Modelling of extra large flat jack (ELFJ) testing at the Bakhtiyari dam site, Iran is the subject of this study. A complete 3D model of dam abutment, exploration gallery, and test set up was constructed. The aim was to reproduce the in-situ test results and determine the extra large jack coefficients manufactured by INTERFELS Corporation. In typical practice the large flat jack (LFJ) coefficients proposed by LNEC is used to calculate the final modulus data. These coefficients are also used to calculate the modulus data from ELFJ, which leads to significant errors. In this study a precise 3D numerical model of typical flat jack test condition was constructed using the Flac-3D code. Accordingly, the flat jack tests conducted at Bakhtiyari dam site, Iran, was simulated numerically. A very good agreement was achieved between numerical and field test results. Moreover, the obtained numerical results provided the coefficients of extra large flat jack. These, coefficients were employed for calculating the in-situ deformation modulus of Bakhtiyari dam rock mass.
Knowledge of rock mass in-situ parameters is essential in the design of large rock engineering projects. Rock mass deformation modulus is one of the most important design parameters. Typically, in most rock engineering projects the rock mass deformation is determined by combining the laboratory and field mapping data of rock mass condition. The combination of lab and field data is carried out through rock mass characterization methods (e.g. RMR, GSI, Q, etc.) aiming at determining rock mass design parameters. Depending on the quality and quantity of data, this approach can be erroneous in determining rock mass design parameters. On the other hand, direct in-situ testing is another method of measuring rock mass parameters. However, in-situ testing of rock is associated with many difficulties and is not feasible for all projects. Flat jack testing is a common method of direct measurement of rock mass modulus. This test is typically carried out for important rock engineering projects such as dams and large caverns. The objective of this study is to demonstrate the mechanisms involved in extra large flat jack testing numerically and to determine the jack coefficients. The study results were used in the flat jack testing program conducted at Bakhtiyari dam site project, Iran.
