The Negative Pore Pressure Cutoff option allows you to define a maximum value for negative pore pressure calculated above a water table. To use this option:
Select the Groundwater page in Project Settings.
Select the Negative pore pressure cutoff checkbox and enter a value.
It does not matter if you enter a positive or negative value, Slide will automatically use the negative of the absolute value.
Negative pore pressure is used in shear strength calculations when Unsaturated Shear Strength parameters (Phib and Air Entry Value) are defined for a material. Negative pore pressures may be computed from finite element seepage analysis, water pressure grids, or above water tables or piezo lines.
If you are using Unsaturated Shear Strength parameters for a material, the Negative Pore Pressure Cutoff value allows you to limit the contribution of negative pore pressure to the material shear strength. If you do NOT define a Negative Pore Pressure Cutoff value, then there is no upper limit on the values of negative pore pressure, and you may generate unrealistic high values of shear strength which may lead to unconservative high values of safety factor.