The Interstate Highway 35 East (IH-35E) running through Dallas and Denton Counties in Texas, United States will undergo significant construction improvements for approximately 48 kms (30 miles). The 1.5 billion US dollars Design-Build project is expected to relieve traffic congestion in one of the most heavily traveled corridors in the North Texas region. In this project, over 120 Mechanically Stabilized Earth (MSE) Retaining Walls are planned to be constructed over the sandy lean and fat clay soils overlying the Eagle Ford Shale and Woodbine Sandstone. To characterize the engineering properties of the foundation soils, 13 consolidated-undrained triaxial compression tests and 13 stress-history controlled direct simple shear tests on reconstituted samples were conducted. The results were analyzed along with the database containing 17 laboratory shear test results from previous projects in the area. Historically, the soils derived from the Eagle Ford shale are known to be problematic resulting in stability issues when exposed to changes in moisture content. These soils usually have an overconsolidation ratio (OCR) between 1 and 6. Statistical analyses were performed to provide recommendations for Mohr-Coulomb effective (long term) strength parameters to be used in external stability analyses of the MSE walls. The analyses were performed on the basis of type of laboratory tests (difference in failure mechanism), index classification (liquid limit and percent sand content), and overconsolidation ratio to account for the desiccated soil layers. Based on the results from these analyses, there exist significant differences in soils engineering parameters in the lean (CL) and fat (CH) clays and the sandy lean (SC) clays and in relation to the sample degree of overconsolidation. The studied behavior and engineering used to propose five Mohr-Coulomb effective strength envelopes to be used in the external stability analyses of the MSE walls.