All righty, guys. We'll get started. I think we got most people in here at this point. So good morning to the West Coast and good afternoon to those out East. Welcome back to the Post-Tensioning Institute's monthly webinar for webinar. My name is Kyle Boyd and I'm the moderator of these sessions. I'm also the chair of the Education Committee EDC 130, which is a Post-Tensioning Institute committee that sponsors these monthly webinars. We host this webinar every month. So for those of you who it's your first time joining, welcome to the webinar. We hope to see you back on future webinars. For those of you who are repeat customers, we're glad you're back. This webinar happens at the exact same time every month. And that time is the second Wednesday at 1 o'clock Eastern, 10 o'clock Pacific. So the second Wednesday of every month, every month of the year, 1 o'clock Eastern, 10 o'clock Pacific, we will host this monthly webinar. In October this year, we were able to plan out all the webinars for 2025. So we do have a strong pipeline of webinars and we're excited for what's coming up in the new year here. Well, we've received a ton of requests for slab on ground design materials. And today we're excited to present part one of a two-part series of slab on ground. Today's topic, as you can see with the title, is focused more on the geotechnical side. So before we dive into the PT concrete design side of slab on ground foundations and structures, the most important thing to fully understand is the soil behavior. So that's why we're doing this one first. And then next month in December, we'll go into the concrete PT slab on ground design side of it. So before we introduce today's speaker, we do always have to go through those first few classic housekeeping slides on there. The first one is a sponsor. We're now starting to have these webinars sponsored, which helps keep this a free webinar to all you all. AOE is the sponsor for today. It's Advancing Organizational Excellence. They have all kinds of services from marketing, event planning, management, association management, websites, graphic design, and so on. They're a huge assistance to the Post-Tensioning Institute amongst many other concrete associations and industries out there. I know we cannot do without them at PTI. So huge support of us and we're happy that they're sponsoring today's webinar. So with that, we'll dive into the next slide, which is the continuing education. If you are on today's webinar and you attend for the full time and you registered with your email, you will get a one continuing education PDH at the end of the webinar. It'll be automatically emailed to you. You do have to be on, logged in with your email to get that. If for whatever reason, you have to step away early for a conflict or you missed today's webinar or a colleague of yours missed today's, we do post these online. You can go watch them online. If you watch online, take the quiz afterwards, you can get that same free PDH credit out there. I know we're getting towards the end of the year and I have quite a few states that are requiring me to now show those continuing education credits and the renewals are coming up here in December. So it's a great way to knock some of those out. Next one's our classic copyright material slide. This is just saying thou shall not copyright. If you guys want to see any of this information, just reach out to us and we can see what we can do about helping you out there. So for the webinar protocol, everybody who's on, you're muted, cameras are off, we can't hear you, we can't see you. So if you have questions, you need to ask it through the Q&A feature that's on the bottom. At the end, we'll go through all those questions. I'll be able to filter those questions on there. We already went over you need to attend the entire webinar to get that one hour PDH on there and we talked about that it's being recorded so you can go back and see it from there. So with that, I can now finally introduce today's speaker. Mr. Dean Reed. Dean is an industry expert in design and evaluation of post-tension slab on ground foundations. He has extensive knowledge in both the geotechnical side and the structural side. So a little bit of a double edged sword there. He's got over 30 years of experience and he's worked with some of the pioneers in this industry for expansive soils, especially with these foundations here. He's developed software that's widely used today to analyze and design slab on ground foundations. He's a fellow at the Post-Tension Institute, which means he's putting an unreasonable amount of time towards PTI and he's the current chair of DC10, which is the committee that's slab on ground on that. So with all that being said, we really can't think of anybody more qualified to be given today's presentation than Dean. So Dean, I'm going to hand it over to you and let you dive into the technicalities because I know you have about four hours worth of presentation that you're going to do in 50 minutes here. Okay. So as was said, typically I do a presentation on the geotechnical provisions of the PTI procedure and it's about four hours long. So I've had to really condense things down into kind of just the fundamentals. We're going to touch base on some of the key areas that I think are important and we're going to gloss over some of the more straightforward, more widely understood portions of it. So just some little introductions. Slab on ground foundations derive their support from near surface soils. These near surface soils can be expansive, stable, or compressible. And I see a lot of people misusing terminology and confusing what each of these soil types are. So I'm going to give you my definitions of each of them. An expansive soil, which is probably the most predominant type of soil that we designed post-tension slab on grounds for, is a material that changes volume with moisture increases and decreases. So it shrinks and swells. A stable soil is a soil that will maintain its structure and strength under load while only experiencing minor deformation or settlement. A compressible soil, also referred to as a settlement sensitive soil, will maintain its structure and strength under the load while experiencing significant deformation or settlement. The first two, expansive soil and stable soils, are designed procedures are presented in PTI's document DC 10.519. Compressible soils, if you want to design for a compressible soil, you have to go all the way back to DC 10.108. We are looking to rectify that in an upcoming version of 10.5 and are going to be including, hopefully, an updated procedure for designing on compressible soils. So what's the main difference between these and how do they impact a slab on ground foundation? Well, an expansive soil changes and a foundation reacts to that change. A stable and compressible soil are changed by the loads applied to the foundation. So slightly different ways to apply loads and stresses to the concrete. And how those loads are applied will be discussed in the next seminar, part two of this, that will be presented, I believe, by Tony Childress. We're going to primarily concentrate on expansive soils today. It's, as I said, what PTI design procedure is most widely used for. And this is a common graph that most of y'all have probably seen before. It's a distribution of expansive soils throughout the United States, the continental US. And as you can see, the red, the blue, the orange, and the green, those are all areas that have variable expansive soils, whether it's low expansive materials like in the green or highly expansive soil in the red. My area of practice is primarily in the diagonal red zone through Texas. That's where most of my work takes place. That red zone encompasses Dallas, Fort Worth, Austin, San Antonio. So that line passes through those major cities, and we have significant issues with expansive clays. I'd like to say, you know, North Dakota and South Dakota have a lot of expansive soils up there, but nobody lives up there. So it's not as big a problem as it is when you have the expansive soils occurring in major cities. So what is an expansive soil? Well, the IBC has a definition of what they consider an expansive soil. Basically, an expansive soil is one that has a PI greater than 15. It has the percent passing the number 200 greater than 10 percent, and a percent finer than five microns. If it meets those three things, it's considered an expansive clay. The expansion index greater than 20 is also another way to define what an expansive clay is per the IBC, the International Building Code. I personally do not think that is a very good definition of what an expansive clay is. Some of the clays in Nevada and Arizona have PI's plasticity indexes less than 15, and they are still known to change volume. So it's important to note that this is just kind of a boundary, that if you are greater than these, you're pretty confident you have an expansive clay. But if you are less than these values, that doesn't mean your clay is not expansive. You have to have a qualified geotechnical engineer evaluate it and determine whether it is expansive or not. Another concern I have about the IBC definition, it's for an expansive soil. It doesn't consider that many soil profiles are not homogeneous and you have different layers. So they are just talking about whether a soil is expansive, not whether or not a soil profile is expansive. I think everybody would agree that what's over on the left, the homogeneous soil profile, you would consider that an expansive soil, but you'd also consider it an expansive soil profile. But it's not so clear on what's occurring on the right. You have a non-expansive soil, five to six feet of it, over expansive soil. Is that considered an expansive soil? What the IBC says is if you have an expansive soil, you have to design foundations using one of two design methods, and one of those methods is the PTI procedure. So it's important to know whether you have an expansive soil, but it's also important to know whether or not you have an expansive soil profile. So PTI kind of rectifies that. PTI incorporates IBC's definition of an expansive soil, but they apply it to a soil profile, not just a single soil. So, and they do that by use of what we refer to as the weighting procedure. So here's an example. You have 10 feet of non-expansive soil over 10 feet of low plasticity soil. There are the properties. And so what the PTI weighting procedure does is you take the upper five feet and give it a weight, the PI value, give it a factor, weighting factor of three. The middle five feet from five to 10 feet, you give it a weighting factor of two. For the third five feet from 10 to 15, you give it a weighting factor of one. Well, in this case, since the soil is non-expansive, it has a PI of zero. And therefore your zero to five will be, have a result of zero. Five to 10 will have a result of zero, but 10 to 15 will have a result of a hundred. Five feet times 20. Then you add them together and you divide by 30 and you get a weighted PI of 3.3. Per the PTI procedure, this is not considered an expansive profile and you can design it either as a stable soil or a compressible soil. So the soil does not meet a criteria for an expansive soil profile. Example number two, we have two and a half feet of high plasticity clay with a PI of 40. Then we have 17 and a half feet of a non-expansive soil. Well, does this meet the definition of an expansive soil? Well, the high PI clearly does, but the non-expansive soil below doesn't. Does it classify as an expansive soil profile? And the answer is maybe. So if you look, you got a weighting factor of three times 2.5 feet. Then you have a weighting factor of three times 2.5 feet for a factor of zero. That gives you 300 weighted factor for the upper five feet. You have non-expansive soil between five and 10, so your weighting factor is zero. 10 to 15, you have a weighting factor of zero. You add all those up, divide by 30, and you come up with a weighted PI of 10. PTI says that if your weighted PI is less than 15, it's not considered expansive. There is a big major but here. This is a very common soil profile we see in central Texas. We'll have two to three feet of clay over limestone. The limestone would be the non-expansive soil. And that profile is known to move about two inches, two to three inches. So it's clearly expansive in terms of applying stresses to a foundation. So what PTI did is they had a additional criteria that says if you have a PI of two feet thick or more, greater than 15, anywhere in the upper five feet it's considered expansive regardless of the weighted PI. And that's a mistake that I see or a provision that I see a lot of geotechnical engineers omit in their analysis. They'll say there's only two feet of high PI clay over non-expansive soil, so they run to weighted PI and they see that it's a PI of 10 which is less than 15, so they classify it as non-expansive. That is not accurate and that is not consistent with the provision in the PTI standard. Okay, so we talked about what an expansive soil is. PTI design procedure is based on a soil structure interaction. The soil does something and then the foundation does something in response. For an expansive soil, the foundations respond to the volume change. The soil is the one that changes, which changes the support conditions for the slab and ground foundation. Slab and ground foundations do not cause a volume change for an expansive soil like they do for a stable or compressible soil, right? If you have a compressible soil, the load and the deflection caused by the foundation actually is what puts the stress in the soil. That's not directly and and that's not predominantly what happens in a slab on ground on expansive soil. The soil moves and the foundation responds to that movement based on the strength and stiffness of the foundation. So the volume change of the soil for an expansive soil results in stresses that the slab on ground must be designed for. Well, the next part two of the seminar will talk about how you determine those stresses. We are going to talk about how you determine the amount of movement that you must design for. So the soil structure action model developed or used by the PTI procedure is based on the concept of edge lift and edge drop. The soil structure interaction model hasn't changed since the first edition of the PTI manual in 1990. The soil structure interaction model is defined by two variables. E of m, which is the edge moisture variation distance, and y of m, which is a differential soil movement. And we're going to talk about both of these in quite a bit of detail. What you will see on these two models is you are getting a little bit of compression of the soil like you would for a stable soil and a compressible soil. But that compression and settlement of the soil is not the predominant cause of the stresses in the foundation. It's the volume change of the expansive soil that it's a predominant cause of the stresses in the concrete. So one thing that I hear a lot of people talk about and there's a misunderstanding about is a soil structure interaction model does not assume that movement is just occurring on two sides of the foundation. When you look at the interaction models that are included in the PTI manual, it looks like you're just modeling the left side going down and the right side going down. That the side of the rectangle closest to you and away from you isn't moving. But that's actually not the case. The model assumes that the entire perimeter of the foundation moves up or the entire perimeter of the foundation moves down. And what that does is that results in the maximum stresses in the foundation. And this was confirmed and remodeled and further evaluated in a dissertation by Dr. Rifat Bulat. So once again, the PTI manual does not just assume that one corner goes up, or one corner goes down, or one side goes up, one side goes down. What it models is the worst case stresses of all four sides going down, or all four sides going up. Therefore, it is an envelope type design. It's not actually trying to predict the actual stresses in the foundation. We are trying to give you the worst case maximum stresses that would occur when there's basically an infinite different modes of movement that the foundation could occur. So one thing to note, and we're going to talk about these a little bit more, Y sub m is a differential soil movement. It's the amount of soil volume change, vertical volume change that will occur over a distance inward from the edge of the slab. That distance inward is referred to as E sub m, which is short for the edge moisture penetration distance. And you can see them, I don't know if you can see my mouse, but you can see in the blue, you can see what represents Y sub m. So what's being represented is the initial soil mound, it's a red line. And then because of the weight of the foundation, you are getting some compression of the mound to result in the final mound shape. But that compression of the mound is small compared to the volume change of the soil. So we're going to talk about Y sub m. Y sub m is a more important of the two variables in my opinion, and it's kind of the least understood. And it's a more difficult to understand. I could spend two and a half, three hours just talking about Y sub m and I have about 15 minutes. So Y sub m is a differential movement. Again, it represents the change in the surface elevation caused by soil volume change at two locations separated by a distance E sub m. Y sub m is based on the principles of unsaturated soil mechanics. That seems to be a dirty phrase in our industry that scares people. They hate to hear the word soil suction. I'm hopefully going to show you during this pre presentation that soil suction isn't bad. Soil suction shouldn't be scary. And that it actually makes a lot of sense. Y sub m is estimated volume change of the soil based on assumed boundary conditions. We're not actually using the in-situ soil conditions in terms of moisture. We're actually using assumed boundary conditions that we refer to as the envelope. Y sub m is also not the expected differential deflection of the foundation. Y sub m should always be greater than the actual deflection of the foundation due to the foundation stiffness. Y sub m would only equal the differential deflection for a perfectly flexible foundation with no externally applied loads, which is not realistic. So therefore, I go back to the Y sub m is not how much deflection you should expect the foundation to experience. So how do we calculate Y sub m? And we calculate it using the theories of unsaturated soil mechanics. And there's kind of two ways to implement this. It can either be hand counts, spreadsheets or computer program. Or if you have simple conditions, you can use a simple stress change factor method included in the PTI manual. Unsaturated mechanics, soil mechanics, Y sub m is based on these two fundamental equations, which were developed by Dr. Robert Litton at Texas A&M University. Basically, what you're doing is you're integrating the soil suction change with depth and adding into it or subtracting from it the overburden pressure of the soil above. These two equations you end up with a volume change for element. Well, soils swell or shrink in all three directions, right? They don't just swell vertically. They also swell horizontally. And you have two horizontal deflection. So we'll get back to that in a section. We'll just go to the fundamental equations. And this kind of talks about it a little bit. Your various components of that equation, you have the matrix suction component, which is the left set, you have the overburden component, and then you have an osmotic component. And basically, everything is a change times some sort of index, which is the indexes, you know, how like on the matrix construction, it's how much a soil will change volume for a given change in suction. So it's a change times an index, all three components. So once you figure out the change in volume, you have to convert that into an estimate for a how much is it going to change vertically. And there has been research done that shows that you have a vertical volume change coefficient, that 50% of the volume change will occur vertically while the clays are shrinking. And I apologize, there's a typo in the swell, it should be 0.8 vertical volume change for swelling. So you get more volume change swelling than you do shrinking. And that makes shrinking, you're not getting any resistance or passive pressures of the soils that swelling against. So once you get the vertical change coefficient from the these equations, you multiply it by this vertical volume change coefficient, and then you end up with how much is it going to change vertically. And that's for a given element, whether it's five centimeters, one foot, then you got to calculate and integrate it vertically, and add up all the element changes. And then you end up with y sub m. So y sub m is a pretty complicated variable, but PTI has done a very good job of simplifying it. And so we kind of touched on it, but in very simple terms, y sub m is a function of a change in suction, and an index that will tell you how much the soil will change volume for a given change in suction. So the change in suction is environmental is based on environmental conditions. But it's also based on the soil, how much it will change is based on soil properties. So we, the PTI procedure takes into account and unsaturated soil mechanics takes into about both the climate effects and the soil effects. So how do we determine soil suction? Well, there are several ways to determine soil suction. And there's three different types of soil suction, or two different types of soil suction. There's matrix suction, which is due to the attraction of water to the soil particle surfaces. And then there's osmotic suction, which is a function of that is all salts or other salts, other solutes into poor water inside the soil. You add those two together and you end up with a total suction. And the total suction is based on the PF scale. And it ranges from 1.0, which is equivalent to the liquid limit of the soil, where basically the soil is behaving as a liquid, not a solid, all the way down to 7, which is an oven dry. The most common range of total suction found ranges from about 3.0 to 4.5. Those are the most common if you go out and measure soil suction, the vast majority, probably upwards of 90% of your soil would fall into that range. Because that is the most common range and includes most of the soil conditions that are out there. That's the range of PTI requires you to use for design. So suction change is again, remember, Y2M is effectively a change in suction times an index. We're not going to talk a whole lot about the index because there's really only one common way to determine that index. And it's a correlation based on the Atterberg limits, we're going to spend most of our time talking about suction change. So suction changes is what results in a change in volume of the soil. When you have a suction change from wet to low suction to dry, which is a high suction, that results in shrink of the soil. When you have a suction change from dry to wet, it swells. Common sense for geotechnical and all engineers. Something that dry, an expansive soil that's drying gets water, it's going to swell. An expansive soil that's wet that dries out, it's going to shrink. So the graphs on the screen kind of represent this phenomenon. The green is your initial condition where you start from. And then you're changing with time to the red light. And you can see at the surface that suction change starts at three and ends at 4.5 or starts at 4.5 and ends at three. So PTI has developed this concept called suction envelopes. And in my opinion, suction envelopes are extremely powerful. You can model just about any climatic or moisture condition you want with the concepts of suction envelopes. This typical trumpet shape that all we really have time to talk about today is the shape of the suction distribution you would get in a site that's only controlled by the environment. Meaning you don't have vegetation that's drying out the soil to deeper depth. You don't have bad drainage or plumbing leak that's adding more water at the surface. But for normal rainfall, normal evaporation, your suction will stay within the boundary defined by that red and green curve. Green is the initial suction, red is the final suction. So in this case, we are starting at a trumpet profile that starts at three. And over the life of the foundation, we're going to change to a suction profile of 4.5. That 4.5, it's a wilting wilting point of vegetation, and most people are going to keep enough water in the ground to allow vegetation to grow. So that is kind of the concept and how PTI implements unsaturated soil mechanics. The design is based on the suction change based on two curves. Again, the trumpet shape you're looking at here is based on environmentally controlled profiles. But you can develop additional profiles if you have a high water table. You can develop additional profiles if you have vegetation that's planted after the foundation is built. You can also create suction profiles based on to model the effects of poor drainage. We don't have time to go into all that today, but PTI has a frequently asked question that illustrates the suction profiles and suction envelopes for various non-climate controlled conditions. So Y sub m is a direct function of the area between the suction profiles. So if you have a smaller suction profile change or suction envelope, like on the left, you're going to end up with a smaller shrink. So this one starting at three, the left one is starting at 3.0 and changing to 4.5. That has a total suction change of 1.5 PF at the surface, you're going to get a shrink of about 3.2. If for some reason, for the exact same soil, the suction change would start at 2.0, which is effectively a liquid and swell all the way to almost oven dry soil, you would get a shrink of approximately 9.1 inches. So the shrink and swell is a direct function of the area between those two curves. And so when I'm doing my longer presentation, I stress that highly and we show multiple examples of you can look at the suction and you can tell me which one is going to shrink and swell more. Not knowing anything about the soil, you can just look at the profiles and tell me which is going to shrink and swell more. And that becomes important because I frequently see geotechnical engineers using the wrong suction profiles to develop Ys of M. So they're either being under or over conservative in their development of Ys of M. So if you're a structural engineer, just understanding this basic concept can help you look at what's in your geotechnical report and say, does this pass a smell test or does it not? So this is where I see a lot of geotechs make mistakes. PTI has developed two different types of standard design suction envelopes. These are the general ones that are going to apply to 90% of your project sites. There's always going to be anomaly. There's always going to be reasons why these standards should not be used. But that's where the geotechnical engineering comes in to understand what the suction profiles and suction envelopes represent and when they're applicable. And more importantly, when they're not applicable. So PTI's implementation of the unsaturated soil mechanics and envelope concept, they have developed two different types of envelopes that are most commonly used for design. They are referred to as post equilibrium and post construction. And understanding the difference of them is important. Just looking at them, which one will end up with greater shrink and swell? Remember what I said, the Y sub m shrink and swell is a direct relationship to the area between the two curves. So by looking at this, you can tell immediately that post construction is going to result in larger shrinks and swells. Well, when do we use post construction versus post equilibrium? Well, post equilibrium is kind of a special envelope for areas where the climate does not experience significant changes over an extended period. So if you're in, a good example would be the Phoenix Valley, hot and dry the vast majority of the year. Therefore, this suction is likely going to be close to the equilibrium value. And therefore, it doesn't make sense to start at a really wet profile because the odds on your foundation being built during a during a wet timeframe is very unlikely. In comparison, Dallas, Austin, where I do most of my work in those two cities, we experiencing weather changes from extreme wet to extreme hot and dry, we may go, we may have four weeks of constant rain, with 60 degree weather, to later on in the year, we have 110 degrees, no rain for three months. So in that case, knowing when your foundation is going to be built, you're less certain. So it's conservative to assume a wider, larger suction profile, it's going to be present. So that's the difference between, excuse me, post equilibrium and post construction is it really comes down to post equilibrium, you are not expecting large changes in the suction at time of construction, where post, sorry, that's post equilibrium post construction, you are expecting large changes in suction at the time of construction. So post construction starts at what we call a dry or wet limit. And then it changes to the opposite limit. So if it starts dry, it swings and changes to the wet. If it starts wet, it will change to dry. Post equilibrium suction envelopes don't do that. They start right because your climate is more constant. So you're likely going to start at equilibrium and change to an either wet or a dry limit. So equilibrium is somewhere in between the two limits. So post equilibrium will always give you a smaller shrink swell than post construction. So, how do you determine what your suction envelopes are? Well, as we've talked about or I've mentioned before, PTI recommends that your design envelope is based on a wet limit and dry limit of 3.0 for the wet limit and 4.5 for the dry limit. Those values are appropriate for 95 or greater percent of your designs. It's only for the anomalies or for the very extreme conditions that you should use anything other than those recommended limits. The design equilibrium suction is determined from a correlation between the equilibrium value and the Thornthwaite Moisture Index. The Thornthwaite Moisture Index is back on this slide and somehow they get out of order, is based on whether you are in a wet climate that will typically have high soil moisture or an arid climate with less soil moisture. So, PTI says if you're in a wet climate and they define a wet climate as one having greater than, a Thornthwaite greater than positive 15, your climate is relatively stable enough or uniform enough that the use of post equilibrium suction profiles are reasonable. If you have in an arid climate, which PTI defines as drier than minus 15, they think you have a relatively stable climate. Therefore, the use of post construction, or sorry, post equilibrium envelopes are recommended. And then you got this zone in between positive 15 and minus 15. Those are areas that are going to have highly variable climates that will range from wet to arid in a short period of time in a given year. And in those cases, PTI recommends you use a more conservative, larger suction chain post construction suction envelopes. So, PTI has a very simple methodology in their procedure for determining Y sub M. It's referred to as, so you don't have to go through all of this analysis. You don't have to go through these equations. You don't have to go through anything. They have developed a simplified method to be used. And it's referred to as the stress chain factor method. And it's used for typical design conditions. If you have an anomaly in your site, like a tree, the stress chain factor method may not be appropriate. If you have a extremely layered soil profile that is very layered, the stress chain factor method may not be appropriate. If it's not assumed by climate, the stress chain factor method may not be appropriate. So, it makes it very simple and basically gets it down to what I said. That Y sub M is a function of an index that tells you how much it's going to shrink and swell for a given change in suction, that's your gamma H, and a change in suction. So, the stress chain factor really represents your change in suction. And it's basically charts that you go into the chart with your starting suction, and you go into it with your ending suction, and you go into it with your equilibrium suction, and it will give you your stress chain factor, which takes out all the concepts of suction profiles, suction envelopes, all of that. And it's basically you get two numbers and you multiply two different indexes, and you have your Y sub M. PTI gives stress chain factor methods for for both post-equilibrium and post-construction. And this slide basically just tells you what the stress chain factor represents. It basically represents the change in suction and the change in overburden. It does not include any osmotic suction. So, if you have a soil like the Del Rio clay, which is a soil that is common in central Texas, which is known to have a lot of salts and high osmotic suction, you should not use the stress chain factor method because it would be unconservative. So, basically it takes the indexes and assumes the overburden index is the suction compression index, and just simplifies it. And so your stress chain factor is a sum of the two changes, the change in total matrix suction and the change in overburden pressure. This is something that I hear quite frequently. You know, people don't like the PTI method because they have to test suction. And I'll tell you right now, if you ever hear that, the person that is stating that does not know what they are talking about. The PTI method in no way, shape, or form requires suction testing. And I heard this from an engineer just last week who testified under oath in a lawsuit that the post-tensioning institute method requires suction testing. And the geotechnical engineer was negligent. The geotechnical engineer of record was negligent because he didn't perform suction testing. That is 1000% wrong. The PTI method does not require suction testing, period. If you hear anybody say that, take everything else they say about the PTI procedure with a huge grain of salt, because they do not understand it. Are there times where suction testing may be appropriate? Yes, if you have an anomaly that you're trying to analyze. But for 99% of all design parameters, suction testing is not required. Okay, so we kind of talked about YSM a little bit. Let's briefly, I got about three more minutes, let's talk about the edge moisture variation distance. The edge moisture variation distance, again, it's a distance that you are expecting water to migrate under the foundation or to be pulled out under the foundation as a result of environmental conditions. It basically helps define the map. YSM is a function of both climatic conditions and the property of the soil. If you have a more permeable soil, water is going to move further underneath the foundation than if you have a very tight, dense clay. Same thing with the climate. If you are in a climate that changes a lot, you're going to have larger ESM than you would in an area where the climate doesn't change a lot. So ESM is a distance that moisture is supposed to be changes. And ESM, the soil side of it, remember you have two sides. You have a climate and soil. The climate is based on your Thornthwaite moisture index. The soil side is based on the diffusion of the soil. And you can kind of think of the unsaturated diffusion as permeability. It's related to it. It's not exactly the same thing, but it's related to it. And PTI implementation of unsaturated soil mechanics has come up with a correlation between the diffusion and the soil water characteristic curves and the gamma H, which is a suction compression index, both of which they provide simple methods to determine. You don't have to run a soil suction curve. They have ways in the PTI manual to approximate what your slope of your water curve would be. And they give you a procedure to estimate what your gamma would be. Well, for very dense soils like CH clays and such that have low permeability, shrinkage causes cracks in those clays. And those cracks allow moisture to move further and further under the foundation than they might have or that they would have without the cracks. So the PTI implementation of unsaturated soil mechanics came up with this concept called the fabric factor. Basically, you multiply your diffusion coefficient by the fabric factor to take into account for how cracked or how fractured your clay is. If your clay is not fractured or it's not a soil like a CL clay, a sandy clay, that is prone to fracture or crack, then you have a fabric factor of one. If you have a lot of cracks, a lot of roots, other things that can all allow water to migrate, your fabric factor can be 1.2. So basically, you would increase the diffusion 20% if you have a CH clay. I highly recommend that all geotechnical engineers use 1.2 for their fabric factor. The reason I recommend that is because let's say you drill it in the middle of a wet period, you may not see the cracks. Let's say you're using augers. How are you going to find and identify the number of cracks in an auger sample? You're not. So I just recommend on default that if you have a non-CH soil, you use a fabric factor of 1.0. And then if you do have a CH soil, you use a fabric factor of 1.2. And that's really all I had time to squeeze in today and apologize that it's so rushed, but I think we kind of talked about the basics and the fundamentals of the PTI design procedure. Yeah, sweet. Great, Dean. That was a lot of information in there. And we have a few questions that we can hit real quick, and then we'll move on to the next thing that we'll be doing. One of them is a lot of different coefficients and equations were gone over and presented today. In your experience, were these derived from empirical testing? Was it derived from an analytical approach and calibrated through testing? How were a lot of these things created? All three. Direct testing, a lot of it is based on correlations between simple tests like the Atterberg limit tests and direct tests that determine the gammas. And then some of them were based on finite element studies. So it's kind of a combination of all three, direct measurement, analytics, and correlations. Sure, sure. We're getting quite a few questions about are the slides available. To answer that one, guys, we don't give actual PDFs out, but this webinar is uploaded to the website, so you can go watch it, pause it, see the different slides that will be available there. Another question for you, Dean, this one kind of, I think, hints a little bit towards next month's presentation, but it is related here. And it says the PTI method allows for ribbed slab design and a flat slab design. Are there any on more the geotechnical side, any factors that may affect the vision or ability to design to go, you know, whether you go ribbed or flat slab from more of that geotechnical perspective? Yes, and I hope it's something that Tony Childress in his next half will discuss. If you have a ribbed slab, your ribs will go down and a lot of times penetrate into the natural clays. For a post-tension slab to achieve pre-stress, you have to move the foundation towards the middle. Well, if you have ribs that go into natural material, to get pre-stress in the foundation, you have to move those ribs. But those ribs are going to get passive pressures from the hard clay soils that will potentially increase or decrease the amount of pre-stress that you have in the slab. Where if you have a uniform thickness slab, you don't have the ribs, so you are relying just your pre-stress loss is just a function of the friction between the bottom of the slab and the top of the soil. You don't have that passive pressure being applied to the side of ribs. So yes, there is a different behavior and different performance based on whether it's a ribbed or uniform thickness slab. These are great questions, guys. With that, we just got one minute left, so we're going to go into showing what the next few webinars are going to be. And as we were just talking about, a hint towards the next one is that fundamentals of post-tensioning slab on ground, which is we're going to go into the more of the design side of it. And then from there, the next presentation that we're going to hit in January will be electric vehicle weights on parking structures. That's a very hot topic that's being discussed right now. And then when we go into February, already looking that far ahead, we're going to be talking about evaluating existing post-tension structures. We have two webinars right now planned for 2025, one in Q1 and the second one late Q3 early Q4. So that's our look ahead from there. In the presentation, you guys could see all the different ways to contact us with questions. We appreciate you guys being on here and we look forward to seeing everybody again at the same time Wednesday, next month in December. Thanks so much, guys, and enjoy the rest of your day. Bye.

Post-Tensioning Institute

webinar

slab on ground foundations

expansive soils

soil-structure interaction

unsaturated soil mechanics

PTI method

suction envelopes

foundation design