Surcharge Surcharge fab123 (Civil/Environmental) (OP) 31 Dec 13 08:39 Probably something more straight forward than im thinking. but simply. How to i convert a 20tonne excavator load working along an excavation into a surcharge (kn/m2) in order to progress stability calcs? RE: Surcharge Stanch (Civil/Environmental) 28 Jan 14 07:11 As a general rule a minimum surcharge of 10 kN/m2 can be used to cover general items of construction plant however heavier plant should be calculated indiviually. Do determine the static pressure from your excavator you need to take the gross weight over the area of tracks in contact with the ground.