FoSSA Software
FoSSA Software
FoSSA (2.0) is an interactive program for assessing stresses and settlements under embankment and footings acting on horizontal ground surfaces.
Within the foundation soil, FoSSA calculates the stress distribution under embankment having complex geometry, the elastic (immediate) settlement, the consolidation settlement (including isochrones: excess porewater pressure and settlement during the consolidation process), accelerated consolidation settlement due to PVDs (triangular and square installation patterns), secondary settlement, and undrained shear strength distribution within consolidating layers.
2-D or 3-D embankments can be input. The embankment needs not be symmetrical nor have horizontal foundation surface. The embankment can be comprised from up to 20 different materials, each having its own geometry. Such an option allows for the description of an embankment comprised from alternating layers of soil and geofoam (or other lightweight fill). Mouse functions or tabulated coordinates can be used to input the geometry; the plot of the geometry is updated as the data is being input. In case of symmetrical embankment with horizontal layers, an option for quick input data is available, taking advantage of the simple geometry.
Note: 3-D embankment is limited in what it can simulate in its longitudinal direction. That is, the ground surface must be horizontal. Furthermore, the soil profile in any longitudinal section cannot change. However, the embankments end may be at a prescribed slope simulating, for example, a bridge abutment. Soil profile, including the embankments in the transverse direction may have variable elevations.
Layers comprimising the embankment (maximum 20) are useful in simulating staged construction.
Foundation stratum can accommodate up to 50 soil layers including layers of consolidating soil. When identifying a consolidating layer, the user needs to select whether it is singly or doubly drained. Boundaries between layers need not be horizontal. Mouse functions or tabulated coordinates can be used to input the foundation layers; the plot of the geometry is updated as the data is being input.
Stresses immediately after load application are either calculated by integrating Boussinesq equation or input by the user (up to 10 stresses along a layer section can be input). The manual option is useful when field data is available (e.g., piezometric data at time zero which enables one to bypass the Boussinesq idealized elastic solution. One can further use the field data to refine the design parameters (e.g., coefficient of consolidation) via calibration.
Elastic (immediate) settlement is calculated by integrating Hookes equation along a desired vertical section.
The 1-D consolidation settlement is calculated by solving Terzaghi differential equation using a finite difference scheme. The boundary conditions (drainage boundaries and initial excess porewater pressure through the consolidating layer) are accounted for in solving the equation. The user can view numerical or graphical results of isochrones (excess porewater pressure at desired time increments) as well as obtain the settlement at each desired time. Multiple layers may consolidate simultaneously, each at its own rate, independent of the other layers.
The user may create a sequence of loading (staged construction). For each consolidating layer, the additional load in the next loading is superimposed on the last porewater pressure to render the new initial conditions. FoSSA keeps a record of loading history which makes it convenient for the designer to refine the design by examining various scenarios.