An investigation into increasing the interface strength of concrete dams on rock foundations by grouting

Currently the stability of concrete dams on rock foundations is usually improved through the installation of tensioned anchors to increase normal stress, or relief drains to decrease the uplift. An alternative and potentially attractive method has recently been investigated, the injection of specifically designed cement-based grouts into the unbonded dam-foundation interface. These strength grouts would develop a cohesion component of the interface strength and thereby improve stability.; A series of laboratory tests was conducted to investigate the bleed, Marsh funnel viscosity, and the tensile strength developed by strength grouts. Results of tests showed that for a grout to develop sufficient tensile strength in an unbonded contact, the bleed should not exceed 0.3% and the water to cement ratio should not exceed a limiting value.; An additional laboratory investigation of bonded concrete-rock contacts showed that the tensile strength will not decrease below a limiting value. This value is consistent with the threshold tensile strength for the strength grouts. This implies that a cohesion of 0.8 MPa may be developed by strength grouts at the dam-foundation interface. It should also be noted that the tensile strengths developed by the strength grouts compare favourably to the tensile strengths of concrete-rock contacts recovered from the dam-foundation interface.; The application of the results to the rehabilitation of existing dams is also discussed. These strength grouts can be injected using conventional grouting procedures. A methodology has also been developed to assess the suitability of a concrete dam for strength grouting. Finally, a cost analysis was performed that indicates the application of strength grouts will increase the factor of safety to acceptable levels at a lower cost than for tensioned anchors.