Foundation method for building over drainage creek

[cbrian]

I have almost finished my house and my father in law wants to build on my five acres for his retirement. My house is on piers which is not ideal, but I had water issues that would threaten a solid concrete curtain wall.

Is there any foundation method other than piers that will allow water to flow through under a structure? His water issues are even more extreme than mine due to the fact the only building site left that isn't on a ridiculously steep slop has a drainage creek running through it. I literally have to span his house over a dry drainage creek. I am afraid that just like in my case a solid concrete wall will hold back to much water. I have a neighbor that during a flash flood had a portion of concrete curtain wall blow out. I hate having to do a pier foundation, even though mine is holding up, but my building sites suck, any ideas?

From the top of the hill where the house will sit:


Looking up the hill where the water gathers during rain, where it forms a creek that is normally dry:


Another view up hill:

[kenhill]

There are companies that auger a post down as far as it will go for footers.  Wish I had done that as with Alaskan poor drainage, frost heave, eqrthquakes, etc.  My posts have moved and I releveled this summer.  We just had a 7.1 earthquake and some of them have moved again!.

[cbrian]

I built mine on pier and post, but like others on the sight, I don't have piece of mind. (Dam them and their logical arguments )

The structure is 16' x 26' the creek is about 10' wide. I was thinking of building a 8' x 16' perimeter block wall on both sides of the creek and just span over the creek to connect them? I know piers seem like the logical choice, but like I say these guys on here make some good arguments against it, and I wish I listened for piece of mind. I don't want to screw my father in laws house up.

[glenn kangiser]

I don't know all of the conditions on your site, but possibly rather than a perimeter wall you could build just some separate walls running parallel to the creek so it could pass by and drain as necessary you could build a foundation base a foot or two below grade to prevent washout by the creek as necessary then block wall up from there to the desired elevation centered on the footing.

I assume 4 of these would be able to support the size structure you are talking about. Size beams or joists as required for desired span.

Just ideas for you to think about.

[UK4X4]

Every time I look at properties near rivers, mountain runoff. ....I think of Vargas Venezuela  where whole villages were destroyed after  heavy  rains brought down rocks and mud from above. 2 and 3 story concrete buildings full of mud and rocks, others washed out to sea.

I think in your case i'd be looking at 2 off oval shaped piers either side of the channel, span the channel and install a glass section of floor to watch  the river go by on rainy days.

[hpinson]

But take a close look at the pictures.  My take on them is that the [limestone?] bedrock is very close to the surface, and that the soil is just a thin layer over that.  It does not seem like a slope that would fail massively, i.e. like a sand, earthen, or loess slope could.  What we can't really tell is what is above. 

Could piers be pinned into the bedrock?

[Don_P]

Why not step to one side or the other of the drainage? If you have the time it looks like there is plenty of stone for retaining/ diversion structures. Heavy equipment can prep a site very reasonably.

[rick91351]

Why not step to one side or the other of the drainage? If you have the time it looks like there is plenty of stone for retaining/ diversion structures. Heavy equipment can prep a site very reasonably.

After going through three flash floods in two years.  In a area that just does not ever get them barring a winter chinook - but I mean cow on a flat rock down south roads all washed out types of flash floods.   I so wanted to post what Don_P posted. 











p posted but no guts.   

[cbrian]

Well I bit the bullet and hired an engineer and concrete contractor. The plans they gave me show a stepped footing 18"x 18" in the limestone. Then a 1' stem wall to level. The concrete perimeter walls will not cross the creek, but will actually form two separate boxes on either side and the center will be spanned. The engineer says the creek is no longer active due to an uphill road I didn't know about, so essentially it is now just a runoff ditch where water collects just a bit above my property. Sure likes it was a raging creek at some point. So now my father in law is in talks with the engineer about putting the creek back into use, by creating a waterfall down the hill to a holding creek below.  They are already at 20k for the foundation only. That is why I did piers on mine, cost is so high for anything else around here. I will definitely post some pictures on this one.

The good news about hiring the engineer is I was able to get him to look at my house, and he made some suggestions, but says that overall with a few minor tweaks my existing house is perfectly safe. About 4,000$ and my foundation will be at the level I want it.  Should have hired him to start with, at least for the advice. I had it in my mind that just asking would cost a cool million. Surprisingly only cost me 300 bucks for his advice on mine and 750 for a drawing. So a cool 1k is cheap for insurance and a good nights sleep.

[MountainDon]

  

[cbrian]

(EDIT: modified links to display images in post.  MD)

Bridge beam style foundation allows for free movement of water on steep downhill sites, but still provides a solid foundation to build on.

[Don_P]

Interesting, not sure I'm understanding what I'm seeing. Are both foundations part of one building or is the bare foundation for another building?

You mentioned previously that the engineer had provided details for your pier foundation... anything you can share?

[UK4X4]

I had similar questions , I presume 2 buildings and you have three parallel  foundation  walls allowing flow through and under the building

Are they secured to rock ? Or have piers beneath ?

You mentioned that water flow has stopped, but i'd still be worried about  erosion around the sides if there is any run off

[cbrian]

We excavated to solid rock, that including removing all soil down to bedrock. This includes removing layers of unsuitable rock that even though may have considerable thickness, has layers of unsuitable building material such as trapped soil layers. So after getting down to actual bedrock we drilled, beat, hammered, and chipped pockets into the rock to create natural footholds for the concrete footing. Essentially we dug into the rock 1' down and 2' across, and every 3 to 4 foot we dug an additional 6" to create pockets within the pockets. We then drilled holes in the rock about 1' deep x 3/4" diameter and inserted rebar which we epoxied. After setting up some forms we poured 2' x 1.5' footers and left rebar exposed to bond the walls along with scoring a 2" x 2" indention (keystone) into the tops of the footings to help lock in the walls later. The walls where formed, rebared, and poured 1' thick. This thing is built like a bridge. We have had record rainfall and everything is holding up as designed. The engineer never actually came to the location, I designed and drew it up had him look at it. He just smiled and said go for it. Never could pin him down on actually numbers and calculations without giving him the entire contents of my wallet. The one thing he did say is, " You can drive your truck on that". There is absolutely no bounce pressure treated sills bolted to the concrete walls, 2x10@16" joists spanning 8', 1 1/8" advantech t&g subfloor, 2x6 exterior walls.

These are two separate structures, one being a master bath, office, master bedroom, and the other a guest bed/bath, living room, kitchen. The structures are connected by the addition of a sky walk that spans from building to building. This entire structure had to be build in a way as to not hold back water, but instead allow the water to flow through and around. It is essentially a house built on 2 bridges 50 degrees parallel to one another connected by a free floating sky walk attached to each structure.

I have forgotten how to post pictures, any advice? I will try, not sure if this will work..











Due to the steep location it is hard to get a straight on picture of the project. It is more visible in winter, but during this time of year everything is green and hides the house.

Water moving under Structure during flooding, we should have final completion in the next couple months providing the weather in Texas chills out:








BEFORE THIS STAGE:






Yes the tree grows through the porch, everyone insisted on it. IF the tree ever fails the porch doesn't stand a chance, but that section of porch should tear out with no damage to the house, unless it falls on the house in which case not much I can do there except pull the tools back out.

[midrover170]

Very cool design, and great use of the topography. Love the bridge connecting the two structures.