Simply press some words with your opinion,
is 850 kPa of bearing capacity with FoS of 3, achievable for 10 m dia 20 m deep caisson rest on medium dense sand with SPT N 30?
850 kPa is a lot of load on sand. But I agree with others that settlement is what matters. What do you know about how far down the sand layer goes, and what is underneath? When you say 850 with a FS of 3, do you mean 850 is the service load bearing pressure?
Are you excavating overburden soils for the caisson? Caisson details? Yours is large enough that it is likely cellular. Will the cells be weighted? Sounds very interesting but very vague.