METHOD FOR INVESTIGATING AN ANCHORED ROD-LIKE BODY HAVING AN ACCESSIBLE END, AND APPARATUS FOR CARRYING OUT THE METHOD

摘要

This invention relates to a method and apparatus for investigating a rod-like body which is anchored in a surrounding material and which has an accessible end, for determining the state of the anchorage of the body and its length. It has long been known in the art that elastic oscillations of a multiplicity of different wave types can be used to determine the state of boltsand other anchors. However, there is a problem in the present art in that the oscillations are highly dampened. The present invention provides the advantage of having oscillations with a much lower damping effect and which do not propagate in bore hole mud. Transient elastic oscillations are excited in the accessible end of the body. The oscillations comprise a flexural wave causing a deformation of the body varying with respect to amplitude and phase over the cross-section of the body. The flexural wave propagates in the longitudinal direction of the body and is partially reflected at discontinuities of the body and/or the anchorage. Transient elastic oscillations comprising flexural waves reflected at such discontinuities and returning to the accessible end of the body are received and detected. The position and magnitude and/or type of at least some of the discontinuities are estimated with the aid of time-position and amplitude of the reflected flexural waves. Discontinuities of interest are the beginning and end of anchorage, the end of the body and possible cracks or fractures in the body and/or its anchorage. The method and the apparatus are primarily intended for in-situ investigation of concrete-bond rock anchors (bolts) although the method and apparatus can be used for at least partially investigating other anchored rod-like bodies.