Technical problen in steel encasing of a vertical water shaft (Surge Shaft)

[struct4me]

Dear Friends...

The Problem: A vertical shaft in rock of 27 m dia of 80 m high is a part of water conductor system, used for damping of transient pressure created by sudden out rush of water flow. Now in order to stop the seepage of water from inside of shaft to outside due to cracked concrete a out of box idea has been floated
Solution: Lowering a cylindrical conduit in to shaft which will be rested on rock at bottom and grouted the annular gap between the concrete all and steel plate of the tank. The idea is to plate acts as a barrier to stop the leakage, the horizontal pressure is to be shared by concrete and rock.
problem: Other than practical problem of lowering this 500 T cylindrical tank what will be structural difficulties.

My Views:
1. Lowering it in filled water of shaft, through the biggest crane and keeping with the accurate alignment is quite impossible when buoyancy is acting. This is practical problem. IS it correct.
2. As the tank is not to be anchored with the concrete lining and only to be grouted the annular gaps, any sudden drawdown due to tripping/starting of machines, there will be chance of plate bucking, as it is not restrained from inside. Am I Correct.

Though, the proposal is very silly, can you please enlighten me on the probable engineering difficulties.
Waiting for your response.

Regards

 

[JStephen]

If you're grouting outside the steel all the way up, you'll have a major external pressure problem on the cylinder due to difference in specific gravity between grout and water.
Building a steel shell that size is a major project in itself, but can be done (may take a year or so). Lifting it as one piece- highly doubtful.

I ran across this video the other day- very compact load that they can get right up close to, but still a major lifting challenge:

https://www.youtube.com/watch?v=MvCoJuZK7K4

 

[LittleInch]

So is this a steel lined concrete shaft or a concrete lined steel shaft - I'm confused.

A 27m diam tank is relatively small in tank building terms so not an issue there but the shaft would need to be dry for a long period. You would then need to inject the gout in small lifts as you go to prevent collapse of the steel liner.

Is this a repair of something existing or a new item? A drawing or sketch of this idea would help a bit in terms of water levels, access from the top etc

Is this a liner or a vessel or what?

You could easily build this one or two rings at a time if you have space and the lower gradually into place with hoses to grout up from the bottom in a staged process displacing water as you go.

Can the shaft be drained and use a fibre glass spray to reduce timescales?

There are multiple sewer repair procedures which might be able to be adapted.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JStephen]

The 27m is not that large, but the 80m is, and right offhand, I can't think of any tanks built of those dimensions.
The 500 ton @ 1000kg/ton works out to 3/8" plate if applied to the shell alone. An actual tank shell of those dimensions would be several times as heavy.

 

[LittleInch]

J s . I agree but this isn't a tank, it's a liner so doesn't have any forces from the liquid, they're all taken by the concrete. So yes 80m is fairly tall but the design would be different to a tank.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JedClampett]

Is this buried or exposed?

 

[dhengr]

Struct4me:
Is this a relatively clean storm water system or a sewerage system, w.r.t. working conditions in the shaft and underwater? I think I would build this liner in place, right over the shaft. You can’t easily transport pieces over about 8-10' wide and 40-50' long, and those are also the outside size ranges/limits of steel plate from a mill. Assuming 8-9' high liner rings, the plates can be roll formed and shop welded into about 50' lengths, and transported to the job site. The remaining vert. welds and the girth welds can be done in a semi-automated approach from a reusable interior scaffolding system. Then the entire liner can be lowered 8', and the whole process repeated. I don’t think I would put a steel bottom on/in the liner. This would be tough to design for this application and has a number of potential construction process problems associated with it. I would let the bot. edge of the liner be a knife edge into the shaft bottom, and then pour a tremied conc. bot. slab as the bot. seal. You might want some shear studs or hardware on the liner pls. into both the bot. seal slab and into the outside grouting. Then pour the outside grouting conc. btwn. the liner and the shaft wall. This might have to be temied too. If you have control over the water level inside the shaft, there might be some significant advantages to having this water level lag the outside grouting elevation by only 6-12".

 

[struct4me]

Thanks everyone for the response...
Now i explain to you about the problem in detail. The is related to a hydro electric system water conductor system where a surge shaft is provided to take the transient pressure due to sudden closing or opening of the turbine.
The operational plant is having a huge concrete lined vertical shaft of dia 16 m for the lower half and 23 m upper half.
Now the problem... due to the crack in lining, water is seeping from inside to outside,though quantity is very less 1 m3/s out of design in flow of 400 m3/s.
At this someone has come up with a wild idea of lower ing down a vertical steel cylinder to stop the seepage.about 30-50 m high and 22.5 m dia steel cylinder of thin plate will be lowered down in water as plant will not be shut down and to be placed just above the small er dia.
What will be the practical and design issue...
I guess..
1. What ever may be the weight of the cylinder or what may be the capacity of crane, due to buyonacy effect, it is impossible to lowered in water with accurate vertical alignment, thereby causing tilting and stuck in the concrete shaft.
2. Surge analysis will certainly show due to constriction of area and damping surface replaceed by steel in place of concrete will increase the upsurge.
3. Due to sudden draw down or sudden up rise of water in the shaft, a force will be exerted due to change in momentum.I am not sure its effect on plate surface and whether it can be equated to drag force 0.5 Cd n A v2.
I am still not sure whether this drag force can have a radial component like lift, which will try to pull or push the plate radially.

Please give your views on the above three points and what other problem may crop up structurally & hydraulically if we assume theoritically the arrangement is erection wise possible.
Thanks
Raj

 

[LittleInch]

struct4me

Please don't double post and add extra elements. Keep this thread to the structural issues and leave the other ones in the pipeline forum.

also changing data doesn't help. It started as a 27m x 80 shaft, now its suddenly a 16m x 40m and a 23m x 40 m shaft.

A thin steel liner will crumple very easily unless re-inforced to account for the differential pressure from the water column on the outside.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cvg]

well, you cant easily anchor and grout this giant liner while it is below the water. that water is nearly 300 feet deep and diving / construction to that depth is very problematic. since you say the water level is rising and falling that makes it even more difficult. you would need to fix it in place with some sort of temporary anchors long enough to grout the outer annulus. that will be difficult (impossible?) as you say, how do you line up a 500 ton steel cylinder, partly under water? that is assuming that you have a large enough crane to pick the liner and lower it the full 80 meters. By the way, when you pick this up with a crane, will it buckle? It also sounds like there are two different radius of liner, so now you need a connecting piece. if you have differential pressure between the outside and the inside, than you would need to design for that as well.

most tunnel liners are segmental and installed above water, since any other method is basically not construct-able. I dont have much confidence in this endeavor since the initial construction of the concrete lining was already unsuccessful.

 

[struct4me]

Now to do away the confusion, the hand sketch is attached with autocad drawings of the vertical shaft.
I want the ideas and engineering practicability both design as well as construction wise.
1st view was to lower it as a free standing cylindrical shell. but which will be having a large thickness at bottom due to hydrostatic internal water pressure.
2nd view was to grout the annular portion so that horizontal load can be transferred to adjoining rock through grout concrete and concrete lining.
One thing we need to keep in mind, the activity will be performed without shutting the plant, thereby water will be there in the vertical shaft between elevation 1770 to 1780 m in line with reservoir regulation and losses in 16 km long tunnel.
Now I think that I can able to express the concern..
But I am thankful to everyone for valued response.

Looking for your response...

Regards
Raj

 

[dhengr]

Struct4me:
You will have to do something to investigate and confirm the condition and diameter of the 23m conc./rock shaft down to the transition btwn. 16m and 23m dia,, at about 50m down. And, it seems that the shaft dia. (27m dia. ?) and depth (1850.3m - 1730m ?) may have changed again. You might have to knock off a bunch of high spots, to make it truly round and the proper dia. Alternatively, the high spots and min. dia. will dictate the design dia. of your liner. When the plant is running normally, can you control the depth of the water in the shaft, with some forewarning of any changes? 1770m to 1780m water elev. down to 1730m at the transition is a lot of water depth to work in. You would probably like to be able to work in the dry down at 50m for some periods of time. I would want to be able to cast a concrete ring/collar down there, against virgin rock or the existing conc. shaft, with a flat/horiz. top for my steel liner to rest on in it final position, in a grove to be grouted later.

I don’t anticipate that drag from the water surging up and down will lift the steel liner, given its height/length/weight and relative smooth surface, vs. its diameter, water volume and velocity, etc. But, I would certainly give that some thought. If you read my first post, I think the liner shell should grouted to the existing shaft, and this may involve some shear connector hardware of some sort. You really do need some local knowledgeable and experienced Civil and Structural Engineers helping you on something like this. They would know the answers to your questions, they would probably already have considered them. You might also want to talk with a couple large, experienced civil contractors about what’s possible, what they have done along these lines, what construction equipment is available and what construction materials are readily available, etc. etc.

You certainly could have a buckling problem of a 22.5m steel liner shell during the construction, handling and external grouting, and this has to be studied and resolved. There might be 8, 10, 12 vert. columns, located by a surveyor for accuracy of location, and fixed to the existing conc. shaft. They would be located at your design dia. and act as guides during the liner shell lowering, and they would act as liner shell supports at each increment (8' ?) of lowering. There might likely be internal stiffener structures on the inside of the liner shell, and these might be left in place. My thought is that they would act as turbulence producers, surge energy reducers/absorbers, to the extend that grouting held to liner shell in place against these forces. This would help hold the height of surge down, but slightly increase the pressure at the bot. of the shaft. I don’t see buoyancy as an issue unless you’re keeping more secrets from us. The steel shell weights more than the water it displaces, if it is open at the bottom.

 

[struct4me]

Thanks dhengr.. for your detailed response, but I am not hiding any secret, you must have missed my attachment in the last post (word file), showing actual condition.
Thanks & regards
Raj

 

[LittleInch]

struct4me,

Doing this on line is adding a x 10 complication factor.

however depending on your access to the top of the shaft, constructing this liner as a series of rings, especially if there is room to pre fabricate the rings before hand, is feasible if complex to organise.

It will though need some thought as to the sealing onto the 16m ledge and be sufficiently strong to withstand the maximum differential water level until you can get in to slowly grout the annulus up from the bottom.

Question though - how are you calculating the outflow in this shaft ( 1m3/sec?)
Is 400 m3/sec the maximum inflow rate? Works out not too fast (1-2 m/sec), but in a 20 something m diam shaft is fast enough...
Could you do this a series of say 3m or 4m or 5m diam shafts instead? connected to a plate structure? Lots more metal but might be easier to handle. You should be able to get long lengths ( 12- 18m) of certainly 3m diam pipe.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.