What we learn in engineering school is often idealistic, with textbook examples showing typical prismatic steel beams with a plastic section classification or excavation in a perfect sand or clay geology. However, in the real world nothing is perfect and engineers will face complex problems not taught in school, where there is little referencing literature and where the design codes do not provide clear guidelines.
One of the tasks I was assigned when I started out as an engineer was to design cofferdams for both abutments of a river bridge with a 30 degree skew across the river due to site constraints. As a result, the abutments at both side of the river are skewed. As a designer for the contractor, often we do not get to dictate the shape of the excavation. Material cost is always a source of great consternation, even more so in temporary works design.
I built a 2D frame for each strut level to do a structural analysis for the odd-shaped cofferdam. However, as the excavation is on a 35 degree slope, the sheet pile wall on the land side has greater lateral earth pressure than the river side. Also, due to the parallelogram shape, I have difficulty balancing the forces.
How should you model the boundary conditions for such an irregularly-shaped cofferdam, where the lateral earth pressure acting at the strut level is not balanced?