The definitive treatment of miqva’ot with double entrances is Ronny Reich, “Mishnah, Sheqalim 8:2 and the Archaeological Evidence,” in Jerusalem in the Second Temple Period, ed. A. Oppenheimer, V. Rappaport and M. Stern (Jerusalem, 1980) (in Hebrew). Reich also identified many other Jerusalem miqva’ot, especially in the City of David, that were uncovered in pre-World War II excavations but were not recognized as such by their excavators.