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Stiffened slabs-on-grade are one of the most efficient and inexpensive foundation solutions for lightweight structures on shrinkswell soils. The Ellison Office Building (EOB) is a 1-story steel-framed building founded on a clay formation of high shrink-swell potential. The foundation system of the EOB is composed of a rectangular stiffened slab-on-grade with approximate dimensions of 18.3 by 38.1 m. The slab thickness is 0.1 m, and the depth of all stiffening beams is 1.05 m. Beam spacing distances, center to center, are 3.05 and 3.81 m in the short and long directions, respectively. Exploration of subsurface soil conditions at the EOB site took place to determine soil index properties as well as unsaturated moisture diffusion and volume change characteristics for unsaturated soils. Monitoring the movements of both the slab-on-grade and the 4.5 m soil underneath continued for 2 years after foundation construction, since September 2004. Investigating the EOB foundation performance in light of the soil-structure interaction characteristics of the foundation showed two main distinct slab movement patterns: continuous global heave and localized fluctuating slab edge heave and drop movements. [ABSTRACT FROM AUTHOR]

Shrink-swell soils can cause distresses in buildings, and every year, the economic loss associated with this problem is huge. This paper presents a comprehensive system for simulating the soil-foundation-building system and its response to daily weather conditions. Weather data include rainfall, solar radiation, air temperature, relative humidity, and wind speed, all of which are readily available from a local weather station or the Internet. These data are used to determine simulation flux boundary conditions. Different methods are proposed to simulate different boundary conditions: bare soil, trees, and vegetation. A coupled hydro-mechanical stress analysis is used to simulate the volume change of shrink-swell soils due to both mechanical stress and water content variations. Coupled hydro-mechanical stress-jointed elements are used to simulate the interaction between the soil and the slab, and general shell elements are used to simulate structural behavior. All the models are combined into one finite element program to predict the entire system's behavior. This paper first described the theory for the simulations. A site in Arlington, Texas, is then selected to demonstrate the application of the proposed system. Simulation results are shown, and a comparison between measured and predicted movements for four footings in Arlington, Texas, over a 2-year period is presented. Finally, a three-dimensional simulation is made for a virtual residential building on shrink-swell soils to identify the influence of various factors. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Lane/shoulder drop-off or heave due to expansive soils beneath is a common distress in both concrete and asphalt pavements, resulting in substantial discomfort, safety hazard and vehicle damage. The situation becomes worse when exposed to moisture changes, particularly in Texas, Colorado, Arizona, California, etc. where many soils are expansive soils. Therefore, expansive soils pose great challenges for the design of pavements and foundations. One of the most difficult issues for designing pavements and foundations on expansive soils is to predict the volume change of the soils. In this study, current methods for movement predictions are summarised and their relationships and shortcomings are discussed. It is found that all these methods have the same theoretical basis. Based on the theory of unsaturated soil mechanics, it is found that the water content and the mechanical stress can be used to determine the soil status. Hence, a void ratio versus mechanical stress and water content surface is constructed, which coupled both mechanical stress and suction's influences on volume change of expansive soils. The new surface is developed into a coupled water content method that can be used to predict the potential vertical swell and the potential vertical shrink simultaneously, while all the existing methods can only predict the potential vertical rise. The method is used to analyse the data collected from a construction site at Arlington, Texas. The predicted movements match the measured data reasonably well. The method is simple and overcomes the shortcomings existing in the current movement prediction methods for expansive soils. [ABSTRACT FROM AUTHOR]

Constitutive surfaces are indispensable for investigation of the behavior of soils. Saturated and unsaturated soils coexist in most engineering problems and it is meaningful to develop constitutive surfaces covering both saturated and unsaturated conditions which help to investigate the behavior for both saturated and unsaturated soils in a unified way. At present, the methodologies used for saturated and unsaturated soils are different and few researchers consider the constitutive surfaces for saturated soils. For unsaturated soils, the suction-controlled triaxial tests are usually laborious, time consuming, costly, and may not justify routine engineering projects. This paper discusses the role of constitutive surfaces in soil mechanics and presents an improved approach over existing interpolation methods to construct the constitutive surfaces for saturated and unsaturated conditions for a stable-structured soil using simple laboratory tests. [ABSTRACT FROM AUTHOR]

Energy piles are bi-functional foundation elements used as structural support as well as ground heat exchangers for shallow geothermal energy systems. Because they are relatively short, energy piles may be partially embedded in unsaturated soils. Saturation conditions influence the thermal properties of the ground and therefore the heat exchange rate, which in turn affects the efficiency of energy piles. This paper combines analytical, experimental and numerical investigations to evaluate the heat exchange rate of energy piles partially or fully embedded in unsaturated soils. The proposed analytical solution is based on the cylindrical heat source theory that treats the soil as a semi-infinite, homogeneous, and isotropic medium. The solution from this theory is multiplied by a function developed analytically in this paper and the outcome is the heat exchange rate for energy piles in unsaturated soils. The proposed function depends on soil saturation, soil and pile thermal properties, and pile geometry. The analytical solution was compared against a finite element solution; which was in turn validated against results from laboratory experiments. Very satisfactory agreements between the analytical, numerical and experimental outputs were observed. The proposed method can be used for a quick and simple evaluation of the efficiency of energy piles in unsaturated conditions. The proposed analytical solution can also be a useful tool for the verification of numerical codes developed for the design of energy piles in unsaturated soils. [ABSTRACT FROM AUTHOR]