Settlement after 53 years
Settlement after 53 years
(OP)
I recently looked at a 53 year old one story masony house. The rear half of the house is built over a basement and the front half over a crawl space. The basement foundation walls show little sign of settlement, but the crawl space foundation walls have settled significantly-approx. 3 to 5 inches. It appears that the settlement has occurred over a long time and is ongoing. I was able to dig several small holes at openings in the crawl space floor slab. The soil appears to be very loose granular fill. There are bits of broken glass, bricks, etc. in the fill. I was able to dig down abount one foot by hand (could have dug further). At that point I could easily push a scewdriver into the ground up to the handle. The house is located in Philadelphia. Records suggest that the house may be located near a buried stream or in an area where significant fill was added. Some adjacent structures also show signs of significant structural distress resulting from settlement.
My questions are:
1. Shouldn't the soil have consolidated over this length of time?
2. Is piping likely to be occurring?
3. Any suggested soils tests that could be performed? (value of the house is relatively low and therefore owners budget is small).
4. Any thoughts on stabilizing the foundation using helical piers? other ideas?
Thanks
My questions are:
1. Shouldn't the soil have consolidated over this length of time?
2. Is piping likely to be occurring?
3. Any suggested soils tests that could be performed? (value of the house is relatively low and therefore owners budget is small).
4. Any thoughts on stabilizing the foundation using helical piers? other ideas?
Thanks





RE: Settlement after 53 years
Helical piers may not be a viable option if there are filled-in obstructions beneath the building. Wood, concrete, steel and other types of fill could make it hard or impossible to install the helical pires. Conventional pit underpinning might be a better stabilization method. But you still need borings.
RE: Settlement after 53 years
However, in my 52 years in the business this usually is caused by sitting on coal ashes. I have never seen it happen that the settlement stopped. So, you probably can look forward to it continuing for the forseeable future.
By passing the stuff is the cure.
RE: Settlement after 53 years
Also, the screwdriver test isn't valid for granular soils. It doesn't surprise me that you could push it in all the way. Even compacted granular soils won't fully resist a screwdriver (that's a pretty high stress on the soil..example...a 1/4" flat blade screwdriver with 10 lbs of force on the handle would exert many thousands of lbs/sf on the soil, thus you failed the soil in bearing with your point load)
RE: Settlement after 53 years
RE: Settlement after 53 years
RE: Settlement after 53 years
Another cause of this kind of setlementis shrinkage of some clay soils.
The usual clues are the presence of fast growing trees nearby, taking moisture out.
Should the test borings show "hard clay",and no significant junk material, well then shrinkage is the probable cause. This effect can extend a deep as 20 feet in some areas.
Correction can take many forms, but interesting enough removing the tree, or watering the ground can make a big difference, without any fancy underpinning, etc. It is not an easy fix otherwise.
For test borings, look in the yellow pages under that subject or foundation exploration, etc.
RE: Settlement after 53 years
May want to have the homeowner check for water lines or have a plumber do so.
RE: Settlement after 53 years
RE: Settlement after 53 years
Philadelphia really doesn't have shrinking clay soils. Usually, we have 1. silts and silty sands over sands and gravels or 2. silts over decomposed mica schist and harder schist.
mjr6550,
I'll try to answer your last question tomorrow. Couldn't get to my office today. All of the river bridges to my office were flooded & closed today. Massive traffic jams and closed roads along the Schuylkill River, Perkiomen Creek, and French Creek. A really bad day!
For borings in the Philadelphia area, I'd recommend Geosystems Consultants in Fort Washington or Schnabel Engineering in West Chester. Unfortunately, Geosystems got flooded badly today. Their office is right at the PA Tpk Fort Washington Interchange.
RE: Settlement after 53 years
RE: Settlement after 53 years
RE: Settlement after 53 years
RE: Settlement after 53 years
BigH hit on a good idea. With all these people flooded out, an easy start with a small back-hoe will tell you (anybody with some eyes) what is there.
Test borings these days, in their hurry for making footage, can miss seeing important things, due to hollow stem augers. I'd vote for test pits below the depth of the foundations of the shallower part.
Not like in the old days with the Gow method (bet many of you never heard of that method started by Raymond).
BigH Ever visit B.K. Hough lab in Ithaca?
RE: Settlement after 53 years
RE: Settlement after 53 years
You might consider flooding (or at least significantly wetting) the area to be observed just prior to the excavation. This will help keep the sandy soils together for viewing.
RE: Settlement after 53 years
RE: Settlement after 53 years
Knowing you also are a Cornellian, thought you might have run into this fellow, a former professor of Soil Mechanics who then left to run a geotech business. He had built a number of the Universal soil testing machines that were there in my time. They were housed in temporary building overlooking Beebe Lake. Nice memories.