Master of Science in Engineering, University of Akron, 2014, Civil Engineering

The Ohio Department of Transportation (ODOT) recently implemented global chemical stabilization for new construction or repair involving major road projects. Pavement heave caused the failure of the road surfaces in three projects in Lake County, Ohio. Subsequent soil investigation revealed surface heave was caused by soil swell from the formation of a calcium alumina sulfate hydrate, ettringite (Ca6Al2(SO4)3(OH)12•26H2O) which may occur in sulfate bearing soils chemically stabilized with lime. Failure of pavement in these three projects caused ODOT to question the whether other regions within Ohio had subgrades with high soluble sulfate concentrations. This report is an investigation into natural and anthropogenic sources of sulfate (SO4) in Ohio soils evaluated via literature review and soil testing. The ODOT provided just under 350 soil samples from 39 different counties throughout the state for assessment of soil chemistry and mineralogy. Soluble SO4, often the primary controlling factor in degree of ettringite formation, was measured within soils using colorimetric methods. Several soils were additionally tested for total metal (Al, Fe and Cr) concentrations using acid digestion and inter coupled plasma optical emissions spectrometry (ICP-OES). Total Al concentration within soils was analyzed, as Al and SO4 are the chemicals within ettringite which have their primary source as the prestabilized soil. Total Fe was assessed as a marker for potential areas where sulfate would have formed from the oxidation of pyrite (FeS2). Total Cr concentration was tested as chromate (CrO4) can be a replacement group for SO4 within the ettringite structure. Additionally initial review of literature identified chromite ore processing residue remediation as a potential source of excess SO4 in soils. Finally, soil mineralogy was analyzed via x-ray diffraction (XRD). Results indicate Lake County, Ohio is not the only region with Ohio where ODOT should expect subgra (open full item for complete abstract)

Committee: Teresa Cutright Dr (Advisor); John Senko Dr (Committee Member); Ala Abbas Dr (Committee Member) Subjects: Civil Engineering; Environmental Engineering; Geochemistry; Geotechnology; Transportation

Master of Science (MS), Ohio University, 2014, Civil Engineering (Engineering and Technology)

Roadbeds are considered one of the most problematic components in pavement design and construction. Its engineering properties differ significantly in terms of soil composition, gradation, and strength parameters. Soil stabilization techniques have been widely used to improve the engineering properties of roadbed soils. Therefore, in order to study the effects of the stabilization of subgrade layers for pavement structures, theoretical and experimental work was carried out to study pavement responses constructed over stabilized subgrade with lime and cement. The theoretical study involved creating finite element models to study the nature of stresses and strains in the subgrade and asphalt layers when stabilized layer is used in the pavement structure. To study the durability and long term performance of chemically stabilized subgrade, FWD and DCP tests were performed on several pavement sections constructed with stabilized layer. The results from the theoretical study showed that the subgrade could be protected from being over-stressed during construction by providing a suitable stabilized layer. Results from field testing showed that the stiffness of chemically stabilized layers increases significantly over time. It also showed that it provides structural stability to the pavement constructed over stabilized subgrades. Based on these results, input parameters were recommended to MEPDG of flexible pavements.

Committee: Shad Sargand (Advisor) Subjects: Civil Engineering; Transportation

Master of Science in Civil Engineering, University of Toledo, 2004, Civil Engineering

Subgrade soil plays a very important role in the construction of roadways. Before the use of asphalt in the construction of roadway, roads were being constructed based on experience. The introduction of paving asphalt in road construction has led to the development of engineering procedures and designs for the methods of construction. The resilient modulus of the underlying material supporting the pavement is now considered as a key material property in the AASHTO mechanistic-empirical design procedure. Attempts have been made by researchers to predict the Subgrade resilient modulus from laboratory/field experimental methods based on the soil properties. This research seeks to develop a model for predicting the subgrade resilient modulus due to environmental conditions by considering the seasonal variation of temperature and moisture content which affects the soil. The limitation of this research model is that it cannot be used universally since environmental conditions vary from place to place, however, it can be modified to suit other local environmental conditions. The detrimental effect of low resilient modulus of subgrade soil is observed in the damaged analysis.

Committee: Andrew Heydinger (Advisor) Subjects: Engineering, Civil

Doctor of Philosophy, The Ohio State University, 2004, Civil Engineering

The objective of this study was to evaluate existing constitutive models currently used by State Department of Transportations (DOTs) and to develop an improved model for predicting resilient modulus (Mr) of cohesive soils from simple soil properties typically measured in DOT laboratories in preference to expensive and complex Mr laboratory testing. The data set used consisted of cohesive soils typical of those used for subgrades in Ohio. Thirteen representative cohesive soils representing A-4, A-6, and A-7-6 soil types collected from road construction sites across Ohio, were tested in the laboratory to determine their basic engineering properties. Mr tests were conducted at three different moisture contents (dry of optimum moisture content, optimum moisture content, and wet of optimum moisture content). Additional tests were performed on samples compacted to optimum conditions but allowed to fully saturate. Mr predicted from six existing models studied showed wide scatter and poor correlation with the measured Mr. An improved constitutive model was developed to account for the effects on Mr of the stress state of the soil and its engineering properties obtained from simple laboratory tests. While most of the existing models investigated in this study significantly overestimated the Mr of a cohesive soil, the proposed model predictions are close to the experimental values and are in most cases a slight underestimation. This implies that Mr values predicted by the proposed model are generally slightly conservative, and can be safely used in the design of flexible pavements to be built on cohesive soils. The proposed model can be a useful and reliable tool for estimating Mr of cohesive subgrade soils using basic soil properties and the stress state of the soil.

Committee: Frank Croft (Advisor) Subjects: Engineering, Civil

Master of Science, University of Akron, 2005, Civil Engineering

When designing pavements, there are three fundamental external design parameters to evaluate (1) the characteristics of the subgrade upon which the pavement is placed, (2) the applied loads, and (3) the environment. The subgrade layer, upon which the pavement is constructed, will have a large impact on structural design. The study was based on extensive laboratory work to characterize cohesive subgrade materials. Permeability of the subgrade was obtained using a flexible wall permeameter, which simulates the actual field conditions. The factors affecting permeability were also discussed. Strength parameters were determined utilizing the static load triaxial apparatus. The Consolidated-Undrained Triaxial Compression Test and Unconfined Compression Test were performed. Resilient modulus testing was conducted using a repeated load triaxial system at different confining pressures employing AASHTO T294-92I. A new testing procedure, stage loading, was used to test the permanent deformation of subgrade materials at different stress levels and load repetitions; this technique allows researchers to explore the effect of stress history on the accumulation of plastic deformation besides saving time, effort, and test specimens. Hydraulic conductivity results showed a practically impermeable subgrade layer. From the measured data of the consolidation test, the pressure-void ratio relationship was plotted and used in determining the compression index, recompression index and maximum past pressure of the soil. In addition, the coefficients of consolidation were obtained. Mohr circles at failure and Mohr failure envelopes were drawn for the total and effective stress data obtained from the CU tests, from which shear strength parameters were determined. On the other hand, Mohr circles at failure were drawn for the unconfined compression test that indicated the cohesive subgrade soils to vary between very stiff and hard consistency. Furthermore, isotropic elasticity analysis was carr (open full item for complete abstract)

Committee: Robert Liang (Advisor) Subjects: