In-Situ Determination of Material Damping in the Soil at Small Deformation Ratios (In situ bepaling van de materiaaldemping in de grond bij kleine vervormingen)

Vibrations in the built environment due to traffic, construction activities, and industry are a matter of concern as they may affect sensitive equipment, cause discomfort to people, and result in structural damage. The accurate prediction of structural vibrations prior to construction and design of vibration mitigating measures is therefore important. For this purpose, small strain (engineering shear strain 0.00001) dynamic soil characteristics as the dynamic shear modulus and the material damping ratio need to be determined by means of laboratory or in situ tests. The focus of this thesis is on the determination of the material damping ratio using in situ techniques. Different methods have been proposed in the literature for the determination of the material damping ratio of the soil, based on the Spectral Analysis of Surface Waves (SASW) test and the Seismic Cone Penetration Test (SCPT). Existing methods based on the SASW test work well when they are applied to regular soil profiles, where the stiffness increases gradually with depth. These techniques can lead to inaccurate results, however, when they are applied to soils with complex layering, where softer layers are overlaid by stiffer layers. The thesis presents two new techniques to improve the existing methods. The first method is based on the application of the half-power bandwidth method to the response of the soil in the frequency-wavenumber domain. This method uses the width of the peak of the spectrum to determine frequency dependent attenuation coefficients. The resulting attenuation curve is inverted in an optimization procedure to determine the material damping ratio profile. The second method is based on the spatial decay of the Arias intensity, which is determined from the acceleration time histories at different locations. The resulting Arias intensity curve is inverted to determine the material damping ratio profile. It is demonstrated that this method also works very well when applied to SCPT data. Synthetic examples along with case histories are used in the thesis to introduce the proposed techniques and to compare them with existing approaches. For application to synthetic profiles, the proposed methods lead to results closer to the original soil profiles. For case histories, the soil profiles determined using the existing and proposed techniques are compared based on the simulation of the response at a certain location. It is shown that the profiles determined with the proposed methods lead to a better simulation of the experimental response.nrpages: 198status: publishe