preload is taken away, the soil will react stiffer and deform less. Additionally, it can be useful during excavations, where the soil body will react stiffer compared to the original soil body.
The collected data with the bender elements is compared to equations of other authors during this study. During analysing the data it is noticed previously published equations are not suitable for Viasvesi sand. These equations underestimated the maximum shear stiffness. This safer estimation can be attributed to the wide range of uniformity coefficients wherefor these equations are proposed for. While the tested Viasvesi sand has a uniformity coefficient Cu of 2, the proposed equations by the other three authors are for much wider ranges of Cu, from 1.5 to 15. Therefore, a possibility exists these equations are not applicable for every type of sand.
To predict the maximum shear modulus of Viasvesi sand, two equations are proposed. The reason of proposing two equations is because of some irregularities in the measurements, some data was not comparable with each other. Therefore a decision is made to propose two equations. Eventually, it is noticed both equations have an R² above 0.90 which is an acceptable accuracy. Additionally, both equations are more correct on Viasvesi sand, compared to previous noticed equations.
After conducting tests, the maximum shear stiffness obtained via bender element and resonant column are plotted against each other. It is noticed the data differed not too much from each other, with R² above 0.98. Additionally, it is noticed bender element measurements estimate the maximum shear stiffness in most cases higher compared to resonant column tests.