Assessing 'Buildability' w/o Land Access

[MSUKeith]

I understand the need to have good soil test data to accurately design proper foundations. But what if you do not have access to the land for testing (such as tax or mortgage foreclosure auction) and are attempting to access 'buildability'.

There are obvious risks associated with using soil type maps to conclude on foundation designs but how much does the amount of risk vary with soil type?

Example: Fox-sandy-loam versus Spinks-Oshtemo versus Houghton (Michigan soil types). All are heterogeneous and probably vary widely regarding bearing capacity and settling dependent on moisture content. In my (limited knowledge and experiance) estimate, these are ordered best to worst but does even the best assume to much risk just going off soil type?

I do not want to end with a deal on land that requires extensive foundation engineering and installation cost.

 

[mas]

I think the first thing you should know is: What are you planning to build on this site?

Based on that answer, what is the range of foundations that the planned structure may require (least to most expensive)?

If you are building a home, you're quite unlikely to need deep piles costing loads of money. So will it really bust your budget if you had to beef up the foundation for the home? Probably not as homes are light weight structures.

But if you're building a manufacturing plant that cannot undergo even the slightest differential settlement, then the riskiness of purchasing this property without a proper geotechnical investigation is great.

Otherwise, without having access to the site to assess the soils, I would do the following:
1. Are there any buildings on the neighboring lots? If so, what kind of foundations do they have? Do any of the buildings show signs of foundation failure which may be indicative of tricky soils.
2. Look for other clues that may help identify soils. Wetlands and lowland vegetation usually indicate high water tables which will impact shallow foundations. Certain trees reach full maturity in certain soils.
3. Are there farmers adjoining this property? Talk to them. They are not soil experts with respect to engineering, but they'll know if you get standing water, or if the soil is well-drained, etc.
4. Ask the construction official in the town if there has ever been any project proposed for this property. Get names of engineers, contractors, or anyone else that may have info.
5. Visit the local SCS office and get details. Perhaps they can tell you with relative confidence (or not) that the soil mapping for your lot has been historically accurate with little variation for the soil descriptions provided. If you're real lucky, perhaps the SCS performed a soil boring on the PIQ as part of their mapping.
6. Does you state or county or town keep a database of all wells drilled (monitoring wells, potable drinking wells, etc.)? If so, perhaps drilling occurred at some prior time on the PIQ and there may exist a boring log. Soils don't change, even if the log is 30, 40, 50 years old.
7. Is bedrock known to exist in the area? If so, at what approximate depth?

In the end, I think you'll have to weigh the risks. What is the likely worst case scenario? And if this scenario panned out, would it bust your project considering the presumed discount you'll be getting on the property for buying it at auction.

Good luck!

 

[PSlem]

Sewer cuts usually give an indication of rock. If there is a wide swale, they probably had rock to remove and had to drag in more dirt from either side to replace. If the ground is level, there's dirt to the sewer invert.

 

[MSUKeith]

mas-

Thanks for the reply - great info. I had not thought to use the well drilling info and I do have access to that data for the area in question.

If the project was only one house this would not be an issue but I have dreams (nightmares?) of becoming a big time developer. The difference between the land supporting 5 houses with engineered foundations or 10 with standard foundations has big affect on the return on investment - plus the hassle of a proper road requiring more prep.

Thanks again.

 

[eric1037]

MSUKeith,

First, an FYI: Houghton soils are known as "Houghton Muck". These are usually relatively deep peat and organic clay or silt deposits. They can be up to 40 feet deep in some areas.

There are several steps that I go through when evaluating sites in Michigan.

I first check out the USGS topographic maps. These can be accessed for free at

http://www.topozone.com

You can also access free aerial photos at

http://www.terraserver.com

You can also check out the Quaternary Geology of Michigan maps. This site has the map:

http://www.deq.state.mi.us/documents/deq-glm-rcim-geology-1982_Glacial_Geology_Map.Pdf

I then check out USDA soil surveys.

Water well logs should be available in most areas. Check out this site for good water well info:

http://www.deq.state.mi.us/well-logs/

All of the other items that mas gives are good. I have a large amount of experience throughout the state of Michigan and I could probably help you out with some conceptual info.