I would like more information before I could offer the best possible advice. When I was doing underground conduit systems we used Speed Shore almost exclusively. I was with (2) different companies, and had exposure to many others after becoming an owner/operator, all of which used the same system. It will provide the most flexibility for "in the street work". You did not say if the existing utilities are crossings, are running parralell, or both. I am wondering why you are digging so wide, and so deep. How many ducts are running in your bank, and what size, composition, and length of each joint are they? IME the width of the trench was always dictated by the width of the conduit run. We were only required to 3" of encasement on either side of the conduit, and 3" in between. I hope you are not digging 2m wide because that's what size bucket you happen to have. 10 klicks of trench is enough to justify buying a custom bucket so you can save on encasement and, I presume, slurry backfill. 2M wide, in my experience, is only required when one does not want to go very deep, and has a lot of conduits to run. Furthermore, I have only done wide duct runs on site, not off site (ie. in the street). Usually off site is in a public ROW and space is at a premium, as well as requiring a priority to keep the impact to the general public at a minimum, so one usually is required to keep things narrow. I am not familiar with the palstic beams you are talking about. We always used plastic spacers that you errected from the trench bottom. Either way (errected from the bottom or hanging from the top) one must ensure that the conduit does not float during the encasement process. I assume that the 4m depth is required while going under existing utilities. There are many other questions that are coming to mind while I type this reply. How much room do you have to work in? What type of traffic control will you employ. Are you replacing with dirt or slurry backfill? Are you even in the pavement, or on the edge of the ROW? Are you digging with rubber tired hoes or excavators? What size? I don't even know what a cat & genny is so sorry, no comment. In the situations that I have worked in, production can be obtained. You will most likely never get the same production as on site work but the price per foot should reflect that. I hope you have a good operator, and a good foreman. They will be the key to your success, or failure. When I was doing that type of work, almost all of the employees were career types who put high value in doing their jobs well.
