Need a book? Engineering books recommendations...
RE: Soils Reports - A Ghost Story[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Soils Reports - A Ghost Story
- From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
- Date: Tue, 22 Jul 2008 15:45:56 +0000
The failures are not always spectacular, but they are always expensive. I recommend a geotech report to anyone. Following are 4 case histories in which I was involved. They are best read at night by candle light, near Halloween with a thunderstorm in the background. |
Let us begin. It was a dark and stormy night and the young structural engineer wanted to feel his blood run cold.
A fellow structural engineer begrudgingly agreed with me and obtained a soil report for his own home that he was planning. He thought the geotech report was a waste of money and his housing development was previously just an old corn field that had been transformed into a housing development. When they started punching holes, they found that there was an old sewer line that ran through his lot. The sewer line was gone so it did not show up on anyone's title search or on anyone's plans. The the fill was not compacted. He had about 20 feet of unconsolidated fill that would have been supporting his home.
The developer had to pay for excavating the lot and compacting the site with a geotech monitoring the placement. The photographs of the excavation showed the classic "V" shape of the excavation for the old sewer line.
His neighbor's house was in the background in a direct line with the old sewer excavation. His neighbor has been fighting settlement issues for a long time, and will have to fight them for a long time to come. His neighbor's house will always have the stigma of being repaired and having settlement problems.
There was a housing development in my area about 15 years ago that had a picturesque view of a creek in the back yard. The site had been filled, and the fill was compacted. But there was no geotech report or monitoring the fill placement. About 4 or 5 houses started sliding toward the creek. The fill had not been benched. The entire fill area slid along the interface between the fill and the native creek bank. About another 6 or 8 homes developed large cracks and were condemned. Insurance only covered a fraction of the losses. A post disaster geotech report showed the sloping profile of the interface, but it was too late for the developer and for the home owners.
A professional golfer wanted to build a home on his property which had a private lake, skeet range, and putting greens on which he could practice. An excavation indicated that his house was going to be founded on rock. The structural engineer (me) was delighted, but the structural engineer was a chicken and wanted a geotech report just for peace of mind. The geotech report indicated a spring and a lot of perched water on top of the rock. The design team developed an extensive subgrade water mitigation plan. The professional golfer's home was constructed in about 1989 and is as dry as a bone today. That bullet whizzed by my ear, and I took note.
Don't forget the movie Poltergeist!! ...OK, that one was fiction. And my involvement was just watching it.
Geotech reports do not cost that much, but they afford a lot of peace of mind. Get the geotech report, and sleep easy. Do not wake up screaming in the middle of the night.
I don’t know about Cali, but in my neck of the woods, we have vastly varying soils within a subdivision. Just going across the street we see a completely different soil. One house I had to do a condition assessment on was built ½ on an expansive clay and the other ½ on a collapsing sand. You should have seen the look on the Geotech when they were running a water level. Turns out a deep foundation should have been required, and we ended up doing a helical pier underpinning effort. In N.W. Wyo, I recommend it to everyone building to get a geotech report. For us, it’s more than just soil bearing pressure, but also soil reaction. Don’t know what the soils are like in Cali.
From: Steve Gordin [mailto:sgordin(--nospam--at)sgeconsulting.com]
It was discussed earlier in the year. In my experience, in 80% of the projects, 1,000 PSF suffices (as it should), if not - find a geotech familiar with the area to write a memo reflecting the requirements of the 2007 code (another 15%), if not - then a full blown soil report will be required.
V. Steve Gordin, SE
Use video conversation to talk face-to-face with Windows Live Messenger. Get started.
- Prev by Subject: Re: Soils Reports
- Next by Subject: Soils Reports - Real situation
- Previous by thread: RE: residential upgrades
- Next by thread: Re :Re: Steel Pipe fabrication & Galvanizing Specifications