Case History 113
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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: I'm Abby Corbett, a project consultant at SME. Today we're gonna discuss case history 113, and it's a fascinating one. It's about a major healthcare provider building a brand new nine story hospital. The terrain was tricky, the materials were unconventional, and the engineers had to really think outside of the box.

Liz: Ooh, and here's the spoiler alert for this one. This case history has a happy ending. It's what we call a higher ground. So not all case histories have this happy ending, but this one in particular saved the client about $600,000 in pavement costs.

Abi: Finally, it's good to have a good one. And when you look at it though, the real story isn't just about the money. It's about [00:01:00] innovation, judgment, and the courage to challenge a precedent. So let's go ahead and set the stage. The site was hilly with cuts up to 60 feet deep and fills up to 50 feet thick.

Underneath you had residual clay overburden less than five feet thick, sitting on limestone bedrock.

Liz: Oh, and of course, with these stories we have to throw in a twist. So in this particular situation, they ended up blasting the limestone, but in the areas where they blasted the limestone from the cuts, they were gonna reuse it as fill, which, I mean, that's a fairly common thing to balance your site.

But in this case, the grading contractor left that clay overburden in place during the blasting. So the fill ended up being this mix of the limestone, blasted rock in soil, all kind of mixed together.

Abi: And that makes compaction control and geotechnical design a [00:02:00] real challenge.

Liz: Exactly, because there's just a little bit more unknowns going on there with that mixed type of material. So for this project, for the building area. It was spec'ed out the, hey, only clean shot rock can be used, right? So they were very specific for the building, you know, which makes sense. However, for the pavement areas, they went ahead and said, Hey, you know what?

You can use that soil and rock mixture material.

Abi: Imagine trying to design pavements on that kind of subgrade. I mean, it's unpredictable, variable and full of boulders.

Liz: right? And see now that is where this story actually really begins.

Abi: So the geotechnical engineer record, the GER had recommended designing pavements for a California bearing ratio or a CBR of four.

Liz: And really a CBR four for a clay type subgrade. Like that's, that's pretty typical. I mean, it's a little bit conservative, but it's safe,[00:03:00] 

Abi: And that seems like that works. But the Comet Firm noticed early on that the fill had a lot of rock. They suspected that the actual CBR would probably be much higher.

Liz: Which is good that they picked up on that and they're like, Hey, maybe we can , make some changes. Right? But the problem with that was, is that. There was really no precedent of, Hey, how do we test this type of material? Because like no one had ever really tried to test a mixed soil rock fill the way that this was, like locally in their area.

It just kind of hadn't been done yet.

Abi: And that makes it hard. And plus there was boulders up to 18 inches thick, so that doesn't make field testing straightforward anyway.

Liz: Right. So, you know, there's some complexities here that kind of had to be worked through. And this is really where that innovation came into play. So the engineers, they kind of face this dilemma. They're like, well, what do we do? [00:04:00] Do we stick with the conservative design?

Right? Hey. Conservative, we know it's gonna work, right? But it's gonna cost more money to build it. Or hey, what else can we do? How can we be innovative but yet still manage risk, right? I mean, 'cause that's what it's all about is, hey, we wanna give good product to our client. And not be too overconservative.

But at the same time, like you, you gotta balance. You gotta balance that risk.

Abi: Yes. Honestly, when risk comes in, that's when the courage has to come in too.

Liz: Right to kind of, okay, like, are we willing, are we willing to step out and do this? But Exactly. In this case, the firm proposed something bold. They're like, Hey, you know what? Like, let, let's try something out here. So they did some plate load tests combined with benkelman beam measurements.

Abi: The plate load tests apply [00:05:00] increasing vertical loads and then measure deflection. They're less affected by those big boulders than the traditional field CB tests.

Liz: Right. So they're like, you know, this is a good example of, okay, the traditional, you know, test isn't gonna work. What else perhaps is out there? Then for the kelman beam, you know, usually that test is performed on pavement services to design overlays. So they're like, Hey, but you know, general concept here, they kind of adapted things a little bit to be able to measure the subgrade deflection.

Abi: Right. So they rolled a loaded dump truck next to the beam and watched the dial gauge. When Subgrade Pumping started, they decided that was the maximum allowable deflection of 0.1 inches.

Liz: So they kind of got a, you know, they took some existing tests and made some modifications and thought about it in a different way to be able to use it to help solve, you know, solve the problem or help justify what they [00:06:00] wanted to do in this case. So from that testing, what they ended up doing is they calculated what's called a modulus of subgrade reaction.

They calculated a value of 250 pounds per cubic inch. And then what they were able to do is they were then able to convert that value into an equivalent CBR value that they could then use for design to determine, hey, how much can we reduce this section from what was originally proposed?

Abi: Absolutely. And here's the payoff. That design CBR jumped from the four to 25.

Liz: That is, that's a big jump. Like that's not just Oh, a little improvement. Right. Like it's kind of a game changer. 'cause it's gonna allow them to really narrow in on what that pavement section needs to be for this project.

Abi: Right, and with that new CBR, the pavements were reanalyzed. Heavy duty [00:07:00] pavements saw asphalt thickness reduced by 2.5 inches, and the stone base reduced by two inches.

Liz: And the light duty pavements, had stone base reduced by four inches. So like you add all of this up and it ends up in a significant cost savings. And it's kind of important to remember that. The two and a half inches of asphalt reduction is huge because asphalt is typically the most expensive component in your pavement section.

Abi: A hundred percent. I mean, that's how they ended up saving that $600,000 we talked about at the beginning. It's the asphalt pavement cost.

Liz: Right. That's a huge savings to a project right there. And since construction occurred, they've been keeping an eye on it to make sure that everything's going all right. And the cool thing is that hey, the pavement has performed well and they've really only had to do just normal maintenance like a normal pavement section. So really it's proving out what they did.

Abi: Exactly. It's, it's [00:08:00] straight up proving that innovation doesn't have to just be clever and it's sound engineering.

Liz: Exactly. So they took some of those existing, you know, um, procedures, kind of adapted them to their situation so that they still had sound engineering to go off of. They just kind of had to, you know, they had to be innovative. They had to think outside the box and really, which takes being willing to put yourself out there, which, you know.

Us engineers sometimes struggle with that a bit. So it's cool to hear, right? So it's, it's cool to hear the story of how they were willing to do this. But I think that there's some lessons that, that we can learn. I know it's kind of a short story, right? But I still think that there's some good lessons that we can take away from this.

Abi: Right. I can always find some lessons and I think with this one, there's four big lessons. The first one, always be sure you're right. Then go ahead. The firm trusted its [00:09:00] engineering judgment and developed a procedure to prove the CBR was higher than originally assumed.

Liz: Right. So they didn't just go, yeah, my gut feel tells me it's right. They actually, they actually went like above and beyond, right? Like, Hey, okay, yeah, my gut feel tells me it's right, but let's do something to at least, you know, try to prove right that what we're doing makes sense here.

Abi: We love a little bit of evidence.

Liz: Right just a little bit.

It goes a long way. So a second lesson learned is understanding the standard of care. So the GER wasn't wrong, right? Like they followed local presedence and, you know, using the CBR four for the original design. Like it was well within like industry standard. But the cool thing in this case is that the CoMET firm, they were able to add some value.

By, by testing during construction when conditions were, were different, right? Because early on in the [00:10:00] geotech, you're making some assumptions. You like really, you only see a small portion of the site with your investigation. And then during construction, as things get opened up and you have a bigger picture as to what's really going on, is where it's awesome to be able to come in and be like, Hey, you know what?

Things look a little differently than what we thought they were. Let's make some adjustments. Let's see what we can do to add additional value to this project,

Abi: Yes, and that's the biggest thing is like additional value. They realized that things were changing and they found a way to make it better for the client.

Liz: which is great when we're able to show the value of our profession, right? Like we're not just another box to check, like, Hey, we can help add value to your projects, and we're here for a reason.

Abi: Absolutely. So the third lesson we see is share and share alike. The firm could have submitted a value engineering change proposal to share in the savings, [00:11:00] and instead they walked away with pride. But actually no bonus.

Liz: Yeah. And that's like, I think that goes to show a lot for the firm that they valued what they did and what they were able to provide. And I'm sure that really helped their relationship with the client as well.

Abi: Absolutely. I bet that got them just that much value in later projects.

Liz: Exactly. And fourth, having the confirmation dependent recommendations. So by observing the actual conditions during construction, it gave the firm, it gave 'em confidence to be able to make those adjustments and suggest, hey.

You know what? There's more that we can do here beyond just what was initially reported. They were able to make those adjustments.

Abi: Yes. And really all of these lessons aren't just technical. They're professional. They remind us that engineering is about judgment, relationships, and even some negotiation.

Liz: Oh, absolutely. And one thing that I really [00:12:00] love about this case is how it shows that innovation doesn't always mean risk. Yes, there's risk in everything that we do, but they, in this case, like it meant reward, like they were able to help. Further the profession right? And further the industry, by being innovative.

Abi: True. But then the flip side, it highlights the importance of compensation that firm took on extra. A risk without negotiating a change order, which I mean, it's a missed opportunity.

Liz: Oh, absolutely. Especially after things, you know, obviously worked out and they saved money, they definitely could have went back and been like, Hey, like, you know, we, we helped you out. Is there some, some sort of compensation we can do here, at least to get our time covered?

Abi: Yes, for sure.

Liz: And really this underscores the value of field observations. I mean, you can't always predict the conditions on site from [00:13:00] borings alone, right? Like actually seeing what's going on during construction. This really goes to show how important those field observations are.

Abi: Yes, the observations could be the difference between even wanting to innovate and not. It really just. I mean, they got to see the earthwork firsthand, and then you get this confidence boost, and why not push for a better design?

Liz: Right, exactly. Well, and it allows 'em that opportunity to offer that as a potential solution for future projects as well. And they have the sample project to show of, Hey, it worked here, let's give it a try on your project. Right. And it goes to show that. Engineering isn't just about the ca the calculations right there.

There's more to it. It's about context, it's about, it's about seeing it as, you know, a whole picture and not just your little part of whatever the project is.

Abi: For sure and another emphasis that it's on courage too.[00:14:00] 

Liz: Oh yeah, absolutely. So let's maybe take a second and maybe let's zoom out for a moment like. Mean for the profession as a whole. What's your take on that?

Abi: Honestly, it shows that geotechnical engineers. It can add value during the construction phases. It's not just their job during design.

Liz: Right. And it also shows that the innovation needs to be paired with like negotiation, right? Like it's so cool to be innovative, but if you're saving a client hundreds of thousands of dollars, like you gotta not be afraid to ask for a change order or ask to be compensated for that. I know that we all get in that mode of it's like uncomfortable to, to ask for more money, but being confident in, Hey, look at this value we provided to you, and asking for that kickback.

Abi: Absolutely. And people wanna have the best thing. They wanna have the newest [00:15:00] and the brightest. So even somebody outside of the profession is gonna understand when we're asking to get paid for our work.

Liz: I

Abi: I think honestly, it also shows that the standard of care isn't static. We can't just go with the status quo.

We have to evolve as new methods are tested and those get proven out.

Liz: Oh yeah, abs. Absolutely right. We're not going to grow as an industry if we're just stagnated and always, oh, well this is what worked before. This is what we're gonna do now. Right,

Abi: That's the truth.

Liz: right. So, so which really what it means is that. Every project is an opportunity to innovate, you know, and to push those boundaries, but carefully and, making sure that you are still assessing risk and managing risk as you're pushing those boundaries and innovating.

Abi: Yes, every engineer has a responsibility to balance risk with reward. So let's, if you had to sum this one up. [00:16:00] How would you do it in just one line?

Liz: Ooh, really, I think what I would say is that smart testing can turn a conservative design into a real cost saving success, right? But don't forget that you gotta negotiate for your share of those savings, right? Go ahead and do it right, but make sure you get compensated.

Abi: A hundred percent. We wanna make sure we are recognized for the value we bring to a project. Engineering isn't just about building the structures. It's about building trust, saving money, and protecting your client's interests.

Liz: Oh, well said. I like that. So this concludes this episode of the Case History Series brought to you by the GBA podcast. I hope you're able to take away some useful information that will help you and others at your firm make good risk-based decisions in the future.