Case History 2 === Liz: [00:00:00] Welcome to the GBA Case History Series, brought to you by the GBA Podcast. My name is Elizabeth Brown, and I'm a principal geotechnical engineer at JLT Consultants Abi: And I'm Abi Corbett, a project consultant at SME Liz: All right, Abi, I'm excited. Today we are gonna dig into case history number two, which is a slab on grade saga Abi: And we're gonna learn why ignoring your geotechnical engineer is, well, pretty much a terrible idea Liz: So this is gonna be a fun and wild one. It is about a custom home builder, a ridge, some expansive clay, and a basement floor that decided it wanted to be modern art Abi: Ooh, as cool as modern art sounds, buckling, cracking, water seeping in, it's basically everything you don't want in your basement Liz: Oh, and to make it even better, all of it could have been avoided. So let's get into [00:01:00] it Abi: I'm excited about this one Liz: All right. So the project starts with a custom home builder in a major, metro area. It was like a pretty typical residential job Abi: Right. I feel like these always start out as a very typical kind of job, Liz: True Abi: and then we get a little bit in the details and we notice the site is on the flank of a ridge. And anytime you hear ridge, your geotechnical spidey senses should start tingling Liz: Ooh, exactly. And the GBA member firm was hired to do subsurface exploration and foundation recommendations, and they had, again, a fairly straightforward scope Abi: Right. Except the project manager already had some concerns. He'd been working with this client before and learned that, quote, "The client [00:02:00] representative did not always follow recommendations," end quote. Liz: Ooh, that's like, uh, hearing your dentist say, "You don't floss, do you?" And you know there's something coming. There's a cavity or something Abi: Oh yes, that's the worst. And let's make it even more fun because this whole project is done on a handshake, no written agreement. And to make it even more fun, the whole project is done on a handshake. Quite literally no written agreement Liz: Which is basically like the geotechnical equivalent of, you know, like skydiving without checking your parachute. We're just gonna take, we're gonna take the risk. We're gonna see what happens Abi: So we just gotta jump, I guess. But I'm gonna be honest, it's a little bit scary. And the firm did end up drilling some borings. They did two, and found about five feet of granular soils overlaying claystone-derived clay Liz: And [00:03:00] that clay had a moderate to high expansion potential. So I mean, they did some laboratory tests, and those tests indicated that the upper bedrock and the clay had moderate to high expansion potential Abi: Expansive clay feels like that friend who totally seems chill until you give them just like a little bit of water, and then suddenly they're flipping tables. Liz: Ah, I love that. That's awesome. Yes, so like water and expansive clays make things interesting for sure. And really something to note is that both borings were dry immediately after the drilling and 24 hours later. Like no water was noted during this investigation Abi: Right. Groundwater wasn't an issue at that time, but we'll come back to that Liz: Oh, way to leave it hanging. [00:04:00] So the firm gave five key recommendations for dealing with what they found on site. And really honestly, they're pretty solid recommendations Abi: All right, I agree. Definitely solid. Number one, support the house on straight shaft piers drilled into competent claystone bedrock Liz: And number two was that the basement floor should be constructed as a structural slab, not in contact with those potentially expansive soils Abi: I like that. Number three, no perimeter drains were needed because the site drained well and no groundwater was found Liz: Okay, so then that is gonna lead us to number four, which is kind of in line here, is that they needed to build swales to carry off the surface water and keep it away from the basement walls. So we're gonna collect it and get it away Abi: Makes sense to me. And definitely number five makes [00:05:00] sense. They wanna have a geotechnical engineer observe the excavation and pier construction Liz: Right. You always want your geotechnical engineer on site during construction because you just, you never know what changes or what things may be different than during their investigation. And really what something to understand of these five themes is that the, the member firm, they really emphasized not using a slab on grade basement floor. The member firm, they stated, this is what they stated, so quote, "The builder would create a risk of significant damage if it opted for a slab on grade basement floor." So I mean, they called it out straightforward Abi: Feels very clear to me. But what did the builder do? Liz: Oh, you know what the builder did Abi: All right, let's fast-forward a little bit. The home is built and occupied for about two [00:06:00] months. Then the geotechnical firm gets a call Liz: Dun, dun, dun. Of course they got a call. So the geotech firm, they show up and surprise, the builder had installed a slab on grade basement floor despite the geotech telling them not to do it. Abi: Floor is cracking, buckling, and water is seeping in along the edges Liz: Wow, it's like their report predicted the future Abi: Really, truly strange. And guess what? The homeowner is threatening to sue the builder unless the repairs are made Liz: Yep, that sounds about right. And the builder, well, he admits that he ignored the recommendations. He said, quote, "He had constructed the slab on grade floor with full knowledge of the report's warnings." Like, he even said that.[00:07:00] Abi: Admitting it, but he tried to blame the geotechnical engineer for not recommending those perimeter drains. Liz: Even though the real issue was that he didn't build the surface drainage swales as recommended. Abi: And then he even claimed irrigation water somehow traveled downslope along the clay layer and infiltrated the slabs upgrade. Liz: Wow, he's getting creative. Abi: Um, uh, this builder, he was ready to remove and replace the basement floor, but insisted the geotechnical firm should pay part of that cost. Liz: But the firm's like, "Uh, no, I don't think so. We told you not to do it, and you did it anyway." Right. But instead of fighting, they agreed to pay a small token amount in exchange for a written [00:08:00] release of liability. Abi: Honestly, I feel like that's a smart move. Sometimes you really just need to settle and move on if you don't wanna rack up the charges Liz: Oh, I agree totally. Like, sometimes it ends up being much cheaper to just swallow your pride even though you know you didn't do anything wrong, right? And like, in this case, history has some excellent lessons, like maybe we should break those down. Abi: I like that idea. Okay, so one of those lessons is residential projects automatically pose higher risk. We found that homeowners expect perfection, and they're known historically for filing suits. Not only that, courts are often gonna side with them. Liz: Yes, definitely. So I mean, that should definitely always be considered when you're dealing with those residential projects. And really, [00:09:00] plus the developers sometimes they like to cut corners and then they just disappear, leaving the engineers to hold the bag. Abi: That's definitely a tough piece of it. Okay, so lesson number two, foolish clients create risk. If a client has a history of ignoring recommendations, that should already be a red flag, and that client probably should be avoided altogether. Liz: Oh, totally agree there. I mean, it's such a huge increase in risk when a client ignores recommendations. And if you know that the client has a history of that, I mean, it's kinda like walking into a gunfight with a knife, right? I mean, like, you're bound to lose. Like, something's not gonna go well here. Abi: That is like literally the perfect description, honestly. Liz: Right. So it's kind of like one of those things of knowing when it's okay to [00:10:00] walk away or knowing and being comfortable with... I mean, 'cause as we talked about, the project manager knew that there were some problems here of knowing, hey, you know what? Like, maybe we just shouldn't even take this project on. Abi: Yeah, I feel like there's always that little thing in the back of your head that's like, "Maybe this time it'll be better." Liz: Right? I think we all do that. So it kind of leads us to lesson number three, which is lack of a written agreement creates risk. And I mean, this one, this one is huge. I mean, proceeding without a written contract is, it's foolish in the extreme. Abi: Not only foolish, some insurers will not even cover you if you don't have one. Liz: Right. So I mean, even more so, it's already maybe a risky project and, oh, we don't have a contract in place, something goes wrong, and then your insurance won't cover you. I mean, that's, that's asking for some headache.[00:11:00] Abi: It's the epitome of the worst risk you would take on. Liz: Exactly. Yeah. So number four is settle and move on. So sometimes paying a small amount is cheaper than litigation. Litigation can be so expensive. It's almost always so time-consuming. Plus it has the potential to damage your reputation. Abi: Absolutely. And I feel like all the time you consume can really wear on the people who are involved with it too, and then it could bleed into other projects. Liz: Right. Which just makes it hard for everybody moving forward. Abi: Absolutely. Okay, lesson number five, use the term confirmation-dependent recommendations because recommendations based on borings alone aren't final. In this case, the final geotechnical engineering report conveyed recommendations that were not final.[00:12:00] Liz: Right. And like, I think it's, it's really important to understand that a geotechnical investigation only assesses a very small portion of a site. I mean, 'cause what this, this site for this investigation, they did two borings. That's two really small areas that were actually assessed. So we have this small amount of information, and then we're gonna provide recommendations, right? But actual conditions once construction starts, right, and the site gets opened up, they're likely to change, which is why it's so important that the geotechnical recommendations be confirmed during construction. It means having that geotechnical engineer come out and take a look and, "Hey, is everything what you expected? Do we need to make changes?" It could really save problems and headache and money in the long run. Abi: Absolutely. That's the only chance you have to make a pivot Liz: Exactly. Okay, so I'll get off my [00:13:00] soapbox and move on to lesson number six, which is be wary of groundwater issues. Even if the borings are dry, groundwater can appear later from other sources that maybe you didn't expect. Abi: Yeah, and like you said, there was only two borings. That doesn't mean there's no groundwater possible. Okay. Liz, what's the real moral of the story here? Liz: Oh, for me, I think really it's don't ignore your geotechnical engineer. I mean, they really do bring value to the project. They're just-- They're not just another check, check the box, I gotta have it to get my permit type of a thing, right? They're there for a reason. And don't negate what they're telling you. So in this case, like don't skip the surface drainage, and for the love of all things claystone, don't build a slab on grade basement floor on expansive soils. Abi: Absolutely. And [00:14:00] always, always get it in writing. Liz: Right. I don't think that we can stress that enough. I think in a lot of the case histories, that is something that we talk about, right? Is that if it's not in writing, it didn't happen. Abi: Exactly my thought. Liz: Perfect. Well, thanks for joining us today. This concludes our episode of the Case History series brought to you by the GBA podcast. I hope you were able to take away some useful information that will help you and others at your firm make good risk-based decisions in the future. If this episode resonated with you, we wanna hear your story, so please email us at info@geoprofessional.org or comment on our LinkedIn post.