A MWE could help. As this works:
julia> a = rand(3,3); b = rand(3,3)
3×3 Array{Float64,2}:
0.985678 0.725839 0.162454
0.235461 0.789938 0.304215
0.303247 0.792388 0.332765
julia> [a;b[1,:]']
4×3 Array{Float64,2}:
0.196151 0.294524 0.332187
0.615515 0.0402781 0.0076374
0.330384 0.841746 0.0751668
0.985678 0.725839 0.162454