Attenuation of Traffic Induced Ground Borne Vibrations due to Heavy Vehicles

Traffic induced vibrations, which are transmitted through the ground, may interfere with the proper operation of vibration sensitive equipments and cause nuisance on local population. Influence of these vibrations on surrounding buildings and sensitive devices play an important role on acceptance of the projects. In this study, main objective is the estimation of ground-borne vibration levels due to operation of heavy vehicles at two different sites where soil type and stratification significantly differs. For this purpose, site specific vibration surveys are conducted. A series of dynamic finite element modeling analyses are performed to predict actual vibration records at measurement points. Parameters used in finite element modeling are obtained through geotechnical and geophysical surveys conducted at the site. Modeling results are in good agreement with the actual vibration levels in the considered frequency range. Frequency range of dominant structural responses due to ground borne vibrations induced by heavy vehicles is found to be between 10 Hz to 50 Hz for a single degree of freedom system with 3% damping. Calibrated finite element models are further used to predict the attenuation of vibrations with distance from the source. Slightly better wave attenuation is observed in soil site compared to the rock site

Seismic earth pressures on flexible cantilever retaining walls with deformable inclusions

In this study, the results of 1-g shaking table tests performed on small-scale flexible cantilever wall models retaining composite backfill made of a deformable geofoam inclusion and granular cohesionless material were presented. Two different polystyrene materials were utilized as deformable inclusions. Lateral dynamic earth pressures and wall displacements at different elevations of the retaining wall model were monitored during the tests. The earth pressures and displacements of the retaining walls with deformable inclusions were compared with those of the models without geofoam inclusions. Comparisons indicated that geofoam panels of low stiffness installed against the retaining wall model affect displacement and dynamic lateral pressure profile along the wall height. Depending on the inclusion characteristics and the wall flexibility, up to 50% reduction in dynamic earth pressures was observed. The efficiency of load and displacement reduction decreased as the flexibility ratio of the wall model increased. On the other hand, dynamic load reduction efficiency of the deformable inclusion increased as the amplitude and frequency ratio of the seismic excitation increased. Relative flexibility of the deformable layer (the thickness and the elastic stiffness of the polystyrene material) played an important role in the amount of load reduction. Dynamic earth pressure coefficients were compared with those calculated with an analytical approach. Pressure coefficients calculated with this method were found to be in good agreement with the results of the tests performed on the wall model having low flexibility ratio. It was observed that deformable inclusions reduce residual wall stresses observed at the end of seismic excitation thus contributing to the post-earthquake stability of the retaining wall. The graphs presented within this paper regarding the dynamic earth pressure coefficients versus the wall flexibility and inclusion characteristics may serve for the seismic design of full-scale retaining walls with deformable polystyrene inclusions

Influence of EPS Geofoam Buffers on the Static Behavior of Cantilever Earth-Retaining Walls

In this study, the effect of expanded polystyrene (EPS) buffers on lateral stresses and deflections of model retaining walls with various flexibility values were investigated. For this purpose, 0.7 m high model walls were instrumented and 1-g model tests were performed in laboratory environment. In the first group of tests, the wall models retain only granular cohesionless backfill whereas in the second and third group of tests, EPS deformable buffers of two different thicknesses were installed between the wall and granular backfill. Tests were repeated for four different wall thicknesses and results were discussed comparatively. As wall flexibility increases, there is a decrease in the load reduction pattern of the buffer. On the other hand, utilization of geofoam buffers with flexible cantilever walls still provides substantial decrease in wall thrust and deflections thus leading to more economical retaining structure design. The lateral earth pressure coefficients determined through model tests were compared to those calculated from Coulomb’s theory for active lateral earth stresses. A graph is provided for the estimation of lateral earth pressure coefficients for various combinations of wall flexibilities and buffer characteristics.Publisher's Versio

Reduction of dynamic earth loads on flexible cantilever retaining walls by deformable geofoam panels

The potential application of geofoam in reducing the dynamic earth forces on flexible cantilever earth retaining walls was investigated through small-scale physical model tests. Tests were carried out using a state-of-the-art laminar container and a uniaxial shaking table. Deformable geofoam panels of low stiffness made from expanded polystyrene (EPS) and extruded polystyrene (XPS) geofoam were utilized as compressible inclusions in the present study. The dynamic stress-strain properties of these geomaterials are discussed based on results from laboratory cyclic triaxial tests. Lateral dynamic earth pressures and wall displacements at different elevations, within the backfill were monitored during the application of various base excitations. The test results revealed that the presence of a deformable geofoain panel of low stiffness behind the flexible retaining wall will result in a reduction of the dynamic wall pressures and displacements. The geofoam efficiency in terms of load and displacement reduction decreases as the flexibility ratio of the model wall increases. On the other hand, load reduction efficiency of the geofoam increases as the amplitude and frequency ratio of the excitation increases. Load reduction efficiencies achieved in the tests were compared to those of the previous physical and numerical modeling studies available in the literature. Comparisons indicate that there is an agreement with the data presented in the previous modeling studies for low acceleration amplitudes and wall flexibility values, however, this agreement diminishes as wall flexibility begins to play role in reducing the earth pressures. Application point of the maximum dynamic thrust varies between 0.4 H to 0.6 H depending on the inclusion type, flexibility ratio of the wall and the characteristics of the harmonic motion applied to the base of the models