Current Research Projects and Interests
Oklahoma Center for the Advancement of Science and Technology (OCAST)
Project #AR062-007: Design of Small Wind Turbine Foundation Elements
PI: Amy Cerato (OU)


    The project "Design of Small Wind Turbine Foundation Elements," will use helical, screw-type anchors instead of concrete for the foundation elements of the small wind towers.  This new technique in anchoring small wind turbines will reduce the time and material needed for installation, reduce the customer's cost of installation, increase the mobility of the units and increase the sales of small wind turbines across the country.
    Currently, foundation elements used for anchoring small wind turbine guyed cables consist of cast-in-place concrete blocks placed 1.8 m in the ground with an embedded anchor battered at a 45° angle which attaches to the guyed cables.  This type of anchor requires a large excavation which is time consuming and necessitates a large volume of soil to be excavated and then compacted around the anchor element, resulting in approximately 8 to 16 man-hours of labor. One alternative to the traditional concrete anchoring system is power-installed, screw-type foundations. These screw-type foundations, or helical anchors, offer attractive benefits in the conservation of labor, materials and equipment, as well as time, which will provide a significant cost reduction during the installation phase of small wind turbine technology. 


Dynamic test set-up on South Campus. 
Click on the picture to go to the photo gallery

  

 As easy and inexpensive as the installation of power installed screw anchors (PISA’s) are, there is relatively little information on the design parameters and field performance of helical anchors experiencing tension, compression or lateral forces in the presence of sustained dynamic loads.  There is also very little field verification of the empirical factors used to predict uplift capacity from installed torque measurements in high plasticity clays, particularly in the event of high water content. 

In order to safely use these helical anchors for small wind turbine foundations, design parameters must be obtained from an extensive field testing program.  The helical anchors in this study will be tested in high plasticity clays with varying ground water conditions under normal and extreme wind turbine operating conditions (vibrations).  It is the objective of the project to 1) validate and further establish the correlation of installation torque to anchor uplift capacity, 2) determine the influence of ground water fluctuations on the measured capacity of helical anchors in expansive clays, 3) determine the influence of vibrations from wind turbines on the short and long-term reliability of helical anchors in high plasticity clays,  and 4) develop a design procedure that incorporates the influence of water table, vibration intensity and measured soil strength parameters in predicting the capacity of helical anchors for use in guyed cable tower foundations.



Instrumented 100 foot guyed pole tower,
10kW Bergey Turbine

Oklahoma Department of Transportation (ODOT) Project:
Development and Comparison of Alternative Approaches to Chemical Manipulation of Soils
PI: Amy Cerato (OU)
co-PI's Jerry Miller (OU), Don Snethen (OSU)

Problem Statement: To optimize and validate Oklahoma Department of Transportation Materials Division’s recommended Standard OHD L-50 entitled, “Soil Stabilization Mix Design Procedure.”

    Due to the prevalence of fine grained soils in Oklahoma it is common practice to use chemical stabilization in the construction of highway subgrades. Additionally, chemical stabilization is sometimes used in the construction of sub-base and base course layers using marginal quality aggregate materials. The traditional method of mix design for stabilized subgrade, according to ASTM D4609 for example, can be time consuming and create delays during design and construction. A test can take a week or more including sample collection, preparation, curing time and testing. If subgrade conditions are well known prior to construction, a mix design may be feasible; however, often times subgrade conditions are not well known during the design phase and differ from those encountered during construction. Thus, if an entirely new mix design is required significant delays in construction may occur.

  <>In an effort to streamline the mix design process, the Oklahoma Department of Transportation Materials Division developed the OHD L-50 Standard entitled “Soil Stabilization Mix Design Procedure.” At the heart of this standard is a table titled “Soil Stabilization Table”, which provides recommended additive amounts for soils in the Soil Group Classifications found in AASHTO Standard M145. Additive amounts are given for Portland Cement (PC), Fly Ash (FA), Cement Kiln Dust (CKD), and Lime (hydrated and quick lime). OHD L-50 recommends a traditional mix design approach to address particular project concerns or non-approved chemical sources but allows projects having no unusual soil conditions to use the soil stabilization table.  While the development of this table is based on a significant amount of research and experience in Oklahoma, it is possible that recommended additive amounts may not be appropriate for all soil and additive combinations within a particular soil group classification. In other words, the use of the recommended additive content may not achieve the desired effect that would normally be targeted in a full mix design process. The desired effect may be quantified, for example, in terms of the unconfined compression strength of the soil-additive combination after a standard amount of curing.



Oklahoma Department of Transportation (ODOT) Project:
Evaluation and Field Verification of Strength and Structural Improvement of Chemically Stabilized Subgrade Soil
PI: Don Snethen (OSU)
co-PI's Jerry Miller (OU), Amy Cerato (OU)





The research project will address the limited information on the rate of development and ultimate, magnitude of strength improvement of chemically stabilized subgrade soils through a combined laboratory and field study using various soil strength measurement methods on soils from projects in design and early construction phases.  Results will be compared to existing structural number relationships for treated soils and adjustments will be made to calibrate and validate the parameters used in pavement design.
   


                                                                                                                                                                                                                                                                                                                                                                                                                                                                         Clayey Soil Mixed with CKD for Resilient Modulus
                                                                                                                                                                                                                                     Testing (click for more pictures).


Oklahoma Transportation Center (OTC):
Heave in Sulfate-Bearing Oklahoma Soils due to Lime Stabilization
PI: Jerry Miller (OU)
co-PI: Amy Cerato (OU)

Lime and other calcium-based stabilizers are added to soils in order to reduce their plasticity, increase their shear strength, reduce their compressibility, and reduce their tendency to undergo volume change when subjected to variations in water content. In simple terms, additives like lime render highly plastic expansive soils non-plastic and non-expansive. However, when a soil stabilizer such as lime is added to soil containing soluble sulfate the resulting reactions can have the opposite effect and actually make the volume change tendencies much more devastating. An example of such devastation was realized on a recently constructed Oklahoma State Highway, where due to what appears to be sulfate-induced heave in lime stabilized soil, miles of new pavement were destroyed resulting in the loss of millions of dollars.

Soils and shales containing gypsum are common in Oklahoma; gypsum is a primary source of soluble sulfate. Generally, when soils/shales containing soluble sulfates are mixed with lime and given access to water, there is the potential for significant increases in soil volume (swelling) due to the formation of calcium-aluminum-sulfate-hydrate minerals such as ettringite. Based on a review of the literature, it appears that soluble sulfates may be problematic at sulfate contents as low as 0.3% (3000 ppm); however, if any soluble sulfate is detected, prudence warrants that appropriate design and mix procedures should be followed.


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