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LABORATORY CHARACTERIZATION OF COHESIVE SUBGRADE MATERIALS
| Title: | LABORATORY CHARACTERIZATION OF COHESIVE SUBGRADE MATERIALS |
| Author: | Khasawneh, Mohammad Ali |
| Description: | 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 carried out. It was found that soil moduli increase as the confining pressure increases according to the elastic theory. Resilient modulus results showed a slight increase in resilient modulus value with an increase in confining pressure. The permanent deformation results showed a constant increasing rate of plastic strain at higher stress levels. The results obtained will be added to the ODOT database to help engineers in characterizing the cohesive subgrade materials. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=akron1124387175
http://hdl.handle.net/2374.OX/3625 |
| Date: | 2005 |
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