Geotechnical investigation is the investigation of the subsurface conditions and soil and groundwater,
as it relates to some sort of site development, buildings, roads, utilities.
Why do people order these things? What's the point?
We developed design parameters for other design engineers.
So subsurface investigation will tell you in all the bearing capacity
so they can make the foundations right size so you don't get excessive settlement, things like that.
What do you not want to find when you're doing this kind of thing?
Soft compressible, very wet soils or organic soils.
So those were things you can really adversely affect anything you put on top of it,
because it settles too much. Generally building can only tolerate about one inch of settlement
and when you put it on compressible soils and it's too much load,
you'll get more than one inch and then you get cracking of the facade
What is the normal, regular equipment? - The normal rig is more like the size of a dump truck
that would have a large boom that comes up probably 20, 25 feet.
And it would be just mounted on tires.
So it would access a site that is probably more level and accessible than this one.
The reason we have this rig on the site is it's all terrain vehicle and it can navigate the terrain
and in a truck would likely get stuck out.
They're doing the exact same thing.
Really, the important thing that they're doing is collecting the sample and that is using
a 140-pound hammer, falling 30 inches. And it doesn't matter the type of rig, the small one or a truck rig.
It still has that piece of equipment on it.
That's our standard for collecting data.
We take the samples back to our lab and we do strength tests on it. Either unconfined compressive strength or
grain size analysis. And we take that data, the lab with the field data that we get
on the 140 pound hammer falling 30 inches, and we develop our recommendations based on the strength of the soil.
And how deep do you have to drill? - It depends on the development. Roadway might be 5 feet
building foundations, 15 or 20 feet and heavily loaded buildings, you could drill 50, 60, 70 feet.
Okay. So it is important to know what you're going to build here before you start doing.
Yeah. - Okay.
Are there different types of geotechnical investigations?
There's kind of a base investigation that would be the soil borings and lab testing and developing recommendations
for site preparation and foundation design parameters.
So if that's your baseline, yeah. You can add a more exotic things to it.
In whole testing in situ testing, resistivity testing, and other types of testing
that might be more specific to say like a power station or some other type of development.
And how much time does it take to do this kind of job?
It depends on the amount of footage you're drilling. Generally wriggle get a 100, 150 feet in a day.
It depends on the conditions how easily can move around the site.
So in this case, we have 8 times 15, 120 feet. So they'll probably get it done in a day.
So when you say 150 feet like linear feet or like square feet? - Linear feet of drilling into the ground.
Say you find something you don't want to find. Is there a way to mitigate that?
Now, there's always a way to mitigate it. It's just a matter of how big it is and deep it is
and what type of developments going on it. But typically you can, you can mitigate it
with just smoke excavation replacement with good soil, more severe cases where it goes to
a depth that that's not really feasible, where you have shallow groundwater that you have to
deal with and digging a hole that deep is not an easy thing to do. Then we may look at a deep foundation system.
So there's always a way around it. It just depends on the cost of the solution.
What makes it cost more or less? Is it purely the amount of coverage or is it like your travel time?
That's several things, the type of equipment. This type of equipment here with the ATV,
it can't drive itself to the site, it has to be carried on a flat bed.
So you have more equipment charge getting it to the site than you would with a truck rig.
And generally there's a church per mile on the mobilization.
So distance. Outside of that, it's the amount of footage you drill on site.
Now, how does this kind of investigation differ from an environmental report?
Yeah, totally different things. Environmental phase two,
for example, would be environmental contamination. You're not looking at strengthened soil for
design parameters for engineers to design foundation.
So the geotechnical study, that's what we're doing. We're helping them design their foundations.
Have you ever found anything like shocking?
No. Unfortunately, not, no gold, no oil and no dinosaur bones.
Could that actually happen? - I imagine it could. You have to remember when we're taking a sample, it's about
an inch and a half roughly diameter tube, we're pounding into the ground.
So even if we were to hit an obstruction like that, you might not even recognize it by the time
the little piece that you get comes up. So it's not a large stamp that you get.
Those nationwide soil maps, how accurate is that?
We don't use those typically a whole lot in our line of work.
I believe they were developed by USDA originally.
So they're more agricultural leaning and upper soils.
There are deeper geologic maps that talk about overburden soils
and then depth based on mining data and well data from regions.
But in general, neither one of those will give you a strength of soil, it will give you a soil type or a soil profile.
What we're doing is determining the strength of the soil to carry a load.
So really the purpose of those is pretty different.
Yeah. Yeah. certainly, the USDA wants to give you a surface soil type is more agricultural
Though, it's used in civil design application.
Okay. So there's some crossover. - Yeah, there's some crossover
Somebody like me when I'm looking to buy a property, could I rely on that for anything?
You probably couldn't rely on it for design necessarily.
You need to get site specific information for each development.
Do people ever do this kind of investigation to determine whether there's wetlands
or is that just two completely different things?
Again, that's a different thing. Wetlands investigation is a different study.
You're not looking at the strength of the soil for design parameters. You're just defining a protected area.
Somebody like myself, if I was driving by a property or walking by a property,
is there anything I could do to just visually inspect| and identify problems or red flags
without getting this kind of investigation?
Michigan building code will tell you there's guidelines. Section 18, Michigan building code
talks about geotechnical investigation.
So I will tell you that you need to drill with the building authority
local building authority can waive that requirement
depending on the type of structure and what they know about the soil conditions at the site.
So to drive by a site and make some assessment of whether it's good and buildable
generally higher and dryer is good and lower and whether is not
There are times that when a person could build and design without
either if they want to take the risk or if the local municipality makes enough
And waves that required. Yes.
And what does a geotechnical investigation not telling you?
Some of the things we talked about, the wetlands protected areas, it doesn't tell you about
the environmental contamination.
It's easier to tell you what it does tell you than what it doesn't.
Are there any other things that you wish people like me knew about these kinds of investigations?
Like why they should order them or what they don't do or anything like that?
I think most people recognize when they're building, why they should order it, I hope.
Certainly, every site is different. Just because this site here is okay, it doesn't mean the one next to it is.
Probably the next thing I would say is important as it's not an exact science.
So all mechanics was developed by doing things a thousand times and developing a curve
and we estimate what's going to happen when you talked about settlment.
So just not an exact science.