Tell me about piers for footings
My lake lot sits about 110′ above the beach. The geology has been in place for a few years. Along the bluff’s edge, in the middle of the lot, sits an enormous red oak estimated at 400 years by the forester. It’s roots are all contained within the bluff – none sticking out to indicate any erosive landslides during it’s lifetime.
Right at the bluff is a dropoff which I estimate at about 20′ before it slopes down and out about 10 feet where another 20′ dropoff occurs, then another slope about 15 to 20′ and another dropoff about 20 to 30′ before the final slope down and out towards the beach. Which is about 300′ deep from the waters edge to the slope’s base. Lake Michigan would have to rise about 6 to 8′ before it would splash up against the slope’s base.
The entire slope is heavily wooded. Rough, never been cut. (Until a mysterious woodcutter recently came and cut down about every cedar tree blocking the view – there’s a number of deciduous ones left.) The topo indicates the slope is about a 45 degree slope in total although I doubt the surveyor’s helper took the time to slither down the slope to take true point readings (and I doubt any readings could be accurately made due to being on the edge of this sandy cliff). It seems more than 45 to me.
The lot came with the 8″ test well for the development. It’s Formation Description is:
Fine sand 6′ thick
Sandy clay 54′ thick
Sand, medium 35′ thick
Sandy clay 15′ thick
Medium sand 35′ thick
Fine sand 81′ thick
Total depth bored is 226′ Report says “rotary.”
Water test results indicate an adequate water quality and quantity at 145′ – measured at 20 gpm for 4 hours. (The topo lines give me the impression that well sits about 120′ above the lake level.)
My question lies in the construction methods we may have to employ. The sandy soils appear to be heavily tied together with tree roots (the lot was heavily wooded – until that mysterious woodcutter took out about everything 6″ and smaller). However, any site prep is gonna remove that around the house area.
Setbacks keep me 50′ from the slope, and 15′ from the road. The building site is about 150′ deep to the edge of the slope. 93′ wide.
I’m thinking right up front that I should include piers in the timber frame’s foundation plan. What are your professional thoughts? Have I sufficient data for the foundation engineer from this well boring?
What depth do they go? Width or size? What formula is used to determine the number? Should they be drilled or pounded? Should the pounding method even be considered?
Of course, this adds a cost, but ruffly, but how much more to the foundation’s total cost?
Edited 6/2/2008 9:01 pm ET by peteshlagor
Replies
Here's a picture of the opportunity:
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Perhaps the woodcutter may come back again in the future?
Edited 6/2/2008 9:04 pm ET by peteshlagor
Edited 6/2/2008 9:04 pm ET by peteshlagor
wow, beautiful spot ! Where's that?
Pat
No help.
you have pretty good soil there, the length of the pile is really how high you want to be off the ground and wind shear. I would have no problem with a slab on grade
I imagine some form of basement would also work?
Anyone else got anything to offer to this shameless bump?
East side of L. Mich. Thanks.
Nice.
Grew up on the other side of that there pond.
With that layer of sand the clay is not likely to liquify in an earthquake, so I wouldn't worry about it. Frost-protected shallow foundation (fancy version of slab-on-grade), or a full basement with good drainage to daylight. Wide footings and plenty of rebar in the walls.
BTW, a 45° slope looks steeper than it is. Double black diamond ski slopes rarely meet that degree of slope.
Thanks.