Environmental vibrations induced by human activities such as traffic, construction or industrial manufacturing can cause disturbance among residents or to vibration sensitive equipment in buildings. In Sweden, geological formations of soft clay overlying a stiff bedrock are soil conditions prone to ground vibrations that are encountered both in urban areas and along parts of the national railway network. This paper presents an extensive investigation of the small-strain soil properties for the prediction of environmental ground vibrations in a shallow clay where the bedrock is situated at 7.5 m depth. The small-strain properties are estimated using available empirical correlations, bender elements, seismic cone penetration tests, seismic refraction and inversion of surface wave dispersion and attenuation curves. The results are synthesised into a dynamic layered soil model which is validated by measurements at the soil's surface at source-receiver distances up to 90 m in the frequency range 1-80 Hz. Analyses of uncertainties in the estimated values of wave speeds and material damping are performed by model investigations, indicating that surface wave tests overestimate the damping compared to bender element tests. The properties of the topmost unsaturated part of the soil is found to have a significant influence on the response at large distances, caused by critically refracted P-waves resonating in the top layer.

This paper presents novel measurement data on the dynamic soil-structure interaction of an end-bearing pile foundation. The purpose is to assess the ability to predict the foundation impedances based on the small-strain properties of the soil obtained from site investigations. Measurements were performed in two stages of construction, allowing to assess interaction between the piles through the soil. First, single pile impedances and interaction factors between the piles were experimentally obtained for the four piles when they were free to move at the surface. Second, the impedances of the square pile group were measured after casting a concrete pile cap. The piles were additionally instrumented with accelerometers at depth along the centerline of each pile, allowing to illustrate the global behaviour of the piles within the soil. Numerical predictions based solely on information of the small-strain soil properties obtained from extensive site investigations are compared to the experimental results. The impedances of the individual piles are overestimated compared to the measurements, while the interaction factors show a better agreement. The pile group impedances are better captured than the individual ones, using the same soil model. The pile-soil-pile interaction is clearly manifested in the experimental results by pronounced peaks in the pile group vertical impedance, validating results from previous numerical studies.

Ground-borne vibration from roads or railways is a growing concern in the planning of new buildings in urban environments. Vibration assessment is often based on initial measurements of the free  eld vibrations to estimate building vibrations by either empirical or numerical procedures. Dynamic interaction between the soil and the foundation has an important influence on the transmitted vibrations, especially for embedded foundations, and should therefore be properly accounted for. This paper presents the results from a series of full-scale  field experiments that were performed to characterise the vibration response of an end-bearing pile group foundation in soft clay subjected to a dynamic load applied at the ground surface. Controlled dynamic excitation is applied vertically at the ground surface from 10 and 20 m horizontal distance usingan electrodynamic inertial shaker. Accelerations are measured at different construction stages: prior to construction, after driving of the piles and after completion of the pile cap. Predictions from a numerical model and from a hybrid method utilizing measurement data acquired in an earlier construction stage are both validated with the data from the field tests. Both the numerical and hybrid predictions successfully capture the vibration response of the foundation. The results also indicate that the relationship between the amplitudes of the vertical foundation and free field responses are independent of source-receiver distance, which justifies the use of adjustment factors to estimate foundation responses from measured free field vibrations.

This paper investigates the vertical response of end-bearing piles in a homogeneous isotropic linear elastic soil on a rigid bedrock subjected to a vertical harmonic point load at the soil's surface. A numerical model is used to compute vibration responses. A novel system of dimensionless parameters is established to bring insight into the influence of the relationships between soil and pile properties on the dynamic pile-soil interaction and to allow for general conclusions to be drawn. The results show the conditions under which the relationship between the axial stiffness of the pile and the stiffness of the soil has a significant influence on the end-bearing pile response. Different pile group configurations are considered where the vertical response is found to be bounded by the single pile response, justifying its use as a conservative estimate for the group response. Finally, an expression including only two dimensionless parameters, the pile slenderness ratio and the pile-soil stiffness ratio, is proposed for calculating an estimation of the vertical response of an end-bearing pilefrom the free field vibrations.

The influence of pile-soil-pile interaction on the vertical response of end-bearing pile groups when subjected to an incident wave field generated from a vertical load at the soil's surface is investigated. A numerical model which allows for considering or disregarding the influence of pile-soil-pile interaction is adopted. Vertical end-bearing pile groups with different pile axial stiffness and pile-to-pile spacing are considered. This study shows that in contrast to floating piles in homogeneous soil, the interaction effects caused by wave scattering between the piles are important for end-bearing piles. These may either reduce or amplify the group response, depending on the wavelength in the soil, the spacing between the piles, the pile slenderness and the pile-soil stiffness ratio. The interaction between the piles which are aligned in the direction transverse to the propagation direction of the incident wave field is found to amplify the group response at certain frequencies. Reducing the pile spacing in this direction is found to influence the vertical vibration response of end-bearing pile group foundations considerably by shifting the amplification effects due to pile-soil-pile interaction to higher frequencies.