Calculation of the effect of Poisson's ratio in laboratory push and pull testing of resin-encapsulated bolts

• Poisson's ratio effect in pull and push tests is formulated based on failure mode analysis.
• The percentage difference of push and pull load has been calculated at bond failure and after bond failure.
• Results from developed formulae were compared with experimental results, and showed good agreement.

Short encapsulated pullout tests are frequently used in the laboratory and in the field to examine the bond performance of rock bolting. Because of the restriction of sample conditions and of testing apparatus, push testing is usually used instead in the laboratory. Rock bolts have a better performance in push testing and this is a thought to be attributed to Poisson's ratio effect of the steel rebar. In this paper Poisson's ratio effect in short encapsulated push/pull tests is evaluated analytically. The percentage difference of axial load in push and pull tests is calculated based on the failure mode analysis and the corresponding mechanical models of rock bolting mechanisms. Analytical results show that Poisson's ratio effect is closely related to the radial stiffness and embedded length. The theoretical predictions were compared with experimental data and showed good agreement, and so can be used as a guideline in laboratory testing design.