Thanks for the reply. That is the method I went for. The ground was cleaned and blinding poured. The strip footing were made oversized in depth. The box culverts I should have added were precast. The backfill of the footing was stabilized sand inside the culvert due to difficulty compacting and...
I've recently did a design for box culvert with an open base that had to protect and allow access to pipes under a road. The pipes travel at a grade of 1 in 8 down a hill. I've designed using a strip footing which has a retaining wall at the end with a key. I found the box culverts were stable...