Filter Diaphragms

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Message: Constructing the filter diaphragm is a critical component of a dam's integrity.

Constructing filter diaphragms using good construction practices is critical to the integrity of a dam. Two common techniques used in filter diaphragm construction include concurrent construction and cut and fill construction.

A few important items to consider:

• Existing Conduits: When retrofitting a filter diaphragm around an existing conduit as part of a rehabilitation project, it may not be possible to get adequate compaction of filter sand under the conduit. In these cases, Reclamation recommends cutting the conduit to allow compaction of the sub-grade prior to re-construction of the conduit (see Design Standards No. 13: Embankment Dams (Ch. 5: Protective Filters)).
• Contamination: If there are contaminations in the filter, concentrated flows can develop that can lead to erosion of embankment particles.
• Compaction: Compaction during construction can further break down particles and lower the permeability of filters. For critical filters and drains, consider specifying material gradations.
• Segregation: On-site soils tend to be gap graded and are prone to segregation. If on-site soils are used in the downstream shell of a dam, carefully place soils to minimize segregation.

Concurrent Construction

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  Maintaining the filter layer one layer higher than adjacent materials will minimize the chance of contaminating the filter.

Note: The content on this page was originally created as part of DamOutletWorks.org (DOWL, 2018). It has subsequently been updated and reformatted as part of the Dam Safety Toolbox.
Revision ID: 6721
Revision Date: 03/17/2023