Dry Parallel Seismic: A Novel Method for Determining Thickness of Buried Concrete Pad Foundations

Abstract

The structural capacity of concrete foundations supporting, for example, telecommunications and electrical transmission towers depends, among other things, upon the thickness of the concrete foundation. Current methodology for investigating the thickness of concrete foundations nondestructively has largely been focused upon deep foundations, such as caissons, and in situations where the top of the foundation is exposed. For example, the parallel seismic (PS) method is a borehole method that uses the arrival times of waves imparted in a foundation at a sensor next to a buried foundation to detect the thickness of the foundation but is typically used for deep caisson type foundations. However, in many instances, these foundations are pad and pier type footings that can be buried deep below ground and can be relatively thin, for example, less than 45 cm in thickness. The objective of the present work is to present a nondestructive method for determining the thickness of concrete pads with no direct access. The dry PS method was developed to determine the thickness of thin, buried concrete foundations. The method was first used to verify the as-built thickness, as mentioned in the engineering drawings of a guyed tower dead-man block. Second, it was used to determine the thickness of the pad foundations of five telecommunication towers with pad and pier concrete foundations in South Asia. These towers had foundation thicknesses ranging from 16 to 36 cm, as verified through excavation. Analysis of the data collected during dry PS testing resulted in a mean absolute error (MAE) of 18 mm, which equates to approximately 6% error. Thus, this paper demonstrates that the dry PS method overcomes the limitations of the current methodology and is capable of accurately determining the thickness of buried concrete foundations.