Gavin, We can't do this directly, but we can get close depending on what information you are interested in. If you can give me a more complete description of your workflow and the problem you are trying to solve, I can give you more direction.
The limitation is that we can't subtract the space occupied by multiple pipes from the trench or calculate the shape based on more than one pipe. Multiple pipes bring lots of complexity to building the model. For instance, how do you want to model multiple pipes into a node? Do they come to a box or does each have a bend?
The Utility module is intended to allow users to visually see how the pipes and nodes interact with other features and to calculate simple volumes and pipe quantities. It is not our main purpose to make a solids model. Think more of a quantity takeoff from a set of plans where the design is schematic.
You can create multiple lines from your diagram at the desired offset and convert each set to a pipe size and material. You do not have to assign each one a trench, so you can see how they interact with your project. Depending on what you want the nodes to look like you will need to decide how to model them. Perhaps one can control the center line location and shape of a junction box and the others just use a point to control their end within the box. You may want to specify 3d points at a bend so that the pipes connect without a conflict. The solution is non trivial and probably can't be modeled by one controlling line.
You can use the largest and lowest one to control the shape of the trench. You can then see the surface of the trench and each of the pipes within the trench. If you want to account for the material displaced by the additional pipes, then this will need to be a manual adjustment based on area and length of the pipes. Maybe you want to just add the note "Contractor to fit in field". Try a simple case like in the following image and see what you want to model and report.
tim
