| Description |
A research study was conducted for the Utah Department of Transportation regarding settlement caused by embankment construction for a new bridge located about V mile east of the Interstate 15-State Route 77 interchange in Springville, Utah. Embankment ramps were about 425-ft long, 106-ft wide, and 30-ft tall at the highest points, with vertical side slopes supported by mechanically stabilized earth (MSE) walls. The primary objectives of this study were as follows: (1) Determine consolidation properties of the cohesive soils; (2) predict time rate of primary consolidation settlement using numerical analyses; (3) compare measured rates of primary consolidation settlement with predicted values; and (4) compare the effectiveness of Asaoka's (1978) method for predicting the time for surcharge removal with more advanced methods. These objectives were attained by performing field and laboratory investigations to determine properties of the soils at the site, installing instrumentation to measure settlement and other relevant parameters, and performing numerical analyses to predict the rate of primary consolidation settlement within each cohesive layer. During the field investigation, undisturbed piston samples were obtained and standard penetration, cone penetration, and vane shear tests were performed. Instruments installed to monitor soil behavior included nineteen piezometers, twenty spider magnets, six settlement manometers, three push-in cells, two ShapeAccelArrays, one vertical inclinometer, one horizontal inclinometer, three pressure cells for vertical stress, and three pressure cells for horizontal stress. The laboratory investigation included classification and constant rate of strain consolidation tests. Primary consolidation settlement was predicted using Terzaghi's (1947) and Davis and Raymond's (1965) one-dimensional consolidation theories in conjunction with the finite difference method. Results from these two analyses were compared with measured primary consolidation settlement data obtained from field instruments. Primary consolidation settlement results using both methods proved to be reasonable, but no conclusion could be reached regarding which method yielded better predictions. Predicted times for surcharge removal analyzed using Asaoka's method based on measured values of surface settlement were incorrect because of the erroneous assumption that the underlying soil is homogenous. Better estimates of time for surcharge removal were obtained by analyzing each of the cohesive layers separately. |
