Direct measurement of pressure behind a basement wall
Direct measurement of pressure behind a basement wall
(OP)
I am working on a report dealing with a bulging, leaky basement wall where a contractor used perf pipe instead of solid pipe to divert flow from roof downspouts. As a result the soil under the garage floor is so saturated that a second contractor drilled a hole in the floor and was able to push a nine foot probe all the way in with one hand. This was witnessed by the homeowners insurance agent.
I intend to calculate the pressures both dry and wet to illustrate the severity of the mistake but since we may be dealing with a jury it would be helpful to have direct pressure measurements at various heights along the wall. I worry that jurors eyes may glaze over when math comes into play. Especially here in my state where they are discussing dropping the math part of the achievement test for high school students because very few of them are passing it.
Can anyone recommend an arrangement of pipe and pressure gages to directly measure the hydrostatic pressure behind the wall? There seems to be enough water back there to activate a pressure gage.
P.S. The contractor who made the mistake tried to claim he had never done any work at that address. Invoices and cancelled checks prove he was lying so I have no sympathy.
Thanks
I intend to calculate the pressures both dry and wet to illustrate the severity of the mistake but since we may be dealing with a jury it would be helpful to have direct pressure measurements at various heights along the wall. I worry that jurors eyes may glaze over when math comes into play. Especially here in my state where they are discussing dropping the math part of the achievement test for high school students because very few of them are passing it.
Can anyone recommend an arrangement of pipe and pressure gages to directly measure the hydrostatic pressure behind the wall? There seems to be enough water back there to activate a pressure gage.
P.S. The contractor who made the mistake tried to claim he had never done any work at that address. Invoices and cancelled checks prove he was lying so I have no sympathy.
Thanks





RE: Direct measurement of pressure behind a basement wall
I would suggest that you investigate the situation properly before writing your report. very often what seems obvious at first review may not be the cause. Just a few questions:
Is this a new home - Likely not
Was the first Contractor the new building Contractor or was he called in to provide a fix for a pre-existing problem.
The garage slab is a slab on grade. Water presumably travelled via the slab on grade to the basement wall. Was this bulging as a result of frost heaving. Was there leakage into the basement.
The above questions are based on a presumed arrangement of the garage and basement.
Anyhow be careful since the first Contractor will also engage his engineer as well.
These problems though seemingly simple are very difficult to pinpoint blame unless you know the history of the site re construction etc.
It may cost you more engineering time that you may have bargained for.
Anyhow it is your observation. Just some opinions from my past experience.
RE: Direct measurement of pressure behind a basement wall
I'll bet local geotech firms even have a stock of these on hand.
You could shove these to various depths in soft stuff or hand auger holes, then properly backfill with sealing material (bentonite).
RE: Direct measurement of pressure behind a basement wall
What you have is saturated mud. Use a dilatometer to find soil modulus, and correlations to soil strength and behavior. I'd also stick a piezometer 20 ft into the ground and measure the depth to the static water table. If you don't have water table conditions above the basement grade how would the hydrostatic pressures actually build up on the basement wall?
Watch out for your assumptions. Some may differ with my post; however. . .
f-d
f-d
¡papá gordo ain't no madre flaca!
RE: Direct measurement of pressure behind a basement wall
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: Direct measurement of pressure behind a basement wall
RE: Direct measurement of pressure behind a basement wall
VAD, there is a lot more history than what my question would indicate. I am just looking for a way to present the data in the way a jury of unknown makeup and background can understand.
Fat Dad, Good point about the earthen dams. However, it would be impossible to push a rod 9 feet into any dry soil with one hand no matter how poorly compacted. The soil under the garage floor is no longer soil but soup. Borings in the garage floor and the use of a bore scope show about a two inch air gap between the soupy soil and the bottom of the garage floor slab. The water build up appears to be due to the fact that the downspouts from the roof are being routed into the soil by the perf pipe which was buried just outside the garage door. Prior to the installation of the perf pipe the downspouts were routed into the ground into gravel beds which then seeped into the adjacent soil.
The contractor who made the mistakes in question was called in to fix an existing condition. However he made it worse. He may not have created the problem but at the very least he should refund the homeowners money. The contractor I am dealing with now was called in to investigate. He has about $150,000 worth of instruments to aid in the investigation including ground penetrating radar, expensive rebar locators not the hardware store variety, thermal imaging electronic bore scopes etc.
Thanks,
dpajr
RE: Direct measurement of pressure behind a basement wall
Next you'll be claiming this homeowner is so badly damaged that the floor and wall all need to be removed and "properly" rebuilt! Maintain your objectivity as the owner's expert engineer, or you'll get your head taken off by lawyer who gets enjoyment from it and has had a lot of practice at it. The lawyers will get paid, the homeowner won't spend the money from the settlement, and you end up looking like a whore.
I started a thread a few years ago asking for ideas on what could cause the webs of a exterior CMU to split causing the wall to bow above an adjacent roof, and similar to what you are doing asked for ideas. In my case an architect, using a cheap probe looked inside the wall and saw the webs were broken, and came to the conclusion the webs separated due to severe moisture infiltration and the wall was in eminent danger of collapsing. That made absolutely no sense to me, but the architect was obstinate about what he saw. I finally got my client, who was a cheapskate lowlife, to open up the wall to do a visual inspection. Guess what we found? The broken webs seen were due to the CMU being laid around a steel support beam, and the wall was built with a bow in it and the masons just left that way.
Be careful that you know the difference between what you think you know and what you know. Engineers get paid for being smart, not for being brave.
RE: Direct measurement of pressure behind a basement wall
You need to demo the slab, you need to pull out the bad dirt, you need to replace the bad dirt with compacted fill. The drain pipe can be fixed concurrently, but your problem is not the drain pipe, it's the soil compaction.
f-d
¡papá gordo ain't no madre flaca!
RE: Direct measurement of pressure behind a basement wall
www.PeirceEngineering.com
RE: Direct measurement of pressure behind a basement wall
f-d
¡papá gordo ain't no madre flaca!
RE: Direct measurement of pressure behind a basement wall
To me, the first step is to fix the downspouts and site grading to get the surface water away from the building - especially if the wall is on the north side of the house.
www.PeirceEngineering.com
RE: Direct measurement of pressure behind a basement wall
An expert is a man who has made all the mistakes which can be made in a very narrow field
RE: Direct measurement of pressure behind a basement wall
A sketch would help for sure!
f-d
¡papá gordo ain't no madre flaca!
RE: Direct measurement of pressure behind a basement wall
The responses given so far are enlightening as it demonstrates how complex a commonly presumed unsophisticated engineeering issue - a house - can get.
There is absolutely no need for all the sophisticated techniques to answer this problem. Observation, past history - talk to the owner, previous owner, neighours, look at past development drawings if available, aerials,examine the basement properly on the inside etc are fewof the basic things that need to be done. In other words try to understand what could lead to the issue at hand. If excess hydrostatic pressure has resulted in the wall bulging, is the weeping tile system of the foundation working or was non installed. This could be possible or it may now be defunct.
Core the basement wall if possible from the inside. Water is the culprit then concentrate on determinimg how this has resulted.
Was the building performing well in the past.
There are a number of steps one can take or else youone may end up facing what smb4050 has indicated.
This is one area that many of us are not good at. Step back and give it some thought before plunging. Lawyers and your fellow engineer love these issues. having lawyers involved can get nasty as they will always find a buddy engineer who will take pride in providing the ammunition for him to shred you.