Application of EPS geofoam in attenuating ground vibrations due to vibratory pile driving

Abstract

Modern day urban construction activities are largely carried out adjacent to existing buildings due to scarcity of land for construction. In order to utilise the available land in the most efficient way, often high-rise buildings are constructed necessitating pile foundations to transfer large design loads to strong and deep soil layers below the ground surface. Although a number of methods are available to install pile foundations, in urban areas several factors need to be taken into consideration when selecting the suitable method. Due to the proximity of new and existing structures, noise disturbance and damages to existing nearby structures resulting from pile installation should be kept to a minimum. In that respect, vibratory pile driving is the most suitable pile installation method for urban construction activities. However, ground vibrations induced by vibratory pile driving may cause damages to existing structures depending on the proximity and sensitivity of the structure. Hence, it is necessary to take proper mitigation measures against vibratory pile driving induced ground vibrations. A possible remedy is to use in-filled wave barriers with concrete, bentonite, water or expanded polystyrene (EPS) geofoam, which can diminish the construction induced vibrations. EPS geofoam offers a number of advantages over other fill materials because of its light weight, cost effectiveness, energy absorbing characteristics, efficiency in terms of construction time and ease of handling. There have been many research studies carried out to investigate the mechanical behaviour of EPS geofoam. However, the full potential of EPS geofoam is yet to be realised. Therefore this thesis aims to investigate the severity of ground vibrations induced by vibratory pile driving and effectiveness of EPS geofoam wave barriers in protecting nearby structures. These investigations are carried out using both two- and three-dimensional finite element models developed based on the Arbitrary-Lagrangian-Eulerian approach. They are discretised in both space and time to capture the wave propagation within ground. First, a finite element formulation of a constitutive model developed to simulate mechanical behaviour of EPS geofoam based on an extended version of the Drucker Prager yield criterion is presented. The formulation is implemented in ABAQUS/Explicit finite element program and verified with data available from triaxial tests conducted on two varieties of EPS geofoam manufactured in Australia and Korea. Also results from the proposed formulation is compared with four other constitutive models found in the literature to confirm the suitability of this model in simulating experimentally observed EPS geofoam behaviour. Wave propagation due to vibratory and resonant pile driving was investigated using a two-dimensional finite element model. First, the proposed model is verified using field data found in the literature and then it is used to simulate vibratory and resonant pile driving. Finite element mesh is truncated at the boundaries of the finite domain using wave transmitting boundaries for both shear and dilation waves. A parametric study was conducted by varying the amplitude and the frequency of the driving forces pertinent for commercially available driving rigs, soil rigidity index and soil material damping. The influence zones for different structures are derived by considering the Peak Particle Velocity (PPV) limits given in a number of design standards. In the next part of the thesis, the efficiency of water and EPS geofoam in-filled wave barriers is investigated using a three-dimensional finite element model. The finite element formulation developed at the first stage of the research is used to simulate the mechanical behaviour of EPS geofoam. The proposed model is first verified using field data available for attenuation of ground vibrations in free field and at the presence of an EPS geofoam wave barrier. Then the model was used to conduct a parametric study varying the physical properties of the wave barrier: depth, length, width and location, as well as the frequency of the vibratory source. Outcomes of this investigation proved that EPS geofoam is the most efficient fill material in attenuating ground vibrations. The effect of EPS geofoam wave barriers in attenuating ground vibrations during vibratory pile driving is then studied using a three-dimensional dynamic finite element model. An advanced finite element model is developed to facilitate deep penetration of the pile from the ground surface avoiding mesh distortions. An EPS geofoam wave barrier is installed between the driven pile and the nearby existing pile. The efficiency of EPS geofoam wave barrier in protecting the existing pile was investigated by observing the maximum bending moment developed in the existing pile during vibratory pile driving. A parametric study was conducted by varying the geometric parameters of the EPS geofoam wave barrier and properties of the soil medium to evaluate the significance of these parameters in attenuating ground vibrations. Finally, the research is concluded with a summary of major conclusions, important design criteria and recommendations for future research on the use of EPS geofoam wave barriers in attenuating ground vibrations.

Date of Award	2014
Original language	English