The new approach that has been implemented in version 7.1 computes the stabilizing weight of the water acting on the ground surface by looking at the positive pore-water pressures that exist along the ground surface. This approach will work for piezometric lines, pressure heads defined using a spatial function or finite element computed heads. The presence of positive pore-water pressures on the ground surface line will be visually represented by a shaded area showing the extent of the ponded water and with arrows indicating the direction that the water force will be acting on the free body. Water forces will act normal to the ground surface line.
Pore-water pressures at the base of each slice will be computed differently depending on the method used. For piezometric lines, the vertical distance from the base of the slice up to the relevant piezometric line multiplied by the unit weight of water as defined under Set Units and Scale will determine the pore-water pressures that exist at the base. For pressure heads developed using a pressure head spatial function, the pore-water pressures will be determined using a numerical process called Kriging. For finite element generated pore-water pressures, the location of the base of the slice, relative to the nearest finite element nodes, will be determined and the pore-water pressures will be interpolated from the finite element computed results.
If the weight of the water was modeled in earlier files using a pressure boundary, you will see a warning message when you open the file in version 7.1 suggesting that the pressure line may be redundant and need to be removed. This message will only occur if the pressure line was drawn to correspond within a specified tolerance of the piezometric line. If the pressure line was drawn at a different elevation for some reason, the warning message will not appear.