Basement Water Intrusion 1

[Yakman256]

Hey All,

I'm more of a flood engineering person and I already posted there but this seems to be a problem more in the geotechnical area. This is actually for me and my house where I’m trying to resolve some water intrusion issues in my basement due to high groundwater. On one side of the house I have an addition supported by brick columns that do not go down as far as the basement footing. I have already diverted the surface water away from the house and that helped but I still have water intrusion through the cinder block walls when the groundwater raises after large storm events. I already have interior perimeter drains that are directed to a pump. I also plan on installing exterior perimeter drains on the other three sides of the house, apply a parge coat to the walls, applying some HLM5000 (Liquid Rubber) and some dimpled membrane before backfilling with #1 stone.

I would love to excavate under the addition and apply a waterproofing membrane but there is a whole host of safety issues associated with this and I’m looking for an alternate solution. I’m considering only having the voids within the block walls pressure grouted but I don’t know much about it. I’ve also read about pumping a bentonite slurry though the wall onto the Wall/Soil interface but I would prefer not to put any additional lateral pressure on the wall when the bentonite reacts with the water. MY hope would be that by pressure grouting the walls, the water would then travel to the perimeter drains on the side of the rather than through the wall. I also have to concerns about degradation of the block to to 50 years of water intrusion.

Any ideas?

 

[oldestguy]

One process that may be usable here is what I call waterproofing the ground. Your term "diverting surface water" would nice, but you may need more than that. Once the water soaks in, if likely follows the weaker planes of backfill. They usually head towards the house. So any infiltration within the area of the backfill, likely will affect the house. That distance out generally is at least 10 feet. Dumping downspouts within that can affect the house. Do you have any decorative area of clear stone, bark, etc, that can collect water?

A belt and suspenders job here would involve two projects. I'd not depend only on a perimeter drain added, if you truly have high groundwater. I'd do the surface waterproofing and also an intercepting perimeter drain, somewhat out from the house at lower elevation. I'd lead it to a manhole where there would be a sump pump. The discharge should go farther away. This may be only a seasonal pumping requirement.

For the surface waterproofing, go to this link where I went through this.

http://www.eng-tips.com/viewthread.cfm?qid=162089

Look for my input there.

Now as to the perimeter drain either at the house or beyond, go to this link and look for my comment.

http://www.eng-tips.com/viewthread.cfm?qid=162089

I've done so many of these posts that I probably should save a copy to paste for this common situation.

 

[oldestguy]

One more item: If it was not clear in the surface waterproofing statements, I always strip of the sod and remove all decorative bark, etc. Also you may have to do some grade changing to create the slope. Walks can remain, but look to seal cracks. Work around plants.

After the sealing of ground surface is done, replace the sod and it will grow even bete.

 

[Yakman256]

Although the surface area has not been waterproofed as oldestguy has suggested, I'm fairly certain my issues are groundwater related. The area around the house is composed of dense clay with zero percolation because I tested it to depth of 3'. I also have a job site about 300 feet from my house where we did extensive soil testing with zero percolation.

As a secondary question.... How close to the brick columns can I safely put a under drain without causing structural issues?

 

[oldestguy]

I don't buy the no perc for the clay soils. I doubt that backfill was compacted back to original density. That backfill situation normally is quite pervious. In addition, even highly plastic clays change in moisture content depending on seasons, etc. and develop cracks, termed "structure" by the soil scientists. In time these become filled with less permeable material and do allow infiltration. I've seen cracks as wide as an inch going very deep (4 ft+) in these clays during dry periods. Take the case of successful disposal of cannery waste water on land that has zero percs. A common thing here in Wisconsin.

However, if sub-drains are planned, the surface waterproofing can come later, if needed. In my experience most of these basement wet conditions are due to surface water, usually related to rainfall or snow melt. Take the house I just bought 4 years ago. I know the water table is high (a swamp outback, elevation a few feet below the basement), but after doing the surface fix, the perimeter drains carry no water. Sump pump never runs. Former owner had the sump pump run a lot. All was known when I bought, but I knew I'd fix it.

Before I would go into this, hand auger down and install some PVC pipes and observe the water levels with time. You can do this with a small post hole auger and extension pipes. With careful elevation readings, you may see a ground water flow direction. Or, it may follow the topography.

However, handling the ground water may require stages of work. The most likely groundwater flow direction deserves an initial "moat" to intercept the flow. Of course that moat is then filled with granular material. It may require surrounding the place with this "moat", possibly done later. In some areas the flow of groundwater is such that it sneaks under the "moat" and comes up inside that protection. In that case drains inside the building may be needed. In my experience, the "cut-off" drains do a good job with down gradient protection. Do not try to draw-down the water table, as with a series of wells around the site, or limited length of the sub-drain, since that is a very questionable method in most areas. Cutting off the flow works best.

When excavating near any foundation, such as the piers, you run the risk of a slip sideways. For temporary open cuts, we commonly say don't cut wihtin a slope of 45 degrees. In some places that is even too risky, while in others, some guys get away with a vertical cut next to the foundation. It all depends on what that soil is. The better situation would be to provide temporary supports and replace that pier to deeper depth, or underpin it in sections.