Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    • CommentAuthortony
    • CommentTimeAug 3rd 2019
     
    Looks to me like the spillway had been eroded away for years before that concrete veneer collapsed.

    Will the dam fail, no

    Why not siphon the water out? Or better drain it out?

    More rain refilling the reservoir should be able to be diverted by design
    •  
      CommentAuthordjh
    • CommentTimeAug 3rd 2019
     
    Posted By: tonyLooks to me like the spillway had been eroded away for years before that concrete veneer collapsed.

    Could be, but they said there was some initial damage that caused water to jet behind the spillway and rapidly erode the earth underneath. So who knows.

    Will the dam fail, no

    Depends how much rain they get tonight and what other damage there is we haven't seen.

    Why not siphon the water out? Or better drain it out?

    Presumably there's no practical way to do either of those things otherwise they would have done them. Priming a syphon of the required size would be an interesting challenge. Maybe that's what the pumps are really doing.

    More rain refilling the reservoir should be able to be diverted by design

    I doubt that's ususally seen as a design requirement. Spillways are needed in any case and can handle normal overflows just as easily as emergencies. Why go to the expense of buying extra land and building an extra canal and then maintaining it for decades whilst it lies unused?
    • CommentAuthortony
    • CommentTimeAug 3rd 2019
     
    “Safety is our prime concern”, surely the design must have been fail, no?
    • CommentAuthormike7
    • CommentTimeAug 3rd 2019 edited
     
    https://www.wired.co.uk/article/whaley-bridge-dam-collapse

    I'd agree with Tony that there's no chance of failure - unless there is sufficient heavy rain to refill the dam to overflowing. It looks a bit overcautious to have restricted residents' access so severely when there was no immediate forecast of such rain.
    • CommentAuthortony
    • CommentTimeAug 3rd 2019
     
    Try are trying to stop water flowing into it which is good,

    Could the inspections have missed the hollowness under the spillway concrete, it looks like soil/aggregate under it, no foundations or reinforcement and the slabs don’t appear to be tied together either.
    •  
      CommentAuthordjh
    • CommentTimeAug 3rd 2019
     
    Reinforced concrete was invented twenty years after the dam was built.
    •  
      CommentAuthordjh
    • CommentTimeAug 3rd 2019
     
    Posted By: mike7It looks a bit overcautious to have restricted residents' access so severely when there was no immediate forecast of such rain.

    So if you were actually taking the decision when it happened instead of sitting at your computer with google two days later, what would you have done?
    • CommentAuthormike7
    • CommentTimeAug 4th 2019
     
    I'd have done the same re. the initial evacuation. Then, assuming an actual inspection revealed no more than my google/TV images once the overspill had ceased, I would have told residents that, while it was urgent to lower the water level as much as possible before further rain, the dam did not appear to be in danger meanwhile, Also that should sufficient heavy rain arrive, any further failure would almost certainly be progressive rather than sudden and total.
    That would perhaps be sufficiently cautious to persuade most residents to stay away most of the time, while sparing them undue anxiety as to the probability of losing their homes and possessions.
    • CommentAuthorgyrogear
    • CommentTimeAug 4th 2019
     
    Posted By: mike7It looks a bit overcautious to have restricted residents' access so severely


    Yes - maybe a case of "lies, dam lies and saturistics"...

    gg
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2019
     
    Posted By: mike7the dam did not appear to be in danger meanwhile, Also that should sufficient heavy rain arrive, any further failure would almost certainly be progressive rather than sudden and total.
    That would perhaps be sufficiently cautious to persuade most residents to stay away most of the time, while sparing them undue anxiety as to the probability of losing their homes and possessions.

    I think the question anybody in charge needs to ask is "Is there any credible possibility of sudden collapse?". Probability and caution don't really cut it. I for one don't see any reason why a collapse wouldn't be sudden and total if it does fail for whatever reason, and I agree the most likely cause appears to be a repeat overtopping.

    The other issue to bear in mind is the strategy for preventing looting. Unless an evacuation is near complete the possibilities for looting and other mischief is very real. A partial evacuation would result in the need for extra police patrols in the danger area.
    • CommentAuthortony
    • CommentTimeAug 4th 2019
     
    Several things spring to mind:-

    Why does the spillway go over the dam at all? Spill it at the top/inlet of the reservoir where it can do no harm.

    The angled wall on the spillway looks wrong

    Enough water has been pumped out now.
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2019
     
    Posted By: tonyWhy does the spillway go over the dam at all? Spill it at the top/inlet of the reservoir where it can do no harm.

    Because that's where spillways go. :tongue:

    When you dam a valley, the outlet stays at the lower end of the valley, where it always was. That's also where the dam is and where the spillway goes. The sides of the valley and the river upstream are higher than the dam. Otherwise water wouldn't flow into the reservoir or stay there.
    • CommentAuthortony
    • CommentTimeAug 5th 2019
     
    So once the dam is full it overflows over an earth wall?
  1.  
    Posted By: tonySo once the dam is full it overflows over an earth wall?

    Yes - except the earth wall has puddled clay on the inside and a concrete cover on the outside. The dam in question was described as a gravity dam which is a dam that stays be virtue of its mass and weight rather than structural shape and strength.

    Gravity dams work well - until damage occurs and water scours out the mass whereupon failure will result (which is what happened) What you don't know is how long the (unseen under the concrete) scouring had been taking place which perhaps dramatically increased with the recent deluge.

    My understanding is that gravity dams are unlikely to suffer sudden catastrophic failure (that's the province of structural dams) but failure will be a slower event with water washing out the mass in ever increasing amounts as the torrent of water widens the hole - so an accelerating failure will result.
    •  
      CommentAuthordjh
    • CommentTimeAug 5th 2019
     
    AIUI from the articles I've seen, there's little chance the damage was caused over a period of time, since the dam is regularly inspected. So it was most likely caused by the recent heavy rain and the hypothesis I saw was that some water overflowed the spillway (fault in the edge?) made a channel in the earth down the side and then undermined the spillway concrete with the resulting damage as seen.

    A search for 'erosion of gravity dam failure' (without quotes) yields quite a lot of info about the rapidity of failure in some cases.
    • CommentAuthorMike1
    • CommentTimeAug 6th 2019
     
    Posted By: djhAIUI from the articles I've seen, there's little chance the damage was caused over a period of time, since the dam is regularly inspected.

    I'm not sure how easily annual inspection would pick up internal erosion, unless it was sufficient to distort the dam. Maybe earth dams need to be continually monitored with seepage sensors or similar - or maybe they already are?
    • CommentAuthortony
    • CommentTimeAug 6th 2019
     
    I suspect some settlement and hollowness under the concrete certainly not none.
    • CommentAuthortony
    • CommentTimeAug 7th 2019 edited
     
    .
    • CommentAuthorowlman
    • CommentTimeAug 7th 2019 edited
     
    .
    • CommentAuthorCWatters
    • CommentTimeAug 11th 2019
     
    According to someone responsible for the dam speaking on the radio recently it was inspected twice a week.
  2.  
    IMO a twice a week inspection is going to be little more than a cursory walk by. If it is done by the same person by the time they have been doing it for a few months it will just be 'looking for changes on the walk past'. A bit like driving a car, you don't notice the breaks getting worse slowly, just when someone else borrows it they come back terrified.
    • CommentAuthorphiledge
    • CommentTimeAug 12th 2019
     
    As PIH says, the routine of a weekly inspection is likely only to pick up that the grass needs mowing or a life ring is missing. If the errosion happened pre heavy rain, I'd be very suprised if anyone noticed a build up of silt at the bottom of the spillway.

    Seems to me that gaps in the concrete covering have either gone unnoticed or their vulnerability with a deluge flowing over them wasnt appreciated.
    • CommentAuthortony
    • CommentTimeAug 12th 2019 edited
     
    +1
    • CommentAuthortony
    • CommentTimeAug 15th 2019
     
    Sniffing round I have discovered that there is (of course) a side spillway capable of draining away 26m3/s and the one that goes over the lip was designed to cope with 100m3/s — problem was the water might have come in at 150 m3/s

    The dam was built a very long time ago but the spillway is much more recent and there have been problems with other similar ones in other places.

    The slanted spillway wall was known to be a problem 11 years ago and the wall was reinforced and the slabs should have been cleaned out and grouted as a minimum but really needed replacing. THERE WERE A RAFT OF OTHER RECOMMENDATIONS THAT NEVER GOT IMPLEMENTED. The slanting wall was identified as a potential big problem if it had to cope with a lot of water.

    I still think it was way OTT moving people out especially once pumping had started.


    THERE IS A MASSIVE PROBLEM BREWING AS LOTS OF SIMILAR DAMS ARE NOW CONTROLLED AND MAINTAINED BY THE CANALS AND WATERWAYS TRUST, A CHARITY WITH TOO FEW FINANCIAL RESOURCES TO PROPERLY MAINTAIN THEM, A CLEVER MOVE BY GOOD OL HMG. BUT COULD LEAD TO A REAL DISASTER ONE DAY.

    Not sure if the press have been doing a very good job of digging but it will all come out at the inquiry. Management can’t do their job without proper resources. Who should have dug their heels in? someone needed to.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press