Normalized distribution of redshift separation, Δz_phot, for pairs of SMGs with reliable photometric redshifts detected in the same ALMA map (separation ≲9″), compared with pairs of SMGs randomly selected from the distribution of all isolated AS2UDS SMGs with photometric redshifts. The strong peak at Δz_phot < 0.25 for the SMGs pairs compared with the random sample, which occurs less than 1% of the time by chance in our simulations, suggests that a moderate fraction of multiple SMGs (at least those with optically bright counterparts) in single fields arise from physically associated galaxies, rather than chance line of sight projections.