Ground vibration due to pile driving is a long-lasting concern associated with the foundation construction industry. It is of great importance to estimate the level of vibration prior to the beginning of pile driving, to avoid structural damage, or disturbance of building occupants. In this study, an axisymmetric finite-element model that utilises an adaptive meshing algorithm has been introduced, using the commercial code Abaqus, to simulate full penetration of the pile from the ground surface to the desired depth by applying successive hammer impacts. The model has been verified by comparing the computed particle velocities with those measured in the field. The results indicate that the peak particle velocity at the ground surface does not occur when the pile toe is on the ground surface; as the pile penetrates into the ground, the particle velocity reaches a maximum value at a critical depth of penetration. Some sensitivity analyses have been performed to evaluate the effect of soil, pile and hammer properties on the level of vibrations. The results show that increase in pile diameter, hammer impact force, soil-pile friction and reduction in soil elastic modulus can increase the peak particle velocity.
Summary
The mechanical response of an assembly of particles depends on the applied boundary conditions. Robust calibration of numerical discrete systems to laboratory results is also a primary step in many studies of granular materials. In this study, a new membrane model was developed for simulating axisymmetric element tests. This membrane model uses a simple algorithm of an array of independently controlled walls and is computationally efficient. The effect of boundary flexibility on the system response was investigated by simulating a series of triaxial tests on dense and loose specimens. At the specimen scale, differences in shear strength and volume change of specimens were observed. It was shown that localization pattern depends on the applied boundary conditions. At the particle scale, particle‐membrane contact forces, coordination number, local void ratio, and anisotropy of fabric were all affected by the boundary flexibility.
Shear wave velocity is a fundamental property of a granular assembly. It is a measure of the true elastic stiffness of a bulk specimen of discrete grains. Shear wave velocity is typically measured in the laboratory (e.g., using bender elements) or in-situ (e.g., using a seismic cone penetrometer, sCPT). In the current work, shear wave propagation is modeled numerically using the discrete element method (DEM). First, an appropriate method for measuring wave velocity is identified. The effects of particle size and elastic properties are investigated. Specimen fabric is quantified before and after wave excitation and the elasticity of the response at the scale of the particle contacts is investigated. The results show that shear wave velocity may be robustly measured for discrete numerical specimens. The ability to measure shear wave velocity using DEM simulations may provide another tool for researchers seeking to link results from physical and numerical experiments.
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