Pile Driving Vibration Energy-Attenuation Relationships in the Charleston, South Carolina Area

Vibrations generated by driven pile installation often affect adjacent and surrounding buildings in tightly spaced urban environments. These vibrations can lead to complaints from neighboring residents and businesses and/or cause structural damage to adjacent structures, especially older and historic buildings. Pile driving vibrations are of particular interest in the Charleston, South Carolina area since the majority of new structures are founded on driven pile foundations bearing within the underlying Cooper Marl Formation. By knowing the vibration attenuation relationship of a project area (i.e. the decrease in vibration amplitude with distance), it is possible to develop pile installation plans that minimize discomfort to residents and the risk of damage to adjacent structures. In addition, knowledge of the vibration attenuation relationship for a site can assist in determining the limits for pre-condition surveys to document the existing conditions of adjacent structures prior to pile driving operations. This paper presents the case histories of vibrations monitored during seven driven pile and one vibratory pile construction projects in the Charleston, South Carolina area. The vibration data was then analyzed to evaluate the energy-attenuation relationships for the individual sites. Comparisons of these analyses were then made in an effort to determine typical energy-attenuation relationships for driven piles within the Charleston, SC area. INTRODUCTION Vibrations generated during driven pile installation are often a cause for concern during the project, since these vibrations have the potential to disturb nearby residents and cause damage to adjacent structures. In Charleston, South Carolina, pile driving vibrations are of special concern for several reasons: the tight spacing of buildings, the age and historic significance of many of the city’s buildings, and the presence of soft clays and loose sands in the local soil stratigraphy require placement of many of the newer structures under construction on deep foundation systems. Due to cost considerations, many of the deep foundation systems chosen are driven piles. It has long been understood that vibrations generated by pile driving dissipate with distance (i.e. attenuate). Modeling pile driving vibration attenuation relationships (i.e. the decrease in vibration amplitude with distance) is dependent on a range of factors, with the primary factors being energy delivered to the pile and the surrounding soil types. Previous research (e.g. Wiss, 1980, Woods and Jedele, 1985, Ali et al., 2003) have published attenuation characteristics of certain soil types based on empirical data. The case histories of vibrations measured at 8 pile installation construction sites in the Charleston area are presented. The attenuation relationships for these sites were analyzed with regards to distance and energy in order to develop typical models for use in future pile driving projects in and around Charleston, SC. Charleston, South Carolina lies within the Lower Coastal Plain geologic province of the Atlantic Ocean coast. The near surface “overburden” soils consist primarily of Pleistocene deposits of the Quaternary Period. Pleistocene formations generally consist of sand and clay deposits with varying amounts of shells and occasional organics. Beneath the “overburden” soils lies a highly calcareous soil stratum called the Cooper Group, known locally as the Cooper Marl Formation. The Cooper Marl Formation is a marine deposit of late Eocene to Oligocene Periods that underlies a significant portion of the Charleston Area. The Cooper Marl is typically classified according to the Unified Soil Classification System as a low plasticity sandy silt (ML) or sandy clay (CL). Refer to Klecan et al. (2001) for additional