⚠ May require more grout than anticipated

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Message: Sliplining perforated CMP can be problematic because grout may fill holes in embankment.

Lessons Learned:

1. If pipe has holes, consider replacement instead of slip lining. It can be difficult to estimate grout needs because voids adjacent to the conduit can fill with grout.
2. Grout mix and placement technique is very important. The grout must be flowable in order to properly seal the annular space.
3. Grout is especially important with mechanical joints – more important than with a fusion welded joint.
4. Low head dams might be more cost effective to replace than slipline.

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  This central Montana dam had holes in the invert of the pipe. The pipe was sliplined with a mechanically joined HDPE pipe.

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  This central Montana dam had holes in the invert of the pipe. The pipe was sliplined with a mechanically joined HDPE pipe.The grout take was significantly higher than the original quantity estimate – voids around the pipe were far worse than anticipated.

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  This central Montana dam had holes in the invert of the pipe. The pipe was sliplined with a mechanically joined HDPE pipe.The grout take was significantly higher than the original quantity estimate – voids around the pipe were far worse than anticipated.It was difficult to get a good seal of annular space and to achieve the correct grout mix (due to winter conditions) – sand caused bridging in the annular space.

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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: 4702
Revision Date: 12/02/2022