What do we need to know for soils and Geotechnical reports?

Hi, I’ve gone through the different kinds of soils and understand shear strength, plasticity, liquidity, etc. I also went through the Geotech report provided by black spectacles. Without the general summary, how can I know which foundation type should be used and how to understand what the geotech engineer is recommending?


Hi @shelly.kimmel ,

Maybe I can help!

In general, I would be very familiar with the soil types and which type of foundation might be suitable for each. I would also be able to organize the soil types from finest to coarsest and understand which are typically the best for building on.

Like Mike says in the lectures, typically the summary is the first place you should look in a report for the important information at a glance! In the report provided by Black Spectacles the information on suggested foundations is in Section 3.1 - Foundation Support. This example report doesn’t have “Summary”, but instead summarizes findings in the “Conclusions” section.

If you are interested in doing a deeper dive into the soil analysis and are an expert level Black Spectacles subscriber we have an upcoming virtual workshop on the subject! See below:

If you are looking for more information beyond the lectures, I recommend checking out Architectural Graphic Standards. If you don’t want to pay for the big book, the student version is a “reasonable” price and contains this information as well! In the student version pages 4-15 do an excellent job expanding on soil types, foundations, and which foundations are appropriate to use where. I like the student version A LOT better for understanding this particular information because it packages it so nicely together. I don’t regret the money I paid for this book.

I’m afraid I only have the 11th version of the full Architectural Graphic Standards so I cannot provide page numbers for the most current 12th edition, but in the older one pages 144-146 talk about soils and excavation and foundations information is spread throughout.

And last but not least, you can find a surprising number of geotechnical reports online for free if you want more practice viewing them! Here are a couple I found by googling “geotechnical report example”:

Hope this helps!

@coachdarionziegler the graphic design is quite helpful.it is actually in chapter 16 site work p178.
another question about soil boring
I’ve seen "weathering rock " in some googling boring log, some are deep some are shallow,
is that something suitable for the foundation to sit on or it needs to be blasted to remove?
are they different than bedrock?

Hi @xurubi ,

According to the Architectural Graphic Standards Student Edition, “If the rock has been weathered or is cracked, its bearing capacity may be compromised”.

I think it’s likely weathered rock is acceptable, but it may require additional evaluation by the geotechnical engineer. I see “partially weathered rock” quite often. This is usually present just above the bedrock. In my experience, unless the foundation was meant specifically to site on bedrock, the presence of partially weathered rock does not effect the foundation design. However, if your foundation was specifically designed to sit on bedrock, the geotechnical engineer would need to advise if the partially weathered bedrock would be appropriate.

I found this report that does a good job explaining the partially weathered bedrock present and the consequences of it: https://www.chathamcountync.gov/Home/ShowDocument?id=23342

Hope this helps!

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