Tree Tech Consulting    The Knothole  Hop To Forum Categories  Construction & Hazards    foundation questions

Closed Topic Closed
Go
New
Find
Notify
Tools
foundation questions
 Login/Join 
<Russ Carlson>
posted
A client is planning an extension to his house that will reach within about 12 feet of a 34" Copper beech. I'm looking for information or ideas on constructing a foundation to support a cement floor such that the roots beneath the floor do not have to be cut. The plan is to have a heated floor (not sure if it will be hot water heat). Any suggestions or sources to check?
 
Report This Post
<Scott Cullen>
posted
Reply to post by Russ Carlson, on June 08, 2000 at 20:40:45:

Russ, check with Larry Hall. He showed slides at an ASCA conference (I think) of an office building constructed over roots. The original idea was to foold the area, let it freeze (Chicago, brrrrr), pour concrete over, let ice thaw and go away. As it turned out I think they put in a permanent gravel bed and poured over that.

2nd, is the point load (pier) and grade beam idea, as you did in the wall in the Academy scenario.

Beeches don't like having their roots fooled with. I don't have solid evidence, but I suspect a large beech we successfully protected throughout construction in the early 80's sustained some very minor damage after the protection zones were removed and landscape lighting was installed. There was not a direct effect but soon afterward the tree developed beech bark disease (none prior) which has been taking its toll ever since.
 
Report This Post
<Colin Bashford>
posted
Reply to post by Russ Carlson, on June 08, 2000 at 20:40:45:

Russ. This one interests me as we spend a great deal of time assisting in such potential arboricultural/structural problems. You however are very shy in giving out some of the essential detail that would be needed to enable an assessment and maybe a prescription to be made for this case. For example what is the proposed relationship of the house to the tree, is the separation distance given at only one point in terms of the probable rootplate or along one 'side' of the tree? What is the existing topography and does the house replace any other previous construction? Is it intended that the house shall have a basement and from what materials is the house to be constructed?
I could go on but you know what I mean. Can you provide this additional data?

Colin
 
Report This Post
<Julian>
posted
Reply to post by Scott Cullen, on June 08, 2000 at 20:40:45:

The Chiocago project actually used the gravel bed as a temporary foundation. The gravel was subsequently removed to leave a suspended slab. I agree that beech does not tolerate disturbances well. Stay away from the roots as much as possible.

Julian
 
Report This Post
<Russ Carlson>
posted
Reply to post by Colin Bashford, on June 08, 2000 at 20:40:45:

OK, Collin, here's some help.

The original house is over 150 years old, stone construction. About 35 feet from the house is a retainer wall, 30 inches high. 22 feet farther back is the trunk of the American beech (Fagus grandifolia). A covered patio will be constructed between the house and the retainer wall. I do not consider this part to be of major impact to the tree.

The retainer wall will stay in place. Beyond it, the owner wants to reconstruct a small barn, moved from 40 miles away. I do not have dimensions of the barn at this time, but it will fit between the tree and rretainer wall, reaching to within 12 feet of the trunk, and near the radius line on one side. Some pruning of low branches will be necessary on one side.

The owner will use the barn as a studio or office, and is currently planning a dug foundation (about 3 feet deep, he said), with a pour concrete slab floor near the current grade level. The slab will have internal heating elements. (The barn will be dismantled, transported, then reconstructed on site.)

The question is, how to construct a suitable support for the barn without disturbing all the roots in the area, and what options should be considered to maintain root health underneath the new floor?
 
Report This Post
<Julian>
posted
Reply to post by Russ Carlson, on June 18, 2000 at 07:25:36:

This is where you need an AIR-SPADE. You could then examine the root structure, then prescribe a solution. Locating piers between critical roots will allow a least damage approach. Use tubes fot the concrete to avoid caustic damage / leaching to the soil.

Julian
 
Report This Post
<mike ellison>
posted
Reply to post by Julian, on June 18, 2000 at 23:47:25:

To the best of my knowledge, piers distribute the load at their base and require a basal area appropriate to the applied force and the load-bearing capacity of the substratum. Mini-piles rely on friction at the face of the pile.

What you are suggesting sounds like a pile. Would not a tube limit friction (the transfer of forces into the soil).
 
Report This Post
<Scott Cullen>
posted
Reply to post by Mike Ellison, on June 20, 2000 at 22:09:02:

Good questions for the engineer.

1. Just how damaging will initial and subsequent alkaline leaching from the concrete be? Could this be overcome by some sort of concrete additive?

2. If the engineered system requires soil friction and leaching is a concern maybe corrugated metal drain pipe could be used for forms.

3. If the system is engineered to rely on bottom bearing surface, there is a system of forms that go on the base of the cardboard Sonotube (TM). Picture a truncated cone with the top diameter mathcing the selected tube. Of course you have to dig the hole to the larger diameter and that might or might not impact more roots. http://www.bigfootsystems.com

4. There is also a system known as pier and gradebeam. I'm unclear if the entire load is transferred to the piers and the beam carrying the structure load above just happens to sit on grade or if part of the load is spread by the beam to the ground between piers.
 
Report This Post
<Julian>
posted
Reply to post by Scott Cullen, on June 23, 2000 at 17:00:39:

Scott:

Concrete leaches most when wet and just poured. Once its cured there is no leaching. I specify 6 mm poly as a barrier when pouring, or especially when using shotcrete to pin up vertical soil faces. Currugated steel forms would be expensive and are not removable. Sonotube works well and I have seen it used many times as a means of making a load bearing pier. Piles are driven into the ground. Sheet steel piles rely on the friction around them, while wooden piles use friction and the compacted surface of soil beneath them created as they are driven in. Sonotubes can be augured into the ground if the conditions are good. I have used the pier and beam approach as a menas of avoiding roots and acrrying structures over the root mat. It allows me to explore where the critical roots are and then locate the piers in between them thus minimising damage.

The grade beam is a structural beam that sites on piers or piles and distributes the load to these but not to the intervening ground areas.

Julian
 
Report This Post
<Scott>
posted
Reply to post by Julian , on June 23, 2000 at 18:05:39:

10-4
 
Report This Post
<Wulkie>
posted
Reply to post by Scott, on June 25, 2000 at 12:09:26:


23 skidoo
 
Report This Post
<Colin Bashford>
posted
Reply to post by Russ Carlson, on June 18, 2000 at 07:25:36:

Hi Russ, sorry it has taken so long to come back to you particularly after your very promprt forwarding of additional detail of your site specific problem. Been out of town and very busy and have only just got back to check up on email etc. Have become involved in another major issue which I am sure we will discuss in Baltimore. Having read the excellent advice from our colleagues it almost seems that most has been said. I particularly agree with Julians comments. However I fel that there is more to add. We frequently use the basic pile and beam concept. We however ensure that the solution is arboriculturally led with the support of a structural engineer rather than being an engineered led solution. That to us is extremely important and as such all solution and specifications will be entirely site specific. I would want even more information before determining the way ahead. Such information would include greater soil info ie soil bulk density, compactability and soil porosity along with soil moisture data to add to soil type. I would also require the assessed loadings to be put on the soil before supplying advice to the arb. led solution. Where concrete piles are specified we have found that the best method to counter problems of leaching is to utilise precast concrete pipes which are readily available in a range of diameters. Concrete then poured into thes as a liner makes a very solid base of high load bearing strength. The height of the pipes can be adjusted above ground level to ensure that the 'ground' beam is carried above the existing and proposed ground levels where slight levels increase might be anticipated or accepted. In tghis manner a minimum 4" air space can be maintained between the supported precast concrete floor and ground level. This area must be ventilated and include any water supply system that might be prescribed and installed. As a result of these operations the formed concrete floor can then be floated over with fooring compound that can include the required subfloor heating system. Where the position of proposed piles conflicts with major roots found with hand dug initial excavation, the position of the piles is relocated and the "ground beam" cantilevered over the roots if necessary, which is often a requirement at the corner of the proposed structure. We also prepare above ground raft type foundations based on what is nominally termed "no dig" specifications. It however has to mean what it says - no dig and frequently utilises 3D geo type grids. There are, despite freely available prescriptions, no standard specifications for this form of foundation. If I am not "teaching my grandmother to suck eggs" and you want more info, let me know and I will bring some over with me to Baltimore. See you in four weeks time. Colin
 
Report This Post
<Wamiq Bin Hamid>
posted
Reply to post by Mike Ellison, on June 20, 2000 at 22:09:02:

I have to repair a foundation that is isolated and square taking a load of 130 kips(max.). There are 32 total foundations supporting a ground + one floor building. This is settling down due to the settlement in clay,which was found upto the depth of 8.0 meter from ground level. The foundation depth is 2.5 meter from existing ground level. The SPT blows are 28 at 3.0 m, 32 at 4.0m and refusal at 6.5m. The Plasticity index is PI = 26 and Liquid limit L.L.= 49.

Now on the basis of the results found during investigation and visual inspection I have recommended the MINI PILES. The Dia of mini piles i recommended is 10 cm and length if upto 6.5m where N=refusal. The load which one mini pile is taking I calculated is only 5.0 tons.
But the lod which foundation is carrying is 58 tons. Now i am in doubt that whether these piles should take all foundation load or part of it?????
Also How many mini Piles can be drilled in one foundation ( the fiundation size is 2.1m by 2.1 m) also whether they will be bored piles or driven piles??? Also concrete piles or Steel piles??? Also if load test of pile should be carried out or not???
If u can advise me by tomorrow i shall bre obliged.
WAMIQ
 
Report This Post
  Powered by Social Strata  

Closed Topic Closed

Tree Tech Consulting    The Knothole  Hop To Forum Categories  Construction & Hazards    foundation questions

© 1997-2003 Tree Tech Consulting. All messages are the property of the original author.