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See detailA Simple Engineering Soil Surface Vibration Prediction Method
Macijauskas, Darius UL; Van Baars, Stefan UL

in Civil Engineering Research Journal (2018), 4(2),

In urban areas where the infrastructure is dense and construction of new structures is near existing and sensitive buildings, frequently vibrations, caused by human activities, occur. Generated waves in ... [more ▼]

In urban areas where the infrastructure is dense and construction of new structures is near existing and sensitive buildings, frequently vibrations, caused by human activities, occur. Generated waves in the soil may adversely affect surrounding buildings. These vibrations have to be predicted a priori by using currently available knowledge of the soil dynamics. In order to make a good prediction of the soil surface vibration, it is necessary to perform calculations with a Finite Element Method (FEM). The disadvantages of the FEM are that this requires a special software package and a long time for the modelling and calculations. Therefore, it would be very useful to derive a simple model for engineering purposes, which could be used to predict geotechnical vibrations close to the source, without the need of special software and long calculations. Such a method is proposed in this article. This method is validated by a vibration test performed on a peaty site in the Netherlands. The predictions made with this method, have been compared with both the field measurements and the FEM calculations. The comparison proves that by using the presented vibration prediction method, the vibrations can be predicted as accurate as with the FEM. [less ▲]

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See detailA 3D shear material damping model for man-made vibrations of the ground
Macijauskas, Darius UL; Van Baars, Stefan UL

in 13th Baltic Sea Region Geotechnical Conference (2016, September)

Man-made vibrations from different types of sources are usually measured on the surface of the ground or building. The measured signal is always the superposition of all travelling basic waves. For a ... [more ▼]

Man-made vibrations from different types of sources are usually measured on the surface of the ground or building. The measured signal is always the superposition of all travelling basic waves. For a homogeneous half space there are three basic waves – the Compressional (P-wave), Shear (S-wave) and Rayleigh wave (R-wave). Depending on the measuring equipment, only the accelerations or velocities in time of the superposed wave can be measured, but not the distribution of the individual basic waves. Additional problems are that each of the basic waves has its own velocity, besides the body and surface waves have different attenuation laws. By using the rules of superposition of harmonic waves and also the propagation laws of the P-, S- and R-waves, it should be theoretically possible to split the measured superposed signal into the basic waves, because mathematically a system of equations can be assembled which describes the displacements at multiple measuring points in time. In this paper this problem has been solved for a homogenous, elastic and isotropic soil, which is disturbed by a harmonically oscillating disc on the surface. A numerical simulation was performed using a finite element method. The displacements in time were recorded in 10 points on the surface and a system of superposed equations was assembled and solved. The findings prove that each of the three basic waves has its own phase shift with the source, something which was not known before. [less ▲]

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See detailImproved Predictions for Geotechnical Vibrations
Macijauskas, Darius UL

Doctoral thesis (2015)

In urban areas where the infrastructure is dense and construction of new structures is near existing and sensitive buildings, frequently vibrations, caused by human activities, occur. Generated waves in ... [more ▼]

In urban areas where the infrastructure is dense and construction of new structures is near existing and sensitive buildings, frequently vibrations, caused by human activities, occur. Generated waves in the soil may adversely affect surrounding buildings. These vibrations have to be predicted a priori by using currently available knowledge of the soil dynamics. Current research, conducted by Deltares research institute, showed that the reliability of methods for prediction of man-made vibrations is disappointingly low. Therefore the models for vibrations in the soil should be improved in order to get more accurate predictions. The main aim of this thesis is to increase the knowledge on dynamic soil behaviour with respect to the fundamental geotechnical aspects of the soil, like non-viscous damping, inhomogeneity, anisotropy, variable degree of saturation, etc. and to give an improved prediction method. The scientific investigations of this thesis started with the following setup: an oscillating plate on an elastic, homogeneous and isotropic half-space, where the plate oscillates harmonically in vertical direction and the soil is unsaturated. In this way, the geotechnical aspects have been left aside in order to check first whether it is possible to predict the vibration amplitudes of the oscillating plate and of the soil surface, without additional complexities. This setting allowed to compare the present analytical methods with the results, obtained from the finite element method (FEM) calculations, and showed that the analytical methods have their limitations. Therefore the wave-field near an oscillating plate had to be investigated more carefully. Unfortunately the state of the art in soil dynamics is such that only the particle vibration velocities are measured without knowing which part of the velocities/vibrations belongs to which type of basic wave (compressional, shear or Rayleigh wave). Therefore first of all, a technique to decompose the measured signal into its basic waves was developed. This new technique showed remarkably that all three basic waves have phase shifts and these phase shifts are all different from each other. The decomposition technique is an important tool for researching soil dynamics. Also a qualitative evaluation of the energy transmission between the basic waves near the vibration source was given, which showed that the R-wave energy starts at zero just at the source and grows in the near-field zone due to an energy transmission (body waves are transferring energy to the R-wave). This means that even without uncertainties in the soil body, there is a lack of understanding of the behaviour of the different waves. A real field test is performed with a shaker on a soft peaty site in the Netherlands, as an attempted to replicate the FE model experiments. It showed the limitations of the analytical methods and highlighted the indispensability of the FEM. Still, for engineering purposes, an improved analytical method is suggested, which is able to predict the geotechnical vibrations with good accuracy. Herein, one of the fundamental aspects, the material damping, was used and a hypothesis was made, that with a more correct physical model of the soil material damping, the vibration predictions with FEM can be improved. The 1D frictional damping model, first suggested by Van Baars (2011), was extended for the 3D and incorporated into the FEM software Plaxis as a User Defined Soil Material model. The results are very interesting scientifically, but do not give much better results as the already existing Rayleigh damping model. [less ▲]

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See detailPROPAGATION OF HARMONICAL VIBRATIONS IN PEAT
Macijauskas, Darius UL; Van Baars, Stefan UL

in International Journal of GEOMATE (2014), 7(2), 1101-1106

In order to check the reliability of man-made vibration prediction methods, vibration tests were performed on one of polders in the North-West of the Netherlands. The polder was chosen because it has a ... [more ▼]

In order to check the reliability of man-made vibration prediction methods, vibration tests were performed on one of polders in the North-West of the Netherlands. The polder was chosen because it has a rather homogenous, thick and soft peat top layer. Here sufficient harmonical vibrations could be generated by a rather small shaker. The shaker was designed and manufactured in order to produce harmonical vibrations at the soil surface. It consists of two counter rotating electric vibrators (with rotating eccentric masses) in order to produce a vertically oscillating force. For the recordings of the vibrations, six 2D or 3D geophones were placed on the soil surface and one 2D geophone was placed on top of the shaker. The measured vibration amplitudes of the vertically oscillating shaker were compared with 1. Two different analytical methods used for the design of vibrating machine foundations, 2. The Confined Elasticity approach and 3. The Finite Element Method, for which Plaxis 2D software was used. Also the measured vibration amplitudes at the soil surface were compared with Barkan-Bornitz’s solution and Finite Element Modeling. [less ▲]

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See detailDecomposition of measured ground vibrations into basic soil waves
Macijauskas, Darius UL; Van Baars, Stefan UL

in Pietruszczak, Stan; Pande, Gyan (Eds.) Proceedings of the 3rd International Symposium on Computational Geomechanics (ComGeo III), Krakow, Poland, 21-23 August, 2013 (2013, August 21)

Man-made vibrations from different types of sources are usually measured on the surface of the ground or building. The measured signal is always the superposition of all travelling basic waves. For a ... [more ▼]

Man-made vibrations from different types of sources are usually measured on the surface of the ground or building. The measured signal is always the superposition of all travelling basic waves. For a homogeneous half space there are three basic waves – the Compressional (P-wave), Shear (S-wave) and Rayleigh wave (R-wave). Depending on the measuring equipment, only the accelerations or velocities in time of the superposed wave can be measured, but not the distribution of the individual basic waves. Additional problems are that each of the basic waves has its own velocity, besides the body and surface waves have different attenuation laws. By using the rules of superposition of harmonic waves and also the propagation laws of the P-, S- and R-waves, it should be theoretically possible to split the measured superposed signal into the basic waves, because mathematically a system of equations can be assembled which describes the displacements at multiple measuring points in time. In this paper this problem has been solved for a homogenous, elastic and isotropic soil, which is disturbed by a harmonically oscillating disc on the surface. A numerical simulation was performed using a finite element method. The displacements in time were recorded in 10 points on the surface and a system of superposed equations was assembled and solved. The findings prove that each of the three basic waves has its own phase shift with the source, something which was not known before. [less ▲]

Detailed reference viewed: 140 (19 UL)