Multiple suppression in GPR image for testing back-filled grouting within shield tunnel

In this study, Ground penetrating radar is used to detect the quality of back-filled grouting in a shield tunnel. A simulated GPR record shows that the steel bars in lining segments usually generate strong scattering and multiples, thereby obscuring the reflections from objects and making it difficult to locate the objects. Various filtering methods for multiple suppression (i.e., predictive deconvolution, f-k multiple attenuation, and Karhunen-Loeve transformation) were applied to the GPR record of a typical grouting defect model. The `wave field prediction and removal method´ is proposed, which involves predicting propagation of the GPR wave field in the lining segment. By subtracting the predicted wave field from the raw GPR record, reflections from objects are precisely abstracted. Application of the method to a synthetic GPR record revealed that the proposed method achieves better results than those obtained using existing methods.