Studying the applicability of non-destructive techniques in diagnosing defects of soil-cement columns

Abstract

This article studies the applicability of the Non-Destructive Techniques (NDT) into semi-rigid structures, particularly in soil-cement columns. A numerical model for the semi-rigid soil-cement column is first created. Different kinds of defects are intentionally allocated in the model, including necking, bulging, and degraded stiffness. The assumption is that by using an excitation as an impact load at the structure head and then letting the structure vibrating freely, studying the wave characteristics inside the structure, i.e., responsive velocity and displacement at various points along the column shaft, the impedance could be determined. If there is any variation in the mechanical impedance Z, which is defined to be the product of mass density, area of the cross-section, and the wave velocity, the defects are confirmed. The shape of the impedance curves with respect to combined defects is analyzed, and spectral response curves are plotted. The process of analysis in the time domain and frequency domain for the soil-cement column is conducted using Fast Fourier Transformation. The theoretical and computed impedance of the structure from the numerical model will be compared with each other, in the shape of the responsive curves, and the distinguished issues; some discussions on the propagation of waves through semi-rigid structures are summarized. There is no distinguishing feature in the characteristics of the impedance of the structure revealed. It comes to the conclusion that the applicability of the vibration test is not clearly recognized. There is quite a difficulty in evaluating the performance of the semi-rigid structures like soil-cement columns by using vibration or impact load test. This outcome suggests that the column is not the same as the pile, and another alternative and/or approach is recommended to apply in quality assurance/control QA/QC for such embedded semi-rigid structures.