Using geostatistical simulation to determine optimal grout injection pressure in dam foundation based on geomechanical characteristics

In operational projects, injection pressure and cement bonding in boreholes are estimated based on the results of geotechnical excavations, the Lugeon test, and pilot injection. However, considering the limited number of pilot boreholes and several structural complexities of rock mass, estimating the structural characteristics of injection boreholes is always associated with errors and in some cases grave mistakes. The present paper focuses on a new approach to determine the exact rock mass engineering characteristics in different parts of the Khersan Dam area. Using geostatistical principles, drawing changes in views, and preparation of an interpolated block model, values such as RQD and Lugeon over different parts of the dam site were estimated by kriging. A solution for determining the amount of pressure required and the cement bonding at any point of the dam axis was also proposed. The results showed that, with the transition from surface horizons to depth, neither cement bonding nor injection pressure were normal and exhibited no specific trend. Accordingly, to achieve optimum results, the engineering characteristics of rock masses in the column of each borehole were estimated; injection design and estimation of required pressure must be done on the spots with regard to the engineering characteristics changes.