We use 2-7/8 oilfield pipe. Take 3-4 joints lay them next to each other a weld together. Make 2 and lay them across ditch at proper width and weld some cross peices to hold it together. Run cables to trees or drive some pieces or pipe on each end to hold it in place. Joints are 35 ft long and cheap here. I don't know how the availabity of it there. Been using pipe bridges on the farm for years never had a problem.