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Trench excavation- protective work-sheet piling

12/20/2009 10:17 AM

I have to lay 2.5 m dia steel pipe encased in concrete, 12m below GL, GWT at GL.

i have only 15 m wide flat ground in between 2 hills. base width reqd for the trench 4m. The soil medium is a combination of silty sand(SM)phi 30-35, clayey silty sand (SC) phi 26 & sandy clayey silt (CI) c-0.15 to 0.25, with SPT N values range 10 - 35.

How can I do the trench excavation under GWT?

Is sheet piling possible upto for 12 m depth trench? how much embedment into ground is required?

the site is in Munnar, kerala. Is there any indian company which can undertake the work? what will be the cost?

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#1

Re: Trench excavation- protective work-sheet piling

12/20/2009 3:30 PM

I don't have any firm information for you, but you might investigate "pipe ramming". You would have to dig and de-water holes and then ram the pipe from hole to hole. It should be cheaper than miles of sheet pile, sometimes it is not possible to pull the sheet pile for re-use.

Edit. I may have misread your post, I though you meant 2.5 miles. If it is 2.5 metres, the sheet pile is the way to go.

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#2

Re: Trench excavation- protective work-sheet piling

12/20/2009 6:13 PM

Dear xhansu,

You need to seriously consult with a qualified geotechnical engineer (who has a license in your country to perform engineering) to design the ground dewatering system (such as a well point system) and the sheet-piling size, strength and minimum drive depths. As with many subsurface work in soils, there are a multitude of unknown factors that must be investigated prior to the commencement of the project work. To undertake this level of work without the expertise of a professional engineer would be foolhardy and may result in workers' being seriously injured or killed.

Good luck with the project, and please, have a great sunny day!

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#3

Re: Trench excavation- protective work-sheet piling

12/21/2009 12:14 AM

Hi xhansu,

If you are ready to do this job now, forget it.

This job should have been or should be planned a whole long time to enable the pilling, and or any construction of wells etc.

This is a huge job and not something you can take "just like another day at work"!

You have one of the worst situations with different types of soft sandy soil. Piling is essential, if you want everyone alive after the work has finished!

To give you some idea of how difficult a job it is and will be. Half of London Underground is built at this depth or lower, so we are talking of a very VERY civil engineering job here.

I hope you will send a reply post saying it will not start for a year or so, as it could easily take this long to pile, dig a trench that deep, and find somewhere to 'store' the soil while you lay the huge pipe, then cover and compact the soil and you will need to do a pretty large 'landscaping' job of the ground after you finish.

Tell me, if you are laying this 2.5 M dia pipe between two hills, can you not bury it to just below the 2.5 M of the pipe? This is just a thought I had and may not be feasible.

These sites below may help you with the piling. But you should get a qualified ground-work engineer and surveyor in to help with the day to day planning of this job, and I mean before it even starts! There is a whole lot of planning, soil testing, and what makes it worse is, as I understand it, you are laying the pipe under the ground water table?

You may find you will have to get lots of pumps in to clear the water as it tries to fill the trench. And you may also need to put a concrete foundation down with side walls to prevent the sandy soil from caving in on you as you work.

piling in sandy soil

  1. Bearing capacity of driven piles in sandy soils according to ...by Z Sirozhiddinov - 1992
    sandy soils in the base, the levels of reliability are too high. This indicates the possibility of raising the transmitted load on piles ...
    www.springerlink.com/index/UU3726817107U378.pdf -
  2. Behaviour of jacked and driven piles in sandy soilby J YANG - 2006 - Cited by 5 - Related articles - All 4 versions
    Behaviour of jacked and driven piles in sandy soil. J YANG, LG THAM, PKK LEE, ST CHAN, F YU Geotechnique 56:44, 245-259, Telford, 2006. ...
    cat.inist.fr/?aModele=afficheN&cpsidt=17717915 - Similar -
  3. [PDF] Investigation of lateral load resistance of laterally loaded pile ...File Format: PDF/Adobe Acrobat - Quick View
    by M Rahman - 2003 - Cited by 1 - Related articles
    laterally loaded pile in sandy soil. Rahman, M., Alim, A. & Chowdhury, A.S.. Department of Civil Engineering, BIT, Rajshahi-6204, Bangladesh ...
    www.geotec.coppe.ufrj.br/ssc2010/arquivos/ssc_samplepaper.pdf -
  4. Benefits and Uses - Composting for the Homeowner - University of ...Whether a compost pile is quick and hot or slow and cool, ... In loose, sandy soil compost helps to bind these particles together and increase the soil's ...
    web.extension.uiuc.edu/homecompost/benifits.html - Cached - Similar -
  5. Increase in Cyclic Liquefaction Resistance of Sandy Soil Due to ...by TC Siegel
    Increase in Cyclic Liquefaction Resistance of Sandy Soil Due to Installation of Drilled Displacement Piles. by Timothy C. Siegel, P.E., M.ASCE, ...
    cedb.asce.org/cgi/WWWdisplay.cgi?0809709 - Cached -

I wish you luck!

This is not the kind of work you can take for granted. It really in like putting in an underground system even though the pipe is not the full size for trains to run in, the basic way of working will be the same when working that deep in that sandy soil.

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#4

Re: Trench excavation- protective work-sheet piling

12/21/2009 12:23 AM

It would be interesting to know some more detail on this project. What does the pipe pass under in the 15m gap between the hills? A river, a road? Why such a large pipe, and what will it contain? Why bury so deep?

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#5

Re: Trench excavation- protective work-sheet piling

12/21/2009 5:37 AM

Dear friends,

Thank you very much for the attention shown.

FIRST OF ALL , I MUST DO THIS WORK, NO WAY TO ESCAPE.!!!

Actually, this pipe is a part of the water conductor system of an hydro electric project. The Head race tunnel ,3.5 m diameter ,in rock, with sill level at this depth (1442 m level) is being driven upstream from an adit . A total length of 1400 m is completed. The remaining is 770 m. On an average we are getting 50m /month. After this 770 m , rock profile is going down, leaving the tunneling medium to be a mixture of weathered and soft rock at the invert and silty sand layer at the overt for another 30 m or so. soil tunneling with rib supports and fore poling is suggested in this reach. After that ,the soil condition is still worse with clayey sandy silt and clayey silty sand , hence soil tunneling is not preferred by the contractor.This length will be around 140 m and then approach channel of 46 m is opening into the reservoir, penstock bellmouth entrance of 1.66 D height is provided in the channel with the sill of pipe intake at 1443m level, This levels are to be maintained to ensure no air entry into the water conductor system as the FRL in the reservoir is 1450.92 m. Due to proximity to reservoir, GWT is almost at the GL i.e at 1454 m level.

so... the options for 140 m length is either to go for open channel excavation or to lay feeder steel pipe in trench with concrete embedment. Both has to be done at 1443 level. Due to the resrtiction in width of flat ground at site, trench excavation and pipe laying is prefered.

hope , now you better understand the situation AND your valuable suggestions are awaited.

XHANSU

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#12
In reply to #5

Re: Trench excavation- protective work-sheet piling

12/21/2009 7:10 PM

Hi xhansu,

After more research and have found pages which are more applicable to your situation. IE. Driven piles, or pushed piles in sandy soil.

There is many more sites. Only 52,000 sites, so good reading!

I understand the pressure you are under and wish you the best of luck.

As has been said by a couple of posts, as you or perhaps part of the company you are contracting for is tunnelling as part of the complete very large earthworks, can you not get advice, and or possibly get the tunnelling contractors to drive a drainage system to lower the water table to below your anticipated pipe depth?

I tried to get over to you that a job like this takes a whole lot of planning, before the pipe is even on-site! The piles will take several months I would think. There are new piling machines which can just push the piles into sandy and clay soils which are quicker, but they still need time to make the trench safe for machines and people to work in.

Please check this search page out:

http://www.google.co.uk/search?q=piling+steel+piles+in+sandy+soil

I am not talking 'down' to you as you must have enough experience in general to be the on-site engineer? The link I have listed above will give you all kinds of piling advice and many companies to ask for different advice on piling in sandy, wet, and clay soils to allow a trench to be built and possibly to remove the piles afterwards?

The piles for buildings like huge office blocks and Hotels in sandy soils are very deep and I cannot see that the depth will be a problem. You need to go down 12 Metres only. Piles can be pushed many times the depth you need. I would suggest a professional piling company which has experience in the soil condition you are working in, and the piles must have lateral support to prevent or minimise water and flowing sandy 'quick-sand' type condition.

These small silent piling machine provide very effective piling and the piling can be done remotely, to load the machine with piles. These are then used as the 'legs' for the 'gripper legs' of the push in piling machine.

You may find it useful to view These:

http://www.youtube.com/watch?v=5tkbyGYBMT8&feature=related

http://www.youtube.com/watch?v=phGMJbV_Ll4&feature=related

http://www.youtube.com/watch?v=Gv7nntBCe-M&NR=1

http://www.youtube.com/watch?v=TnWgQxZTooA&NR=1

A professional pile company will understand what is necessary.

The most obvious to a level and hard enough structure along one side of the trench to support the pipe lowering machines. This can be achieved by a temporary concrete base for the machine. Or perhaps compacted soil with railway 'sleepers' or if you do not have these where you are then square section trees laid flat, at least leave a sturdy enough platform to take the weight of the machines and the pipe and supporting rigs, as the pipe is lowered into the trench.

I recall seeing one job of pipe laying where there was about six machines over a space of about one kilometre, and the trench was deep. The weight and leverage the lowered pipe was estimated wrongly, and a couple of the machines feel into the trench.

I understand 'time is money' but, to complete this job at all will take careful and accurate building and planning, as once the earth is removed from between the piles, you may have a limited time to place the pipe into the trench.If it is possible it may be easier to lower the end of the pipe between the piles and, as the trench is made, drag the pipe into place at the correct depth. That way you may need less machinery and so less ground pressure trying to collapse the piles?

Keep in touch and please let me know if and when you find any sites listed a help. And if possible give some kind of schedule you will have to follow?

Good luck and I mean that!

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#23
In reply to #5

Re: Trench excavation- protective work-sheet piling

12/28/2009 6:18 PM

Have you considered Microtunnelling with Heavywall Steel pipe c/w Gunite/Concrete Coating?

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#6

Re: Trench excavation- protective work-sheet piling

12/21/2009 9:54 AM

Hi xhansu,

You are asking one helluva question! Both the captain and B-B are giving you wise advice and all I will do is to add my suggestion that the method has yet to be determined, because the depth and soil type suggests that there will be substantial lateral pressure on the trench sheeting, which will require extensive cross bracing etc. There are other ways of stabilising the profile which can include dewatering and freezing but all serve to escalate costs. The example cited of the London Underground was in many parts a cut and refill with pure tunnelling inbetween.

As the others have said safety is of paramount importance and only those with a proven track record of this type of work should be entertained.

Question: why put the thing down at that depth and what length is involved?

Good luck,

Massey.

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#9
In reply to #6

Re: Trench excavation- protective work-sheet piling

12/21/2009 4:40 PM

Hi Massey,

I have to say a thank you for the mention!........ And. I am getting famous now, yeah! Do you want my Autograph, going cheap!

Your post unlike mine was short and to the point, and well written as well. Good sensible advice for a very nasty tunneling/pipe laying situation!

Good luck.

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#7

Re: Trench excavation- protective work-sheet piling

12/21/2009 1:43 PM

You don't need a consulting engineer as much as you need experienced dewatering, sheet piling, and deep excavation contractors who are intimately familiar with the conditions your site presents. Given the 'N' values you posted, there is considerable chance of flowing soils and 'sand boils' if the dewatering system is not properly designed and installed.

At the depth you are installing the pipe, the system will have to lower the GWT to several feet below the trench bottom, requiring a deep dewatering system. Its design will be dependent upon the soil permeability and permittivity, and will likely require a vacuum system (not well points) that utilize typical dewatering well casings, packed in pea gravel, and fitted with a large-diameter vacuum manifold system that creates vacuum in the well casings to draw ground water to the pump. This is a sophisticated system that will have to be installed and operated for some time before excavation can commence in order to permit the lowering of the GWT to an acceptable level.

The sheet piling system will have to be installed as the excavation proceeds to permit the installation of the significant amount of internal bracing that will be required to support the piling laterally. In my experience, you will not find consulting engineers with the expertise to design and recommend the procedures required unless they are employed by the contractors who specialize in this work, as the responsibility for performance lies with the contractor as a part of his 'means and methods' obligation.

If you have been using tunnelling methods for other sections of this project, you are certainly familiar with complexity, risk, high cost, and the need for an experienced contractor team.

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#10
In reply to #7

Re: Trench excavation- protective work-sheet piling

12/21/2009 4:51 PM

Hi Doogleass,

Compliments to you for a well written post with good advice to the OP.

I can understand his worries for sure. However, with other very specific tunneling work to connect the mentioned pipe, there really should be enough experience on site to complete this safely?

I agree with you when you mention the tunnel designers and excavator's. There is probably a lack of discussion between these necessary sub-contractors.

I too had the possibility of 'quicksand', flowing sand and just nasty conditions to work in. I also tried to get over, as you have mentioned, that the work needed to prepare the site in this sandy area should have started at least a year ago and, is much more complex than perhaps the OP may realise?

Great post, thanks once again.

Good luck.

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#25
In reply to #7

Re: Trench excavation- protective work-sheet piling

01/01/2010 11:15 AM

dear doogleass,

what dewatering system can be suggested when the water table is almost at the ground level and the area is just at the bank of a reservoir ?

see the ground level is at 1455 m. full reservoir level is at 1450.92 m. the ground water table is almost at the ground level.

we have to lay the pipe at 1443 m level i.e 12 m below. what dewatering method can be adopted to lower the water table to below the trench bottom?

if you have any methods ,please share.

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#26
In reply to #25

Re: Trench excavation- protective work-sheet piling

01/01/2010 3:05 PM

Hi xhansu,

Happy new year to you sir!

The way I have used for draining farm fields, is to have a machine which digs and lays 6" (~150 mm) pipe which already has holes all round it to allow the water to seep through and drain away.

In your case you will have to dig lower that I ever have but this should be possible by using a machine which digs the hole and places the pipe with holes in at the same time. You may have to do it in two or more stages. Say drain down to 6M then the 13M. It all depends on how deep your machines can reach? 13 M is quiet a deep trench.

Can you tell me if you have used this method before? The pipes are a metre long and about 6" (~150 mm) and they do not need to be laid very accurately, just pushed up to the previous length of pipe laid. As long as there is not to much soil in the spaces between the pipes there will always be more 'air' than soil so the drain will work. These are laid in the soil with no cement or concrete.

Here is some sites which may give you an idea of what I mean.

http://www.google.co.uk/search?q=land+drainage+pipe+and+machines

Good luck

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#27
In reply to #25

Re: Trench excavation- protective work-sheet piling

01/01/2010 9:53 PM

Hi xhansu,

The field drainage system as proposed by Babybear is essentially a shallow solution for keeping fields from being water logged and are typically laid using a rotary cutter and a hollow blade follower which enables the 'tile drains' (a UK style) to be continuously inserted into the narrow trench.

I have successfully dewatered to 25 feet using well points. These are vertical bores drilled at regular intervals along eitherside of the area to be excavated. Suction lines are inserted into each hole and extraction occurs as a mixture of air and water are pulled upward. The pitch(spacing) of each bore depends greately upon the permeability of the soil but in a clayey sand a spacing equal to the depth could be a good starting point.

Unfortunately at the depth you propose you will have to think about higher vacuum or air lifting as the height of the water column would be too great.

It is for these reasons that freezing becomes a serious contender. But plant costs rise accordingly.

Good luck,

Massey.

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#28
In reply to #27

Re: Trench excavation- protective work-sheet piling

01/02/2010 5:41 AM

Hi Massey,

Yes you are right I was talking of relatively shallow work, roughly 1 to 4 metres.

I like your idea though. One or two metre pre-cast drain sections can be pushed into the sandy soil. There may need to be a lot perhaps even side by side?

One thing I recall from many years ago and I am pretty sure it still stands. The Chinese moved the most earth by hand with something round about half a million people to allow the building of a particular Dam. Do not ask which one though! A brilliant achievement when compared to the huge prime movers of earth doing it mechanically?

The Chinese have found way before and I am sure xhansu will complete these. Partly because he has no choice! Sorry for the bad spelling my Chinese friend!

Take care and happy new year to you Massey.

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#8

Re: Trench excavation- protective work-sheet piling

12/21/2009 4:04 PM

This idea is from an EE, so please forgive if it seems frivilous or inappropriate.

If the "soil" is so sandy and already basically wet and if you are already into tunneling, then would it be possible to "stabilise" the material by injectiion of cement slurry and effectivey lock the material into a "concrete" condition that is then suitable for tunneling?

As I said, just an "out there" thought from an EE.

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#11
In reply to #8

Re: Trench excavation- protective work-sheet piling

12/21/2009 4:54 PM

Hi Just an Engineer,

I think this may possibly help. Though I am not sure if the tunneling machines can tunnel through concrete? Worth a mention though!

Good luck.

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#15
In reply to #11

Re: Trench excavation- protective work-sheet piling

12/22/2009 5:16 AM

Thanks for the feedback.

I used the word "cement" with caution in a hope that it would be interpreted to provide an end condition that was stable for tunnelling, not necessarily 25MPa rated or even structural.

Discussions with another colleague this afternoon even suggested "plaster of paris". The tunneling machine would chew through that like butter (I presume).

As an aside, the colleague seems to also be a member on this site.

Small world!!!!!!

The water board that I work for also "pothole and drive" for sandy areas so that less than 25% of the pipe length is actually trenched, but I'm definately staying on the sidelines for this one.

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#17
In reply to #15

Re: Trench excavation- protective work-sheet piling

12/22/2009 11:31 PM

Hi Just an Engineer,

I really appreciate your reply post thank you.

I guess what we do is pretty to the point and exacting with well, my advice anyway.

This job taking part on the other side of the world, and in a situation I/we have no control of at all, other than trying to stop the site agent, if that is who is posting, from loosing his rag and panicking?

This kind of job as I say and you know, should not have these questions asked at what is apparently such a late date in the construction. I really cannot see this happening to a 'western' development. The work for each sub-contractor would be known from day 1 !!! It is not the kind of job anyone can rush into or 'play catch-up' to save time. It is a very tricky deep foundation in the worst possible soil type, and I am not sure the OP will not be pressurised to try and find a quick route and the danger is worrying me a lot.

There is absolutely no way I would have asked this kind of detailed request at, what seems to be, at the point in the job the pipe is ready to be laid, you know?

I am not even sure if any digger will be able to reach that far, and still stay above the trench, if that is the plan? I cannot see anyway round the need for piling and then a machine working its way through the trench pulling the pipe behind it as it goes. That is if the pipe does not need a concrete foundation, which I think it may well need. But although the tunnellers are apparently working to an International spec, I am guessing, it seems the various parts of the sub-contractors do not communicate. On such a risky job good communication is vital. The communication must be necessarily between the various deputy site manages, for want of a better phrase, and they should in my opinion all have equal say in what happens and how it happens, and that crucial point, seems to have been forget here. That is, if there was or is any such communication. It worries me to think that the OP who sound like the site foreman, has no idea how this job should be accomplished. It is scary!

I am hoping the OP has written in asking this question to further his career. Because in such a complex multifaceted structure, the various companies should have overall control, and already know what to do and how to do it, down to the smallest detail. I do not think we will ever get to know if that is the way "Chinese" site agents operate or not, but is should be the way to move forward. I was seriously scared this OP was about to start to dig this trench, under pressure from above, and I could see the sand flowing and the water start to flood and break down the banks of this foundation?

I should not worry because there is nothing I can physically do to alter anything, apart from giving more or less up to date advice, going on the tiny detail we have at the moment. It is very close to being a farce. That is how I feel about this.

Take care and good luck, OK?

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#20
In reply to #17

Re: Trench excavation- protective work-sheet piling

12/23/2009 7:10 PM

Dear All,

After reading my post again, in bold below, I would just like to add feedback:

When I said "....... well, my advice anyway", I was not inferring in anyway other posts advice was not helpful! OK? Actually, I think all that have posted here on this topic have given very sensible and well explained detail of what to do....... And what not to! LOL!. Sorry.

Take care and happy holiday.

I guess what we do is pretty to the point and exacting with well, my advice anyway.

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#13

Re: Trench excavation- protective work-sheet piling

12/22/2009 2:15 AM

Greetings all,

As a civil contractor in Alaska we encounter all sorts of soil conditions and all the advice given so far is very relevant. Especially the advice on seeking qualified contractors. A firm with expertise and the proper equipment will likely be able to present a plan to de-water and excavate in relatively short order. They may well be able to do the job with a large excavator and trench box that is pulled along the pipe excavation as the job progresses. The main thing is to let the guy who has to do the work come up with the plan and then make sure he can bond and insure it.

Good luck and happy holidays

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#14
In reply to #13

Re: Trench excavation- protective work-sheet piling

12/22/2009 4:51 AM

Hi Guest,

It is nice to hear I/we have given sensible advice, coming from a civil contractor in Alaska you obviously have experience in this kind of situation.

I suggested pulling the pipe as the trench was dug not knowing for sure if it was possible. Though it is only about 7.5' (2.5M) in dia.

Anyway welcome and why not join? It is a great place!

Take care and good luck.

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#16

Re: Trench excavation- protective work-sheet piling

12/22/2009 10:05 AM

Due to the excavation depths that you have outlined herein, you may also want to investigate the use of slurry walls by soil injection means in lieu of driving or pushing piles/sheet piling. Installing soil wicks for dewatering of the site works well too!

Good luck, may you have a great sunny day!

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#18

Re: Trench excavation- protective work-sheet piling

12/23/2009 5:41 AM

thanks for advices and concern!

Actually the situation is not that pipes are already in the site.

we have time to plan and do the work.

it is for 140 m length trench excation required.

we are thinking of this alternative(feeder pipe in trench) to open channel.

we are also well aware of the situation. But how to tackle the problem and evolve a reliable solution is the major concern.

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#22
In reply to #18

Re: Trench excavation- protective work-sheet piling

12/24/2009 3:15 AM

Hi xhansu,

I am pleased to hear that this is not going to be a rush to complete this trench!

Just a thought. Are you going to concrete this pipe and perhaps run scaffold poles or bamboo into the bottom of the trench to try and keep the pipe from moving? Such as floating in the already soaked ground?

A backfill of rocks and large stones with concrete will prevent any buoyancy problems.

When will you be starting and what are your plans to do the job in sequence?

I know it sounds unlikely, but on this thread:

Stopping pipe floating.

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#19

Re: Trench excavation- protective work-sheet piling

12/23/2009 5:44 AM

Dear xhansu,

You have received some extremely wise and pertinent advice on what appears to be a demanding and potentially risky activity. I took the liberty of looking up your piece of territory on Goole Earth and the Munnar Valley looks an attractive location. Some of the 'touristy' photos also help inform about the topography which I would describe from a geological point of view as chaotic. There appears in some shots to be a lot of moranic material and other detritus. Therefore as you suggest in your descriptions the task is to be executed in a confined areas, in a narrow defile, and with the distinct possibility of high pore water pressures which will serve to exacerbate the failure potential of the sub-water table stratum.

It is unfortunate that the work has progressed to the point that you suggest before this predicament has been revealed. Is this because you are trying to do the job on a 'piece-meal' basis with on-site execution methodology being left in the hands of those not experienced in such variable terrain?

You definitely need to call upon the services of an experienced civil engineer before going any further. In this respect you should not confine your search to India alone.

'Take heed and ca' canny' as they say in this part of the world.

Massey.

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#21
In reply to #19

Re: Trench excavation- protective work-sheet piling

12/23/2009 7:18 PM

Hi Massey,

Why did I not think to view this detail on Google earth? Very good idea!

GA to you Sir.

It is good to hear the OP is not so far advance on this project as I at first had the impression he was!

Is there any chance of posting the exact address, so I can view it please? You can PM if you prefer.

Good luck.

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#24

Re: Trench excavation- protective work-sheet piling

01/01/2010 9:32 AM

HAPPY NEW YEAR , FRIENDS....

I was also busy with some meetings.sorry that i couldn't write to you promptly.

Actually this is an extension (60 MW) of pallivasal hydel Scheme (37.5MW) installed in 1929 & 1945 .In the DPR of extension scheme which is being carried out now, it was envisaged to carry out the soil tunneling through this stratum. In the earlier bohr logs, weathered rock with N value >100 in SPT is reported to be present in this stratum. But on actual excavation at some borehole locations,the strata revealed to be bouldery like nuts and plums in a clayey silty sand cake.so we can not opt for an open cut excavation for the ramp to do soil tunneling , as already planned.

That is the reason why we are changing to a feeder pipe laid at depth and instead of an intake pool , a channel intake option. resevoir is shallow.FRL 1450.92 m and river bed 1445.5 m. water inflow is there from the upper reservoirs.It is a small head works constructed in 1929 and spills majority of the year. As this extension scheme is utilising only the available spill, no extra submergence is there. so it is an eco-friendly project.

To lay the pipe,what are the options? we had thought of

1. dig a trench and lay the pipe with really designed vertical supportive measures .

2. to excavate with a flatter slope and protective measures .

Contracing firm has come with proposal of open cut excavation with side slope 1 in 1 with 3.5 m berm at intermediate level. As this excavation has to be done under GWT, WHAT ADDITIONAL PROTECTIVE MEASURES ARE TO BE CARRIED OUT FOR SAFELY EXECUTING THE WORK?, if we are doing the work in 10 m reaches i.e excavate, lay the pipe with concrete encasement and bury it .(Total length to be covered is 140 m.)

sir , you have suggested micro tunneling? how it is done? any reference site ? what will be the cost? what type of equipments required?

thank you for the interest and help offered. I am a design engineer . actually I was in charge of the designs of pressure shaft, penstock and anchors and eventhough we had some problematic loactions, we could solve it. Very recently this intake design is also handed over to me and i have to find a way out. I know it is a very challenging work, but with the rest of the world's help, i am sure we will solve it.

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#29

Re: Trench excavation- protective work-sheet piling

01/02/2010 9:06 AM

You can always inject Bentonite clay mixture/slurry both sides of the trench to mitigate groundwater movement, or you may have to inject all around the planned trench excavation.

OR....

In regard to using well points, carve out several horizontal benches and install well points laterally along the trench in each bench. The object of this arrangement is to draw-down the groundwater level sequentially. It may take the construction 2 or 3 excavation step-benches (with paralleling well points and headers).

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#30

Re: Trench excavation- protective work-sheet piling

01/07/2010 7:00 AM

Hi,

I think, we can help you in this situation.

I'm working with ArcelorMittal & we are dealing in sheet piling. We can suggest you better solution for your problem

So you can reach me on my mobile no : 09920160019.

Best wishes,

Kiran

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#31
In reply to #30

Re: Trench excavation- protective work-sheet piling

01/14/2010 4:58 AM

Hai Kiran,

I would like to send you the details through e mail .

can you give me your e mail id.

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