The strength of the foundation determines the life of the structure. We haven't had to, but it's probably a good idea to add a layer of gravel underneath the grade beam and have a way to drain it. It is dark in color and soft, dry and crumbly to the touch. This is very light loading from a geotechnical and foundation engineering point of view. Subsidence or settlement is when the building foundation drops, caused by the loss of support of the site beneath the foundations. However, my main reason for ignoring their recommendations is of course, due to limited funds. It sounds like you and I are working on parallel tracks towards the same goal. The foundation design engineer shall prepare the plans and specifications for the foundation, and shall be the engineer of record. If foundation engineering is ever required, it's in areas with expansive clay soils. This seems to only show up several years after being built...about as long as it takes for the surrounding trees to get their roots under the walls. This type of soil is made of over 25% clay – and, because of the spaces found between clay particles, clay soils hold a high amount of water. The foundation shall be built in This won't delete the articles you've saved, just the list. If you would be interested in having MLAW Engineers present a one to two hour seminar on soils, foundations or structures, call (512) 835-7000. 3. slip zone punched wedge As we discussed in the earlier arti… Another unique clay exists in the Ottawa and St. Lawrence Valleys. Our climate here is semi-arid and yes we do experience the extremes of wet and dry from time to time. I gather that the piers' function is to get below the risky soil. http://en.wikipedia.org/wiki/On-Grade_Mat_Foundation_for_Expansive_Soils. For such soils very stiff and strong soil supported slab foundations are necessary. This way, a 12" thick double wall (modified Larsen Truss) frame will cover both exterior and slab edge foam. Contents:Types of Soil Investigations for Foundation SelectionSubsurface Soil InvestigationsSurface Soil … The prime design problem for these foundations is swelling or expansive clays. Foundation design recommendations. When strip foundation is construction in desiccated clay in dry soil, then the foundation shall be loaded with building prior to the return of rains. Maybe it can help. Change in water content is almost unrelated to the structural loadings of these types of foundations, but is instead related to environmental factors or artificial factors. Here's my own opinion: don't be tempted to cut corners with foundation details in a region with expansive clay soils. Thanks again and thanks for the offer to contact you. A cushion of granular soil below the foundation absorbs the effect of swelling and so its effect on foundation will considerably reduce. Options and Concepts . Foundation Design - Soils from Building Structures, 2nd ed., Ambrose, 1993 . A foundation transfers the load of a structure to the earth and resists loads imposed by the earth. Wall or slab movement and cracking? Garth: Is building on pilings an option in your area? A cushion of granular soil below the foundation absorbs the effect of swelling and so its effect on foundation will considerably reduce. We have very expansive soils in Dallas and almost all foundations are designed by engineers but builders must learn to hire the right subcontractor no matter what the trade is. Foundation type and features at a particular lot are chosen on the basis of soil characteristics. However, engineers have the ability to recognize swelling clay soils and to design structures that can withstand the effects. My email is hamptond76 at hotmail dot com. 4. soil if the percentage of clay is more than about 5 percent by weight. Loam – Loam is the ideal soil type: typically it’s a combination of sand, silt and clay. Expansive clays are expansive or, more accurately, reactive, when their volume changes relative to a change in moisture content. Expansive soils are not problematic unless they go through significant wetting/drying cycles. 4. The job of a foundation is to transfer the loads of the building safely to the ground. Usually, steel reinforced concrete slabs are the best foundation design for expansive clay soils. Other examples include standing water such as from excessive watering of a near slab planter, or adverse drainage grades on the surface which do not permit ready shedding of storm water. But if the site has soft, wet clay, the foundation will be much more likely to settle, leading to cracked tile, drywall and even masonry. Uniform firm and stiff clay 3. Our soil was tested last year, and a soil engineer provided foundation details suitable for our moderate shrink/swell clay. CNS Technology: – In this technology we intercept Cohesive Non-Swelling soil layer below the shallow foundations on expansive soils. With the use of a large "apron" area around the structure, and the avoidance of plantings and especially trees to close by, maybe it is possible to avoid problems??? Clay soil as a garden design foundation can accommodate a pretty wide range of shrubs, climbers, conifers and trees. Most local builders just dig as deep as their skidsteer rigs will go. Some foundations used for light buildings on shrink-swell soils. Contact me at HouseWright at Ponds-Edge dot net if you'd like more information. Robert The main concern with the FPSF technology is that it is susceptible to damge from soil movement. First, let’s discuss expansive soils. On the order of three to four times as much cost may be involved. This system requires maintaining a complete void space beneath all grade beams and slabs of the foundation and isolating all soil supported elements such as steps, patios, sidewalks or driveway slabs. Does your climate include alternating wet and dry periods or is it mostly wet? We can tailor our program content to your specific needs. I was hoping you would weigh in here, I always look forward to all your comments. During the foundation work, water logging causes the problem of mud or may cause the dislodging of side soil. The problem is actually quite complex and involves analysis of partially saturated flow interacting with the volume change properties of the soil and water matrix. Our soils here in southern Saskatchewan (9000 HDD) are quite variable when it comes to clay content, but almost all of the homes in the local area (regular concrete basements on wide footers) eventually end up having some problems with foundation movement due to expansive soils. I'm an advocate of FPSFs, but I've had the luxury of building on well-drained soils with enough slope to run the perimeter drain to daylight. Examples of environmental factors include wet weather and dry weather, heavy rains or lack of rain. JKLINGEL Usually, steel reinforced concrete slabs are the best foundation design for expansive clay soils. Foundation is the base of any structure. Soft clay 4. Generally, you can prevent foundation problems in expansive clay soil environments by doing two things. Prolonged drought can also cause soil shrinkage beneath a building. You must be a magazine subscriber to access this feature. where trees, hedges, and shrubs are close to foundation location, or there is a plan to plant these trees near the structure in the future. The cost to repair foundation problems will bankrupt most builders (and some small insurance companies). Interior bearing points could be provided by concrete piers as well, as long as they are sleeved wear they penetrate the floor. Other environmental factors could include tree roots extending under the foundations withdrawing moisture and causing the resulting shrinkage phenomena. Don't know if the expansive soil effects can be prevented here, but with good drainage, site grading etc. This feature has been temporarily disabled during the beta site preview. Such loadings provide almost no restraint to the expansive clay activity, whereas a more heavily loaded foundation would tend to restrain swelling movements. We insulate the bottom 8" of the foundation and backfill it to slope the water away from the house. At the wilting point tree roots can no longer pull water out of the ground. Whatever may be the reason for water logging either it is due to the rain or groundwater, in both the cases, quality of construction work cannot be easily achieved, particularly when soil is clay, silt or mix of clay, silt and sand. slip zone punched wedge . The higher the clay content, the stronger … |  Website by Pallasart Web Design, deep pier and suspended structural foundation. Paving design recommendations. So, right now I don’t really trust his work. Foundations are recommended based on the different soil types which are provided below: 1. FOUNDATION DESIGN FOR EXPANSIVE SOILS. Good luck. I would think that building on pilings is an option just about everywhere. D. ESIGN . Too much hassle? Case II. For instance, dense, dry soil will be stable, forgiving of less-than-perfect construction and less likely to settle after the house has been built. CNS Technology: – In this technology we intercept Cohesive Non-Swelling soil layer below the shallow foundations on expansive soils. ARCH 631 Note Set 24.1 F2010abn 3 . With all this being said, I'll bet a variation of this design or Robert's would get you not only the best option structurally, but the lowest cost as well. One of the reasons that raft foundations are used on clay soils is to reduce the soil contact area and concentrate the building loads on smaller areas of soil. Without a solid foundation, the structure would not hold for long. This method utilizes the Atterberg limits, specifically the Plasticity Index, to estimate a support condition relative to a climatic condition. The design of foundation depends on the total load on the building and the type of sub soil and its bearing capacity. Allowable stress design is utilized for soils because of the variability do determine the allowable bearing capacity, q a = q u/(safety factor). Values of q a range from 3000 – 4000 psi for most soils, while clay type soils have lower capacities and sandy soils to rock have much higher capacities. On the order of three to four times as much cost may be involved. Neverthe- less, it is useful to consider the specific aspects of the foundation design that must be dealt with. So what makes you think that it would be advisable to ignore the recommendations of an engineer? As a deigner I'm always intrigued why a client wants to "have it all" on a limited budget vs. reducing the size of the house or "lower" some of the decorative or secondary specs. The difficulty comes in supplying the actual values of these variables in a given situation. How can you prevent foundation problems in expansive clay soil environments? any foundation design. Armando Foundation Design Notation: a = name for width dimension A = name for area ... supports that transmits the loads to the soil or rock. That solution comes from Earthlok. You are right to advise listening to the engineers, but it is my experience that engineers tend to over design to "cover their butts". Using wide footings is not a solution to heaving ground, as the bearing is more dispersed and there is less building weight per square foot to resist uplift. Foundation systems for buildings on expansive soils shall be designed and constructed in a manner that will minimize damage to the structure from movement of the soil. We have to be very cautious with the design of foundations because our entire structure rests on the foundation. I can't speak to your situation though....14000HDD is much colder than where I live. The third procedure coming into use is the evaluation of the change of soil suction profiles. Sounds like you've already looked at it. http://foundationperformance.org/projects/FPA-SC-01-0.pdf, And there's a decent entry in Wikipedia on waffle mat foundations: This procedure fairly accurately models the physical phenomena of what actually is occurring under the foundation and accounts for all the variables. Everything from popular conifers like ginkgo biloba and a deciduous evergreen like cotoneaster to rosa and fuchsia shrubs makes a great complement to clay soil. Site Exploration RE: clay soils foundation design - to do not to do DRC1 (Civil/Environmental) 28 Jan 04 08:28 You and Focht3 know the engineering climate down there, but if you know engineers who have done this, talk to them. Soils with smectite clay minerals, ... Foundation Damage ... A design for a swimming pool shell in a highly expansive soil environment is presented in Fig 7. The PVR technique does not always predict accurately (sometimes overpredicting and sometimes underpredicting the actual swell by as much as 100%). Similarly in dry weather, assuming the entire underslab soil is at a uniform moisture content, the edges can be dried out causing loss of edge support due to shrinkage. Any of the home builders who get an engineer involved end up building very costly foundations involving deep concrete piers and void form. But we’ve had a LOT of rain over the last month. In this article, various types of soil investigations, their reports and suitable types of foundations for various types of soils are discussed. We also save a lot of money and use less resources with our design. A scenario is developed which would change this profile to different suction levels and formulas are applied which will produce predicted vertical movement, either shrink or swell. This technique was developed by Chester McDowell and others 30 to 40 years ago and is widely utilized by the geotechnical community today as a method for predicting potential swell. http://www.toolbase.org/PDF/DesignGuides/revisedFPSFguide.pdf If necessary, I can construct the interior non bearing walls so that the floor can move a little and have no effect on the structure. Our footing is 12" wide by approx. I also plan to do most of the construction myself. Become a GBA Prime member and get full access to GBA articles, enyclopedia, videos, CAD library, and more. Methods for predicting and analyzing the differential movements of expansive clay soils include empirical or rule of thumb methods, pressure-volume change relationship predictions, and the more recently introduced soil suction profile variation methods. Of course I'm interested to hear the opinions of other GBA readers. Clay: Clay is an CNS MSM Technologies. Lucas Robert The volume of a compact clay typically increases causing swelling when moisture content increases and decreases causing shrinkage when water content declines. Garth: "The only reason that I would consider it is to try to avoid structural damage caused by expansive soils...." •• That is why I asked if you had considered it for yourself. Garth, I would have to use void form between the piers to be sure that all the weight of the structure is borne by the piers. Course Content . The portion that is wetted expands, whereas the portion that is not yet wet will not expand, causing differential support under the foundation. A foundation in residential construction may consist of a footing, wall, slab, pier, pile, or a combination of these elements. Or maybe there is reluctance to move away from proven (though more expensive) methodology? I know that in our design, the beam does bear some load. Residential Foundation Design . Values of q a range from 3000 – 4000 psi for most soils, while clay type soils have lower capacities and sandy soils to rock have much higher capacities. ARCH 631 Note Set 24.1 F2010abn 4 from Foundation Analysis and Design, 5th ed., Bowles, 1996 . These structures generally apply a load to the surface of the ground of between 150 to … These are commonly referred to as post-tension cable concrete slabs. These are commonly referred to as post-tension cable concrete slabs. Sounds like you and I are dealing with similar soils as well as climates....and maybe similar budgets too... Actually, I am trying to avoid a basement and am planning a very modestly sized, modestly decorative, super insulated home. I was really hoping to use a monolithic slab (FPSF frost protected shallow foundation). Foundation systems and soil types go hand-in-hand as the type of soil you encounter on your plot will inform the best foundation system for you to use for your project. Here is another perspective, without sounding like a preacher... Typical values of pF range from about 2.0 for a very saturated soil condition up to about 4.5 for a very dry condition, which the agriculturists would call the wilting point. 3. To avoid the easily Expansive soils cause major damage to light foundations and associated structures. Even subgrade piers aren't foolproof if they're not deep enough to get below the expansion layer. The method relies on Atterberg limits to predict the swell based on extensive correlation with pressure-swell tests done in the laboratory. This method then determines what the potential expansion might be under certain pressure regimes in the ground and assuming unlimited water is made available to the clay soils. Sufficient research has been done to demonstrate what the equilibrium values might be for various localities. P. ROCEDURE FOR This support condition in turn drives the structural design for stiffness and strength of the shallow slab. But you’ll also need a structural engineer to oversee the project since the design and soil analysis are vital factors for a safe and robust build. If you can keep the soil under your foundation either consistently wet or consistently dry, you can avoid problems and the drastic and expensive measures to mitigate them. Loam is great for supporting foundations because of its evenly balanced properties, especially how it maintains water at a balanced rate. Bearing capacity of soil. But you’ll also need a structural engineer to oversee the project since the design and soil analysis are vital factors for a safe and robust build. I'll put that record against anyone's design. Your thoughts are appreciated. One inch of rain on a 1000 sf roof will drop almost 625 gallons of water at the eaves. A pier and beam foundation is ideal where the soil is clay and has high plasticity. When differential volume change occurs under shallow soil supported foundations, the support conditions change from uniform to non-uniform. I build the forms 12" wide to pre-install the exterior 2" foam insulation with galvanized deck screws sticking out on the interior to bind to the concrete, and a 2" thick by 6" deep slab edge insulation attached to the top inside edge of the forms. This can lead to subsidence or settlement. The following guidelines are intended to … 1.1 General . In extreme cases and where the sensitivity of the superstructure and the non-compact shape of the foundation footprint dictate, it may be important to utilize a structural floor system with drilled and underreamed piers.