Regarding payment for carriage of excavated material

If I excavate a area 10x10x10m total volume of excavated soil will be 1000cum.For carriage of excavated soil ,client will pay for 1000cum or 30% more than 1000cum(1300cum).
As per my opinion, due to swelling, volume of compacted soil will be increased after excavation, more than-20-30% .
Please suggest me about this matter.