Evaluation of Hydraulic Jacking Mechanism during In Situ Rock Grouting Using a Strain Energy Release Rate Method

Abstract

During the hydraulic jacking process, the preexisting joints in a rock mass under grout pressure that exceeds the in-situ normal stress become unstable. This process thus causes the tensile opening and crack growth of joints. In this paper, we describe an analytical approach to evaluating the hydraulic jacking mechanism based on the strain energy release rate method (SERRM). By employing the first law of thermodynamics, it is shown that the amount of energy stored in a grout mixture is equal to the amount of energy released during crack growth. This concept helped us to develop the SERRM. Accordingly, the paper presents development of new analytical equations to determine the allowable grout pressure and length of the resulting crack growth. These equations are fracture-toughness dependent, so as to avoid causing unwanted deformations due to jacking during grouting. The proposed allowable grout pressure equation accorded very well with the existing empirical rules, field data obtained from the Sardasht Dam project, and with the results of a numerical method.