Riprap - launchable toe - trenched toe and construction 1

[vicki932]

If constructing underwater or construction “in the wet”, does anyone know if there are guidelines to when to excavate and construct a “trench toe”? I’m looking in an area that can be as deep as 15 feet below sea level. The trench toe (launchable riprap toe) would be excavated under the toe of the slope to launch as scouring occurs to the max scour depth. The slope toe in several areas of the river can be more than 10 feet below the mean lower low, so am concerned if it is possible for this type of rock protection. The other option was the mounded toe, but my concern is that due to the volume required that it would be a problem with the obstruction to flow.

 

[cvg]

"launchable" riprap is generally mounded or laid flat in a trench on the invert of the channel. As opposed to a "toe-down" where a trench is dug at the final slope, lined with riprap and then backfilled. I think it would be very difficult in the wet to construct anything other than the mounded launchable riprap toe. This is also consistent with guidance from the Corps of Engineers Engineer Manual
1110-2-1601, see section 3.10(d)

 

[vicki932]

Thank you for the good response. I have read USACE 1601, but was hoping to find a case study or construction info of the "toe-down" type where a trench is dug. But I like you said, it's probably too difficult to attempt in the wet. Thanks for the informative response.

 

[cvg]

we have looked at numerous projects in the area and unless the scour depth is minimal, a launchable toe always ends up the most cost effective, quickest schedule, least environmental impact and least risky method.

 

[vicki932]

Do you have much experience with using a mounded toe excavated back into the slope to avoid obstruction of flow on top of the bank? If so, do you know of any good examples I may find online, and what your experience with them has been?