Hi Tan,<br><br>Defining boundary conditions is done in two stages. First, you will need to specify the boundary conditions, such as the action, boundary type, and the boundary function number. Second, you will need to select all nodes or edges on which to apply the boundary conditions.<br><br>You can find more about defining boundary conditions in the online help in the Draw Menu topic of Chapter 4. You can also send an e-mail to GEO-SLOPE's discussion forum at <A HREF="mailto:forum@list.geo-slope.com">forum@list.geo-slope.com</A> to ask your question to other end-users of the software.<br><br>Cheers, MO