For this reason we look at the boundary conditions for Eq. 3-60 again in closer detail, which can be defined in the following way:

The set union of the two boundaries and _{ }makes up the whole element boundary . T_{i} are the components of the total shear force at the element boundary, which is composed of the inner friction forces and the (... hydrostatic) pressure. The total shear force T_{i} or at the element boundary can be expressed as:

With these boundary conditions in mind we approach the weak form of our basis equations, the continuity equation being a simple first practice: