Cutoff

Cutoff wall construction along the American River.

(Image Source: USACE)

"Seepage barriers, or cutoff walls, can be an effective means for controlling seepage through an earthfill dam or its foundation. Since approximately the early 1970s, the various types of cutoff walls available to embankment designers have increased with advances in construction methodologies and technology. The industry has made significant improvements in the equipment used to construct cutoff walls and in the efficiency of their operation. Increasingly, cutoff walls are being considered as a primary modification component within existing earthfill embankments that have a history of chronic seepage related problems or that undergo an acute seepage incident. With the wide array of cutoff wall alternatives, they can be the technically preferred and most cost-efficient methods to remediate an identified seepage problem given the difficulties of creating an earthfill cutoff within an existing embankment with an active reservoir."^[1]

"Various methods of seepage and percolation control can be used, depending on the requirements for preventing uneconomical loss of water and the nature of the foundation in regard to stability from seepage forces. Cutoff trenches, sheet piling, mixed-in-place concrete pile curtains, slurry trenches, grouting of alluvium, or combinations of these methods have been used to reduce the flow and to control seepage forces. Blankets of impervious material, extending upstream from the toe of the dam and possibly covering all or part of the abutments, are frequently used for the same purpose."^[2]

"Construction of conventional rolled earthfill cutoff trenches, whether in a new earthfill dam or as a component to the modification of an existing dam, can be a prohibitively expensive operation, depending on the required depth, the existing natural groundwater conditions, and the availability of suitable impervious material. Cutoff walls can be a viable alternative for reducing seepage through embankment dams and their foundations. Cutoff walls can be constructed by a variety of methods that do not require foundation dewatering and that greatly reduce the amount of excavation from that required for a rolled earthfill cutoff. Another advantage to cutoff walls is that they can often be constructed in very limited working spaces."^[1]