Engineering of Grout Curtains to Standards

The desirable permeabilities of curtains vary for different types of dams and conditions. The paper examines these issues and for them suggests standards of permeability expressed in lugeon units. To engineer curtains to desired standards, the split spacing or closure method is used, and closure is preserved until the target standards are reached. This procedure is applied to hole spacing and, separately, to hole depth. The upper stages of curtains can be constructed to tighter permeabilities than lower stages. At earth core dams, the curtain permeability should ideally produce pore pressures immediately above the foundation slightly in excess of pressures in foundation joints. The curtain's position affects the ideal permeability. At concrete dams, the curtain permeability should relate to the ability of the drainage system to discharge seepage.