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Dam Breach Emergency

Dam Breach Emergency

Dam Breach Emergency

(OP)
dam is 25' wide across the top...50' wide across at the toe...150' long...constructed with 4' boulders and rubble fill...then topped with concrete...several times because the first and each successive time they did a crappy job without much thought to what they were actually trying to do and the extreme hydraulic force of flowing water...6' deep x 120' water behind it...

The hole is big enough to fish a 40 foot long 24" diameter CMP (corrugated metal pipe) into it...with about 10-12 feet protruding from the upstream side...do this with a Komatsu PC400 trackhoe...a piece of iron big enough to handle the pipe with the swift flow of water pulling on it/flowing through it as the pipe is submerged...so the trackhoe doesn't get pulled into the creek (really a river) by the hydraulic force of the flowing water...also with a boom/stick length long enough so that the trackhoe isn't close to the (substantially) undermined portion of the concrete roadway across the top of the dam...you could drive a go-cart through the hole...

also, make sure no one drowns during the above process of fishing the pipe in...I'm considering having a swift-water rescue team standing there while this is going on...

then start backfilling the upstream end of the pipe (projecting out 10-12 feet past the dam) with 3"-6" screen crushed rock...some of this material will be swept into the void along the sides of the pipe...which is the goal...keep back filling (with the trackhoe) until the flow is minimal through the hole, and most of the water is going through the 24" pipe...... See More

then begin backfilling with flex base (crushed limestone roadbase)...not so much of this material...the fines will be carried into the voids of the 3"-6" rock...at this point the hole should be plugged on the upstream side of the dam...

problem...I've just installed a 24" dia pipe where there was a hole with the equivalent flow of a 48"-60" diameter pipe with a 1-2 fps flow...so, I've constricted the flow, and the dam will start to do it's job...the water will begin to rise behind the dam and begin to overtop the dam...within a day or two or possibly less...be running over the top of the low water crossing...as it is supposed to...but I have not dealt with the void/cavity under the concrete roadway, and now it's underwater...

no bueno...

my other option is to build a fifty foot long temporary dam from the shore...isolating the hole so we can install the pipe and effect repairs on the hole/cavity/roadway...basically filling with high-strength flowable grout...but would need to bypass the 3,000-5,000 gallon per minute flow with a 10"-12" self-priming trash pump...probably two of them...one as a backup/standby...with a day tank to run continuously for the 3-4-5 days it would take to do all the repairs...

any ideas?

RE: Dam Breach Emergency

Use  grout bags to fill the cavitys with grout.You might need some anchors when filling the bags but they will expand into any voids. Probably some grout tubes throug the bags should also be installed to catch any small voids left after the bags are pumped. To block the water flow find a steel barge fill it with rock and sit it in front of the hole if possible this will reduce the force of the current in that area. What you have done so far seems fine large rock then smaller etc could finish with pea gravel that will find the voids then grout. This can be done underwater.

Intrusion Prepakt /marineconcrete.com
 

RE: Dam Breach Emergency

When the dam was built, did they employ a diversion tunnel that could be brought back to life?

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Dam Breach Emergency

(OP)
thanks mike and prepakt...problem solved this afternoon...going to cut in a four barrel 18"-24" DIP with gates to open and control water level behind the dam...once we have this gravity bypass cut in, then we can dam off (rubble fill & fines) the breach and effect necessary repairs/grouting there...

thanks again...

thread closed...can't figure out how to delete it...?

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