Weeping Tile Blockage

[Willbert]

Not sure if this is the right area to post this. If not please direct me to the proper area as I am new here.

To begin I will describe to you the area with the problem. The title indicates that I am having a weeping tile problem and am seeking a second opinion from what an engineer already informed me. I see some flaws in his logic. Mind you it would be a temporary fix but I can see down the road how his solution would cause more grievances and headaches. Also add additional funds to repair the problem. Here is his description and solution on fixing the problem. I will include my questions to him about my concerns which have yet to be answered.

I will also edit out pricing and names to safeguard his reputation and the fields pricing as this holds not bearings to my problem.




"
INTRODUCTION
We have had an opportunity to discern the problem of water penetration at the basement floor level at the exterior wall facing ****** Street. On June 12, 2003 the author visited the site and reviewed the condition of the water damage present at floor level along the exterior foundation wall. At the time of the site visit, moisture damage, dampness but no liquid water was visible. In addition, we reviewed the electronic photographs forwarded to us as well as a portion of the original foundation drawings. Apparently there was sufficient wetness that goods could not be stored in this area without incurring damage to the package goods. Although the LOCATION has been at this location for over 25 years, the moisture damage was noticed only in the last 12 months.
Engineering Company was requested to review the moisture damage and provide solutions to prevent future moisture ingress
Our comments and recommendations are presented below for your consideration.

OBSERVATIONS
According to the LOCATION, moisture had penetrated the north facing basement wall at floor level causing damage to the plaster at the base of the wall, debonding of several vinyl floor tiles and wetting the contents of adjacent stored products. The moisture damage was limited to about a 10 foot long stretch along the basement wall with adjacent areas along the wall showing no signs of moisture damage. The moisture damage extended up the wall plaster about 2 feet. The construction plans indicate that the exterior foundation wall consists of 12 reinforced concrete blocks with only the voids containing rebars being grouted. The other block voids were empty.
The basement floor level is approximately 8 feet below grade which is topped with a concrete sidewalk extending from the exterior wall to the curb along Soudan Street. A tree about 15 feet in height was located within 5 feet of the wall where the basement moisture damage was present.
At the time of the site visit no liquid water was observed. However, the bottom of the wall and adjacent floor tiles were damp. A view of the first floor joist space did not indicate any past or current signs of moisture penetration or wetness. A view of the sump in the basement floor did not indicate evidence of high water tables. The sump was almost dry and the Owner indicated that the sump was never used.

COMMENTS
The likely cause of water ingress is a temporary localized high water table created due to a blocked weeping system at that specific location. The proximity of the tree on the sidewalk could have caused the blockage of the weeping tile system as tree roots can easily penetrate the weeping tiles. The fact that the sump is relatively dry and that the moisture penetration appears to be localized to a relatively small portion of the exterior wall suggests that the weeping tile system effectively drains ground water in both directions from the blockage. One can envision rain water running down along the foundation wall until it reaches the weeping tile system and is effectively drained away thereby maintaining the water table below the top of basement slab and likely below the top of footing. However, at the blockage location, water running down the foundation wall can not easily or very slowly enters the weeping tiles and the water table temporarily rises up the foundation wall. In such a case provided there is sufficient water, the rain water can not only penetrate through the joint between the footing and the bottom of floor slab but also through the cracks and mortar joints in the foundation blocks. We noted the use of damproofing in the construction drawings. However, such damproofing is not effective at crack or joint locations. Eventually the water that has built up along the outside of the wall will drain down. However, until that happens water has an opportunity to enter and cause the observed damage.

RECOMMENDATIONS
1. The least expensive approach is to determine if a sewer snake used by plumbers can reach the supposedly plugged weeping tile location from the sump area. The author is not sure if this can be done as the type of connection from the weeping tile system to the sump is not known. The LOCATION may consider calling some one like A PLUMBER OR DRAIN SPECIALIST who for a minimal charge will come to the site and attempt to unplug the weeping tile system.
2. If the above suggestion is unsuccessful, we recommend that we drill 2 four inch diameter cores through the floor slab in the moisture damaged area. These cores would be next to one another one on top of the footing and one through the slab into the gravel subgrade. The cores would not be replaced for several weeks and the core holes observed for any collection of liquid water, especially after heavy rain falls and when interior wetness becomes visible. If liquid water does appear in the core holes to a height of the top of slab, a blocked weeping tile system will be confirmed as the likely cause of the moisture ingress. The solution in such a case would be to cut an interior drain form the wet area to the sump. This approach will be significantly less costly than digging from the outside.
"

Now option one is not feasible due to the fact that our weeping tile system has 12" clay tiles with 3/4" spacing. These gaps will prevent any snakes or optical cameras from being inserted. Entrance to the weeping tile is from the sump which T's off. From the T junction is approx. 15' feet to where we assume the blockage is.

Here are my questions I posted to the engineer regarding his method of repair.

"Hello *****,



I wish to thank you for pointing out a cost effective method that would fit our budget. But I have some concerns in the approach you wish to take. I realize I’m no engineer such as you. But I’d rather solve the problem once than find other problems associated with it down the road. Here are a few of my concerns.



This method is the most cost effective but is it the most effective method to remedy the problem. So we agree that this could spread over time. And when it does, from what I understand, is that additional drains would be incorporated further up the wall to alleviate the pooling of water on the other side.



With the depreciation of coverage the weeping tile has along the wall will this not cause further problems? And the drain that was originally installed becomes redundant with further collapse of the tiles? Even if the drain is not redundant will it also not cause problems with the cinder blocks on the other side of the wall as water and dirt may corrode the blocks and mortar?



Also with the drain being incorporated inside of the building will this also not cause a void when not only water but sand and dirt are also drained from the other side of the wall? Will this not cause a void and possibly collapse the sidewalk over time?
"



Any suggestions or thoughts from anyone would be appreciated. Just want to know if I'm over reacting and his method is a norm? Just that I never heard of an internal draining method before. Mind you his method is cost effective but I am not looking for cost alone. Don’t want to fork out additional funds later to find out I would have to end up digging outside anyhow.


Thank You.

John

 

[Focht3]

You have a tough problem. The problem must be fixed - or risk structural damage to the wall.

Where is the site located? (city, state) Do you know what your subsurface soil profile is like? We will need this in order to provide anything more than general comments.

I suspect the clay tile has either collapsed, or the gravel backfill (and possibly the clay tile) has become plugged with clay soil. A "gravel pack" (filter) around the clay tile would be appropriate in medium to coarse sand - finer soils (silts, clays) will penetrate between the gravel particles and ruin the drain over time. This seems to be your problem. And it is consistent with loss of ground along the basement wall and above the drain.

If I have described your problem, then you will need to replace the clay tile drain - and gravel filter. Hire a good geotechnical engineer, and be sure the replacement drain uses sand, not grave, as the filter media. Pay him to monitor the construction, with a staff engineer present during the critical phases of work. It's well worth the extra money.



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[Willbert]

"Where is the site located? (city, state) Do you know what your subsurface soil profile is like? We will need this in order to provide anything more than general comments."

The site is located in the city. As for the subsurface soil profile I will need to do some digging and will get back to you.

Thank you for your prompt reply. Could you verify for me if it’s a norm for internal drainage system to be in place? By this I mean the engineer is suggesting a hole be drilled in the wall and a pipe inserted then extended to our sump pump in the basement. I can actually envision that the pipe will be above the foundations footing hence not draining all the water on the out side of the building.

I can actually see future problems with this if the weeping tile continues to collapse. Mind you I might be using worst case scenario as no-one knows for sure what’s causing the blockage. This engineer’s method would basically make the weeping tile system obsolete. That is what concerns me is the dynamics of the system on the outer wall will be altered.


John

 

[jimbo]

In Michigan, companies trench thru the floor [inside the basement] and put in a new drain system to the sump pump.
Replacing the defective drainage system outside is usually not an option, due to the existence of a porches, walks, landscaping, garage, etc. which you do not want to disturb.

A few years ago, and man dug down with a backhoe to the exterior drain system and cleaned a part of the plugged pipe with a hose and a special nozzle. That lasted quite well, but was not permanent. The work disrupted the exterior quite a bit, and that was a repair expense. Also, a crack in the brick exterior wall showed in a year or two.

 

[Willbert]

Hi Jimbo,

Thanks for your reply. Where you indicated that an individual did some digging outside to remove the clog he ended up damaging the wall of the building?

And you implied that it is a norm in Michigan for some locations to have an internal drainage system set up. Would this internal drainage system then be installed at level with the external weeping tile or it really does not matter what elevation the new internal drain is located in conjunction with the external weeping tile.

 

[Focht3]

{i]WHICH city? WHICH state?[/i]

Internal drains are not the norm, but can be an inexpensive solution. However, if the remaining exterior wall drain system fails also... But you have already seen the potential for that problem.

The original report wasn't bad, or even wrong. The report author only gave you one set of "inexpensive" solutions. This may have been due to impressions he received from his client contact requesting a "cheap" fix, told the repair budget is only $xxx.xx, etc. I would have given more options - but that does not mean the other guy did a bad job.



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[GeoPaveTraffic]

Willbert;

The installation of internal drains for remedial work is not uncommon. You are correct that the preferred location for drains is on the outside of the structure below the interior floor level, however, once the structure is completed it is very difficult (and expensive) to install drains in that location. As long as the drains (internal or external) are below the floor level they will drain the water to the sump.

The fact that the drain on the inside does not cause the water to do more damage to the blocks and mortar. Remember that even if the drain is on the outside the water runs down the wall to get to the drain.

In your reply to the engineer, you discuss loss of ground. Have you seen a hole form on the outside of the house near the area where the leak is occurring? If you have not seen a hole form, I would not be too concerned about loss of ground. If you have seen a hole form, then you probably do not have any choice but to dig up the drain from the out side and fix the problem there.

One last point. In the vast majority of wet basement cases that I have looked at the problem is not in the basement but on the outside of the house near the wet area. Most times it is a clogged downspout or overflowing gutter that is dumping water right at the edge of the house. Another common cause of these problems is a flower bed or other similar feature that is "funneling" or directing water toward the house.

Keep us informed as to what you end up doing.

 

[Willbert]

Focht3 I would agree he was giving his best assessment based on budget. And I would agree his method would work, but for a short time. Since we don’t really know what’s causing the blockage its safe to say that the single drain he would add would only be redundant if it continues to cave in.

Also to have an effective internal drain one would expect it to be at a similar elevation as the external weeping tile. If its not then one would expect water pooling below the elevation of the drain hence allowing water to sit and have time to allow the mortar or cinder block to absorb the water further destabilizing not only on the wall but the foundation and structure as a whole.

Our location is situated in Ontario, Canada. Hence we have to also consider winter and summer months that has freezing and contraction due to hot and cold days.

 

[Willbert]

GeoPaveTraffic (Geotechnical)

Sorry I should have perhaps described the location. It’s a retail store. The north wall is two stories tall with no windows and the wall is cinder blocks. The wall has a stucco finish. The ground next too the wall has a sidewalk approx 14' wide. In the center of the boulevard is a tree that is centered where the damage is originating. Hence his concern that it my be tree related but has yet to be confirmed. The depth of the wall bellow ground is approx. 11' with about another 2' to the bottom of the foundation footing. The surrounding outside consists of sidewalk and roadway.

Is there a hole? Not so much a hole as the sidewalk besides the building where the leak or dampness is showing is slightly leaning or angling towards the building. I'd approximate about 1/6 of the slab of sidewalk is slopping. Water does pond on the walkway next to the wall. It would be very difficult to see any hole unless the area is excavated.

Here is the Engineers response to my concerns.


"John, you have raised a number of good questions. The ultimate and most costly solution is to dig up the perimeter drainage system from the outside.



However, lets take the first step only and drill the 2 holes that I have suggested and determine what happens when it rains or the floor gets wet.



We will be able to make a more informed decision later on.



Thanks"

Is it true that after making two holes one could determine a better course of action?

 

[GeoPaveTraffic]

The core holes on the inside will allow you to estimate the quantity of water and to some extend where the water is comming from. One thing I would suggest is that after the holes are made and you get a rain, keep a close watch on the holes. If you see water in the holes bail it out and see how quickly the water returns to the pre-bailing level. If the water returns quickly but does not come higher then you know that rest of the drain system is working but you have a large source of water. If the water does not return quickly then you probably have a small source of water or a long seepage path.

On a separate note, I would try to prevent water from ponding next to the building and get the water to flow away from the building as quickly as possible. Also there may be hole under the sidewalk, not a problem if you divert the water away from the area.

 

[Focht3]

[blue]GeoPaveTraffic[/blue] is right - you need to do something about the water against the side of the building. This will probably require replacement of a portion of the sidewalk; be sure your engineer is present after removal so he can get a good look at what you uncover.

Given the site conditions (retail store, wide sidewalk, "deep" drain, etc.) I would likely make the same recommendations as your engineer. Seems like sound advice to me. Unless you really want to dig up that sidewalk (and possibly others) right now...



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[dicksewerrat]

Look into having a contractor push a small sewer inspection camera up the tile to look for a plug. Use what you learn from the inspection to decide if you repair existing drain system or put one inside under the floor. Also replace the sidewalk slab that slopes toward your bldg.

 

[RDK]

Often instead of replacing a sidewalk or other slab outside a building you can mud jack the slab to provide the desired slope.

This involves drilling a hole 50 mm diameter and pumping a concrete slurry into the space underneath the slab. The slab will rise and an experienced operator can control the amount of lift with some accuracy.

This costs about $Cdn 150 per hour and may be a cost effective solution provided that the surface of the slab is in good condition.


Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[Willbert]

dicksewerrat (Civil/Environme)

Already inquired about a camera. The are forced in similar to a snake. Due to 12" tiles with 3/4 gaps between each one it would be next to impossible to feed the camera. Unless as one individual suggested was to dig out the corners of the building to get a straight line. Then Id rather digs out the damaged area in question. But thanks anyhow.


RDK (Civil/Environme)

Interesting concept RDK. Think I heard of a similar method on TLC aka "The Learning Channel" or something similar. Been some time. Definitely will be looking to see if that method can be done. Thanks a ton there.


Just need to find out if the sidewalk angled towards the building due to loose of soil. Or if the building settled or if the tree in the middle of the boulevard caused a heaving effect.

 

[Focht3]

Given what you have described, it's not building settlement or a tree. It's loss of ground caused by the wall drain failure -

I have a similar project here - client is the local phone company. I identified the problem during my initial site visit; our geotechnical report provided recommendations for a replacement drain. The knuckleheads decided the fix was too expensive - so they omitted it from the repairs. And I got a call - literally - last Friday. The contractor (replacing the parking lot) found voids, and wants to know what to use to refill them before the pavement is replaced...

And the basement wall next to the voids beneath the pavement is bulging, and leaks -





Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[Willbert]

Well gave it some consideration and came to the conclusion that using "concrete slurry" may not be an option due to the fact that the sidewalk is 7'away from the wall by 15' along the wall. They are not individual slabs. Also with the amount of pressure required to lift the slab would probably case more damage to the clay weeping tiles.

 

[Willbert]

opps when I ment 7' away from the wall I ment the sidewalk is 7' wide from the wall.

 

[scofie]

Isn't it possible that your problem could be moisture intrusion above ground into the block walls that travels down block cells to the wall base, which is your basement floor? As such, remediation would focus on things like exterior wall painting/coating deterioration, clogged roof gutters, exposed roof parapet coping, etc... in the problem area. This seems like a much more likely senario than a local collapse of perimeter drain tiles. I didn't see any discussion of this possibility, so maybe this has already be ruled out?

 

[Willbert]

scofie (Structural)

My engineer already looked at the drains from the roof and also along the height of the wall there are no signs of runs going to the base of the wall where it meets the floor.

The engineer pointed out that the water is rising on the insulation and the drywall from the floor up. Leaving him to believe it’s a weeping tile problem. If he found dampness from the ceiling or anywhere else from the wall leading down to the floor then we would have investigated further to the source.

The dampness on the wall runs appox. 15 feet and has a height of approx. 2 feet from the basement floor.

 

[Willbert]

Ids also like to point out that the only time it really leaks is when it’s in a winter thaw or severe downpours. Water only accumulates on the floor in the winter months after a thaw. During the heavy rains the floor does not pond but the wall does get moist.