Correlation between Laboratory Tested Soil Samples to Obtain Effective Strength Envelopes Based on Field Data

As part of the 1.4 billion U.S. dollars Design-Build Interstate Highway 35 East (IH-35E) project running through Dallas and Denton Counties in Texas, over 120 mechanically stabilized earth (MSE) retaining walls and 16 bridge widening are planned along the 30-mile alignment. This paper describes the methodology implemented to obtain site specific correlations of shear strength parameters (effective cohesion and friction angle) in residual clays derived from the Eagle Ford shale, Woodbine sandstone formations, and alluvial soils from 3 valleys for the analysis of the MSE retaining walls. These correlations are derived from borings drilled along the project alignment and consist of field measured descriptions, SPT and Texas cone penetrometer blowcounts, and laboratory index property tests. Historically, the soils derived from Eagle Ford shale are known to be problematic resulting in stability issues especially when modified from their in-situ conditions. These soils are overconsolidated, in the laboratory we quantified the overconsolidation ratio (OCR) between 2 and 6. To characterize these soils, 13 consolidated-undrained (CUIC) triaxial tests at peak principal stress ratio (39 data points) and 13 stress-history controlled direct simple shear tests on reconstituted samples (39 data points) were completed to assess OCR against effective cohesion and friction angle. Twelve 1-D consolidation tests were performed to evaluate stress history in the laboratory and estimate preconsolidation pressure and OCR range. The results were analyzed along with a database containing 17 laboratory CUIC triaxial tests (51 data points) from previous projects within the area. A correlation matrix with five Mohr-Coulomb drained effective strength envelopes at peak principal strength ratio and soil OCR has been proposed for the lean (CL), fat (CH) and sandy lean (SC) clays within these formations.