Waterproofing a Leaking 10-Million Liter Water Tank

Take note of the maximum level at which the tank can be filled without leaking. Your leak is somewhere at this level. Use a dye penetrant or something similiar to locate the leak, then repair it. Determine what caused the leak as well so that it can be rectified.

DVader1000,

you do make a good point; however I would think that one would be able to see a leak if said tank was above ground.

In this case I would believe that the poster has answered his own question as to where and why this tank leaks. As for the repair, I would suggest that this tank be emptied. Then provide several horizontal borings across the underside of the slabs, cross wise to the joints. Provide footings at the each end of each boring, and reinforcing steel bars within each horizontal boring, and footing. Fill the now open areas with a good cement mix designed for this application by an engineer. Another option would be to add a new bottom, doweled to the side walls and use something such as flowable fill, a cement mix, with fiber entrained within this mix to create a new one piece bottom. This of course will slightly reduce the holding capacity, but that may be better than any other option.

TMF

I would agree, I am not a civil engineer but could it be that cracks in the base allow the water to escape due to capillary effect under "high" pressure. When the water gets above a certain level the pressure might be enough to open these cracks and away flows the water. This is a known problem in general plumbing.

Dutchy

Hello All,

For starters we need additional information about this tank in order to make some sort of recommendations. I would like answers to the following before proceeding any further for safety of a possible served population and/or for structural integrity of the tank:

a). Where in the world are you located?

b). Are you a General Contractor or Sub-Contractor or Speciality Contractor? Or are you the Owner/Operator of the tank?

c). Is this tank holding water for potable drinking water use and does it serve a downstream population or is it used for industrial use?

d). Are you following AWWA guidelines and procedures for leakage testing?

e). Were the additives used in the concrete mix and the compounds used to patch the slab conforming to NSF and AWWA standards for use in potable water facilities? Did an Engineer of Record for your project approve them? Also, has the Health Department having jurisdiction reviewed and approved these compounds for use on the tank if iit is storing potable water?

f). Is there a Engineer of Record involved in this tank rehab project?

g). How old is the tank and how was it constructed?

h). Who was the Contractor that built the tank?

i). Do you know if the original Construction Documents still exist and can you obtain them for planning and review purposes?

j). Does the concrete wall incorporate segmental precast sections that were prestressed or post-tensioned, or was it cast-in-place?

k). Does the tank have some sort of cover, like a segmental precast concrete dome supported by an annular tension ring located at the top periphery of the tank?

l). Do you know if a continuous waterstop exists at the base of the tank wall? Material and condition verified?

m). Is the tank wall partially or fully backfilled? Has any part of it been partially excavated down to the base of the wall? Has this been done during the leak tests to verify water tightness of the tank at the base of the wall and any purported waterstop?

n). How may times have you conducted the leak test? Have you taken into account possible water absorption of the concrete slab and wall, especially if the tank has been out of service for a period of time?

o). Are yiou absolutely positive that all valves are closed "bubbletight" and not leaking? How often have the existing valves been exercised? Valve and seat types involved?

p). Has any destructive and non-destructive testing of the existing concrete been conducted? ````````````````````````````````````````````````````````````````````````````````````````````````````````````````````````

Okay, that's just a start of my questionaire....

I recently salvaged an old concrete tank that had numerous structural problems by lining the inside with fiberglass. The lining was done in such a way that, when the original concrete tank finally disintegrates completely, there will be this fiberglass replacement tank already in place.

There are also elastomeric coatings (Liquid Rubber out of Canada, and Rhino-Hide out of somewhere else) that are suitable for potable water systems. The issue with these are that they require significant equipment to apply, and when the water tank on top of a hill 120 miles from the nearest road, only access by boat, then these spray-on solutions look less attractive.

Hello cwarner7 11; Et. al.

I have read the 14 responses this morning, other than my own. I have had an evening to sleep on the need to resolve this problem economically. I may have the least expensive solution. Providing that the compacted soils beneath the bottom has not been structurally compromised so much that it must be reinforced/repaired in some fashion in order to continue use of this tank without danger of collapse and or personal injury to life and or surroundings.

We have learned that out land fills and sewage storage areas must be lined with a polymer/rubberized lining in order to protect seepage into the ground water and resulting contamination. We have for years been constructing in ground swimming pools, etc. from concrete blocks and lining the sides and bottom with a plastic liner.

I am quite certain that a suitable liner can be made to fit within the existing structure for a reasonable cost, that will likely extend the life of said storage facility.

TMF

And may I add, even without further information about the tank construction, that I suspect that the wall base and slab joint may be leaking, possibly at the waterstop if it exists. The reason I am basing this assumption on is that when the water reaches a certain level (about mid-height according to KOPEND) there's enough horizontal deflection of the tank wall resluting from by the ever-increasing hydrostatic pressure as the tank fills, thus there is a distinct possibility that the wall base/slab joint starts to open up more and more, possibily facilitating a slowly increasing failure of a waterstop there, if it exists. There's also the distinct possibility that (if the tank walls were constructed of precast concrete segments & later wire wound [post tensioned] and shotcreted) the wall post tensioning strands are delaminating from the shotcrete. Again, this assumption is made on a certain type of tank common around the world.....the writer doesn't give us enough information. Also, alot of concrete tank construction and its integrity depends a lot on the quality of the concrete products placed and how it was constructed....with a fair amount of quality assurance coming from the independent materials testing agency testing the concrete as it's being placed as some sort of yardstick verifying its quality. If this oversight is lacking, then there's a question in my mind whether the placed materials met or exceeded specifications as well as the design intentions.

Hope that makes some sort of sense...it's late and it's been a long long day!

Hi Kopend,

By lining completely the inside with fiberglass is far expensive, however it is more durable and reliable, if the application is properly done for sure there will be no leak. as I did in most of my Domestic water tank and sewage treatment plant. as we can't afford downtime once it operational.

Kind regards

Roman

Kopend,

I am in agreement that you likely have a deflection problem either in the slab or the point where the slab connects to the walls. I would think that a leak of this size would allow you to detect which it is. You may have to bore a test hole under the edge of the slab to verify. Pressure grouting or mudjacking under the slab may be the most cost effective way to solve either issue unless the sub base is so weak that piling or helical coils have to be used to support the tank floor. A test bore will likely be necessary to determine the most feasible repair. Moose is right on track when he says research of records could provide the answers.

Good luck

I don't know anything about this sort of thing, but:

15 to 30 thousand litres of water a day is almost certainly going to have washed away some of the "underlying" support in areas where the leaks were worst.

You almost certainly need to pump some concrete into the voids under the existing structure to prevent the whole thing deforming when it is filled.

from previous experence

have you checked the expansion joints in the floor

in a job we did before the polysuphide jointinting compound in the expansion joints was failing at aproxiamatly the same pressure

a cheap fix is to check these and relay them if failing

the last poster was correct to tell to check for scour in the foundations

Have you seen this stuff - http://www.sani-tred.com

I am not a rep or salesperson. I have used the stuff to repair and protect concrete and am getting ready to use it in a waterproofing application.

It is a really good product. Check with company to see if they can meet your requirements.

Good Answer especially:-

Another thing to consider is the employment of a high-powered Ground Penetrating Radar (GPR) to locate voids under the tank slab and around the perimeter of the tank. Make sure you hire a company well experienced in the use of a GRP.

Randall,

As a contractor who has dealt with foundation compromise issues after the fact, Unless the radar is ultra sensitive, and capable of determining the loss of compaction as the result of water having migrated through the prepared foundation courses and finds as opposed to just seeing soil vs cavity, said radar likely will not be of much use in determining a possible loss of carrying capacity, of the prepared soil foundation.

Nothing compacts dry sand like flooding with lots of water. But if clay, marl, and asst. courses and fines of suitable non organic material are the materials that were compacted to at least maximum capacity, these materials can lose their carrying capacity if water is permitted to migrate through the compacted areas.

TMF

In the case of this original post, it seems that when filled beyond the mentioned level it is the additional water that is lost. Thus it seems that either the leak is at that level or it is the weight of the additional water that is causing movement at joints below that level, thus causing the leak/loss.

If the concrete structure is salvageable as a water storage facility, then even if patches were required or under slab reinforcement must be put in place, the addition of a poly liner is likely the least expensive option as a semi permitted repair.

Thanks for all that. I said in my original post to this thread that I don't know anything about this sort of thing, and that is of course still true.

What worries me is that even after the initial attempt to waterproof the tank it is still leaking nearly 8,000 US gallons per day. Presumably before they undertook the work the problem was worse. The OP seems confident that the walls are not leaking so the only explanation for the leak turning on and off depending on whether the tank is more or less than half full is that the structure is flexing enough to open up "cracks" in the base.

The idea of a 150 foot disc of concrete flexing and un-flexing on a regular basis seems like a recipe for disaster.

It just seems to me that they need to find some way to identify the problems with, and, repair the foundations.

If you know a scuba diver they can go down with the dye used to find leaks or trace out fall in sewer lines or and and easily find the leak if it is above ground and you might get lucky and find it if it is around the edge of the bottom. Me and a dive buddy of mine did this on a few tanks and concrete dams and it works pretty good. If it is not in the side above the level you spoke about the leak may be occurring from the weight of the water pushing down the slab after it gets to a certain level. This will be allot harder to fix but I have leveled smaller tanks that had started to sink by boring 4" holes through the slab and using an expandable grout mixture to seal underneath the slab as well as to add support and actually pick the side up. I am not sure what the grout is called but it comes in non expanding type for just sealing proposes and then the type we used which expands. The stuff raised the side of the tank very well and nearly raised it to much, so be careful if you decide to try using this type of grout to repair the tank floor. You may also have to coat the inside of the tank floor with an epoxy based coating after you repair your problem(if it is actually a foundation problem) to get a 100% seal. They are many very good epoxy based concrete coatings and I have used them to seal different concrete structures that are normally submerged with success. Good luck and let us know what the problem/solution turns out to be.

Been thinking on this one overnight. Not my expertise, but some questions for those that know about large concrete tanks.

Is it possible that the tank "stretches" overnight when full due to the internal pressure of the water? A diameter increase of 60mm would provide the drop in height nominated.

Can the base of such tanks "flex" into the subfloor fill? I've seen railroad sleeper "sinking" into ballast as trains move over them and then recover their alignment once the train has passed. surely 10,000 tons of water (full tank) would have more effect than 5,000 tons (half full).

What about thermal equilibrium effects? temperature of water, temperature of concrete, temperature of re-inforcement?

What about evaporation? Areas like central Australia with 5%RH in summer nights or some parts of other continents can have notoriously high evaporation.

I'm asking because I don't know and I've recently moved into this field of Engineering and want to learn.

Dear Expert Circles ( If I may say ),

I just got back from our tank site ( Remote area, no internet connectivity ) .Thus, the late reply. I appreciate all the feedbacks and find them very useful and resourceful.

Reinforcement and additional structural repair is not part of our contract and I believe our client are engaging C& S Consultants to do further inpections after our waterproofing fails. Nevertheless, we are going to do one final shot of doing lining for the base-slabs. We hope we can solve this leak problems.

We had drained the tanks ( yes , there are 2 tanks with same capacity ) and now doing remedial work. We opting for liners for both tanks ( Yes, both tanks leaking )

Just to answer some questions about our work :

1. Water Tanks for domestic use for rural areas.

2. Location, Sabah, Malaysia's Borneo

3. Water tanks are 5 years old and was unfinished until we took over and did the

roof slabs and waterproofing works.

4.Concrete is Grade 35

5. We are new company with 3 years experience on waterproofing and civil & structural works and any help advices we get is much aprreciated.

6. My background is Mechanical Engineering :)

We will proceed with our base slabs liner solutions next month and hope it's all home and dry before Christmas. Will update. Many Thanks to ALL who contributed. Cheers

hi..i think its on the wall thats leaking not in the base slab..or may be the waterproofing have leakage..better re checked it....wondering why half full the leakage disapear?im sure its in the wallleakage...ive tried sealcrete and its good.