A Comparison of Trencher Method Versus Slurry Trenching and Soil Mixing for Seepage Barriers in Dams

The chain-style trencher is a relatively new technique to mitigate seepage and stability related potential failure modes in dams and levees. One of the primary uses of the trencher method in dam and levee applications is in-situ mixing to create seepage barriers within earthen embankments. A trencher is a vertical, rotary chain mixing blade fixed to a track-mounted chassis. In-situ mixing approaches can be beneficial to dam and levee projects as cutoff walls can be constructed on the upstream, crest or downstream sides, or combination thereof on the embankment.

Possible seepage barriers constructed with the Chain-Mixing-Method (CMM), also known as the trencher method, includes soil-bentonite or soil-cement-bentonite. In addition to seepage barriers, soil-mixing techniques can be used for stabilization and gravity buttresses. Furthermore, the trenchers can also be outfitted with backfill delivery attachments to install groundwater relief trenches. These relief trenches are typically installed along the toe of the slope by emplacing a granular backfill to provide a planned pathway for seepage without causing erosion issues to the earthen embankment. (Continued)