Experimental Study of the Core-Drilling Method for Evaluating In Situ Stresses in Concrete Structures

Abstract

The core-drilling method (CDM) is a stress-relief technique used to determine in situ stresses in concrete. A small hole is drilled into the concrete of a structure and the resulting displacements are measured and then converted into in situ stresses using elasticity theory. Three major factors that influence stresses determined with the CDM have been identified: (1) swelling of concrete around the core hole caused by exposure to water used during the drilling process; (2) changes in the measured deformations caused by relief of differential shrinkage stresses; and (3) steel reinforcement in close proximity to a core hole. Recent research has addressed each of these factors through analytical and numerical techniques that adjust CDM-calculated stresses. This paper describes experiments performed to verify these approaches and to show that the CDM can determine accurate in situ stresses in concrete structures. Concrete plates loaded in compression were subjected to hole drilling, and the resulting displacements were measured with three-dimensional digital image correlation. Stresses calculated from measured displacements agreed with applied stresses to within 28%. When the calculated stresses were modified to account for the effects of the three influencing factors, the relative error in applied versus measured in situ stresses in the experiments was less than 10%.