Question
How do I model a king-post wall in LimitState:GEO?
Solution
LimitState:GEO can model king-post walls within a plane strain analysis using an 'Engineered element' to model the pile. The wall panels will be fully modelled in conventional plane strain. To accommodate the pile modelling within a plane strain framework it is necessary to pre calculate the lateral and axial capacity of the piles per unit length of pile (in terms of the soil/pile interaction) as an input to the software. These can typically be determined from pile formulae and can be defined as a constant or a function of depth.
An animation from an example of a wall retaining sand with the king posts embedded in clay is shown. If the piles are of diameter D then the lateral capacity might be estimated at approximately 9.D.cu per unit length and the axial capacity approximately Π.D.cu per unit length, depending on interface adhesion. In the animation only the soil retained by the wall (red) is deforming (in plane strain) as the wall rotates at failure. The king post pile (blue) is also rotating through the clay, mobilising the specified lateral and axial capacities, but this is not leading to gross plane strain deformation of the clay layer itself. Bending failure of the wall and/or king post pile can also be modelled.
While this is not as precise as a full 3D model, it is much simpler to model and captures most of the key components of the interaction.