This should work:
a = torch.arange(0, 6).view(3, 2)
b = torch.arange(6, 12).view(3, 2)
c = torch.arange(12, 18).view(3, 2)

ret = torch.cat((a.unsqueeze(1), b.unsqueeze(1), c.unsqueeze(1)), dim=1).view(9, 2)