Evaluation of turbulent flow conditions in rock cracks and feasibility of a new grouting method for laminar and turbulent conditions

Precise evaluation of the permeability in a dam foundation is extremely important for reasonable dam foundation treatment. The Lugeon test of permeability assumes a laminar flow around a test section in a test hole. However, it is often pointed that the flow around the section is usually a turbulent flow. In such cases, the permeability is underestimated. To investigate this matter further, laboratory tests of permeability were conducted on single cracks of boring cores. In this experiment, water was used to evaluate the transfer condition from a laminar flow to a turbulent flow. Results show that the critical Reynolds numbers were on the order of several hundreds, which is much lower than the standard number of 2,000 for the flow between a pair of parallel plates. Subsequently, the progressive conditions of the turbulent flow in the Lugeon tests were evaluated using a new theoretical equation representing the relation between the injection pressure and flow rate under laminar and turbulent conditions on a radial flow model between parallel plates. The outcome indicated that the turbulent flow was highly developed in the tests. Based on the results presented above, the flow condition in a rock mass during grouting was evaluated. The evaluation model was the previous model expanded for use with non-Newtonian fluids. Using this model, a new injection method was proposed for grout particles to penetrate to the target area, and then subsequently settle and block up cracks from the far side toward the near side around a borehole. Using this method, the grout-flow condition is kept turbulent with high carrying power in the interval of penetration to the target area. Then the condition becomes laminar for settlement. The feasibility of this method was evaluated using results of calculations done with the model.