Stress distribution and displacement in multi-layer soil system

In this research project an axisymmetric-two dimensional finite element model was developed in ANSYS program to predict the vertical stress distribution and surface displacement for threes type of uniform soil profiles and four different sequences of layered soil profiles. Three air dry soils, silt clay loam, silt loam and sand soil, having different mechanical properties and at initial loose conditions were employed in the simulation and measurement. In the case of uniform soil profile agreement between Boussinesq's vertical stress distribution and that obtained from the finite element model was good. Differences between the various treatments of different soil type and the linear and nonlinear soil behaviors on the vertical stress predicted by the model for case of uniform soil profile were small. The measured vertical stress was higher and extended to deeper depth compared to model prediction. Surface displacements predicted by the model were influenced greatly by the soil type and the simulated soil behaviors. Linear soil behavior obtained from one-D confined test showed lowest surface displacement while the nonlinear soil behavior obtained from semi-confined tests gave the largest values. Margin of discrepancy in the predicted surface displacements between the treatments of soil type, linear and nonlinear soil behavior was large. Measured surface displacement was higher than the predicted one, but the margin of discrepancy between the two was reduced for the case of uniform soil profile of silt clay loam soil with nonlinear soil behavior at high load levels.; In the case of layered soil profile the vertical stress distribution pattern predicted by the model was affected by the type of soil make up the layered system and by the simulated soil behaviors. Soft soil overlaid by stiff soil tends to produce predicted stress higher than Boussinesq's solution especially with nonlinear soil behavior and larger load levels; while stiffer soil underlie by softer soil gives opposite results. Laboratory measured vertical stress at depth 20 cm-30 cm showed higher values than the predicted. Surface displacement for the layered soil profile was influenced mainly by the surface layer in the system and the simulated soil behavior. Model prediction was closer to the measured surface displacement for a layered profile having a soft surface soil with nonlinear behavior at higher load levels. Results indicate that the soil test method that allowed large strain were more suitable to simulate agricultural soil behavior. Also, a 50 percent difference between the model prediction or measured vertical stress and the theoretical Boussinesq's solution was used as a base for evaluate how well the measured results correlated to the predicted one. Percentage of computed differences between showed that laboratory measured vertical stress and the finite element model prediction was close better to each other compared to the differences between the measured results and Boussinesq's solution. Result of the percentage of computed differences between the measured surface displacement and the finite element indicate that the measured surface displacements were close to the finite element prediction than to Boussinesq's estimations. Results indicate that the finite element model can be used effectively to examine and evaluate the pattern of stress distribution and surface displacement under wide range of soil and load conditions. (Abstract shortened by UMI.)...