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For knowing the answer to your question in a better way, one of the option should be to treat each set of buildings (supported on one raft) as an independent Etabs model with an independent SAFE model for the raft. Results of this option should be compared with those of the combined Etabs model and the separate raft models of different sets of building obtained from export of reactions of combined Etabs model to a single SAFE model. This comparion will clarify how & how much the adjacent rafts are affecting each other, with reference to the results obtained for independent rafts. After comparison, results requiring a larger raft thickness and/or reinforcement should be adopted for final drawings & construction. Regards.

WA. Researchers have observed that "the characteristic behaviours of an isolated footing are affected if there exist other footing or group of footings close to each other and their individual zone of influence interfere with each other leading to interference phenomenon. The ultimate bearing capacity increases with decrease in the clear spacing between the footings and attains a peak magnitude at some critical spacing and thereafter with further decrease in clear spacing, the ultimate bearing capacity decreases and at spacing equal to zero the two footings act as an isolated footing of twice the width when width of two interfering footings are similar and loaded symmetrically. Moreover, the settlement at failure of interfering footing is observed to be greater than that of isolated footing at failure and the same decreases with increase in clear spacing between the footings." "The bearing capacity and the settlement of footings are the basic criterion which influence in the design of the footings and these are affected by the presence of one or more of the footings close to each other; however the interference phenomenon is not considered in the design of shallow footing." Accordingly, there may some influence of closeby rafts in the stated case. However, IMO this affect would not be prominent or negative, keeping in view that the rafts are about 3 m away, especially if the buildings are of low height. Regards. [Reference: Interference of the footings]