Geotechnical Survey
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A geotechnical (geotech) survey evaluates the soil under your proposed building so that your structural engineer can determine what type of building foundation your building should will need.
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The geotech company will take a drilling rig out to your site and drill down to evaluate all the different layers of soil above the bedrock. They will also drill into the bedrock to evaluate its bearing strength. If they hit any ground water with their borings, they will note that in their report, and recommend ground water mitigation techniques, like casing piers.
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The soil type on a site can change quickly over a short distance, so you want to drill your borings where you are going to place your building so that you can evaluate the soil at that specific area. After you have a conceptual site plan showing your building location on the site, share that with your structural engineer and ask him to draw the locations of where he wants the borings on that site plan. Your structural engineer will usually place a boring at each corner of the building, and one in the center. Send those boring locations to your geotech engineer so he knows where to bore. With that information, he will be able to give you a price proposal for the geotech survey. Your civil engineer may also want a boring at one or more paved areas so he knows how to design the strength of that paving to ensure it wont crack.
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The report will describe the soil and make recommendations to the structural engineer on what type of foundation the building should get based on the soil. The structural engineer will likely go with that recommendation so that he sheds any liability of with foundation problems back to the geotech engineer.
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Click here for an example of a geotech report.
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Geotech surveys are expensive. They usually cost somewhere in the $12,000 range, depending on the number of borings. If you are performing due diligence on a site and want to get a preliminary idea of what type of soil is likely at your site in order for your GC to put together rough construction numbers, but you don't want to spend $12,000 yet, you can ask your GC or civil engineer if they have an old geotech report from a nearby site from a past project. You can then assume that your site has similar soil, and the GC can use that info to price out his foundation work.
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Sometimes your geotech engineer will recommend building foundations and soil treatments that are expensive. An engineer is typically conservative, knowing that he could be exposed to law suits if there was a structural problem with a building based upon his recommendations. Therefore, he will likely err on the side of caution and make building foundation recommendations that make the building extra stable. The problem is that this is expensive, but he is not paying the bill to make the building extra stable - you as the developer are. All buildings move some. They are designed to move some. However, if they move a lot, they start to crack and have problems. It is a balancing act between how solid to make the foundation and the associated cost.
If your building foundation recommendations in the geotech report are driving up the construction costs significantly, challenge your geotech engineer by asking for a more cost effective recommendation. Or you may want a second opinion from another geotech engineer. Lastly, your general contractor might have a recommendation on how to design the building foundation. If the GC has built a similar building, on top of similar soil, but it had a foundation design that was cheaper than what the geotech engineer and structural engineer recommend, share that with your geotech and structural engineer to see if that is a viable option for them.
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Next Page: Purchasing the Land
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