RCC Hydration Heat - Hadlock Dam Failure

[dickg]

In reference to the Hadlock Dam Failure (Northern NY) they poured RCC until January 17th. The slab was approx 3- 4 feet Thick x 40 feet across the dam and 125 feet long. A picture taken on January 27th showed part of the dam bare and about 70% having 1-3" of snow on it. There was no additional snow of any concequence prior to the resumption of construction on March 23rd when they resumed pouring RCC. The average temperature during that span was 20 degrees f. Overlaying the pre-failure structure with the Clough Harbour failure drawing the initial whirlpool center is nearly in line with the end of the RCC where it transitions to the existing earthen structure. From my calculations the RCC would have contracted approx 3/4" for every 10 degrees of cooling. From what I have read, RCC does not produce a significant amount of hydration heat and with a relatively thin slab and a large amount of surface area it is hard for me to believe that the tempeture of the slab did not drop. Once it contracted any compaction at the juncture with the earthen dam is gone creating a conduit across the entire width of the dam. The only other factor would be the frost in the ground adjacent to the slab at the end. Once they resumed pouring they added insulation over the cold concrete. The Clough Harbour report did not address this issue. I e-mailed the engineer at Clough Harbour questioning this and they acknowleged receipt. They have not commented on this or returned my follow up e-mail. Am I barking up the wrong tree.

 

[BigH]

Can you give this poor lad overseas a reference to the Hadlock Dam failure - to help me understand what happened?

 

[dickg]

Go to

http://www.hadlockpond.org

At the bottom of the page there are links to allow you to download the Clough Harbour Reports. There are also pictures of the dam failing on that website.

 

[cvg]

first of all, you don't "pour" RCC. Roller compacted concrete is an extremely lean mixture of concrete which is placed using normal earthmoving equipment and rolled to compact. It is constructed in lifts which might be 6 - 8 inches in finished thickness. There is very little water in the mix, therefor very little shrinkage. It doesn't perform like conventional concrete.

However, you are right to look at the interface between the soil and concrete. Any shrinkage, lack of compaction or settlement along the interface would offer a preferred location for piping to occur. Standard practice (in this neck of the woods) would be to place a layer of filter material between the structure and the earth embankment. This is often called a filter diaphram and would prevent internal erosion and formation of a pipe along the structural interface.

 

[dgillette]

You may not have the exact right tree, but you certainly have a likely one.

The interface between embankment and RCC is definitely a suspect. The filter CVG mentions should be standard practice. Also, the drawings show vertical sides on the RCC walls, which is not the preferred way of doing things. Battered walls are easier to compact against (often by wheel rolling with a rubber-tire loader), and are more forgiving of small movements (such as slab shrinkage or consolidation settlement) because the soil is less prone to pulling away to leave a gap or an area with very low contact pressure against the wall. Those would be likely places for internal erosion to initiate.

I just skimmed the CH report and didn't notice any mention of the vertical walls, which doesn't necessarily mean they didn't mention it.

 

[dgillette]

The new (Feb 2006) 'Civil Engineering' magazine has a two-page article on Hadlock. Not much new information.

There is also one on the recent Taum Sauk failure in Missouri.

 

[PEinc]

Shouldn't this thread be in the Dam Engineering Forum where more could appreciate it?

 

[cvg]

unfortunately, that forum has very little activity - I see only 4 posts in the last 5 years - and two of those went unanswered... Most of the posts regarding dam safety either appear in this forum or in the flood control forum for the hydrology related questions.

 

[PEinc]

If people put the damn (sorry, dam) posts in the right forum, there would be more than 4 in the last 5 years.

 

[dickg]

You have to go back to the original question. It had to do with the way RCC would react exposed to very cold temperature from 3 sides of the structure for an extended time. They mixed it and spread it out and compacted it in cold weather. Typically when you do that you heat the components and from the test reports that appears to have been done. As the rcc sits in an average of 20 degree weather for many weeks is there enough heat generated by the curing concrete to offset the cooling from the surrounding air. From what I can find literature the answer is no and the structure cooled. Also from literature they came a cooeficient of expansion for RCC. Based on the length of RCC a 10 degree decrease in temperature would cause the slab to shorten by .75".

The fact that this is in reference to the Hadlock Dam is not relly impotant. This could be any slab of RCC.

I posed this concern to Clough Harbour in an e-mail several monthes ago and they said they would review it. I have sent them a follow up e-mail which they have not resonded to. I felt there report only looked at the "normal failure modes".

Is there a real posibility that the failure occurred from the shrinkage due to temperature opening up a crack across the entire dam. This slab traversed the entire dam. It extended from the main spillway 120 feet west where it ended against the existing embankment. Even if they compacted the soil between the RCC and the embankment as they built up the RCC, the slab was exposed all winter and any shrinkage could have negated the compaction or even opened up a crack at the transition. Before it warm up they resumed construction and covered that RCC with more RCC and fill insullating the wintered over material.

The CE Mag is just a rehash of everything that has bounced around locally.

 

[dgillette]

Just for fun, here's a web cam on a new RCC dam going up in Boulder CO. This one does not have the kind of embankment interfaces that Hadlock does/did. At 5-minute intervals, you don't get much feel for the flow of the work, but you can see the equipment and construction methods being used.

http://www.pinebrookwater.com/