That's a fantastic and very common struggle—you've hit the nail on the head! Dedicated 'Nailed Wall' input features are surprisingly rare in general excavation add-ons because soil nailing is highly specialized engineering. The way you're currently handling it—modeling the shotcrete face as a simple shell object and then adding the nails as separate structural elements—is actually the industry standard method for rigorous structural analysis in most geotechnical software packages. If the add-on is primarily for volume calculations or project planning, your 3D/2D method is perfectly golf hit sufficient, but if you need to calculate the actual forces, the separate 1D nail elements will always be necessary to simulate the structural behavior correctly.