Experimental and Theoretical Diagnostics of Defects in Ferroconcrete Piles Based on Reflection of Longitudinal and Transverse Waves

Abstract

The new theoretical model of wave propagation in a pile was obtained. The hyperbolic equations system with boundary conditions can be used for modeling the nonlinear dynamics of a ferroconcrete pile. It takes into account the propagation of a longitudinal and two types of transverse waves. The numerical solution of these equations with specific boundary and initial conditions, which depend on the method of stimulation of low frequency impulse wave, gives more complex information about the pile stress-strain state. This information gives an opportunity not only to find the length of the pile and locations of defects, but also to identify small defects, their types and geometric shape of a pile. In one-dimensional case the developed model agrees with the already known models and in the three-dimensional case it is their new generalization. It is difficult to clearly answer, which of methods is optimal. The experiments confirmed that each of these approaches provides a timing signal, which can be recorded by a transducer and used to determine the actual length and defects locations for a shaft, as well as to identify the geometric shape of a pile arranged in the soil. The problem, obviously, is not the choice of a pulse excitation method, but the further interpretation of a recorded signal. The theoretically justified criteria are necessary for the identification and classification of defects in piles; otherwise a decision as to the defects presence and their characteristics depends entirely on the skills and abilities of the operator, that is, on the human factor.