Detecting steel rods and micro-piles: A case history in a civil engineering application

Investigating engineered structures with GPR is challenging because quite often the scale of important features is similar or smaller that the natural scale of heterogeneity in the material.In this paper I summarize the key factors and use numerical simulations and real data examples to illustrate the tradeoff between detection and resolution. The targets were micro-piles and steel bars with diameters 0.13. m and 0.02. m, respectively, and embedded in an ancient wall that consists of an aggregate of stones ranging in size from 1. cm to half meter, mortar and air. The data were collected with center frequency antennas of 200, 600, 2000. MHz which provide increasing resolution. The model and measurement results indicate that lower resolution may result in a better understanding of the structure imaged with GPR. In fact, high resolution profiles show enhanced anomalies caused by heterogeneities in the host material, making data interpretation more difficult.This study shows that GPR survey design must be clear about the particular engineering objective and requires selecting the optimal frequency and bandwidth depending on the target dimension. © 2012 Elsevier B.V..