Investigation of Ground Deformations and Vibrations Due to Impact Pile Driving: Measurements and Prediction Model

Pile driving, a commonly used method for installing deep foundations, has gained prominence as a foundation solution to transfer structural loads to deep competent strata. However, this method of installation can generate noise, ground vibrations, and deformations. These effects pose risks to adjacent structures and buried utilities, jeopardizing the safety and serviceability of urban infrastructure. Researchers and public and private agencies have proposed many vibration limit criteria to avoid damage to infrastructure. However, these criteria for construction vibrations are not linked to the ground densification associated with repetitive and cumulative loadings in sandy soils. This dissertation focuses on developing a prediction semi-empirical model to determine ground deformations and vibrations induced by impact pile driving in granular soil deposits. Field data of ground deformations and vibrations were collected by monitoring 13 project sites in Central Florida during the installation of precast prestressed concrete piles using impact hammers. A continuous pile driving modeling approach, in which the pile is driven without any interruption to a final target depth, was coupled with an Updated Lagrangian approach in the numerical framework. An advanced constitutive soil model (i.e., hypoplasticity for sands enhanced with the intergranular strain concept) capable of reproducing changes in the soil void ratio during pile driving was adopted by computationally matching the nonlinear behavior of the granular layer with published shear modulus degradation curves. A critical highly disturbed zone was defined due to the computed soil liquefaction. The developed prediction model is validated with field data, previously published vibration attenuation curves, and vibration-induced ground surface settlement prediction methods in terms of its ability to estimate ground vibrations and deformations induced by impact pile driving in this study. Semi-empirical equations and charts are proposed using a combination of field measurements and numerical analyses to consider the following variables for the ground response due to impact pile driving operations: (1) rated energy of the hammer, (2) scaled distance from the pile, (3) pre-drilling depth, and (4) soil relative void ratio, which is related to relative density. The findings indicated that large ground deformations can occur even in cases where vibration levels (i.e., peak particle velocities) do not exceed the vibration limits

Seismic Response of MSE Walls with Various Reinforcement Configurations: Effect of Input Ground Motion Frequency

Mechanically stabilized earth (MSE) walls perform well under earthquake loads, and hence they are preferred in earthquake-prone regions. The multifaceted load transfer between the components of the MSE wall under seismic loads can be captured using numerical analysis. This study presents the results of a series of numerical analyses performed to investigate the effects of the frequency of the input ground motion on the seismic response of MSE walls. MSE wall design configurations were prepared using various reinforcement designs (length, vertical spacing, and stiffness). A frequent wall height of 8 m was selected for the analysis. Using two-dimensional finite element analysis, each MSE model was excited with seven (7) different input ground motion accelerograms with equal Arias Intensity, but with different frequencies ranging between 1 Hz and 8 Hz. The results of the numerical analyses indicated rotation at the top of the MSE wall in seismic conditions. The frequency versus acceleration plot for a point close to the top of the MSE wall indicated peaks for the excitations with frequencies f = 1.5 Hz and f = 4 Hz, which are close to the estimated natural frequency of the overall model (including the foundation soil) and the MSE wall, respectively. The highest normalized acceleration amplification factor solely within the MSE wall was recorded as 1.86 for the excitation with a frequency equivalent to its fundamental frequency (f ≅ 4 Hz). In this study, the 8 m high MSE wall models placed on a firm clayey foundation soil with the reinforcement parameters with length over height ratio in 0.5–1 range, axial stiffness in 600–1200 kPa range, and reinforcement vertical spacing in 0.4–0.6 m range performed satisfactorily under moderate seismic loads